When the variable displacement piston pump fails, it is related to the damage of the pump regulator after troubleshooting. In order to find out the cause of the fault, the control principle of the regulator should be analyzed first.
(1) Negative feedback control oil circuit
The negative flow control system is adopted for the main pump control of excavator, which is widely used in all kinds of excavators. When the excavator does not operate, the pressure oil output by P1 pump and P2 pump enters the oil return pipe through two throttle valves respectively through the middle oil passage of the main valve, and then returns to the hydraulic oil tank. Negative feedback pressure is generated when flowing through the overflow valve. The pressure controls the negative flow control ports of P1 pump and P2 pump respectively through PS1 pipeline and PS2 pipeline to minimize the swashplate swing angle of P1 pump and P2 pump, so as to reduce its output flow and achieve the effect of energy saving when the excavator does not act.
(2) Control principle of main pump regulator
Take the main pump regulator of P2 pump as an example. When the excavator does not act, the return oil from the middle oil passage of the main valve passes through the negative feedback pressure generated by the overflow valve, which enters the negative feedback oil port of the regulator and acts on the pilot piston to make the pilot piston compress the spring to the right and push the drive connecting rod II to drive the servo valve rod to the right. When the servo valve rod moves, the pressure oil output by P2 pump enters the large aperture section of the servo cylinder through the internal oil passage to push the servo cylinder to move to the right, so as to reduce the swashplate angle of P2 pump, so as to reduce the main pump flow and engine load.
When the excavator is in the working state, the return oil in the middle oil passage of the main valve is cut off, the pilot oil pressure in front of the throttle valve drops to zero, the pilot piston moves to the left under the action of the spring, driving the servo valve rod to the left. The output pressure oil of the main pump enters the small cavity of the servo cylinder and pushes the servo cylinder to the left, so as to increase the swashplate angle of the P2 pump and increase the displacement of the P2 pump Meet the requirements of excavator excavation.
