Semi-automatic transmission

A semi-automatic transmission (also known as automated transmission, self-changing transmission, clutchless manual transmission, automated manual transmission, flappy-paddle gearbox, or paddle-shift gearbox) is an automobile transmission that does not change gears automatically, but rather facilitates manual gear changes by dispensing with the need to press a clutch pedal at the same time as changing gears. It uses electronic sensors, pneumatics, processors and actuators to execute gear shifts on the command of the driver or by a computer. This removes the need for a clutch pedal which the driver otherwise needs to depress before making a gear change, since the clutch itself is actuated by electronic equipment which can synchronise the timing and torque required to make quick, smooth gear shifts. The system was designed by automobile manufacturers to provide a better driving experience through fast overtaking maneuvers on highways.

 

Operation

In standard mass-production automobiles, the gear lever appears similar to manual shifts, except that the gear stick only moves forward and backward to shift into higher and lower gears, instead of the traditional H-pattern. The Bugatti Veyron uses this approach for its seven-speed transmission. In Formula One, the system is adapted to fit onto the steering wheel in the form of two paddles; depressing the right paddle shifts into a higher gear, while depressing the left paddle shifts into a lower one. Numerous road cars have inherited the same mechanism.

The clutch is really only needed to start the car. For a quicker upshift, the engine power can be cut, and the collar disengaged until the engine drops to the correct speed for the next gear. For the teeth of the collar to slide into the teeth of the rings, both the speed and position must match. This needs sensors to measure not only the speed, but the positions of the teeth, and the throttle may need to be opened softer or harder. The even-faster shifting techniques like powershifting require a heavier gearbox or clutch or even a dual clutch transmission.

Electrohydraulic manual transmission

Electrohydraulic manual transmission is a type of semi-automatic transmission system, which uses an automated clutch unlike conventional manual transmissions where the driver operates the clutch. The clutch is controlled by electronic computers and hydraulics. To change gears, the driver selects the desired gear with the transmission shift lever, and the system automatically operates the clutch and throttle to match revs and engage the clutch again. Also, many such transmissions operate in sequential mode where the driver can only upshift or downshift by one gear at a time.

Depending on the implementation, some computer-controlled electrohydraulic manual transmissions will automatically shift gears at the right points (like an automatic transmission), while others require the driver to manually select the gear even when the engine is at the redline. Despite superficial similarity, clutchless manual transmission differ significantly in internal operation and driver's 'feel' from manumatics, the latter of which is an automatic transmission (automatics use a torque converter instead of clutch to manage the link between the engine and the transmission) with ability to signal shifts manually.

 

Use in road cars

The most famous application of a sequential transmission on road-cars would be their use in some Ferraris since the late-nineties, beginning with the F355 F1. Their system, the most current version of which is called "F1-Superfast," with shift times of 60 ms is designed to serve as a link to their Formula One efforts. This technology has also trickled down to the cars of their sister company, Maserati where it is known as "Cambiocorsa". Alfa Romeo's Selespeed in 1999 was the first sequential transmission in a mainstream car, derived from the Ferrari system.

BMW offered a system simply called "sequential manual gearbox" (SMG) on the E36 M3, and later "SMG-II" on the E46 M3. The BMW SMG transmission has both automatic and manual shift modes. Inside the different modes there are different programmes, with six settings to control the upshift/downshift speed for manual operation, and five settings for automatic mode.

Later, the 3rd generation Toyota MR2 used Toyota's version, known as the "Sequential Manual Transmission" (SMT). Although it does not perform as well as the European-designed transmissions, Toyota's is the cheapest system to manufacture, and the MR2 is the least expensive car to possess a true sequential gearbox.

Finally, Volkswagen Group (parent owner of Lamborghini) introduced a sequential transmission to the Lamborghini Gallardo (E gear), and then adding it to the Audi R8 (R tronic).

BMW has since switched over to a Getrag dual clutch transmission in the latest M3, and Ferrari as well in 2009 with the California and 458 Italia.

Applications

• Alfa Romeo 156 JTS/GTA
• Alfa Romeo 147 TS/GTA
• Alfa Romeo GT
• Alfa Romeo 159
• Alfa Romeo Brera
• Alfa Romeo Spider
• Alfa Romeo 8C Competizione & 8C Spider (Q-Select)
• aston-martin
• Audi R8 (R tronic)
• 1997 BMW E36 M3 (SMG)
• BMW E46 M3 (SMG II)
• BMW E60 M5 (SMG III)
• BMW E63/64 M6 (SMG III)
• BMW E85 Z4 (Optional SMG)
• Fiat Stilo Abarth (Selespeed)
• Fiat Bravo Brazil (Dualogic)
• 1997 Ferrari F355 (F1)
• ferrari-fxx-evolution
• Ferrari 360
• Ferrari Enzo
• Ferrari F430
• ferrari-612-scaglietti
• Ferrari 599
• lamborghini-gallardo
• 2010 Lexus LFA (ASG)
• Maserati (certain models)
• 2001 Toyota MR2 (SMT)

Dual-clutch transmission

A dual-clutch transmission, (DCT) (sometimes referred to as a twin-clutch gearbox or double-clutch transmission), is a type of semi-automatic or automated manual automotive transmission. It uses two separate clutches for odd and even gear sets. It can fundamentally be described as two separate manual transmissions (with their respective clutches) contained within one housing, and working as one unit. They are usually operated in a fully automatic mode, and many also have the ability to allow the driver to manually shift gears, albeit still carried out by the transmission's electro-hydraulics.

Applications

Bmw

BYD

Chrysler

Fiat Group

Ford Motor Company

General Motors

Honda

Hyundai

Lotus

McLaren Automotive

Mercedes-Benz

Mitsubishi

Mitsubishi Fuso Truck and Bus Corporation

Nissan

PSA Peugeot Citroën

Porsche

Renault

Volkswagen Group

Railcar use

A different type of dual-clutch transmission has been used in some railcars. The two clutches are placed one on the gearbox input shaft and the other on the gearbox output shaft. When a gearchange is to be made, both clutches are disengaged simultaneously and a brake is applied inside the gearbox. The gearchange is made with all gears stationary, so no synchronizing mechanism is needed. After the gearchange, both clutches are re-engaged. There would be a significant break in transmission so this system would be unsuitable for shunting locomotives.

Saxomat

Saxomat was a type of automatic clutch available as an option on Fiat 1800, Saab 93, Borgward Isabella, Goliath/Hansa 1100, Auto Union 1000, BMW, Opel, Ford Taunus, NSU, Glas, Trabant Wartburg and Volkswagen cars. Opel sold it as Olymat; Trabant and Wartburg named the system Hycomat. The Hydrak, used in some Mercedes-Benz vehicles between 1957 and 1961, was a similar system with a hydrodynamic torque converter in place of the Saxomat's centrifugal clutch, this H.T.C. system was standard on NSU Ro 80 and was optional on the Porsche 911 (Sportomatic). The system also reappeared in the 1990s as Sensonic.

Cars with a Saxomat clutch did not have a clutch pedal. The Saxomat consisted of two independent systems, the centrifugal clutch, and the servo clutch. The centrifugal clutch was engaged above certain engine rpms by centrifugal force, acting on spinning weights inside the clutch, similar to a centrifugal governor.

The servo clutch used an electric switch that supplied manifold vacuum via an actuator valve to a reservoir that disengaged the cluch. The clutch is disengaged automatically whenever the gear shift lever was touched.