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Asequential manual transmission, also known as asequential gearbox orsequential transmission, is a type ofnon-synchronousmanual transmission used mostly inmotorcycles andracing cars.[1] It produces fastershift times than traditionalsynchronized manual transmissions, and restricts the driver to selecting either the next or previous gear, in a successive order.
A sequential manual transmission isunsynchronized, and allows the driver to select either the next gear (e.g. shifting from first gear to second gear) or the previous gear (e.g., shifting from third gear to second gear), operated either via electronic paddle-shifters mounted behind the steering wheel or with a sequential shifter. This restriction avoids accidentally selecting the wrong gear; however, it also prevents the driver from deliberately "skipping" gears.[2] The use ofdog clutches (rather thansynchromesh) results in faster shift speeds than a conventional manual transmission.[3][4]
On a sequential manual transmission, the shift lever operates a ratchet mechanism that converts the fore-and-aft motion of the shift lever into rotation of aGear shift drum or selector drum (sometimes called a barrel) which has three or four tracks machined around its circumference.[5] Selector forks are guided by the tracks, either directly or via selector rods. The tracks deviate around the circumference and as the drum rotates, the selector forks are moved to select the required gear.[6]
When upshifting or downshifting a sequential manual transmission, there is no need to operate the clutch, which is only required when the vehicle starts. Since the engagement ring (or "dog ring") is pushed by the shift fork and moves quick, and the engagement ring begins to transmit power synchronously while it comes into contact, the sequential manual transmission has the shortest shift speed, and the shift time is usually 5 milliseconds or less, and is therefore now used in all Formula 1 cars.
A sequential manual transmission is not to be confused with themanumatic sequential shifting function sometimes fitted tohydraulic automatic transmission, marketed with terms such as "Tiptronic" or "SportShift". This function allows the driver to select the previous or next gear through the use of buttons or a lever (usually near the gear shifter or steering wheel); however, the mechanics of the transmission are unrelated to a true sequential manual transmission.
Most motorcycles use a sequential manual transmission. The rider controls the gear shifter with their foot, allowing their hands to remain on the handlebars, and gear selection uses a layout of1 - N - 2 - 3 - 4 - 5 - 6 (for a typical 6-speed gearbox, said as "one down, five up").[7] However, most modernmotor scooters do not use a sequential manual transmission; instead using either ahydraulicautomatic transmission, or abelt-driven orchain-drivencontinuously variable transmission.Underbones, however, often use asemi-automatic transmission with an automaticcentrifugal clutch, but will still retain the conventional foot-operated gearshift lever, such as theHonda Super Cub.
The first proper sequential manual gearbox used in a racecar was with thePorscheType 360 Cisitalia in 1946,[8] followed by the infamously unreliableQueerbox design, pioneered by Richard Ansdale andHarry Mundy, which was used in variousLotus Grand Prix racecars during the late-1950s and early-1960s, beginning with the 1958Lotus 12, and is technically the first proper "sequential" gearbox used in a racecar.[9] Most racing cars also use a sequential transmission now (via a sequential shift lever, with a mechanical linkage, or electronic paddle-shifters),[10] rather than the oldH-pattern stick shift, beginning with the paddle-shiftedFerrari 640Formula One car in 1990, which used a sequential drum-rotation mechanism.[11][12]
The first modern sequential manual gearbox with a manualshift lever was used in the 1990Peugeot 905Group Csports car, followed by theFerrari 333 SPLMPracecar andCARTChamp Cars/Indycars in 1994 and 1996,[13] and then theMcLaren F1 GTR,Mercedes-Benz CLK GTR,Porsche 911 GT1, andPanoz Esperante GTR-1GT1racecars in 1996 and 1997. This was closely followed byWRCRally cars in 1997, 1998, and 1999, and also thePorsche LMP1-98,Nissan R390 GT1,Toyota GT-One, and theBMW V12 LM' andLMRLe Mans Prototyperacecars in 1998 and 1999.
Touring cars have also used sequential manual gearboxes; starting with the EuropeanDTM series in 2000, which used it for 12 seasons, until a switch to apaddle-shift system in 2012. The AustralianV8 Supercars series started using sequential manual gearboxes in 2008, after switching from anH-pattern manual gearbox.
NASCAR introduced a 5-speed sequential manual transmission with theirGen-7 car in 2022, after using a conventional 4-speed H-pattern manual transmission for many years.[14][15][16][17]
Due to the high rate of wear and abrupt shifting action, sequential manual transmissions are rarely used in passenger cars, albeit with some exceptions.
Motorcycle transmissions and the latest auto-racing gearboxes are of the sequential type
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