1、精選優質文檔-傾情為你奉上精選優質文檔-傾情為你奉上專心-專注-專業專心-專注-專業精選優質文檔-傾情為你奉上專心-專注-專業Automobile Brake SystemThe braking 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 i

2、nto thermal energy (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.Two complete independent braking systems are used on the

3、 car. They are the service brake and the parking brake.The service brake acts to slow, stop, or hold the vehicle during normal driving. They are foot-operated by the driver depressing and releasing the brake pedal. The primary purpose of the brake is to hold the vehicle stationary while it is unatte

4、nded. The parking brake is mechanically operated by when a separate parking brake foot pedal or hand lever is set. 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

5、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 conditions, fills the system. “Shoes” and “pads” are pushed by the slave cylind

6、ers to contact the “drums” 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 (Figure).B

7、asically, all car brakes are friction brakes. When the driver applies the brake, the control device forces brake shoes, or pads, against the rotating brake drum or disks at wheel. Friction between the shoes or pads and the drums or disks then slows or stops the wheel so that the car is braked.In mos

8、t modern brake systems (see Figure 15.1), there is a fluid-filled cylinder, called master cylinder, which contains two separate sections, there is a piston in each section and both pistons are connected to a brake pedal in the drivers compartment. When the brake is pushed down, brake fluid is sent f

9、rom the master cylinder to the wheels.At the wheels, the fluid pushes shoes, or pads, against revolving drums or disks. The friction between the stationary shoes, or pads, and the revolving drums or disks slows and stops them. This slows or stops the revolving wheels, which, in turn, slow or stop th

10、e car. The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent r reservoir so that you can see the level without opening the cover. The brake fluid level will drop slightly as the brake pads wear. This is a normal condition and no cause for concern. If the leve

11、l drops noticeably over ashort period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep the reservoir covered except for the amount of time you need to fill it and never leave a cam of brake fluid uncovered. Brake fluid must maintain a very high boilin

12、g 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

13、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 all attachment points. If a steel line requires a repair, the best procedure is to replace the compete line. If this is not practical, a line can be rep

14、aired using special splice fittings that are made for brake system repair. You must never use copper tubing to repair a brake system. They are dangerous and illegal.Drum brakes, it consists of the brake drum, an expander, pull back springs, a stationary back plate, two shoes with friction linings, a

15、nd anchor pins. The stationary back plate is secured to the flange of the axle housing or to the steering knuckle. The brake drum is mounted on the wheel hub. There is a clearance between the inner surface of the drum and the shoe lining. To apply brakes, the driver pushes pedal, the expander expand

16、s the shoes and presses them to the drum. Friction between the brake drum and the friction linings brakes the wheels and the vehicle stops. To release brakes, the driver release the pedal, the pull back spring retracts the shoes thus permitting free rotation of the wheels.Disk brakes, it has a metal

17、 disk instead of a drum. A flat shoe, or disk-brake pad, is located on each side of the disk. The shoes squeeze the rotatin g disk to stop the car. Fluid from the master cylinder forces the pistons to move in, toward the disk. This action pushes the friction pads tightly against the disk. The fricti

18、on between the shoes and disk slows and stops it. This provides the braking action. Pistons are made of either plastic or metal. There are three general types of disk brakes. They are the floating-caliper type, the fixed-caliper type, and the sliding-caliper type. Floating-caliper and sliding-calipe

19、r disk brakes use a single piston. Fixed-caliper disk brakes have either two or four pistons. The brake system assemblies are actuated by mechanical, hydraulic or pneumatic devices. The mechanical leverage is used in the parking brakes fitted in all automobile. When the brake pedal is depressed, the

20、 rod pushes the piston of brake master cylinder which presses the fluid. The fluid flows through the pipelines to the power brake unit and then to the wheel cylinder. The fluid pressure expands the cylinder pistons thus pressing the shoes to the drum or disk. If the pedal is released, the piston ret

21、urns to the initialposition, the pull back springs retract the shoes, the fluid is forced back to the master cylinder and braking ceases. The primary purpose of the parking brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by the driver when a

22、 separate parking braking hand lever is set. The hand brake is normally used when the car has already stopped. A lever is pulled and the rear brakes are approached and locked in the “on” position. The car may now be left without fear of its rolling away. When the driver wants to move the car again,

23、he must press a button before the lever can be released. The hand brake must also be able to stop the car in the event of the foot brake failing. For this reason, it is separate from the foot brake uses cable or rods instead of the hydraulic system.Anti-lock Brake SystemAnti-lock brake systems make

24、braking safer and more convenient, Anti-lock brake systems modulate brake system hydraulic pressure to prevent the brakes from locking and the tires from skidding on slippery pavement or during a panic stop.Anti-lock brake systems have been used on aircraft for years, and some domestic car were offe

25、red with an early form of anti-lock braking in late 1990s. Recently, several automakers have introduced more sophisticated anti-lock system. Investigations in Europe, where anti-lock brakin g systems have been available for a decade, have led one manufacture to state that the number of traffic accid

26、ents could be reduced by seven and a half percent if all cars had anti-lock brakes. So some sources predict that all cars will offer anti-lock brakes to improve the safety of the car. Anti-lock systems modulate brake application force several times per second to hold the tires at a controlled amount

27、 of slip; all systems accomplish this in basically the same way. One or more speed sensors generate alternating current signal whose frequency increases with the wheel rotational speed. An electronic control unit continuously monitors these signals and if the frequency of a signal drops too rapidly

28、indicating that a wheel is about to lock, the control unit instructs a modulating device to reduce hydraulic pressure to the brake at the affected wheel. When sensor signals indicate the wheel is again rotating normally, the control unit allows increased hydraulic pressure to the brake. This release

29、-apply cycle occurs several time per second to “pump” the brakes like a driver might but at a much faster rate.In addition to their basic operation, anti-lock systems have two other things in common. First, they do not operate until the brakes are applied with enough force to lock or nearly lock a w

30、heel. At all other times, the system stands ready to function but does not interfere with normal braking. Second, if the anti-lock system fail in any way, the brakes continue to operate without anti-lock capability. A warning light on the instrument panel alerts the driver when a problem exists in t

31、he anti-lock system. The current Bosch component Anti-lock Braking System (ABS), is a second generation design wildly used by European automakers such as BWM, Mercedes-Benz and Porsche. ABS system consists of : four wheel speed sensor, electronic control unit and modulator assembly.A speed sensor is

32、 fitted at each wheel sends signals about wheel rotation to control unit. Each speed sensor consists of a sensor unit and a gear wheel. The front sensor mounts to the steering knuckle and its gear wheel is pressed onto the stub axle that rotates with the wheel. The rear sensor mounts the rear suspen

33、sion member and its gear wheel is pressed onto the axle. The sensor itself is a winding with a magnetic core. The core creates a magnetic field around the winding, and as the teeth of the gear wheel move through this field, an alternating current is induced in the winding. The control unit monitors

34、the rate o change in this frequency to determine impending brake lockup. The control units function can be divided into three parts: signal processing, logic and safety circuitry. The signal processing section is the converter that receives the alternating current signals form the speed sensors and

35、converts them into digital form for the logic section. The logic section then analyzes the digitized signals to calculate any brake pressure changes needed. If impending lockup is sensed, the logic section sends commands to the modulator assembly.Modulator assemblyThe hydraulic modulator assembly re

36、gulates pressure to the wheel brakes when it receives commands from the control utuit. The modulator assembly can maintain or reduce pressure over the level it receives from the master cylinder, it also can never apply the brakes by itself. The modulator assembly consists of three high-speed electri

37、c solenoid valves, two fluid reservoirs and a turn delivery pump equipped with inlet and outlet check valves. The modulator electrical connector and controlling relays are concealed under a plastic cover of the assembly.Each front wheel is served by electric solenoid valve modulated independently by

38、 the control unit. The rear brakes are served by a single solenoid valve and modulated together using the select-low principle. During anti-braking system operation, the control unit cycles the solenoid valves to either hold or release pressure the brake lines. When pressure is released from the bra

39、ke lines during anti-braking operation, it is routed to a fluid reservoir. There is one reservoir for the front brake circuit. The reservoirs are low-pressure accumulators that store fluid under slight spring pressure until the return delivery pump can return the fluid through the brake lines to the

40、 master cylinder.汽車制動系統制動系統是汽車中最重要的系統。 如果制動失靈，結果可能是損失慘重的。制動器實際就是能量轉換裝置，它將汽車的動能（動量）轉化成熱能（熱量）。當駕駛員踩下制動踏板，所產生的制動力是汽車運動時動力的10倍。制動系統能對四個剎車系統中的每個施加數千磅的力。 每輛汽車上使用兩個完全獨立的制動系統，即行車制動器和駐車制動器。行車制動器起到減速、停車、或保持車輛正常行駛。制動器是由司機用腳踩、松制動器踏板來控制的。駐車制動器的主要作用就是當車內無人的時候，汽車能夠保持靜止。當獨立的駐車制動器踏板或手桿，被安裝時，駐車制動器就會被機械地操作。制動系統是由下列基本的

41、成分組成:位于發動機罩下方，而且直接地被連接到制動踏板的“制動主缸”把駕駛員腳的機械力轉變為液壓力。鋼制的“制動管路”和有柔性的“制動軟管”把制動主缸連接到每個輪子的“制動輪缸”上。 制動液, 特別地設計為的是工作在極端的情況，填充在系統中。“制動盤”和“襯塊”是被制動輪缸推動接觸“圓盤”和“回轉體”如此引起緩慢的拖拉運動, (希望)使汽車減慢速度。 典型的制動系統布置有前后盤式，前盤后鼓式，各個車輪上的制動器通過一套管路系統連接到制動主缸上。基本上講，所有的汽車制動器都是摩擦制動器。當司機剎車時，控制裝置會迫使制動蹄，或制動襯片與車輪處的旋轉的制動鼓或制動盤接觸。接觸后產生的摩擦使車輪轉動減

42、慢或停止，這就是汽車的制動。在最基本的制動系統中，有一個制動主缸，這個主缸內部填充制動液，并包含兩個部分，每個部分里都有一個活塞，兩個活塞都連接駕駛室里的制動踏板。當制動踏板被踩下時，制動液會從制動主缸流入輪缸。在輪缸中，制動液推動制動蹄或制動襯片與旋轉的制動鼓或制動盤接觸。靜止的制動蹄或制動襯片與旋轉的制動鼓或制動盤之間產生摩擦力使汽車的運動逐漸減緩或停止。制動液的裝置位于主缸的頂部。目前大多數的車都有一個容易看見的裝制動液的裝置，為的是不用打開蓋子就可以看得見制動液的油面。隨著制動踏板的運動制動液就會緩慢的下降，正常情況下是這樣的。如果制動液在很短的時間內下降得明顯或者下降了三分之二，那么

43、就要盡快的檢查你的制動系統了。保持制動液裝置充滿制動液除非你需要維修它，制動液必須保持很高的沸點。位于在空氣中的制動液就會吸收空氣中的潮氣引起制動液低于沸點。制動液通過一系列的管路從主缸到達各車輪。橡膠軟管只用在需要彈力的地方，比如應用在前輪。在車的行進中上下來回運動。系統的其它部分在所有的連接點上都應用了無腐蝕性的無縫鋼管。如果鋼線需要修理的話，最好的方法就是代替這條線。如果這不符合實際，那么為了制動系統可以用特殊的裝置修理它。你不可以用銅管來修理制動系。它們是危險也是不正確的。鼓式制動器包括制動鼓，一個輪缸，回拉彈簧，一個制動底版，兩個帶摩擦層的制動蹄。制動底版固定在輪軸外部的法蘭或轉向節

44、。制動鼓固定在輪轂上。制動鼓的內部表面與制動蹄的內層之間有空隙。要使用制動器時，司機就要踩下踏板，這時輪缸擴大制動片，對其施加壓力，是制動蹄觸碰制動鼓。制動鼓與摩擦片之間產生的摩擦制動了車輪，從而使汽車停止。要釋放制動器時，司機松開踏板，回拉彈簧拉回制動片，這樣車輪會自由轉動。盤式制動器包括制動盤而不是鼓，在它的兩面上各有一個薄的制動片或叫盤式制動器的制動片。制動片是靠擠住旋轉的制動盤來停住汽車。制動主缸里流出的制動液迫使活塞向里部的金屬盤移動，這便使摩擦片緊緊地貼住制動盤。這時制動片與制動盤產生的摩擦使汽車減速、停止，出現了制動行為。活塞分金屬或塑料。盤式制動器主要有三種，即：浮動卡鉗型、固定卡鉗型和滑動卡鉗型。浮動卡鉗型和滑動卡鉗型盤式制動器使用單活塞。固定卡鉗型盤式制動器既可以使用兩個活塞有可以使用四個活塞。 制動系統是由機械能，液壓能或氣壓能裝置驅動的。在機械杠桿適合所有的汽車的駐車制動器中使用。當踩下制動踏板時，杠桿就會推動制動器主缸的活塞給制動液施加壓力，制動液通過油管流入輪缸。制動液的壓力施加到輪缸活塞以使制動片被壓到制動鼓或制動盤上。如果松開踏板，活塞回到原來的位置上，回拉彈簧拉回制動片，制動液返回制動主缸，這樣制動停