外文翻译--汽车液压制动系统

附 录 A Hydraulic Brake Systems When 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 brake s 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 wheel 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. Friction materials will vary between manufacturers and type of pad and the material compound may be referred to as asbestos,organic,semi-metallic,metallic.The difference between these compounds lies in the types and percentages of friction materials used,material binders and performance modifiers. Generally speaking,organic and non-metallic asbestos compound brakes are quiet,easy on rotors and provide good feel.But this comes at the expense of high temperature operation,so they may not be your best choice for heavy duty use or mountian driving.In most cases,these linings will wear somewhat faster than metallic compound pads,so you will usually replace them more often.But,when using these pads,rotors tend to last longer. Semi-metallic or metallic compound brake linings will vary in performance based on the metallic contents of the compound.Again,generally speaking,the higher the metallic content,the better the friction material will resist heat.This makes them more appropriate for heavy duty applications,but at the expense of braking performance before the pad reaches operating temperature.The first few applications on a cold morning may not give strong braking.Also,metallics and semi-metallics are more likely to squeal,In most cases,metallic compounds last longer than non-metallic pads,but they tend to cause more wear on the rotors.If you use metallic pads,expect to replace the rotors more often. When deciding what type of brake lining is right for you,keep in mind that todays modern cars have brake materials which are matched to the expected vehicles performance capabilities.Changing the material from OEM specification could adversely addect brake feel or responsiveness.Before changing the brake materials,talk to your deaker or parts supplier to help decide what is most appropriate for your application. Remenber that use applications such as towing,stop and go driving,driving down mountain roads,and racing may require a change to a higher performance material. Some more exotic materials are also used in brake linings,among which are Kevlar and carbon compounds.These materials have the capability of extremely good performance for towing,mountain driving or racing.Wear characteristics can be similar to either applications tend to wear like metallic linings,while many of the streetapplications are more like the non-metallics. 附 录 B 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