Dual-parameter controlled ABS consists of a vehicle speed sensor (speed radar), wheel speed sensor, control device (computer) and actuator.
The working principle is that the vehicle speed sensor and wheel speed sensor input the vehicle speed and wheel speed signals into the computer respectively, and the computer calculates the actual slip rate and compares it with the ideal slip rate of 15% to 20%. , and then increase or decrease the braking force of the brake through the solenoid valve.
This type of drag speed sensor commonly uses Doppler speed radar. When the car is driving, the Doppler radar antenna continuously emits electromagnetic waves to the ground at a certain frequency, and at the same time receives the reflected electromagnetic waves. By measuring the difference between the car radar transmission and reception, the car speed can be accurately calculated. The wheel speed sensor is installed in the transmission housing and driven by the transmission output shaft. It is a pulse motor, and the frequency generated is proportional to the wheel speed.
The actuator is composed of solenoid valves and relays. A solenoid valve adjusts the braking force to maintain the ideal slip rate.
This kind of ABS can ensure ideal control of slip rate and good anti-lock braking performance, but due to the addition of a speed radar, the structure is more complex and the cost is higher. For example
The patent (Patent No. 92221809.9) reviewed by Shen Shusheng of the Automobile Magazine. It aims to control the angular deceleration of the wheel, control the braking force of the wheel, and achieve anti-lock braking. Its structure is mainly composed of a wheel speed sensor, a controller (computer) and a solenoid valve.
The wheel speed sensor consists of a sensor and a ring gear steel ring
2. In order to accurately measure wheel speed, there should be a 1mm gap between the sensing head and the wheel ring gear. In order to avoid the influence of water, mud and dust on the sensor, the sensor should be filled with butter before installation.
Solenoid valves are used to regulate wheel brake pressure. For a four-channel braking system, there is one solenoid valve for each wheel rim; for a three-channel braking system, there is one for each front wheel and one for both rear wheels. The solenoid valve has three hydraulic holes, which are connected to the brake master cylinder and the wheel brake branch cylinder respectively, and can realize the pressure regulation functions of pressure increase, pressure maintenance and pressure reduction. Here's how it works.
1) Boost When the solenoid valve is not working, the brake master cylinder interface and each brake branch cylinder interface are directly connected. Due to the strong strength of the main spring, the oil inlet valve opens and the brake pressure increases.
2) Pressure maintenance When the pressure in the brake cylinder of the wheel increases to a certain value, the oil inlet valve is cut off and closed. The bracket remains in the middle, and the three holes are sealed against each other to maintain braking pressure.
3) Pressure reduction When the solenoid valve works, the bracket overcomes the elastic force of the two springs and opens the unloading meat to reduce the pressure of the brake cylinder. Once the pressure is reduced, the solenoid valve switches to the pressure maintenance state or the pressure increase preparation state.
The main task of the control device ECU is to calculate, analyze, amplify and discriminate the signals returned by the sensors of each wheel, and then the output stage outputs the command signal to the solenoid valve to perform brake pressure adjustment. Task. The electronic control device consists of four parts, input stage A, controller B, output stage C, and voltage stabilization and protection device D.
The electronic controller drives the solenoid valve at a frequency of 4 to 101tz, which is something the driver cannot do.
This single-parameter control ABS is currently widely used due to its simple structure and low cost.
Most Chrysler luxury cars in the United States are equipped with ABS with this single-parameter control method. It is equipped with wheel speed sensors on all four wheels of the car. The structure is shown in Figure 4.
The distribution valve is a three-channel distribution valve located under the brake oil pump assembly.
A 45-tooth or 100-tooth ring gear is installed on the wheel axle, and the sensing head of the wheel speed sensor is installed on the top of the ring gear. When the wheel rotates, the sensor continuously generates voltage signals and inputs them into the computer. Compared with the ideal speed in the RoM, the wheel speed increase or deceleration is calculated, and a pressure increase or pressure relief command is issued to the solenoid valve to control the brake cylinder system. power.