Rexroth's hydraulic pump has a small displacement and needs to adjust the variable piston to increase the swash plate angle. The oil discharge in the middle position is not zero, and the inclination angle of the swash plate of the A10VSO variable pump is zero, which is called the middle position. At this time, the output flow of the pump should be zero. For a swash plate plunger pump controlled by a solenoid valve, the swash plate and the cylinder are at a certain angle, so when the cylinder rotates, the plunger reciprocates in the cylinder, turning from 0° to 180°, that is, turning to the position of the upper plunger. The volume of the cylinder gradually increases, and the liquid is sucked into the cylinder through the oil suction port of the oil divider plate; when the plunger rotates from 180° to 360°. The volume of the plunger cylinder gradually decreases, and the liquid in the cylinder is discharged through the outlet of the oil distribution plate. As long as the drive shaft keeps rotating, the pump keeps working. Changing the magnitude of the current in the solenoid valve changes the angle of the tilting element, thereby changing the stroke length of the plunger in the pump cylinder, that is, changing the flow rate of the pump. The fixed inclination angle is called a quantitative pump, and the variable inclination angle is called a variable pump.