附录：Manual Transmissions Marshall BrainThe earliest form of a manual transmission is thought to have been invented by Louis-Ren Panhard and Emile Levassor in the late 19th centuryAmanual transmission，also known as amanual gearboxorstandard transmission，it is a typeoftransmissionused inmotor vehicleapplications It generally uses a driver-operatedclutch，typically operated by a pedal or lever，for regulatingtorque transfer from theinternal combustion engineto the transmissionA conventional manual transmission is frequently the base equipment in a car，other options include automated transmissions such as anautomatic transmission，a semi-automatic transmission，or a continuously variable transmission(CVT)Manual transmissions often feature adriver-operatedclutchand a movablegear stickMost automobile manual transmissions allow the driver to select any forwardgear ratio at any time，but some，such as those commonly mounted onmotorcyclesand some types of racing cars，only allow the driver to select the next-higher or next-lower gearThis type of transmission is sometimes called asequential manual transmissionSequential transmissions are commonly used in auto racing for their ability to make quick shiftsManual transmissions are characterized by gear ratios that are selectable by locking selected gear pairs to the output shaft inside the transmissionConversely，mostautomatic transmissionsfeature is planetary gearing controlled by brake bands and/or clutch packs to select gear ratioAutomatic transmissionsthat allow the driver to manually select the current gear are called ManumaticsA manual-style transmission operated by computer is often called anautomatedtransmission rather than anautomaticContemporary automobile manual transmissions typically use four to six forward gears and one reverse gear，although automobile manual transmissions have been built with as few as two and as many as eight gearsTransmission for heavy trucks and other heavy equipment usually have at least 9 gears so the transmission can offer both a wide range of gears and close gear ratios to keep the engine running in thepower bandAny engine has a redline- a maximum rpm value above which the engine cannot go without explodingEngines have narrow rpm ranges where horsepower and torque are at their maximumFor example，an engine might produce its maximum horsepower at 5，500 rpm The transmission allows thegear ratiobetween the engine and the drive wheels to change as the car speeds up and slows downYou shift gears so the engine can stay below the redline and near the RPM band of its best performanceMercedes-Benz Actros, manual transmissionIdeally，the transmission would be so flexible in its ratios that the engine could always run at its single，best-performance rpm valueThat is the idea behind thecontinuously variable transmission(CVT)Continuously Variable TransmissionsA CVT has a nearly infinite range of gear ratiosIn the past，cvts could not compete with four-speed and five-speed transmissions in terms of cost，size and reliability，so you didnt see them in production automobiles，These days，improvements in design have made cvts more commonTheToyota Priusis ahybrid carthat uses a CVTThe transmission is connected to the engine through theclutchThe input shaft of the transmission therefore turns at the same rpm as the engineMercedes-Benz, six-speed manual transmission, graphic illustrationA five-speed transmission applies one of five different gear ratios to the input shaft to produce a different rpm value at the output shaftHere are some typical gear ratios：GearRatioRPM at Transmission Output Shaft with Engine at3,000 rpm1st2.315:11,2952nd1.568:11,9133rd1.195:12,5104th1.000:13,0005th0.915:13,278A Very Simple TransmissionTo understand the basic idea behind a standard transmission，the diagram below shows a very simple two-speed transmission in neutral：Lets look at each of the parts in this diagram to understand how they fit together：The green shaft comes from the engine through theclutchThe green shaft and green gear are connected as a single unit(The clutch is a device that lets you connect and disconnect the engine and the transmissionWhen you push in the clutch pedal，the engine and the transmission are disconnected so the engine can run even if the car is standing stillWhen you release the clutch pedal，the engine and the green shaft are directly connected to one anotherThe green shaft and gear turn at the same rpm as the engine)The red shaft and gears are called thelayshaftThese are also connected as a single piece，so all of thegearson the layshaft and the layshaft itself spin as one unit.The green shaft and the red shaft are directly connected through their meshed gears so that if the green shaft is spinning，so is the red shaftIn this way，the layshaft receives its p