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1、精选学习资料 - - - - - - - - - 原文：CHASSIS 1.clutch The engine produces the power to drive the vehicle . The drive line or drive train transfer the power of the engine to the wheels . The drive train consists of the parts from the back of the flywheel to the wheels . These parts inclu de the clutch , the t
2、ransmission ,the drive shaft ,and the final drive assembly . The clutch which includes the flywheel ,clutch disc , pressure plate , springs , pressure plate cover and the linkage necessary to operate the clutch is a rotating mechanism between the engine and the transmission . It operates through fri
3、ction which comes from contact between the parts . That is the reason why the clutch is called a friction engagement, the clutch must continue to transmit mechanism . After all engine torque to transmission depending on the friction without slippage . The clutch is also used to disengage the engine
4、from the drive train whenever the gears in the transmission are being shifted from gear ratio to another . To start the engine or shift the gears , the driver has to depress the clutch pedal with the purpose of disengagement the transmission from the engine . At that time , the driven members connec
5、ted to the transmission input shaft are either stationary or rotating at a speed that is slower of faster than the driving members connected to engine crankshaft . There is no spring pressure on the clutch assembly parts . So there is no friction between the driving members and driven members . As t
6、he driver lets loose the clutch pedal , spring pressure increase on the clutch parts . Friction between the parts also increases . The pressure exerted by the springs on the driven members is controlled by the driver through the clutch pedal and linkage. The positive engagement of the driving and dr
7、iven members is made possible the friction between the surfaces of the members . When full spring pressure is applied , the speed of the driving and driven members should be the same . At the moment , the clutch must act as a coupling device and transmit all engine power to the transmission , withou
8、t slipping . 名师归纳总结 - - - - - - -第 1 页,共 14 页精选学习资料 - - - - - - - - - However , the transmission should be engaged to the engine gradually in order to operate the car smoothly and minimize torsional shock on the drive train because an engine at idle just develop little power . Otherwise , the drivin
9、g members are connected with the driven members too quickly and the engine would be stalled . The flywheel is a major part of the clutch . The flywheel mounts to the engine crankshaft and transmits engine torque to the clutch assembly . The flywheel , when coupled with the clutch disc and pressure p
10、late makes and breaks the flow of power the engine to the transmission . The flywheel provides a mounting location for the clutch assembly as well . When the clutch is applied , the flywheel transfers engine torque to the clutch disc . Because of its weight , the flywheel helps to smooth engine oper
11、ation . The flywheel also has a large ring gear at its outer edge , which engages with a pinion gear on the starter motor during engine cranking . The clutch disc fits between the flywheel and the pressure plate . The clutch disc has a splined hub that fits over splines on the transmission input sha
12、ft . A splined hub has grooves that match splines on the shaft . These splines fit in the grooves . Thus , the two parts held together . However , back C and C forth movement of the disc on the shaft is possible . Attached to the input shaft , the disc turns at the speed of the shaft . The clutch pr
13、essure plate is generally made of cast iron . It is round and about the same diameter as the clutch disc . One side of the pressure plate is machined smooth . This side will press the clutch disc facing are against the flywheel . The outer side has shapes to facilitate attachment of spring and relea
14、se mechanism . The two primary types of pressure plate assemblies are coil spring assembly and diaphragm spring . In a coil spring clutch the pressure plate is backed by a number of coil springs and housed with them in a pressed C steed cover bolted to the The spring push against the cover . Neither
15、 the driven plate nor flywheel . the pressure plate is connected rigidly to the flywheel and both can move either towards it o away . When the clutch pedal is depressed a thrust pad 名师归纳总结 - - - - - - -第 2 页,共 14 页精选学习资料 - - - - - - - - - riding on a carbon or ball thrust bearing is forced towards t
16、he flywheel . Levers pivoted so that they engage with the thrust pad at one end and the pressure plate tat the other end pull the pressure plate back against its springs . This releases pressure on the driven plate disconnecting the gearbox from the engine . Diaphragm spring pressure plate assemblie
17、s are widely used in most modern cars . The diaphragm spring is a single thin sheet of metal which yields when pressure is applied to it . When pressure is removed the metal spring back to its original shape . The center portion of the diaphragm spring is slit into numerous fingers that act as relea
18、se levers . When the clutch assembly rotates with the engine these weights are flung outwards by centrifugal plate and cause the levers to press against the pressure plate . During disengagement of the clutch the fingers are moved forward by the release bearing . The spring pivots over the fulcrum r
19、ing and its outer rim moves away from the flywheel . The retracting spring pulls the pressure plate away from the clutch plate thus disengaging the clutch . When engaged the release bearing and the fingers of the diaphragm spring move towards the transmission . As the diaphragm pivots over the pivot
20、 ring its outer rim forces the pressure plate against the clutch disc so that the clutch plate is engaged to flywheel . The advantages of a diaphragm type pressure plate assembly are its compactness , lower weight , fewer moving parts , less effort to engage , reduces rotational imbalance by providi
21、ng a balanced force around the pressure plate and less chances of clutch slippage . The clutch pedal is connected to the disengagement mechanism either by a cable or , more commonly , by a hydraulic system . Either way , pushing the pedal down operates the disengagement mechanism which puts pressure
22、 on the fingers of the clutch diaphragm via a release bearing and causes the diaphragm to release the clutch plate . With a hydraulic mechanism , the clutch pedal arm operates a piston in the clutch master cylinder . This forces hydraulic fluid through a pipe to the cutch release cylinder where anot
23、her 名师归纳总结 - - - - - - -第 3 页,共 14 页精选学习资料 - - - - - - - - - operates the clutch disengagement mechanism by a cable . The other parts including the clutch fork , release bearing , bell C housing , bell housing cover , and pilot bushing are needed to couple and uncouple the transmission . The clutch
24、fork , which connects to the linkage , actually operates the clutch . The release bearing fits between the clutch fork and the pressure plate assembly . The bell housing covers the clutch assembly . The bell housing cover fastens to the bottom of the bell housing . This removable cover allows a mech
25、anic to inspect the clutch without removing the transmission and bell housing . A pilot bushing fits into the back of the crankshaft and holds the transmission input shaft . 2 automatic transmission The modern automatic transmission is by far , the most complicated mechanical component in today.s au
26、tomobile . It is a type of transmission that sifts itself . A fluid coupling or torque converter is used instead of a manually operated clutch to connect the transmission to the engine . There are two basic types of automatic transmission based on whether the vehicle is rear wheel drive or front whe
27、el drive . On a rear wheel drive car , the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal position . A drive shaft connects the transmission to the final drive which is located in the rear axle and is us
28、ed to send power to the rear wheels . Power flow on this system is simple and straight forward going from the engine , through the torque converter , then trough the transmission and drive shaft until it reaches the final drive where it is split and sent to the two rear transmission . On a front whe
29、el drive car , the transmission is usually combined with the final drive to form what is called a transaxle . The engine on a front wheel drive car is usually mounted sideways in the car with the transaxle tuc ked under it on the side of the engine facing the rear of the car . Front axles are connec
30、ted directly to the transaxle and provide power to front wheels . In this example , power floes from the engine , through the torque converter to 名师归纳总结 - - - - - - -第 4 页,共 14 页精选学习资料 - - - - - - - - - a larger chain that sends the power through a 180 degree turn to the transmission that is along s
31、ide the engine . From there , the power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles . There are a number of other arrangements including front drive vehicles where the engine is mounted front to back instead of side
32、ways and there are other systems that drive all four wheels but the two systems described here are by far the most popular . A much less popular rear and is connected by a drive shaft to the torque converter which is still mounted on the engine . This system is found on the new Corvette and is used
33、in order to balance the weight evenly between the front and rear wheels for improved performance and handling . Another rear drive system mounts everything , the engine , transmission and final drive in the rear . This rear engine arrangement is popular on the Porsche. The modern automatic transmiss
34、ion consists of many components and systems that designed to work together in a symphony of planetary gear sets , the hydraulic system, seals and gaskets , the torque converter , the governor and the modulator or throttle cable and computer controls that has evolved over the years into what many mec
35、hanical inclined individuals consider to be an art from . Here try to used simple , generic explanation where possible to describe these systems . 3 The Differential System When a vehicle is cornered the inner wheel moves through a shorter distance than the outer wheel . This means that the inner wh
36、eel must slow down and the outer wheel must speed up . During this period it is desirable that each driving maintains its driving action . The differential performs these two tasks . The principle of the bevel type differential can be seen if the unit is considered as two discs and a lever . When th
37、e vehicle is traveling straight , the lever will divide the diving force equally and both discs will move the same amount . When the vehicle corners , the driving will still be divided equally but the 名师归纳总结 - - - - - - -第 5 页,共 14 页精选学习资料 - - - - - - - - - inner disc will now move through a smaller
38、 distance ；this will cause the lever to pivot about its center which will prize forward the outer disc to give it a greater movement . This action shows that the torque applied to each driving wheel is always equal torque equalizer . 4 Brake System C hence the differential is sometimes called a The
39、breaking system is the most important system in cars . If the brakes fail , the result can be disastrous . Brakes are actually energy conversion devices , which convert the kinetic energy momentum of the vehicle into thermal heat . When stepping on the brakes , the driver commands a stopping force t
40、en times as powerful as the force that puts the car in motion . The braking system can exert thousands of pounds of pressure on each of the four brakes . The brake system is composed of the following basic components : the master cylinder. which is located under the hood , and is directly connected
41、to the brake pedal , converts driver foots mechanical pressure into hydraulic pressure . Steel brake lines. and flexible brake hoses.connect the master cylinder to the slave cylinders. located at each wheel . Brake fluid , specially designed to work in extreme condition , fills the system . Shoes an
42、d Pads are pushed by the salve cylinders to contact the drum and rotors thus causing drag , which hopefully slows the car . The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel
43、to the master cylinder . Stepping on the brake pedal , a plunger is actually been pushing against in the master cylinder which forces hydraulic oil brake fluid through a series of tubes and hoses to the braking unit at each wheel . Since hydraulic fluid or any fluid for that matter cannot be compres
44、sed , pushing fluid through a pipe is just like pushing a steel bar through pipe . Unlike a steel bar , however , fluid can be directed through many twists and turns on its way to its destination , arriving with the exact same motion and pressure that 名师归纳总结 - - - - - - -第 6 页,共 14 页精选学习资料 - - - - -
45、 - - - - it started with . It is very important that the fluid is pure liquid and that there are no air bubbles in it . Air can compress , which causes a sponginess to the pedal and severely reduced braking efficiency . If air is suspected , then the system must be bled to remove the air . There are
46、 bleeder screws at each wheel and caliper for this purpose . On a disk brakes , the fluid from the master cylinder is forced into a caliper where it pressure against a piston . The piton , in-turn , squeezes two brake pads against the disk rotor which is attached to the wheel , forcing it to slow do
47、wn or stop . This process is similar to the wheel ,causing the wheel to stop . In either case , the friction surface of the pads on a disk brake system , on the shoes on a drum brake convert the forward motion of the vehicle into heat . Heat is what causes the friction surfaces lining of the pads an
48、d shoes to eventually wear out and require replacement . Brake fluid is a special oil that has specifics properties . It is designed to withstand cold temperatures without thickening as well as very high temperatures without boiling . If the brake fluid should boil , it will cause you to have a spong