What are the control methods for the displacement of Rexroth variable piston pumps?
Rexroth variable piston pumps can also be referred to as "Rexroth oil pumps". Of course, Rexroth oil pumps are partial Rexroth variable piston pumps and Rexroth fixed piston pumps, and we use more variable piston pumps in our life. There are several ways to control the displacement of the Nexroth oil pump as follows:
I. Guiding Ideas:
1. The pressure depends on the pressure output of the load oil pump in inverse proportion to the flow rate. In the electronically controlled state, when the external load increases, the system pressure increases. When the system pressure increases, the pressure of the front pump oil flow and the rear pump oil flow entering the rear pump increases, and the pilot secondary pressure at the outlet of the proportional valve controlled by the computer detects relevant signals also increases. The former acts on the first piston, while the latter acts on the second piston, which forces the piston to overcome the spring force and move to the left. The piston pushes the spool of the spool valve to the left to overcome the spring force of the spool valve and move it to the left so that the spool of the spool valve is in the left position.
2. The oil flow of the rear AY oil pump can act on the large end of the variable piston through the left position of the spool of the sliding valve. The oil passage here changes from normally closed to normally open. Because the cross-section area of both ends of the piston is different, the pressure acting on the large end of the variable piston in the swashplate is higher than that on the small end of the variable piston, and the piston moves to the left.
3. Drive the position change of swash plate and slide valve sleeve at the same time: make the swash plate swing angle smaller gradually, reduce the displacement of oil pump, at the same time, slide valve sleeve moves to the left, gradually cut off the oil passage connecting the variable piston cavity and the oil flow of the rear pump. When the oil port is completely cut off, the swash plate piston will not swing any more, the oil pump completes the variable, and the flow output is stable.
II. When the external load becomes small, the system pressure decreases, the three oil flow pressures acting on the first and second stage pistons become smaller, the balance between oil flow pressure and spring force is broken, the spring gradually pushes back, pushing the spool of the sliding valve to the right, connecting the oil passage of the swashplate piston large cavity with the oil drain port, and starting to reduce the pressure of the variable piston large cavity. When the pressure of the variable piston small cavity is greater than the pressure of the large cavity, the piston moves to the right.
III. Drive the change of swash plate and sliding valve sleeve at the same time: make the angle of swash plate larger gradually and increase the displacement of oil pump; At the same time, the sliding sleeve of the sliding valve moves to the right and closes the oil passage between the large cavity of the swashplate piston and the oil drain port step by step. When the spring force and oil flow pressure form a new balance and the oil passage between the large cavity of piston and the oil drain port is completely cut off, the plunger does not move any more. At this time, the swashplate does not oscillate any more, the oil pump completes the variable and the flow output is When the external load changes, the balance between oil flow pressure and spring force is broken again, and the displacement also changes. They always change with the load and are in a dynamic balance.
IV. Electronically controlled state: the control hydraulic signal related to displacement change is the oil flow of the front pump, the oil flow of the rear pump and the pilot oil and negative flow. The oil flow of the front and rear pump directly controls the oil pump. The pilot oil is throttled by the electric proportional valve and then controls the oil pump. We can call it the pilot secondary pressure. Now let's take pump control as an example to analyze the displacement variation.