Anti-lock braking system ABS (Anti-lock Braking System) belongs to automobile active safety system. The configuration of ABS system can not only effectively avoid the occurrence of wheel locking (slipping) during emergency braking, but also keep the vehicle stable during braking. With the increasing demand for automobile safety performance, some middle and high-end cars are not satisfied with ABS. ASR (Accelerated Slip Adjustment, also called Traction Control System) is installed to prevent vehicles, especially high-power vehicles, from slipping when starting and accelerating again, so as to maintain the stability of vehicle driving direction.
The difference between ASR and ABS is that ABS is to prevent the wheel from slipping when braking, while ASR is to prevent the vehicle from slipping when the driving wheel slips when accelerating. ASR is an extension of ABS, and the two complement each other. Or ESP (Electronic Control Ride Comfort System) can further improve the safety performance of vehicles.
The function of ASR is to control the sliding rate of the car during acceleration within a certain range and prevent the driving wheel from sliding quickly. Its first function is to improve traction; The second is to keep the car running smoothly. Driving on the slippery road, the driving wheel is easy to slip when the car without ASR accelerates; If the rear-drive vehicle is prone to tail flick, if the front-drive vehicle is prone to lose control of the direction. With ASR, the car will not have or can alleviate this phenomenon when accelerating. When turning, if the driving wheel slips, the whole vehicle will shift to one side, and when there is ASR, the vehicle will turn along the correct route. Traction control of automobile can reduce engine power by reducing throttle opening, and can also control wheel slip by braking. The car equipped with ASR is a combination of these two ways, that is, ABS/ASR. On the vehicle equipped with ASR, the mechanical connection from the accelerator pedal to the gasoline engine accelerator (diesel fuel injection pump joystick) is replaced by an electronic throttle device. When the sensor sends signals of accelerator pedal position and wheel speed to the control unit (CPU), the control unit will generate a control voltage signal, and the servo motor will readjust the position of the throttle valve (or the position of the diesel longitudinal rod) according to this signal, and then feed back the position signal to the control unit so as to adjust the braking in time.
ESP (Electronic Stability Program) includes ABS and ASR, which are the functional extensions of these two systems. Therefore, ESP can be regarded as the most advanced form of automobile anti-skid device at present. ESP system consists of control unit, steering sensor (monitoring the steering angle of the steering wheel), wheel sensor (monitoring the rotating speed of each wheel), sideslip sensor (monitoring the rotation state of the car body around the vertical axis), lateral acceleration sensor (monitoring the centrifugal force when the car turns) and so on. The control unit judges the driving state of the vehicle through the signals of these sensors, and then sends out control instructions. The difference between a car with ESP and a car with ABS and ASR is that ABS and ASR can only react passively, while ESP can detect and analyze the condition of the car and correct the driving mistakes before they occur. ESP is particularly sensitive to oversteer or understeer. For example, when a car turns left and oversteers (turns too fast), it will flick its tail to the right. When the sensor senses the slip, it will quickly brake the right front wheel to restore its adhesion and generate the opposite torque to keep the car in the original lane. Of course, there is a limit to everything. If the driver drives too fast blindly, it is difficult to guarantee the safety of any safety device now.
According to the prediction of automobile engineering experts, ASR will be as popular as ABS in the future, because ABS, ASR and ESP all contain technical and performance links. Some experts believe that devices such as ASR may replace four-wheel drive in a certain range. For example, people used to think that it was best to use four-wheel drive to improve the driving performance of cars, but compared with four-wheel drive, ASR and other devices are more suitable for cars. This is because the four-wheel drive has complex structure, high cost, increased vehicle weight and high fuel consumption, while ASR and other devices have simple structure and convenient installation, and the use effect is not bad in general urban roads. ABS/ASR/VDC system ABS/ASR system successfully solves the problem of directional stability when braking and driving, but it cannot solve the problem of directional stability when turning. For example, when a car turns, it will inevitably be subjected to horizontal and vertical forces. Only when the ground can provide enough lateral and longitudinal forces can the driver control the car. If the lateral adhesion ability of the ground is low, it will damage the ability of the car to travel in the predetermined direction. When a car turns at high speed in rainy days, it often slips, which is the reason for the lack of lateral adhesion on the ground.
In order to solve this problem, recently, developed countries in automobile industry have developed vehicle dynamics control system (VDC) based on ABS/ASR system. The system organically integrates the control systems of the main assembly of the automobile, such as braking, driving, suspension, steering, engine, etc., and can make the automobile have good directional stability under various bad working conditions, such as ice and snow pavement, lane separation, curve, lane change by evasive action, braking, acceleration, downhill, etc., and show the best driving performance. The application of VDC completely alleviates the high requirements of drivers for braking, acceleration and steering, and sets a new milestone for active and safe driving of automobiles.
The steering control of VDC system is mainly realized by braking control of each wheel and engine power output control. For example, when the car turns left, if the front wheel tends to slip out of the curve due to insufficient steering ability, the VDC system can detect that side slip is about to happen and take appropriate measures to brake the left rear wheel. The braking force generated by the left rear wheel can help the car turn and keep the car driving along the ideal route. If the rear wheel tends to sideslip and turn too much on the same curve, VDC system will take appropriate measures to brake the right front wheel to maintain the stable running of the vehicle. In extreme cases, the VDC system can also reduce the driving speed by reducing the power output of the engine and reduce the demand for lateral adhesion on the ground to maintain the stable driving of the vehicle. After the VDC system is adopted, the braking distance of the car on the open road or the curve can be further shortened.
The VDC system mainly uses the following sensors: wheel speed sensor, which is used to track the motion state of each wheel; A steering wheel angle sensor for sensing the steering wheel angle; The yaw rate sensor is used to record all the movements of the car rotating around the vertical axis; The lateral acceleration sensor is used to detect the magnitude of centrifugal force during steering; The wheel displacement sensor is used to measure the change of the relative position between the wheel and the car body. The core part of these sensors is yaw rate sensor, because the ratio of yaw rate to steering wheel angle is an important parameter reflecting the steering quality of automobile. The signal of the displacement sensor is transmitted to the electronic control device to control the semi-active suspension and improve the grounding performance of the automobile.
Other sensors transmit the information of the instantaneous motion state of the vehicle to the electronic control device and compare it with the ideal motion state. Once the vehicle deviates from the ideal route, it will take corrective measures in a very short time and send corresponding instructions to the brake control system or engine control system to maintain the vehicle running on the ideal route. Electronic braking force distribution system (EBD) EBD can automatically adjust the braking force distribution ratio of front and rear axles according to the difference of axle load transfer caused by vehicle braking, thus improving braking performance.
When the car brakes, the ground conditions of the four tires are usually different. For example, sometimes the left front wheel and the right rear wheel are stuck on the dry concrete floor, and the right front wheel and the left rear wheel are stuck in water or muddy water. This situation will lead to different friction between the four wheels and the ground when braking, which will easily lead to side slip, rollover and vehicle rollover accidents. EBD senses and calculates the different ground on which the four tires are attached at braking moment by high-speed computer, and obtains different friction values, so that the braking devices of the four tires can brake in different ways and with different strength according to different situations, and constantly adjust at high speed during the movement, thus ensuring the stability and safety of the vehicle.
Airbag (SRS) Airbag is an eye-catching high-tech device in modern automobiles. The steering wheel of an automobile equipped with an airbag device is usually the same as the ordinary steering wheel, but once the front end of the automobile collides strongly, the airbag will instantly "jump out" from the steering wheel and pad between the steering wheel and the driver to prevent the driver's head and chest from hitting the steering wheel or dashboard and other hard objects. Many people's lives have been saved since the appearance of airbags. The research shows that when a car with airbag device collides head-on, the driver's death rate of a large car decreases by 30%, that of a medium-sized car by 1 1%, and that of a small car by 14%. The airbag is mainly composed of sensor, microprocessor, gas generator and airbag.
The sensor and the microprocessor are used for judging the collision degree and sending signals; The gas generator generates an ignition action according to the signal indication, ignites the solid fuel and generates gas to inflate the airbag, so that the airbag expands rapidly, and the airbag is equipped with a safety valve. When the airbag is over-inflated or the pressure in the airbag exceeds a certain value, it will automatically release part of the gas to avoid squeezing passengers and causing injuries. The gas used in the airbag is mainly nitrogen or carbon monoxide. In addition to the driver's airbag, some cars are equipped with airbags for front passengers (that is, double airbag specifications). The airbags used by passengers are similar to those used by drivers, but the airbags are bigger and need more gas. In addition, some cars have side airbags installed on the side of the seat near the door.