英文原文
Spin control for cars
Stability control systems are the latest in a string of technologies focusing on improved diriving safety. Such systems detect the initial phases of a skid and restore directional control in 40 milliseconds, seven times faster than the reaction time of the average human. They correct vehicle paths by adjusting engine torque or applying the left- or-right-side brakes, or both, as needed. The technology has already been applied to the Mercedes-Benz S600 coupe.
Automatic stability systems can detect the onset of a skid and bring a fishtailing vehicle back on course even before its driver can react.
Safety glass, seat belts, crumple zones, air bags, antilock brakes, traction control, and now stability control. The continuing progression of safety systems for cars has yielded yet another device designed to keep occupants from injury. Stability control systems help drivers recover from uncontrolled skids in curves, thus avoiding spinouts and accidents.
Using computers and an array of sensors, a stability control system detects the onset of a skid and restores directional control more quickly than a human driver can. Every microsecond, the system takes a "snapshot," calculating whether a car is going exactly in the direction it is being steered. If there is the slightest difference between where the driver is steering and where the vehicle is going, the system corrects its path in a split-second by adjusting engine torque and/or applying the cat's left- or right-side brakes as needed. Typical reaction time is 40 milliseconds - seven times faster than that of the average human.
A stability control system senses the driver's desired motion from the steering angle, the accelerator pedal position, and the brake pressure while determining the vehicle's actual motion from the yaw rate (vehicle rotation about its vertical axis) and lateral acceleration, explained Anton van Zanten, project leader of the Robert Bosch engineering team. Van Zanten's group and a team of engineers from Mercedes-Benz, led by project manager Armin Muller, developed the first fully effective stability control system, which regulates engine torque and wheel brake pressures using traction control components to minimize the difference between the desired and actual motion.
Automotive safety experts believe that stability control systems will reduce the number of accidents, or at least the severity of damage. Safety statistics say that most of the deadly accidents in which a single car spins out (accounting for four percent of all deadly collisions) could be avoided using the new technology. The additional cost of the new systems are on the order of the increasingly popular antilock brake/traction control units now available for cars.
The debut of stability control technology took place in Europe on the Mercedes-Benz S600 coupe this spring. Developed jointly during the past few years by Robert Bosch GmbH and Mercedes-Benz AG, both of Stuttgart, Germany, Vehicle Dynamics Control (VDC). in Bosch terminology, or the Electronic Stability Program (ESP), as Mercedes calls it, maintains vehicle stability in most driving situations. Bosch developed the system, and Mercedes-Benz integrated it into the vehicle. Mercedes engineers used the state-of-the-art Daimler-Benz virtual-reality driving simulator in Berlin to evaluate the system under extreme conditions, such as strong crosswinds. They then put the system through its paces on the slick ice of Lake Hornavan near Arjeplog, Sweden. Work is currently under way to adapt the technology to buses and large trucks, to avoid jack-knifing, for example.
Stability control systems will first appear in mid-1995 on some European S-Class models and will reach the U.S. market during the 1996 model year (November 1995 introduction). It will be available as a $750 option on Mercedes models with V8 engines, and the following year it will be a $2400 option on six-cylinder $1650 of the latter price is for the traction control system, a prerequisite for stability control.
Bosch is not alone in developing such a safety system. ITT Automotive of Auburn Hills, Mich., introduced its Automotive Stability Management System (ASMS) in January at the 1995 North American International Auto Show in Detroit. "ASMS is a quantum leap in the evolution of antilock brake systems, combining the best attributes of ABS and traction control into a total vehicle dynamics management system," said Timothy D. Leuliette, ITT Automotive's president and chief executive officer.
"ASMS monitors what the vehicle controls indicate should be happening, compares that to what is actually happening, then works to compensate for the difference," said Johannes Graber, ASMS program manager at ITT Automotive Europe. ITT's system should begin appearing on vehicles worldwide near the end of the decade, according to Tom Mathues, director of engineering of Brake & Chassis Systems at ITT Automotive North America. Company engineers are now adapting the system to specific car models from six original equipment manufacturers.
A less-sophisticated and less-effective Bosch stability control system already appears on the 1995 750iL and 850Ci V-12 models from Munich-based BMW AG. The BMW Dynamic Stability Control (DSC) system uses the same wheel-speed sensors as traction control and standard anti-lock brake (ABS) systems to recognize conditions that can destabilize a vehicle in curves and corners. To detect such potentially dangerous cornering situations, DSC measures differences in rotational speed between the two front wheels. The DSC system also adds a sensor for steering angle, Utilizes an existing one for vehicle velocity, and introduces its own software control elements in the over allantilock-brake/traction-control/stability-control system.
The new Bosch and ITT Automotive stability control systems benefit from advanced technology developed for the aerospace industry. Just as in a supersonic fighter, the automotive stability control units use a sensor-based computer system to mediate between the human controller and the environment - in this case, the interface between tire and road. In addition, the system is built around a gyroscopelike sensor design used for missile guidance.
Beyond abs and traction control
Stability control is the logical extension of ABS and traction control, according to a Society of Automotive Engineers paper written by van Zanten and Bosch colleagues Rainer Erhardt and Georg Pfaff. Whereas ABS intervenes when wheel lock is imminent during braking, and traction control prevents wheel slippage when accelerating, stability control operates independently of the driver's actions even when the car is free-rolling. Depending on the particular driving situation, the system may activate an individual wheel brake or any combination of the four and adjust engine torque, stabilizing the car and severely reducing the danger of an uncontrolled skid. The new systems control the motion not only during full braking but also during partial braking, coasting, acceleration, and engine drag on the driven wheels, circumstances well beyond what ABS and traction control can handle.
The idea behind the three active safety systems is the same: One wheel locking or slipping significantly decreases directional stability or makes steering a vehicle more difficult. If a car must brake on a low-friction surface, locking its wheels should be avoided to maintain stability and steerability.
Whereas ABS and traction control prevent undesired longitudinal slip, stability control reduces loss of lateral stability. If the lateral forces of a moving vehicle are no longer adequate at one or more wheels, the vehicle may lose stability, particularly in curves. What the drive "fishtailing" is primarily a turning or spinning around the vehicle's axis. A separate sensor must recognize this spinning, because unlike ABS and traction control, a car's lateral movement cannot be calculated from its wheel speeds.
Spin handlers
The new systems measure any tendency toward understeer (when a car responds slowly to steering changes), or over-steer (when the rear wheels try to swing around). If a car understeers and swerves off course when driven in a curve, the stability control system will correct the error by braking the inner (with respect to the curve) rear wheel. This enables the driver, as in the case of ABS, to approach the locking limit of the road-tire interface without losing control of the vehicle. The stability control system may reduce the vehicle's drive momentum by throttling back the engine and/or by braking on individual wheels. Conversely, if the hteral stabilizing force on the rear axle is insufficient, the danger of oversteering may result in rear-end breakaway or spin-out. Here, the system acts as a stabilizer by applying the outer-front wheel brake.
The influence of side slip angle on maneuverability, the Bosch researchers explained, shows that the sensitivity of the yaw moment on the vehicle, with respect to changes in the steering angle, decreases rapidly as the slip angle of the vehicle increases. Once the slip angle grows beyond a certain limit, the driver has a much harder time recovering by steering. On dry surfaces, maneuverability is lost at slip-angle values larger than approximately 10 degrees, and on packed snow at approximately 4 degrees.
Most drivers have little experience recovering from skids. They aren't aware of the coefficient of friction between the tires and the road and have no idea of their vehicle's lateral stability margin. When the limit of adhesion is reached, the driver is usually caught by surprise and very often reacts in the wrong way, steering too much. Oversteering, ITT's Graber explained, causes the car to fishtail, throwing the vehicle even further out of control. ASMS sensors, he said, can quickly detect the beginning of a skid and momentarily activate the brakes at individual wheels to help return the vehicle to a stable line.
It is important that stability control systems be user-friendly at the limit of adhesion - that is, to act predictably in a way similar to normal driving.
The biggest advantage of stability control is its speed - it can respond immediately not only to skids but also to shifting vehicle conditions (such as changes in weight or tire wear) and road quality. Thus, the systems achieve optimum driving stability by changing the lateral stabilizing forces.
For a stability control system to recognize the difference between what the driver wants (desired course) and the actual movement of the vehicle (actual course), current cars require an efficient set of sensors and a greater computer capacity for processing information.
The Bosch VDC/ESP electronic control unit contains a conventional circuit board with two partly redundant microcontrollers using 48 kilobytes of ROM each. The 48-kB memory capacity is representative of the large amount of "intelligence" required to perform the design task, van Zanten said. ABS alone, he wrote in the SAE paper, would require one-quarter of this capacity, while ABS and traction control together require only one half of this software capacity.
In addition to ABS and traction control systems and related sensors, VDC/ESP uses sensors for yaw rate, lateral acceleration, steering angle, and braking pressure as well as information on whether the car is accelerating, freely rolling, or braking. It obtains the necessary information on the current load condition of the engine from the engine controller. The steering-wheel angle sensor is based on a set of LED and photodiodes mounted in the steering wheel. A silicon-micromachine pressure sensor indicates the master cylinder's braking pressure by measuring the brake fluid pressure in the brake circuit of the front wheels (and, therefore, the brake pressure induced by the driver).
Determining the actual course of the vehicle is a more complicated task. Wheel speed signals, which are provided for antilock brakes/traction control by inductive wheel speed sensors, are required to derive longitudinal slip. For an exact analysis of possible movement, however, variables describing lateral motion are needed, so the system must be expanded with two additional sensors - yaw rate sensors and lateral acceleration sensors.
A lateral accelerometer monitors the forces occurring in curves. This analog sensor operates according to a damped spring-mass mechanism, by which a linear Hall generator transforms the spring displacement into an electrical signal. The sensor must be very sensitive, with an operating range of plus or minus 1.4 g.
Yaw rate gyro
At the heart of the latest stability control system type is the yaw rate sensor, which is similar in function to a gyroscope. The sensor measures the speed at which the car rotates about its vertical axis. This measuring principle originated in the aviation industry and was further developed by Bosch for large-scale vehicle production. The existing gyro market offers two widely different categories of devices: $6000 units for aerospace and navigation systems (supplied by firms such as GEC Marconi Avionics Ltd., of Rochester, Kent, U.K.) and $160 units for videocameras. Bosch chose a vibrating cylinder design that provides the highest performance at the lowest cost, according to the SAE paper. A large investment was necessary to develop this sensor so that it could withstand the extreme environmental conditions of automotive use. At the same time, the cost for the yaw rate sensor had to be reduced so that it would be sufficiently affordable for vehicle use.
The yaw rate sensor has a complex internal structure centered around a small hollow steel cylinder that serves as the measuring element. The thin wall of the cylinder is excited with piezoelectric elements that vibrate at a frequency of 15 kilohertz. Four pairs of these piezo elements are arranged on the circumference of the cylinder, with paired elements positioned opposite each other. One of these pairs brings the open cylinder into resonance vibration by applying a sinusoidal voltage at its natural frequency to the transducers; another pair, which is displaced by 90 degrees, stabilizes the vibration. At both element pairs in between, so-called vibration nodes shift slightly depending on the rotation of the car about its vertical axis. If there is no yaw input, the vibration forms a standing wave. With a rate input, the positions of the nodes and antinodes move around the cylinder wall in the opposite direction to the direction of rotation (Coriolis acceleration). This slight shift serves as a measure for the yaw rate (angular velocity) of the car.
Several drivers who have had hands-on experience with the new systems in slippery cornering conditions speak of their cars being suddenly nudged back onto the right track just before it seems that their back ends might break away.
Some observers warn that stability controls might lure some drivers into overconfidence in low-friction driving situations, though they are in the minority. It may, however, be necessary to instruct drivers as to how to use the new capability properly. Recall that drivers had to learn not to "pump" antilock brake systems.
Although little detail has been reported regarding next-generation active safety systems for future cars (beyond various types of costly radar proximity scanners and other similar systems), it is clear that accident-avoidance is the theme for automotive safety engineers. "The most survivable accident is the one that never happens," said ITT's Graber. "Stability control technology dovetails nicely with the tremendous strides that have been made to the physical structure and overall capabilities of the automobile." The next such safety system is expected to do the same.
中文译文
汽车的转向控制
控制系统稳定性是针对提高驾驶安全性提出的一系列措施中最新的一个。这个系统能够在40毫秒内实现从制动开始到制动恢复的过程，这个时间是人的反应时间得七倍。他们通过调整汽车扭矩或者通过应用汽车左侧或右侧制动，如果需要甚至两者兼用，来实现准确的行车路线。这个系统已被应用于奔驰S600汽车了。
稳定的机械自动系统能够在制动时发现肇端，并且在驾驶人员发现能够反应以前实现车辆的减速。
安全玻璃，安全带，撞击缓冲区，安全气囊，ABS系统，牵引力控制系统还有现在的稳定调节系统。汽车安全系统的连续升级，已经产生了一种为保护汽车所有者安全的设计模式。稳定调节系统帮助驾驶员从不可控制的曲线制动中解脱出来，从而避免了汽车的摆动滑行和交通事故。
利用计算机和一系列传感器，稳定调节系统能够检测到制动轮的打滑并且比人更快的恢复对汽车的方向控制。系统每百万分之一秒作出一次快速捕捉，以及断断汽车是否在按照驾驶员的路线行驶。如果检测到汽车行驶路线和驾驶员驾驶路线存在一个微小的偏差 ，系统会在瞬间纠正发动机扭矩或者应用汽车左右制动。过程的标准反应时间是40毫秒----人的平均反应时间的七分之一。
罗伯特博世工程系统负责人安东·范·桑特解释说：“一个稳定的控制系统能够‘感觉到”驾驶员想要运动的方向，通过控制转向角度，油门踏板的位置，制动板的状态来确定汽车实际运动路线的偏航比率（汽车偏离方向轴的角度）和横向加速度”。项目负责人阿明·马勒领导着范桑特的工作小组和奔驰汽车公司的工程师发明了第一个完全有效的稳定调节系统，该系统由发动机扭矩控制系统，制动系统，牵引控制系统组成以实现理想与现实运动之间的最小差距。
汽车安全专家相信稳定调节系统能够减少交通事故的发生，至少是在伤亡严重的事故方面。安全统计表明，多数的单车撞击事故伤亡（占伤亡事故发生的4%），事故能够通过应用这项新技术避免。这项新系统的额外费用主要用于一系列目前汽车日益普遍应用的制动/牵引控制锁组件。
稳定调节系统技术首次应用于欧洲的奔驰S600汽车，是由德国斯图加特市的罗伯特博世公司和奔驰公司在过去几年共同研制的。该系统在博世公司被称为汽车动力控制（VDC），而默西迪称它为稳定电控系统（ESP），作用就是在任何状况下维持车辆的稳定性。博世公司开发了这项系统，奔驰公司把它应用于车辆。工程师默西迪丝在柏林应用戴姆勒奔驰汽车虚拟驾驶模拟器在极限情况下对系统进行评估，例如极强的侧风。然后他们在瑞典的安杰普劳附近的后娜瓦安湖的冰面上进行性能测试。工作通常是在公路上进行以适用于公共汽车和大卡车，例如避免的折合问题。
稳定调节系统将在1995年中应用于欧洲S系列产品上，随后会在1996年进入美国市场（1995年11月产品）。用户可以选择750美元的系统，就像应用于默西迪丝的试验用的V8发动机上的，也可以选择价格为2400美元的应用于六缸发动机汽车的系统。后者的系统中差不多有1650美元是用于牵引控制系统，该系统是稳定性系统的先决条件。
并不是只有博世公司一家在开发这样的安全系统，美国密歇根州的ITT（美国国际电信公司）汽车公司的奥伯恩·希尔，在1995年1月底特律北美国际汽车展览会上展示了了悇管理系统（ASMS），“车辆控制器应该像空对地导弹的控制器那样，比较而言，事实上那已经实现了，不同的是两者的费用不同”，美国国际电信公司驻欧洲空对地导弹控制工程负责人约翰尼斯·格雷得说。北美ITT公司“汽车制动和底盘工程”主管汤姆·麦兹指出，在未来十年美国国际电信公司的系统要首先出现在车辆上。很多工程师正在六辆特殊制造的精密车辆模型上调试这种系统。
一个比较简单和较低效率的博世的稳定调节系统也在1995年出现在慕尼黑宝马公司的AG系列750iL和850Ci V-12两款车上。宝马公司的稳定调节系统（DSC）运用的车轮速度传感器同牵引控制系统和标准ABS防抱死系统一样能够识别外部情况，使车辆更容易实现曲线行驶和转弯。为了检测出车辆转弯时潜在的危险，DSC系统检测的是两前轮在转弯时的速度差，DSC系统添加了一个更高级的角度传感器利用现有的一个车辆速度，并且引入了它自身带有的关于完全抱死系统，牵引控制系统，稳定调节系统软件控制原理。
新的博世和ITT自动稳定调节系统得益于航空工业高级技术的发展，就像超音速发动机，汽车的稳定调节单元运用一个基于计算机系统的传感器来调和人与系统之间的，还有轮胎与地面之间差异。另外，系统采用了用于导弹制导系统的回旋传感器。
优于ABS防抱死系统和牵引控制系统之处
根据范·桑特和博世公司的瑞娜·伊哈德，杰瑞·帕夫在《汽车工程师》杂志所提到的，稳定调节系统是ABS防抱死系统和牵引控制系统的合理扩展。但是ABS系统的作用发生在制动时车轮转向将被锁死时，牵引控制是预防加速时的车轮滑动，稳定系统是当汽车自由转向时能独立于驾驶员作出操作。依靠不同的驾驶状况系统可以使每个车轮制动或者迅速使四个轮转速适合于发动机的扭矩，从而使车辆稳定和减少由于制动失控带来的危险。新系统不仅仅控制完全制动还可以作用与部分制动，行车路线，加速度，车轮与发动机动作的滞后等，这些是ABS防抱死系统和牵引控制系统所远远不能达到的。
三种主动的安全系统的作用时刻是一致的，那就是一个车轮被锁死或者车轮渐渐失去方向稳定性或者车轮使得行驶更加困难。如果一辆车必须在较低摩擦系数的路面制动，必须避免车轮抱死以保持行驶稳定性和可驾驶性。
ABS防抱死系统和牵引控制系统能够预防侧滑，而稳定性系统采取减少侧面受力的稳定措施。如果行驶车辆的侧力不再适当的分配在一个或者更多轮上，车辆就会失稳，尤其是车辆沿曲线行驶时。驾驶员感觉到的“摇摆”起初是转弯或者与车的轴线形成一个纺锤形时。一个独立的传感器必须能够识别这个“纺锤”，而 ABS防抱死系统和牵引控制系统通过车轮的转速不能检测车辆的横向运动。
转向操作
新系统通过对微小的汽车不足转向（当车辆对于方向盘操作反应迟缓）和方向盘的“过敏”反应（后轮发生来回摆动）。当车辆在转向时如果发生不足转向和过度转向运动时，稳定调节系统能够通过后轮进行内部制动（针对曲线）纠正错误。这种情况是驾驶员不能感觉类似于ABS防抱死系统接近于抱死极限，而使车辆不失去控制。稳定调节系统能够通过发动机降速或者单轮制动来减小推动力。
博世公司的研究员解释说：“侧面偏离角度表明此时车辆的偏航灵敏性，并反映为转向角度，转向角度随着车辆偏离角度的增大而减小。一旦偏离角度超过某一限度，驾驶员就很难重新进行操作。在干燥的路面偏离角度不能够超过10度，而在积雪路面上极限偏离角度为4度。
多数司机没有从制动中恢复的经验。他们不知道轮胎和地面之间的摩擦系数，更不知道他们的车的侧缘稳定边界。当极限被冲破时，驾驶员通常会很紧张以至于做出错误的反应。ITT的格雷柏解释说：“过度转向引起车辆摆尾，使汽车更快的失控。ASMS传感器能够快速的检测到制动开始时各个车轮的活动，从而使车辆恢复到稳定行驶轨道。
对于稳定调节系统界面的可操作性是很重要的，这样可以预示带有稳定系统的驾驶和普通驾驶给人的感觉没有什么区别。
稳定系统最大的优点在于速度，它不仅可以对制动作出快速反应，还可以对车辆状况（例如车重变化，轮胎磨损），路面质量作出快速反应统就能够通过改变侧面受力平横处理，达到最好的驾驶稳定性。
稳定系统识别驾驶员想达到的（理想路线）和车辆实际行驶路线（实际路线）的不同，目前的汽车需要一套高效的传感器和一台高效处理信息的处理器。
博世公司的VDC/ESP电子控制单元是一个由两个48兆的ROM组成的传统实验电路板。范桑特说：“48KB的内存容量是大量用以完成设计任务的‘智能’的代表”。他在SAE中指出。ABS防抱死系统是独立的，只提供四分之一的这样的容量，而ABS和牵引控制系统组合在一起的容量只有这个软件容量的一半。
除了ABS防抱死系统和牵引控制系统所具有的关系传感器外，VDC/ESP运用了偏航比率传感器，横向加速度传感器，转向角传感器，制动压力传感器来获取汽车的加速，摇摆或者刹车的信息。系统通过管理员获得所需的通常的路面信息。方向盘上的传感器由一组安装在方向盘上的发光二极管和光敏二极管上组成。一只硅压力传感器通过控制前轮刹车内压力油的压力控制制动压力（因为制车压力来源于驾驶员）。
确定车辆实际的行驶路线是一项非常复杂的工作。通过必须的纵向滑动车轮速度传感器提供给反向制动或者牵引控制系统的车轮转速信号，以对可能发生的动作作出精确的分析，无论如何侧向难预料的运动分析是必须的，所以系统必须再拓展两个额外的传感器---偏航比率传感器和侧向加速度传感器。
横向加速度表检测沿曲线行驶时所带来的受力状况。这种类似的传感器通过一台直线霍尔发电机把弹簧的直线运动转变成电信号来实现对弹簧机构的控制。这种传感器必须很灵敏，它的控制角为±1.4g。
偏航比率回转仪
最新的稳定调节系统的核心在于类似于陀螺仪的偏航比率回转仪。传感器测量车辆对竖直轴的旋转。这个测量原理来源于航空工业，并且被博施公司大规模的应用于汽车工业。现有的回转仪市场提供两种选择，一种是应用与航空航天业的价值6000美元（由位于英国罗彻斯特的美国通用电器公司航空股份有限公司提供），另一种是用于照相机的价值160美元。由SAE报得知博施公司采取一种圆柱形设计方案以实现低成本下的高性能。这种传感器需要一项更大的投资以应对汽车所处的极端环境状态。同时偏航比率回转仪的价格必须降低，这样才能充分应用与汽车。
偏航比率回转仪有一个复杂的内部结构，其内部是有一个很小的圆柱形钢管伺服测量元件。圆柱的薄壁上有压电元件能够在15千赫兹的频率下震动。四对这样的感应器安放在圆柱体的周围，一对元件的位置与另一对的位置相对。其中的一对通过应用正弦电压引起柱体在其固有频率下产生共振，并将振动传送给变频器。在每一对传感器之间，振颤节点绕着汽车的垂直轴作细微的运动。这时如果没有偏航输入，震动曲线就是一条稳定的曲线。如果有信号输入，节点的位置和曲线的波谷就会在相对的防线绕着圆筒壁做旋转运动（科里奥利加速度）。这个轻微的位移就会成为汽车偏航比率的度量标准。
许多司机都相互宣传他们的车辆在光滑转弯处，车尾部将要被甩出去的时候，新系统会把车辆“推”回到正确的轨迹上方面的经验。
许多观察员指出，稳定调节系统可能会使司机在较低摩擦力的路面上过分自信，尽管他们占少数。或许需要指导司机怎样来恰当的使用车辆稳定调节系统。就像当初让司机学习不能向防抱死制动系统里泵油一样。
虽然只介绍了很少的关于为未来汽车研制的新一代主动安全系统（远远超过了雷达扫描仪类似的系统），但避免交通事故仍然是汽车安全工程的主题。美国国际电信公司负责人指出“当稳定调节技术伴随着汽车结构全面性能稳步提高的时候，多数可避免的事故将不再发生了”。新一代的安全系统也会起到同样的效果。
