Semi-automatic transmission

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Semi-automatic transmission denotes a multi-speed motor vehicle transmission where part of its operation is automated (typically the clutch actuation), but the driver's input is still required to launch the vehicle from a standstill and to manually change gears. Most semi-automatic transmissions used in cars and motorcycles are based on conventional manual transmissions or a sequential manual transmission, but use an automatic clutch system. However, some semi-automatic transmissions have also been based on standard hydraulic automatic transmissions, with, or incorporating a fluid coupling or torque converter, and a planetary gearset.[1][2]

Names for specific types of semi-automatic transmissions include clutchless manual,[3] auto-manual,[4][5] auto-clutch manual,[6][7] and paddle-shift transmissions.[8][9][10] These systems facilitate gear shifts for the driver by operating the clutch system automatically, usually by means, or under control of an actuator or servo, and sensors, 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 made available on various car and motorcycle models, and currently remain in production. Semi-automatic transmissions with paddle-shift operation have been used in various racing cars, and were first introduced to control the electro-hydraulic gear shift mechanism of the Ferrari 640 Formula One race car in 1989. These systems are currently used on a variety of top-tier racing car classes; including Formula One, Indycar, and Touring car racing. Other applications include motorcycles, trucks, buses, and railway vehicles.

Design and operation[edit]

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, design, and age of the vehicle, they can use anything from, or a combination of hydraulic, pneumatic, or electric servos, solenoids, electrical sensors, electric switches, motors, processors, and actuators, to execute gear shifts on demand when requested by the driver, which is typically initiated when the driver touches and moves the gearshift. Most cars that have a semi-automatic transmission are not fitted with a standard 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 conventional clutch lever on the handlebar.

Automated manual / clutchless manual transmissions[edit]

Most semi-automatic transmissions are actually based on conventional manual transmissions, but usually are operated with an automatic clutch or another kind of partially automated transmission mechanism, thus partially automating the manual transmission, to a certain degree. Once the clutch becomes automated, then the transmission becomes semi-automatic. However, these systems still require full control and input of the manual gear selection by the driver. This type of transmission is called a clutchless manual, or an automated manual. Most semi-automatic transmissions in older passenger cars retain the normal H-pattern shifter of a manual transmission, similarly, semi-automatic transmissions on older motorcycles retain the conventional foot-shift lever, as on a motorcycle with a fully-manual transmission. However, semi-automatics in newer 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.[11][12][13][14][15][16][17]

Several different forms of automation for clutch actuation have been used over the years, from hydraulic, pneumatic, and electro-mechanical-operated clutches, while other manufactures have used alternate methods of actuation; like vacuum-operated clutches,[18] electromagnetic clutches, and even centrifugal clutches. Fluid couplings (most commonly and formerly used in early automatic transmissionss) were also been used by various manufacturers, usually alongside some form of mechanical friction clutch, to prevent the vehicle from stalling when the driver came to a standstill, and when at idle.

A typical semi-automatic transmission design may work by using hall-effect sensors to detect the direction of the requested shift, and with this input, together with a sensor connected to the gearbox, which senses the current speed and gear selected, and may (but not necessarily) feed into either a transmission control unit, electronic control module, microprocessor,[19][20] central processing unit, or another type of electronic control system. This control unit will then determine the optimal timing and torque required for smooth clutch engagement, based on input from these sensors.

When the driver touches the gearshift to change gear, this activates an electric micro-switch. The electronic control 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 hydraulic fluid from the braking system to impel a hydraulic cylinder which moves the main clutch actuator, therefore disengaging the clutch. In other cases, the internal clutch actuator may be completely electric (sometimes through the use of a solenoid); where the main clutch actuator is powered by an electric motor, or even pneumatic; where the main clutch actuator is a pneumatic actuator, and uses compressed air to impel the pneumatic cylinder that disengages the clutch, allowing the driver to make a smooth gear change.

One now-famous application of this clutchless manual system was the Autostick semi-automatic transmission, introduced by Volkswagen for the 1968 model year. Marketed as the Volkswagen Automatic Stickshift; a conventional three-speed manual transmission was connected to a vacuum-operated automatic clutch system. The top of the gear shift was designed to easily depress and activate an electric switch, i.e., when touched/engaged by the driver's hand. When pressed, the switch operated a 12-volt solenoid, in turn, operating the vacuum clutch servo, thus disengaging the clutch and allowing shifting between gears. With the driver's hand removed from the gearshift, 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.[21][22][23]

Starting in the late-1990s, automotive manufacturers introduced what is now called an Automated Manual Transmission (AMT), which are mechanically similar, and have their roots in earlier clutchless manual transmission systems – These function in the same way as older semi-automatic and clutchless manual transmissions, but with two exceptions; they can do everything fully-automatically, and they do not 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.[24] 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.[25][failed verification] It has a lower cost than any other types of automatic transmissions.[26]

These transmissions are not to be confused with the superficially similar automatic transmissions with "manumatic" functions, which are marketed under tradenames such as Tiptronic, Steptronic, Sportmatic, and Geartronic. While these systems do seem superficially similar, they are largely unrelated in their mechanical design and build of a true clutchless manual transmission.

Sequential manual transmissions[edit]

Several semi-automatic transmissions used by motorcycles and racing cars are actually mechanically based on a sequential manual transmission. (Semi-auto motorcycle transmissions generally omit the clutch lever, but retain the conventional heel-and-toe foot-shifter lever.)[27][28][29][30][31][32]

Semi-automatic motorcycle transmissions are based on conventional sequential manual transmissions, and typically 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[edit]

Fully-automatic transmissions require no driver input when changing gears; semi-automatic transmissions will only require partial driver involvement, usually in the form of manually selecting the next gear, with the clutch operation being completely automated. Transmissions that 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 true semi-automatic transmissions, because the transmission is capable of operating in a fully-automatic mode. This type of transmission is called a manumatic.

Usage in passenger cars[edit]

1900s to 1920s[edit]

Bollée Type F Torpedo with gear shift ring located 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.[33] One car using this system was the 1912 Bollée Type F Torpedo.

1930s to 1940s[edit]

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.[34] 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,[35][36][37][38] 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.[39]

In 1937, the Oldsmobile 4-speed Automatic Safety Transmission was introduced on the Oldsmobile Six and Oldsmobile Eight models.[35] It used a planetary gearset with a clutch pedal for starting from standstill and switching between the "Low" and "High" ranges.[40][41][42] The Automatic Safety Transmission was replaced by the fully-automatic Hydra-Matic for the 1940 model year.[43][44]

The 1938–1939 Buick Special was available with the Self-shifter 4-speed semi-automatic transmission.[45][46][47] 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 an integral underdrive unit, a traditional manual clutch, and a fluid coupling between the engine and the clutch.[48][49][50] 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 the High range, and then release the clutch. Once 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 a similar M6 Presto-Matic transmission for the 1946 model year.

Similar designs were used for the 1941–1950 Hudson Drive-Master[51][52] and the ill-fated 1942 Lincoln Liquimatic.[53][54] Both of these used a 3-speed manual 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 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[edit]

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 lever 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.[55] 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.[56]

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 column selector mounted behind the steering wheel, while the driver simultaneously lifted off the accelerator to change gear. This system was nicknamed "Citro-Matic" in the U.S.

For the 1962 model year, American Motors introduced the "E-Stick" that eliminated the clutch pedal on the compact Rambler American with standard three-speed manual transmissions.[57] This automatic clutch used engine oil pressure as a hydraulic source and was available for less than $60.[58] Compared to the fully-automatic transmissions of the time, the E-Stick offered the fuel economy of a stick-shift with vacuum and electric switches controlling the clutch. The E-Stick three-speed transmission was offered on the larger Rambler Classic models and also together with an overdrive unit.[59] The system was only available with 6-cylinder engines and the clutch-less option proved be unpopular so it was dropped after 1964.[60]

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.[61]

The Chevrolet Torque-Drive transmission, introduced on the 1968 Chevrolet Nova and Camaro, is one of a few examples where a semi-automatic transmission was based on a conventional hydraulic automatic transmission (rather than a standard manual transmission). The Torque-Drive was essentially a 2-speed Powerglide automatic 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.

Other examples[edit]

Illustration of Saab's Sensonic clutchless manual transmission system.
Years Name Notes
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.[62][63]
1957–1961 Mercedes-Benz Hydrak Automatic clutch (vacuum-powered), plus a torque converter for standing starts.[64]
1959–???? Citroën Traffi-Clutch Automatic clutch (centrifugal). Used in the Citroën 2CV, Citroën Traction Avant, and Citroën Dyane.
1965-1990 VEB Sachsenring Hycomat Automatic clutch (electro-hydraulic). Used in the Trabant 601.
1966–???? Simca automatic clutch Automatic clutch plus a torque converter. Used in the Simca 1000.[65][66][67][68]
1967–1977 NSU automatic clutch Automatic clutch (vacuum-powered) plus a torque converter. Used in the NSU Ro 80.
1967–1976 Porsche Sportomatic Automatic clutch (vacuum-powered) plus a torque converter. Used in the Porsche 911.[69][70]
1968–1976 Volkswagen Autostick Automatic clutch (electro-pneumatic) plus a torque converter. Used in the Volkswagen Beetle and Volkswagen Karmann Ghia.[71]
1976–1980 Citroën C-matic Automated clutch plus a torque converter. Used in the Citroën GS and Citroën CX.
1991–1993[72] Ferrari Valeo Automatic clutch (electro-mechanical). Used in the Ferrari Mondial t.[73]
1992-1998 RUF EKS[74] Automatic clutch (electro-hydraulic). Used in the Ruf BTR and Ruf BTR2.
1993–1998[75][76] Saab Sensonic Automatic clutch (electro-hydraulic). Used in the Saab 900 NG.
2020–present Hyundai/Kia iMT Automatic clutch (electro-hydraulic). Used in the Hyundai Venue, Hyundai i20, and Kia Sonet. Gear stick has shift pattern similar to a fully manual car unlike AMTs with their + or - only gear selectors.

Usage in motorcycles[edit]

An early example for motorcycles was the use of an automatic centrifugal clutch in the early 1960s by the Czechoslovakian manufacturer Jawa Moto.[77] 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.[77]

Other semi-automatic transmissions used in motorcycles include:

Usage in motor racing[edit]

Semi-automatic transmissions in racing cars are typically operated by paddle-shift systems, which is connected to a designated Gearbox control unit (GCU).

The first Formula One car to use a semi-automatic transmission was the 1989 Ferrari 640.[33][113] This system used hydraulic actuators, powered by hydraulic fluid, and electrical solenoids 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 (i.e., stationary).[114] The car won its debut race at the Brazilian Grand Prix, however, for much of the season suffered from reliability problems.[115] 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 transmission) to produce a more compact design that required only one actuator to rotate the drum and move the gear selector forks, and this was the direction that semi-automatic transmissions in Formula One took. 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.[116] 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.[117]

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[118] that ensured that gear changes only occurred when instructed by the driver. Pre-programmed, computer-controlled, fully-automatic upshifts and downshifts were re-introduced and allowed from 2001, and were permitted from that year's Spanish Grand Prix, but were banned again in 2004.[119][120][121][122][123][124][125][126] 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 mandatory 8-speed paddle-shift gearboxes, being increased from the previous 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 IR-05 chassis for 2008.[127] 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 and clutch actuator controlled by an internal GCU (Gearbox Control Unit).[128][129][130][131][132]

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, since 2000.

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[edit]

Other notable uses for semi-automatic transmissions include:

See also[edit]


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