Working principle:
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When the proportional valve is not working, the differential piston is in the upper limit position under the action of spring. At this time, the valve remains open, so it is in the initial stage of synchronous growth of input control pressure and output pressure from zero, and it is always equal. But the hydraulic force above the piston is greater than the hydraulic force below the piston.
In the process of synchronous increase of input and output pressure, when the difference of hydraulic action between the upper and lower ends of the piston exceeds the preload of the spring, the piston starts to move down. When the input and output pressure increases to a certain value, the valve seat in the piston cavity contacts with the valve, and the oil inlet cavity and the oil outlet cavity are isolated. This is the balance state of the proportional valve.
If the input pressure is further increased, the piston will pick up and the valve will open again. The fluid continues to flow into the outlet chamber, increasing the output pressure, but the piston drops to the balance position.
The working point of the proportional valve to control the rear wheel pipeline pressure has nothing to do with the load of the car. This is the non load sensing proportional valve. In order to make its working point adapt to the vehicle load, it is necessary to change the spring force, which is the load sensing proportional valve.
Function of load sensing proportional valve:
The assembly is connected in series in the service hydraulic brake pipeline, and the brake pressure of the rear wheel of the vehicle under different loads is adjusted in proportion to make full use of the adhesion conditions to produce as much brake force as possible; at the same time, the slip phenomenon caused by the first locking of the rear wheel during the service brake is avoided to ensure the direction stability of the vehicle brake.