In the compression stroke, it means that the car wheels move closer to the body and the shock absorber is compressed. At this time, the piston in the shock absorber moves downward. The volume of the lower chamber of the piston decreases, the oil pressure rises, and the oil flows through the flow valve to the chamber (upper chamber) above the piston. The upper cavity is occupied by a part of the space by the piston rod, so the increased volume of the upper cavity is less than the reduced volume of the lower cavity, so a part of the oil will open the compression valve and flow back to the oil storage cylinder. The oil saving of these valves forms the damping force of the suspension under compression movement. When the shock absorber is stretched, the wheel is equivalent to far away from the body, and the shock absorber is stretched. At this time, the piston of the shock absorber moves upward. The oil pressure in the upper cavity of the piston increases, the flow valve is closed, and the oil in the upper cavity pushes open the expansion valve and flows into the lower cavity. Due to the existence of the piston rod, the oil flowing from the upper cavity is not enough to fill the increased volume of the lower cavity, and the lower cavity is mainly caused to generate a vacuum degree. At this time, the oil in the oil storage cylinder pushes open the compensation valve 7 and flows into the lower cavity. supplement. Because of the throttling effect of these valves, the suspension has a damping effect during extension movement.
Since the spring stiffness and pre-tightening force of the expansion valve are designed to be greater than that of the compression valve, under the same pressure, the sum of the channel load areas of the expansion valve and the corresponding normally open gap is smaller than the sum of the cross-sectional area of the compression valve and the corresponding normally open gap. This makes the damping force generated by the extension stroke of the shock absorber greater than the damping force of the compression stroke, which meets the requirements of rapid shock absorption.