Editing Semi-automatic transmission (section)

== Design and operation ==
Semi-automatics facilitate easier [[gear shift]]s by removing the need to depress a clutch pedal or lever at the same time as changing gears. Most cars that have a semi-automatic transmission are not fitted with a standard clutch pedal since the clutch is remotely controlled. Similarly, most motorcycles with a semi-automatic transmission are not fitted with a conventional clutch lever on the [[Motorcycle handlebar|handlebar]].

=== Clutchless manual transmissions ===
Most semi-automatic transmissions are based on conventional manual transmission. They can be partially automated transmission. Once the clutch becomes automated, the transmission becomes semi-automatic. However, these systems still require manual gear selection by the driver. This type of transmission is called a ''clutchless manual'' or an ''automated manual''.

Most semi-automatic transmissions in older passenger cars retain the normal H-pattern shifter of a manual transmission; similarly, semi-automatic transmissions on older motorcycles retain the conventional foot-shift lever, as on a motorcycle with a fully manual transmission. However, semi-automatics systems in newer motorcycles, racing cars, and other types of vehicles often use gear selection methods such as shift paddles near the [[steering wheel]] or triggers near the [[Motorcycle handlebar|handlebars]].<ref>{{cite web |title=Electronic Shift Transmission |url= https://shiftfx.com/electronic-shift-transmission |website=shiftfx.com |access-date=17 November 2020}}</ref><ref>{{cite web |title=Motorsport, Motorcycle race & kit car quickshifter systems |url= https://www.quickshifters.com |website=quickshifters.com |access-date=17 November 2020}}</ref><ref name="flatshifter.com">{{cite web|url=https://www.flatshifter.com/flatshifter-max-electronic-gear-selector-kit/|title = Flatshifter Max (Electronic Gear Selector Kit)}}</ref><ref>{{cite web|url=https://powersportsbusiness.com/top-stories/2016/06/08/yamaha-introduces-new-yxz1000rss-with-paddle-shifting/|title = Yamaha introduces new YXZ1000R SS with paddle shifting &#124; Powersports Business|date = 8 June 2016}}</ref><ref>{{Cite web |title=Formula Racecar Paddle Shifters |url=http://www.eecs.ucf.edu/seniordesign/su2015fa2015/g05/files/SDI/1.%20InitialDocument.pdf |access-date=16 October 2023 |website=[[University of Central Florida College of Engineering and Computer Science]]}}</ref><ref>{{Cite web |title=2014_RT Spec Sheet EN.pdf |url=https://can-am.brp.com/content/dam/canam-spyder/Canada/English/MY2014/Documents/Lineup/2014_RT%20Spec%20Sheet%20EN.pdf |access-date=16 October 2023 |website=can-am.brp.com}}</ref><ref>{{cite web|url=https://www.lemans.org/en/news/the-history-of-the-paddle-shift/2922|title = The history of the 'paddle shift'}}</ref>

Several different forms of automation for clutch actuation have been used over the years, from [[hydraulic actuator|hydraulic]], [[pneumatic actuator|pneumatic]], and [[Electromechanics|electromechanical]] clutches to [[Vacuum pump|vacuum-operated]],<ref>{{Cite web |title=Hudson Drivemaster Service Info |url=http://hudsonterraplane.com/tech/other/DrivemasterServiceInformation.pdf |access-date=16 October 2023 |website=hudsonterraplane.com}}</ref> [[electromagnetic clutch|electromagnetic]], and even [[centrifugal clutch]]es. [[Fluid coupling]]s (most commonly and formerly used in early automatic transmissions) have also been used by various manufacturers, usually alongside some form of mechanical friction clutch, to prevent the vehicle from stalling when coming to a standstill or at [[Idle (engine)|idle]].

A typical semi-automatic transmission design may work by using [[Hall effect sensor]]s or [[Miniature snap-action switch|micro switches]] to detect the direction of the requested shift when the gear stick is used. These sensors' output, combined with the output from a sensor connected to the [[gearbox]] which measures its current speed and gear, is fed into a [[transmission control unit]], [[electronic control unit]], [[engine control unit]], or [[microprocessor]],<ref>{{cite news|url= https://www.independent.co.uk/arts-entertainment/auto-biography-the-saab-900-turbo-sensonic-in-0-60-seconds-by-john-fordham-1304895.html |title = Auto Biography the Saab 900 Turbo Sensonic in 0–60 Seconds by John|website = [[Independent.co.uk]]|date = 23 October 2011}}</ref><ref>{{cite web|url= https://www.saabplanet.com/how-stuff-works-saab-900-ng-sensonic-clutchless-technology-in-practice/|title = How Stuff Works: Saab Sensonic (Clutchless Technology in Practice)|date = 28 January 2019}}</ref> or another type of electronic control system. This control system then determines the optimal timing and torque required for smooth clutch engagement.

The electronic control unit powers an actuator, which engages and disengages the clutch in a smooth manner. In some cases, the clutch is actuated by a [[servomotor]] coupled to a gear arrangement for a [[linear actuator]], which, via a [[hydraulic cylinder]] filled with [[hydraulic fluid]] from the [[Brake|braking system]], disengages the clutch. In other cases, the internal clutch actuator may be completely electric, where the main clutch actuator is powered by an [[electric motor]] or [[solenoid]], or even pneumatic, where the main clutch actuator is a [[pneumatic actuator]] that disengages the clutch.

A clutchless manual system, named the ''[[Autostick]]'', was a semi-automatic transmission introduced by [[Volkswagen]] for the 1968 model year. Marketed as the ''Volkswagen Automatic Stickshift'', a conventional three-speed manual transmission was connected to a vacuum-operated automatic clutch system. The top of the gear stick was designed to  depress and activate an electric switch, i.e. when touched by the driver's hand. When pressed, the switch operated a 12-volt [[Solenoid valve|solenoid]], which in turn operated the vacuum clutch actuator, thus disengaging the clutch and allowing shifting between gears. With the driver's hand removed from the gearshift, the clutch would re-engage automatically. The transmission was also equipped with a torque converter, allowing the car to idle in gear like with an automatic, as well as stop and start from a standstill in any gear.<ref>{{cite web |title=How Does An Autostick Work? |url= http://vwar.org/forum/index.php?topic=903.0 |publisher=VW Automatic Register |date=8 October 2009 |access-date=11 November 2020}}</ref><ref>{{cite web |title=Autostick |url= http://www.vw-resource.com/automatic.html |publisher=Rob and Dave's Aircooled Volkswagen Web Pages |access-date=11 November 2020}}</ref><ref>{{cite web|url=https://www.cargurus.com/Cars/Discussion-c6916_ds457882#:~:text=Almost%20all%20of%20the%20original,gear%20stick%20to%20change%20gears.|title = Automatic or standard (Volkswagen Beetle) – CarGurus}}</ref>

=== Automated manual transmissions ===
{{main|Automated manual transmission}}
[[File:Paddle Shifter Honda Accord 2013.JPG|thumb|Paddle shifter on a car.]]
Starting in the late 1990s, automotive manufacturers introduced what is now called an [[automated manual transmission]] (AMT), which is mechanically similar to, and has its roots in, earlier clutchless manual transmission systems. An AMT functions in the same way as older semi-automatic and clutchless manual transmissions, but with two exceptions; it is able to both operate the clutch and shift automatically, and does not use a torque converter. Shifting is done either automatically from a [[transmission control unit]] (TCU), or manually from either the shift knob or shift paddles mounted behind the steering wheel. AMTs combine the fuel efficiency of manual transmissions with the shifting ease of automatic transmissions. Their biggest disadvantage is poor shifting comfort due to the mechanical clutch being disengaged by the TCU, which is easily noticeable as "jolting".{{Citation needed|date=October 2021}} Some transmission makers have tried solving this issue by using oversized synchronizer rings and not fully opening the clutch during shifting—which works in theory, but as of 2007, there have not been any series production cars with such functions.{{Update inline|date=October 2021}} In passenger cars, modern AMTs generally have six speeds (though some have seven) and a rather long gearing. In combination with a smart-shifting program, this can significantly reduce fuel consumption. In general, there are two types of AMTs: integrated AMTs and add-on AMTs. Integrated AMTs were designed to be dedicated AMTs, whereas add-on AMTs are conversions of standard manual transmissions into AMTs.{{Citation needed|date=October 2021}}

An automated manual transmission may include a fully automatic mode where the driver does not need to change gears at all.<ref name="x-engineer1">{{cite web |url=https://x-engineer.org/automotive-engineering/drivetrain/transmissions/automated-manual-transmissions-amt/ |title=Automated Manual Transmission (AMT) |website=x-engineer.org |access-date=2020-02-29 }}</ref> These transmissions can be described as a standard manual transmission with an automated clutch and automated gear shift control, allowing them to operate in the same manner as traditional automatic transmissions. The TCU automatically shifts gears if, for example, the engine is [[redline]]d. The AMT can be switched to a clutchless manual mode wherein one can upshift or downshift using a [[Center console (automobile)|console]]-mounted shift selector or paddle shifters.<ref>{{cite news|last=Woodyard|first=Chris|title=Among bells and whistles, cars shift to buttons, knobs|url= https://www.usatoday.com/story/money/cars/2014/08/10/cars-shifting-knobs-buttons/13721433/|access-date=2021-10-15|website=USA Today|language=en-US}}</ref> It has a lower cost than conventional automatic transmissions.<ref name="zf1">{{cite web |url=https://www.zf.com/products/en/cars/products_29280.html |title=Automated Manual Transmission |website=zf.com |access-date=2020-02-29 |archive-date=26 September 2020 |archive-url=https://web.archive.org/web/20200926015226/https://www.zf.com/products/en/cars/products_29280.html |url-status=dead }}</ref>

The automated manual transmission (trade names include ''SMG-III'') is not to be confused with "[[manumatic]]" automatic transmission (marketed under trade names such as ''Tiptronic'', ''Steptronic'', ''Sportmatic'', and ''[[Geartronic]]''). While these systems seem superficially similar, a manumatic uses a torque converter like an automatic transmission, instead of the clutch used in the automated manual transmission. An automated manual can give the driver full control of the gear selection, whereas a manumatic will deny a gear change request that would result in the engine stalling (from too few [[RPM]]) or over-revving.<ref name="x-engineer1" /> The automatic mode of an automated manual transmission at low or frequent stop start speeds is less smooth than that of manumatics and other automatic transmissions.<ref>{{cite web|url=http://www.leftlanenews.com/review-m5s-smg-sucks-all-the-joy-from-experience.html|title=Review: M5's SMG "sucks all the joy" from experience |website=leftlanenews.com |access-date= 24 March 2019}}</ref>

=== Sequential manual transmissions ===
Several semi-automatic transmissions used by motorcycles and racing cars are actually mechanically based on [[sequential manual transmission]]s. Semi-automatic motorcycle transmissions generally omit the clutch lever, but retain the conventional heel-and-toe foot shift lever.<ref>{{cite web |url=https://www.wikihow.com/Shift-Gears-on-a-Motorcycle |title=How to Shift Gears on a Motorcycle |website=wikiHow}}</ref><ref name="itstillruns.com">{{cite web |url=https://itstillruns.com/shift-automatic-transmission-dirt-bike-7577353.html |title=How to Shift a 4 Speed Semi Automatic Transmission on a Dirt Bike |website=It Still Runs}}</ref><ref>{{cite web |url= https://www.cycleworld.com/top-automatic-motorcycles-you-can-buy-in-2019/ |title = Top Automatic Motorcycles You Can Buy in 2019}}</ref><ref name="autowise.com">{{cite web |url = https://autowise.com/automatic-dirt-bike/ |title = 10 Best Automatic Dirt Bike Models |date= 17 May 2021 |access-date=18 August 2020|archive-date = 25 October 2021 |archive-url = https://web.archive.org/web/20211025210426/https://autowise.com/automatic-dirt-bike/ |url-status = dead}}</ref><ref name="dirtbikehouse.com">{{cite web |url= https://dirtbikehouse.com/what-is-a-semi-automatic-dirt-bike/ |title = What is a Semi-Automatic Dirt Bike and How does it work? |date = 19 January 2020}}</ref><ref name="ktm.com">{{cite web |url=https://www.ktm.com/en-int/error-page.html |title=Error Page |website=www.ktm.com}}</ref>

Semi-automatic motorcycle transmissions are based on conventional sequential manual transmissions and typically use a [[centrifugal clutch]].<ref>{{cite web |date=8 May 2000 |title=How Chain Saws Work |url=https://home.howstuffworks.com/chainsaw4.htm}}</ref> At idle speed, the engine is disconnected from the gearbox input shaft, allowing both it and the bike to [[freewheel]], unlike with torque converter automatics, there is no [[idle creep]] with a properly adjusted centrifugal clutch. As the engine speed rises, counterweights within the clutch assembly gradually pivot further outwards until they start to make contact with the inside of the outer housing and transmit an increasing amount of engine power and torque. The effective "bite point" or "biting point"<ref>{{cite web |title=biting point |url= https://dictionary.cambridge.org/dictionary/english/biting-point |access-date=2021-10-15 |website=Cambridge Dictionary |language=en}}</ref> is found automatically by equilibrium, where the power is transmitted through the (still-slipping) clutch is equal to what the engine can provide. This allows relatively fast full-[[throttle]] takeoffs (with the clutch adjusted so the engine is at peak torque) without the engine slowing or being bogged down, as well as more relaxed starts and low-speed maneuvers at lower throttle and [[Revolutions per minute|RPMs]].