制动器的英文版及翻译

The Brakes

The brakes function by absorbing in friction the energy possessed by the moving car. In so doing they convert the energy into hear. There are tow types of brakes, the drum brake and the disc brake. Either or both types may be fitted. But where both types are used it is usual for the disc brakes to be fitted to the front wheels. In both drum and disc brakes, a hydraulic system applies the brakes. The hydraulic system connects the brake pedal to the brake parts at each wheel. 1 、 Drum Brakes

The drum brake consists of a pair of semicircular brake shoes mounted on a fixed back plate and situated inside a drum. This drum is fixed to the road wheel and rotates with it .One end of each shoe is on a pivot and a spring holds the other end in contact with the piston of a hydraulic cylinder.(In front brakes it is usual to use two hydraulic cylinders in order to equalize the pressures exerted by the shoes, as shown in Fig.7.1)Each shoe is faced with material ,known as brake lining ,which produces high frictional resistance.

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The hydraulic system comprises a master cylinder and the slave cylinders which are the cylinders on the road wheels. The slave cylinders are connected to the master cylinder by tubing and the whole system is filled with hydraulic fluid .A piston in the master cylinder is connected to the brake pedal, so that when the driver depresses the pedal the fluid is forced out to each slave cylinder and operates their pistons. The fluid pushes the pistons out of their cylinders. They ，in turn, push against the inner ends of the brake shoes and force them against the drums in each wheel. We say that the brakes are on. This friction of the shoes against the drums, which are fixed to the road wheels, slows down or stops the car.

As the brake pedal is allowed to come up, the hydraulic fluid returns to its original position, the pistons retract, and a spring attached to each brake shoe returns it also to its original position. Free of the brake drum. Now we say that the brakes are off.(Fig.7.2)

The brakes may also be operated by mechanical linkages from the foot pedal and hand brake lever. Common practice is to operate both front and rear brakes hydraulically with a secondary mechanical system operating the rear brakes only from the hand lever. One of the great advantages of hydraulic operation is that the system is self-balancing, which means that the same pressure is automatically produced at all four brakes, whereas mechanical linkages have to be very carefully adjusted for balance. Of course, if more pressure is put on one of the brakes than on the others there is a danger that the car will skid.

The mechanical linkage on the rear brakes is a system of rods or cables connecting the handbrake lever to the brake-shoe mechanism, which work entirely independently of the hydraulic system. Drum brakes are prone to a reduction in the braking effort, known as “fade”, caused by the overheating of the brake linings and the drum. Fade can affect all or only some of the brakes at a time, but it is not permanent, and full efficiency returns as soon as the brakes have cooled down. However, fading is unlikely to occur except after the brakes have been used repeatedly in slowing the car from a high speed or after braking continuously down a steep hill. Descending such a hill, it would have been preferable to use engine braking by changing down into a lower gear. Drum brakes can be made less prone to fade by improving the cooling arrangements, by arranging for more air to be deflected over them, for example.

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2 Disc Brakes

The disc brake consists of a steel disc with friction pads operated by slave hydraulic cylinders. The steel disc is attached to the road wheel and rotates with it. Part of this steel disc is enclosed in a caliper. This caliper contains two friction pads，one on each side of the disc, and two hydraulic cylinders, one outside each pad. The pads are normally held apart by a spring, but when the driver depresses the brake pedal, pistons from the hydraulic cylinders force the pads against the sides of the disc. Because the disc is not enclosed all the way round, the heat generated when the brakes are applied is dissipated very much more quickly than it is from brake shoes which are entirely enclosed inside a drum. This means that disc brakes are less prone to fade than drum brakes.(Fig.7.3)

3 、Anti-lock Brake System (ABS)

The function of an anti-lock, or anti-skid, braking system is to prevent the wheels from locking under hard braking. Maximum braking force is obtained just before the wheels lock and skid. Such anti-skid system ate useful on slippery surfaces, such as ice and snow, where the wheels may lock easily. Locked wheels are dangerous because the car needs a much longer distance to stop. Locked wheels also can cause the driver to lose control.

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The system uses a sensor that knows when one wheel (or a pair of wheel) is skidding. (Fig.7.4) The sensor sends a signal to a computer, which signals a modulator valve. The modulator connects into the hydraulic system and can momentarily release the brake pressure and prevent the wheels from locking.(The pressure release is so fast that a driver is seldom aware of it.) pressure is then reapplied until the sensor again senses that the wheel is about to lock up. Thus, this system keeps the wheels as close to lock up as possible, without actually allowing the wheels to lock up and skid. This is called incipient lock up. Maximum braking occurs at that point. If any part of the system should fail to work, the system goes into a “fail-safe” mode. The brakes operate normally, as they would on a car that is not equipped with ABS. Today , ABS is an optional or standard feature that typically is found on expensive luxury cars and sports cars. In the future, ABS may be available for all cars.

3.1、ABS overview

Anti-lock braking system is using the body of a rubber balloon, while hitting the brakes, will give brake oil pressure, feeding through to the ABS body, using of the air in the middle of the air layer to return the pressure, make wheels evade the locked points. When the wheel will arrive next locked point, brake oil pressure makes balloon in a repeat function, so can function eight to thirty times in one second equivalent constantly brake, relax, namely, similar to the \\’s lateral sliding coming up and the wheels rubbing on one point with the ground without being locked in the emergency brake，so it can make the brake friction efficiency achieves ninety percent. It also can reduce the braking consumption and prolong the brake wheel drum, disc and tire twice with the service life of the vehicle in the ABS. On the dry tarmac road or on snowy or on rainy days, the slippery performance reached 80% - 90%, 30% -10%, 15% - 20%. Ordinary braking system on a wet road surface brake, or in the emergency brake, it’s easy for wheels to be locked owing to the braking force exceeds the friction force of the tires and ground. In recent years, the consumers of the vehicle emphasis on the safety , so most of the cars have ABS listed as standard. Without ABS, emergency brake usually cause tire locked, then, the rolling friction becomes sliding friction, as a result, braking force dramatically decreased. And if front wheels are locked first, the vehicle will lose the steering ability; if the rear tires are first locked, the vehicle is easy to slide laterally , so the direction becomes impossible to control. Through electronic or mechanical control, the ABS system controls the braking fluid pressure at a fast speed to avoid the wheels

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locked. Insure the tire have the biggest braking force and the turning ability when braking, and make the vehicle have the ability to evade the obstacles in emergency braking. With the rapid development of the automotive industry, safety increasingly become the important basis of that people choose and buy cars. At present the widespread adoption of holding brake system (ABS) that people can fully meet the safety of requirements. Automobile brake prevent embrace system, referred to as the ABS, is to improve the car an important device passive safety. Someone said brake prevent embrace system is auto safety measures relay belts after another major progress. Automobile braking system is the bus passengers safety is the most important relationship to one of the second systems. With the rapid development of the automotive industry, automobile safety for people appeals more and more attention. Automobile brake prevent embrace system, is another major progress to improve the safety.

ABS braking system is controlled by automobile microcomputer, when braking, it can keep the wheel rotating to help driver control vehicle parking safely. The anti-locked braking system detects wheel speed by speed sensor, and then send the wheel speed signals to the microcomputer. The microcomputer controls wheel slipping rate by increasing or decreasing the brake pressure repeatedly according to the input wheel speed to keep wheel rotate. In braking process, keeping wheel rotate not only ensures the ability of controlling driving direction, but also provides higher brake force than the locked wheel in most circumstances, . 3.2、The working principle of ABS

It includes control devices and ABS warning lights, in different ABS system, the structure of brake pressure adjusting device and working principle of electronic control devices are often different, the internal structure and control logic of ABS system usually includes the wheel speed sensors, brake pressure adjusting device, electronic identical and so on. In common ABS system, each wheel is installed a rotational speed sensor on the wheel speed, input the signal to electronic control device. The electronic control unit states monitoring and determination according to each wheel speed sensors’ signal about each wheel movement, and has formed the corresponding control instruction. Brake pressure adjusting device is mainly composed by pressure regulating solenoid valves, electric pump composition and liquid container components compose an independent whole, braking main cylinder and the cylinder brake wheel connected by the brake pipe. Brake pressure adjusting device is controlled by the electronic unit to control all brake wheel cylinders’ brake pressure. The working process of ABS can be divided into general braking, brake pressure kept brake pressure decrease and brake pressure increase stage. In general braking phase, ABS doesn't intervene brake pressure control, pressure regulating electromagnetic valve assembly in various into liquid solenoid valves are no electricity and is open, each produced liquid are no electricity and electromagnetic valve is in the closed position, electric pump also operates without electricity, and brake main cylinder to each brake wheel cylinder brake lines are in communication condition, and the brake wheel cylinder to liquid brake lines are in close condition, the brake wheel cylinder brake pressure change with the output pressure brake master cylinder, the braking

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process at this time is completely the same with conventional braking system braking process. In braking process, when the electronic control detects that the wheels primarily tend to embrace dies according to the wheel speed sensors of the wheel speed signal input, ABS came into the braking anti-lock process. For example, when the electronic control unit judges the front-right wheel tends to embrace, the electronic control unit will make control scrape the dynamic pressure front-right wheel failure into liquid solenoid valves electricity, make the fluid electromagnetic valve closed, brake main cylinder output brake fluid no longer enter into brake wheel cylinder, right now, right at the end of a fluid electromagnetic valve still energized and closed, the right brake wheel cylinder brake fluid also won't outflow, the right brake wheel cylinder scraping dynamic pressure stays certain, and other arms tend to be dead wheel with still brake pressure braking main cylinder and the increase of output pressure increases; If the right brake wheel cylinder brake pressure keep certain, the electronic control unit front-right wheel failure still tend to judge lock, the electronic control unit and move out liquid solenoid valves also electrify into a state of opening, the part right brake wheel cylinder brake wave will pass is open from fluid electromagnetic valve flow back to liquid container, make right brake wheel cylinder brake pressure holding diminishes quickly front-right wheel failure will start to eliminate death trend, with the right brake wheel cylinder brake pressure decreases, the front-right wheel under the action of inertia force will speed up gradually; accelerate gradually When the electronic control device determines the lock front-right wheel failure to completely eliminate according to the wheel speed sensors input signal, the electronic control unit makes right into the fluid electromagnetic valve and a liquid solenoid valves are without electricity, make into fluid electromagnetic valve to open, use liquid into closed electromagnetic valve, also make electric pump operation, energized to brake wheel cylinder pump brake fluid, output by brake main cylinder brake fluid electromagnetic valve into the right brake wheel cylinders, make right brake wheel cylinder brake pressure increased rapidly, opening up a front-right wheel failure and slow rotation. ABS control the sliding rate of wheels which tend to be locked through holding the brake force of wheels that tends to be locked repeatedly ,adhesion coefficient is in peak within the scope of the sliding rate, until the bus speed reduced to very low or brake main cylinder pressure no longer tend to be locked. Brake pressure to adjust cycle of frequency can reach 3 ~ 20HZ. In the ABS each has on the fluid and the fluid electromagnetic valve in corresponding at each brake wheel cylinder, but by the electronic control device to control, therefore, respectively, the brake wheel cylinder brake pressure can be independently adjustment so that four wheels are not occur braking lock phenomenon. Although various ABS structure form and working process is not exactly the same, are based on the brake holding pressure adaptive cycle adjustment of wheel which tends to be locked, to prevent the controlled wheels holding in death occurred when brake.

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3.3、 ABS function

The braking performance is one of main auto performance, it is also related to the security of driving. Evaluate the braking performance of a car , the basic index is brake acceleration ,braking distance and direction of braking time and braking stability.

Braking stability points to that the vehicle can still be specified in the direction of auto brake when driving in the direction of track. If cars proceed high-speed brake (especially when emergency brake) and make the wheel fully embrace die, it is very dangerous. If front wheel is locked, it will make cars lose steering ability. If the rear wheel is locked, it will appear to swing tail or switching (running deviation, sideslip) especially in the road is all wet slippery case, it will cause the traffic safety great harm. Automobile braking force depends on the brake friction, but the braking force which can make the car brake to slow, and also restricted by ground adhesion coefficient. When brake produces braking force increases to certain value, the tires will appear slipping on the ground. Its sliding rate

δ = (Vt - Va) / Vt x 100% δ: delta - sliding rate; Vt - theoretical speed of the car; Va - the actual speed of the car.

According to the experiments confirm, when wheel sliding rate delta range from 15% to 20% , the ground adhesion coefficient reach maximum, therefore, in order to get the best braking effect, we must control the slip rate in 15% ~ 20% range.

ABS function will namely decrease the brake force when the wheels will embrace dies, , and when the wheel will not hold died and increase braking force, so repeated action, braking effect is the best.

3.4、The problems needing attention when ABS is used

(1) After replace brake or replace hydraulic brake system components, it should exhaust the air in the brake pipe, lest affect braking system work normally.

(2)The car equipped with ABS should be replaced every year. Otherwise, brake fluid hygroscopic is very strong, water will not only reduce the boiling point to make it easy to produce corrosion, and still can cause braking performance recession. (3) To examine ABS braking system should pull power firstly.

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制动系简介

制动器通过摩擦的形式吸收运动车辆所具有的能量而起作用。并且将这些能量转化为热能。有两种类型的制动器，即鼓式制动器和盘式制动器。在一辆车上，可安装其中一种类型的制动器，也可同时安装两种类型的制动器。但在使用两种类型制动器的车上，盘式制动器通常安装在前轮。

在鼓式和盘式两种制动系统中，都利用液压系统实现制动，液压系统将制动器踏板与每个车轮上的制动器构件连接起来。 1 鼓式制动

鼓式制动器含有一对（副）半圆形的制动蹄，制动蹄位于制动鼓内并安装固定于底板上。 制动鼓与车轮固定连接，随车轮一起转动。每个制动蹄的一端安装于枢轴上，而另一端在弹簧的作用下与液压缸内的活塞保持接触。（在前制动器内，通常用两个液压缸，以便均衡由两制动蹄产生的压力。（如图7.1所示）

每个制动蹄的表面都覆盖有制动衬垫，制动衬垫（制动蹄摩擦片）产生高的摩擦阻力.（每个制动蹄的表面都覆盖有产生高摩擦阻力的制动蹄摩擦片）。

图7.1 鼓式制动器

1—制动器后盖 2—制动蹄 3—制动衬片 4—弹簧 5—液压缸

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图7.2 液压制动系统的主要组成部分

图7.3 盘式制动器

液压系统包含一个制动主缸和多个位于车轮上的制动轮缸。制动轮缸通过管道与制动主缸相连，并且整个系统都充满液压油。制动主缸中的一个活塞与制动踏板相联，所以当驾驶员踩下制动踏板时，迫使油液向外流到每一个制动轮缸，并使它们的活塞移动。油液将活塞推出液压缸，接着，活塞又推动制动蹄的内端，并将制动蹄挤向位于车轮内的制动鼓。我们说这时制动产生（起作用）。制动蹄对固联于车轮的制动鼓产生的摩擦力，使汽车减速或停止。当允许制动踏板抬起时，液压油返回原处，活塞缩回，安装在每个制动蹄上的弹簧使制动蹄也返回原位。释放制动鼓，此时我们说制动解除。（图7—2）制动器也可以用制动踏板和制动手柄的机械制动装置操纵。 通常惯例是前、后制动器均为液压操纵，同时仅仅利用手柄的辅助机械系统来操纵后制动器。液压操纵的最大优点之一是系统的自动平衡（自动调节），这就意味着所有的四个制动器自动产生相等的压力，而机械传动装置必须经过非常仔细的调整才能达到平衡。当然，

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如果一个制动器上的压力比其他制动器大，那就有汽车制动测滑的危险后制动器的机械传动装置是一套将制动手柄与制动蹄装置连接起来的杠系或缆绳，它们完全独立于液压系统而工作。

鼓式制动器的制动效能将会有减弱的趋势，或称为“制动热衰退”，它是由制动蹄摩擦片和制动鼓过热而引起的。制动衰退一次可影响全部或其中一部分制动器，但不是永久性的（长期的），一旦制动器冷却下来，又恢复到全部效能。然而，除了为使高速行驶的汽车减速而反复使用制动器，或者下陡坡连续制动外，制动（热）衰退是不太可能发生的。下这样的陡坡，更好的办法是（变速器）挂上低档用发动机制动。可通过改进冷却布置，如增加透气通风来减少鼓式制动器受制动热衰退的影响。

2 盘式制动

盘式制动器由钢制圆盘和制动液压轮缸操纵的制动衬块构成。钢制圆盘固定于车轮上并随车轮一起转动。钢盘的一部分装在制动钳内。制动钳有两个制动衬块（钢盘的每侧各一个）和两个液压轮缸（每个制动衬块的外侧各一个）。制动衬块正常情况下由弹簧保持分离，但是当驾驶员踩下制动踏板时，液压缸内的活塞就将制动衬块压向钢盘的侧面。因为制动盘没有被完全包围，制动过程中所产生热的耗散，比从完全包围在制动鼓中的制动蹄上热的耗散更快得多。这就意味着盘式制动器受制动衰退的影响比鼓式制动器更小。（图7.3）

图7.4 ABS制动系统组成示意图

3 ABS

防抱死或防侧滑制动系统的功用是防止车轮在急剧制动中抱死。最大的制动力是正好在车轮抱死滑动之前得到的。这种防滑系统在光滑的表面很有用，如在冰和雪上，在这种表面车轮容易抱死。车轮抱死是危险的，因为这时需要更长的距离才能使汽车停止行驶。 车轮抱死也能导致驾驶员失去对汽车的控制。 系统使用了一个传感器，它能分辨（识别）一个车轮（或一副车轮）即将开始滑动的信息。传感器将信号发送到计算机，计算机向调节器阀发出信号。调节器联入到液压系统，并能瞬间（立刻）释放制动压力，防止车轮抱死.（压力释放非常迅速，驾驶员很难觉察得到。）随后，又再度施加制动压力，直到传感器再次感测到车轮即将抱死为止。因此，系统将车轮保持在尽可能接近抱死的状态，而实际上又

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不让车轮抱死滑动。这叫做初始（期）抱死。这个时刻产生最大的制动效果（作用）。如果系统的任何部分不能正常工作，系统就进入失效保护模式。 制动器像在没有装备ABS的汽车上一样正常工作（操作）。

当今，ABS是可选装的配置，也是豪华轿车和运动型轿车（跑车）的标准配置。 将来，所有汽车可能都会装配ABS。 3.1、ABS概述

防抱死制动系统是利用阀体内的一个橡胶气囊，在踩下刹车时，给予刹车油压力，充斥到ABS的阀体中，此时气囊利用中间的空气隔层将压力返回，使车轮避过锁死点。当车轮即将到达下一个锁死点时，刹车油的压力使得气囊重复作用，如此在一秒钟内可作用8~30次，相当于不停地刹车、放松，即相似于机械的“点刹’。因此，ABS防抑死系统，能避免在紧急刹车时方向失控及车轮侧滑，使车轮在刹车时不被锁死，不让轮胎在一个点上与地面摩擦，从而加大摩擦力，使刹车效率达到90%以上，同时还能减少刹车消耗，延长刹车轮鼓、碟片和轮胎两倍的使用寿命。装有ABS的车辆在干柏油路、雨天、雪天等路面防滑性能分别达到80%—90%、30%—10%、15%—20%。普通制动系统在湿滑路面上制动，或在紧急制动的时候，车轮容易因制动力超过轮胎与地面的摩擦力而完全抱死。近年来由于汽车消费者对安全的日益重视，大部分的车都已将ABS列为标准配备。如果没有ABS，紧急制动通常会造成轮胎抱死，这时，滚动摩擦变成滑动摩擦，制动力大大下降。而且如果前轮抱死，车辆就失去了转向能力；如果后轮先抱死，车辆容易产生侧滑，使行车方向变得无法控制。所以，ABS系统通过电子或机械的控制，以非常快的速度精密的控制制动液压力的收放，来达到防止车轮抱死，确保轮胎的最大制动力以及制动过程中的转向能力，使车辆在紧急制动时也具有躲避障碍的能力。随着世界汽车工业的迅猛发展，安全性日益成为人们选购汽车的重要依据。目前广泛采用的防抱制动系统（ABS）使人们对安全性要求得以充分的满足。 汽车制动防抱系统，简称为ABS，是提高汽车被动安全性的一个重要装置。有人说制动防抱系统是汽车安全措施中继安全带之后的又一重大进展。汽车制动系统是汽车上关系到乘客安全性最重要的二个系统之一。随着世界汽车工业的迅猛发展，汽车的安全性越来越为人们重视。汽车制动防抱系统，是提高汽车制动安全性的又一重大进步。

ABS防抱制动系统由汽车微电脑控制，当车辆制动时，它能使车轮保持转动，从而帮助驾驶员控制车辆达到安全的停车。这种防抱制动系统是用速度传感器检测车轮速度，然后把车轮速度信号传送到微电脑里，微电脑根据输入车轮速度，通过重复地减少或增加在轮子上的制动压力来控制车轮的打滑率，保持车轮转动。在制动过程中保持车轮转动，不但可保证控制行驶方向的能力，而且，在大部分路面情况下，与抱死〔锁死〕车轮相比，能提供更高的制动力量。

3.2、ABS的工作原理 ??

控制装置和ABS警示灯等组成，在不同的ABS系统中，制动压力调节装置的结构形式和工作原理往往不同，电子控制装置的内部结构和控制逻辑也可能ABS通常都由车轮转速传感器、制动压力调节装置、电子不尽相同。在常见的ABS系统中，每个车轮上各安装一个转速传感器，将有关各车轮转速的信号输入电子控制装置。电子控制装置根据各车轮转速传感器输入的信号对各个车轮的运动状态进行监测和判定，并形成相应的控制指令。制动压力调节装置主要由调压电磁阀组成，电动泵组成和储液器等组成一个独立的整体，通过制动管路与制动主缸和各制动轮缸相连。制动压力调节装置受电子控制装置的控制，对各制动轮缸的制动压力进行调节。ABS的工作过程可以分为常规制动，制动压力保持制动压力减小和制动压力增大等阶段。在常规制动阶段，ABS并不介入制动压力控制，调压电磁阀总成中的各进液电磁阀均不通电而处于开启状态，各出液电磁阀均不通电而处于关闭状态，电动泵也不通电运转，制动主缸至各制动轮缸的制动管路均处于沟通状态，而各制动轮缸至储液

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器的制动管路均处于封闭状态，各制动轮缸的制动压力将随制动主缸的输出压力而变化，此时的制动过程与常规制动系统的制动过程完全相同 ??在制动过程中，电子控制装置根据车轮转速传感器输入的车轮转速信号判定有车轮趋于抱死时，ABS就进入防抱制动压力调节过程。例如，电子控制装置判定右前轮趋于抱死时，电子控制装置就使控制右前轮刮动压力的进液电磁阀通电，使右前进液电磁阀转入关闭状态，制动主缸输出的制动液不再进入右前制动轮缸，此时，右前出液电磁阀仍末通电而处于关闭状态，右前制动轮缸中的制动液也不会流出，右前制动轮缸的刮动压力就保持一定，而其它末趋于抱死车轮的制动压力仍会随制动主缸输出压力的增大而增大；如果在右前制动轮缸的制动压力保持一定时，电子控制装置判定右前轮仍然趋于抱死，电子控制装置又使右前出液电磁阀也通电而转入开启状态，右前制动轮缸中的部分制动波就会经过处于开启状态的出液电磁阀流回储液器，使右前制动轮缸的制动压力迅速减小右前轮的抱死趋势将开始消除，随着右前制动轮缸制动压力的减小，右前轮会在汽车惯性力的作用下逐渐加速；当电子控制装置根据车轮转速传感器输入的信号判定右前轮的抱死趋势已经完全消除时，电子控制装置就使右前进液电磁阀和出液电磁阀都断电，使进液电磁阀转入开启状态，使出液电磁阀转入关闭状态，同时也使电动泵通电运转，向制动轮缸泵输送制动液，由制动主缸输出的制动液经电磁阀进入右前制动轮缸，使右前制动轮缸的制动压力迅速增大，右前轮又开抬减速转动。ABS通过使趋于抱死车轮的制动压力循环往复而将趋于防抱车轮的滑动率控制，在峰值附着系数滑动率的附近范围内，直至汽车速度减小至很低或者制动主缸的常出压力不再使车轮趋于抱死时为止。制动压力调节循环的频率可达3~20HZ。在该ABS中对应于每个制动轮缸各有对进液和出液电磁阀，可由电子控制装置分别进行控制，因此，各制动轮缸的制动压力能够被独立地调节，从而使四个车轮都不发生制动抱死现象。尽管各种ABS的结构形式和工作过程并不完全相同，但都是通过对趋于抱死车轮的制动压力进行自适应循环调节，来防止被控制车轮发生制动抱死。 ???? 3.3、ABS的功用 ??

制动性能是汽车主要性能之一，它关系到行车安全性。评价一辆汽车的制动性能最基本的指标是制动加速度、制动距离、制动时间及制动时方向的稳定性。 ??制动时方向的稳定性，是指汽车制动时仍能按指定的方向的轨迹行驶。如果因为汽车的紧急制动（尤其是高速行驶时）而使车轮完全抱死，那是非常危险的。若前轮抱死，将使汽车失去转向能力；若后轮抱死，将会出现甩尾或调头（跑偏、侧滑）尤其在路面湿滑的情况下，对行车安全造成极大的危害。汽车的制动力取决于制动器的摩擦力，但能使汽车制动减速的制动力，还受地面附着系数的制约。当制动器产生的制动力增大到一定值时，汽车轮胎将在地面上出现滑移。其滑移率 ??

δ＝(Vt-Va)/Vt×100％ ?? 式中：δ--滑移率； Vt--汽车的理论速度； Va--汽车的实际速度。

据试验证实，当车轮滑移率δ＝15％一20％时附着系数达到最大值，因此，为了取得最佳的制动效果，一定要控制其滑移率在15％～20％范围内。ABS的功能即在车轮将要抱死时，降低制动力，而当车轮不会抱死时又增加制动力，如此反复动作，使制动效果最佳。 3.4、ABS使用中注意的问题

（1）更换制动器或更换液压制动系部件后，应排净制动管路中的空气，以免影响制动系统的正常工作。

（2）装有ABS的汽车，每年应更换一次制动液。否则，制动液吸湿性很强，含水后不仅会降低沸点，产生腐蚀，而且还会造成制动效能衰退。 （3）检查ABS防抱死制动系统前应先拔去电源。

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