A suspension is a device that connects and transfers power between a car body (or frame) and a wheel (or axle). All front and rear vehicle axle loads act on wheels through suspension. At present, many medium and high-end vehicles and large buses are equipped with electronically controlled air suspension (ECAS) or oil-air suspension system, which can automatically adapt stiffness, damping and height of suspension body to different vehicle loads, different road conditions and different conditions. According to needs of driving environment, comfort of car is further improved, provided that car's handling is good. A quality off-road vehicle should not only have comfort of a passenger car, but also take into account off-road performance of an off-road vehicle. Air suspension system is best choice to achieve this goal. According to different road conditions and distance sensor signal, control computer will judge change in vehicle body height, and then air compressor and exhaust valve are controlled to automatically compress or expand spring, thereby reducing or increasing ground clearance of chassis to increase vehicle body stability at high speeds or flotation in difficult road conditions
Classification and components of electronically controlled suspension system
The electronically controlled suspension system is divided into two categories: semi-active suspension system and active suspension system, and active suspension system is divided into two forms: air spring suspension system and oil-air spring suspension system.
The so-called electronically controlled active suspension system refers to a suspension system equipped with a suspension ECU, which can adjust stiffness of elastic components of suspension, damping force of shock absorber and height of car body, but only adjust suspension The suspension system with damping force is called semi-active suspension system .
The electronic air suspension control system consists of a mode switch, a vehicle speed sensor, a steering angle sensor, an acceleration sensor, a vehicle height sensor, a suspension ECU, an adjustable damping shock absorber (also known as an "air shock absorber"), an air compressor. , air spring and height control solenoid valve and other components.
The main signals collected by vehicle's air suspension ECM include vehicle speed, steering angle, pressure signal, brake light switch, vehicle body vertical acceleration, suspension mode selection switch, actual vehicle body level, and selected vehicle height. Driver.
Main functions of electronically controlled air suspension
For traditional mechanical suspension system, leaf spring rate, shock absorber damping force, and vehicle body height are fixed, and it can only passively absorb wheel shock caused by uneven ground, so ride is not comfortable.too comfortable. The electronically controlled air suspension system is equipped with sensors, electronic control units (ECUs) and actuators that can adjust stiffness of elastic elements and damping force of shock absorbers depending on vehicle speed, driving conditions and changes in number of shock absorbers. number of passengers and quality of loading, and three parameters, such as body height, are automatically and steplessly adjusted without driver intervention, which greatly improves driving comfort and driving stability.
(1) Control damping force of shock absorber.
The air suspension system collects signals from vehicle speed sensor, steering angle sensor, body height sensor, etc. After processing, suspension ECU controls action of electromagnetic drive or stepper motor actuator to adjust damping force. shock absorber. When car makes a sharp turn, rapid acceleration and emergency braking, it can keep car from "falling backwards", "nodding" and rollover, prevent car's position from changing too much, and improve stability of car.
(2) Adjust stiffness of elastic element.
The air suspension system adjusts damping force by changing coefficient of elasticity of shock absorber, so that car can freely select sport or comfort mode according to actual driving needs.
(3) Adjust vehicle body height.
One of main functions of air suspension system is to maintain height of vehicle body within reasonable limits under various operating conditions. If body is too high off ground for a long time, it will feel very bumpy while driving, as if a shock absorber was not installed; if body is too close to ground, bottom of car chassis will easily collide with raised ground while driving and even make car unable to move. The electronically controlled air suspension system automatically compresses or expands air spring by controlling action of air compressor, height adjustment valve and exhaust valve, thus reducing or increasing chassis ground clearance and keeping body at appropriate height. When vehicle is moving at high speed, let vehicle body height be lowered to reduce air resistance and improve handling stability; when car is driving on a bad road, let car body height be increased to improve car's flotation; in parking state, due to decrease in number of passengers and luggage, height of vehicle body is reduced in order to maintain a good parking posture.
3. The standard for good air suspension performance
The car doesn't nod when braking, doesn't lean back when accelerating, doesn't roll when cornering, rides without motion sickness, goes up bad roads, exits on good roads, comfortable on regular roads, safe on highways. .
Of course, compared with traditional suspension, due to complex structure of air-type adjustable suspension, probability and failure rate will be higher than coil spring suspension system, and use of air as power source to adjust height of chassis, tightness of related components is also a problem. In addition, if chassis height is adjusted frequently, it may cause localized overheating of air pump system, which will greatly shorten service life of air pump. Of course, with continuous improvement of technical level, many problems have been well solved, and at same time, application models are becoming more and more extensive.