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].