Transmission (mechanical device)
Atransmission(also called agearbox) is a mechanical device which uses agear set—two or moregearsworking together—to change the speed or direction of rotation in amachine.[1][2]Many transmissions have multiplegear ratios,but there are also transmissions that use a single fixed-gear ratio.
Most currently-produced passenger cars with gasoline or diesel engines use transmissions with 5–8 forward gear ratios (also called speeds) and one reverse gear ratio.Electric vehiclestypically use a fixed-gear or two-speed transmission with no reverse gear ratio.
Fixed-ratio
[edit]
The simplest transmissions used a fixed ratio to provide either a gear reduction or increase in speed, sometimes in conjunction with a change in the orientation of the output shaft. Examples of such transmissions are used inhelicoptersandwind turbines.In the case of a wind turbine, the first stage of the gearbox is usually a planetary gear, to minimize the size while withstanding the high torque inputs from the turbine.[3][4]
Multi-ratio
[edit]
Many transmissions - especially for transportation applications - have multiple gear ratios that can be switched between while the machine is operating. The multiple ratios are used to match the range of input speeds (e.g. engine rpm) with the output speed (e.g. the speed of a car) required for a given situation.
Manual
[edit]A manual transmission requires the driver to manually select the gears[5]by operating agear stickandclutch(which is usually a foot pedal for cars or a hand lever for motorcycles).
Most transmissions in modern cars usesynchromeshto synchronise the speeds of the input and output shafts. However, prior to the 1950s, most cars usednon-synchronous transmissions.
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Transmission internals for a 2009Volkswagen Golf -
16-speed tractor transmission (plus 8 reverse gears)
Sequential manual
[edit]A sequential manual transmission is a type of non-synchronous transmission used mostly for motorcycles and racing cars. It produces faster shift times than synchronized manual transmissions, through the use ofdog clutchesrather than synchromesh.[6]Sequential manual transmissions also restrict the driver to selecting either the next or previous gear, in a successive order.
Automatic and semi-automatic
[edit]
Anautomatic transmissiondoes not require any input from the driver to change forward gears under normal driving conditions. Asemi-automatic transmissionis where some of the operation is automated (often the actuation of the clutch), but the driver's input is required to move off from a standstill or to change gears.
Hydraulic automatic
[edit]The most common design of automatic transmissions is the hydraulic automatic, which typically usesplanetary gearsetsthat are operated usinghydraulics.[7][8]The transmission is connected to the engine via atorque converter(or afluid couplingprior to the 1960s), instead of thefriction clutchused by most manual transmissions and dual-clutch transmissions.[9]
Dual-clutch (DCT)
[edit]A dual-clutch transmission (DCT) uses two separateclutchesfor odd and evengear sets.[10]The design is often similar to two separatemanual transmissionswith their respective clutches contained within one housing, and working as one unit.[11][12]In car and truck applications, the DCT functions as an automatic transmission, requiring no driver input to change gears.
Continuously variable (CVT)
[edit]A continuously variable transmission (CVT) can change seamlessly through a continuous range ofgear ratios.This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constantRPMwhile the vehicle moves at varying speeds.
CVTs are used in cars, tractors,side-by-sides,motor scooters,snowmobiles,bicycles, andearthmoving equipment.
The most common type of CVT uses twopulleysconnected by abeltorchain;however, several other designs have also been used at times.
Automated manual / clutchless manual
[edit]An automated manual transmission (AMT) is essentially a conventional manual transmission that uses automatic actuation to operate the clutch and/or shift between gears.
Many early versions of these transmissions were semi-automatic in operation, such asAutostick,which automatically control only theclutch,but still require the driver's input to initiate gear changes. Some of these systems are also referred to asclutchless manualsystems.[13]Modern versions of these systems that are fully automatic in operation, such asSelespeedandEasytronic,can control both the clutch operation and the gear shifts automatically, without any input from the driver.[14][15]
Applications
[edit]Early uses
[edit]Early transmissions included the right-angle drives and other gearing inwindmills,horse-powered devices, andsteam-powered devices. Applications of these devices includedpumps,millsandhoists.[citation needed]
Automobiles
[edit]
The need for multiple gear ratios inICE-poweredmotor vehiclesis because the engines typically operate over a range of approximately 600–7000rpm,while the road speed of the vehicle typically equates to arotational speedof the wheels in the range of 0-1800 rpm. In addition, the engine's characteristics result in different optimal rpm ranges for thepower bandand achieving highestfuel efficiency.[16]
Motorcycles
[edit]See also
[edit]
References
[edit]- ^J. J. Uicker; G. R. Pennock; J. E. Shigley (2003).Theory of Machines and Mechanisms(3rd ed.). New York: Oxford University Press.ISBN9780195155983.
- ^B. Paul (1979).Kinematics and Dynamics of Planar Machinery.Prentice Hall.
- ^Stiesdal, Henrik (August 1999),The wind turbine: Components and operation(PDF),retrieved2009-10-06
- ^Musial, W.; Butterfield, S.; McNiff, B. (May 2007),Improving Wind TurbineGearbox Reliability(PDF),National Renewable Energy Laboratory, archived fromthe original(PDF)on September 23, 2012,retrievedJuly 2,2013
- ^"Manual Transmission Operation".YouTube.Retrieved21 January2023.
- ^"How Sequential Gearboxes Work".www.howstuffworks.com.4 April 2003.Retrieved2 January2020.
- ^"How Automatic Transmissions Work".www.howstuffworks.com.29 November 2000.Retrieved22 November2020.
- ^"What Makes Automatic Transmissions Automatic".Popular Mechanics.Hearst Magazines: 169–173. February 1955.Retrieved22 November2020.
- ^"How does the AT work?".AW North Carolina.Archived fromthe originalon 6 October 2014.Retrieved6 October2014.
- ^"Powertrain — transmissions: Shift in power to the gearbox"(PDF).AMS.UnofficialBMW.com. September–October 2003.Archived(PDF)from the original on 17 July 2011.Retrieved31 October2009.
- ^"Automatic-shifting dual-clutch transmissions are poised to grab share from traditional transmissions thanks to their combination of efficiency and convenience"(PDF).AEI-online.org.DCTfacts.com. June 2009. Archived fromthe original(PDF)on 7 October 2011.Retrieved31 October2009.
- ^"Porsche Doppelkupplung (PDK)".Porsche.com. Archived fromthe originalon 5 December 2008.Retrieved31 October2009.
- ^"Hyundai Created a Clutch-less Manual Transmission".10 July 2020.
- ^"Directly from the Formula 1".www.magnetimarelli.com.Retrieved26 July2020.
- ^"Introduction to Automatic Transmission Systems".www.tranzmile.com.Retrieved1 August2020.
- ^Naunheimer, Harald; Bertsche, Bernd; Ryborz, Joachim; Novak, Wolfgang (2011). "Power Conversion: Selecting the Ratios".Automotive Transmissions: Fundamentals, Selection, Design and Application.Springer. pp. 100–114.doi:10.1007/978-3-642-16214-5_4.ISBN978-3-642-16214-5.Retrieved21 January2023.
