【正文】 the speed of the driving member When the speeds of the members bee equal there is no slip the two members are in firm contact and the clutch is said to be fully engaged The driving member of a clutch is the flywheel mounted on the crankshaft the driven member is the pressure plate mounted on the transmission shaft Friction surfaces clutch plates are between the two members When the clutch is engaged the engine is connected to the transmission and the power flows from the engine to the rear wheels through the transmission system When the clutch is disengaged by pressing a clutch pedal the engine is disconnected to the transmission Thus the power does not flow to the rear wheels while the engine is still running The driving members consist of a flywheel mounted on the engine crankshaft The flywheel is bolted to a cover which carries a pressure plate or driving disc pressure springs and releasing levers Thus the entire assembly of the flywheel and cover rotates all the times The clutch housing and the cover provided with openings to dissipate the heat by the friction during the clutch operation The driven member consists of a disc or plate called the clutch plate It is free to slide the lengthwise on the splines of the clutch shaft It carries friction materials on both of its surfaces When it is gripped between the flywheel and the pressure plate it rotates the clutch shaft through the splines The operating members consists of a foot pedal linkage release or throwout bearing release levers and the springs necessary to insure the proper operation of the clutch The clutches used in motor vehicles are almost very similar in construction and operation There are some differences in the details of the linkages as well as in the pressure plate assemblies In addition some clutches for heavy duty applications have two friction plates and an intermediate pressure plate Some clutches are operated by hydraulic means The dry single plate type of friction clutch is used almost exclusively in American passenger cars Where the dry plate clutch operates drywithout using oil the wet plate clutch operates in a bath of oil Most designs of the clutches use member of coil springs but some use a diaphragm or conical type spring The type of friction materials also varies in the clutches of different passenger cars 2 Transmission Next to the clutch is the transmission in the transmission system of a motor vehicle The word transmission is used for a device that is located between the clutch and the propeller shaft It may be a gear box a torque converter overdrive fluid drive or hydraulic drive The function of a vehicle transmission is to adapt the traction available from the drive unit to suit the vehicle the surface the driver and the environment The main parameters are technical and economic petitiveness The transmission has a decisive effect on the reliability fuel consumption ease of use road safety and transportation performance of passenger cars and mercial vehicles The main goal when developing a vehicle transmission is to convert the power from the engine into vehicle traction as efficiently as possible over a wide range of road speeds This has to be done ensuring a good promise between the number of speeds climbing performance acceleration and fuel consumption of the vehicle The four main functions of a vehicle transmission are to Enable the vehicle to move off from rest Adapt power flow Enable reverse motion Enable permanent power transmission Positive or force locking engine power transmission with minimal loss The transmissions are classified as follows 1Manually operated selective transmission A type used in cars buses and trucks It is also known as standard or stick shift It is of three typesconstant mesh sliding mesh and synchromesh 2Overdrive A semiautomatic type used in conjunction with a selective transmission 3Chrysler semiautomatic An electric and hydraulic controlled type used in conjunction with a fluid drive or a torque converter 4Automatic transmissions a hydrometric drive b torque converter transmissions 5Continuously variable transmission A type used in cars it is known being driven by a belt and pulleys transmission system or conjunction with an plaary gear set The modern passenger cars are generally provided with the manually operated selective transmission It consists of five forward speed ratios and one reverse ratio The car driver may select any one of these ratios by operating a gearshift lever usually located on the steering column benefit the steering wheel The transmissions of trucks and buses are usually provided with five or more forward speeds and reverse The sliding mesh gearbox is the simplest type of transmission however the constant mesh gearbox is more monly used Because all the gears are in constant mesh they are safe from being damaged and unpleasant grinding sound does not occur while engaging and disengaging them The modern cars use helical gears and synchromesh devices in the gear boxes that synchronize the rotation of gears that are about to be meshed This eliminates clashing of the gears and make gear shifting easier The synchromesh gear box is similar to the constant mesh gear box but the synchromesh gear box is provided with a synchromesh device by which the two gears to be engaged are first brought into frictional contact which equalizes their speed after which they are engaged smoothly In most of the cars the synchromesh devices are not fitted to all the gears They are fitted only on the top gears Reverse gear and in some cases the first gear do not have synchromesh device since they are intended to be engaged when the vehicle is stationary In an ordinary gearing the axles of the various gears are fixed the motion of the gears being simply rotations a