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A semi-automatic transmission (SAT) (also known as a 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.
- 1 Early semi-automatic transmissions
- 2 Comparison to other automated transmissions
- 3 Operation
- 4 History
- 5 Other applications
- 6 Marketing names
- 7 Types
- 8 See also
- 9 References
Early semi-automatic transmissions
Beginning 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. It was also applied to some road vehicles. It is covered by US patent 2505842.
Comparison to other automated transmissions
Modern "Semi-automatic transmissions" usually have a fully automatic mode, where the driver does not need to change gears at all, operating in the same manner as a conventional type of automatic transmission by allowing the transmission's computer to automatically change gear if, for example, the driver were redlining the engine. The semi-automatic transmission can be engaged in manual mode wherein one can up-shift or down-shift using the console-mounted shifter selecter 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 certain automatic transmissions (manumatics such as Tiptronic) and continuous variable transmissions (CVTs) (such as Lineartronic).
Despite superficial similarity to other automated transmissions, semi-automatic transmissions differ significantly in internal operation and driver's "feel" from manumatics 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. A semi-automatic transmission 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,  and CVTs are generally found in gasoline-electric hybrid engine applications.
Typically semi-automatic transmissions are more expensive than manumatics and CVTs, for instance BMW's 7-speed Double Clutch Transmission is a $3900 (Canadian dollar) upgrade from the standard 6-speed manual, while the 6-speed Steptronic Automatic was only a $1600 (Canadian) option in 2007. 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 semi-automatic transmission until after the 2008 model year, when the SMG III was dropped. 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 semi-automatic gearbox for their high-performance models (the BMW M3 and BMW M5).
The semi-automatic transmission may be derived from a conventional automatic; for instance Mercedes-Benz's AMG Speedshift MCT semi-automatic transmission is based on the 7G-Tronic manumatic, however the latter's torque converter has been replaced with a wet, multi-plate launch clutch. Other semi-automatic 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 an Formula One style transmission. The most common type of semi-automatic 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).
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.
Hall effect sensors sense the direction of 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 a 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 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 to allow a complete clutch operation without the intervention of the driver.
For the needs of parking, reversing and neutralizing the transmission, the driver must engage both paddles at once; after this has been accomplished, the car will prompt for one of the three options.
The clutch is really only needed to get the car in motion. 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.
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 and Nova. 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 cancelled semi-automatic Torque Drive and continued to offer Powerglide until 1974, when the three-speed Turbo Hydramatic became the sole automatic available.
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 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 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 carburettor 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 smaller range of cars: C1, C2 and C3 have all been offered with a semi-automatic transmission named Sensodrive. This is based on a standard 5-speed gearbox with servo-controlled clutch. The operation is automatic, but it also has a manual mode where the driver changes gear manually; although gears are always changed by an electric servo.
An improved version of Sensodrive is EGS, which has six gears.
An even further improved version is called ETG6 (6 speed Efficient Tronic Gearbox). It has slightly better characteristics compared to EGS and an added "creep" function. The ETG6 gearbox is used by the 2013 Citroën C4 Picasso. The gearbox is also utilized by PSA Group's other offerings, like the Peugeot 208.
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 ¼mile 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 gearbox in a road car (They had used them previously in their Formula One cars since 1989) went on sale in 1997 in the Ferrari F355. The most recent version of its semi-automatic was introduced in the Ferrari 599 GTO which was capable of changing gear in 60 ms. In the new Ferrari California & Ferrari 458 Italia, Ferrari has opted to use a double-clutch transmission.
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.
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. The design is noteworthy because it preserves engine braking by eliminating a sprag between first and second gears.
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 Japanese domestic market only).
Mercedes used a system 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.
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, in an almost desperate attempt to compete with Ford and Chevrolet who both had fully automatic transmissions, Plymouth fitted a torque converter to their standard 3-speed manual gearbox and called this optional transmission "Hy-Drive." 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 utilize 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 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 dry clutch that engaged and disengaged by touching the gearshift, similar to driver operation of Volkswagen's Autostick, but without the torque converter of the VW.
For the SAAB 900NG a semi-automatic transmission was available for Turbo models only betwhen 1995 and 1996, mostly for European market. The 'Sensonic' clutch variant provided a manual gear lever as in a standard manual transmission car, but omitted the clutch pedal in favor of electronics which could control the clutch faster than an average driver.
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. The clutch disengaged when the selector was touched.
The Smart Fortwo employs an automated manual transmission designed and manufactured by Getrag to eliminate the clutch pedal. The first generation used a six-speed version, and the second generation used a five-speed version, model 5AMT130. Input from floor-mounted shifter or optional steering-wheel-mounted paddles controls a servo-operated clutch and sequential automated gearbox. The vehicle may be driven in automatic mode or via paddle shifters, where the operator controls the shift points but cannot feather or adjust the speed of the clutch.
Opel (Vauxhall Motors in the United Kingdom) produced an semi-automatic transmission gearbox, the Easytronic gearbox. As with all standard automateds, the Easytronic car has only two pedals (accelerator pedal and brake pedal) but it does have a clutch, though this is inbuilt into the car and is electrohydraulic. The Easytronic can be driven in "manual mode" simply by using the paddle shifter selector to change gears if the driver wishes to do so, or alternatively it can be driven in exactly the same way as a fully conventional automatic—however, many Easytronic owners have complained that gear shifts in "automatic mode" are jerky; a common complaint with semi-autos based on a conventional manual gearbox. As with conventional, full automatic transmission cars, the Easytronic will "creep" forwards when the driver's foot is released from the brake pedal when the car is stationary.
For the 1968 model year, the Volkswagen Beetle offered an optional transmission marketed as Automatic Stickshift which was essentially a three-speed manual without a clutch pedal. When the driver put his/her hand on the gearshift the clutch would disengage by a 12 volt solenoid operating the vacuum clutch, allowing shifting between gears, once he/she removed his/her hand, 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 1967 Volkswagen Beetle, and was made available on the Karmann Ghia in 1967. VW dropped the transmission option altogether in 1976. Some older (early 1960s) VW's sold in Europe had a "Saxomat" system which used a centrifigal clutch coupled to a standard 4-speed transmission.
According to the Car Crazy episode "Le Mans Museum of the Automobile", the paddle shifter interface could be found as early as 1912. The system used an inner steering wheel to select a gear level and can be seen on the "Bollée Type F Torpédo" of 1912, on show at the "Musée Automobile de la Sarthe" at the Le Mans race circuit.
In Formula One, the first attempt at clutch-less gear changing was in the early 1970s, with the system being tested by the Lotus team. However, it would be much later that attention was turned back to the concept. In 1989, John Barnard and Harvey Postlethwaite, then-Ferrari engineers and designers, created an automated gearbox for use in the Ferrari 640 single-seater. Despite serious problems in testing, the car won its first race at the hands of Nigel Mansell. By 1994, the semi-automatic transmission was dominant in terms of gearbox technology, and the last F1 car fitted with a manual gearbox raced in 1995.
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 change 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, buses, and trains
Semi-automatic 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, 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. These gearboxes have a place in public transport as they have been shown to reduce fuel consumption in some specific cases.
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 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 favour. 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 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 engine/automated gearbox units mounted under the floor. Synchronising controls by control cables connected through the train ensured all the gearboxes under all coaches of the train changed gear together.
In addition to the Hondamatic system noted above, Yamaha Motor Company introduced an 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.
The BRP Can-Am Spyder Roadster is available with a clutchless automatic transmission (the SE5 or SE6, with five or six speeds, depending on the model).
Honda released automated electric shift ATVs starting in 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 current 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 assy, 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.
- 2-tronic, EGC (Electric Gearbox Control) or Piloted Manual – Peugeot
- Twin Clutch SST – Mitsubishi
- Dual clutch transmission (DCT), a generic term – Volkswagen Group, Bugatti, Koenigsegg
- Direct-Shift Gearbox (DSG) – Volkswagen Group: SEAT, Skoda Auto, Volkswagen
- Dualogic – Fiat
- Duo Select – Maserati
- Durashift EST – Ford
- E-Gear – Lamborghini
- Easytronic – Opel
- Multimode manual transmission – Toyota
- NAVi5 - Isuzu
- PDK (Porsche Doppelkupplungen)/Sportomatic (Clutchless manual pre-1969) – Porsche
- Pleasure Shift – Saleen
- EDC-Efficient Dual Clutch – Renault
- Retrotek, MasterShift, Twist Machine, etc. – Detroit's Big 3
- Opticruise – Scania AB
- Sensonic or ACS – Saab
- Selespeed – Alfa Romeo, Fiat
- SensoDrive, EGS (Electronic Gearbox System), BMP or ETG6 (Efficient Tronic Gearbox) – Citroen
- SMG/SSG (Electrohydraulic manual transmission) – BMW
- Speedgear – Fiat
- Sportshift – Aston Martin, Subaru
- MasterShift – Aftermarket
- Dual clutch transmission
- Electrohydraulic manual transmission (e.g., BMW sequential manual gearbox, SMG)
- Multimode manual transmission
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