Working principle of transmission solenoid valve
The transmission solenoid valve plays a vital role in the operation of the automobile transmission. Its main function is to control the mechanical valve to complete the switching of the oil circuit and the pressure regulation of the oil circuit flow, which is controlled by the transmission electronic control module TCU.
In terms of structure and working mode, the solenoid valve generally adopts a two-position three-way valve or a three-position three-way valve. Simply put, it is like a faucet. Different openings have different hydraulic oil flows and different pressures. In neutral and in gear, the pressure is basically a constant value, but during the shifting process, the TCU will adjust the opening of the solenoid valve to improve the smoothness of the shifting.
From the working principle type of the transmission solenoid valve, it can be roughly divided into the following situations:
For single-solenoid coil solenoid valve (single coil): the valve core changes direction after power is turned on, but it will recover after power is turned off.
Double-solenoid coil solenoid valve (double coil): the valve core changes direction after one side is powered on, and the valve core will not return after power is turned off. It will return only after the coil on the other side is powered on. This is like an electrically controlled switch. The ECU (engine control unit) determines whether to shift gears through various sensor feedback signals, and then conducts the oil circuit through the solenoid valve to change gears. In the hydraulic system, the solenoid valve is also divided into pilot control and direct drive control. The control pressure and flow of the pilot solenoid valve are relatively low, and it cannot directly drive the actuator, but can only provide pilot control pressure; the direct drive solenoid valve has a greater electromagnetic force than the pilot valve, and the control pressure and flow can directly drive the actuator. In addition, there is a solenoid valve product called proportional solenoid.
Compared with other solenoid valves, it only has an electromagnetic part that provides electromagnetic force, and the hydraulic part is integrated on the hydraulic valve body. It is designed by the customer according to the specific system requirements. Although this is more flexible, it also increases the difficulty of integrating the hydraulic system.
In the hydraulic system of the automatic transmission of the car, the types of solenoid valves can be further divided into:
Switch type solenoid valve: controlled by the switch signal output by the computer, its state has only two positions: on and off. Most of them are used for shift oil circuit control, and early vehicles also use it for locking clutch control.
Proportional solenoid valve: The throttle valve is controlled by a proportional solenoid. The output pressure of the throttle valve is in linear proportion to the input current of the solenoid. It is used for hydraulic control of the shift oil circuit, main oil pressure, accumulator back pressure, locking clutch, etc.
Duty ratio solenoid valve: It is controlled by the duty ratio signal output by the computer. Its valve core has countless positions for expansion and contraction. It is also used for hydraulic control of the shift oil circuit, main oil pressure, accumulator back pressure, locking clutch, etc.
The gearbox solenoid valve uses the reversing function of the two-position three-way solenoid valve to make the oil pressure of the brake cylinder constantly reciprocate between pressure increase, pressure maintenance, and pressure relief. It can reciprocate thousands of times per second, so that the wheel is in a critical state of sliding and locking, so that the wheel has sufficient adhesion, so as to prevent the car from losing control during braking.
