I. What is an ASR control system?
The function of ASR (Action Steering) is to ensure optimal traction for a vehicle under various driving conditions. The control unit of the traction control system is a computer that detects the speed of the four wheels and the steering wheel angle. When the car accelerates, if it detects a significant difference in speed between the drive wheels and non-drive wheels, the computer immediately determines that the driving force is excessive and issues a command signal to reduce the engine's fuel supply, thereby reducing the driving force and decreasing the slip rate of the drive wheels. The computer uses a steering wheel angle sensor to understand the driver's steering intention and then uses left and right wheel speed sensors to detect the speed difference between the left and right wheels; this determines whether the car's steering degree matches the driver's steering intention. If understeer (or oversteer) is detected, the computer immediately determines that the driving force of the drive wheels is excessive and issues a command to reduce the driving force to achieve the driver's steering intention.
ASR (Automatic Throttle Control) can reduce engine power by decreasing throttle opening or control wheel slippage via brakes to control vehicle traction. In vehicles equipped with ASR, the mechanical connection between the accelerator pedal and the gasoline engine throttle (or diesel engine fuel injection pump control lever) is replaced by an electronically controlled throttle device. When sensors transmit accelerator pedal position and wheel speed signals to the control unit, the control unit generates a control voltage signal. The servo motor readjusts the throttle position (or diesel engine control lever position) based on this signal and then feeds this position signal back to the control unit for timely brake adjustment.
When a car is driving on a slippery surface, without ASR (Automatic Responsiveness), the drive wheels are prone to slipping during acceleration. If the rear-wheel drive wheels slip, the vehicle is prone to fishtailing; if the front-wheel drive wheels slip, the vehicle is prone to losing steering control. With ASR, this phenomenon is prevented or mitigated during acceleration. When turning, if drive wheel slippage occurs, the entire vehicle will veer to one side; with ASR, the vehicle will steer along the correct path.
In summary, ASR can maximize the use of the engine's driving torque to ensure stability during vehicle starting, acceleration, and steering.
The difference between ASR and ABS is that ABS prevents the wheels from locking up during braking and causing sideslip, while ASR prevents the car from sideslipping due to the drive wheels slipping during acceleration. ASR is an extension of ABS, and the two complement each other.
ASR is only installed on some high-end cars, but because ASR and ABS share similar performance and technology, it is expected that ASR will become as widespread as ABS in the next few years.
II. ASR Device Principle
1. When not braking: Both solenoid valves are not conducting. The intake solenoid valve is normally closed, the exhaust solenoid valve is normally open, and both diaphragm valves are closed under the action of their springs, so braking can be engaged at any time.
2. During braking, neither of the two solenoid valves is activated. Compressed air from the brake valve enters the right side of the diaphragm-type intake valve. Because the intake solenoid valve is closed, it cuts off the passage of compressed air to the left control chamber of the intake diaphragm. At this time, the control chamber is open to the atmosphere. Under the action of the pressure difference, the diaphragm-type intake valve opens, and compressed air enters the pipeline leading to the brake chamber. Since the exhaust solenoid valve is also not activated and is in the open state, compressed air enters the right control chamber of the diaphragm-type exhaust valve. Under the action of its spring force and air pressure, the diaphragm-type exhaust valve remains reliably closed, allowing compressed air to flow unimpeded into the brake chamber, producing a follow-up braking effect.
3. Anti-lock braking and pressure reduction: When a wheel is about to lock up, the wheel speed signal is sent to the ECU (Electronic Control Unit), which, in a duty cycle mode, activates both the intake and exhaust solenoid valves. The intake solenoid valve opens, closing the atmospheric passage, allowing compressed air to enter its diaphragm valve control chamber, thus closing the diaphragm intake valve. Meanwhile, the exhaust solenoid valve closes, cutting off the passage between the diaphragm valve control chamber and the compressed air, and opening the atmospheric passage. The diaphragm opens under the pressure difference, allowing the brake chamber to connect with the atmosphere, causing the brake pressure to drop and preventing the wheel from locking up.
4. Anti-lock braking and pressure maintenance: When the wheel angular velocity signal indicating impending lock-up is at its optimal state, the ECU only activates the intake solenoid valve, opening it and cutting off the passage between the left control chamber of the diaphragm valve and the atmosphere. Compressed air closes the diaphragm intake valve, cutting off the passage between the brake valve and the brake chamber. Since the exhaust solenoid valve remains open and its diaphragm valve remains closed, the air pressure in the brake chamber remains constant (dual valves closed).
5. Anti-lock braking system pressure increase: When the wheel speed signal of the wheel increases from the optimal state, the ECU commands both solenoid valves to deactivate, restoring normal braking state, and the air pressure in the brake chamber increases accordingly.
