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Semi-automatic transmission

From Wikipedia, the free encyclopedia

A semi-automatic transmission (also known as an automated manual[1][2][3], clutchless manual[4], auto-manual[5], auto-clutch, semi-manual[6], trigger shift, flappy-paddle or paddle-shift gearbox) is an automobile transmission that combines manual transmission and automatic transmission. It's a partially automatic (and partially manual) transmission.

Semi-automatic transmission refers to a conventional manual transmission with an automatic clutch. It requires full driver-control of the manual gear ratio selection, and the driver must manually shift through all the gears. They facilitate gear shifts for the driver by operating the clutch system automatically, while still requiring the driver to manually shift gears. This system is commonly found on older vehicles, such as automobiles and buses, without a clutch pedal, and on some motorcycles, minus the hand clutch lever.[7][8]

Throughout automotive history, conventional automatic transmissions already allowed some control of gear selection using the console or shifter, usually to limit the transmission shifting beyond a certain gear (allowing engine braking on downhills) and/or locking out the use of overdrive gears when towing. It enhanced such features by providing either steering wheel-mounted paddle shifters or a modified shift lever, allowing the driver to enter a "manual mode" and select any available gear, usually in a sequential "up-shift/downshift" manner. The modern transmission is a computer-controlled manual transmission, operated by an ECU & TCU, and generally uses an electromechanical, hydraulic or pneumatic shift actuator to operate the electronic clutch and automated shifting process.[9][10]

Some automated transmissions allow the driver to have full control of gear selection, though most will intervene to prevent engine stalling and redlining by shifting automatically at the low end and/or high end of the engine's normal operating range. Hydraulically-coupled and most clutch transmissions also provide the option of operating in the same manner as a conventional automatic transmission, by allowing the transmission's computer to select gear changes. A few also allow an alternative automatic mode, often called "sport" mode, where gear selection is still fully automatic but the transmission will favor higher engine speeds (at which the engine will produce the highest horsepower and/or torque) by upshifting later when accelerating and downshifting earlier when slowing.


Amédée BOLLÉE Fils Type F gear shift ring (mounted inside the steering wheel)
Amédée BOLLÉE Fils Type F gear shift ring (mounted inside the steering wheel)

In 1901, Amédée Bollée developed a method of shifting gears which did not require the use of a clutch and was activated by a ring mounted within the steering wheel.[11]

In the 1930s, automakers began to market cars with some sort of device that would reduce the amount of clutching and de-clutching and shifting required in stop and go driving. Most typically, a fluid coupling or a centrifugal clutch replaced the standard manual clutch to allow for stop and go driving without using the clutch pedal every time the car was brought to a stop. More sophisticated systems allowed for shifting while driving without using the clutch, and some systems did away with the clutch pedal altogether. Semi-automatic transmissions were phased out as technology advanced and automatic controls were developed to take care of changing gear ratios. Smaller, lower-powered cars used semi-automatic transmissions with a dry clutch because the mechanical connection offered a more efficient powertrain compared to a fluid coupling.

Another early semi-automatic transmission was the Sinclair S.S.S. (synchro-self-shifting) Powerflow gearbox. which was applied to Huwood-Hudswell diesel mines locomotives.[12] It was also applied to some road vehicles.[13]

Improved semi-automatics appeared in the 1950s and 1960s. The Automotive Products Manumatic and Newtondrive systems were also known as "two-pedal transmissions". They relieve the driver of the need for skill in operating clutch and engine speed in conjunction with the gear change. The Manumatic has a clutch servo powered by the vacuum at the induction manifold operating the automatic clutch - a conventional clutch incorporating centrifugal operation. A switch in the gear lever operates a solenoid valve so that when the gear lever is moved, the clutch is disengaged. A control unit made throttle adjustments to keep the engine speed matched to the driven clutch plate and also varied the speed of clutch operation appropriate to road speed.[14] The Newtondrive system differed in making a provision for choke control and a cable linkage from clutch operating mechanism to the throttle. These systems could be fitted to smaller cars such as the Ford Anglia.

The Ferrari 640 racecar incorporated, in 1989, an electo-hydraulic gear shift mechanism activated by paddles mounted behind the steering wheel.[11][15]

Comparison to modern transmissions

Semi-automatic transmissions are conventional manual transmissions, usually operated with an automatic clutch or another kind of partially automatic transmission mechanism. However, they require full control of the manual gear selection by the driver. The driver must manually operate and shift through the gear ratios via the H-pattern shifter. An example of this transmission type in automobiles is the VW Autostick semi-automatic transmission. The semi-automatic transmission does not have an automatic mode, unlike the more modern automated manual transmissions, which are essentially conventional manual transmissions containing both manual and automatic shifting modes.

Modern automated manual transmissions are a type of Automatic transmission which have a fully-automatic mode, where the driver does not need to change gears at all, operating in the same manner as a conventional torque converter automatic transmission, by allowing the transmission's computer to automatically shift gear if, for example, the driver were redlining the engine. The AMT can be engaged in a manual mode wherein one can up-shift or down-shift using the console-mounted shifter selector or the paddle shifters just behind the steering wheel, without the need of a clutch pedal. The ability to shift gears manually, often via paddle shifters, can also be found on other automatic transmissions (manumatics such as Tiptronic) and continuous variable transmissions (CVTs) (such as Lineartronic). Automated manual transmission is a modern type of Automatic transmission. It consists of a conventional manual transmission with an electronically-actuated hydraulic clutch and computerized gear shift control, and the driver can usually override the computer control with a clutchless "manual" mode.[16] It has a lower cost than any other types of automatic transmissions[10] An automated manual transmission can simply and best be described as a standard manual transmission, with an automated clutch, and automated clutch and gear shift control. It is a type of automatic transmission.[5]

Despite superficial similarity to other automated transmissions, modern automated manual and older semi-automatic transmissions differ significantly in internal operation and driver's "feel" from manumatic and CVTs. A manumatic, like a standard automatic transmission, uses a torque converter instead of clutch to manage the link between the transmission and the engine, while a CVT uses a belt instead of a fixed number of gears. An AMT utilizes a clutch, and offers a more direct connection between the engine and wheels than a manumatic and this responsiveness is preferred in high-performance driving applications, while a manumatic is better for street use because its fluid coupling makes it easier for the transmission to consistently perform smooth shifts,[17][18] and CVTs are generally found in gasoline-electric hybrid engine applications.

Typically automated manual transmissions are more expensive than manumatics and CVTs, for instance BMW's 7-speed Dual Clutch Transmission is a CAD 3900 upgrade from the standard 6-speed manual, while the 6-speed Steptronic Automatic was only a CAD 1600 option in 2007.[19] In a given market, very few models have two choices of automated transmissions; for instance the BMW 545i (E60) and BMW 645Ci/650i (E63/64) (standard 6-speed manual) had as an option a 6-speed automatic "Steptronic" transmission or a 7-speed Getrag SMG III single-clutch automated manual transmission until after the 2008 model year, when the SMG III was dropped.[20] Many sport luxury manufacturers such as BMW offer the manumatic transmissions for their mainstream lineup (such as the BMW 328i and BMW 535i) and the automated manual gearbox for their high-performance models (the BMW M3 and BMW M5).[19]

Modern clutch-based automatic transmission can be derived from a conventional hydraulic automatic; for instance, Mercedes-Benz's AMG-Speedshift MCT automatic transmission is based on the 7G-Tronic manumatic, however, the torque converter has been replaced with a wet, multi-plate launch clutch.[21] Chevrolet's Torque-Drive was based on GM's conventional Powerglide, but lacked the vacuum modulator that controls automatic gear shifts. Other automated manual transmissions have their roots in a conventional manual; the SMG II drivelogic (found in the BMW M3 (E46) is a Getrag 6-speed manual transmission, but with an electrohydraulically actuated clutch pedal, similar to a Formula One style transmission. Alfa Romeo "Selespeed" and Ferrari "F1" transmissions worked in the same way.[22][23][24] The most common type of automated manual transmission in recent years has been the dual clutch type, since single-clutch types such as the SMG III have been criticized for their general lack of smoothness in everyday driving (although being responsive at the track).[25]


VW Autostick semi-automatic transmission diagram
VW Autostick semi-automatic transmission diagram
How a typical semi-automatic transmission operates
How a typical semi-automatic transmission operates

Semi-automatics facilitate gear shifts by dispensing the need to depress a clutch pedal at the same time as changing gears. Depending on the mechanical build and design, they can use electronic sensors, hydraulics, pneumatics, processors, and actuators to execute gear shifts when requested by the driver. 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 synchronize 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. Motorcycles with this system use a conventional sequential foot-shift lever (like on a manual motorcycle), but use a centrifugal (automatic) clutch system, removing the need for a hand-clutch lever, and manual clutch actuation.[26]

The operation of semi-automatic transmissions has evolved over time. Many different times of clutch actuation systems have been used, from electro-hydraulic, pneumatic, and electromechanical clutches, while other manufactures have used alternate methods of actuation, like vacuum-operated or electromagnetic clutches. automated manuals have evolved as vehicle manufacturers experimented with different systems. The clutches are usually connected to an electronic control system, which uses various electrical sensors and actuators to detect when the driver touches the gearshift and requests a shift. The gearshift will usually be connected electronically to the clutch, and the clutch will disengage once the driver moves the gearshift. In one example, Ferrari offered their Mondial model with a clutchless manual, which Ferrari called the Valeo transmission. In this system, the gearshift of a conventional manual transmission was retained; and moving the shifter automatically engaged the electro-mechanical clutch. Saab's Sensonic transmission worked in a similar fashion. Most semi-automatic transmissions work in a similar fashion, once the driver moved the shift lever to switch gears, the clutch would disengage, and re-engage once the gear was selected.

Hall effect sensors sense the direction of the requested shift, and this input, together with a sensor in the gear box which senses the current speed and gear selected, feeds into a central processing unit. This unit then determines the optimal timing and torque required for smooth clutch engagement, based on input from these two sensors as well as other factors, such as engine rotation, the Electronic Stability Control, air conditioner and dashboard instruments.

The central processing unit powers a hydro-mechanical unit to either engage or disengage the clutch, which is kept in close synchronization with the gear-shifting action the driver has started. In some cases, the hydro-mechanical unit contains a servomotor coupled to a gear arrangement for a linear actuator, which uses brake fluid from the braking system to impel a hydraulic cylinder to move the main clutch actuator. In other cases, the clutch actuator may be completely electric. The actuators and sensors which control the clutch are usually connected to an electronic servomechanism, operated via the transmission control unit (TCU).

The power of the system lies in the fact that electronic equipment can react much faster and more precisely than a human and takes advantage of the precision of electronic signals and hydraulic actuators to complete the clutch operation faster, and without the manual intervention of the driver.



For the 1968 model year, Chevrolet introduced a simplified version of Powerglide marketed under the name "Torque Drive." This unit was basically two-speed Powerglide without the vacuum modulator, requiring the driver to manually shift gears between Low and High. The quadrant indicator on Torque Drive cars was, Park R N Hi 1st. The driver would start the car in "1st," then move the lever to "Hi" when desired.

Torque Drive was only offered on low-horsepower engines for Camaro, Nova, and the 1971 Vega. It was available on the Nova four-cylinder engine, and on the Turbo-Thrift Sixes for Camaro as well as Nova. Despite its low introductory price of $68.65, most buyers apparently considered the Torque Drive a nuisance to shift, and for a hundred dollars more they could get fully automatic Powerglide, making Torque Drive installations very rare. Apparently the transmission wasn't very durable since it depended on the driver's ability to shift between gears in a way that wouldn't damage the unit. After 1971, Chevrolet canceled semi-automatic Torque Drive.


Historically, the first semi-automatic transmission which was marketed by a major manufacturer was the 1941 M4/Vacamatic Transmission by Chrysler. It was an attempt to compete against rivals' automatic transmissions, though it still had a clutch, it was primarily used to change range. The main difference was the addition of a fluid coupling between engine and the clutch, and the shifting mechanism.

In normal driving, the clutch was used to select low, high, or reverse. Attached to the transmission was an "underdrive" with a reduction gear of 1.75/1. The shift lever was column-mounted and had three positions: Low (in the "2nd" position of a conventional 3-speed manual unit), High (in the "3rd" position), and Reverse (same as the 3-speed). The clutch had to be depressed every time the gear shift lever was moved. When the lever was put in Low, the car started in "underdrive" low; when the vehicle reached a minimum speed of 6 mph (9.7 km/h), the driver lifted his foot off the accelerator, the underdrive unit would kick out and the car would be in Low. Similarly, with the lever in High position, the car would start in underdrive high, and at any speed above 13 mph (21 km/h), the driver would lift his foot and the car would "shift" into direct drive. This configuration had the effect of providing 4 gear ratios: Underdrive Low, 3.57/1, Low 2.04/1, Underdrive High, 1.75/1, High, 1/1. In order for the unit to work without gear clashing, it contained a freewheeling device (in Underdrive, Low and High), and the Owner's manual cautioned drivers not to use "1st or 3rd" gear when descending hills because there was no engine compression braking in those free-wheeling ranges. Generally, most drivers started an M6 car in High and accomplished the shift to direct drive somewhere between 13 and 25 MPH by releasing the accelerator pedal and waiting for the "clunk" that signaled the disengagement of the underdrive. An M6 car would automatically shift from High down to underdrive high when car speed dropped below approximately 11 MPH.

Citroën and Peugeot

Citroën produced a number of variants on semi-automatic transmission. The Citroën DS, introduced in 1955, used a hydraulic system to select gears and operate the conventional clutch using hydraulic servos. There was also a speed controller and idle speed step-up device, all hydraulically operated. This allowed clutchless shifting with a single selector mounted behind the steering wheel. This system was nicknamed 'Citro-Matic' in the U.S.

The Citroën 2CV gained an optional centrifugal clutch, marketed in English-speaking countries as "Trafficlutch". It did not help with gear changing, but it disengaged automatically when the engine slowed to an idle. A device was fitted to the carburetor to prevent the throttle closing abruptly, and the resultant clutch disengagement and lack of engine braking.

Later, the manufacturer introduced optional semi-automatic transmissions on their medium and large saloon and estate models in the 1970s; the Citroën GS and CX models had the option of three-speed, semi-automatic transmission marketed as 'C-Matic'. This was simpler than the DS implementation: instead of hydraulics, it used a floor-mounted quadrant lever operating conventional gear selector rods and an electrically controlled wet plate clutch in conjunction with a torque converter. The torque converter gave more of the feel of a conventional automatic transmission, which was completely lacking in the DS. Citroën semi-automatic transmission of this era made no use of electronics: the entire gear selecting operation was carried out by simply moving the gear lever from one ratio to the next.


The 993 cc Daihatsu Charade from 1985 until 1991 had the option of a two-speed semi-automatic transmission called "Daimatic". This unit is similar to a conventional auto, featuring both a torque converter and a planetary gearset but lacking a full valve body for making decisions regarding shifting. This was left entirely to the driver and as a result could be accelerated from rest in top gear if desired, depending entirely on the torque converter action. The standing quarter-mile time with two 60 kg (130 lb) occupants and using low gear appropriately was 21.0 sec while using top gear only was 21.5 sec. This unit was also installed in the Innocenti Matic of the same time period.


Ferrari's first automated manual gearbox in a road car (used them previously in their Formula One cars since 1989) went on sale in 1993 in the Ferrari Mondial; the Mondial Valeo retained the traditional gated shifter but removed the clutch pedal, and the clutch mechanism was electro-mechanically actuated each time the gearshift was moved.


Ford Motor Co. offered the Semi-Automatic Transmission on the 1970 Maverick 6-cylinder model as a lower-cost option to the popular 3-speed C4 Cruise-o-Matic transmission. The shift quadrant featured "P R N Hi 2 1" and the Maverick owner's manual provides the speeds at which the driver should move the selector between the three forward gears. Like Chevrolet's Torque-Drive, the Ford Semi-Automatic was essentially the regular automatic without the self-shifting capability. At $121.00 retail, it was pricey, rarely ordered, and was discontinued the following year.

General Motors

In 1937, Oldsmobile introduced the four-speed Automatic Safety Transmission as an option. This was an automatic transmission with automated control and shifting between a pair of ranges, with manual control over high and low ratio pairs of the four. It was not a semi-automatic transmission. This transmission was replaced by fully automatic Hydra-Matic for the 1940 model year.

In 1938, Buick introduced a five-speed semi-automatic[citation needed] transmission for the Buick Special. This unit was failure prone, however, and eventually was replaced by the fully automatic Dynaflow transmission for 1948.[27]


Honda marketed both cars and motorcycles with the Hondamatic transmission in the 1970s and early 1980s. This transmission is frequently referred to as the 'Bang-O-Matic' by mechanics.[citation needed] The design is noteworthy because it preserves engine braking by eliminating a sprag between first and second gears.[citation needed]


Drive-Master, 1941–1950.


Isuzu introduced the "NAVi5" (New Advanced Vehicle with Intelligence 5-speed) in 1984. Based on a traditional 5-speed manual with a dry clutch, it was controlled by two hydraulic actuators and an electronic computer. The earlier version only had an automatic mode, but a manual mode was later added. It was first available in the Aska and subsequently the other Isuzu vehicles (for the Japanese domestic market only).


For 1942, Ford Motor Company announced a new semi-automatic transmission for Lincolns and Mercurys, called Liquimatic. Liquimatic consisted of fluid coupling, as well as an electro-mechanical vacuum control that automated the shift between second and third speeds. Like Chrysler's Fluid Drive, a clutch was used to start the car from a standstill. Lincolns got an overdrive gear as a bonus.

The transmission proved to be so trouble-prone that Ford recalled virtually every unit, and replaced them with standard manual transmissions. The only known unit to exist is in the possession of the Early Ford V8 Foundation Museum in Auburn, Indiana. While Ford gave up on semi-automatic transmissions after Liquimatic, Lincoln started using General Motors' Hydra-Matic in 1949, while Mercury got its own automatic, Merc-O-Matic, in 1951.


Mercedes used a system from 1957–61 similar to the VW Autostick, called Hydrak. Hydrak had one major flaw: the oil supply for the torque converter was sealed within the converter itself and did not circulate via a pump, and also had no oil cooler. Idling in gear for even short periods would overheat the oil and burn up the seals in the converter, which would then need to be replaced.[28]


The German automobile manufacturer NSU produced an automated system for the rotary-engined NSU Ro 80 saloon car in the 1960s, similar in concept to VW's Automatic Stickshift: a three-speed manual gearbox with a vacuum-operated dry clutch controlled by a contact in the gear lever, and a torque converter. There was no clutch pedal, but slightly moving the gearshift closed an electric switch that operated a vacuum system which disengaged the clutch. The gear lever itself then could be moved through a standard 'H pattern' gate.


Also in 1941, Packard introduced the Electro-Matic clutch, which was a vacuum-operated clutch pedal, signaled by the position of the accelerator. Significantly, it came with an 'off' switch, probably due to the fact that the system was somewhat unstable during engine warm-up. Packard's system was used in conjunction with their regular transmission so the H-pattern shifting remained.

Earlier, and by many manufacturers, an arrangement to disengage the clutch (via a ratchet-like device) during coasting was tried to ease shifting. Called "freewheeling", it was bedeviled by the absence of adequate brakes.


In 1953, Plymouth fitted a torque converter, called 'Hy-Drive', to their standard 3-speed manual gearbox. The torque converter allowed the car to remain in High gear for most driving, providing fluid torque multiplication as needed. A clutch was provided for manual gear engagements and the driver could use all three speeds as desired. Hy-Drive was also offered for the 1954 model year but was soon replaced with Chrysler's fully automatic two-speed PowerFlite transmission.


For the Renault Dauphine, a Ferlec semi-automatic was offered from 1957 until 1963, when the "fully-automatic" Jaeger electromechanical transmission control became available. The Ferlec transmission was a manual-selection transmission coupled to a dry clutch that engaged and disengaged by touching the gearshift, similar to the driver operation of Volkswagen's Autostick, but without the torque converter of the VW.


Self-Shifter, 1933–35. The Self-Shifter first appeared in May 1933 and was offered as standard on the REO Royale and as an option on the Reo Flying Cloud S-4.[29]


Illustation of the Saab "Sensonic" transmission system
Illustation of the Saab "Sensonic" transmission system

For the Saab 900 NG a semi-automatic transmission was available for Turbo models only in 1995 and 1996, mostly for the European market. The 'Sensonic' clutch variant provided a manual gearshift, as in a standard manual transmission car, but omitted the clutch pedal in favor of electronic and hydraulic equipment which could automate the clutch faster than an average driver could.


Starting the 1966 model year, the Simca 1000 was available with a semi-automatic Ferodo gearbox. In 1966 only as the 1000 GLA model, but afterwards the semi-automatic gearbox was available on other models as an option. The gearbox used a torque converter and had four positions: "AR" for reverse gear, "Exceptionnel" for low gear, "Ville Montagne" for city and mountain use and "Route" for open road.[30] The clutch disengaged when the selector was touched.[31]


VW Automatic Stickshift diagram
VW Automatic Stickshift diagram

For the 1968 model year, the Volkswagen Beetle offered an optional transmission marketed as Automatic Stickshift (in the United States and Canada, in most of the world it was simply called an "Automatic") which was essentially a three-speed manual without a clutch pedal.[32] Application of the driver's hand to gearshift knob caused the clutch to disengage via a 12 volt solenoid operating the vacuum clutch, thereby allowing shifting between gears. Once the driver's hand was removed, the clutch would re-engage automatically. The transmission was also equipped with a torque converter, allowing the car to idle in gear, like an automatic. The torque converter was operated by transmission fluid. This would allow the car to stop in any gear and start from a standing stop in any gear. This transmission was first available on the 1968 Volkswagen Beetle (on sale in August 1967), and was made available on the Karmann Ghia during 1968. VW dropped the transmission option in North America in 1976, although it continued to be available in other markets until 1979.[32] Some older (the early 1960s) VW's sold in Europe had a Saxomat system which used a centrifugal clutch coupled to a standard four-speed transmission.[32]

Other applications


In racecars, this system denotes an electronic-controlled single-clutch transmission. The system is usually operated sequentially, via steering-wheel-mounted paddle-shifters, and an electrohydraulic or electro-pneumatic actuated, semi-automatic clutch and shifting mechanism, with dog gear engagement, as is used in most racecars today. This system will briefly initiate and send a single to the transmission, via the ECU, and electronic sensors and actuators will momentarily cut the ignition, power, and torque to the wheels when the driver requests a shift, therefore allowing the driver to quickly and smoothly shift between gears. These can be designed with both a manual or automatic clutch system.[33][34]

In Formula One, the first attempt at clutch-less semi-automatic sequential gear shifting was in the early 1970s, with the system being tested by the Lotus team.[citation needed] In 1989, then-Ferrari engineers and designers John Barnard and Harvey Postlethwaite created a paddle-shift semi-automatic gearbox for use in the Ferrari 640. This system used electrohydraulic actuators for controlling the clutch and shifting, and was operated by paddle-shifters mounted behind the steering wheel.[15][35] Despite problems in testing, the car won its first race at the hands of Nigel Mansell. The downshifts on these early Ferrari semi-auto gearboxes were just like in a conventional manual transmission, in that the engine revs had to be matched by the driver and the clutch used manually. The actuator was a simple switch as opposed to a looped control system. When other teams began to develop similar semi-auto paddle-shift systems, the shift-speed was such that they felt a sequential drum-rotation mechanism, like the ones found on motorcycle transmissions, would be more compact and would require only one hydraulic or pneumatic actuator to rotate the drum, and move the gear selector forks. Williams made this change with the FW14 in 1991, and this was the direction semi-autos then took. The final step for this technology was as a means of controlling the synchronization of downshifts and engine speed. The arrival and implementation of electro-hydraulic throttle systems allowed computer-controlled blips to replace the heel-and-toe technique.[36] By 1993, the sequential semi-automatic transmission was dominant in terms of gearbox technology. The last F1 car fitted with a conventional manual gearbox, the Forti FG01, raced in 1995.[37]

After concerns that the technology allowed software engineers to pre-program the cars to automatically change to the optimum gear according to the position on the track, without any driver intervention, a standardized software system was mandated, ensuring the gears would only shift up or down when instructed to by the driver. Buttons on the steering wheel, which go directly to a certain gear—rather than sequentially—are still permitted.

Trucks and buses

Automated manual transmissions have also made their way into the truck and bus market in the early 2000s. Volvo offers its I-Shift on its heavier trucks and buses as well UD Trucks with ESCOT, while ZF markets its ASTronic system for trucks, buses and coaches. In North America, Eaton offers the "AutoShift" system which is an add-on to traditional non-synchromesh manual transmissions for heavy trucks.[38] These gearboxes have a place in public transport as they have been shown to reduce fuel consumption in some specific cases.

Bristol/Daimler/Leyland buses

The British employed pneumatic valve bodies to regulate gear shifting by charging pistons with compressed air within the gearbox. These pneumatic pistons or gear-levers are activated by a series of valve bodies and controlled by electronic actuators linked to the gear shifter. As each gear cycle is energized, air valves open and close to engage the corresponding gear-lever. Compressed air is drawn from the braking system and in the event of loss of pressure, the transmission will remain in the last gear selected or if in neutral, will not shift into gear.

In the UK though, semi-automatic transmissions have been very popular on buses for some time, from the 1950s right through to the 1980s, an example being the well known London AEC Routemaster, although the latter could also be driven as a full automatic in the three highest gears. Most heavy-duty bus manufacturers offered this option, using a gearbox from Self-Changing Gears Ltd of Coventry, and on urban single- and double-deck buses it was the norm by the 1970s. This coincided with the development of city buses with engines and transmissions at the rear rather than the front, which was beyond the capability of a manual gearchange/clutch linkage from the driver's position. Leyland manufactured many buses with semi-automatic transmissions, including its Leopard and Tiger coaches. Fully automatic transmission became popular with increasing numbers of continental buses being bought in the UK, and more and more British manufacturers began offering automatic options, mostly using imported gearboxes (such as those made by Voith and ZF), and semi-automatic transmissions lost favor. These days, very few buses with semi-automatic transmissions remain in service, although many are still on the roads with private owners. Modern types of manumatic and automated manual transmissions, though, are becoming more common, mostly replacing manual gearboxes in coaches.



The Self-Changing Gears automated gearbox was also fitted to the several thousand diesel railcars built for the British railway system in the late 1950s-early 1960s, which lasted in service until the 1990s-2000s. Their whole engine-transmission system was based on that from the main bus manufacturers of the period such as Leyland and AEC. Gear selection was by the train driver with a hand-held lever as the train accelerated. Such trains were formed of a number of such railcars coupled together and each power car had two engines/automated gearbox units mounted under the floor. Synchronizing controls by control cables connected through the train ensured all the gearboxes under all coaches of the train changed gear together.


The semi-automatic transmission was also used on many small diesels shunting locomotives, such as British Rail Class 03 and British Rail Class 04. A widely used type was the Wilson-Drewry epicyclic gearbox.

A less common type was the SSS (synchro-self-shifting) Powerflow gearbox. This gearbox was of the layshaft type with constant-mesh gears and dog clutch engagement. A special feature was that the drive was maintained during upward gear changes. This system was used on Huwood-Hudswell diesel mines locomotives[12] and on the British Rail Class D2/7 and British Rail Class D2/12.


The first motorcycles with semi-automatic gearboxes were developed and patented in the mid 1960s by the Czechoslovakian Jawa motorcycle company.[39]

In 1965, Honda copied the Jawa semi-automatic clutch for the Honda Cub step-through motorcycle series and so Jawa sued them in court for patent infringement. Honda settled out of court and Jawa granted them indefinite license with royalties charged on each Honda motorcycle that used the Jawa system.[39]

The first large-capacity motorcycle with a semi-automatic gearbox was the 1975 948 cc (57.9 cu in) Moto Guzzi Convert (the name was chosen to denote the torque converter which was at the heart of this 110 mph motorcycle)[citation needed] a fairly heavy motorcycle which despite its weight still handled, and cornered remarkably well, which was thanks to the race-bred frame from the Moto Guzzi Le Mans.[citation needed]

Honda also had a range of bikes fitted with a gearbox that mated a torque converter and a two speed gearbox. This style of gearbox still required the rider to manually select neutral and either of the two gears using the foot gear lever.[40] These models were the CB750A, CB400A, CM400A and CM450A. These bikes were badged and marketed as Hondamatics.

In addition to the Hondamatic system noted above, Yamaha Motor Company introduced a semi-automatic transmission on its 2007 model year FJR1300 sport-touring motorcycle in 2006. Notably, this system can be shifted either with the lever in the traditional position near the left foot, or with a switch accessible to the left hand where the clutch lever would go on traditional motorcycles.

Honda began production of the VFR1200F on 8 September 2009,[41] which includes an optional dual clutch transmission, the first to be fitted to a motorcycle.

The BRP Can-Am Spyder Roadster is available with a clutchless semi-automatic transmission (the SE5 or SE6, with five or six speeds, depending on the model).

Small capacity underbone or "step-thru" types of motorcycles, such as the Honda Super Cub, Suzuki FR50 and FR80 and Yamaha Townmate, use a semi-automatic gearbox with a "heel and toe" foot change in the standard motorcycle position but without the need for conventional clutch operation.

Many modern motorcycles feature a device called quick-shifter for up-shifts without pressing the clutch lever or closing (rolling-off) the throttle. The special sensor recognizes pressure on the gear shift rod and quick-shifter sends a signal to the ECU to either stop fuelling for a short time (milliseconds) or suppress the spark at the plug, which unloads the gearbox and allows a gear change. The idea came from racing where it helps to minimize the time when the motorcycle is not at full power. An alternative device for down-shifts is called auto-blipper and is less widespread. It artificially "blips" the throttle to match engine speed to speed of the rear wheel to avoid sudden spikes in torque transfer.[citation needed]


Honda released automated electric shift ATVs starting in the model year 1998 with the TRX450FE aka Foreman 450ES ESP (Electric Shift Program). Shifting is accomplished by pressing either one of the gear selector arrows on the left handlebar control. The currently selected gear is indicated by a digital display. The primary components of the shifting mechanisms were the same on both the manual and electric shift models, but the major difference was the deletion of the shift pedal and the addition of an internal electric shift servo which actuated the components (clutch assembly, shift drum, etc.)in one motion instead of the traditional foot lever. In the event of a malfunction, a supplied override lever can be placed on a shaft protruding from the crankcase in the traditional spot where the pedal would have been. This electric shift technology was later applied to their complete line of ATVs.


See also


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