Unit+14+防抱死制动系统和牵引力控制系统.doc

Unit 14 ABS and TCS 第十四课 防抱死制动系统和牵引力控制系统14.1 制动系统基本原理和基本制动 There are two usual force inputs to a motor vehicle: engine torque to provide acceleration (+ X acceleration) and brake friction to provide deceleration(-X acceleration). 对于汽车，通常有两个输入力：发动机转矩提供加速力（X正方向加速）和制动摩擦提供减速力（ X负方向加速）。幻灯片5 When an operator actuates the brake pedal, he or she is actually pushing on a lever that pushes a piston in a master cylinder to generate hydraulic pressure that is transmitted through the brake lines to the wheel actuators (either wheel cylinders or caliper pistons). 当驾驶员动作制动踏板，他（她）实际上推动拉杆，由拉杆推动主缸的活塞来产生液压。液压通过制动管路传送到车轮的作动器上（轮缸或者制动钳活塞）。幻灯片6 The wheel actuators force a friction material (brake shoes or disk pads) against a rotating surface (brake drums or disk rotors)to generate a force that stops the vehicle. 车轮作动器强迫摩擦材料（制动蹄块或制动衬片）与旋转的表面接触（制动鼓或制动盘），从而产生使车辆停止的力。幻灯片7 The energy to stop the vehicle is normally dissipated as heat in the drums or rotors. Thus, applying the brakes is really the act of dissipating the rolling energy of the vehicle as heat, hence slowing the vehicle down. 停止车辆的能量通常被转化为热能形式在制动鼓或制动盘消耗掉。因此，施加制动实际上就是将汽车的动能转为热能并消耗掉，从而使汽车减速。幻灯片8 The operation of the braking system depends on the integrity of the hydraulic system. Modern boosted master cylinders can generate 2000 psi or more, and the hydraulic system must distribute that pressure without leaking. 制动系统的操作取决于整个液压系统。现代助力型主缸可以产生2000psi，甚至更多的压强，液压系统必须要能够将压力分配，并不产生泄漏。幻灯片9 Almost all modern braking systems use a booster (or operator force amplifier) that uses engine vacuum to increase the force the brake lever applies to the master cylinder. 几乎所有的现代制动系统都使用助力器（或操作力放大器）。它利用发动机真空增加制动拉杆施加在主缸上的力。幻灯片10 Generally, disk brakes require higher application pressure than do drums because they are not self-actuating. 一般来说，盘式制动器比鼓式制动器需要施加更多的制动力，因为它不能够自行增力。幻灯片11 When drum brakes are combined with disk brakes in a vehicle (usually with drums in the rear), there is always “a proportioning valve” to proportionally reduce the effective hydraulic pressure at the drum brake wheel cylinders and to always keep the rear wheels turning to preserve directional stability. 当鼓式制动器和盘式制动器在汽车上混合使用（一般鼓式制动器用于后轮）的时候，通常需要一个比例阀按比例减少施加在鼓式制动器轮缸的液压，从而总是使得后轮旋转，保证方向稳定性。幻灯片1214.2 Antilock Braking Systems14.2 防抱死制动系统 A vehicle braking system, including the tires is most effective, i.e., produces the optimum retarding force, when the wheel speeds are approximately, 85% to 90% of the vehicle speed. The difference (100%-85%=15%) is called the percent slip of a particular wheel. 当车轮速度大约为85%至90%的车速时，汽车轮胎制动系统最有效，也就是说它可以产生最优的制动力。这个15%的差值被称作车轮的滑移率。幻灯片13 The 10% to 15% slip retarding force is greater than the locked wheel retarding force, so optimum braking is achieved when the slip is 10% to 15% and no more. 当滑移率在10%至15%之间时，制动力要大于车轮抱死时的制动力，因此只有当滑移率在10%至15%之间，系统取得最佳制动效果。幻灯片14 Over-applying foundation brakes can cause wheels to lock (100% slip), so a system that prevents this can improve braking effectiveness. Antilock braking systems (ABS) have been developed to do this. 过多制动会导致车轮抱死（100%的滑移率）。因此，能够防止这种现象发生的系统就可以提高制动效果。防抱死制动系统(ABS)的设计就是实现这个目的。幻灯片15 However, prevention of lock to improve braking effectiveness is not the most important reason for ABS. Once a wheel is locked, it does not provide any lateral control of the vehicle(+/-Y axis) , and if multiple wheels lock, the vehicle will start to yaw. 但是，通过防止车轮抱死来提高制动效果并不是ABS的首要目的。一旦车轮抱死，它无法给汽车提供任何横向控制（正负Y方向），如果多个车轮抱死，汽车开始偏移。幻灯片16 This means that if the rear wheels lock, the vehicle will tend to spin out (rear end moving forward) , and if the front wheels lock, the vehicle cannot be steered. Control of vehicle track is the most important reason for the use of ABS. 这意味着如果后轮抱死，汽车趋向侧滑（汽车后端向前运动）。如果前轮抱死，汽车失去转向能力。因此，控制汽车行驶是ABS的首要目的。幻灯片17 It has been shown that for poor road conditions (sand, ice, snow, water, etc.）, a system that prevented wheel lockup and gave significantly increased directional control, in exchange for a small loss of absolute stopping distance, provided a major benefit to overall vehicle performance. 已经证明，当汽车在较差路面（沙、冰、雪、水等）行驶时，ABS系统可以防止车轮抱死，显著改善行驶方向控制。这是牺牲较小的制动距离换来的，但对整个汽车性能有大的改善。幻灯片18 This is accomplished by using an ECU to sense individual wheel speeds, and then isolate and reduce brake fluid pressure to the wheel or wheels that are locking up. The controller is an ECU, the controlled parameter, is wheel cylinder pressure (via electrical solenoid valves), and the feedback elements are individual electronic wheel speed sensors (WSS). 这是通过使用ECU来检测单个车轮转速，并对锁死的车轮进行保压和减压控制实现的。ABS系统的控制器是ECU，受控参数是轮缸压力（通过电磁阀调节），反馈元件是单个车轮电子转速传感器。幻灯片19 The WSS signals are typically generated via a pickup coil mounted adjacent to a toothed ring at each controlled wheel, where the pickup coil generates a varying voltage output proportional to the amplitude and frequency of the magnetic flux change as the ring teeth pass by it. 轮速传感器信号是由一个靠近每个被控轮齿圈安装的耦合线圈产生的。当齿圈经过耦合线圈，耦合线圈产生一个与磁通量幅值和频率变化成比例变化的电压输出信号。幻灯片20 By monitoring the frequency output of each WSS, the ECU can decide if an individual wheel slip exceeds a desired threshold. When such a threshold is exceeded at a particular wheel, the ECU directs the hydraulic control unit to isolate that wheel and reduce hydraulic pressure at that wheel, so that the wheel can resume rotation. 通过监测每个轮速传感器的频率输出，ECU能够判断出哪个车轮滑移率超过设定的阀值。当某个轮滑移率超过了阀值，ECU通过液压控制单元对那个车轮实行保压和减压控制，从而使得车轮恢复旋转状态。幻灯片21 Once the wheel is again rotating at about optimum slip (assuming the brakes are still applied) pressure is reapplied to that particular wheel. Typically, each wheel control circuit is called a channel and the hydraulic control unit is typically called a hydraulic modulator. 一旦车轮重新以最优的滑移率旋转（假设此时依然处于制动状态），压力重新施加在那个车轮上。每个车轮的控制回路被称作通道，液压控制单元被称做液压调节器。幻灯片22 Hydraulic modulators typically include three functions for each controlled wheel circuit: isolation, pressure-dump, and pressure-reapply. This control sequence causes a pulsed apply/release/apply as ABS is controlling a wheel in an emergency stop, often up to ten times per second. 液压调节器实现每个车轮控制通道的三个功能：保压，减压和增压。紧急制动中，当ABS控制一个车轮时，这个控制信号产生高频的制动/释放动作，经常每秒钟要达到10次以上。幻灯片23 Because of practical slip-threshold tradeoffs, ABS equipped vehicles may show a slightly increased stopping distance, but a marked increase in track control over the ensemble of many emergency braking situations. That trade off is deemed to be beneficial for the average driver on modem vehicles. 由于实际液压阀值的折中考虑，装备ABS的汽车制动距离有轻微增长，但对许多紧急制动状态的总体制动效果而言，它显著改善了方向控制。因此，这个折中对驾驶现代汽车的普通驾驶员而言是有利的。幻灯片24 Thus, the primary purpose of ABS is to preserve directional stability and allow the driver to continue steering during emergency braking, with an acceptable tradeoff of slightly longer stopping distance. 因此，ABS的首要目的是保持车辆方向稳定性，使得汽车在紧急制动下可以继续转向。当然，这是以一个可以接受的略微增加的制动距离换来的。幻灯片25 Also, because wheel slip is limited with ABS vehicles, hard braking stops will not produce typical tire scrub artifacts on road surfaces, thus, complicating traditional accident reconstruction methods. When ABS is not activated, the foundation brakes operate normally; thus, normal stops are unaffected by ABS. 同样，由于ABS车辆的车轮滑移率受到限制，猛烈制动时不会在路面下留下常见的轮胎磨擦痕迹。因此，这给传统的事故重减方法造成麻烦。当ABS不被启动，基本制动正常工作。因此，一般制动不受ABS影响。幻灯片2614.3 Traction Control Systems14.3 牵引力控制系统 In the past few years, selected manufacturers have introduced systems that add traction and tracking control functions during acceleration as well as braking. 近几年来，部分厂商推出了当车辆加速和制动时，可以增加额外的牵引力和牵引力控制系统。幻灯片27 ABS releases the brakes momentarily whenever wheel speed sensors indicate a locked wheel during braking, whereas traction control applies the brakes momentarily to one of the drive wheels whenever the wheel speed sensors indicates a wheel is going faster than the others during acceleration. 当车辆制动时，当轮速传感器监测到车轮抱死，ABS立刻停止制动。当车辆加速时，当轮速传感器监测到一个车轮比其余车轮转得快时，牵引力控制系统立刻对那个车轮施加制动。幻灯片28 Note that the TCS is designed to operate only in the engine-acceleration mode, and its function is suspended if the operator applies the brake. 注意：TCS设计只是在发动机加速状态下工作。如果驾驶员踩下制动时，TCS的作用就会暂停。幻灯片29 Some TCS systems also have the capability to also reduce engine power via electronic control of fuel injectors and/ or spark timing. This is accomplished via bidirectional communications between the TCS ECU and the PCM. 一些TCS系统还具备通过燃油喷射器和/或点火时间的电子控制来减小发动机功率。这需要TCS的ECU和动力系统控制模块之间的双向通讯。幻灯片3014.4 Combined ABS and TCS14.4 防抱死制动系统和牵引力控制系统结合使用 Since the primary function of both TCS and ABS is control of a wheel whose speed significantly varies from the averaged speed of the other wheels（for TCS, -for ABS), where both features are incorporated in a vehicle, these functions are usually combined into one hydraulic control unit, sharing a common ECU. 由于TCS和ABS的首要作用都是控制转速与其余车轮平均转速明显不同的车轮（对于TCS是大于，对于ABS是小于），这两个系统可以在一辆汽车上实现合作。这些功能通常集成在一个液压控制单元，共用一个ECU。幻灯片31 The objective of both ABS and TCS is for them to operate transparently to the consumer operator so as to provide enhanced vehicle tracking stability under both braking and acceleration under adverse road surface conditions. ABS和TCS的目的是通过驾驶员对它们的操作，即使在不利的路面条件下，无论是制动还是加速，都能保证车辆更加可靠的操纵稳定性。幻灯片32 This feature provides the ordinary driver with advanced tracking stability that was previously accomplished only by skilled racing and police drivers. 这使得普通驾驶员也可以实现良好的汽车行驶稳定性。而以前这只有技术高超的赛车手和警察才能做得到。幻灯片33 Thus, for combined ABS/TCS ECUs with the brake applied in ABS modes, if the speed of one wheel drops significantly compared with the other wheels, the brake pressure on that wheel is momentarily reduced (using isolation and dump valves) to stop the wheel from locking, and it is reapplied (using a motor/pump) when the wheel speed is near the average of the other wheel speeds. 因此，对于ABS/TCS集成ECU，处于ABS制动模式，如果一个车轮转速明显低于其他车轮，那个车轮的制动压力迅速减小（使用保压和减压阀）来避免车轮抱死，当轮速接近到其它车轮的平均速度时，压力重新施加（使用电机/泵）。幻灯片34 With no brake applied and under acceleration in TCS modes, if the speed of one wheel increases significantly compared to the other wheels, that wheel brake is momentarily applied to reduce that wheel speed (and with differential systems to redistribute traction power to the opposite wheel). Braking is removed when that wheel speed returns to near the average of the other wheel speeds. 当没有制动且处于TCS加速模式，如果一个车轮的转速明显快于其他车轮，制动力迅速施加到那个车轮上，从而减小小轮速（差速系统用来给反侧的车轮重新分配牵引力）。当车轮转速又接近到其它车轮的平均转速时，制动力去除。幻灯片35 Given that ABS, TCS, and ABS/TCS systems variously monitor parameters such as wheel speeds, brake application, accelerator application, etc. for normal operation, there is an obvious capability to save them in event triggered snapshot/freeze frames. 正常运转下，A