JPH0319396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a regulating device for a variable displacement pump of the type in which the actuating member can be adjusted by a pressure regulator or a flow regulator to regulate the amount delivered to a load. Regarding.

[Prior art]

As long as the pressure in the pressure regulator does not reach the operating pressure set by the spring, the actuating member of the variable displacement pump will be subject to system pressure, so that the variable displacement pump will be regulated to its maximum displacement. . When the pressure reaches the set value, the piston moves within the pressure regulator, so that the actuating member of the variable displacement pump experiences a low pressure. In this case, the stator ring of the variable displacement pump will move toward the zero position, and the feed rate will be adjusted to a value that maintains the set operating pressure.

If no liquid is drawn off by the load and the pressure therefore reaches a maximum value, the variable displacement pump is regulated to zero delivery. This is the so-called zero stroke range in which the operating pressure is maintained and only the amount of leaked oil is replenished. Variable displacement pumps operate in a zero stroke position, but require relatively high drive power.

[Purpose of the invention]

An object of the present invention is to reduce the power consumption of a hydraulic system including a variable displacement pump when the amount of feed to a load is adjusted to an extremely small amount.

[Configuration advantages of the invention]

This purpose is to provide, in accordance with the invention, a small-capacity fixed-displacement pump in parallel with a variable-displacement pump in a regulating device of the type mentioned at the outset, so that if the feed rate falls below a predetermined value, the variable-displacement pump This is accomplished by disconnecting the fixed displacement pump from the load and connecting it to the tank, while simultaneously connecting the constant displacement pump to the load to maintain operating pressure.

Therefore, variable displacement pumps and fixed displacement pumps are different from each other when the variable displacement pump is connected to the load up to the switching point of the characteristic curve, and then when the feed rate falls below a predetermined value, i.e. When operating in the zero stroke range, it is switched so that it is connected to the tank without pressure loss.

Fixed displacement pumps have a lower output than variable displacement pumps. The power ratio of both pumps may be greater than 15. That is, the sum of the drive output of the constant displacement pump and the throttling loss of the variable displacement pump connected to the tank is only a fraction of the zero stroke output of the variable displacement pump.

Once the switching point is reached and the variable displacement pump is connected to the tank, the system will not become unstable. This is because only fixed-displacement pumps are activated, which are additionally protected by a relief valve that regulates and maintains the operating pressure.

Embodiments of the invention are set out in the dependent claims.

According to claim 2, the switching point of the variable displacement pump depends on the feed rate measuring device and the adjustable reference voltage, so that when the feed rate falls below a certain value, the high-pressure circuit of the pump is activated. A directional control valve is triggered to switch from a variable displacement pump to a constant displacement pump or from a constant displacement pump to a variable displacement pump.

According to claim 3, the constant displacement pump is connected to the tank as long as the variable displacement pump is connected to the load.

Embodiments of the invention will be described below with reference to the drawings.

[Embodiments of the invention]

FIG. 1 shows a known variable displacement pump 10. As shown in FIG. Stator ring of the above pump (not shown)
In the illustrated adjustment position of the pressure regulator 15, the pressure regulator 15 is fixed between the two pistons 11, 12 which receive the system pressure of the pump high-pressure circuit 20.

When no liquid is withdrawn by the load and therefore the pressure reaches a maximum value, the delivery of the variable displacement pump is regulated to approximately zero and the pressure (referred to as zero stroke pressure) is maintained.

The zero stroke pressure of the pump high pressure circuit 20 can be set to a desired value by means of the spring 14 of the pressure regulator 15. The spring 14 initially holds the piston of the pressure regulator 15 in an output position corresponding to the illustrated switching position of the pressure regulator, and the pump high-pressure circuit 20 is connected to the space behind the piston 12. The stator ring of the variable displacement pump is thus set to maximum delivery volume.

The feed flow reaches the load 23 via the pump high-pressure circuit 20 , the directional control valve 21 and the feed rate measuring device 22 .

When the pressure reaches the value set by the spring 14, the piston of the pressure regulator 15 is moved, so that the pressure regulator 15 reaches the regulating position in which the space behind the piston 12 is regulated to a low pressure.
Thus, the piston 11 shifts the stator ring and the pump delivers only the amount necessary to maintain the set zero stroke pressure to the load. Figure 2 shows the characteristic curve.

If the load requires very little delivery, the variable displacement pump will reach a zero stroke range, but the drive power of the pump will still be relatively large.

To switch to a constant displacement pump with a smaller output than the variable displacement pump 10, the comparator 25 compares the voltage of the feed rate measuring device 22 with the target voltage 24, and the driver circuit 26 is activated based on the output voltage of the comparator. This is done by activating the directional control valve 21 and switching the directional control valve 21 using the circuit described above.

When the directional control valve 21 is switched, the variable displacement pump 10 is connected to the tank, while the constant displacement pump 30 delivers a constant delivery flow to the load. In this case, the squeezing losses that occur are extremely small.

A relief valve 33 is provided in the path between the constant displacement pump 30 and the directional control valve 21, which is set at the operating pressure and discharges the excess flow of the constant displacement pump into a tank.

As shown in FIG. 2, the switching point for disconnecting the variable displacement pump 10 and connecting the constant displacement pump 30 is at time 33. In this case, the relief valve 32 is set to exactly the same pressure as the pressure regulating valve 15 so that the same maximum pressure can be obtained in both operating modes.

As shown by the broken line in FIG. 2, the relief valve 32
can also be set to another operating pressure required for the load 23, and therefore there is a , a characteristic curve diagram is obtained.

For example, if the relief valve 32 is set to a smaller value (pressure) than the valve 15, when the directional control valve 21 is switched, that is, when the feed rate falls below a predetermined value, the load pressure will be relieved. Only the pressure value set in valve 32 is reached. Therefore, when the directional control valve 21 is switched, the pressure drops to the above value, so the variable displacement pump 10 is not affected in any way. In this further switching position of the directional control valve 21, the variable displacement pump delivers the maximum amount to the tank without pressure loss.

For regulating the variable displacement pump, instead of the illustrated pressure regulator 15, a flow regulator or a power regulator can also be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the adjusting device, and FIG. 2 is a diagram showing characteristic curves of the adjusting device of FIG. 10... Variable displacement pump, 15... Pressure regulator, 21... Directional control valve, 23... Load, 30...
...Constant displacement pump.

Claims (1)

[Scope of Claims] 1. A variable displacement pump regulating device of a type in which the actuating member can be adjusted by a pressure regulator or a flow rate regulator to adjust the amount of supply to a load, which includes a small-capacity fixed-displacement pump. 30 is a variable displacement pump 1
0, and when the feed rate falls below a predetermined value, the variable displacement pump is disconnected from the load 23 and connected to the tank, and at the same time, the constant displacement pump is connected to the load. Features an adjustment device. 2 The feed amount measuring device 22 is connected to the high pressure circuit 2 of the pump.
0, and the output signal of the measuring device is compared with an adjustable reference signal in a comparator 25, the output signal of the comparator being connected between the feed rate measuring device and the variable displacement pump. Regulation according to claim 1, characterized in that the directional control valves 21, 210 connecting the variable displacement pump to the tank are triggered at the same time as the constant displacement pump 30 is connected to the high pressure circuit of the pump. Device. 3. In one switching position, the directional control valve 21 connects the variable displacement pump 10 to the load and also the constant displacement pump 30 to the tank; in another switching position, it connects the variable displacement pump to the tank. 3. Regulating device according to claim 1, further comprising a constant displacement pump connected to the load.