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Semi-automatic transmission

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A semi-automatic transmission is a 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. An automated transmission (also known as self-changing transmission, clutchless manual transmission, automated manual transmission, flappy-paddle gearbox, or paddle-shift gearbox) is a system which 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 gear shifts quick and smooth. The system was designed by automobile manufacturers to provide a better driving experience, especially in cities where congestion frequently causes stop-and-go traffic patterns.

Many modern automated transmissions can also operate 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 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, automated 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 is preferred in high performance driving applications, while a manumatic is often preferred 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.

The automated transmission may be derived from a conventional automatic; for instance Mercedes-Benz's AMG SPEEDSHIFT MCT automated transmission is based on the 7G-Tronic manumatic, however the latter's torque converter has been replaced with a wet, multi-plate launch clutch.[1][2] Other automateds 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.[3][3][3][4][5] The most common type of semi-automatic transmission in recent years has been the dual clutch type.

OperationEdit

Red Ferrari F430 Spider steering wheel

Steering wheel of Ferrari F430 with paddle-shifters

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

HistoryEdit

RacingEdit

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 a 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 automated 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.

ChryslerEdit

Main article: Vacamatic

Historically, the first automated 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 not used. The transmission itself was a fully synchronised manual type, with four forward gears, one reverse, where the shifting was done 'automatically' by either vacuum cylinders (early, M4, Vacamatic), or hydraulic cylinders (late, M6, Presto-Matic).

PackardEdit

Nearly simultaneously, 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 during coasting was tried to ease shifting. Called "freewheeling", it was bedeviled by the absence of adequate brakes.

VolkswagenEdit

In later production years, the Volkswagen Beetle offered an optional "Autostick", which was essentially a clutchless manual with three forward gears, using the Saxomat auto-clutch.

RenaultEdit

For the Renault 8, an automated transmission was offered in 1965. It was produced by Jaeger, and consisted of a three speed electrically operated gearbox and a powder ferromagnetic coupler.

Mercedes-BenzEdit

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.

CitroënEdit

Citroën produced a number of variants on automated 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 automated 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, automated 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 automated 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.

NSUEdit

The German automobile manufacturer NSU produced a automated system for the rotary-engined Ro80 saloon car in the 1960s, similar in concept to Citroën's system except that it used an electric switch on the gear shifter which disengaged the clutch.

HondaEdit

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[citation needed].

DaihatsuEdit

The 993 cc Daihatsu Charade in 1985 at least had the option of a two-speed automated transmission, which was similar to a conventional auto with torque converter and planetary gearset but lacked 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.

FerrariEdit

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 iteration of its robotised manual came forward 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.

VauxhallEdit

Main article: Easytronic

Vauxhall Motors in Great Britain (Opel in continental Europe) produced a automated 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.

Other applicationsEdit

Trucks, buses, and trainsEdit

Automated transmissions have also made its 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.[6] These gearboxes have a place in public transport as they have been shown to reduce fuel consumption in some specific cases.

Bristol/Leyland BusesEdit

Main article: Pneumocyclic

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, sem-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-automated 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, and semi-automated transmissions lost favour. These days, very few buses with semi-automated 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.

MotorcyclesEdit

In addition to the Hondamatic system noted above, Yamaha Motor Company introduced a automated 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 has begun production of the VFR1200F, which includes an optional dual clutch transmission, the first to be fitted to a motorcycle.

ATVsEdit

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.

Marketing namesEdit

TypesEdit

See alsoEdit

ReferencesEdit

External linksEdit


Smallwikipedialogo This page uses some content from Wikipedia. The original article was at Semi-automatic transmission. The list of authors can be seen in the page history. As with Tractor & Construction Plant Wiki, the text of Wikipedia is available under the Creative Commons by Attribution License and/or GNU Free Documentation License. Please check page history for when the original article was copied to Wikia

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