车辆工程外文翻译---制动系统.docx

附 录1 brake systems1.drum vs. discbrake technology, just like suspension technology and fuel-system technology, has come a long way in recent years.1）drum brakesearly automotive brake systems, after the era of hand levers of course, used a drum design at all four wheels. they were called drum brakes because the components were housed in a round drum that rotated along with the wheel. inside was a set of drum that, when the brake pedal was pressed, would force the shoes against the drum and slow the wheel. fluid was used to transfer the movement of the brake pedal into the movement of the brake shoes, while the drum themselves were made of heat-resistant friction material similar to that used on clutch plates. this basic design proved capable under most circumstances, but it had one major flaw. under high braking conditions, like descending a steep hill with a heavy load or repeated high-speed slow downs, drum brakes would often fade and lose effectiveness. usually this fading was the result of too much heat build-up within the shoes. remember that the principle of braking involves turning kinetic energy (wheelmovement) into thermal energy (heat). for this reason, drum brakes can only operate as long as they can absorb the heat generated by slowing a vehicles wheels. once the brake components themselves become saturated with heat, they lose the ability to halt a vehicle, which can be somewhat disconcerting to the vehicles operator. 2） disc brakesdisc brakes are used on the front wheels of most cars and on all four wheels on many cars. a disc rotor is attached to the wheel hub and rotates with the tire and wheel. when the driver applies the brakes, hydraulic pressure from the master cylinder is used to push friction linings against the rotor to stop it.in the disc brake rotor assembly, the rotor is usually made of cast iron. the hub may be manufactured as one piece with the rotor or in two parts. the rotor has a machined braking surface on each face. a splash shield, mounted to the steering knuckle, protects the rotor from road splash.a rotor may be solid or ventilated. ventilated designs have cooling fins cast between the braking surfaces. this construction considerably increases the cooling area of the rotor casting. also, when the wheel is in motion, the rotation of these fan-type fins in the rotor provides increased air circulation and more efficient cooling of the brake. disc brakes do not fade even after rapid, hard brake applications because of the rapid cooling of the rotor.the hydraulic and friction components are housed in a caliper assembly. the caliper assembly straddles the outside diameter of the hub and rotor assembly. when the brakes are applied, the pressure of the pistons is exerted through the shoes in a clamping action on the rotor. because equal opposed hydraulic pressures are applied to both faces of the rotor throughout application, no distortion of the rotor occurs, regardless of the severity or duration of application. there are many variations of caliper designs, but they can all be grouped into two main categories: moving and stationary caliper. the caliper is fixed in one position on the stationary design. in the moving design, the caliper moves in relation to the rotor.most late-model cars use the moving caliper design. this design uses a single hydraulic piston and a caliper that can float or slide during application. floating designsfloat or move on pins or bolts. in sliding designs, the caliper slides sideways on machined surfaces. both designs work in basically the same way.in the single piston floating caliper, the single-piston caliper assembly is constructed from a single casting that contains one large piston bore in the inboard section of the casting. inboard refers to the side of the casting nearest the center line of the car when the caliper is mounted. a fluid inlet hole and bleeder valve hole are machined into the inboard section of the caliper and connect directly to the piston bore.the caliper cylinder bore contains a piston and seal. the seal has a rectangular cross section. it is located in a groove that is machined in the cylinder bore. the seal fits around the outside diameter of the piston and provides a hydraulic seal between the piston and the cylinder wall. the rectangular seal provides automatic adjustment of clearance between the rotor and shoe and linings following each application. when the brakes are applied, the caliper seal is deflected by the hydraulic pressure and it inside diameter rides with the piston within the limits of its retention in the cylinder groove. when hydraulic pressure is released, the seal relaxes and returns to its original rectangular shape, retracting the piston into the cylinder enough to provide proper running clearance. as brake linings wear, piston travel tends to exceed the limit of deflection of the seal; the piston therefore slides in the seal to the precise extent necessary to compensate for lining wear.the top of the piston bore is machined to accept a sealing dust boot. the piston in many calipers is steel, precision ground, and nickel chrome plated, giving it a very hard and durable surface. some manufacturers are using a plastic piston. this is much lighter than steel and provides for a much lighter brake system. the plastic piston insulates well and prevents heat from transferring to the brake fluid. each caliper contains two shoe and lining assemblies. they are constructed of a stamped metal shoe with the lining riveted or bonded to the shoe and are mounted in the caliper on either side of the rotor. one shoe and lining assembly is called the inboard lining because it fits nearest to the center line of the car. the other is called the outboard shoe and lining assembly.the application and release of the brake pressure actually causes a very slight movement of the piston and caliper. upon release of the braking effort, the piston and caliper merely relax into a released position. in the released position, the shoes do not retract very far from the rotor surfaces.as the brake lining wears, the piston moves out of the caliper bore and the caliper repositions itself on the mounting bolts an equal distance toward the car. this way, the caliper assembly maintains the inboard and outboard shoe and lining in the same relationship with the rotor surface throughout the full length of the lining.sliding calipers are made to slide back and forth on the steering knuckle support to which it is mounted. there is a v shaped surface, sometimes called a rail, on the caliper that matches a similar surface on the steering knuckle support. these two mating surfaces allow the caliper to slide in and out. the internal components of the caliper are the same as those previously described.the stationary or fixed caliper has a hydraulic piston on each side of the rotor. larger calipers may have two pistons on each side of the rotor. the inboard and outboard brake shoes are pushed against the rotor by their own pistons. the caliper is anchored solidly and does not move. the seals around the pistons work just like those already described. the main disadvantage of the stationary caliper is that it has more hydraulic components. this means they are more expensive and have more parts to wear out .2.other components in the hydraulic system:1）proportioning valve or equalizer valvethese valves are mounted between the master cylinder and the rear wheels. they are designed to adjust the pressure between the front and rear brakes depending on how hard you are stopping. the shorter you stop, the more of the vehicles 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 rear the harder you stop. this minimizes the chance of premature lockup at the rear wheels.2）pressure differential valvethis valve is usually mounted just below the master cylinder 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 pressures 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 valvethe combination valve (figure) is simply a proportioning valve and a pressure differential valve that is combined into one unit.the parking brake (akaemergency 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 idea 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.on drum brakes, the cable pulls on a lever mounted in the rear brake and is directly connected to the brake shoes. this has the effect of bypassing the wheel cylinder and controlling the brakes directly.disk brakes on the rear wheels add additional complication for parking brake systems. there are two main designs for adding a mechanical parking brake to rear disk brakes. the first type uses the existing rear wheel caliper and adds a lever attached to a mechanical corkscrew device inside the caliper piston. when the parking brake cable pulls on the lever, this corkscrew device pushes the piston against the pads, thereby bypassing the hydraulic system, to stop the vehicle. this type of system is primarily used with single piston floating calipers, if the caliper is of the four piston fixed type, then that type of system cant be used. the other system uses a complete mechanical drum brake unit mounted inside the rear rotor. the brake shoes on this system are connected to a lever that is pulled by the parking brake cable to activate the brakes. the brake “drum” is actually the inside part of the rear brake rotor.on cars with automatic transmissions, the parking brake is rarely used. this can cause a couple of problems. the biggest problem is that the brake cables tend to get corroded and eventually seize up causing the parking brake to become inoperative. by using the parking brake from time to time, the cables stay clean and functional. another problem comes from the fact that the self adjusting mechanism on certain brake systems uses the parking brake actuation to adjust the brakes. if the parking brake is never used, then the brakes never get adjusted.the power brake booster (figure) is mounted of the firewall directly behind the master cylinder and, along with the master cylinder, is directly connected with the brake pedal. its purpose is to amplify the available foot pressure applied to the brake pedal so that the amount of foot pressure required to stop even the largest vehicle is minimal. power for the booster comes from engine vacuum. the automobile engine produces vacuum as a by-product of normal operation and is freely available for use in powering accessories such as the power brake booster. vacuum enters the booster through a check valve on the booster. the check valve is connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the booster but dose not let it escape. the booster is an empty shell that is divided into two chambers by a rubber diaphragm. there is a valve in the diaphragm that remains open while foot is off the brake pedal so that vacuum is allowed to fill both chambers. when stepping on the brake pedal, the valve in the diaphragm closes, separating the two chambers and another valve opens to allow air in the chamber on the brake pedal side. this is what provides the power assist. power boosters are very reliable and cause few problems of their own. however, other things cam contribute to a loss of power assist. in order to have power assist, the engine must be running. if the engine stalls or shuts off while you are driving, you will have a small reserve of power assist for two or three pedal applications but, after that, the brakes will be extremely hard to apply and you must put as much pressure as you can to bring the vehicle to a stop.the last topic is the anti-lock brakes (abs). the most efficient braking pressure takes place just before each wheel lock up. when you slam on the brakes in a panic stop and the wheels lock up, causing a screeching sound and leaving strips of rubber on the pavement, you do not stop the vehicle nearly as short as it is capable of stopping. also, while the wheels are locked up, you loose all steering control so that , if you have an opportunity to steer around the obstacle, you will not be able to do so. another problem occurs during an extended skid is that you will burn a patch of rubber off the tire which causes a “flat spot” on the tread that will produce an annoying thumping sound as you drive.anti-lock brake systems solve this lockup problem by rapidly pumping the brakes whenever the system detects a wheel that is locked up. in most cases, only the wheel that is locked will be pumped, while full braking pressure stays available to the other wheels. this effect allows you to stop in the shortest amount of time while maintaining full steering control even if one or more wheels are on ice. the system uses a computer to monitor the speed of each wheel. when it detects that one or more wheels have stopped or are turning much slower than the remaining wheels, the computer sends a signal to momentarily remove and reapply or pulse the pressure to the affected wheels to allow them to continue turning. this “pumping” of the brakes occurs at tem or more times a second, far faster then a human can pump the brakes manually. if you step on the brakes hard enough to engage the anti-lock system, you may feel a strong vibration in the brake pedal. this is a normal condition and indicates that the system is working; however, it can be disconcerting to some people who dont expect it. if your vehicle has anti-lock brakes, read your owners manual to find out more about it.the system consists of am electronic control unit, a hydraulic actuator, and wheel speed sensors at each wheel. if the control unit detects a malfunction in the system, it will illuminate an abs warming light on the dash to let you know that there is a problem. if there is a problem, the antilock system will not function but the brakes will otherwise function normally.3.friction materialsbrake shoes and pads are constructed in a similar manner. the pad or shoe is composed of a metal backing plate and a friction 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 mountain 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, metallic and semi-metallic 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 affect brake feel or responsiveness. before changing the brake materials, talk to your dealer or parts supplier to help decide what is most appropriate for your application. remember that heavy 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 the metallic or the non-metallic linings, depending on the product you buy. most race applications tend to wear like metallic linings, while many of the street applications are more like the non-metallic制动系统1. 刹车：鼓与盘制动技术，就像悬浮技术和燃料系统技术，已走过了漫长的道路1）鼓式制动器早在后时代，手杠杆的汽车制动系统用鼓装在所有的四个车轮。它们被称为鼓式制动器的组成部分，因为装在圆鼓上，随着车轮旋转。里面是一套系统，当刹车踏板被按下时，会迫使系统对鼓和车轮速度减缓。流体被用来促使刹车踏板到运动的制动系统的运动，而所用的离合器片本身与一个耐热摩擦材料相似，。 这一基本设计能力的表明，在大多数情况下，它有一大缺陷。高压下的制动条件，想在陡峭的山上降低沉重的负荷或反复高的速度缓慢，鼓式制动器往往会褪色，失去效力。通常这褪色是由于太多的热量累积与鼓。记得的原则，涉及制动转向动能（车轮运动）到热能（热） 。基于这个原因，鼓式制动器的操作，他们能吸收产生的热量可以减缓车辆的车轮。可有令人不安之处，一旦制动元件本身饱和，他们失去停止车辆的能力。2） 盘式制动器盘式制动器用于大多数车的前轮和一些车的四个轮子。制动盘依附于轮毂上，随轮胎一起转动。当司机刹车时，主缸的液压用于推动摩擦衬料，制动钳夹紧制动盘，从而使车停下来。在盘式制动器中，制动盘通常由铸铁构成。毂可以被制造成一片，和车轮在一起；或者分成两部分。盘式制动器的每一个面都有机械闸。一