History

Many early automobiles were rear-engined, with a simple belt drive that operated as a single-speed system. The Panhard et Levassor transmission of 1891 was considered a significant advance, as it had three speeds.[5][6]​ It was a sliding asynchronous system, in which changing gears involved sliding the gears on their shafts to obtain the desired combination.[7]​ Even after passenger cars had synchronous transmissions, many transmissions for heavy trucks, motorcycles, and racing cars remained unsynchronized to withstand high forces or have a faster shift actuation.

The first car to use a manual transmission with synchromesh was the 1929 Cadillac,[8]​ although most cars continued to use non-synchronous transmissions until at least the 1950s. In 1947, Porsche patented the "split ring" synchromesh system, which became the most common design for passenger cars.[9]​ The 1952 Porsche 356 was the first car to use a synchromesh transmission. all forward gears.[10]​[11]​ In the early 1950s, most cars only had timing for shifting from third to second (the driver's manuals on the vehicles suggested that if the driver needed to shift from second to first, it was best to bring the vehicle to a complete stop beforehand).

Until the late 1970s, most transmissions had three or four forward gear ratios, although five-speed manual transmissions were occasionally used in sports cars such as the 1948 Ferrari 166 Inter or the 1953 Alfa Romeo 1900 Super Sprint. Five-speed transmissions became widespread during the 1980s, as did the use of synchromesh in all forward gears.

Six-speed manual transmissions began to emerge in high-performance vehicles in the early 1990s, such as the 1990 BMW 850i or the 1992 Ferrari 456. The first 6-speed manual transmission was introduced in the 1967 Alfa Romeo 33 Stradale, and the first 7-speed manual transmission was introduced in the 2012 Porsche 911 (991).[12]​.

In 2008, 75.2% of vehicles produced in Western Europe were equipped with manual transmission, compared to 16.1% with automatic transmission and 8.7% with other systems.[13]​.

Generalities

In a gearbox the speed ratios are formed by pairs of gears.[14]​ The most common version of a manual gearbox is the spur gear arrangement. The transmission has a lever that is used to change gears using a mechanical linkage, or less frequently, using a cable drive.

Torque is transmitted to the gearbox input shaft from the clutch through a hole. The most common configuration is for the input shaft and output shaft (collectively called main shafts) to be aligned, although physically they are separate pieces. The gear rings of the individual gears, which mesh with the output shaft of the box, are mounted on a second shaft parallel to the main axles.

Manual transmissions can be distinguished first by the type of input and output:.

When the engines are very long, such as in the case of six or more in-line cylinders (luxury cars and trucks), coaxial gearboxes dominate, since there is enough space in the vehicle for long engines and a long gearbox, with a small diameter.

Designs with coaxial shafts usually have several of the following characteristics:.

The total number of gears is obtained as:.

The upstream group is used in vehicles that need many gear ratios, such as trucks. For the downstream group, planetary gears are available that rotate like a block in normal operation (1:1 transmission ratio, without power loss) and are only activated when a reduction gear is needed on off-road routes or on steep slopes.

Gearboxes with offset parallel shafts conduct power from the input shaft through gear stages to the output shaft; There is no need for an auxiliary intermediate shaft. However, a 1:1 gear ratio is only possible through a pair of gears, so the favorable efficiency of a direct gear in a coaxial case is not possible. In the passenger car sector, generally only a few gears are required, so the upstream group generally only consists of one set of gears, and a downstream group is not required.

In all vehicle transmissions, an attempt is made to place the output near the center of the imaginary axis of the driving wheels, in order to avoid the effect of drive shafts of different lengths and technical limitations regarding the steering angle. Meeting this requirement is particularly difficult with front-wheel drive units and transversely installed engines, only short gears are possible here, which may have a slightly larger diameter. The outlet to the differential is on the engine side. To make the gearbox shorter and larger in diameter, several output shafts are usually used, each of which is connected to a gear on the main output shaft via a sprocket; and each output shaft only carries part of the gears.

To change gears, the flow of energy must be interrupted. This is done using a clutch. The driver operates the clutch lever, the clutch is disengaged and a gear can be changed with the shift lever and the associated shift mechanism in the transmission (shift process). The manual transmission remains the most common type of transmission in motor vehicles today.[15]​.

In countries like Venezuela it is known as synchronous box.

Operation of a manual transmission

Shift sleeve gearboxes are the most common type of gearbox in motor vehicles. All sprockets are helical and constantly engaged (except reverse gear). The friction connection is established using sleeves"), which are pushed on a pair of fixed shaft hubs and a loose gear. The sleeves are driven by the gear lever and determine the flow of energy from the input shaft to the output shaft. Depending on the design of the gearbox (coaxial or parallel transmission and output shaft), the structure may be different. The following describes as an example the mode of operation of a coaxial type gearbox with a sleeve:.

The power flow starts from the engine (drive shaft) via an intermediate shaft to the output shaft, through which the force coming out of the gearbox is transmitted. Starting from the front of the drive shaft, the intermediate shaft is driven through the first pair of gears. In the following gear stages, the torque is transferred from the intermediate shaft to the rear of the main shaft and from there to the output. One gear is firmly connected to the shaft, while the other can be used to shift a positive connection to the shaft using the shift sleeve"), which is moved by the gear lever. As a rule, shift sleeves are located on the main shaft, but they can also be located on the intermediate shaft. By directly coupling the drive shaft with the output shaft, it is driven directly (direct gear). In this case, the intermediate shaft runs with it, but without transmitting the torque. The intermediate shaft also works at idle, but neither shift hose produces a frictional connection to the output shaft.

These changes allow free gear selection, at least in theory: you can change from any gear to any other. The reverse gear occupies a special position, and even in modern transmissions, not a shift sleeve is used, but an intermediate sliding gear, which reverses the direction of rotation of the output shaft.

Until the late 1950s, vehicles with non-synchronized shift sleeve transmissions were widespread and trucks continued to use them into the 1980s. Sometimes these gears are also included in dog clutches. If the gear change was started when there was a speed difference, the difference had to be adjusted first. If this condition was not met, a rattling noise accompanied the change process was produced. The cause was the multi-tooth gear shift sleeve pushed into the gear wheel clutch body, which operated at different speed. It used to be a matter of the driver's skill to avoid the noise produced when changing gears.[16]​.

In addition to the simple synchronization described, there is also a forced synchronization (also called lockup synchronization), in which the shift sleeve is only activated when the synchronization is correct.

Modern selector sleeve drives are synchronized mechanisms. Synchronizing rings[17]​ and synchronous cone gears make it possible for the gear speed to adapt smoothly to the shaft speed when the shift sleeve moves over the shaft and gear (freewheeling). This process does not replace the clutch, and even with the synchronous gearbox, the flow of power from the engine to the gearbox must be interrupted by engaging the clutch before shifting.

Other types

In sliding gear gearboxes, the sprockets are almost always straight-toothed and the gear hubs and shafts are slotted, so they cannot rotate on the secondary shaft. They shift on the shaft during shifting and therefore do not mesh constantly.

The sliding gears are basically out of sync. The straight teeth make it difficult to change gears without noise, and double clutching is required both when up and down gears. In addition, a loud characteristic howl can be heard during operation. On the other hand, claw or sleeve switched gears allow the use of gears with helical teeth and smoother tooth engagement as well as synchronization. Forcing a gear may damage the sliding gears.

Sliding gearboxes[18]​ were widespread until the 1930s. The last German cars with a sliding gear were some Lloyd "Lloyd (automobile)" types. Also in the Volkswagen Beetle, the 1st and 2nd gears were initially designed as sliding gears, while the 3rd and 4th gears had low-noise, claw-shift helical teeth, which were designed as longitudinally movable round pins and matching semicircular grooves in shafts and gears.[19] For reverse gear, the sliding gear principle is still used, making it relatively difficult to engage and It usually produces a clearly audible sound.

Gearboxes for racing vehicles are still built as sliding gearboxes. With the same dimensions, this configuration allows a high load capacity due to the greater maximum torque that can be transmitted, since larger section axles can be sized. This is relevant for rally and Cup class vehicles, and due to their reduced weight, for touring cars and racing cars. Current development in racing is moving towards uninterrupted upward transmissions. Racing cars lose 2-3 km/h when shifting with a conventional gearbox due to high air resistance and low weight.

To avoid this, the boxes of many racing cars allow two gears to be briefly engaged at the same time. There are several ways to avoid damage to the gearbox that this situation could cause: one is to use one or more freewheels so that when there is an overlapping upshift, the faster rotating gear of the higher speed overtakes the slower rotating gear of the lower speed.[20]​ The freewheel prevents stress on the reducer. The other variant is that two gears are engaged at the same time for a few milliseconds. To allow this without generating stresses, a margin of torque is required between the sprockets and their axle. If the previously engaged gear is not taken out in time, the transmission will be damaged. During switching operations, very strong impacts can occur, so such designs are not suitable for most cars.

In the case of wedge gearing, the frictional connection is established not by a shift sleeve"), but by a system of stepped stops. However, the terms cannot always be clearly distinguished from each other. In some cases, non-synchronized gearboxes are also called wedge or claw type shifts to distinguish them from synchronized shift sleeve transmissions.

Contenido

Las transmisiones semiautomáticas son un tipo especial de caja de cambios manual, donde no se necesita embragar cuando se cambia de marcha. Cuando se toca la palanca de cambios, el embrague se desacopla automáticamente y cuando se introduce la siguiente marcha, el embrague se acopla de nuevo. En principio, son sistemas mecánicos con un embrague de partículas magnéticas o un embrague seco de un disco de accionamiento automático.

Para transmisiones con embrague convertidor, se combina una transmisión manual convencional con un convertidor de par, que se ubica entre el motor y el embrague y permite un arranque y realizar maniobras a baja velocidad más cómodamente y sin desgaste, como en las transmisiones automáticas convencionales. Para cambiar de marcha, el conductor tiene que accionar el embrague convencional, como con una transmisión manual normal, para interrumpir el flujo de potencia y también para cambiar manualmente. A menudo, el convertidor se desactiva a partir de una determinada velocidad, de modo que el flujo de potencia se transmite totalmente a través del embrague mecánico, aumentando la eficiencia de la transmisión. Hoy en día, este tipo de construcción se utiliza principalmente en camiones de trabajo pesado o todo terreno, como el MAN gl").

En algunos vehículos se combinaron ambos conceptos (la transmisión semiautomática y el embrague convertidor).

Ejemplos de vehículos con transmisión semiautomática son el Ford 17 M"), el Volkswagen Escarabajo y el Karmann Ghia, algunos DKW, el Opel Rekord F 11/12, el Auto Union AU 1000; y el Saxomat (con el sistema Olymat). Por su parte, el embrague de polvo magnético Ferlec se podía suministrar bajo pedido para el Renault 4 CV y el Dauphine. Modelos disponibles con convertidor y embrague automático eran los Mercedes-Benz 219/220 S/220 SE (Hydrak), Porsche 911 (Sportomatic), NSU Ro 80 (en toda la serie), Citroën DS y Renault Frégate (sistema Transfluide) o el Citroën CX (C-Matic). El Trabant disponía de una transmisión semiautomática llamada Hycomat.

Desde principios de la década de 1990, también ha habido transmisiones semiautomáticas sin pérdidas con sistemas de acoplamiento automático"), en las que el cambio manual y el embrague de disco convencional se accionan electrónicamente-hidráulicamente, como por ejemplo en el Renault Twingo Easy, el Mercedes-Benz Clase A W168") con sistema de embrague automático (AKS), o Saab y BMW con el SMG semiautomático.

Assisted manual transmission

Assisted manual transmissions, also known as AMT, make it possible to combine greater driving comfort through easy-to-use transmission control, with the economy resulting from lower fuel consumption and reduced emissions due to driving programs specially coordinated with the transmission control.[23]​ The main difference between classic semi-automatic manual transmissions and the dual-clutch transmissions discussed below is that the former have only one clutch. Its main disadvantage is the interruption of tractive effort: the flow of energy must be briefly interrupted during the gear change. Its advantage is that the clutch is engaged in an inactive state and only needs energy to open, which is why it is usually installed in particularly economical and light vehicles.

The two-clutch system features two couplings.[24]​ Its advantage is that when one clutch is opened, the other can be engaged at the same time and the tractive force is not interrupted. The disadvantage is that both clutches are open in the inactive state and the clutch in the active power branch must remain engaged, generating a waste of energy.

An assisted manual (or semi-automatic) gearbox is a conventional gearbox expanded to include automated components.[23]​ The fundamental difference with a conventional manual transmission is that the drive is carried out by a system consisting of hydraulically driven cylinders and electric servomotors that control the actuators. During gear shifting, the activated clutch actuator separates the gearbox from the tractive effort, and then the gear change calculated in the gearbox control unit is transmitted to the actuators, which engage the next higher or lower gear.[25]​.

With the automated manual transmission, gear changes can usually be made autonomously using a program stored in the control unit (manumatic transmissions), although the driver can also use the shift knob on the center console or paddles on the steering wheel to set the next higher or lower gear. On the other hand, the switching program prevents shifting errors.[26]​ As a general rule, it is only possible to skip the sequence to a limited extent, since the control electronics only allow certain switching operations if the engine remains within an admissible speed range.

In trucks for long-distance transport, this type of automated transmissions have been used since the mid-1980s, in which the driver preselects the gear and the electronic control of the transmission performs the gear change using electro-pneumatic shift cylinders. With the classic "electro-pneumatic circuit") from Daimler-Benz,[27]​ for example, the driver selects 6th/low gear and depresses the clutch pedal. This activates the control electronics and checks whether the switching process can also be carried out depending on the engine speed. If this is the case, the control electronics shifts to the selected gear via the pneumatic shift cylinder. If it refuses to shift because the engine threatens to accelerate too much, it indicates this to the driver by means of a warning tone. As As a general rule, the transmission shifts into neutral.

Newer systems in trucks or coaches also shift fully automatically, and lack a clutch pedal (which in some models can be deployed if necessary). Modern trucks are equipped as standard with an eight-speed gearbox, which is usually based on a four-speed manual gearbox, expanded by an additional group to have a total of 16 gears.

A semi-automatic gearbox shares most of the advantages of a manual gearbox:

In addition, it offers other advantages such as:

The semi-automatic transmission is used in some vehicles instead of a conventional gearbox to comply with special approval regulations, since the switching program can be adapted to the official procedures for measuring consumption and exhaust gases in order to offer better measurement results than with a manual transmission. This allows the vehicle to be approved with a better efficiency rating, although in practice it can generate higher consumption or lower acceleration capacity for the end customer, which is actually due to a reduction in the technical possibilities of the transmission system.

Its main disadvantages are:

This results in certain jerks during the gear changing process, especially under strong acceleration. To avoid this, newer systems use a second secondary shaft, on which the shifting process can be prepared for the respective adjacent gear, as with the double clutch system, so that the interruption of tractive power during clutch release is noticeably reduced (e.g. to 50 ms with Graziano's ISR in the Lamborghini Aventador).[28]​.

The first automatic gearboxes with hydraulic actuators used in series-produced vehicles were in the BMW M3 in 1997, in which the existing classic gearbox was upgraded to an automated gearbox using a hydraulic system, and the Smart Fortwo from 1998, which was the first vehicle to have an automated gearbox operated by an electric motor. The special feature of the Smart was that it was only manufactured with an automatic transmission, and the manually operated variant was only available by modifying the transmission control software. A unit with manual shift can easily be modified to automatic by changing the software. Both transmissions were developed by Getrag Firm.[29]​.

Due to its high efficiency, the automatic-manual gearbox is a popular equipment variant, especially in small cars such as the Audi A2 1.2 TDI, the Opel Corsa or the Smart. The VW Lupo 3L was available exclusively with this option, although gearboxes with a relatively high failure rate and very expensive to repair negatively influenced demand for the vehicle.

Several automakers offer automated manual transmissions under different trade names:.

A variant of the automated gearbox is the dual-clutch gearbox. It consists of two subtransmissions with associated clutches. One part of the transmission carries the even gears, and the other the odd ones. Reverse gear can be assigned to both subtransmissions. Before shifting, the next higher gear is engaged in the unloaded branch when accelerating or the next lower gear when decelerating. Then the clutch of the unloaded gear is closed and at the same time the clutch of the other is opened. This means that the change can take place without interrupting the traction force. The time it takes to change gears depends solely on how quickly the clutches open and close.

This system is also known as a "direct shift gearbox", also abbreviated as DSG, DKG, PDK, DCT or TCT.

The main advantages of the two-clutch system are:.

The disadvantage compared to the automatic-manual system is the (often permanent) energy consumption required to keep the clutch closed in the power branch.

Due to their properties, two-clutch systems compete with conventional transmissions with converters and planetary gears.

Originally developed by Porsche for racing in the 1980s, Volkswagen and Audi pioneered the use of this technology in their large-scale production, achieving technological leadership in the market. A two-clutch transmission has been in series production in the Golf and Passat classes since 2002 (6-speed, wet clutch supplier is BorgWarner). VW's internal designation is DQ250 (acronym for double clutch - transverse installation - 250 N·m, although it can transmit 320 N·m of torque).

In the following years, VW introduced a 7-speed system with the internal designation DQ200 (for the Polo and small Golf). LuK "LuK (company)") supplies a dry double clutch for this transmission.

In 2009, the first dual-clutch system developed especially for Audi with the designation DL501 came on the market with the Audi Q5. A BorgWarner-sourced wet double clutch was again used in this gearbox. The acronym DL501 means double clutch - longitudinal installation - 500 N·m, and was gradually marketed in the A4, A5 and A6 models.

The DQ500 (7-speed DCT) for the VW T5 van appeared in autumn 2009, and was also available in the Tiguan from June 2010. The wet clutch was developed and manufactured by the VW factory in Kassel, marking the first time that a double clutch developed by the company was used. All variants (DQ200, DQ250, DQ500 and DL501) were also produced in Kassel.

Since July 2008, Porsche offered the 7-speed PDK transmission for the 911 developed by ZF. It was also available to order for the Boxster and Cayman. Likewise, it was added to the Porsche Panamera since September 2009 and to the Turbo since October 200.

A dual-clutch transmission with seven forward gears designed by Magna PT has been available since March 2008 for the BMW M3. Ford, Mitsubishi, Ferrari, Mercedes-Benz and Volvo also offered models with Getrag dual-clutch transmissions since 2008.

For the first time, a dual clutch was installed on a production motorcycle in the summer of 2010 - a Honda VFR1200F").

Sequential transmissions cannot be changed at will, you can only change to the next highest or lowest gear immediately, that is, the next one in the sequence.[31]​ It is not possible to skip one or more steps. Such a transmission can be found, for example, on the Smart Fortwo and on many motorcycles. Dual-clutch gearboxes are also always operated sequentially, and experience a break in tractive power when jumping one or two gears.

Wedge gears, like sliding gears, have fixed gear wheels. They are mainly used in stationary machines and light vehicles. With the sliding wedge transmission"),[32]​ a key moves longitudinally on a splined shaft when changing gears and the respective gear is locked with a positive adjustment. They are used on mopeds and on motorcycles by brands such as DKW, Simson&action=edit&redlink=1 "Simson (company) (not yet drafted)") and Zündapp, also on two-stroke motorcycles up to 250 cm³ displacement and on the small Janus car, as well as in the electromagnetically operated preselector gearbox Selectromat of the Goggomobil.

The shift shims are eliminated in the bevel gear gearbox. A cone is attached to a rod inside the hollow interior, which pushes the balls out through the holes in the intermediate shaft of the sprockets, ensuring "form fit" between the shaft and the sprocket.[33]​.

At the end of the 1920s, the British company Daimler developed an assisted transmission, which consisted of the combination of a gearbox with coupled planetary gear sets based on the concept devised by the Englishman Walter Gordon Wilson of a hydraulic coupling, based in turn on the ideas of the German Hermann Föttinger). The gears were selected by a compressed air system controlled by a small selector lever (the preselector) located on the steering column, combined with the left clutch pedal. This operation was considerably easier and did not require the physical effort necessary to change gears using the double clutch through a mechanical link, the usual system until then The Associated Equipment Company (AEC) used the preselector with a fluid flywheel for thousands of buses (for example, the AEC. Regent III") = RT) of the London Passenger Transport Board") (LPTB) and its successor, the London Transport Executive") (LTE).

Operation

It is common for the selector lever with the adjustment options to be located in the central tunnel of the vehicle floor. The options are usually:

In automatic transmissions this sequence is generally followed, since there are legal regulations that require it in some countries, such as the United States.[35]​.

Some transmissions offer more gear steps and often have a manual mode, such as:.

Use in Western Europe

In an international comparison, the percentage of cars equipped with automatic transmission in Western Europe is well below the percentage values ​​in countries such as the United States and Japan. This is due to certain disadvantages compared to the manual gearbox (although some have practically already been overcome), such as lower acceleration (if there is no increase in torque), lower top speed, higher consumption, delayed response at the beginning of an overtaking maneuver, higher price compared to a manual gearbox (not common in all markets), certain traffic conditions and the sometimes unsporty image of the automatic gearbox, which is rarely found in motorsport in the classic form of the converter with planetary gear.

According to a Swedish study, the use of an automatic transmission reduces the number of driving errors in the elderly, while there is no such correlation among middle-aged drivers.[36]​.

In Germany, automatic transmissions were much less common than manual transmissions for a long time. In the recent past, this proportion has been tilted in favor of automatic transmissions: while in 2010 only 27 percent of new cars manufactured in Germany were equipped with an automatic transmission, this figure increased to 48 percent in 2018.[37]​ As the first major German brand, Mercedes-Benz announced in 2020 that in the future it would completely dispense with manual transmissions when developing new vehicle generations.[38]​.

Automatic transmission with converter

An automatic transmission with a converter differs in structure from a manual transmission mainly in the following points:.

The main advantages of a transmission with a converter are:.

The most well-known disadvantages are:

In exceptional cases, planetary gear sets are not used with automatic transmissions, such as in Hondamatic gearboxes and with the automatic transmission of the Mercedes-Benz A-Class") (W168). The structure of such a gearbox is similar to that of a manual gearbox. The main distinguishing feature is that, instead of synchronizers and shift sleeves, they have an independent multi-plate clutch for each gear stage of the automatic transmission.[39]​.

The friction lock connection of the individual planetary gear sets with the input and output shafts is carried out by multi-disc clutches. Its operation is predetermined by a driving and switching program in the control unit. [39] Transmission control until the late 1980s was carried out hydraulically. Currently (as of 2016), it is done electronically and the actuation of the clutches is done by electrically controlled hydraulic valves.

In the torque converter, some of the engine's power is transferred to the oil in the form of frictional heat due to slippage. To reduce the associated loss of efficiency, converter automatic transmissions are often equipped with a lock-up clutch that allows direct mechanical engagement by friction after starting or changing gears.

Additionally, energy is required to generate hydraulic pressure using an oil pressure pump. Inactive multi-plate clutches that are not required in the engaged stage cause additional drag losses because the clutches are open.[40]​ Due to these drag losses, fuel consumption is higher compared to an otherwise equal manual transmission equipped vehicle. Modern automatic transmissions offer a torque converter lockup clutch from first gear to reduce this additional fuel consumption. A further reduction in consumption is possible thanks to the stationary decoupling, which shifts the transmission to idle when the vehicle is stationary and the service brake is activated, thus avoiding drag losses through the converter. The consumption drawbacks of the automatic system are usually not very evident in standard consumption, unlike the consumption that occurs in normal road traffic, since the gear change points are adapted to standardized cycles.

A level change takes place by switching off a switching element and simultaneously connecting the switching element to the next higher or lower level. The second change element thus assumes the torque of the first piece until the second change element assumes all the torque at the end of the change. The time span for this process is in the range of two to three digit milliseconds. Since the introduction of electronic transmission controls in the late 1980s, a "torque reduction request" is sent to the engine control unit to protect the transmission from overloads and/or achieve better shift quality. This has also been done via the CAN Bus since the late 1990s, allowing the engine control to reduce engine torque during shifting. Another means of increasing shift quality is to open the converter clutch in certain shift situations. Gear changes between up to eight gear ratios are very smooth. The fact that the power flow is not completely interrupted due to the design also leads to the well-known "creeping" of vehicles with an engaged automatic transmission whenever it is not idling. This drag can be very useful when maneuvering.

Continuous variable transmission

A planetary gear as a timing system is not continuous, but they can make one input shaft act almost continuously, as long as the second input shaft of the adder gear regulates the overall ratio. The second input can be, for example, hydrostatic (as in tractors), electric (Toyota Prius) or also mechanical (as in a continuously variable transmission).

This transmission design offers the following advantages:.

Torque capacity can be improved with a power split, for example. The continuously variable transmission is combined with a planetary adding or dividing gear. However, this reduces the spread of the transmission or the overall efficiency of the gear combination deteriorates.

With optimized consumption characteristics, the disadvantage of low transmission efficiency can be partially compensated. Thanks to the optimization of engine consumption and wider speed ranges for the best fuel consumption, dual-clutch transmissions are currently the strongest competitors to the consumption-optimized continuously variable transmission.

In practice, optimized features are not accepted by the majority of customers, which means that the theoretical advantages are subject to certain restrictions.

In practice it has been found that many drivers are not satisfied when the vehicle accelerates from zero to, for example, 100 km/h, since the engine practically always rotates at the same speed ("rubber band effect"). To avoid this, many continuously variable transmission systems offer a gearshift program in which they work with fixed gear ratios and thus imitate a normal stepped automatic transmission. However, this additional function is not expressly required from a technical point of view. The dissatisfaction of some users is a purely psychological effect that dates back to decades of experience with conventional gearboxes or multi-step automatic transmissions and their characteristics.

Several small manufacturers used transmissions with friction wheels until the 1920s. Starting in 1958, the Dutch manufacturer DAF" produced cars with the Variomatic system, a transmission that used V-belts"). combined with variable width pulleys (see continuously variable transmission).

The principle devised by DAF has since been developed using metal link push chains for higher torques. These gearboxes were available in utility vehicles such as the Ford Fiesta or the Fiat Uno. Audi brought to the market around 2000 the new Multitronic gearbox for powerful cars, which uses a chain drive.

The Toyota Prius electric hybrid has a pseudo-continuously variable automatic transmission, in which a planetary gear with power division superimposes the speeds and torques of the combustion engine and the electric motor, as well as the electric generator. The electronically controlled variable distribution of drive power between the electric motor and the generator allows the relationship between the speed of the internal combustion engine and the output speed to be varied.

Electric variable drive

Electric variable transmission (EVT or e-CVT) is used in hybrid vehicles, combining the output of an electric motor and a gasoline engine. It provides continuously variable gear ratios, just like a conventional mechanical stepless gear system.

In its most common form, a gasoline engine is connected to a traditional transmission, which in turn is connected to a planetary gear system carrier. In turn, the electric motor/generator is connected to the "solar" sun gear, which is not normally driven in typical epicyclic systems. Both power sources can feed the transmission output at the same time, splitting the power between them. Typically, one-quarter to one-half of the motor's power can be supplied to the sun gear. Depending on the design, the transmission to the epicyclic system can be greatly simplified or eliminated entirely, as EVTs are capable of continuously modulating output/input speed ratios like mechanical CVTs, but offer the distinct benefit of also being able to apply power from two different sources to a single output, as well as potentially reducing the overall complexity of the transmission system.

The power distribution ratio is established based on common driving conditions, such as road speed for a car or traffic speed for a city bus. When the driver presses the accelerator, the associated electronics interpret the pedal position and immediately adjust the gasoline engine to the RPM that provides the best fuel economy for that setting. As the gear ratio is normally set far from the maximum torque point, this setting would normally result in very poor acceleration. Unlike gasoline engines, electric motors offer efficient torque over a wide rpm range and are especially effective at low rpm, where the gasoline engine is inefficient. By varying the electrical load or supply of the electric motor connected to the sun gear, additional torque can be provided to compensate for the low torque output of the combustion engine. As the vehicle accelerates, the power provided by the electric motor reduces and eventually stops, creating the illusion of a CVT.

A classic example of an EVT system is Toyota's Hybrid Synergy Drive, which lacks a conventional transmission and the sun gear always receives 28% of the engine's torque. This available electrical energy can be used to operate any electrical load in the vehicle, recharge the batteries, power the entertainment system, or run the air conditioning. Additionally, any residual power is fed back to a second motor which feeds the powertrain output directly. At highway speeds, this additional generator/motor boost is less efficient than simply driving the wheels directly. However, during acceleration, the electric support is much more efficient than the internal combustion engine which operates far from its maximum torque point. GM uses a similar system in the hybrid powertrains of Allison buses and in the Tahoe and Yukon pick-up trucks, although the latter use a two-speed transmission as opposed to the epicyclic system, and the sun gear receives about half of the total power.

Manual transmissions are characterized by allowing the driver to choose at will the two usual ways of operating the change, being able to decide for himself the most appropriate gear (as with a manual or semi-automatic gearbox), or allowing an electromechanical or electronic system to autonomously determine the correct gear ratio based on the vehicle's gear parameters (as with a classic automatic transmission system). The first systems of this type were automatic transmissions modified so that the driver could choose between a range of "short" or "long" gears, in order to obtain greater control over the vehicle in some particular situations, such as on steep and long descents. This configuration took advantage of the maturity of the development since the 1930s of automatic transmissions, capable of effectively managing the engine speed autonomously thanks to two key elements: the epicyclic gear systems and the hydraulic torque converter. Subsequently, the development of electronics has made it possible to devise different manumatic systems, automatic gearboxes that in turn include the option of manually selecting gears sequentially, such as the Tiptronic system popularized by Volkswagen, the Steptronic from BMW, or the G-Tronic from Mercedes-Benz.[44]​.

direct transmission

In a direct drive mechanism power (physical) power and torque are transmitted from an electric motor to the output device (such as the drive wheels of a car) without using speed reducers. Several cars from the turn of the century used direct drive wheel hub motors, as did some prototypes in the early 2000s. On the other hand, most modern electric cars use one or several internal motors, where the transmission is transferred directly to the axles "Axle (mechanical)") of the wheels.[48]​[49]​.

indirect transmission

Electric transmissions convert the mechanical power of engines into electricity using an electrical generator and convert it back to mechanical power using an electric motor. Electrical or electronic control systems with adjustable speed drive") are used to control the speed and torque of motors. If the generator is driven by a turbine, such a device is called a turboelectric transmission"). Likewise, transmissions powered by a diesel engine are called diesel-electric.

Diesel-electric transmissions are used in many railway locomotives, ships, large mining trucks and some bulldozers. In these cases, each driven wheel is equipped with its own electric motor, which can be powered with variable electrical power to provide any required torque or power output to each wheel independently, producing a much mechanically simpler solution for very large vehicles with multiple drive wheels, where the drive shafts would be much larger or heavier than the electric cable that can provide the same amount of power. It also improves the ability to allow different wheels to operate at different speeds, which is useful for steering wheels on large construction vehicles.

Hydrostatic transmissions transmit all power hydraulically, using the components of a hydraulic machine. They are similar to electric transmissions, but use hydraulic fluid as a power distribution system instead of electricity.

The transmission input drive is a central hydraulic pump and the final drive unit(s) is a hydraulic motor or hydraulic cylinder. Both components can be placed physically separately on the machine, being connected only by flexible sleeves. Hydrostatic drive systems are used in excavators, tractors, forklifts, winch drive systems, heavy lifting equipment, agricultural machinery or in earth moving equipment. An exceptional case was the Ferguson P99, a Formula 1 car from around 1961 that used a hydraulic transmission system.[50]​.

The Human Friendly Transmission system used on the Honda DN-01 motorcycle is also hydrostatic.[51]​.

We speak of a hydrodynamic transmission when the hydraulic pump or hydraulic motor makes use of the effects of the flow of a fluid as it passes through the blades of a turbine. The pump and motor usually consist of jointless rotating vane systems, and are usually placed in close proximity to each other. The gear ratio can be made to vary by additional rotating blades, an effect similar to varying the pitch of an airplane propeller.

The torque converter in most automotive automatic transmissions is itself a hydrodynamic transmission. Hydrodynamic transmissions are used in many passenger rail vehicles, those that do not use electric transmissions. In this application, the advantage of smooth power delivery can outweigh the reduced efficiency caused by energy losses generated by turbulence in the fluid.

Muchos vehículos comerciales también requieren una transmisión que permita expandir el rango de velocidad de giro del motor de combustión interna al régimen de giro de las ruedas necesario para conducir.

Por ejemplo, la velocidad de maniobra de un camión pesado es de unos 3 km/h. Esto se logra a una velocidad del motor de aproximadamente 550 rpm. Al conducir, el camión viaja a 89 km/h en una autopista. Por razones de consumo, se desea alcanzar esta velocidad (en tráfico de larga distancia) a aproximadamente 1100 rpm. A partir de una relación de velocidades de giro del motor de combustión interna de 2 (550 rpm respecto a 1100 rpm), es necesario de una relación de velocidad de giro de las ruedas de 30 (3 km/h respecto a 90 km/h). Esto significa que la relación de la marcha más baja y la relación de la marcha más alta difieren en un factor de 15. La relación de la relación entre la marcha más alta y la marcha más baja se llama dispersión.[52]​ Para disponer de una distribución amplia y a la vez tener marchas poco espaciadas (algo necesario para reducir el consumo de combustible), se utilizan transmisiones con 12 o 16 marchas en camiones pesados. Dichas transmisiones se componen de varias subtransmisiones, la denominada transmisión primaria (2 etapas), la transmisión principal (3 o 4 etapas) y la transmisión grupal (2 etapas). Dado que las etapas de las subtransmisiones se pueden combinar de forma multiplicativa, se obtienen 12 o 16 marchas, aunque no todas las combinaciones de transmisión dan resultados utilizables en la práctica.

La marcha atrás (inversión del sentido de giro de la transmisión) forma parte de la transmisión principal. Esto permite combinar la marcha atrás con las 2 etapas de la caja de cambios primaria y las 2 etapas de la transmisión del grupo, obteniéndose (al menos teóricamente) cuatro marchas atrás. Sin embargo, a menudo se bloquean, y no se pueden seleccionar.

Los camiones ligeros suelen tener 6 marchas. La distribución de velocidad del motor es mayor en los camiones ligeros, y la velocidad de maniobra se establece un poco más alta para que sean suficientes 6 marchas (con un diseño más similar al de los turismos).

Primary gearbox

This transmission is an extension of a conventional transmission, attaching an additional gear stage to the input shaft. This has the effect that the power can be distributed in two stages. So, there is a small step and a big step for each stage. This gives this gear the name "divider" and the overall construction the name split gear. The term primary gearbox indicates that this gearbox is installed in front of the basic gearbox. However, more often, the upstream group is housed directly in the gearbox itself.

Split transmissions are found on heavy trucks and are usually operated with a switch on the shift lever. If only the splitter is operated or if a gear is changed from a high gear to the next lower gear, then it is called "up half a gear." If you shift from a low gear to the next lower gear, you shift "half a gear down."

rear gearbox

It is a two-stage planetary gear installed between the base gear and the cardan. This doubles the number of gears available (the range or range). This is why constructions using a rear-mounted gearbox are also called range gearboxes (see overdrive "Overdrive (mechanical)").

First you change gears in the basic transmission and then you activate the range group switch. This is done either by a switch on the gear lever or by what is known as "rollover." In the first gear, the switch is switched to the upper (large) group before the gear change, and then the gear lever is put back into the first gear. However, this is 5th gear on a basic 4-speed transmission or 4th gear on a basic 3-speed transmission. The driver has an 8-speed split setup, which breaks between 3rd and 4th gear and 5th and 6th gear. Here you move the gear lever to neutral after shifting into 4th gear and pressing the lever to the right with the palm of your hand. This changes the range group and the lever no longer turns to the right in neutral, but to the left. From the driver's point of view, you are now facing the 5th or 6th aisle. The lever is actually in front of the 1st or 2nd gear of the basic transmission, but the group shift now converts it to 5th or 6th gear. This is also known as a "double H" circuit. These transmissions can be found in heavy duty trucks.

A combined upshift and downshift gearbox is often used, meaning that up to 16 speed levels are available on heavy trucks.

Automatic transmission with range divider group

Most modern trucks are equipped with automatic transmissions, as noted above. They offer low fuel consumption and ease of use.

These electronic shift aids for commercial vehicles were developed in the early 1980s with the desire to save fuel, protect transmission components and also give relief to the driver, although the new system met with strong rejection from truck drivers at first.

In 1984, Scania was the first manufacturer to bring an electronic gearshift aid to the market under the name CAG ("Computer Assisted Gear Shift"). The conventional gear lever was replaced by a small joystick in the engine tunnel. Electronics that recorded various driving parameters, such as speed and engine speed, showed the trucker a gear change recommendation on a screen on the instrument panel. If the driver accepted the suggested gear, all he had to do was engage the clutch. In the case of a different gear selection, the desired gear was selected using a lever. If the system failed, the box with the selector switch could be folded to the side and a conventional lever, which was carried in the vehicle, inserted.

About a year later, Mercedes-Benz followed suit as a manufacturer of its own commercial vehicle transmissions, and ZF began production of its own shift aids. At the 1985 Frankfurt Motor Show, Mercedes introduced the Electro-Pneumatic Circuit (EPS),[53]​ which was offered as standard on the 1644 model, the most powerful at the time. It was also available for smaller models and the O 303 coach. Unlike Scania's CAG and some ZF models, the EPS did not offer a gearshift recommendation, so selecting gears to up or down Lowering them always had to be done by touching the lever forward or backward. With the introduction of the Mercedes-Benz Actros series, the "Telligent" (telematics and intelligent) system appeared in 1996, initially as a semi-automatic circuit, and later as a fully automatic circuit.

At the same time, as a manufacturer of truck transmissions, ZF offered semi-automatic shift aids under the name AVS (automatic preselection circuit), which could be operated by push buttons, gear shift knobs or a rocker switch on the steering wheel.

However, in terms of handling, all initial systems are largely identical: The controller outputs a switching pulse via a switch, which is carried out by electronic management that controls a series of pneumatic drive cylinders.

The prevailing trend has been to relieve the driver of almost all gear changing tasks. With all available shift aids, standstill and reverse are only operated using special buttons or key combinations. In some fully automated manual transmissions, there is no longer a clutch pedal; In the Actros, for example, it folds into the footwell and can be used as an option. Since the electronics completely control all shifting and clutch processes, non-synchronized claw gears can also be used here, which are lighter and more compact in terms of design and can be shifted faster in full gear. However, these fully automatic gearshift aids should not be confused with a torque converter automatic transmission.

transfer case

"Transfer cases" are installed after the basic gearbox. They are typically used in vehicles that have multiple driven axles (such as four-wheel drive cars). The transmission distributes the drive power to multiple axles (two in a 4x4 vehicle) through one output per axle.

Depending on the type of transmission, the axles can be activated and deactivated individually. Reductions can also be integrated into the transfer case; a common configuration in off-road vehicles. The function of the transfer case should not be confused with drive axles that have an integrated transmission, such as on heavy trucks with a 6x4 transmission.

hydraulic transmission

Engines with a very high torque output, which require a transmission due to the narrow and optimally usable speed range, can be found in diesel locomotives. Since conventional transmissions would place extremely high demands on a friction clutch at start-up, the use of hydraulic power transmission is common.[16] The gearboxes used employ a torque converter at start-up, and individual gears are changed without interrupting tractive effort, emptying one hydraulic coupling while another is filled with oil at the same time. In some cases, lockup clutches are also used to keep power losses due to slipping low. An example of diesel-hydraulic locomotives is the German DB-Baureihe 218").

However, the most commonly used alternative is the electric transmission, so that the diesel engine drives a generator that in turn delivers the current produced to an electric traction motor, which can transmit the available power to the tractor wheels in a practically continuous and progressive manner.[16]​.

Almost all vehicles use sets of gears to operate different systems, such as windshield wipers, which are moved by an electric motor through gears. The same applies to electric windows.[55] Seat adjustment using rotary controls or the servomotors used to adjust the angle of the backrest also use gear sets. The mechanisms for opening doors and hoods or the transmission of the movement of a pedal to a mechanical organ of the vehicle are also transmission systems in the mechanical-kinematic sense: the turning movement of the pedal is converted into a linear movement or a rotary movement, for example, via a push rod. The fluid-bound power transmission path between the brake pedal and the brake cylinders is also represented by a hydraulic transmission.

Bicycles usually have a system for selecting different gear ratios. There are two main types: derailleur shifters and internal shifters. The derailleur type is the most common and the most visible, using several gears called pinions "Pinion (mechanism)"). There are usually several gears available in the ring gear set, attached to the rear wheel axle. There are also usually several sprockets on the pedal axle (called "chainrings"). By multiplying the number of gears in the front by the number of gears in the rear, you get the number of gear ratios, often called "gears."

Several attempts have been made to arrange bicycle derailleurs in a closed box, which would provide obvious advantages for better lubrication and avoiding the problems associated with dirt. These designs typically use a rigid bar drive, as a traditional chain-based gearbox is difficult to confine. The requirement to modify the bicycle frame has been a serious drawback to its adoption. One of the most recent attempts to provide a bicycle gearbox is the P1.18 18-speed Sprocket.[56]​[57][58]​ This gearbox is closed, but still uses a traditional chain. When installed on a bicycle with rear suspension, it retains a chain tensioner similar to a derailleur, although further away from the ground.

Causes of bicycle gear failure include worn teeth, damage caused by a defective chain, damage due to thermal expansion, broken teeth due to excessive pedaling force, interference from foreign objects, or loss of lubrication due to poor maintenance.

History

Many early automobiles were rear-engined, with a simple belt drive that operated as a single-speed system. The Panhard et Levassor transmission of 1891 was considered a significant advance, as it had three speeds.[5][6]​ It was a sliding asynchronous system, in which changing gears involved sliding the gears on their shafts to obtain the desired combination.[7]​ Even after passenger cars had synchronous transmissions, many transmissions for heavy trucks, motorcycles, and racing cars remained unsynchronized to withstand high forces or have a faster shift actuation.

The first car to use a manual transmission with synchromesh was the 1929 Cadillac,[8]​ although most cars continued to use non-synchronous transmissions until at least the 1950s. In 1947, Porsche patented the "split ring" synchromesh system, which became the most common design for passenger cars.[9]​ The 1952 Porsche 356 was the first car to use a synchromesh transmission. all forward gears.[10]​[11]​ In the early 1950s, most cars only had timing for shifting from third to second (the driver's manuals on the vehicles suggested that if the driver needed to shift from second to first, it was best to bring the vehicle to a complete stop beforehand).

Until the late 1970s, most transmissions had three or four forward gear ratios, although five-speed manual transmissions were occasionally used in sports cars such as the 1948 Ferrari 166 Inter or the 1953 Alfa Romeo 1900 Super Sprint. Five-speed transmissions became widespread during the 1980s, as did the use of synchromesh in all forward gears.

Six-speed manual transmissions began to emerge in high-performance vehicles in the early 1990s, such as the 1990 BMW 850i or the 1992 Ferrari 456. The first 6-speed manual transmission was introduced in the 1967 Alfa Romeo 33 Stradale, and the first 7-speed manual transmission was introduced in the 2012 Porsche 911 (991).[12]​.

In 2008, 75.2% of vehicles produced in Western Europe were equipped with manual transmission, compared to 16.1% with automatic transmission and 8.7% with other systems.[13]​.

Generalities

In a gearbox the speed ratios are formed by pairs of gears.[14]​ The most common version of a manual gearbox is the spur gear arrangement. The transmission has a lever that is used to change gears using a mechanical linkage, or less frequently, using a cable drive.

Torque is transmitted to the gearbox input shaft from the clutch through a hole. The most common configuration is for the input shaft and output shaft (collectively called main shafts) to be aligned, although physically they are separate pieces. The gear rings of the individual gears, which mesh with the output shaft of the box, are mounted on a second shaft parallel to the main axles.

Manual transmissions can be distinguished first by the type of input and output:.

When the engines are very long, such as in the case of six or more in-line cylinders (luxury cars and trucks), coaxial gearboxes dominate, since there is enough space in the vehicle for long engines and a long gearbox, with a small diameter.

Designs with coaxial shafts usually have several of the following characteristics:.

The total number of gears is obtained as:.

The upstream group is used in vehicles that need many gear ratios, such as trucks. For the downstream group, planetary gears are available that rotate like a block in normal operation (1:1 transmission ratio, without power loss) and are only activated when a reduction gear is needed on off-road routes or on steep slopes.

Gearboxes with offset parallel shafts conduct power from the input shaft through gear stages to the output shaft; There is no need for an auxiliary intermediate shaft. However, a 1:1 gear ratio is only possible through a pair of gears, so the favorable efficiency of a direct gear in a coaxial case is not possible. In the passenger car sector, generally only a few gears are required, so the upstream group generally only consists of one set of gears, and a downstream group is not required.

In all vehicle transmissions, an attempt is made to place the output near the center of the imaginary axis of the driving wheels, in order to avoid the effect of drive shafts of different lengths and technical limitations regarding the steering angle. Meeting this requirement is particularly difficult with front-wheel drive units and transversely installed engines, only short gears are possible here, which may have a slightly larger diameter. The outlet to the differential is on the engine side. To make the gearbox shorter and larger in diameter, several output shafts are usually used, each of which is connected to a gear on the main output shaft via a sprocket; and each output shaft only carries part of the gears.

To change gears, the flow of energy must be interrupted. This is done using a clutch. The driver operates the clutch lever, the clutch is disengaged and a gear can be changed with the shift lever and the associated shift mechanism in the transmission (shift process). The manual transmission remains the most common type of transmission in motor vehicles today.[15]​.

In countries like Venezuela it is known as synchronous box.

Operation of a manual transmission

Shift sleeve gearboxes are the most common type of gearbox in motor vehicles. All sprockets are helical and constantly engaged (except reverse gear). The friction connection is established using sleeves"), which are pushed on a pair of fixed shaft hubs and a loose gear. The sleeves are driven by the gear lever and determine the flow of energy from the input shaft to the output shaft. Depending on the design of the gearbox (coaxial or parallel transmission and output shaft), the structure may be different. The following describes as an example the mode of operation of a coaxial type gearbox with a sleeve:.

The power flow starts from the engine (drive shaft) via an intermediate shaft to the output shaft, through which the force coming out of the gearbox is transmitted. Starting from the front of the drive shaft, the intermediate shaft is driven through the first pair of gears. In the following gear stages, the torque is transferred from the intermediate shaft to the rear of the main shaft and from there to the output. One gear is firmly connected to the shaft, while the other can be used to shift a positive connection to the shaft using the shift sleeve"), which is moved by the gear lever. As a rule, shift sleeves are located on the main shaft, but they can also be located on the intermediate shaft. By directly coupling the drive shaft with the output shaft, it is driven directly (direct gear). In this case, the intermediate shaft runs with it, but without transmitting the torque. The intermediate shaft also works at idle, but neither shift hose produces a frictional connection to the output shaft.

These changes allow free gear selection, at least in theory: you can change from any gear to any other. The reverse gear occupies a special position, and even in modern transmissions, not a shift sleeve is used, but an intermediate sliding gear, which reverses the direction of rotation of the output shaft.

Until the late 1950s, vehicles with non-synchronized shift sleeve transmissions were widespread and trucks continued to use them into the 1980s. Sometimes these gears are also included in dog clutches. If the gear change was started when there was a speed difference, the difference had to be adjusted first. If this condition was not met, a rattling noise accompanied the change process was produced. The cause was the multi-tooth gear shift sleeve pushed into the gear wheel clutch body, which operated at different speed. It used to be a matter of the driver's skill to avoid the noise produced when changing gears.[16]​.

In addition to the simple synchronization described, there is also a forced synchronization (also called lockup synchronization), in which the shift sleeve is only activated when the synchronization is correct.

Modern selector sleeve drives are synchronized mechanisms. Synchronizing rings[17]​ and synchronous cone gears make it possible for the gear speed to adapt smoothly to the shaft speed when the shift sleeve moves over the shaft and gear (freewheeling). This process does not replace the clutch, and even with the synchronous gearbox, the flow of power from the engine to the gearbox must be interrupted by engaging the clutch before shifting.

Other types

In sliding gear gearboxes, the sprockets are almost always straight-toothed and the gear hubs and shafts are slotted, so they cannot rotate on the secondary shaft. They shift on the shaft during shifting and therefore do not mesh constantly.

The sliding gears are basically out of sync. The straight teeth make it difficult to change gears without noise, and double clutching is required both when up and down gears. In addition, a loud characteristic howl can be heard during operation. On the other hand, claw or sleeve switched gears allow the use of gears with helical teeth and smoother tooth engagement as well as synchronization. Forcing a gear may damage the sliding gears.

Sliding gearboxes[18]​ were widespread until the 1930s. The last German cars with a sliding gear were some Lloyd "Lloyd (automobile)" types. Also in the Volkswagen Beetle, the 1st and 2nd gears were initially designed as sliding gears, while the 3rd and 4th gears had low-noise, claw-shift helical teeth, which were designed as longitudinally movable round pins and matching semicircular grooves in shafts and gears.[19] For reverse gear, the sliding gear principle is still used, making it relatively difficult to engage and It usually produces a clearly audible sound.

Gearboxes for racing vehicles are still built as sliding gearboxes. With the same dimensions, this configuration allows a high load capacity due to the greater maximum torque that can be transmitted, since larger section axles can be sized. This is relevant for rally and Cup class vehicles, and due to their reduced weight, for touring cars and racing cars. Current development in racing is moving towards uninterrupted upward transmissions. Racing cars lose 2-3 km/h when shifting with a conventional gearbox due to high air resistance and low weight.

To avoid this, the boxes of many racing cars allow two gears to be briefly engaged at the same time. There are several ways to avoid damage to the gearbox that this situation could cause: one is to use one or more freewheels so that when there is an overlapping upshift, the faster rotating gear of the higher speed overtakes the slower rotating gear of the lower speed.[20]​ The freewheel prevents stress on the reducer. The other variant is that two gears are engaged at the same time for a few milliseconds. To allow this without generating stresses, a margin of torque is required between the sprockets and their axle. If the previously engaged gear is not taken out in time, the transmission will be damaged. During switching operations, very strong impacts can occur, so such designs are not suitable for most cars.

In the case of wedge gearing, the frictional connection is established not by a shift sleeve"), but by a system of stepped stops. However, the terms cannot always be clearly distinguished from each other. In some cases, non-synchronized gearboxes are also called wedge or claw type shifts to distinguish them from synchronized shift sleeve transmissions.

Contenido

Las transmisiones semiautomáticas son un tipo especial de caja de cambios manual, donde no se necesita embragar cuando se cambia de marcha. Cuando se toca la palanca de cambios, el embrague se desacopla automáticamente y cuando se introduce la siguiente marcha, el embrague se acopla de nuevo. En principio, son sistemas mecánicos con un embrague de partículas magnéticas o un embrague seco de un disco de accionamiento automático.

Para transmisiones con embrague convertidor, se combina una transmisión manual convencional con un convertidor de par, que se ubica entre el motor y el embrague y permite un arranque y realizar maniobras a baja velocidad más cómodamente y sin desgaste, como en las transmisiones automáticas convencionales. Para cambiar de marcha, el conductor tiene que accionar el embrague convencional, como con una transmisión manual normal, para interrumpir el flujo de potencia y también para cambiar manualmente. A menudo, el convertidor se desactiva a partir de una determinada velocidad, de modo que el flujo de potencia se transmite totalmente a través del embrague mecánico, aumentando la eficiencia de la transmisión. Hoy en día, este tipo de construcción se utiliza principalmente en camiones de trabajo pesado o todo terreno, como el MAN gl").

En algunos vehículos se combinaron ambos conceptos (la transmisión semiautomática y el embrague convertidor).

Ejemplos de vehículos con transmisión semiautomática son el Ford 17 M"), el Volkswagen Escarabajo y el Karmann Ghia, algunos DKW, el Opel Rekord F 11/12, el Auto Union AU 1000; y el Saxomat (con el sistema Olymat). Por su parte, el embrague de polvo magnético Ferlec se podía suministrar bajo pedido para el Renault 4 CV y el Dauphine. Modelos disponibles con convertidor y embrague automático eran los Mercedes-Benz 219/220 S/220 SE (Hydrak), Porsche 911 (Sportomatic), NSU Ro 80 (en toda la serie), Citroën DS y Renault Frégate (sistema Transfluide) o el Citroën CX (C-Matic). El Trabant disponía de una transmisión semiautomática llamada Hycomat.

Desde principios de la década de 1990, también ha habido transmisiones semiautomáticas sin pérdidas con sistemas de acoplamiento automático"), en las que el cambio manual y el embrague de disco convencional se accionan electrónicamente-hidráulicamente, como por ejemplo en el Renault Twingo Easy, el Mercedes-Benz Clase A W168") con sistema de embrague automático (AKS), o Saab y BMW con el SMG semiautomático.

Assisted manual transmission

Assisted manual transmissions, also known as AMT, make it possible to combine greater driving comfort through easy-to-use transmission control, with the economy resulting from lower fuel consumption and reduced emissions due to driving programs specially coordinated with the transmission control.[23]​ The main difference between classic semi-automatic manual transmissions and the dual-clutch transmissions discussed below is that the former have only one clutch. Its main disadvantage is the interruption of tractive effort: the flow of energy must be briefly interrupted during the gear change. Its advantage is that the clutch is engaged in an inactive state and only needs energy to open, which is why it is usually installed in particularly economical and light vehicles.

The two-clutch system features two couplings.[24]​ Its advantage is that when one clutch is opened, the other can be engaged at the same time and the tractive force is not interrupted. The disadvantage is that both clutches are open in the inactive state and the clutch in the active power branch must remain engaged, generating a waste of energy.

An assisted manual (or semi-automatic) gearbox is a conventional gearbox expanded to include automated components.[23]​ The fundamental difference with a conventional manual transmission is that the drive is carried out by a system consisting of hydraulically driven cylinders and electric servomotors that control the actuators. During gear shifting, the activated clutch actuator separates the gearbox from the tractive effort, and then the gear change calculated in the gearbox control unit is transmitted to the actuators, which engage the next higher or lower gear.[25]​.

With the automated manual transmission, gear changes can usually be made autonomously using a program stored in the control unit (manumatic transmissions), although the driver can also use the shift knob on the center console or paddles on the steering wheel to set the next higher or lower gear. On the other hand, the switching program prevents shifting errors.[26]​ As a general rule, it is only possible to skip the sequence to a limited extent, since the control electronics only allow certain switching operations if the engine remains within an admissible speed range.

In trucks for long-distance transport, this type of automated transmissions have been used since the mid-1980s, in which the driver preselects the gear and the electronic control of the transmission performs the gear change using electro-pneumatic shift cylinders. With the classic "electro-pneumatic circuit") from Daimler-Benz,[27]​ for example, the driver selects 6th/low gear and depresses the clutch pedal. This activates the control electronics and checks whether the switching process can also be carried out depending on the engine speed. If this is the case, the control electronics shifts to the selected gear via the pneumatic shift cylinder. If it refuses to shift because the engine threatens to accelerate too much, it indicates this to the driver by means of a warning tone. As As a general rule, the transmission shifts into neutral.

Newer systems in trucks or coaches also shift fully automatically, and lack a clutch pedal (which in some models can be deployed if necessary). Modern trucks are equipped as standard with an eight-speed gearbox, which is usually based on a four-speed manual gearbox, expanded by an additional group to have a total of 16 gears.

A semi-automatic gearbox shares most of the advantages of a manual gearbox:

In addition, it offers other advantages such as:

The semi-automatic transmission is used in some vehicles instead of a conventional gearbox to comply with special approval regulations, since the switching program can be adapted to the official procedures for measuring consumption and exhaust gases in order to offer better measurement results than with a manual transmission. This allows the vehicle to be approved with a better efficiency rating, although in practice it can generate higher consumption or lower acceleration capacity for the end customer, which is actually due to a reduction in the technical possibilities of the transmission system.

Its main disadvantages are:

This results in certain jerks during the gear changing process, especially under strong acceleration. To avoid this, newer systems use a second secondary shaft, on which the shifting process can be prepared for the respective adjacent gear, as with the double clutch system, so that the interruption of tractive power during clutch release is noticeably reduced (e.g. to 50 ms with Graziano's ISR in the Lamborghini Aventador).[28]​.

The first automatic gearboxes with hydraulic actuators used in series-produced vehicles were in the BMW M3 in 1997, in which the existing classic gearbox was upgraded to an automated gearbox using a hydraulic system, and the Smart Fortwo from 1998, which was the first vehicle to have an automated gearbox operated by an electric motor. The special feature of the Smart was that it was only manufactured with an automatic transmission, and the manually operated variant was only available by modifying the transmission control software. A unit with manual shift can easily be modified to automatic by changing the software. Both transmissions were developed by Getrag Firm.[29]​.

Due to its high efficiency, the automatic-manual gearbox is a popular equipment variant, especially in small cars such as the Audi A2 1.2 TDI, the Opel Corsa or the Smart. The VW Lupo 3L was available exclusively with this option, although gearboxes with a relatively high failure rate and very expensive to repair negatively influenced demand for the vehicle.

Several automakers offer automated manual transmissions under different trade names:.

A variant of the automated gearbox is the dual-clutch gearbox. It consists of two subtransmissions with associated clutches. One part of the transmission carries the even gears, and the other the odd ones. Reverse gear can be assigned to both subtransmissions. Before shifting, the next higher gear is engaged in the unloaded branch when accelerating or the next lower gear when decelerating. Then the clutch of the unloaded gear is closed and at the same time the clutch of the other is opened. This means that the change can take place without interrupting the traction force. The time it takes to change gears depends solely on how quickly the clutches open and close.

This system is also known as a "direct shift gearbox", also abbreviated as DSG, DKG, PDK, DCT or TCT.

The main advantages of the two-clutch system are:.

The disadvantage compared to the automatic-manual system is the (often permanent) energy consumption required to keep the clutch closed in the power branch.

Due to their properties, two-clutch systems compete with conventional transmissions with converters and planetary gears.

Originally developed by Porsche for racing in the 1980s, Volkswagen and Audi pioneered the use of this technology in their large-scale production, achieving technological leadership in the market. A two-clutch transmission has been in series production in the Golf and Passat classes since 2002 (6-speed, wet clutch supplier is BorgWarner). VW's internal designation is DQ250 (acronym for double clutch - transverse installation - 250 N·m, although it can transmit 320 N·m of torque).

In the following years, VW introduced a 7-speed system with the internal designation DQ200 (for the Polo and small Golf). LuK "LuK (company)") supplies a dry double clutch for this transmission.

In 2009, the first dual-clutch system developed especially for Audi with the designation DL501 came on the market with the Audi Q5. A BorgWarner-sourced wet double clutch was again used in this gearbox. The acronym DL501 means double clutch - longitudinal installation - 500 N·m, and was gradually marketed in the A4, A5 and A6 models.

The DQ500 (7-speed DCT) for the VW T5 van appeared in autumn 2009, and was also available in the Tiguan from June 2010. The wet clutch was developed and manufactured by the VW factory in Kassel, marking the first time that a double clutch developed by the company was used. All variants (DQ200, DQ250, DQ500 and DL501) were also produced in Kassel.

Since July 2008, Porsche offered the 7-speed PDK transmission for the 911 developed by ZF. It was also available to order for the Boxster and Cayman. Likewise, it was added to the Porsche Panamera since September 2009 and to the Turbo since October 200.

A dual-clutch transmission with seven forward gears designed by Magna PT has been available since March 2008 for the BMW M3. Ford, Mitsubishi, Ferrari, Mercedes-Benz and Volvo also offered models with Getrag dual-clutch transmissions since 2008.

For the first time, a dual clutch was installed on a production motorcycle in the summer of 2010 - a Honda VFR1200F").

Sequential transmissions cannot be changed at will, you can only change to the next highest or lowest gear immediately, that is, the next one in the sequence.[31]​ It is not possible to skip one or more steps. Such a transmission can be found, for example, on the Smart Fortwo and on many motorcycles. Dual-clutch gearboxes are also always operated sequentially, and experience a break in tractive power when jumping one or two gears.

Wedge gears, like sliding gears, have fixed gear wheels. They are mainly used in stationary machines and light vehicles. With the sliding wedge transmission"),[32]​ a key moves longitudinally on a splined shaft when changing gears and the respective gear is locked with a positive adjustment. They are used on mopeds and on motorcycles by brands such as DKW, Simson&action=edit&redlink=1 "Simson (company) (not yet drafted)") and Zündapp, also on two-stroke motorcycles up to 250 cm³ displacement and on the small Janus car, as well as in the electromagnetically operated preselector gearbox Selectromat of the Goggomobil.

The shift shims are eliminated in the bevel gear gearbox. A cone is attached to a rod inside the hollow interior, which pushes the balls out through the holes in the intermediate shaft of the sprockets, ensuring "form fit" between the shaft and the sprocket.[33]​.

At the end of the 1920s, the British company Daimler developed an assisted transmission, which consisted of the combination of a gearbox with coupled planetary gear sets based on the concept devised by the Englishman Walter Gordon Wilson of a hydraulic coupling, based in turn on the ideas of the German Hermann Föttinger). The gears were selected by a compressed air system controlled by a small selector lever (the preselector) located on the steering column, combined with the left clutch pedal. This operation was considerably easier and did not require the physical effort necessary to change gears using the double clutch through a mechanical link, the usual system until then The Associated Equipment Company (AEC) used the preselector with a fluid flywheel for thousands of buses (for example, the AEC. Regent III") = RT) of the London Passenger Transport Board") (LPTB) and its successor, the London Transport Executive") (LTE).

Operation

It is common for the selector lever with the adjustment options to be located in the central tunnel of the vehicle floor. The options are usually:

In automatic transmissions this sequence is generally followed, since there are legal regulations that require it in some countries, such as the United States.[35]​.

Some transmissions offer more gear steps and often have a manual mode, such as:.

Use in Western Europe

In an international comparison, the percentage of cars equipped with automatic transmission in Western Europe is well below the percentage values ​​in countries such as the United States and Japan. This is due to certain disadvantages compared to the manual gearbox (although some have practically already been overcome), such as lower acceleration (if there is no increase in torque), lower top speed, higher consumption, delayed response at the beginning of an overtaking maneuver, higher price compared to a manual gearbox (not common in all markets), certain traffic conditions and the sometimes unsporty image of the automatic gearbox, which is rarely found in motorsport in the classic form of the converter with planetary gear.

According to a Swedish study, the use of an automatic transmission reduces the number of driving errors in the elderly, while there is no such correlation among middle-aged drivers.[36]​.

In Germany, automatic transmissions were much less common than manual transmissions for a long time. In the recent past, this proportion has been tilted in favor of automatic transmissions: while in 2010 only 27 percent of new cars manufactured in Germany were equipped with an automatic transmission, this figure increased to 48 percent in 2018.[37]​ As the first major German brand, Mercedes-Benz announced in 2020 that in the future it would completely dispense with manual transmissions when developing new vehicle generations.[38]​.

Automatic transmission with converter

An automatic transmission with a converter differs in structure from a manual transmission mainly in the following points:.

The main advantages of a transmission with a converter are:.

The most well-known disadvantages are:

In exceptional cases, planetary gear sets are not used with automatic transmissions, such as in Hondamatic gearboxes and with the automatic transmission of the Mercedes-Benz A-Class") (W168). The structure of such a gearbox is similar to that of a manual gearbox. The main distinguishing feature is that, instead of synchronizers and shift sleeves, they have an independent multi-plate clutch for each gear stage of the automatic transmission.[39]​.

The friction lock connection of the individual planetary gear sets with the input and output shafts is carried out by multi-disc clutches. Its operation is predetermined by a driving and switching program in the control unit. [39] Transmission control until the late 1980s was carried out hydraulically. Currently (as of 2016), it is done electronically and the actuation of the clutches is done by electrically controlled hydraulic valves.

In the torque converter, some of the engine's power is transferred to the oil in the form of frictional heat due to slippage. To reduce the associated loss of efficiency, converter automatic transmissions are often equipped with a lock-up clutch that allows direct mechanical engagement by friction after starting or changing gears.

Additionally, energy is required to generate hydraulic pressure using an oil pressure pump. Inactive multi-plate clutches that are not required in the engaged stage cause additional drag losses because the clutches are open.[40]​ Due to these drag losses, fuel consumption is higher compared to an otherwise equal manual transmission equipped vehicle. Modern automatic transmissions offer a torque converter lockup clutch from first gear to reduce this additional fuel consumption. A further reduction in consumption is possible thanks to the stationary decoupling, which shifts the transmission to idle when the vehicle is stationary and the service brake is activated, thus avoiding drag losses through the converter. The consumption drawbacks of the automatic system are usually not very evident in standard consumption, unlike the consumption that occurs in normal road traffic, since the gear change points are adapted to standardized cycles.

A level change takes place by switching off a switching element and simultaneously connecting the switching element to the next higher or lower level. The second change element thus assumes the torque of the first piece until the second change element assumes all the torque at the end of the change. The time span for this process is in the range of two to three digit milliseconds. Since the introduction of electronic transmission controls in the late 1980s, a "torque reduction request" is sent to the engine control unit to protect the transmission from overloads and/or achieve better shift quality. This has also been done via the CAN Bus since the late 1990s, allowing the engine control to reduce engine torque during shifting. Another means of increasing shift quality is to open the converter clutch in certain shift situations. Gear changes between up to eight gear ratios are very smooth. The fact that the power flow is not completely interrupted due to the design also leads to the well-known "creeping" of vehicles with an engaged automatic transmission whenever it is not idling. This drag can be very useful when maneuvering.

Continuous variable transmission

A planetary gear as a timing system is not continuous, but they can make one input shaft act almost continuously, as long as the second input shaft of the adder gear regulates the overall ratio. The second input can be, for example, hydrostatic (as in tractors), electric (Toyota Prius) or also mechanical (as in a continuously variable transmission).

This transmission design offers the following advantages:.

Torque capacity can be improved with a power split, for example. The continuously variable transmission is combined with a planetary adding or dividing gear. However, this reduces the spread of the transmission or the overall efficiency of the gear combination deteriorates.

With optimized consumption characteristics, the disadvantage of low transmission efficiency can be partially compensated. Thanks to the optimization of engine consumption and wider speed ranges for the best fuel consumption, dual-clutch transmissions are currently the strongest competitors to the consumption-optimized continuously variable transmission.

In practice, optimized features are not accepted by the majority of customers, which means that the theoretical advantages are subject to certain restrictions.

In practice it has been found that many drivers are not satisfied when the vehicle accelerates from zero to, for example, 100 km/h, since the engine practically always rotates at the same speed ("rubber band effect"). To avoid this, many continuously variable transmission systems offer a gearshift program in which they work with fixed gear ratios and thus imitate a normal stepped automatic transmission. However, this additional function is not expressly required from a technical point of view. The dissatisfaction of some users is a purely psychological effect that dates back to decades of experience with conventional gearboxes or multi-step automatic transmissions and their characteristics.

Several small manufacturers used transmissions with friction wheels until the 1920s. Starting in 1958, the Dutch manufacturer DAF" produced cars with the Variomatic system, a transmission that used V-belts"). combined with variable width pulleys (see continuously variable transmission).

The principle devised by DAF has since been developed using metal link push chains for higher torques. These gearboxes were available in utility vehicles such as the Ford Fiesta or the Fiat Uno. Audi brought to the market around 2000 the new Multitronic gearbox for powerful cars, which uses a chain drive.

The Toyota Prius electric hybrid has a pseudo-continuously variable automatic transmission, in which a planetary gear with power division superimposes the speeds and torques of the combustion engine and the electric motor, as well as the electric generator. The electronically controlled variable distribution of drive power between the electric motor and the generator allows the relationship between the speed of the internal combustion engine and the output speed to be varied.

Electric variable drive

Electric variable transmission (EVT or e-CVT) is used in hybrid vehicles, combining the output of an electric motor and a gasoline engine. It provides continuously variable gear ratios, just like a conventional mechanical stepless gear system.

In its most common form, a gasoline engine is connected to a traditional transmission, which in turn is connected to a planetary gear system carrier. In turn, the electric motor/generator is connected to the "solar" sun gear, which is not normally driven in typical epicyclic systems. Both power sources can feed the transmission output at the same time, splitting the power between them. Typically, one-quarter to one-half of the motor's power can be supplied to the sun gear. Depending on the design, the transmission to the epicyclic system can be greatly simplified or eliminated entirely, as EVTs are capable of continuously modulating output/input speed ratios like mechanical CVTs, but offer the distinct benefit of also being able to apply power from two different sources to a single output, as well as potentially reducing the overall complexity of the transmission system.

The power distribution ratio is established based on common driving conditions, such as road speed for a car or traffic speed for a city bus. When the driver presses the accelerator, the associated electronics interpret the pedal position and immediately adjust the gasoline engine to the RPM that provides the best fuel economy for that setting. As the gear ratio is normally set far from the maximum torque point, this setting would normally result in very poor acceleration. Unlike gasoline engines, electric motors offer efficient torque over a wide rpm range and are especially effective at low rpm, where the gasoline engine is inefficient. By varying the electrical load or supply of the electric motor connected to the sun gear, additional torque can be provided to compensate for the low torque output of the combustion engine. As the vehicle accelerates, the power provided by the electric motor reduces and eventually stops, creating the illusion of a CVT.

A classic example of an EVT system is Toyota's Hybrid Synergy Drive, which lacks a conventional transmission and the sun gear always receives 28% of the engine's torque. This available electrical energy can be used to operate any electrical load in the vehicle, recharge the batteries, power the entertainment system, or run the air conditioning. Additionally, any residual power is fed back to a second motor which feeds the powertrain output directly. At highway speeds, this additional generator/motor boost is less efficient than simply driving the wheels directly. However, during acceleration, the electric support is much more efficient than the internal combustion engine which operates far from its maximum torque point. GM uses a similar system in the hybrid powertrains of Allison buses and in the Tahoe and Yukon pick-up trucks, although the latter use a two-speed transmission as opposed to the epicyclic system, and the sun gear receives about half of the total power.

Manual transmissions are characterized by allowing the driver to choose at will the two usual ways of operating the change, being able to decide for himself the most appropriate gear (as with a manual or semi-automatic gearbox), or allowing an electromechanical or electronic system to autonomously determine the correct gear ratio based on the vehicle's gear parameters (as with a classic automatic transmission system). The first systems of this type were automatic transmissions modified so that the driver could choose between a range of "short" or "long" gears, in order to obtain greater control over the vehicle in some particular situations, such as on steep and long descents. This configuration took advantage of the maturity of the development since the 1930s of automatic transmissions, capable of effectively managing the engine speed autonomously thanks to two key elements: the epicyclic gear systems and the hydraulic torque converter. Subsequently, the development of electronics has made it possible to devise different manumatic systems, automatic gearboxes that in turn include the option of manually selecting gears sequentially, such as the Tiptronic system popularized by Volkswagen, the Steptronic from BMW, or the G-Tronic from Mercedes-Benz.[44]​.

direct transmission

In a direct drive mechanism power (physical) power and torque are transmitted from an electric motor to the output device (such as the drive wheels of a car) without using speed reducers. Several cars from the turn of the century used direct drive wheel hub motors, as did some prototypes in the early 2000s. On the other hand, most modern electric cars use one or several internal motors, where the transmission is transferred directly to the axles "Axle (mechanical)") of the wheels.[48]​[49]​.

indirect transmission

Electric transmissions convert the mechanical power of engines into electricity using an electrical generator and convert it back to mechanical power using an electric motor. Electrical or electronic control systems with adjustable speed drive") are used to control the speed and torque of motors. If the generator is driven by a turbine, such a device is called a turboelectric transmission"). Likewise, transmissions powered by a diesel engine are called diesel-electric.

Diesel-electric transmissions are used in many railway locomotives, ships, large mining trucks and some bulldozers. In these cases, each driven wheel is equipped with its own electric motor, which can be powered with variable electrical power to provide any required torque or power output to each wheel independently, producing a much mechanically simpler solution for very large vehicles with multiple drive wheels, where the drive shafts would be much larger or heavier than the electric cable that can provide the same amount of power. It also improves the ability to allow different wheels to operate at different speeds, which is useful for steering wheels on large construction vehicles.

Hydrostatic transmissions transmit all power hydraulically, using the components of a hydraulic machine. They are similar to electric transmissions, but use hydraulic fluid as a power distribution system instead of electricity.

The transmission input drive is a central hydraulic pump and the final drive unit(s) is a hydraulic motor or hydraulic cylinder. Both components can be placed physically separately on the machine, being connected only by flexible sleeves. Hydrostatic drive systems are used in excavators, tractors, forklifts, winch drive systems, heavy lifting equipment, agricultural machinery or in earth moving equipment. An exceptional case was the Ferguson P99, a Formula 1 car from around 1961 that used a hydraulic transmission system.[50]​.

The Human Friendly Transmission system used on the Honda DN-01 motorcycle is also hydrostatic.[51]​.

We speak of a hydrodynamic transmission when the hydraulic pump or hydraulic motor makes use of the effects of the flow of a fluid as it passes through the blades of a turbine. The pump and motor usually consist of jointless rotating vane systems, and are usually placed in close proximity to each other. The gear ratio can be made to vary by additional rotating blades, an effect similar to varying the pitch of an airplane propeller.

The torque converter in most automotive automatic transmissions is itself a hydrodynamic transmission. Hydrodynamic transmissions are used in many passenger rail vehicles, those that do not use electric transmissions. In this application, the advantage of smooth power delivery can outweigh the reduced efficiency caused by energy losses generated by turbulence in the fluid.

Muchos vehículos comerciales también requieren una transmisión que permita expandir el rango de velocidad de giro del motor de combustión interna al régimen de giro de las ruedas necesario para conducir.

Por ejemplo, la velocidad de maniobra de un camión pesado es de unos 3 km/h. Esto se logra a una velocidad del motor de aproximadamente 550 rpm. Al conducir, el camión viaja a 89 km/h en una autopista. Por razones de consumo, se desea alcanzar esta velocidad (en tráfico de larga distancia) a aproximadamente 1100 rpm. A partir de una relación de velocidades de giro del motor de combustión interna de 2 (550 rpm respecto a 1100 rpm), es necesario de una relación de velocidad de giro de las ruedas de 30 (3 km/h respecto a 90 km/h). Esto significa que la relación de la marcha más baja y la relación de la marcha más alta difieren en un factor de 15. La relación de la relación entre la marcha más alta y la marcha más baja se llama dispersión.[52]​ Para disponer de una distribución amplia y a la vez tener marchas poco espaciadas (algo necesario para reducir el consumo de combustible), se utilizan transmisiones con 12 o 16 marchas en camiones pesados. Dichas transmisiones se componen de varias subtransmisiones, la denominada transmisión primaria (2 etapas), la transmisión principal (3 o 4 etapas) y la transmisión grupal (2 etapas). Dado que las etapas de las subtransmisiones se pueden combinar de forma multiplicativa, se obtienen 12 o 16 marchas, aunque no todas las combinaciones de transmisión dan resultados utilizables en la práctica.

La marcha atrás (inversión del sentido de giro de la transmisión) forma parte de la transmisión principal. Esto permite combinar la marcha atrás con las 2 etapas de la caja de cambios primaria y las 2 etapas de la transmisión del grupo, obteniéndose (al menos teóricamente) cuatro marchas atrás. Sin embargo, a menudo se bloquean, y no se pueden seleccionar.

Los camiones ligeros suelen tener 6 marchas. La distribución de velocidad del motor es mayor en los camiones ligeros, y la velocidad de maniobra se establece un poco más alta para que sean suficientes 6 marchas (con un diseño más similar al de los turismos).

Primary gearbox

This transmission is an extension of a conventional transmission, attaching an additional gear stage to the input shaft. This has the effect that the power can be distributed in two stages. So, there is a small step and a big step for each stage. This gives this gear the name "divider" and the overall construction the name split gear. The term primary gearbox indicates that this gearbox is installed in front of the basic gearbox. However, more often, the upstream group is housed directly in the gearbox itself.

Split transmissions are found on heavy trucks and are usually operated with a switch on the shift lever. If only the splitter is operated or if a gear is changed from a high gear to the next lower gear, then it is called "up half a gear." If you shift from a low gear to the next lower gear, you shift "half a gear down."

rear gearbox

It is a two-stage planetary gear installed between the base gear and the cardan. This doubles the number of gears available (the range or range). This is why constructions using a rear-mounted gearbox are also called range gearboxes (see overdrive "Overdrive (mechanical)").

First you change gears in the basic transmission and then you activate the range group switch. This is done either by a switch on the gear lever or by what is known as "rollover." In the first gear, the switch is switched to the upper (large) group before the gear change, and then the gear lever is put back into the first gear. However, this is 5th gear on a basic 4-speed transmission or 4th gear on a basic 3-speed transmission. The driver has an 8-speed split setup, which breaks between 3rd and 4th gear and 5th and 6th gear. Here you move the gear lever to neutral after shifting into 4th gear and pressing the lever to the right with the palm of your hand. This changes the range group and the lever no longer turns to the right in neutral, but to the left. From the driver's point of view, you are now facing the 5th or 6th aisle. The lever is actually in front of the 1st or 2nd gear of the basic transmission, but the group shift now converts it to 5th or 6th gear. This is also known as a "double H" circuit. These transmissions can be found in heavy duty trucks.

A combined upshift and downshift gearbox is often used, meaning that up to 16 speed levels are available on heavy trucks.

Automatic transmission with range divider group

Most modern trucks are equipped with automatic transmissions, as noted above. They offer low fuel consumption and ease of use.

These electronic shift aids for commercial vehicles were developed in the early 1980s with the desire to save fuel, protect transmission components and also give relief to the driver, although the new system met with strong rejection from truck drivers at first.

In 1984, Scania was the first manufacturer to bring an electronic gearshift aid to the market under the name CAG ("Computer Assisted Gear Shift"). The conventional gear lever was replaced by a small joystick in the engine tunnel. Electronics that recorded various driving parameters, such as speed and engine speed, showed the trucker a gear change recommendation on a screen on the instrument panel. If the driver accepted the suggested gear, all he had to do was engage the clutch. In the case of a different gear selection, the desired gear was selected using a lever. If the system failed, the box with the selector switch could be folded to the side and a conventional lever, which was carried in the vehicle, inserted.

About a year later, Mercedes-Benz followed suit as a manufacturer of its own commercial vehicle transmissions, and ZF began production of its own shift aids. At the 1985 Frankfurt Motor Show, Mercedes introduced the Electro-Pneumatic Circuit (EPS),[53]​ which was offered as standard on the 1644 model, the most powerful at the time. It was also available for smaller models and the O 303 coach. Unlike Scania's CAG and some ZF models, the EPS did not offer a gearshift recommendation, so selecting gears to up or down Lowering them always had to be done by touching the lever forward or backward. With the introduction of the Mercedes-Benz Actros series, the "Telligent" (telematics and intelligent) system appeared in 1996, initially as a semi-automatic circuit, and later as a fully automatic circuit.

At the same time, as a manufacturer of truck transmissions, ZF offered semi-automatic shift aids under the name AVS (automatic preselection circuit), which could be operated by push buttons, gear shift knobs or a rocker switch on the steering wheel.

However, in terms of handling, all initial systems are largely identical: The controller outputs a switching pulse via a switch, which is carried out by electronic management that controls a series of pneumatic drive cylinders.

The prevailing trend has been to relieve the driver of almost all gear changing tasks. With all available shift aids, standstill and reverse are only operated using special buttons or key combinations. In some fully automated manual transmissions, there is no longer a clutch pedal; In the Actros, for example, it folds into the footwell and can be used as an option. Since the electronics completely control all shifting and clutch processes, non-synchronized claw gears can also be used here, which are lighter and more compact in terms of design and can be shifted faster in full gear. However, these fully automatic gearshift aids should not be confused with a torque converter automatic transmission.

transfer case

"Transfer cases" are installed after the basic gearbox. They are typically used in vehicles that have multiple driven axles (such as four-wheel drive cars). The transmission distributes the drive power to multiple axles (two in a 4x4 vehicle) through one output per axle.

Depending on the type of transmission, the axles can be activated and deactivated individually. Reductions can also be integrated into the transfer case; a common configuration in off-road vehicles. The function of the transfer case should not be confused with drive axles that have an integrated transmission, such as on heavy trucks with a 6x4 transmission.

hydraulic transmission

Engines with a very high torque output, which require a transmission due to the narrow and optimally usable speed range, can be found in diesel locomotives. Since conventional transmissions would place extremely high demands on a friction clutch at start-up, the use of hydraulic power transmission is common.[16] The gearboxes used employ a torque converter at start-up, and individual gears are changed without interrupting tractive effort, emptying one hydraulic coupling while another is filled with oil at the same time. In some cases, lockup clutches are also used to keep power losses due to slipping low. An example of diesel-hydraulic locomotives is the German DB-Baureihe 218").

However, the most commonly used alternative is the electric transmission, so that the diesel engine drives a generator that in turn delivers the current produced to an electric traction motor, which can transmit the available power to the tractor wheels in a practically continuous and progressive manner.[16]​.

Almost all vehicles use sets of gears to operate different systems, such as windshield wipers, which are moved by an electric motor through gears. The same applies to electric windows.[55] Seat adjustment using rotary controls or the servomotors used to adjust the angle of the backrest also use gear sets. The mechanisms for opening doors and hoods or the transmission of the movement of a pedal to a mechanical organ of the vehicle are also transmission systems in the mechanical-kinematic sense: the turning movement of the pedal is converted into a linear movement or a rotary movement, for example, via a push rod. The fluid-bound power transmission path between the brake pedal and the brake cylinders is also represented by a hydraulic transmission.

Bicycles usually have a system for selecting different gear ratios. There are two main types: derailleur shifters and internal shifters. The derailleur type is the most common and the most visible, using several gears called pinions "Pinion (mechanism)"). There are usually several gears available in the ring gear set, attached to the rear wheel axle. There are also usually several sprockets on the pedal axle (called "chainrings"). By multiplying the number of gears in the front by the number of gears in the rear, you get the number of gear ratios, often called "gears."

Several attempts have been made to arrange bicycle derailleurs in a closed box, which would provide obvious advantages for better lubrication and avoiding the problems associated with dirt. These designs typically use a rigid bar drive, as a traditional chain-based gearbox is difficult to confine. The requirement to modify the bicycle frame has been a serious drawback to its adoption. One of the most recent attempts to provide a bicycle gearbox is the P1.18 18-speed Sprocket.[56]​[57][58]​ This gearbox is closed, but still uses a traditional chain. When installed on a bicycle with rear suspension, it retains a chain tensioner similar to a derailleur, although further away from the ground.

Causes of bicycle gear failure include worn teeth, damage caused by a defective chain, damage due to thermal expansion, broken teeth due to excessive pedaling force, interference from foreign objects, or loss of lubrication due to poor maintenance.