JP2010059839A - Hydraulic pump control system in working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid drop of work speed of a hydraulic actuator due to reduction of pump flow rate following rise of pump delivery pressure when load increases in a working machine equipped with the hydraulic pump driven by an engine. <P>SOLUTION: This system is constructed in such a manner that a suction side pressure of the hydraulic pump 1 can be pressurized by hydraulic pressure supplied from an accumulator 5 by connecting the accumulator 5 to a suction side line 4 of the hydraulic pump 1, and is provided with a control valve 8 opening and closing a hydraulic pressure supply oil passage 6 from the accumulator 5 to the suction side line 4 in such a manner that opening can be adjusted, and a control part 9 controlling the control valve 8 according to the load. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention belongs to the technical field of a hydraulic pump control system in a working machine such as a hydraulic excavator.

In general, a working machine such as a hydraulic excavator is equipped with a variable displacement hydraulic pump that is driven by an engine and sucks and discharges oil from an oil tank as a hydraulic pressure supply source of various hydraulic actuators. As a control device for such a hydraulic pump, conventionally, a pump that is absorbed by the hydraulic pump from the engine, a signal pressure corresponding to an operation amount of an operation tool such as an operation lever, a pump discharge pressure, and a displacement control means of the hydraulic pump. A configuration is known in which a signal pressure (power shift pressure) for controlling the absorption torque is input, and the discharge flow rate control of the hydraulic pump is performed based on the input pressure to the capacity control means (for example, Patent Document 1). In such a configuration, the pump output is controlled by the power shift pressure, and the constant flow control based on the pump discharge pressure is used to reduce the pump flow rate when the pump discharge pressure is high. When the engine is low, control is performed to increase the pump flow rate, so that the engine output can be fully utilized and the pump power can be prevented from exceeding the engine output to stop the engine. Yes.
Further, in Patent Document 1, the control for keeping the engine speed at the target speed (the speed near the rated speed) is based on the engine speed detected by the engine speed detecting means. A technique for controlling the pump absorption torque is disclosed.
JP 2001-280256 A

By the way, in the conventional hydraulic pump control device, when the load increases during work and the pump discharge pressure rises, control is performed to reduce the flow rate of the hydraulic pump so that the required pump power does not exceed the engine output. However, if the flow rate of the hydraulic pump is reduced by this control, the operating speed of the hydraulic actuator supplied with pressure oil from the hydraulic pump becomes slow even if the operation amount of the operation tool such as the operation lever is the same. . For this reason, the relationship between the operation amount of the operating tool and the operating speed of the hydraulic actuator differs depending on the pump discharge pressure, which makes it difficult for the operator to predict the operating speed of the hydraulic actuator, resulting in poor operability.
Furthermore, when the pump discharge pressure suddenly increases, the conventional pump that controls the pump flow rate by inputting the signal pressure to the capacity variable means inevitably causes a delay in the response of the hydraulic pump and temporarily increases the load on the engine. Thus, the engine speed temporarily decreases, but there is a problem that the fuel injection amount increases and the fuel consumption deteriorates until the lowered engine speed is restored to the original speed. There is a problem to be solved by the present invention.

The present invention was created with the object of solving these problems in view of the above circumstances, and the invention of claim 1 is driven by an engine and sucks and discharges oil from an oil tank. In a working machine equipped with a hydraulic pump, a hydraulic pressure supply means is connected to the suction side line of the hydraulic pump, and the suction side pressure of the hydraulic pump can be increased by supplying pressure oil from the hydraulic pressure supply means. A control system for a hydraulic pump in a working machine, characterized by comprising control means for controlling the supply of pressure oil from the hydraulic supply means to the suction side of the hydraulic pump in order to control the suction side pressure of the hydraulic pump according to a load It is.
According to a second aspect of the present invention, the control means is configured such that the engine speed detected by the engine speed detecting means is the target speed so as to maintain the engine speed at a preset target speed during the maximum output operation of the engine. 2. The hydraulic pump of the working machine according to claim 1, wherein when the pressure is smaller, the supply of pressure oil from the hydraulic supply unit to the suction side of the hydraulic pump is controlled to increase the suction side pressure of the hydraulic pump. Control system.
According to a third aspect of the present invention, the control means controls to increase or decrease the pressure oil supply from the hydraulic pressure supply means to the hydraulic pump suction side in accordance with the difference between the target speed and the engine speed detected by the engine speed detection means. The control system for a hydraulic pump in a working machine according to claim 2, wherein:

With the invention of claim 1, when the load increases, the load on the engine can be reduced by increasing the suction side pressure of the hydraulic pump and reducing the required power of the hydraulic pump, Thus, the load can be increased without decreasing the pump flow rate. This eliminates the problem that the operating speed of the hydraulic actuator varies depending on the pump discharge pressure, improves operability, and is efficient even for high-load work exceeding the engine output. Can be done well. Moreover, the control for increasing the suction side pressure by supplying pressure oil from the hydraulic supply means to the suction side of the hydraulic pump is superior in response to the conventional control for inputting the signal pressure to the capacity variable means of the hydraulic pump. When the load suddenly increases, the amount of decrease in the engine speed that temporarily drops can be reduced, and thus the amount of fuel consumed until the lowered engine speed returns to the original speed is reduced. Can contribute to lower fuel consumption.
According to the invention of claim 2, even if the load increases at the maximum output of the engine, the engine speed can be maintained at the target speed by increasing the suction side pressure of the hydraulic pump. Therefore, it is not necessary to control the flow rate of the pump in response to the increase in operability, so that the operability is improved and the work can be efficiently performed even at a high load exceeding the maximum output of the engine. Moreover, since the control to increase the suction side pressure of the hydraulic pump is excellent in responsiveness, it can respond quickly to a decrease in the engine speed, and thus the engine can be operated at the maximum output in a stable state. The amount of fuel consumed until the engine speed that has decreased due to an increase in load is returned to the target speed can be reduced, which contributes to lower fuel consumption.
According to the invention of claim 3, the suction side pressure of the hydraulic pump is controlled to increase / decrease according to the difference from the engine speed, and the engine speed is kept at the target speed with little fluctuation. Thus, the engine can be operated at the maximum output in a more stable state.

  Next, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, A is a hydraulic actuator (hydraulic cylinder, hydraulic motor, etc.) provided in a working machine such as a hydraulic excavator, 1 is a variable displacement hydraulic pump that serves as a hydraulic supply source of these hydraulic actuators A, 2 It is a capacity variable means of the hydraulic pump 1. C is a control valve unit arranged in an oil passage from the hydraulic pump 1 to the hydraulic actuator A. The control valve unit C includes operating tools (operating levers, operating pedals, A control valve (not shown) for performing oil supply / discharge control for the hydraulic actuator A based on the operation of the handle or the like is incorporated.

  The hydraulic pump 1 is driven by an engine E, and sucks and discharges oil from an oil tank 3. An accumulator 5 (corresponding to the hydraulic pressure supply means of the present invention) is connected to a suction side line 4 of the hydraulic pump 1. A hydraulic oil supply passage 6 through which pressure oil is supplied from is connected. In FIG. 1, reference numeral 7 denotes a check valve that blocks the flow of oil from the hydraulic supply oil passage 6 to the oil tank 3.

  Further, 8 is a control valve disposed in the hydraulic supply oil passage 6, and the control valve 8 is connected to the suction side of the hydraulic pump 1 from the accumulator 5 based on a control signal output from a control unit 9 described later. In order to control the supply of pressure oil to the line 4, the hydraulic supply oil passage 6 is opened and closed so that the opening amount can be adjusted. The control valve 8 and the control unit 9 constitute the control means of the present invention.

  In the state where the control valve 8 is in the closed position N for closing the hydraulic supply oil passage 6, no pressure oil is supplied from the accumulator 5 to the suction side line 4 of the hydraulic pump 1. The suction side pressure Pps of 1 is held at the tank pressure Pt. On the other hand, when the control valve 8 is in the open position X that opens the hydraulic supply oil passage 6, the pressure oil accumulated in the accumulator 5 is supplied to the suction side line 4 of the hydraulic pump 1 through the control valve 8. As a result, the suction side pressure Pps of the hydraulic pump 1 rises higher than the tank pressure Pt. As the suction side pressure Pps increases, the pressure difference (Ppd-Pps) between the discharge side and the suction side of the hydraulic pump 1 decreases, and the required power of the hydraulic pump 1 decreases, and the hydraulic pump 1 The required power reduction amount is increased or decreased by adjusting the opening amount of the control valve 8. The required power of the hydraulic pump 1 is obtained by the product of the differential pressure (Ppd-Pps) between the discharge side and the suction side and the pump flow rate.

  On the other hand, as shown in the block diagram of FIG. 2, the control unit 9 is an engine speed sensor 10 (corresponding to the engine speed detection means of the present invention) for detecting the speed (rotation speed) of the engine E, which will be described later. The dial value D of the accelerator dial 11 is inputted, and the control valve 8 and the capacity variable means 2 of the hydraulic pump 1 are controlled based on these input signals.

  The accelerator dial 11 is a setting operation tool for the operator to arbitrarily set the engine speed when there is no load in accordance with the work content and the like. The accelerator dial 11 has a plurality of positions (for example, “1” to “10”). The dial value D of 10 positions) is provided, and the dial value D of the accelerator dial 11 can set the engine speed at no load in a plurality of stages. In this case, as the dial value D of the accelerator dial 11 becomes smaller, the set engine speed at no load becomes slower. Then, the dial value D of the accelerator dial 11 is input to an engine controller (not shown), and based on the engine speed-output characteristic corresponding to each no-load engine speed set by the dial value D, Although the fuel injection amount control of the engine E is performed, the dial value D of the accelerator dial 11 is also input to the control unit 9 as described above.

  The displacement variable means 2 is a means for varying the pump displacement so as to control the discharge flow rate of the hydraulic pump 1. The displacement variable means 2 includes a signal pressure corresponding to the operation tool operation amount for the hydraulic actuator A. (For example, a negative control signal pressure derived from the center bypass flow rate of the control valve, a signal pressure output based on a detection value of an operation tool detection sensor for electrically detecting an operation tool operation amount, etc.) Pa and a hydraulic pump 1 discharge pressure (pump discharge pressure) Ppd and a power shift pressure Ps for controlling pump absorption torque set based on the dial value D of the accelerator dial 11 are input.

  Next, the control performed by the control unit 9 will be described. The control by the control unit 9 is executed in the present embodiment because the accelerator dial 11 has the largest dial value D (hereinafter referred to as the maximum dial value Dm). If the dial value D is set to a value other than the maximum dial value Dm, the control by the control unit 9 is not executed. The maximum dial value Dm is a dial value that is set when the engine E is operated at the maximum output. For example, when the excavation work or the loading work is performed with a hydraulic excavator, the operator selects the largest value. Dial value to be used.

  When the accelerator dial 11 is set to the maximum dial value Dm, the controller 9 controls the hydraulic pump 1 from the accumulator 5 so as to keep the engine E at the preset target speed Nt. The pressure oil supply to the suction side line 4 is controlled. Here, the target rotational speed Nt is an engine rotational speed that is set in advance to output the maximum horsepower while the engine E is stable, and is, for example, slightly slower (for example, about 20 rpm) than the rated rotational speed. A rotation speed is set (see FIG. 3).

  The control of the control unit 9 will be described with reference to the flowchart of FIG. 4. First, the control unit 9 first inputs the current rotational speed Na of the engine E inputted from the engine rotational speed sensor 10 (hereinafter referred to as the actual rotational speed Na). Is determined to be smaller than the target rotational speed Nt (Na <Nt?) (Step S1).

  If the determination in step S1 is “YES”, that is, if it is determined that the actual rotational speed Na is smaller than the target rotational speed Nt (Na <Nt), the controller 9 controls the control valve 8 to the open position X. A control signal is output so as to be positioned at. As a result, the pressure oil accumulated in the accumulator 5 is supplied to the suction side line 4 of the hydraulic pump 1 via the control valve 8, and the suction side pressure Pps of the hydraulic pump 1 increases. Thus, the pressure difference (Ppd-Pps) between the discharge side and the suction side of the hydraulic pump 1 is reduced, and the required power of the hydraulic pump 1 is reduced. In this case, the control unit 9 obtains the difference between the target rotational speed Nt of the engine E and the actual rotational speed Na, and reduces the required power of the hydraulic pump 1 as the rotational speed difference increases, that is, the accumulator 5. The opening amount of the control valve 8 is adjusted so as to increase the supply flow rate to the suction side line 4 of the hydraulic pump 1 to increase the suction side pressure Pps (step S2).

  On the other hand, if it is determined in step S1 that “NO”, that is, the actual rotational speed Na is equal to or higher than the target rotational speed Nt (Na ≧ Nt), the control unit 9 A control signal is output so as to be in the closed position N (step S3). Thereby, the pressure accumulation oil of the accumulator 5 is not supplied to the suction side line 4 of the hydraulic pump 1, and the suction side pressure Pps of the hydraulic pump 1 is held at the tank pressure Pt.

  That is, when the output of the hydraulic pump 1 increases, the load on the engine E increases accordingly, and the engine speed decreases. However, when the actual speed Na of the engine E becomes smaller than the target speed Nt, the above-described case is described. As described above, pressure oil is supplied from the accumulator 5 to the suction side of the hydraulic pump 1, and the suction side pressure Pps increases. As a result, the required power of the hydraulic pump 1 is reduced, the load on the engine E is reduced, and the engine speed is increased. In this case, control is performed so that the suction side pressure Pps of the hydraulic pump 1 increases as the difference between the target rotational speed Nt of the engine E and the actual rotational speed Na increases, that is, the required power of the hydraulic pump 1 decreases. Is done. On the other hand, when the engine speed increases and the actual speed Na becomes equal to or higher than the target speed Nt, the supply of pressure oil from the accumulator 5 to the suction side line 4 of the hydraulic pump 1 is stopped. In this manner, the pressure oil supply from the accumulator 5 to the suction side of the hydraulic pump 1 is controlled according to the difference between the actual rotation speed Na and the target rotation speed Nt to increase or decrease the suction side pressure Pps of the hydraulic pump 1. Thus, the engine speed is maintained at the target speed Nt, that is, the engine speed at which the engine E outputs the maximum horsepower.

  Furthermore, when the control for maintaining the engine speed at the target engine speed Nt is performed, the control unit 9 corresponds to the operation amount of the operation tool for the capacity variable means 2 of the hydraulic pump 1. Among the signal pressure Pa, the pump discharge pressure Ppd, and the power shift pressure Ps, the capacity control based on the signal pressure Pa corresponding to the operation tool operation amount is performed, but the capacity control by the pump discharge pressure Ppd and the power shift pressure Ps is performed. Control to not. Thereby, irrespective of the pump discharge pressure Ppd, the discharge flow rate of the hydraulic pump 1 is controlled to increase or decrease in accordance with the increase or decrease of the operation amount of the operation tool.

  On the other hand, as described above, when the accelerator dial 11 is set to a dial value D other than the maximum dial value Dm, the control by the control unit 9 is not executed, but in this case, the control valve 8 is normally closed. Control is performed so as to be located at the position N. Thereby, there is no pressure oil supply from the accumulator 5 to the suction side line 4 of the hydraulic pump 1, and the suction side pressure Pps of the hydraulic pump 1 is held at the tank pressure Pt.

  When the dial value D is set to a value other than the maximum dial value Dm, the displacement variable means 2 of the hydraulic pump 1 causes the signal pressure Pa, the pump discharge pressure Ppd, and the power shift pressure corresponding to the operation amount of the operation tool described above. Capacity control is performed based on Ps. Accordingly, when the operation tool operation amount is small, the hydraulic pump 1 is controlled so that the pump flow rate increases or decreases in accordance with the increase or decrease of the operation tool operation amount by the signal pressure Pa corresponding to the operation tool operation amount. The Further, when the operating tool is fully operated or when a plurality of operating tools are operated, according to a preset discharge pressure-pump capacity characteristic curve (see FIG. 5) so as to keep the pump horsepower constant. The pump capacity is controlled to decrease as the pump discharge pressure Ppd increases. Further, the discharge pressure-pump capacity curve is shifted according to the dial value D of the accelerator dial 11 by the power shift pressure Ps (see FIG. 5).

  In the present embodiment configured as described, the working machine is provided with a hydraulic pump 1 that is driven by an engine E and supplies pressure oil to various hydraulic actuators A. The suction side line 4 of the hydraulic pump 1 is provided. Is connected to an accumulator 5 via a hydraulic supply oil passage 6, and therefore, by supplying pressure oil from the accumulator 5 to the suction side line 4 of the hydraulic pump 1, the suction side pressure of the hydraulic pump 1 is Pps can be pressurized. Further, a control valve 8 for opening and closing the hydraulic supply oil passage 6 so that the opening amount thereof can be adjusted based on a control signal from the control unit 9 is disposed in the hydraulic supply oil passage 6, and the accumulator 5 is controlled by the control valve 8. By controlling the pressure oil supply to the suction side of the hydraulic pump 1 to increase the suction side pressure Pps of the hydraulic pump 1, the required power of the hydraulic pump 1 can be reduced.

  Thus, when the load increases, the load on the engine E can be reduced by increasing the suction side pressure Pps of the hydraulic pump 1 to reduce the required power. As a result, even if the load increases and the pump discharge pressure rises, it is not necessary to perform control to reduce the pump flow rate so that the pump output does not exceed the engine output. Therefore, it is possible to eliminate the problem that the operating speed of the hydraulic actuator A varies depending on the pump discharge pressure, improve the operability, and the pump output is the engine output. It is possible to efficiently perform high-load work exceeding the above.

  Moreover, the control to increase or decrease the suction side pressure Pps of the hydraulic pump 1 by supplying pressure oil from the accumulator 5 to the suction side line 4 of the hydraulic pump 1 is performed by inputting a signal pressure to the capacity variable means 2 of the hydraulic pump 1. Therefore, it is possible to reduce the amount of engine speed that temporarily drops when the load increases rapidly. The amount of fuel consumed before returning to a low level can be reduced, contributing to a reduction in fuel consumption.

  Further, in the present embodiment, the control for increasing or decreasing the suction side pressure Ps of the hydraulic pump 1 is performed during the maximum output operation of the engine E. That is, the control unit 9 sets the actual engine speed Na detected by the engine engine speed sensor 10 to the target engine speed Nt so as to maintain the engine engine speed at a preset target engine speed Nt during the maximum output operation of the engine E. When the rotation speed is smaller than the rotation speed Nt, the pressure oil supply from the accumulator 5 to the suction side of the hydraulic pump 1 is controlled according to the difference between the target rotation speed Nt and the actual rotation speed Na to control the suction side pressure Pps of the hydraulic pump 1. Increase or decrease. Thus, even if the load increases at the maximum output of the engine E, the load side pressure Pps of the hydraulic pump 1 is increased to reduce the required power of the pump, so that the load can be increased without reducing the pump flow rate. Therefore, the operability is improved, and even a work in which the pump output exceeds the maximum output of the engine E can be handled. In addition, since the control for increasing or decreasing the suction side pressure Pps of the hydraulic pump 1 is excellent in responsiveness as described above, it can respond quickly to a decrease in the engine speed, and the suction side pressure Pps of the hydraulic pump 1 can be set to the target rotation. Since the increase / decrease control is performed in accordance with the difference between the number Nt and the actual number of revolutions Na, the engine number of revolutions can be maintained at the target number of revolutions Nt with little blurring, and thus the engine can be stably maintained E can be operated at the maximum output, and the amount of fuel consumed until the engine speed lowered due to the increase in load is returned to the target speed Nt can be reduced, which contributes to lower fuel consumption.

Needless to say, the present invention is not limited to the above embodiment, and in the above embodiment, when the accelerator dial 11 is set to the maximum dial value Dm, the engine speed is set to the target speed Nt. The suction side pressure Pps of the hydraulic pump 1 is controlled to increase or decrease so as to be held at the same position. However, the present invention is not limited to this. In the case where the setting means is provided, the suction side pressure Pps of the hydraulic pump 1 can be increased or decreased according to the work mode set by the work mode setting means.
Furthermore, when performing a heavy load operation, the suction side pressure Pps of the hydraulic pump 1 can be arbitrarily increased or decreased based on an operation of a switch or the like.
Furthermore, in the above-described embodiment, the control valve 8 whose opening amount can be adjusted is used as a control valve for opening and closing the pressure oil supply oil passage 6 to the suction side line 4 of the hydraulic pump 1. Of course, the present invention can be implemented by using a control valve that opens and closes the pressure oil supply oil passage 6 but cannot adjust the opening amount in place of 8. When such a control valve is used, the suction side pressure Pps of the hydraulic pump 1 cannot be increased or decreased in accordance with the magnitude of the load, but there is an advantage that the system can be simplified and the cost can be reduced.

  In the above-described embodiment, the accumulator 5 is used as the hydraulic pressure supply means. For example, in the hydraulic excavator, high-pressure oil discharged from the head side oil chamber of the boom cylinder when the boom is lowered is used. By adopting a configuration for accumulating pressure, the oil discharged from the boom cylinder can be recovered and reused. Further, the hydraulic pressure supply means is not limited to an accumulator, and for example, high pressure oil discharged from the head side oil chamber of the boom cylinder described above can be used as it is as the hydraulic pressure supply means.

It is a hydraulic circuit diagram of a working machine. It is a figure which shows the input / output of a control part. It is a figure which shows an engine speed-output characteristic. (A) is a flowchart showing the control by the control unit, (B) is a timing chart. It is a figure which shows a discharge pressure-pump capacity characteristic curve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 3 Oil tank 4 Suction side line 5 Accumulator 8 Control valve 9 Control part 10 Engine speed sensor E Engine

Claims (3)

  In a working machine that is driven by an engine and includes a hydraulic pump that sucks and discharges oil from an oil tank, hydraulic pressure supply means is connected to the suction side line of the hydraulic pump, and pressure oil is supplied from the hydraulic pressure supply means. A control means for controlling the pressure oil supply from the hydraulic pressure supply means to the hydraulic pump suction side is provided to control the suction side pressure of the hydraulic pump in accordance with a load. A control system for a hydraulic pump in a working machine.   When the engine speed detected by the engine speed detecting means is smaller than the target speed in order to keep the engine speed at a preset target speed during the maximum output operation of the engine, the control means 2. The control system for a hydraulic pump in a working machine according to claim 1, wherein the supply of pressure oil from the supply means to the suction side of the hydraulic pump is controlled to increase the suction side pressure of the hydraulic pump.   The control means controls to increase or decrease the pressure oil supply from the hydraulic pressure supply means to the hydraulic pump suction side according to the difference between the target speed and the engine speed detected by the engine speed detection means. Item 3. A hydraulic pump control system for a work machine according to Item 2.

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