Automated manual transmission (AMT), also known as a clutchless manual, denotes a type of motor vehicle transmission that is closely based on the mechanical design and build of a conventional manual transmission, but uses automation to operate the clutch and/or the gear shift mechanism.
Many early versions of these transmissions that are semi-automatic in operation, such as Autostick, which only automatically control the clutch — often using various forms of clutch actuation, such as electro-mechanical, hydraulic, pneumatic, or vacuum actuation — but still require the driver's manual input and full control to initiate gear changes by hand. Modern versions of these systems that are fully automatic in operation, such as Selespeed and Easytronic, can control both the clutch operation and the gear shifts automatically, by means of an ECU, therefore requiring no manual intervention or driver input over gear changes.
The usage of modern computer-controlled AMTs in passenger cars increased during the mid-1990s, as a more sporting alternative to the traditional hydraulic automatic transmission. During the 2010s, AMTs were largely replaced by the increasingly widespread dual-clutch transmission design.
Design and operation
Automated manual transmissions can be semi-automatic or fully-automatic in operation. Several different system to automate the clutch and/or shifting have been used over the years, but they will generally use one of the following methods of actuation for the clutch and/or shifting: hydraulic or electro-hydraulic actuation, electro-mechanical, pneumatic, electromagnetic, or even purely electrical by means of an electric motor.
Gear shifting, clutch actuation, shift-timing, and rev-matching are all under automated control via the electronic sensors, computers, and actuators. When shifting gears, the driver selects the desired gear with the transmission shift lever, while electronic sensors and actuators connected to a TCU (transmission computer) or microprocessor will automatically operate the clutch and throttle to match revs and to re-engage the clutch in milliseconds. Torque and power transfer to the drive wheels will also be electronically controlled. Most modern implementations of this transmission function in a sequential mode, where the driver can only upshift or downshift by one gear at a time. However, this is not the case for all modern transmissions. For example, BMW's "SMG" and Ferrari's "F1" transmission can skip gears on both downshifts and upshifts, when selecting gears manually via the steering wheel-mounted paddle-shifters, as seen on most modern transmissions. Older clutchless manual transmissions (mostly prior to the 1990s) will retain H-pattern shifters, plus the shift gate, and will require the driver to select the required gear ratios manually. The clutch, however, will be a servo-controlled unit, connected to various actuators, a solenoid and sensors which control the clutch automatically.
Another alternate means of clutch automation is the "clutch-by-wire" system. The system generally uses an electric actuator and electronic sensors, which replace the mechanical clutch linkage or hydraulic clutch connection, to monitor and control clutch positioning, completely replacing the hydraulic linkage between the mechanical clutch and pedal itself with a single electro-mechanical actuator.
Depending on the mechanical build and design, some (mostly modern) automated manual transmissions will automatically shift gears at appropriate points (like a conventional automatic transmission), while traditional semi-automatic and clutchless manuals require the driver to manually select the gear even when the engine is at redline, since they only automate part of the transmission (namely the clutch), and will not shift gears by themselves. Despite the superficial similarity, automated manual transmissions differ significantly in internal operation and driver's "feel" from a manumatic, the latter of which is an automatic transmission (automatics use a torque converter instead of a clutch like in an automated manual, to manage the mechanical linkage between the transmission and motor) with the ability to override the automatic transmission's computer, and actuate shifts manually.
Add-on AMTs can also function as a regular manual gearbox (with a manual shift lever), whereas integrated AMTs do not need a "normal" shift layout, so they can be designed with an optimized AMT shifting layout (which would have an unusual pattern to manually shift). Integrated AMTs either have gear-selector drums (which only allows serial shifting and no gear-skipping, but this system is fairly inexpensive, because it needs only one actuator), or single actuators. Single-actuator systems require one actuator for each shifting sleeve (which is why this type of system is more expensive, but it also shifts faster). The actuators can either be electro-hydraulic (more expensive, but faster, well-suited for single-actuator systems, and allow for higher torque), or electro-mechanical (less expensive, but usually limited to 250 N·m (184.5 lb-ft) of gearbox input torque). This limit is because the clutch actuation force increases with higher torque, and short shifting times; electro-mechanical actuators are just electric motors – using larger motors reduces the motor dynamics due to the motors' higher mass moment of inertia (which is not good for fast shifting), and bigger motors also put more stress on the car's 12-volt electrical system. As a result, one can have either slow shifting and a very large lead-acid battery (not suitable for cars), or fast shifting and a smaller battery (works up to 250 N·m of torque).
Usage in passenger cars
The automated manual transmission has its origins in early clutchless manual transmissions that began to appear on mass-production cars in the 1940s and 1950s. An early example of this transmission was introduced with the Hudson Commodore in 1942, called Drive-Master. This unit was an early semi-automatic transmission, based on the design of a conventional manual transmission which used a servo-controlled vacuum-operated clutch system, with three different gear shifting modes, at the touch of a button; manual shifting and manual clutch operation (fully-manual), manual shifting with automated clutch operation (semi-automatic), and automatic shifting with automatic clutch operation (fully-automatic).
Another early example is the 1955 Citroën DS, which used a 4-speed "BVH" transmission. This semi-automatic transmission used an automated clutch, which was actuated using hydraulics. Gear selection also used hydraulics, however, the gear ratio needs to be manually selected by the driver. The 1956 Renault Dauphine 3-speed manual transmission was available with an optional Ferlec automated clutch, which used an electromagnetically-operated clutch system. Other clutchless manual transmissions included the 1967 NSU Ro 80 (3-speed Fichtel & Sachs) and 1967 Porsche 911 (4-speed Sportomatic), both of which used vacuum-actuated clutches and hydraulic torque converters. The 1968 Volkswagen Beetle and Volkswagen Karmann Ghia offered a 3-speed Autostick transmission, which used an electric switch on the gear shifter connected to a solenoid, to operate the electro-pneumatic vacuum clutch servo.
In 1963, Renault switched from the automated clutch to a fully-automatic 3-speed Jager transmission, which consisted of an electro-mechanical control unit that operated both the clutch and shifting, effectively making it one of the earliest automated manual transmissions. The Jager transmission was controlled via dash-mounted electronic push-buttons.
The Isuzu NAVi5 5-speed automatic transmission was introduced in the 1984 Isuzu Aska mid-size sedan (sold in the Japanese domestic market only). This transmission, originally designed for trucks, was based on a manual transmission with the addition of hydraulic actuators for the gear shifter and the clutch. Initial versions did not allow direct selection of gear ratios, instead only allowing drivers to lock out higher gears (as per many traditional automatic transmissions). Later versions added a manual mode, allowing the driver to control the gear selection.
Several companies owned by Fiat S.p.A. were influential in the development of automated manual transmissions. Ferrari's involvement with automated manual transmission began with the 7-speed semi-automatic paddle-shift transmission used in the 1989 Ferrari 640 Formula One racing car. In 1992, the Ferrari Mondial T introduced the option of a "Valeo" 5-speed semi-automatic transmission. This transmission used an electro-mechanical actuator to automatically operate the clutch, while the gearshift mechanism was a standard H-pattern shifter operated as per normal transmissions. In 1997, the Ferrari F355 became available with an "F1" 6-speed transmission, which uses paddle-shifters located behind the steering wheel or can be driven in a fully-automatic mode. The F355's successors offered similar transmissions, until the company switched to a dual-clutch transmission for the Ferrari 458 in 2009.
Sister company Alfa Romeo introduced the related Selespeed 5-speed automatic transmission for the Alfa Romeo 156 in 1999. This was followed by Maserati's 2001 introduction of the related Cambiocorsa 6-speed automatic transmission in the Maserati Coupé.Selespeed was also used in the Fiat Punto and Stilo models.
BMW's involvement with automated manual transmissions began in 1993, when the "Shift-tronic" 6-speed semi-automatic was offered on the Alpina B12 coupe (based on the E31 850CSi). Using an automated clutch paired to a standard H-pattern shifter (as per the Ferrari Mondial T), the transmission was supplied by LuK and fitted to less than 40 cars. Mass-production of automated manual transmissions began for BMW in 1997 with the introduction of the "SMG" 6-speed automatic transmission in the BMW E36 M3 coupe. Although the name "SMG" was an abbreviation of "Sequential Manual Gearbox", the transmission internal were as per a typical (synchromesh-equipped) manual transmission, not a true sequential manual transmission. The SMG was replaced by the SMG-II when the E46 M3 was introduced in 2000. BMW's final AMT (before being replaced by a dual-clutch transmission) was the 7-speed SMG-III used in the 2004-2010 BMW E60 M5 and related BMW E63 M6. The SMG-III could achieve a shift time of 65 milliseconds in its most aggressive mode
From 2002 to 2007, the Toyota MR2 (3rd generation) was available with an "SMT" 6-speed automated manual transmission. The SMT system utilized an electro-hydraulic activation system for both the clutch and shifting, but no H-pattern shifter like with the standard transmission. Instead, there was a shift lever that could be pulled and pushed forward or backward to upshift and downshift, as well as the addition of electronic steering-wheel-mounted shift buttons.
Brands within the Volkswagen Group have typically used dual-clutch transmissions instead of automated manual transmissions, however a 6-speed "E-gear" automated manual transmission was introduced for the 2004 Lamborghini Murciélago. and Lamborghini Gallardo. The E-gear was used on the successors to the Murciélago and Gallardo, and it was also available on the 2007-2012 Audi R8 (Type 42), marketed as the "R-tronic" transmission.
Usage in semi-trucks / tractors
- Volvo I-Shift: an automated manual transmission; introduced in 2001 and used in trucks and buses. This system is an add-on for the conventional unsynchronized manual transmission.
- ZF AS Tronic: an automated manual transmission; introduced in 2003, and used in trucks, buses, and coaches.
- Eaton AutoShift: introduced in the early 2000s as an add-on to traditional non-synchromesh manual transmission for heavy trucks.
- Mack mDRIVE and mDRIVE HD: an automated manual transmission with synchronizers; introduced in 2010, and used in Mack semi-trucks.
- Renault Optidriver: an automated manual transmission; introduced in 2004, and used in Renault heavy-duty commercial semi-trucks.
- Daimler Trucks DT12: an automated manual transmission; introduced in 2012, and used in the Freightliner Cascadia semi-truck, and the Western Star 49X line of commercial semi-, crane, and dump trucks.
- Mercedes-Benz PowerShift: A non-synchronous automated manual transmission, used in Mercedes-Benz heavy-duty semi-trucks.
- UD Trucks ESCOT: An add-on for non-synchronized and synchronized manual transmission; introduced in 1995. Six different versions of this transmission have been made: ESCOT, ESCOT-II, ESCOT-III, ESCOT-IV, ESCOT-V, and ESCOT-VI. Used in UD Trucks' range of commercial vehicles.
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