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 cats 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 drivers desired motion from the steering angle, the accelerator pedal position, and the brake pressure while determining the vehicles 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 Zantens 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. 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 Automotives 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. ITTs 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 drivers 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. 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 vehicles 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 arent aware of the coefficient of friction between the tires and the road and have no idea of their vehicles 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, ITTs 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 cylinders 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 ITTs 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. 汽車的轉向控制 控制系統穩定性是針對提高駕駛安全性提出的一系列措施中最新的一個。這個系統能夠在 40 毫秒內實現從制動開始到制動恢復的過程，這個時間是人的反應時間得七倍。他們通過調整汽車扭矩或者通過應用汽車左側或右側制動，如果需要甚至兩者兼用，來實現準確的行車路線。這個系統 已被應用于奔馳 S600 汽車了。 穩定的機械自動系統能夠在制動時發現肇端，并且在駕駛人員發現能夠反應以前實現車輛的減速。 安全玻璃，安全帶，撞擊緩沖區，安全氣囊， ABS 系統，牽引力控制系統還有現在的穩定調節系統。汽車安全系統的連續升級，已經產生了一種為保護汽車所有者安全的設計模式。穩定調節系統幫助駕駛員從不可控制的曲線制動中解脫出來，從而避免了汽車的擺動滑行和交通事故。 利用計算機和一系列傳感器，穩定調節系統能夠檢測到制動輪的打滑并且比人更快的恢復對汽車的方向控制。系統每百萬分之一秒作出一次快速捕捉，以及斷斷汽車是否在按照駕駛員的路線行駛。如果檢測到汽車行駛路線和駕駛員駕駛路線存在一個微小的偏差 ，系統會在瞬間糾正發動機扭矩或者應用汽車左右制動。過程的標準反應時間是 40 毫秒 -人的平均反應時間的七分之一。 羅伯特博世工程系統負責人安東范桑特解釋說：“一個穩定的控制系統能夠感覺到”駕駛員想要運動的方向，通過控制轉向角度，油門踏板的位置，制動板的狀態來確定汽車實際運動路線的偏航比率（汽車偏離方向軸的角度）和橫向加速度”。項目負責人阿明馬勒領導著范桑特的工作小組和奔馳汽車公司的工程師發明了第一個完全有效的 穩定調節系統，該系統由發動機扭矩控制系統，制動系統，牽引控制系統組成以實現理想與現實運動之間的最小差距。 汽車安全專家相信穩定調節系統能夠減少交通事故的發生，至少是在傷亡嚴重的事故方面。安全統計表明，多數的單車撞擊事故傷亡（占傷亡事故發生的 4%），事故能夠通過應用這項新技術避免。這項新系統的額外費用主要用于一系列目前汽車日益普遍應用的制動 /牽引控制鎖組件。 穩定調節系統技術首次應用于歐洲的奔馳 S600 汽車，是由德國斯圖加特市的羅伯特博世公司和奔馳公司在過去幾年共同研制的。該系統在博世公司被稱為汽車動力控制（ VDC），而默西迪稱它為穩定電控系統（ ESP），作用就是在任何狀況下維持車輛的穩定性。博世公司開發了這項系統，奔馳公司把它應用于車輛。工程師默西迪絲在柏林應用戴姆勒奔馳汽車虛擬駕駛模擬器在極限情況下對系統進行評估，例如極強的側風。然后他們在瑞典的安杰普勞附近的后娜瓦安湖的冰面上進行性能測試。工作通常是在公路上進行以適用于公共汽車和大卡車，例如避免的折合問題。 穩定調節系統將在 1995 年中應用于歐洲 S 系列產品上，隨后會在 1996 年進入美國市場（ 1995 年 11 月產品）。用戶可以選擇 750 美元的系統，就像應用于梅 賽德斯的試驗用的 V8 發動機上的，也可以選擇價格為 2400 美元的應用于六缸發動機汽車的系統。后者的系統中差不多有 1650 美元是用于牽引控制系統，該系統是穩定性系統的先決條件。 并不是只有博世公司一家在開發這樣的安全系統，美國密歇根州的 ITT（美國國際電信公司）汽車公司的奧伯恩希爾，在 1995 年 1 月底特律北美國際汽車展覽會上展示了管理系統（ ASMS），“車輛控制器應該像空對地導彈的控制器那樣，比較而言，事實上那已經實現了，不同的是兩者的費用不同”，美國國際電信公司駐歐洲空對地導彈控制工程負責人約翰尼斯格雷得 說。北美 ITT 公司“汽車制動和底盤工程”主管湯姆麥茲指出，在未來十年美國國際電信公司的系統要首先出現在車輛上。很多工程師正在六輛特殊制造的精密車輛模型上調試這種系統。 一個比較簡單和較低效率的博世的穩定調節系統也在 1995 年出現在慕尼黑寶馬公司的 AG 系列 750iL 和 850Ci V-12 兩款車上。寶馬公司的穩定調節系統（ DSC）運用的車輪速度傳感器同牽引控制系統和標準 ABS 防抱死系統一樣能夠識別外部情況，使車輛更容易實現曲線行駛和轉彎。為了檢測出車輛轉彎時潛在的危險， DSC系統檢測的是兩前輪在轉彎時的速度差 ， DSC 系統添加了一個更高級的角度傳感器利用現有的一個車輛速度，并且引入了它自身帶有的關于完全抱死系統，牽引控制系統，穩定調節系統軟件控制原理。 新的博世和 ITT 自動穩定調節系統得益于航空工業高級技術的發展，就像超音速發動機，汽車的穩定調節單元運用一個基于計算機系統的傳感器來調和人與系統之間的，還有輪胎與地面之間差異。另外，系統采用了用于導彈制導系統的回旋傳感器。 優于 ABS 防抱死系統和牽引控制系統之處 根據范桑特和博世公司的瑞娜伊哈德，杰瑞帕夫在汽車工程師雜志所提到的，穩定調節系統是 ABS 防抱死 系統和牽引控制系統的合理擴展。但是 ABS系統的作用發生在制動時車輪轉向將被鎖死時，牽引控制是預防加速時的車輪滑動，穩定系統是當汽車自由轉向時能獨立于駕駛員作出操作。依靠不同的駕駛狀況系統可以使每個車輪制動或者迅速使四個輪轉速適合于發動機的扭矩，從而使車輛穩定和減少由于制動失控帶來的危險。新系統不僅僅控制完全制動還可以作用與部分制動，行車路線，加速度，車輪與發動機動作的滯后等，這些是 ABS 防抱死系統和牽引控制系統所遠遠不能達到的。 三種主動的安全系統的作用時刻是一致的，那就是一個車輪被鎖死或者車輪漸漸失去方向 穩定性或者車輪使得行駛更加困難。如果一輛車必須在較低摩擦系數的路面制動，必須避免車輪抱死以保持行駛穩定性和可駕駛性。 ABS 防抱死系統和牽引控制系統能夠預防側滑，而穩定性系統采取減少側面受力的穩定措施。如果行駛車輛的側力不再適當的分配在一個或者更多輪上，車輛就會失穩，尤其是車輛沿曲線行駛時。駕駛員感覺到的“搖擺”起初是轉彎或者與車的軸線形成一個紡錘形時。一個獨立的傳感器必須能夠識別這個“紡錘”，而 ABS防抱死系統和牽引控制系統通過車輪的轉速不能檢測車輛的橫向運動。 轉向操作 新系統通過對微小的汽車不足轉向（當車輛對于方向盤操作反應遲緩）和方向盤的“過敏”反應（后輪發生來回擺動）。當車輛在轉向時如果發生不足轉向和過度轉向運動時，穩定調節系統能夠通過后輪進行內部制動（針對曲線）糾正錯誤。這種情況是駕駛員不能感覺類似于 ABS 防抱死系統接近于抱死極限，