Semi-automatic transmission describes an automobile transmission where part of its operation is automated (typically the clutch operation) but the driver's input is still required to start from a standstill or to shift gears. Most semi-automatic transmissions are based on a manual transmission or a sequential manual transmission with an automatic clutch.
Names for specific types of semi-automatic transmissions include clutchless manual, auto-manual, and paddle-shift transmissions. These systems facilitate gear shifts for the driver by operating the clutch system automatically, usually by means, or under control of a servomechanism or actuator, while still requiring the driver to manually shift gears.
The first usage of semi-automatic transmissions was in automobiles, increasing in popularity in the mid-1930s when they were offered by several American car manufacturers. Less common than traditional (hydraulic) automatic transmissions, semi-automatic transmissions have nonetheless been available on various car models and currently remain in production. Semi-automatic transmissions with paddle-shift operation have been used in various racing cars, including Formula One, Indycar, and touring car racing. Other applications include motorcycles, trucks, buses, and railway vehicles.
Design and operation
Semi-automatics facilitate easier gear shifts by removing the need to depress a clutch pedal or lever at the same time as changing gears. Depending on the mechanical build and design, they can use hydraulic, pneumatic, or electronic servos, electrical sensors, motors, processors, and actuators to execute gear shifts when requested by the driver. Most cars which have a semi-automatic transmission are not fitted with a clutch pedal, since the clutch is remotely controlled, solely by electronic equipment. Similarly, most motorcycles with a semi-automatic transmission are not fitted with a hand-clutch lever.
Automated manual transmissions
Many clutchless manual and semi-automatic transmissions are actually conventional manual transmissions, usually operated with an automated clutch or another kind of partially automatic transmission mechanism, thus partially automating the manual transmission, to a certain degree. Once the clutch becomes automated, then the transmission becomes semi-automatic. However, they still require full control of the manual gear selection, which is controlled by the driver. Most semi-automatic transmissions in older passenger cars retain the normal H-pattern shifter of a manual transmission, however, semi-automatics in motorcycles, racing cars and other types of vehicles often use gear selection methods such as paddle-shifters near the steering wheel or triggers near the handlebars.
Several different clutch actuation systems have been used, from hydraulic, pneumatic, and electro-mechanical clutches, while other manufactures have used alternate methods of actuation, like vacuum-operated or electromagnetic clutches.
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 transmission control unit. This unit then determines the optimal timing and torque required for smooth clutch engagement, based on input from these sensors.
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 internal clutch actuator may be completely electric, or even pneumatic (using compressed air). The actuators and sensors which control the clutch are connected to the transmission control unit (TCU).
Starting in the late-1990s, automotive manufacturers introduced what is now called an Automated Manual Transmission (AMT) – these function in the same way as older clutchless manual and semi-automatic transmissions, but with two exceptions; they can do everything fully-automatically, and they don't have or require a hydrodynamic torque converter. The shifting signal comes either automatically, from the Transmission Control Unit (TCU), or via manual control from the shift knob, or shift paddles mounted behind the steering wheel. These AMTs combine the fuel efficiency of manual transmissions with the shifting ease of an automatic transmission. Their biggest disadvantage is the poor shifting comfort because shifting requires a disruption in power and torque transmission from the engine to the wheels, due to the mechanical clutch being disengaged by the TCU (transmission computer), which is easily noticeable as "jolting". Some transmission makers have tried solving this issue by using oversize synchronizer rings and not fully opening the clutch during shifting – now in theory, this works, but as of 2007, there have not been any series production cars with such functions. In passenger cars, modern AMTs generally have at least six gears (though some have seven-speeds) and a rather large spreading. In combination with a smart-shifting program, this can significantly reduce fuel consumption. In general, there are two types of AMTs: Integrated AMTs, and add-on AMTs. Integrated AMTs were designed to be AMTs, whereas an add-on AMT is a conversion of a regular manual gearbox into an AMT.
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. These transmissions can be described as a standard manual transmission with an automated clutch and automated gear shift control. Therefore the transmission can operate in the same manner as a traditional 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.[failed verification] It has a lower cost than any other types of automatic transmissions.
Sequential manual transmissions
Several semi-automatic transmissions used by motorcycles and racing cars are actually internally a sequential manual transmission. (Semi-auto motorcycle transmissions generally omit the clutch lever, but retain the conventional heel-and-toe foot-shifter lever.)
Semi-automatic motorcycle transmissions typically also use a centrifugal clutch, which operates in a different fashion, by using centrifugal force. At idle, the engine is disconnected from the gearbox input shaft, allowing both it and the bike to freewheel (unlike torque converter automatics, there is no "idle creep" with a properly adjusted centrifugal clutch). As the throttle is opened and engine speed rises, counterweights attached to movable inner friction surfaces (connected to the engine shaft) within the clutch assembly are thrown gradually further outwards, until they start to make contact with the inside of the outer housing (connected to the gearbox shaft) and transmit an increasing amount of engine power and torque. The effective "bite point" is found automatically by equilibrium where the power being transmitted through the (still-slipping) clutch is equal to what the engine can provide. This allows relatively fast full-throttle takeoffs (with the clutch adjusted so the engine will be turning near its maximum-torque rpm) without the engine slowing or bogging down, as well as more relaxed starts and low-speed maneuvers at lower throttle settings and RPMs.
Comparison to automatic transmissions
Fully automatic transmissions require no driver input when changing gears; semi-automatic transmissions will only require partial driver involvement, usually in the form of selecting the next gear with the clutch operation being automated. Transmissions which offer the driver the option of manually selecting a gear (such as with paddle shifters or "+" and "-" controls on the gear selector) are not considered semi-automatic transmissions, because the transmission is capable of operating in a fully automatic mode.
Usage in passenger cars
1900s to 1920s
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. One car using this system was the 1912 Bollée Type F Torpedo.
1930s to 1940s
Prior to the arrival of the first mass-produced hydraulic automatic transmission in 1940 (the General Motors Hydra-Matic), several American manufacturers offered various devices to reduce the amount of clutch or gear shifter usage required. These devices were intended to reduce the difficulty of operating the unsynchronised manual transmissions ("crash gearboxes") that were commonly used, especially in stop-start driving.
An early step towards automated transmissions was the 1933-1935 REO Self-Shifter, which automatically shifted between two forward gears in the "Forward" mode (or between two shorter gear ratios in the "Emergency low" mode). Standing starts required the driver to use the clutch pedal. The Self-Shifter first appeared in May 1933 and was offered as standard on the Royale and as an option on the Reo Flying Cloud S-4.
In 1937, the Oldsmobile 4-speed Automatic Safety Transmission was introduced on the Oldsmobile Six and Oldsmobile Eight models. It used a planetary gearset with a clutch pedal for starting from standstill and switching between the "Low" and "High" ranges. The Automatic Safety Transmission was replaced by the fully automatic Hydra-Matic for the 1940 model year.
The 1938–1939 Buick Special was available with the Self-shifter 4-speed semi-automatic transmission. transmission. This transmission uses a manual clutch for starting from standstill, and an automated clutch for gear changes.
The 1941 Chrysler M4 Vacamatic transmission used a two-speed manual transmission with integral underdrive unit, a traditional manual clutch and a fluid coupling between the engine and the clutch. The two-speed transmission was used as "High" and "Low" ranges, and the clutch was needed when the driver wanted to switch between ranges. For normal driving, the driver would press the clutch, select High range and then release the clutch. One the accelerator was pressed, the fluid coupling would engage and the car would begin moving forward, with the underdrive unit engaged to provide a lower gear ratio. At between 15–20 mph (24–32 km/h), the driver would lift off the accelerator and the underdrive unit would disengage. The Vacmatic was replaced by the similar M6 Presto-Matic transmission for the 1946 model year.
Similar designs were used for the 1941–1950 Hudson Drive-Master and the ill-fated 1942 Lincoln Liquimatic. Both of these used a 3-speed transmission with automated shifting between 2nd and 3rd gears, instead of the Vacamatic's underdrive unit.
The Packard Electro-Matic — introduced in the 1941 Packard Clipper and Packard 180 — is an early a clutchless manual transmission that uses a traditional friction clutch with automatic operation. In the case of the Electro-Matic, the clutch was vacuum-operated and controlled by the position of the accelerator.
1950s to 1960s
The Automotive Products Manumatic system, available on the 1953 Ford Anglia 100E was a vacuum-powered automatic clutch system that was actuated by a switch that was triggered whenever the gear level was moved. The system could control the throttle cable (to keep the engine at the required RPM for the gear change) and could vary the rate of clutch engagement. The successive Newtondrive system, available on the 1957-1958 Ford Anglia, also had a provision for choke control. A similar product was the German Saxomat automatic clutch system, which was introduced in the mid-1950s and available on various European cars.
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 1967 VW WSK (Wandlerschaltkupplungsgetriebe; English: "hydrodynamic torque converter shift/clutch gearbox"), used in the Beetle and Karmann Ghia, was one of the first gearboxes of this kind, which had an automatic mechanical clutch and a hydrodynamic torque converter; shifting gears was done manually by the driver. The automatic mechanical clutch enabled the "taking off" function, whereas the hydrodynamic torque converter enabled "taking off in any gear", it dampened the engine vibrations, and it provided torque multiplication, functioning as some sort of "reduction gearbox", so the actual mechanical gearbox only needed three forward gears (maybe you've wondered why "traditional" automatic transmissions with hydrodynamic torque converters normally have fewer gears than manual gearboxes – this is why). In the WSK, there was no "first" gear, instead, the first gear was converted into reverse gear, the second gear was labeled first, the third second, and the fourth third.
The Chevrolet Torque Drive transmission, introduced on the 1968 Chevrolet Nova and Camaro, is one of few examples where a semi-automatic transmission was based on a hydraulic automatic transmission (rather than a manual transmission). The Torque Drive was essentially a 2-speed Powerglide transmission 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. The torque drive was discontinued at the end of 1971 and replaced by a traditional hydraulic automatic transmission. Other examples of semi-automatic transmissions based on hydraulic automatics are the Ford Semi-Automatic Transmission 3-speed transmission used in the 1970–1971 Ford Maverick (Americas), early versions of Honda's 1976-1988 Hondamatic 2-speed and 3-speed transmissions, and the Diahatsu Diamatic 2-speed transmission used in the 1985-1991 Daihatsu Charade.
|1953–1954||Plymouth Hy-Drive||Torque converter added to a 3-speed manual transmission, so it could be driven solely in top gear (to avoid using the manual clutch).|
|1956–1963||Renault Ferlec||Automatic clutch (electro-magnetic). Used in the Renault Dauphine.|
|1957–1961||Mercedes-Benz Hydrak||Automatic clutch (vacuum-powered), plus a torque converter for standing starts.|
|1959–????||Citroën Trafficlutch||Automatic clutch (centrifugal). Used in the Citroën 2CV.|
|1966–????||Simca automatic clutch||Automatic clutch plus a torque converter. Used in the Simca 1000.|
|1967–1977||NSU automatic clutch||Automatic clutch (vacuum-powered) plus a torque converter. Used in the NSU Ro 80.|
|1967–1980||Porsche Sportomatic||Automatic clutch (vacuum-powered) plus a torque converter. Used in the Porsche 911.|
|1968–1979||Volkswagen Autostick||Automatic clutch (electro-pneumatic) plus a torque converter. Used in the Volkswagen Beetle and Volkswagen Karmann Ghia.|
|1976–1980||Citroën C-matic||Automated clutch plus a torque converter. Used in the Citroën GS and Citroën CX.|
|1988–1993||Ferrari Valeo||Automatic clutch (electro-mechanical). Used in the Ferrari Mondial.|
|1995–1996||Saab Sensonic||Automatic clutch. Used in the Saab 900 NG.|
|2020–present||iMT (Intelligent Manual Transmission)||Automatic clutch (electro-hydraulic). Used in the Hyundai Venue and Kia Sonet|
Usage in motorcycles
An early example for motorcycles was the use of an automatic centrifugal clutch in the early 1960s by Czechoslovakian manufacturer Jawa Moto. This design was also used without Jawa's permission in the 1965 Honda Cub 50, which resulted in Jawa suing Honda for patent infringement. Eventually, Honda agreed to pay royalties for each motorcycle that used the Jawa design.
Other semi-automatic transmissions used in motorcycles include:
- Hondamatic (a name also used for several fully-automatic transmissions) two-speed transmission fitted with a torque converter, as used in the 1976 Honda CB750A, 1977 Honda CB400A Hawk, 1978 Honda CM400A and 1982 Honda CM450A.
- Yamaha used an automatic clutch system called YCCS on motorcycles such as the 2006 Yamaha FJR1300AE sports-touring. 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.
- 2007 BRP Can-Am Spyder Roadster 5-speed (SE5) or 6-speed (SE6) transmission
- Several underbone (step-thru) motorcycles in the 1970s, such as the Suzuki FR50 and Suzuki FR80 and Yamaha Townmate used 3-speed transmissions with a heel-and-toe gear shift.
- Some high-performance sport bikes[clarification needed] use a trigger-shift system with a handlebar-mounted trigger or paddle, and an automatically operated clutch.
- Some dirt bikes use this system, which is sometimes be referred to as an auto-clutch transmission. They retain the conventional motorcycle foot-shifter, but the need for a manual hand-clutch lever isn't required. Also, many dirt bikes which people refer to as having an "automatic transmission" are actually clutchless semi-automatic transmissions, where the driver still has to click through the gears manually with a foot-shifter, but manual clutch actuation isn't required, as there is no hand-clutch lever, and the clutch system is operated automatically, typically through a centrifugal clutch.
Usage in motor racing
The first Formula One car to use a semi-automatic transmission was the 1989 Ferrari 640. This system used electro-hydraulic actuator for controlling the clutch and shifting, and was operated by paddle-shifters mounted behind the steering wheel. Another paddle on the steering wheel controlled the clutch, which was only needed when starting from a standstill. The car won its debut race at the Brazilian Grand Prix, however for much of the season suffered from reliability problems. Other teams began switching to similar semi-automatic transmissions, and the 1991 Williams FW14 was the first to use a sequential drum-rotation mechanism (similar to the system used in motorcycle manual transmissions) to produce a more compact design that required only one actuator to rotate the drum and move the gear selector forks. A further development was made possible by the introduction of electronic throttle control soon after, which made it possible for the car to automatically rev-match during downshifts. By 1993, most teams were using semi-automatic transmissions. The last F1 car fitted with a conventional manual gearbox, the Forti FG01, raced in 1995.
Following concerns about the potential for Formula One cars to shift gears automatically without any driver input (i.e. a fully automatic transmission), mandatory software was introduced in 1994 that ensured that gear changes only occurred when instructed by the driver. Buttons on the steering wheel to skip directly to a particular gear (instead of stepping through the gears using the paddles) are also permitted. Formula 1 cars currently use 8-speed paddle-shift gearboxes, being increased from 7-speed gearboxes for the 2014 season. The 2005 Minardi PS05, Renault R25 and Williams FW27 were the last Formula 1 cars to utilize a 6-speed gearbox respectively, before the switch to a mandatory 7-speed gearbox for the 2006 season.
The now-defunct CART Champ Car Series switched from sequential manual transmissions with the manual shift lever, to a new 7-speed paddle-shift system for the 2007 season. This transmission system was introduced with the new Panoz DP01 chassis for 2007.
The rival IRL IndyCar series introduced their 6-speed semi-automatic paddle-shift system for the 2008 season, also replacing the previous sequential manual transmission with the shift lever. This was introduced with the Dallara IR5 chassis for 2008. IndyCars currently use the #P1011 sequential gearbox, supplied by Xtrac. This gearbox uses a semi-automatic shifting system called AGS (Assisted Gearshift System), supplied by Mega-Line. This is a paddle-operated shifting system, which uses a pneumatic gearshift actuator controlled by an internal GCU (Gearbox Control Unit).
The European DTM series currently use a 6-speed sequential transmission with steering-wheel-mounted paddle-shifters, which was introduced for the 2012 season with the new rule change. The gearbox is the DTT-200 model, which is supplied by Hewland. This new system replaced the older sequential gearbox with the manual shift lever, which had been used for the previous 12 seasons.
Both the FIA Formula 2 and Formula 3 Championships currently use 6-speed sequential gearboxes with electro-hydraulic operation via paddle-shifters. The clutch systems are multi-plate clutches, controlled via a hand-clutch lever behind the steering wheel, and are manually used to launch the cars.
Usage in other vehicles
Other notable uses for semi-automatic transmissions include:
- During the 1940s to 1960s, many small diesels shunting locomotives used epicyclic semi-automatic transmissions. For example, the British Rail Class 03 and British Rail Class 04 used the Wilson-Drewry CA5 R7 transmission.
- Sinclair S.S.S. Powerflow: Used from the 1950s to the early 1960s in Huwood-Hudswell diesel mining locomotives, the British Rail Class D2/7 and the British Rail Class D2/12. The Powerflow design is the layshaft-type with constant-mesh gears and dog clutch engagement, allowing it provide seamless power delivery during upshifts. This transmission was also used in some road vehicles.
- Self-Changing Gears Pneumocyclic: an epicyclic transmission built in the United Kingdom from the 1960s to the 1980s. Using a similar design to their previous preselector gearboxes, the Pneumocyclic transmission was used in several buses, such as the Leyland Leopard Leyland Panther and Leyland Tiger. It was also fitted to several thousand British diesel railcars during this time.
- Honda Electric Shift Program: Used in all-terrain vehicles such as the 1998 Honda TRX450FE (also called the Foreman 450ES ESP). Shifting is accomplished by pressing either one of the gear selector arrows on the left handlebar control, which activates an electric shifting system.
- Automated manual transmission (AMT)
- Automatic transmission (AT)
- Dual-clutch transmission (DCT)
- Shift time
- "The next shift: The clutchless manual". www.autonews.com. Retrieved 29 February 2020.
- "Automated Manual Transmission (AMT)". x-engineer.org. Retrieved 29 February 2020.
- "Mission transmission". www.aa.co.nz. Retrieved 20 August 2020.
- "Automated Manual Transmission". www.zf.com. Retrieved 29 February 2020.
- "The history of the 'paddle shift'". www.lemans.org. 21 February 2011. Retrieved 16 February 2020.
- "6 of the worst automatic transmissions ever". www.hagerty.com. 8 August 2019. Retrieved 9 August 2020.
- "How Reo Cars Work". 15 June 2007. Retrieved 24 October 2017.
- "The Oldsmobile automatic safety transmission operated by the short lever shown on the steering column". www.nypl.org. Retrieved 9 August 2020.
- "No clutch to press! No gears to shift!". www.autonews.com. 18 August 1997. Retrieved 9 August 2020.
- "How Oldsmobile Cars Work". www.howstuffworks.com. 20 June 2007. Retrieved 9 August 2020.
- "How Buick Works". www.howstuffworks.com. 5 June 2007. Retrieved 8 August 2020.
- "The M6 automatic transmission". www.allpar.com. Retrieved 9 August 2020.
- "Chrysler transmissions-Vacamatic semi automatic". www.gottransmissions.com. Retrieved 9 August 2020.
- "How Chrysler Works". www.howstuffworks.com. 1 June 2007. Retrieved 9 August 2020.
- "1941-1947 Hudson". www.howstuffworks.com. 16 September 2007. Retrieved 8 August 2020.
- "Step-Down: The 1948-1954 Hudsons". www.ateupwithmotor.com. 6 September 2009. Retrieved 8 August 2020.
- "Automatic Failure: Ford's 1942 Liquamatic Experiment". www.macsmotorcitygarage.com. 7 February 2017. Retrieved 8 August 2020.
- "Automotive History: Lincoln's Liquamatic Drive – Failure to Upshift". www.curbsideclassic.com. Retrieved 8 August 2020.
- Staton, Abbey. Practical Automobile Engineering - Clutch Systems. pp. 193–194.
- "Rare Rides: An Incredibly Rare 1965 Lancia Flaminia Super Sport Zagato". www.thetruthaboutcars.com. 14 May 2020. Retrieved 17 August 2020.
- "1956-1968 Renault Dauphine". www.howstuffworks.com. 20 August 2007. Retrieved 8 August 2020.
- "Renault Dauphine buyer's guide: what to pay and what to look for". www.classicandsportscar.com. Retrieved 8 August 2020.
- Miller, Jeff. "Mercedes-Benz Ponton Hydrak Automatic Clutch". www.mbzponton.org. Retrieved 24 October 2017.
- "Theme: Simca – 1965 1000 GLS Short Road Test". www.driventowrite.com. 4 March 2017. Retrieved 8 August 2020.
- "Simca 1100". www.uniquecarsandparts.com.au. Retrieved 8 August 2020.
- "Simca 1000 GLA Automatique 1966 lever". Flickr.com. 4 December 2008. Retrieved 1 March 2020.
- Thompson, Andy. "Simca 1000 cars". Rootes-Chrysler.co.uk. VerticalScope Inc. Retrieved 8 August 2012.
- Dingeldein, Wolfgang (2011). "VW Automatic - der Käfer mit halbautomatischem Getriebe" [VW Automatic - the Beetle with a semi-automatic transmission]. Käfertreter Siegerland (in German). Archived from the original on 10 April 2013.
- Kožušník, Marek (20 January 2015). "Válka mechaniků: Japonci okopírovali český vynález!". EpochaPlus (in Czech). Retrieved 27 December 2019.
- "Cycle magazine". Ziff Davis. May 1976: 67–73. Cite journal requires
- "FJR1300AE - YCC-S Electric Shift System". www.yamaha-motor.com. Archived from the original on 6 June 2012.
- "Ferrari F1-89". ferrari.com. Archived from the original on 27 September 2013. Retrieved 15 February 2020.
- "Sequential Sorrow - 1989 Ferrari 640". www.drivetribe.com. 1 February 2017. Retrieved 11 August 2020.
- "Forti-Corse - full profile". f1rejects.com. Archived from the original on 10 October 2007. Retrieved 29 October 2006.
- "Motor Racing: McLaren face charges over automatic gearbox: Benetton choose a temporary replacement for Schumacher as they prepare to explain Hockenheim fire". The Independent. 6 September 1994. Retrieved 17 August 2020.
- "Vehicle Diagram Book No. 120 for shunting diesel locomotives" (PDF). www.barrowmoremrg.co.uk. BRB Residuary Ltd. Retrieved 14 August 2020.
- Durham Mining Museum (17 December 2012). "Durham Mining Museum - Colliery Engineering". Dmm.org.uk. Retrieved 18 July 2014.
- "Vulcan-Sinclair Fluidrive Makes Headway". The Commercial Motor. 16 August 1946. p. 69. Archived from the original on 6 September 2017.
- "Leyland Make "Air" Gearbox". www.commercialmotor.com. Retrieved 14 August 2020.
- "Transmissions: a period of change". www.commercialmotor.com. Retrieved 14 August 2020.