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Automobile chassis

Abstract
As car is becoming more and more popular, car maintenance,is becoming a kind of normal, but yet people in automobile maintenance process often to easily neglected for automobile chassis for maintenance. A complete car by the engine, chassis, body, and automobile electric appliances four parts, chassis is an important part for the engine transfer power from car produces sports, ensure the normal car driving this article mainly discusses the basic structure of the automotive chassis and the main function was introduced. Chassis include the clutch , the transmission, the drive shaft, the final drive assembly, the front suspension, the rear suspension, the steering system ,the brake system, the wheels and tires.
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 include the clutch , the transmission ,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 friction which comes from contact between the parts . That is the reason why the clutch is called a friction mechanism . After engagement, the clutch must continue to transmit all engine torque to transmission depending on the friction without slippage . The clutch is also used to disengage the engine 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 connected 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 the 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 driven 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 , without slipping . 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 driving members are connected with the driven members too quickly and the engine would be stalled .
2.Automatic Transmission
The modern automatic transmission is by far,the most complicated mechanical component in today’s automobile .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 wheel 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 used 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 wheel 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 tucked under it on the side of the engine facing the rear of the car . Front axles are connected directly to the transaxle and provide power to front wheels . In this example , power floes from the engine , through the torque converter to a larger chain that sends the power through a 180 degree turn to the transmission that is along side 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 sideways 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 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 transmission 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 mechanical inclined individuals consider to be an art from .
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 wheel 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 the 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 inner disc will now move through a smaller 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 – hence the differential is sometimes called a torque equalizer .
4．Brake System
The 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 ten 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 to the brake pedal , converts driver foot’s 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” and “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 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 compressed , 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 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 “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 down 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 and 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 spongy pedal and the car will be hard to stop ) . The brake fluid reservoir is on top of the master cylinder . Most cars today have a transparent reservoir so that you can see the level without opening the cover . The brake fluid lever will drop slightly as the brake pads wear . This is a normal condition and no cause for concern . If the lever drops noticeably over a short period of time or goes down to about two thirds full , have your brakes checked as soon as possible . Keep the reservoir covered expect for the amount of time you need to fill it and never leave a can of brake fluid uncovered . Brake fluid must maintain a very high boiling point . Exposure to air will cause the fluid to absorb moisture which will lower that boiling point . The brake fluid travels from the master cylinder to the wheels through a series of steel tubes and reinforced rubber hoses . Rubber hoses are only used in places that require flexibility , such as at the front wheels , which move up and down as well as steer . The rest of the system uses non-corrosive seamless steel tubing with special fittings at attachment points . If a steel line requires a repair , the best procedure is to replace the complete line . If this is nit practical , a line can be repaired using special splice fittings that are made for brake system repair . You must never use brass “compression” fittings or copper tubing repair a brake system . They are dangerous and illegal . Other Components in the Hydraulic System
(1)Proportioning Valve or Equalizer Valve   
   These valves are mounted between the master cylinder and the rear wheels . They are designed to adjust the pressure between the front and the rear brakes depending on how hard you are stopping . The shorter you stop , the more of the vehicle’s weight is transferred to the front wheels , in some cases , causing the rear to lift and the front to dive . These valves are designed to direct more pressure to the front and less pressure to the harder you stop . This minimizes the chance of premature lockup at the rear wheels .
(2)Pressure Differential Valve   
This valve is usually mounted just below the master and is responsible for turning the brake warning light on when it detects a malfunction . It measures the pressure from the two sections of the master cylinder and compares them . Since it is mounted ahead of the proportioning or equalizer valve , the two pressure it detects should be equal . If it detects a difference , it means that there is probably a brake fluid leak somewhere in the system .
(3)Combination Valve   
The Combination valve is simply a proportioning valve and a pressure differential valve that is combine into one unit . The parking brake system controls the rear brakes through a series of steel cables that are connected to either a hand lever or a foot pedal . The ideal is that the system is fully mechanical and completely bypasses the hydraulic system so that the vehicle can be brought to a stop even if there is a total brake failure .
5．Steering System   
     The steering converts the steering –wheel rotary motion into a turn motion of the steered wheels of the vehicle . The basic steering system in most cars is the same . The steering gear of steering box is the heart of the steering system .This is usually next to the engine . A shaft extends from the back of the steering gear . This shaft is connected to the steering column or steering shaft . The steering wheel is at the top of the steering column . Another shaft comes from the bottom of the steering gear . This shaft connects to the arms , rods , and links . This parts assembly , called the steering linkage , connects the steering gear to the parts at the wheels . The wheels and tires mount to the steering knuckles , As shown in fig , the knuckles are pivoted at the top and bottom . Thus , the wheels and rites can turn from side top side .
While the steering system may look complicated , it works quite simply . When a driver drives a car straight down the road , the steering gear is centered . The gear holds the linkage centered so that the wheels and tires point straight ahead . When the driver turns the steering wheel , the steering shaft rotates and the steering gear moves toward that side . The shaft coming out the bottom of the steering gear turns , as well . When the shaft turns , it pulls the linkage to one side and makes the steering knuckles turn slightly about their pivot points . Thus , the steering knuckle , spindle , wheels , and tires  turn to one side , causing the car to turn . The type of steering layout depends on the suspension system . The beam axle used on heavy commercial vehicle has a king pin fitted at each end of the axle and this pin is the pivot which allows the wheels to be steered . Cars have independent suspension and this system has ball joints to allow for wheel movement .
    For these reasons , these are several different types of steering gears . However , there are only two types of steering systems : manual steering systems and power steering systems . In the manual type , the driver dose all the work of turning the steering wheel , steering gear , wheels and tires . In the power , hydraulic fluid assists the operation so that driver effort is reduced .
6． Front Suspension   
    The front suspension is more complicated than the rear suspension . This is because the front wheels must move in several different directions . The wheels must move up and down with the suspension and turn left to right with the steering . Since the car goes in the direction in which the front wheels point , the alignment of the front wheels is important . The wheels must point in just the right direction for the car to move straight down the road and turn properly . Modern cars uses an independent front suspension . In this system , each wheel mounts separately to the frame and has its own individual spring and shock absorber . Thus , the wheels act independently of one another . When one wheel hits a bump or hole in the road , the other wheel dose no9t deflect . As a car moves down the high-way , the suspension moves the front wheels up and down . At the same time , the steering mechanism moves the front wheels , sometimes to make turns and sometimes to make the travel straight . The angular relationship between the wheels and suspension parts during this motion is the front-end geometry . Since the geometry can change the alignment of front wheels is adjustable . You can change the adjustment to compensate for spring sag . The alignment of the front wheels affects the operation of a car . Poor alignment ca make a car pull to one side and stop the front wheels from returning to the straight-ahead position after a turn . The three normally adjustable angles are caster , camber , and toe .
(1 )Caster
Caster is the forward or backward of spindle or steering the knuckle at the top when viewed from the side . Forward tilt is negative caster and backward tilt positive caster . Caster is measured in the number of degrees that it is forward or backward from true vertical and is adjustable on many vehicle .
(2) Kingpin Angle  
   The kingpin angle is the inclination of the steering axis relative to the longitudinal plane , measured in the transverse plane of the vehicle . Kingpin angle is 2°-16°and determines the steering aligning torque in conjunction with steering offset and wheel caster . It is measured only with the vehicle loaded .
(3) Camber
   Camber is the inward or outward tilt of the wheel at the top . Inward tilt is negative camber and outward tilt is positive camber . The tilt of the wheel is measured inn degrees and is adjustable on many vehicles .
(4) Toe-in
   Toe-in specifies the degree to which non-parallel front wheels are closer together at the front than at th e rear ; measured at the edges of the rims at the wheel center height . front  non-driven wheels , toe-in is approximately 2-3 mm , and between 3mm and-2mm for driven wheels . Toe-in reduces the tendency of the wheels to shimmy .
7．Rear Suspension   
The purpose of the rear suspension is to support the weight of the rear of the vehicle . As with the front suspension , this system contributes to the stability and ride of the vehicle . Rear suspension may be of the solid axle or independent design . Many cars have solid axle rear suspension . Either design may have different kinds of springs , including torsion bars . However , the coil spring and leaf spring types are most popular .
8．Wheels and Tires
    To maintain grip when a vehicle is traveling at speed over a bumpy surface , a wheel must be light in weight . Also it must be strong , cheap to produce , easy to clan and simple to remove .The structure of the wheel is shown in Fig . The rim is made in one piece , with the wheel center welded or riveted to it . Most modern vehicles use the drop center type . This drop center provides a well for tire bead to drop into for tire removal . A slight hump at the head ledge holds the tire in place should it go flat while driving .Tires are important to your safety and comfort . They transmit the driving and braking power to the road . The car’s directional control , road-ability and riding comfort are greatly dependent on the tires . Tires should be selected and maintained with great care . There are two basic types of tires – those with inner tubes and those without ( called “tubeless” tires ) . Most modern automobile tires are of the tubeless type . Truck and bus tire are usually of the tube type .  Tires are made of several layers of nylon , rayon , or polyester fabric bonded together with belts of rayon , fiberglass , or steel cord . The rubber used in tires is a blend of natural and synthetic rubber .

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