A8L is an air suspension. You can write this if you can.

But all the suspensions that can be changed are active suspensions.

I majored in cars, too. Come on, get your diploma.

Compared with the traditional fixed-height spiral spring suspension system used by most cars at present, the air suspension system can increase or decrease the chassis height according to different road undulations, so that the vehicle can meet the driving needs under various road conditions. For this design purpose, the air suspension system is mostly used for off-road vehicles that often run in bad road conditions to ensure that vehicles can smoothly pass through muddy, wading, gravel and other roads. Air suspension system is a very advanced and practical configuration, but it is very fragile. Because of the complex structure of the system, its failure probability and frequency are much higher than that of the spiral spring suspension system. However, if air is used as "propulsion power" to adjust the height of the chassis, the sealing performance of the shock absorber needs to be further improved. If the air shock absorber leaks, the whole system will be in a "paralyzed" state. Moreover, if the chassis height is adjusted frequently, it may cause local overheating of the air pump system and greatly shorten the service life of the air pump.

Active suspension

Active suspension is to adjust the stiffness and damping of the suspension in time according to the motion state and road state of the car, so as to make it in the best vibration reduction state. It is a device that adds a controllable force to the passive suspension (elastic element, shock absorber and guide device). It usually consists of four parts: actuator, measurement system, feedback control system and energy system. The function of the actuator is to execute the instructions of the control system, which is generally a generator or a torque generator (hydraulic cylinder, air cylinder, servo motor, electromagnet, etc.). ). The function of the measuring system is to measure various states of the system and provide basis for the control system, including various sensors. The function of the control system is to process data and issue various control instructions, and its core component is the electronic computer. The function of the energy system is to provide energy for the above parts.

The active suspension system can control the suspension actuator by the electronic control unit (ECU) according to the signals such as vehicle height, vehicle speed, steering angle and speed, and braking. The stiffness of the suspension system, the damping force of the shock absorber and the height of the car body can be changed, so that the car has good riding comfort and handling stability.

Active suspension system is a new type of suspension system controlled by computer developed in recent ten years. It combines the technical knowledge of machinery and electronics, and is a relatively complex high-tech device. For example, the French Citroen Sandia installed an active suspension system. The center of the vehicle suspension system is a microcomputer. Five kinds of sensors on the suspension system transmit data such as vehicle speed, front wheel braking pressure, the speed of stepping on the accelerator pedal, the amplitude and frequency of the vertical direction of the vehicle body, the steering wheel angle and steering speed to the microcomputer, and the computer continuously receives these data and compares them with the preset critical value to select the corresponding suspension system state. At the same time, the microcomputer independently controls the actuators on each wheel, and twitches by controlling the change of oil pressure in the shock absorber. Therefore, Sandia cars are equipped with a variety of driving modes. As long as the driver pulls the "normal" or "sports" button on the auxiliary instrument panel, the car will be automatically set in the best suspension system state to obtain the best comfort performance. The active suspension system has the function of controlling the body movement. When the inertia of automobile braking or turning distorts the spring, the active suspension system will produce a force opposite to the inertia force, reducing the change of body position. For example, the sensor of the suspension system will detect the inclination and lateral acceleration of the car body immediately when the car turns. According to the information of the sensor, the computer will compare and calculate with the preset critical value, and immediately decide where to add how much load to the suspension system, so as to minimize the inclination of the car body.

(1) Working principle of active air suspension system

Fig. 4 is the structural diagram of the electronically controlled active air suspension system of Toyota Soara luxury car. It is mainly composed of air compressor, dryer, air solenoid valve, body height sensor, air spring with shock absorber, suspension control actuator, suspension control selector switch and electronic control unit. The air compressor is driven by a DC motor to form compressed air, which is dried by a dryer and sent into the main air chamber of the air spring through an air solenoid valve through an air pipeline. When the car body needs to be lifted, the electronic control unit controls the air solenoid valve to make compressed air enter the main air chamber of the air spring (see Figure 5(b)), so that the air spring is extended and the car body is lifted; When the vehicle body needs to descend, the electronic control unit controls the solenoid valve to exhaust the compressed air in the main air chamber of the air spring to the atmosphere (see Figure 5(a)), and the air spring compresses and the vehicle body descends. There is a communication width between the primary and secondary air chambers of the air spring, and the upper part of the air spring is equipped with a suspension control actuator (not shown in the figure). The electronic control unit control that suspension actuator according to the output signal of each sensor, on the one hand, the communication valve between the main air chamber and the auxiliary air chamber of the air spring is chan, and the gas flow rate between the main air chamber and the auxiliary air chamber is changed, thereby changing the stiffness of the suspension spring; On the other hand, the actuator drives the damping force adjusting lever of the shock absorber, so that the damping force of the shock absorber also changes.

In the active air suspension system of Toyota Soara car, the car height, spring stiffness and damping force of shock absorber can be controlled at the same time, each taking three values, which are determined by the electronic control unit according to the current working condition and the control mode selected by the driver. Drivers can choose four automatic control modes at will, namely "normal automatic control" and "high automatic control" to control the height of the car body, "normal automatic control" and "high speed automatic control" to control the spring stiffness and damping force of the shock absorber. Specific control contents are as follows:

1. controlled by the spring stiffness/damping force of the shock absorber.

(1) Anti-recoil: The moving speed and displacement of the accelerator pedal are detected by sensors. When the vehicle speed is lower than 20km/h and the acceleration is high (sudden start acceleration), the ECU will adjust the spring stiffness and damping force of the shock absorber to a higher value through the actuator, so as to resist the recoil of the car body in auto start. If the driver chooses the "normal automatic control" state at this time, the spring stiffness and damping force of the shock absorber are adjusted from soft to hard; If the driver chooses the "high-speed automatic control" state at this time, the stiffness and damping force will be adjusted from it to hard.

(2) Anti-roll: The photoelectric steering sensor installed on the steering shaft detects the working state of the steering wheel. When turning sharply, ECU converts the spring stiffness and damping force of the shock absorber into high (hard) values through actuators to resist the body roll.

(3) Anti-nodding: When the vehicle speed is higher than 60 km/h, emergency braking is performed, and the ECU adjusts the spring stiffness and damping force of the shock absorber to a high (hard) value through the actuator, regardless of the control state selected by the driver, so as to resist the sagging of the front part of the vehicle body.

(4) High-speed induction: When the vehicle speed is greater than 1 10km/h, the system will adjust the spring stiffness and damping force of the shock absorber to the middle value, thus improving the handling stability at high speed. Even if the driver selects the "normal value automatic control" state (stiffness and damping are at low and soft values), the system will adjust the stiffness and damping force to intermediate values.

(5) Context control: When the vehicle speed is in the range of 30-80 km/h, if the front wheel height sensor detects that the road surface is small and uneven (such as the joint where the front wheel passes through the concrete road surface, etc.). ), the system will adjust the spring stiffness and damping force of the shock absorber to a low (soft) value before the rear wheel bumps, thus improving the ride comfort of the car. At this time, even if the driver chooses the high-speed driving state (the stiffness and damping force are intermediate values), the system will still adjust the stiffness and damping force to low (soft) values. In order not to affect the handling stability at high speed, this action only occurs when the vehicle speed is lower than 80 km/h.

(6) Poor road surface, pitching and vibration induction: when the vehicle speed is within the range of 40- 100km/h and the front wheel height sensor detects that the road surface is bumpy (for example, the vehicle passes through the damaged paved road surface, etc.). ), the system will adjust the spring stiffness and damping force of the shock absorber to the middle value to suppress the large movement of the car body, such as back and forth bumps and vibrations, so as to improve the ride comfort and passability of the vehicle, regardless of the driver's choice.

When the vehicle speed is higher than 100km/h, the system will adjust the stiffness and damping force to high (hard) values.

(7) Good road surface for normal driving: the spring stiffness and damping force of the shock absorber are selected by the driver and are in the state of "normal automatic control", and the stiffness and damping force are in low (soft) values; In the state of "high-speed automatic control", stiffness and damping force are intermediate values.

2. Body height control

The car height signal is sent by three car body height sensors on the left and right front wheels and the left rear wheel, and ECU gives instructions to adjust the car body height.

(l) High-speed guidance: When the vehicle speed is higher than 90 km/h, reduce the height of the vehicle body by one level to reduce wind resistance and improve driving stability. If the driver selects the "normal automatic control" state, the car body height value is adjusted from the intermediate value (standard value) to a low value; If the driver selects the "high value automatic control" state, the vehicle height will be adjusted from the high value to the intermediate value (standard value). When the vehicle speed is 60km/h, the vehicle height returns to its original state.

(2) Continuous bad road surface induction: When the car runs continuously on bad roads and the car height signal changes greatly by more than 2.5s and exceeds the specified value, the car height will increase by one level, so that the sudden lifting feeling from the road surface will be weakened and the passing performance of the car will be improved.

When the road is continuously blocked and the speed is more than 4 km/h and less than 90km/h, no matter what control state the driver chooses, the car will be raised to a higher value to reduce the road roughness, ensure sufficient ground clearance and improve the ride comfort.

When the vehicle speed is less than 4 km/h, the vehicle height is completely selected by the driver. When "Normal Automatic Control" is selected, the vehicle height is the intermediate value (standard value); When "high value automatic control" is selected, the vehicle height is high.

On continuous bad roads, when the vehicle speed is higher than 90km/h, no matter what control state the driver chooses, the vehicle height will be adjusted to the middle value, so as to avoid the adverse impact of excessively high vehicle body on high-speed driving stability.

In addition, it also has the function of controlling the height when parking. When the car is in the parking state, in order to balance the appearance of the car body and maintain a good parking posture, after the ignition switch is turned off, the ECU will issue instructions to keep the height of the car body in the low state of the normal mode.

(2) Working principle of active hydro-pneumatic spring suspension system.

Oil-gas spring takes gas (usually inert gas-nitrogen) as elastic medium and oil as force transmission medium. Generally, it consists of gas spring and hydraulic cylinder equivalent to hydraulic shock absorber. The stiffness characteristic is realized by oil compressing the air in the air chamber, and the variable damping characteristic is realized by solenoid valve controlling the throttle hole in the oil circuit. Fig. 6 is the layout of the active hydro-pneumatic spring suspension of Citroen XM car. As can be seen from the figure, it has five sensors for basic driving conditions.

Among them, the steering wheel angle sensor is installed on the steering column, and the information of the steering degree (speed and size) of the automobile is indirectly sent to the microcomputer through the steering wheel angle signal.

The acceleration sensor is actually an accelerator action sensor connected with the accelerator pedal, which indirectly sends the acceleration action signal to the microcomputer. The brake pressure sensor is installed in the brake pipeline. When braking, it sends a step signal to the microcomputer to indicate braking, which makes the microcomputer produce a signal output to suppress "nodding".

The speed sensor is installed on the wheel and sends out pulses proportional to the speed. Microcomputer can use it and the steering wheel angle signal to calculate the roll degree of the car body.

The body displacement sensor is installed between the body and the axle to measure the relative height between the body and the axle. The frequency and amplitude of its change can reflect the riding comfort information of the car body and also be used for automatic height adjustment.

The working principle of the system is shown in Figure 7. In fig. 7, the solenoid valve 7 is moved to the right under the instruction of the microcomputer, thereby connecting the pressure oil path and moving the spool of the auxiliary hydraulic valve 8 to the left. The middle oil-gas chamber 9 communicates with the main oil-gas chamber, which increases the volume of the total air chamber and reduces the air pressure, thus reducing the stiffness, so 9 is also called the stiffness regulator. Throttles A and B are dampers, and the system is in a "soft" state in the position shown in the above figure.

In the figure below, no current flows in solenoid valve 7. Under the action of the spring, the valve core moves to the left, closing the pressure oil passage. The pressure oil originally used to push the hydraulic valve 8 is discharged through the left oil passage of the valve 7, and the valve core moves to the right, closing the stiffness regulator 9, so that the total volume of the air chamber is reduced and the stiffness is increased, thus making the system in a "hard" state.

In the normal driving state, the system is in a "soft" state to improve the ride comfort, and in a "hard" state to improve the handling stability of the vehicle when driving at high speed, turning, starting and braking.

(3) Active suspension system with road condition prediction sensor

Fig. 8 is a schematic diagram of an active suspension with a road condition prediction sensor. The system includes a suspension spring 16 and a one-way hydraulic actuator 14, and the control valve 6 communicates with the oil pressure chamber of the one-way hydraulic actuator through an oil pipe 8. The oil pipe is also connected with the branch pipe 8a, which is connected with the accumulator 1 1. The accumulator is filled with gas, and these compressible gases can produce a spring-like effect. In addition, there is a main orifice 12 in the middle of the branch pipe to limit the oil flow between the accumulator and the oil pressure chamber, thus forming a vibration reduction effect. There is also a bypass pipeline 8b between the oil pipe and the accumulator. The bypass pipeline 8b is provided with a selector valve 10 and an auxiliary throttle 9, and the diameter of the auxiliary throttle is larger than that of the main throttle. When the selector valve is opened, oil flows between the accumulator and the oil pressure chamber through the auxiliary orifice of the selector valve, thus reducing vibration damping. With such a device, the suspension system can have two different damping parameters under the action of the selector valve.

The opening of the control valve can be changed by controlling the current to control the amount of oil entering the oil pipe, and then control the oil pressure acting on the hydraulic actuator. With the increase of current input of control valve, the bearing capacity of hydraulic actuator also increases.

In this suspension system, the signals input to the control unit ECU include: the output signal of the sensor installed on each wheel to detect the longitudinal acceleration of the vehicle body, the detection signal of whether there is a bump in front of the vehicle and its size detected by the road condition prediction sensor, the output signal of the sensor to detect the height of the vehicle body at each wheel, and the vehicle speed signal output by the vehicle speed sensor. Based on these signals, the control unit controls the control valve and the selector valve arranged on each wheel.

Fig. 9 shows the setting of the road condition prediction sensor. This kind of sensor is usually an ultrasonic sensor with a frequency of about 40kHz, which is installed in front of the car body to detect the road conditions below it.

When the vehicle runs normally, the selector valve is closed, and the oil pressure chamber of the hydraulic actuator communicates with the accumulator through the main throttle hole, which can absorb and reduce the tiny vibration caused by uneven road surface. When the road condition prediction sensor on the vehicle finds that the road surface has bumps that will cause vibration, the control unit controls the selection valve to open, reducing the damping coefficient of the suspension system to a specific value.

Fig. 10 shows the output signal of the road condition prediction sensor, and the amplitude of the output signal is proportional to the size of the bump on the road surface. If the control is completely based on the output signal of the sensor, the damping of the suspension system will change too frequently, so a low threshold value V 1 is set in the control system. In addition, if the damping coefficient of the suspension system is adjusted too low when the vehicle passes through a big bump, it may produce a great impact force and form a rigid collision between the bottom of the suspension and the axle. Therefore, a high threshold V2 is set in the control system. Only when the road condition prediction signal is between V 1 and V2, the control unit outputs a control signal to open the selection valve.

The control unit continuously detects the vehicle speed and simultaneously detects the output signal of the road sensor. According to the vehicle speed, the lag time between the measured bump and the actual wheel passing bump can be estimated. The selector valve should be opened when the wheel passes through the bump, so that the damping coefficient of the suspension only changes briefly when the wheel passes through the bump, and the selector valve will be closed again after the wheel passes through the bump.

Active suspension system with road condition prediction sensor (sonar system) can predict the road condition before the arrival of the car, thus greatly improving the working performance of the suspension. When the vehicle equipped with this system is driving on uneven roads, it may even lose control of the steering wheel. Figure 1 1 shows the suspension structure of Nissan with sonar system.