ABS controlled by two parameters consists of speed sensor (speed radar), wheel speed sensor, control device (computer) and actuator. Its working principle is that the vehicle speed and wheel speed signals are respectively input into the computer by the vehicle speed sensor and the wheel speed sensor, and the actual slip rate is calculated by the computer and compared with the ideal slip rate 15%-20%, and then the braking force of the brake is increased or decreased by the solenoid valve.
This kind of resistance sensor usually uses Doppler velocimetry radar. When the car is running, the Doppler radar antenna constantly 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 automotive radar transmission and reception, the speed of the car 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 its frequency is directly proportional to the wheel speed.
The actuator consists of solenoid valve and relay. The solenoid valve adjusts the braking force to maintain the ideal slip rate. This kind of ABS can ensure the ideal control of slip rate and has good anti-lock braking performance, but due to the addition of a speed measuring radar, the structure is more complicated and the cost is higher. For example, the patent (patent number 9222 1809.9) reported by Shen Shusheng, an automobile magazine. 2. Single parameter control
The purpose is to control the angular deceleration of the wheel, control the braking force of the wheel and realize anti-lock braking. Its structure is mainly composed of wheel speed sensor, controller (computer) and solenoid valve.
The wheel speed sensor consists of a sensor and a ring gear steel ring.
1 .cable 2. Permanent magnet 3. A housing 4, an induction coil 5, and a polar shaft 6. ring gear
In order to accurately measure the wheel speed, there should be a gap of 1 mm between the sensor head and the wheel gear ring. In order to avoid the influence of water, mud and dust on the sensor, the sensor should be filled with butter before installation.
Solenoid valve is used for pressure adjustment of wheel brake. For a four-channel braking system, one wheel has a solenoid valve; Three-channel braking system, one for each front wheel and one for two rear wheels. The solenoid valve has three hydraulic holes, which are respectively connected with the master brake cylinder and the wheel brake cylinder, and can realize the pressure adjustment functions of boosting, maintaining and reducing pressure. The working principle is as follows.
1) Boost: When the solenoid valve is not working, the brake master cylinder interface is directly connected with each brake cylinder interface. Due to the force of the main spring, the oil inlet valve opens and the braking pressure increases.
2) Pressure maintenance: When the pressure in the wheel brake cylinder increases to a certain value, the oil inlet valve is cut off and closed. The bracket is kept in the middle state, and the three holes are sealed with each other to maintain the braking pressure.
3) Depressurization: When the solenoid valve works, the bracket overcomes the elasticity of two springs, opens the unloading meat, and reduces the pressure of the brake cylinder. Once the pressure is reduced, the solenoid valve is switched to the pressure holding state or the pressurization preparation state.
The main task of the control device ECU is to calculate, analyze, amplify and judge the signals sent back by the sensors of each wheel, and then the output stage outputs command signals to the solenoid valve to perform the task of brake pressure adjustment. The electronic control device consists of four parts: input stage A, controller B, output stage C and voltage stabilizing protection device D. 。
The electronic controller drives the solenoid valve at a frequency of 4- 10 1tz, which the driver cannot do.
This single-parameter control mode of ABS is widely used at present because of its simple structure and low cost.
Most Chrysler luxury cars in the United States are equipped with ABS with this single parameter control mode. It is equipped with wheel speed sensors on all four wheels of the car. The distribution valve is a three-channel distribution valve located under the brake oil pump assembly.
The wheel shaft is equipped with a gear ring with 45 teeth or 100 teeth, and the sensing head of the wheel speed sensor is installed at the top of the gear ring. When the wheel rotates, the sensor constantly generates a voltage signal, which is input into the computer, and compared with the ideal speed in RoM, the speed increase or deceleration of the wheel is calculated, and the command of boosting or depressurizing is sent to the solenoid valve to control the braking force of the cylinder.