JP4003644B2 - Hydraulic control device for work machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a work machine controlled by hydraulic pressure such as a hydraulic excavator or a crane, and more particularly to a hydraulic control device capable of reducing a pump flow rate.
[0002]
[Prior art]
In hydraulic circuits of hydraulic work machines, bleed-off circuits are widely used for flow rate control. In this bleed-off circuit, for example, when the control valve is provided with a bleed-off throttle that communicates the pump and the tank, the opening degree of the bleed-off throttle formed in the spool of the control valve changes according to the lever operation amount. It is configured as follows.
[0003]
As a result, when the lever is operated, the surplus flow that flows directly from the pump to the tank without going through the actuator changes according to the lever operation, so that the inflow flow to the actuator changes, and as a result, the actuator speed is controlled. Can do. However, such a bleed-off circuit has a problem that the bleed-off loss due to the excess flow rate is large and the energy efficiency is low.
[0004]
It can be easily considered that energy efficiency can be improved by reducing the bleed-off flow rate. However, since the bleed-off circuit has a function of reducing and stabilizing the pressure fluctuation in the circuit, simply reducing the bleed-off flow rate increases the pressure fluctuation in the circuit and impairs stability. become.
[0005]
In response to this problem, a hydraulic system has been proposed in which the bleed-off loss can be reduced by detecting the load pressure and controlling the pump flow rate (see, for example, Patent Document 1).
[0006]
[Patent Document 1]
Japanese Examined Patent Publication No. 3-64655 (page (13), FIG. 6)
[0007]
[Problems to be solved by the invention]
In the conventional hydraulic system described above, when the load pressure is large, the pump flow rate is reduced by detecting the load pressure. Therefore, when the load pressure is large and the actuator speed is low, the pump flow rate is reduced and the bleed is reduced. It is possible to reduce the excessive flow rate and loss in the off state.
[0008]
However, when the load pressure is low, the pump flow rate is not reduced. Therefore, in the region where the lever operation amount is small and the actuator speed is low, the surplus flow rate is generated by bleed-off, and the surplus flow rate and energy loss cannot be sufficiently reduced. There's a problem. Further, in this hydraulic system, when the load pressure becomes high, the pump flow rate is cut abruptly, so that there is a problem that pressure fluctuation is likely to occur and the stability is low.
[0009]
The present invention has been made in consideration of the problems in the conventional hydraulic system as described above, and provides a hydraulic control device for a work machine that can reduce the pump flow rate while maintaining stable operation. .
[0010]
[Means for Solving the Problems]
The present invention relates to a variable displacement pump that supplies hydraulic oil, a control valve that is operated by an operating body and controls hydraulic oil discharged from the pump, an actuator that is operated by hydraulic oil from the control valve, and the actuator A bleed-off means provided in a flow path for returning a part of the hydraulic oil flowing into the tank to the tank, a pressure sensor for detecting the pump pressure of the variable displacement pump , the variable displacement pump, and and control means for controlling the bleed-off means, said control means, in a region where the actuator required flow rate corresponding to the operation of the operation body exceeds the minimum pump flow rate of the variable displacement pump, closing the bleed-off means with cutting, the pump flow rate of the variable displacement pump, the bleed-off manually to the maximum operating position of the operating member Bleed-off opening characteristic of the pump flow rate as a reference which is set in advance in correspondence with the actuator required flow assumes, pump operation amount and the pressure sensor of the operation member assumes the bleed-off opening characteristic is detected that the open This is a hydraulic control device for a working machine configured to decrease by a bleed-off flow rate obtained based on the pressure .
[0011]
According to the present invention, for example, when an operating body such as an operation lever is operated and the actuator required flow rate is operated to a position exceeding the pump minimum flow rate, the bleed-off is first closed and the surplus flow becomes zero, and the bleed-off loss is reduced. It is suppressed. When operated further deeply, the variable displacement pump is controlled such that the pump flow rate is reduced by the flow rate calculated by a predetermined formula in accordance with the pump pressure and the lever operation amount. As a result, when the bleed-off loss is reduced, a stable operation can be performed without causing pressure fluctuations even when the bleed-off is completely closed.
[0012]
More specifically, in a region where the actuator required flow rate exceeds the minimum pump flow rate, the bleed-off means is closed and the pump flow rate of the variable displacement pump is reduced to the maximum operating position of the operating body. On the premise of the bleed-off opening characteristic opened by the means, the operation amount of the operating body and the pressure sensor detect the bleed-off opening characteristic on the basis of the pump flow rate set in advance corresponding to the actuator required flow rate. By reducing the bleed-off flow rate determined based on the pump pressure, an actuator supply flow rate equivalent to the conventional bleed-off control in which the bleed-off is not closed up to the maximum operation amount can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.
[0014]
FIG. 1 shows a hydraulic circuit of a hydraulic control apparatus according to the present invention.
[0015]
Reference numeral 1 denotes a variable displacement pump that supplies hydraulic oil to a hydraulic cylinder 2 as an actuator, and is driven by a motor 1a.
[0016]
3 is a control valve for controlling the supply flow rate to the hydraulic cylinder 2, and 4 is a bleed-off throttle (bleed-off throttle) provided in the control valve 3 and provided on an oil passage communicating the pump 1 and the tank 5. Off means).
[0017]
Reference numeral 6 denotes a meter-in throttle provided on an oil passage that connects the pump 1 and the hydraulic cylinder 2, and reference numeral 7 denotes a meter-out throttle provided on an oil passage that communicates the hydraulic cylinder 2 and the tank 5.
[0018]
When the operating lever (operating body) 8 is operated, the pilot pressure P1 (or P2) derived from the remote control valve 9 acts on one of the pilot ports of the control valve 3 through the pilot line 10a (or 10b). 3 is switched from the neutral position a to the b position or the c position.
[0019]
When the control valve 3 is switched to the position b, the hydraulic oil from the hydraulic pump 1 is supplied to the hydraulic cylinder 2 through one supply / discharge passage 11a of the supply / discharge passage 11, and the return oil is supplied to the tank 5 through the other supply / discharge passage 11b. Return to.
[0020]
When the position is switched to the position c, the hydraulic oil is supplied to the hydraulic cylinder (actuator) 2 through the supply / discharge passage 11b, and the return oil returns to the tank 5 through the supply / discharge passage 11a.
[0021]
12a and 12b are port relief valves, and 13a and 13b are make-up check valves. The make-up check valves 13a and 13b are for preventing cavitation in the supply / exhaust passage 11 when the pump flow rate is insufficient with respect to the actuator consumption flow rate. Configure.
[0022]
Reference numeral 14 denotes a main relief valve for keeping the circuit pressure constant, and reference numeral 15 denotes a pressure sensor for detecting a pump pressure Pp as an upstream pressure of the main relief valve 14.
[0023]
Reference numerals 16a and 16b denote pressure sensors for detecting the pilot pressures of the pilot lines 10a and 10b. The pressure signals output from the pressure sensors 16a and 16b and the pressure signal output from the pressure sensor 15 are respectively controlled by a controller (control). Means) 17.
[0024]
The control operation of the controller 17 will be described below.
[0025]
FIG. 2A shows a conventional bleed-off control shown as a comparative example, that is , control based on a bleed-off opening characteristic in which the bleed-off diaphragm 4 opens to the maximum operating position of the operating lever 8 as shown in FIG. FIG. 5B shows the bleed-off control according to this embodiment. In both figures, the upper part shows the bleed-off opening characteristic, and the lower part shows the actuator flow characteristic with respect to the lever operation amount.
[0026]
In FIG. 2 (a), C1 indicates a change in the actuator required flow rate. In the conventional bleed-off control, the actuator required flow rate increases as the lever operation amount increases, and the lever operation amount decreases as indicated by C2. It is configured to be closed when Lmax is reached.
[0027]
On the other hand, in the bleed-off control according to the present embodiment, as shown in FIG. 2B, at the position of the lever operation amount L1 where the required flow rate of the actuator is larger than the minimum discharge amount Q1 of the variable displacement pump 1, As shown, the bleed-off aperture is configured to be fully closed.
[0028]
If the bleed-off is closed halfway in this way, the flow rate control cannot be performed. However, in this embodiment, the pump control is performed instead of the bleed-off control for the minimum discharge amount Q1 of the pump.
[0029]
That is, according to the present embodiment, the bleed-off control is performed for the range where the pump control cannot be performed below the minimum discharge amount Q1, and the pump flow rate is reduced by performing the pump control for the range above the minimum discharge amount Q1. It has become.
[0030]
Next, flow control of the variable displacement pump 1 will be described.
[0031]
Conventionally, in a hydraulic circuit generally used, as shown in FIG. 3A, a bleed-off opening characteristic is used in which the bleed-off means is completely closed when the lever operation amount becomes the full lever Lmax. The bleed-off flow rate Qref assuming such bleed-off opening characteristics is obtained by the following equation (first bleed-off flow rate calculation formula).
[0032]
Qref = Cv / Aref / √P (1)
Here, Cv: flow coefficient Aref: conventional bleed-off opening area (FIG. 3), P: pump pressure.
[0033]
On the other hand, the bleed-off flow rate Q according to the present embodiment is obtained by the following formula (second bleed-off flow rate calculation formula).
[0034]
Q = Cv · A · √P (2)
Here, A is the bleed-off opening area of the present invention (FIG. 2).
[0035]
Since in the present embodiment as possible close prematurely bleed off, Chi elevational become the relation of A <Aref, the A = 0 in the region where as possible close the bleed-off.
[0036]
Therefore, the pump flow rate is given by:
[0037]
Qp = Qpref− (Qref−Q) = Qpref− (Aref−A) Cv · √P (3)
However, Qpref is a lever on the premise of a pump flow rate according to the conventional method , that is, a bleed-off opening characteristic in which the bleed-off throttle 4 opens to the maximum operating position of the operating lever 8 as shown as a comparative example in FIG. This is the pump flow rate set corresponding to the operation amount . Further, in this embodiment, in the region where the bleed-off restrictor 4 is closed, that is, the region where the actuator required flow rate exceeds the pump minimum flow rate, A = 0, so the above equation (3) can be expressed as Q p = Q pref −A ref · C v ・ √P It becomes. The pump flow rate Q p set in this embodiment is set corresponding to the lever operation amount on the premise of the bleed-off opening characteristic in which the bleed-off throttle 4 opens to the maximum operation position of the operation lever 8. based on the pump flow rate Q pref, the bleed-off opening characteristic assuming the operation amount of the operation member and the bleed-off flow rate the pressure sensor is determined based on the pump pressure P to detect (= a ref · C v · It shows that the amount is reduced by √P).
[0038]
Next, the effects of the present invention will be described with reference to FIGS.
[0039]
FIG. 3 is a simplified version of the hydraulic circuit of FIG. 1 for explaining the bleed-off control. In FIG. 5A, the inflow flow rate Qmi to the actuator is represented by the following equation in the conventional method.
[0040]
Qmi1 = Qpref−Qref (4)
On the other hand, the inflow flow rate of the actuator according to the present invention is expressed by the following equation as shown in FIG.
[0041]
Qmi2 = Qp-Q (5)
Here, since Qp is defined as in equation (3), the following equation is obtained by substituting equation (3) into equation (5).
[0042]
Qmi2 = Qpref− (Qref−Q) −Q = Qpref−Qref (6)
That is, Qmi1 = Qmi2 and the actuator inflow rate of this embodiment is equivalent to the conventional method. Thus, according to the present embodiment, the actuator can move in the same manner as in the past with respect to the lever operation. In other words, the same operability as before can be obtained.
[0043]
FIG. 4 shows the bleed-off control (see FIG. 4B) according to the present embodiment in comparison with the conventional bleed-off control (see FIG. 4A). In addition, the same code | symbol is attached | subjected about the same element as FIG. 2 in each graph, and the description is abbreviate | omitted.
[0044]
In the middle stage of FIG. 4 (a), with respect to the conventional bleed-off loss, as shown in C3, the pump flow rate is larger than the actuator required flow rate until the full lever Lmax is reached. Therefore, as shown in the lower stage of FIG. The bleed-off flow rate C4 does not become zero until Lmax, and the bleed-off loss is large (see the shaded portion S1 in the figure).
[0045]
On the other hand, according to this embodiment, as shown in the middle part of FIG. 4B, the pump flow rate and the actuator required flow rate coincide in the region where the lever operation amount is L1 or more (see C1 and C5). (b) As shown in the lower stage, the bleed-off flow rate C6 becomes 0, and the bleed-off loss can be reduced (see the hatched portion S2 in the figure).
[0046]
【The invention's effect】
As is apparent from the above description, according to the present invention of claim 1, the control means closes the bleed-off when the operating body is operated and the actuator required flow rate exceeds the pump minimum flow rate, and the pump minimum After the flow rate is exceeded, the pump flow rate of the variable displacement pump is configured to decrease by a predetermined amount according to the operation amount of the operating body. In the range where the operation amount is large, the variable displacement pump can be controlled to reduce the pump flow rate. As a result, even if the bleed-off is completely closed, stable operation can be performed without causing pressure fluctuations, and the excess flow rate can be reduced to improve energy efficiency.
[0047]
Specifically, in a region where the actuator required flow rate exceeds the minimum pump flow rate, the bleed-off means is closed and the pump flow rate of the variable displacement pump is increased to the maximum operating position of the operating body. A pump that is detected by the operation amount of the operating body and the pressure sensor on the assumption of the bleed-off opening characteristic on the basis of a pump flow rate set in advance corresponding to the actuator required flow rate on the premise of a bleed-off opening characteristic that opens. By reducing the bleed-off flow rate required based on the pressure, it is possible to obtain an actuator supply flow rate equivalent to the conventional bleed-off control that does not close the bleed-off until the maximum operation amount. Energy efficiency can be improved while maintaining the same operability.
[Brief description of the drawings]
FIG. 1 is a hydraulic circuit diagram showing a configuration of a hydraulic control apparatus according to the present invention.
2A is a conventional bleed-off opening characteristic diagram as a comparative example, and FIG. 2B is a bleed-off opening characteristic diagram according to the present invention.
FIG. 3A is an explanatory diagram of a conventional bleed-off as a comparative example, and FIG. 3B is an explanatory diagram of a bleed-off according to the present invention.
FIG. 4 is a comparison of bleed-off losses, (a) is a conventional bleed-off flow graph, and (b) is a bleed-off flow graph according to the present invention.
[Explanation of symbols]
1 Variable displacement pump 2 Hydraulic cylinder 3 Control valve 4 Bleed-off throttle 5 Tank 6 Meter-in throttle 7 Meter-out throttle 8 Operation lever 9 Remote control valve 10 Pilot line 11 Supply / discharge path 14 Main relief valve 15 Pressure sensor 17 Controller

Claims (1)

A variable displacement pump that supplies hydraulic oil, a control valve that is operated by an operating body and controls hydraulic oil discharged from the pump, an actuator that is operated by hydraulic oil from the control valve, and an operation that flows into the actuator A bleed-off unit provided in a flow path for returning a part of the oil to the tank, and a pressure sensor for detecting the pump pressure of the variable displacement pump; the variable displacement pump and the bleed-off unit; Control means for controlling,
Said control means, in a region where the actuator required flow rate corresponding to the operation of the operation body exceeds the minimum pump flow rate of the variable displacement pump, with as possible close the bleed-off means, the pump flow rate of the variable displacement pump The bleed-off opening characteristic is assumed on the basis of the pump flow rate set in advance corresponding to the actuator required flow rate on the premise of the bleed-off opening characteristic that the bleed-off means opens to the maximum operating position of the operating body. A hydraulic control device for a working machine, wherein the hydraulic pressure control device is configured to decrease by a bleed-off flow rate obtained based on an operation amount of an operating body and a pump pressure detected by the pressure sensor .

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