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1液压制动系统当踩下制动踏板，您希望该车辆停下。液压制动踏板控制两个部分。首先，在液压作用下，由于采用细小的软管或金属线因此不必占用很大的空间。其次，液压机构提供了一个很大的优势，由一个很小的力踩在制动踏板上，会产生很大的力作用于车轮上。制动踏板连接在充满制动液的制动液压缸的活塞上，液压缸由活塞和油箱组成。现代主缸其实是两个独立的腔体。这种结构称之为双回路系统，因为前腔连接到前制动器与后腔连接到后制动器。（有些车辆是对角连接）。两个腔实际是分离的，允许紧急制动时一个系统失效另一个系统起作用。整个液压系统是从主缸到车轮都充满制动液。当制动踏板放松时，活塞在总泵中移动，在整个液压回路中产生压力。回路中充满液压力，强制轮（鼓式制动器）或（盘式制动器）压迫制动蹄或制动盘。压力压迫制动蹄或制动片作用于制动鼓或制动盘最终是车辆停止。此外，制动踏板控制一个灯的开关，刹车灯的踏板放松时，开关回到正常位置而灯灭。每一个鼓式制动器包含两个活塞，二个并排放置，向相反方向推动施加制动力。盘式制动器中，轮缸都是制动钳（有的可能有多达4个或是1个 ）的一部分。所有活塞都使用某种类型的橡胶密封，防止液压液泄漏出活塞，以及用橡胶密封防尘或污垢和水分进入轮缸。当制动踏板被释放，弹簧推动总泵活塞移动到总泵活塞在正常位置。回流阀允许液体流向轮缸或流回制动总缸。当制动液流向制动轮缸，多余的液体回流，补偿已被活塞移动距离的液压油。液压油若泄露也由回油阀回流。所有双回路制动系统使用一个开关来激活，并监控液压油的压力。开关阀门位于警告位置安装在主缸主阀门附近。活塞每次从前回路和后回路之间循环。当结束制动是压力是平衡的，活塞位置是稳定的，但是当一个回路有泄漏，在更大的制动系统压力下将迫使偏向活塞一方或另一方，关闭开关，就启动警示灯. 点火开关起动发动机时或驻车制动时报警灯也是被激活的。前盘，后鼓制动系统也有一个计量阀，以防止前，后制动器有制动间隙。用以确保前盘式制动器一般不会单独使用，停止汽车。压力控制阀也可以用来2限制压力，以防止在后轮制动中锁定。制动蹄和制动片使用相似材料。制动蹄或制动块由金属信号板和摩擦衬片组成。衬片是由粘结剂(被胶合)粘结或铆接的。通常，铆接的衬片效果比较好，但是粘结的衬片是更能充分表现摩擦材料的性能。摩擦材料在不同的制造商中生产是不同的，并且大致的类型可被分为：石棉类，有机类，半金属类，金属类。在不同的类型中成分和成分的百分比是不同的。一般来说，有机和非金属石棉化合物是常用的，容易在电子设备中有好的表现。但是对于高温操作来，他们可能不是您的耐用或山地驾驶的最佳的选择。在许多情况下，这些衬片将比有些金属化合物片更快速磨损，因此您经常得将替换他们。但是，当使用这些制动衬片时，电子设备将有更长的寿命。 半金属刹车片或金属化合物的表现因成分的不同而有所不同。一般来说，金属含量越高，性能越好，摩擦材料的散热性将越好。所以使它们更适合重型汽车使用，但是，金属和半金属为更容易发生啸叫，在大多数情况下，金属化合物比非金属片更容易发生啸叫。因此需要更经常更换衬片。当你想确定什么类型的刹车片是适合你，请记住，在今天现代汽车制动系统是汽车的预期相匹配的表现性能之一。原始设备制造商从规格材质到刹车材料感觉并不能给你提供帮助。所以在你改变刹车材料前，先谈谈你的零件供应商，以帮助决定什么是最适合您的刹车片。记住若你经常使用例如拖曳，停止并且频繁驾驶，行驶在山路和赛跑也许都对性能材料有更高的要求因此需要你经常更换刹车片。一些特殊的材料也用在刹车片中，其中有芳纶，碳材料。这些材料具有极其良好的刹车性能，山区驾驶或在赛场上驾驶都表现很好。耐磨性可能更胜于金属材料，而许多的其他性能更像非金属。3附 录Hydraulic Brake SystemsWhen you step on the brake pedal,you expect the vehicle to stop.The brake pedal operates a hydraulic that is used for two reasons.First,fluid under pressure can be carried to all parts of the vehicle by small hoses or metal lines without taking up a lot of room of causing routing problems.Second,the hydraulic fluid offers a great mechanical advantage-little foot pressure is required on the pedal,but a great deal of pressure is generated at the wheels.The brake pedal is linked to a piston in the brake master cylinder containing a small piston and a fluid reservoir.Modern master cylinders are actually two separate cylinders.Such a system is called a dual circuit,because the front cylinder is connected to the front brakes and the rear cylinder to the rear brakes.(Some vehicles are connected diagonally).The two cylinders are actually separated,allowing for emergency stopping power should one part of the system fail.The entire hydraulic system from the master cylinder to the wheels is full of hydraulic brake fluid.When the brake pedal is depressed,the piston in the master cylinder are forced to move,exerting tremendous force on the fluid in the lines.The fluid has nowhere to go,and forces the wheel cylinder pistons(drum brakes) or caliper pistons(disc brakes) to exert pressure on the brake shoes or pads.The friction between the brake shoe and wheel drum or the brake pad and rotor (disc) slows the vehiche and eventually stops it.Also attached to the brake pedal si a switch that lights the brake lights as the pedal is depressed.The lights stay on until the brake pedal is released and returns to its normal position.Each wheel cylinder in a drum brake system contains two pistons,one at either end,which push outward in opposite directions.In disc brake systems,the wheel cylinders are part of the caliper (there can be as many as four or as few as one ).Whether disc or drum type,all pistons use some type of rubber seal to prevent leakage around the piston,and a rubber dust boot seals the outer of the wheel cylinders against dirt and moisture.When the brake pedal is released,a spring pushes the master cylinder pistons back to their normal positions.Check valves in the master cylinder piston allow fluid to flow toward the 4wheel cylinders or calipers as the piston returns.Then as the brake shoe return springs pull the brake shoes back to the released position,excess fluid returns to the master cylinder through compensating ports,which have been uncovered as the pistons move back.Any fluid that has leaked from the system will also be replaced through the compensating ports.All dual circuit brake systems use a switch to activate a light,warning of brake failure.The switch si located in a valve mounted near the master cylinder.A piston in the valve reveives pressure on each end from the front and rear brake circuits.When the pressures are balanced,the piston remains stationary,but when one circuit has a leak,greater pressure during the application of the brakes will force the piston to one side or the other,closing the switch and activating the warning light.The light can also be activated by the ignition switch during engine starting or by the parking brake.Front disc,rear drum brake systems also have a metering valve to prevent the front disc brakes from engaging before the rear brakes have contacted the drums.This ensures that the front brakes will not normally be used alone to stop the vehicle.A proportioning valve is also used to limit pressure to the rear brakes to prevent rear wheel lock-up during hard braking. Brake shoes and pads are constructed in a similar.The pad or shoe is composed of a metal backing plate and a priction lining.The lining is either bonded(glued) to the metal,or riveted.Generally,riveted linings provide superior performance,but good quality bonded linings are perfectly adequate.
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