Electronically Controlled State

Electronically controlled state: The control hydraulic signal related to the displacement change is the oil flow of the front pump, the oil flow of the back pump and the pilot oil and negative flow. The oil flow of the front and back pump directly controls the oil pump, and the pilot oil throttles through the electric proportional valve and then controls the oil pump. We can call it the pilot secondary pressure. Next, we will take pump control as an example to analyze the change of displacement.

First of all, we must define several concepts.

1. The source signals of displacement control are: the front pump oil flow, the back pump oil flow and the pilot secondary oil flow and negative flow. The front pump oil flow controls the first piston, and the back pump oil flow controls the first piston and the swashplate piston (one end controls the small end of the swashplate piston, which is in the normal open state, the other end controls the main pressure piston), the negative flow controls the first piston and the second pilot piston. Secondary Piston Controlled by Secondary Oil Flow

2. The control element is

Slide valve: It is a three-way three-way valve. It consists of a spool and a slip sleeve, which can move relative to each other. The movement of the spool is balanced by the first piston and the second piston at the right end of the spool and the spring at the left end of the spool. The sliding sleeve movement is controlled by the swashplate piston. It moves with the swashplate piston movement, and its moving distance and direction are the same as that of the swashplate piston.

(2) Secondary piston: In the electronically controlled state, the pilot secondary oil flow controls the secondary piston separately, and the negative flow does not take part in direct control, but collects its pressure parameters by the negative pressure sensor and provides them to the computer. The pilot secondary oil flow is controlled as a parameter to control the current of the proportional valve by the computer. In the electronically controlled state, the pilot secondary oil flow is cut off by the hydraulic control valve instead of participating in the control. For the control of the second piston, the negative flow rate alone directly controls the second piston. The working direction of the second piston is to push the spool of the sliding valve to the left, which is balanced by the return of the self-contained spring.

The first piston is controlled by the front pump oil flow, the back pump oil flow and the pilot primary oil flow (only in the state of hydraulic control). Its working direction is to push the spool of the slide valve to the left, and to return from the self-contained spring to form balance.

3. The actuator is a variable piston:

The variable piston consists of a fixed piston sleeve and a plunger with different cross-sectional area at both ends. The plunger is connected with the inclined plate and the slide valve sleeve. When the pressure difference between the two ends is produced, the plunger drives the other two to move together.

Next, we will analyze the specific relationship between the pressure and flow control in the hydraulic system in the middle of the oil pump.

Guidelines: 1. Pressure depends on the load. 2. The output pressure of the oil pump is inversely proportional to the flow rate.

In the state of electronic control, when the external load increases, the system pressure increases. When the system pressure increases, the pressure of the front and rear pump oil flows into the rear pump increases. The pilot secondary pressure of the proportional valve outlet controlled by computer detection signals also increases. The former acts on the first piston, and the latter acts on the second piston. Both of them push the piston to overcome the spring force and move to the left. The piston pushes the spool of the sliding valve to the left to overcome the spring force of the spool and make the spool of the sliding valve move to the left. At this time, the oil flow of the AY oil pump can act on the large end of the variable piston through the left end of the spool of the sliding valve. The oil passage here changes from normal closed to normal, because the cross-section area of the two ends of the piston varies, the pressure acting on the large end of the variable piston of the inclined disc is greater than that on the small end of the variable piston. The plunger moves to the left, and at the same time drives the position of the swash plate and the slide valve sleeve to change: the swash angle decreases gradually, the displacement of the oil pump decreases, and the slide valve sleeve moves to the left, and gradually cuts off the oil passage connecting the variable piston chamber and the back pump oil flow. When the oil outlet is completely cut off, the swash plate piston is stationary, then the swash plate no longer sways, the pump completes the variable, and the flow output is stable. When the external load decreases, the system pressure decreases, the three oil pressure acting on the first and second piston decreases, the balance between oil pressure and spring force is broken, the spring gradually pushes back, pushes the spool of the slide valve to the right, connects the large chamber oil passage of the swashplate piston with the oil outlet, and begins to reduce the large chamber pressure of the variable piston. When the small chamber pressure of the variable piston is greater than the large chamber pressure, the pressure of the variable piston starts to decrease. The plunger moves to the right while driving the change of the swashplate and the slide valve sleeve: the swashplate angle increases gradually and the displacement of the pump increases; at the same time, the slide valve sleeve moves to the right and closes the oil passage between the large cavity of the swashplate piston and the oil outlet step by step. When the spring force and the oil flow pressure form a new balance and the oil passage between the large cavity of the piston and the oil outlet is completely cut off, the plunger does not move at this time, the swashplate piston no longer moves. No more swing, the pump completes variables, and the flow output is stable. When the external load changes, the balance between oil flow pressure and spring force breaks again, and displacement changes with it. They always change with the change of load and are in a dynamic balance.

Hydraulic control state

In the state of hydraulic control, its working principle is the same, but there is a pilot primary pressure acting on the first piston, and the action on the second piston is only controlled by negative flow.