At present, most automobile suspension systems are equipped with springs and shock absorbers, and there is no energy supply device in the suspension system, so its elasticity and damping cannot change with the external working conditions, so it is called passive suspension.
The active suspension has an actuator as a direct force generator, which can perform optimal feedback control according to the input and output, so that the suspension has the best damping characteristics, thus improving the ride comfort and handling stability of the automobile. It consists of elastic element c and force generator Fe.
Semi-active suspension can be regarded as a suspension system composed of springs and shock absorbers with variable characteristics. Although it cannot be optimally controlled and adjusted by external input, it can adjust the stiffness of the spring and the damping state of the shock absorber under various conditions according to the optimal parameter instructions of the optimal spring and shock absorber stored in the computer. It consists of an elastic element C and a damper whose damping coefficient can be adjusted in a large range.
The automobile suspension system controlled by electronic technology is mainly composed of sensors (car height, steering angle, acceleration, road condition prediction), electronic control ECU, suspension control actuator and so on. The control function of the system usually has the following three functions:
1 car height adjustment When the car is driving on the uneven road, the car body can be raised to facilitate passing; When driving at high speed on the road with good road conditions, it can reduce the body, reduce the air assist and improve the handling stability.
Damping force control is used to improve the handling stability of the car, and can restrain the change of the body posture under the conditions of sharp turn, rapid acceleration and emergency braking.
3 spring stiffness control changes the spring stiffness to make the suspension meet the requirements of sports or comfort.
After using active suspension, the control of roll, pitch, yaw and body can be more rapid and accurate, which can improve the stability of high-speed driving and cornering and reduce the body roll. When braking, the body leans forward slightly, and starting and rapid acceleration can reduce the backward tilt. Even on bad roads, the car body bounces less and the adhesion of tires to the ground is improved.
I. Active hydraulic suspension
The electronically controlled active hydraulic suspension can actively control the vibration of the automobile by using hydraulic components according to the mass and acceleration of the suspension. The arrangement of active hydraulic suspension on the car is shown in the figure. Gyroscope sensors for longitudinal and lateral acceleration and yaw are installed near the center of gravity of the car, which are used to collect signals such as car body vibration, wheel bounce, car body height and tilt state. These signals are input to the control unit ECU, which sends out control instructions according to the input signals and preset programs to control the servo motor and operate the front and rear four execution cylinders.
Two. Active air suspension
In the electronically controlled active air suspension system, the microcomputer sends instructions to the suspension after calculation and analysis according to the signal sent by the sensor and the control mode given by the driver. The suspension can change the stiffness and damping coefficient of the suspension according to the instructions given by the microcomputer, so as to maintain the good stability of the car body during driving and control the vibration response of the car body within the allowable range. Generally speaking, the control contents of active air suspension include body height, damping force of shock absorber and spring elastic coefficient.
1 car height control; There are three working conditions: standard, lifting and only lifting the rear wheel;
2. The damping force of the shock absorber is controlled in three grades: low, medium and high;
The elastic coefficient of air spring is divided into two grades: soft and hard.
Working principle of electronic control system of air suspension; Compressed air is formed by an air compressor and sent to the air chambers of springs and shock absorbers to change the height of the vehicle. Vehicle height sensors are installed near the front and rear wheels. The microcomputer judges the vehicle height according to the output signal of the vehicle height sensor, and then controls the compressor and the exhaust valve to compress or stretch the spring, thus controlling the vehicle height.
There is a motor in the shock absorber, which is controlled by the signal of microcomputer. The size of the vent hole can be changed by using the motor, thus changing the damping force.
Specifically, there is a switch of air suspension system on the dashboard of the car, and six different working modes can be formed by using this switch. The picture shows the arrangement of Toyota Motor Corporation's air suspension control device on the vehicle.