JPH0874743A - Control circuit for variable displacement pump - Google Patents

Abstract

PURPOSE: To modify the pump for making use of the reserve power of an engine driving the pump. CONSTITUTION: Pressure at the discharge side 26 will never be led to a regulator 32 before the pressure P2P at the discharge side 26 of a constant capacity pump P2 reaches the operating pressure Pr of a relief valve 56. Since the pressure of a variable cylinder chamber 54 is regarded as the pressure of drain 60, a plunger pump P1 is so controlled as to be similar to a case where a hydraulic circuit C2 is unused. By this constitution, the input torque of the plunger pump P1 will never decreased before the pressure P2P at the discharge side 26 of the constant capacity pump P2 reaches the operating pressure Pr of the relief valve 56, and input torque to the constant capacity pump P2 is provided by the reserve power of an engine. Therefore, the reserve power of the engine can thereby be made use of by the driving torque of the constant capacity pump P2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a variable displacement pump driven by an engine.

[0002]

2. Description of the Related Art Conventionally, there has been a hydraulic machine such as a construction machine, which operates one pump out of a plurality of pumps driven by an engine as a variable displacement pump at all times and operates other pumps according to a working condition. is there.

In such a hydraulic machine, the regulator horsepower set in the regulator for controlling the discharge amount of the variable displacement pump is, for example, as shown in FIG. 3, to avoid engine stall in a region where the engine speed is low. In addition, the maximum input torque Tp to the variable displacement pump is set while maintaining the torque surplus Ts with respect to the minimum value Tmin of the engine output torque T. Therefore, as the engine speed increases, the actual engine output torque T becomes significantly larger than the maximum input torque Tp. For example, at the engine speed Tm at which the engine output torque T reaches the maximum value Tmax, Tm
Although there was an engine reserve of ax-Tp = ΔT, it could not be used effectively.

In Japanese Patent Laid-Open No. 4-63975, in a hydraulic circuit including a variable displacement pump P1 and a constant displacement pump P2, as shown in FIG. 4, the discharge side pressure P2p of the constant displacement pump P2 is P2p = 0 to 0. Setting circuit pressure (Ps) [kg
f / cm ² ] (A to C in FIG. 4), by increasing or decreasing the input torque of the variable displacement pump P1 according to P2p, the total torque applied to both pumps becomes the above-mentioned maximum input torque Tp. A control circuit for a variable displacement pump that adjusts as described above is disclosed. According to the technique disclosed in Japanese Patent Laid-Open No. 4-63975, it is possible to effectively use the engine torque corresponding to the maximum input torque Tp, but there is room for improvement in the use of the above engine surplus.

[0005]

SUMMARY OF THE INVENTION The present invention aims to improve the effective utilization of the engine surplus capacity existing in the above-mentioned prior art.

[0006]

As a means for solving the above problems, a control circuit for a variable displacement pump according to claim 1 is configured so that the displacement of a variable displacement pump driven by an engine is driven by the engine. In a control circuit of a variable displacement pump including a regulator that controls according to the pressure of the discharge side circuit of another pump, when the pressure of the discharge side circuit of the other pump is less than a preset connection pressure, Pipe line disconnecting means is provided for cutting off a pipe line for guiding the pressure of the discharge side circuit of the pump to the regulator, and for communicating the pipe line when the pressure of the discharge side circuit of the other pump reaches the connection pressure. It is characterized by that.

A control circuit for a variable displacement pump according to a second aspect is the control circuit for a variable displacement pump according to the first aspect, in which the relief valve whose operating pressure is the connection pressure is used as the pipe passage disconnecting means. It is characterized by being installed in the road. A control circuit for a variable displacement pump according to a third aspect is the control circuit for a variable displacement pump according to the first aspect, wherein the pressure of a discharge side circuit of the other pump is equal to or higher than the connection pressure as the conduit disconnecting means. A pressure switch that is turned on at times and a solenoid valve that connects the pipeline when the pressure switch is on and shuts off the pipeline when the pressure switch is off are provided.

[0008]

In the control circuit for a variable displacement pump according to claim 1, which has the above-mentioned structure, the conduit disconnecting means is provided when the pressure in the discharge side circuit of another pump is less than the preset connection pressure. The line for guiding the pressure of the discharge side circuit of the pump to the regulator is shut off, and the line is connected when the pressure of the discharge side circuit of another pump reaches the connection pressure.

That is, when the pressure of the discharge side circuit of the other pump is less than the connection pressure, the pressure of the discharge side circuit of the other pump is not guided to the regulator, so that the input torque of the variable displacement pump due to the action of the regulator is increased. There is no decrease. Therefore, the engine drives the other pump while driving the variable displacement pump with the maximum input torque Tp, for example. Therefore, the portion used as the driving force in the output of the engine becomes the maximum input torque Tp + the driving torque of the other pumps, so that the engine surplus power can be effectively used for the driving torques of the other pumps.

In a control circuit for a variable displacement pump according to a second aspect, a relief valve which is activated when the pressure in the discharge side circuit of another pump becomes equal to or higher than the connection pressure to communicate the pipeline,
Since the pipe is connected to the pipe as the pipe disconnecting means, the same operation and effect as in claim 1 can be obtained with a simple device configuration.

In the control circuit of the variable displacement pump according to the third aspect, the pressure switch is turned on when the pressure of the discharge side circuit of the other pump is equal to or higher than the connection pressure. The solenoid valve is
When the pressure switch is on, the line is connected, and when the pressure switch is off, the line is shut off. Since the solenoid valve is used, the configuration is slightly more complicated than that of the second aspect, but the disconnection of the pipeline and the switching of the communication are more accurate.

[0012]

Next, two embodiments of the present invention will be described. (Embodiment 1) This Embodiment 1 is an example in which the present invention is applied to a hydraulic pressure generator mounted on a construction machine (not shown) to supply hydraulic oil, and an example in which a relief valve is used as a pipe passage disconnecting means. is there.

As shown in FIG. 1, the hydraulic pressure generator 10 includes:
Plunger pump P driven by an engine (not shown)
1, a constant-volume pump P2 and a constant-volume pilot pump P3 are provided. The plunger pump P1 and the constant-volume pump P2 are driven independently of each other, but the pilot pump P3 has a structure interlocking with the constant-volume pump P2. is there.

The suction side 18 of the plunger pump P1 is connected to the hydraulic oil tank 20, and the discharge side 22 is connected to the hydraulic circuit C1. Similarly, the suction side 2 of the constant volume pump P2
4 is connected to the hydraulic oil tank 20, and the discharge side 26 is connected to the hydraulic circuit C2. In addition, the pilot pump P3
Of the constant volume pump P2 is branched from the suction side 24 of the constant capacity pump P2, and the branch 30 of the discharge side 28 is connected to the hydraulic oil tank 20 via the relief valve 31, and the pressure on the discharge side 28 is substantially constant. Maintained at pilot pressure.

In this hydraulic pressure generator 10, a well-known regulator 32 for controlling the discharge amount of the plunger pump P1 by changing the tilt angle of the plunger pump P1.
Is provided. This regulator 32 has a plunger connected to the ram piston 38 by reciprocally displacing a ram piston 38 having a large diameter side inserted in a large diameter cylinder 34 and a small diameter side inserted in a small diameter cylinder 36 between the cylinders 34, 36. The configuration is such that the tilt angle of the pump P1 is changed.

The small diameter cylinder 36 is connected to the discharge side 22 of the plunger pump P1 via a check valve 40 by a pipe (not shown), and the large diameter cylinder 34 is connected to a check valve via a throttle control valve 42. It is connected to 40. A pilot pressure piston 44 and a fluctuating pressure piston 46 for controlling the position of the throttle control valve 42 are connected to the throttle control valve 42. Pilot pressure piston 44
Is inserted into the pilot pressure cylinder 48, and the pilot pressure cylinder 48 is connected to the discharge side 28 of the pilot pump P3 via the pilot line 50.

The fluctuating pressure piston 46 is inserted through the main cylinder chamber 52 and the fluctuating cylinder chamber 54, and the main cylinder chamber 52 is connected to the discharge side 22 of the plunger pump P1 via the check valve 40. There is. On the other hand, the fluctuating cylinder chamber 54 is provided with the relief valve 5 installed in the connection pipe 55.
It is connected to the discharge side 26 of the constant capacity pump P2 via 6. The operating pressure Pr of the relief valve 56 is set to be lower than the circuit setting pressure P2s of the discharge side 26 of the constant displacement pump P2, and when the relief valve 56 operates,
The pressure on the discharge side 26 is introduced into the fluctuating cylinder chamber 54.
Furthermore, a drain 60 is connected to the secondary side of the relief valve 56 in the connecting pipe 55 via a throttle 58.

The secondary side 40a of the check valve 40 is connected to the pilot line 50 via the check valve 62, and either the pressure on the discharge side 22 of the plunger pump P1 or the pressure on the pilot line 50 is determined. This is a configuration in which a high pressure is introduced. In the regulator 32 described above, as the force acting on the fluctuating pressure piston 46 increases (the hydraulic pressure introduced into the main cylinder chamber 52 and the fluctuating cylinder chamber 54 increases), the position of the throttle control valve 42 is displaced to the right in the figure, The hydraulic oil flows into the large-diameter cylinder 34, and the ram piston 38 is displaced rightward in the drawing to reduce the discharge flow rate of the plunger pump P1. On the other hand, if the force acting on the fluctuating pressure piston 46 becomes smaller, the ram piston 38 is displaced leftward in the figure contrary to the above, and the discharge flow rate of the plunger pump P1 is increased.

Next, the hydraulic pressure generator 1 having the above-mentioned structure
The operation of 0 will be described. First, the plunger pump P
When only the hydraulic circuit C1 connected to 1 is used and there is almost no load on the hydraulic circuit C2 on the constant displacement pump P2 side, the pressure P2p on the discharge side 26 of the constant displacement pump P2 is the operating pressure of the relief valve 56. Since it does not reach Pr, discharge side 2
The pressure P2p of 6 is not introduced into the regulator 32, and the pressure of the fluctuating cylinder chamber 54 becomes the pressure (= 0) of the drain 60. Therefore, the hydraulic pressure introduced to the regulator 32 is only the hydraulic pressure P1p on the discharge side 22 of the plunger pump P1 and the hydraulic pressure (pilot pressure) on the discharge side 28 of the pilot pump P3. As a result, the plunger pump P1 is controlled according to the pressure P1p on the discharge side 22 of the plunger pump P1 or the pilot pressure, and is operated at the maximum input torque Tp (see FIG. 4). In this case, the plunger pump P1
The relationship between the discharge amount Q1 and the discharge pressure P1p is represented by the line A in FIG.

When the hydraulic circuit C2 on the constant capacity pump P2 side is used, the pressure P2p on the discharge side 26 increases as the load increases, but as long as this pressure does not reach the operating pressure Pr of the relief valve 56, The pressure on the discharge side 26 is not guided to the regulator 32, and the pressure in the fluctuating cylinder chamber 54 is set to the pressure (= 0) in the drain 60. Therefore, the plunger pump P1 does not use the hydraulic circuit C2 described above. It is controlled as in the case.

When the pressure on the discharge side 26 further rises to the operating pressure Pr of the relief valve 56, the relief valve 56 operates and the pressure P2p on the discharge side 26 is guided to the regulator 32. Therefore, the plunger pump P1 has a pressure P2p on the discharge side 26 of the constant displacement pump P2 and a discharge side 22 of itself.
Is controlled according to the pressure P1p or the pilot pressure. In this case, the relationship between the discharge amount Q1 of the plunger pump P1 and the discharge pressure P1p is the relationship shown by the line B in FIG.
That is, the input torque of the plunger pump P1 is reduced in proportion to the input torque of the constant displacement pump P2, and the total input to both pumps is prevented from exceeding the output of the engine.

When the pressure P2p on the discharge side 26 is in the range of the operating pressure Pr of the relief valve 56 to the set circuit pressure Ps, the plunger pump P1 is on the discharge side 2 on the constant volume pump P2 side.
The pressure is controlled between the line B and the line C in accordance with the pressure P2p of No. 6 and the pressure P1p of the discharge side 22 of its own or the pilot pressure. The input torque of the plunger pump P1 is increased or decreased according to the input torque of the constant displacement pump P2, and the total input to both pumps is prevented from exceeding the output of the engine.

As described above, while the pressure P2p on the discharge side 26 on the constant displacement pump P2 side does not reach the operating pressure Pr of the relief valve 56, the plunger pump P1 is the same as when the hydraulic circuit C2 is not used. Since it is controlled, the input torque of the plunger pump P1 is not reduced from line A → line B shown in FIG. 4 unlike the prior art. That is, the input torque to the constant displacement pump P2 is covered by the remaining power of the engine. Therefore, the remaining power of the engine can be effectively used by the driving torque of the constant displacement pump P2. (Embodiment 2) This embodiment 2 is an example in which the present invention is applied to a hydraulic pressure generator that is mounted on a construction machine (not shown) and supplies hydraulic oil, as in Embodiment 1. It is different from the first embodiment in that a pressure switch and a solenoid valve are provided. Since the configuration other than the conduit disconnecting means (pressure switch and solenoid valve) is the same as that of the first embodiment, the same part numbers as those of the first embodiment are used for the respective parts, and the detailed description thereof will be omitted.

As shown in FIG. 2, a two-position, two-port solenoid valve 72 is provided in the connection line 55 of the hydraulic pressure generator 70. In the non-energized state, the solenoid valve 72 cuts off the communication between the fluctuating cylinder chamber 54 and the discharge side 26 of the constant capacity pump P2 as shown in the figure, and the pressure in the fluctuating cylinder chamber 54 becomes the pressure (= 0) of the drain 74. To be done. On the other hand, the solenoid valve 72
When energized and the position is switched, the variable cylinder chamber 54 and the discharge side 26 of the constant volume pump P2 are communicated with each other.

The discharge side 26 of the constant volume pump P2 is equipped with a pressure switch 76 which is turned off when the pressure P2p on the discharge side 26 is less than the set pressure Pr and turned on when the pressure P2p is equal to or higher than the set pressure Pr. The solenoid valve 72 and the pressure switch 76 described above are electrically connected to a control panel (not shown),
The power to the solenoid valve 72 is cut off depending on whether the pressure switch 76 is turned on or off.

The hydraulic pressure generator 7 configured as described above
At 0, when only the hydraulic circuit C1 connected to the plunger pump P1 is used and there is almost no load on the hydraulic circuit C2 on the constant displacement pump P2 side, the pressure P2p on the discharge side 26 of the constant displacement pump P2 is Since the set pressure Pr of the pressure switch 76 has not been reached, the pressure switch 76 is off and the solenoid valve 72 is not energized. Therefore, the pressure P2p on the discharge side 26 is not introduced into the regulator 32, and the pressure in the fluctuating cylinder chamber 54 becomes the pressure (= 0) in the drain 74. Therefore, the hydraulic pressure introduced to the regulator 32 is only the hydraulic pressure P1p on the discharge side 22 of the plunger pump P1 and the hydraulic pressure (pilot pressure) on the discharge side 28 of the pilot pump P3. As a result, the plunger pump P1 is controlled according to the pressure P1p on the discharge side 22 of the plunger pump P1 or the pilot pressure, and is operated at the maximum input torque Tp (see FIG. 4). In this case, the plunger pump P1
The relationship between the discharge amount Q1 and the discharge pressure P1p is represented by the line A in FIG.

When the hydraulic circuit C2 on the constant displacement pump P2 side is used, the pressure P2p on the discharge side 26 rises as the load increases, but as long as this pressure does not reach the set pressure Pr of the pressure switch 76, the electromagnetic pressure is reduced. The valve 72 is not energized. Therefore, the pressure on the discharge side 26 is not guided to the regulator 32, and the pressure in the fluctuating cylinder chamber 54 is set to the pressure (= 0) in the drain 74, so that the plunger pump P1 is used by the hydraulic circuit C2 described above. It is controlled in the same way as when it is not done.

When the pressure P2p on the discharge side 26 further rises to the set pressure Pr of the pressure switch 76, the pressure switch 76 is turned on and the solenoid valve 72 is energized to switch the position. As a result, the connection conduit 55 is brought into communication, and the pressure P2p on the discharge side 26 is guided to the regulator 32. Therefore, the plunger pump P1 has a pressure P2p on the discharge side 26 on the constant volume pump P2 side and a discharge side 22 on its own side.
Is controlled according to the pressure P1p or the pilot pressure. In this case, the relationship between the discharge amount Q1 of the plunger pump P1 and the discharge pressure P1p is the relationship shown by the line B in FIG.
That is, the input torque of the plunger pump P1 is reduced in proportion to the input torque of the constant displacement pump P2, and the total input to both pumps is prevented from exceeding the output of the engine.

When the pressure P2p on the discharge side 26 is in the range from the set pressure Pr of the pressure switch 76 to the set circuit pressure Ps, the plunger pump P1 discharges the pressure P2p on the discharge side 26 on the constant volume pump P2 side and its own discharge. Pressure P1p on side 22
Alternatively, it is controlled between the line B and the line C according to the pilot pressure. The input torque of the plunger pump P1 is increased or decreased according to the input torque of the constant displacement pump P2, and the total input to both pumps is prevented from exceeding the output of the engine.

As described above, while the pressure P2p on the discharge side 26 on the constant volume pump P2 side does not reach the set pressure Pr of the pressure switch 76, the plunger pump P1 operates on the hydraulic circuit C2.
Is controlled in the same manner as when not used, the input torque of the plunger pump P1 is the same as in the prior art.
There is no reduction from line A to line B shown in FIG.
That is, the input torque to the constant displacement pump P2 is covered by the remaining power of the engine. Therefore, the remaining power of the engine can be effectively used by the driving torque of the constant displacement pump P2.

The second embodiment has a slightly more complicated structure than the first embodiment in that the solenoid valve 72 and the pressure switch 76 are required, but the disconnection of the connecting pipe 55 and the switching of the communication are more accurate. Becomes Although the present invention has been described above according to the two embodiments, it is needless to say that the present invention is not limited to such embodiments and can be variously implemented without departing from the gist of the present invention.

[0032]

As described above, according to the control circuit of the variable displacement pump according to the first aspect, when the pressure of the discharge side circuit of the other pump is less than the connection pressure, the variable displacement pump is operated by the regulator. Since there is no decrease in the input torque of, the engine drives the variable displacement pump, for example, with the maximum input torque Tp while driving the other pumps. Therefore, the portion used as the driving force in the output of the engine is the maximum input torque Tp + the driving torque of the other pumps, so that the engine surplus can be effectively used for the driving torques of the other pumps. .

According to the control circuit of the variable displacement pump of the second aspect, the same effect as that of the first aspect can be obtained with a simple device configuration. According to the control circuit of the variable displacement pump described in claim 3, the configuration is slightly more complicated than that in claim 2, but the interruption of the pipeline and the switching of the communication are more accurate.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic pressure generator according to a first embodiment.

FIG. 2 is a hydraulic circuit diagram of a hydraulic pressure generator according to a second embodiment.

FIG. 3 is an engine torque diagram showing a relationship between engine output torques of Examples 1 and 2 and a conventional example and maximum input torque of a variable displacement pump.

FIG. 4 is a pump horsepower diagram of the variable displacement pumps according to the first and second embodiments and the conventional example.

[Explanation of symbols]

10 ... Oil pressure generator, 22 ... Discharge side, 26 ...
・ Discharge side (discharge side circuit), 32 ... Regulator, 5
5 ... Connection pipe (pipe), 56 ... Relief valve, 7
0 ... Oil pressure generator, 72 ... Solenoid valve, 76 ...
Pressure switch, P1 ... Plunger pump (variable displacement pump), P2 ... Constant displacement pump (other pump), P
3 ... Pilot pump, Pr ... Operating pressure, set pressure (connection pressure).

Claims (3)

[Claims] 1. A control circuit for a variable displacement pump, comprising a regulator for controlling a discharge amount of a variable displacement pump driven by an engine according to a pressure of a discharge side circuit of another pump driven by the engine, When the pressure of the discharge side circuit of the other pump does not reach the preset connection pressure, the conduit for guiding the pressure of the discharge side circuit of the other pump to the regulator is shut off, and the discharge side circuit of the other pump is cut off. A control circuit for a variable displacement pump, characterized in that a conduit disconnecting means is provided for communicating the conduit when the pressure reaches the connection pressure. 2. The control circuit for the variable displacement pump according to claim 1, wherein a relief valve whose operating pressure is the connection pressure is interposed in the conduit as the conduit disconnection means. 3. A pressure switch that is turned on when the pressure in the discharge side circuit of the other pump is equal to or higher than the connection pressure, and the pipe line when the pressure switch is turned on. 2. A control circuit for a variable displacement pump according to claim 1, further comprising: an electromagnetic valve which is connected to the valve and shuts off the pipe when the pressure switch is off.