阅读说明：本技术 工作机器的液压控制回路 (Hydraulic control circuit for working machine ) 是由 中岛秀树 于 2020-02-13 设计创作，主要内容包括：为了实现减少燃料消耗和提高可操作性,提出了一种液压控制回路,该液压控制回路设置有通过从液压泵的排出管线分支并且延伸到油箱而形成的旁通油路和具有可变打开面积以控制旁通油路的流量的旁通阀,并且通过旁通阀的打开面积控制精确地执行泵压力控制,而不受每次的条件影响。液压控制回路被配置为执行旁通阀(11)的打开面积的闭环控制,使得在操作杆(7)的非操作期间,泵压力维持在设定压力,另一方面,在操作杆(7)的操作期间,执行开环控制以根据操作杆的操作输入减小旁通阀(11)的打开面积,并且进一步被配置为基于闭环控制期间旁通阀(11)的打开面积纠正开环控制期间操作杆的操作输入与旁通阀(11)的打开面积之间的对应关系。(In order to achieve reduction in fuel consumption and improvement in operability, a hydraulic control circuit is proposed which is provided with a bypass oil passage formed by branching from a discharge line of a hydraulic pump and extending to a tank and a bypass valve having a variable opening area to control a flow rate of the bypass oil passage, and which accurately performs pump pressure control by opening area control of the bypass valve without being affected by conditions at each time. The hydraulic control circuit is configured to perform closed-loop control of the opening area of the bypass valve (11) such that the pump pressure is maintained at a set pressure during non-operation of the operating lever (7), on the other hand, during operation of the operating lever (7), open-loop control is performed to reduce the opening area of the bypass valve (11) in accordance with an operation input of the operating lever, and is further configured to correct the correspondence relationship between the operation input of the operating lever during the open-loop control and the opening area of the bypass valve (11) based on the opening area of the bypass valve (11) during the closed-loop control.)

1. A hydraulic control circuit of a work machine, the hydraulic control circuit comprising:

a variable displacement type hydraulic pump;

a hydraulic brake that drives the hydraulic pump as a hydraulic pressure supply source;

a control valve for performing control of supplying/discharging oil to/from the hydraulic brake based on an operation of an operation lever;

a bypass oil passage formed by branching from a discharge line of the hydraulic pump and extending to a tank;

a bypass valve having a variable opening area to control a flow rate of the bypass oil passage; and

a controller for controlling the hydraulic pump and the displacement varying means of the bypass valve,

wherein the controller

During non-operation of the operation lever, closed-loop control is performed to maintain a pump flow rate constant, and an opening area of the bypass valve is controlled so that a pump pressure is maintained at a set pressure, and on the other hand,

during operation of the operation lever, open-loop control is performed to increase the pump flow rate in accordance with an operation input of the operation lever, and to decrease the opening area of the bypass valve in accordance with the operation input of the operation lever, and

wherein the controller includes correction means for correcting a correspondence relationship between an operation input of the operation lever and an opening area of the bypass valve in open-loop control based on the opening area of the bypass valve during closed-loop control.

2. The hydraulic control circuit of a work machine according to claim 1, wherein the correcting means controls the opening area of the bypass valve at the time of start of the open-loop control so that the opening area of the bypass valve does not become discontinuous at the time of switching from the closed-loop control to the open-loop control.

3. The hydraulic control circuit of a work machine according to claim 1 or 2, wherein the correction means includes a standard map indicating a correspondence relationship between an operation input of the operation lever and an opening area of the bypass valve in open-loop control, and corrects the standard map based on the opening area of the bypass valve during closed-loop control.

4. The hydraulic control circuit of a work machine according to claim 1 or 2, wherein the correction means obtains a relationship between the pump flow rate, the pump pressure, and the open area of the bypass valve during closed-loop control, and corrects the open area of the bypass valve corresponding to the operation input of the operation lever during open-loop control based on the relationship.

Technical Field

The present invention relates to the technical field of hydraulic control circuits for work machines such as hydraulic excavators.

Background

In general, for example, a hydraulic control circuit is used in a working machine such as a hydraulic excavator. Some known hydraulic control circuits include a hydraulic pump of a variable displacement type, a hydraulic actuator that drives the hydraulic pump as a hydraulic supply source, and a control valve for performing control for supplying/discharging oil to/from the hydraulic actuator based on an operation of an operation lever. In such a hydraulic control circuit, it is necessary to appropriately control the flow rate and pressure of the hydraulic pump in order to improve fuel consumption and work efficiency. For this reason, there has conventionally been known a technique of a hydraulic control circuit including a bypass oil passage formed by branching from a discharge line of a hydraulic pump and extending to a tank, a bypass valve having a variable opening area to control a flow rate of the bypass oil passage, and a controller for controlling a displacement varying device of the hydraulic pump and the bypass valve. (for example, see patent document 1).

The hydraulic control circuit disclosed in patent document 1 is configured such that during non-operation (standby state) of the operation lever, the pump flow rate is controlled to be minimum and the opening area of the bypass valve is controlled to a position where the opening area is limited to a preset set value, and on the other hand, during operation of the operation lever, the pump flow rate is increased in accordance with an increase in operation input and the opening area of the bypass valve is controlled to a position where the opening area is decreased in accordance with operation input from the set value. With this configuration, an improvement in fuel consumption can be achieved during non-operation of the operation lever, and an improvement in responsiveness at the start of operation can be achieved. During the operation of the operation lever, the pump flow rate and the pump pressure corresponding to the operation input can also be ensured.

Documents of the prior art

[ patent document ]

[ patent document 1] Japanese patent application laid-open No.2013-

Disclosure of Invention

[ problem to be solved by the invention ]

Meanwhile, in the hydraulic control circuit of patent document 1, during non-operation of the operation lever, as described above, the opening area of the bypass valve is limited to the set value, whereby the pump pressure is maintained at a specific value or more to improve the responsiveness at the start of operation. However, in this case, in order to further improve the fuel efficiency by stabilizing the pump pressure, it is more desirable to perform control for keeping the pump pressure constant by feeding back a detection value of the pump pressure to the open area control of the bypass valve, that is, closed-loop control for keeping the pump pressure at the set pressure. On the other hand, during the operation of the operation lever, since the pump pressure fluctuates according to the state of the hydraulic actuator, closed-loop control for feeding back the detected value of the pump pressure to the open area control of the bypass valve is not appropriate.

Therefore, it is proposed to perform closed-loop control to maintain the pump pressure at the set pressure during non-operation of the operation lever, and to perform open-loop control of the opening area of the bypass valve according to an operation input of the operation lever during operation of the operation lever.

However, when the closed-loop control is performed during non-operation of the operation lever, the opening area of the bypass valve for setting the pump pressure to the set pressure has different values depending on conditions such as the hydraulic oil temperature and the individual difference of the hydraulic devices. For this reason, when the operation lever is operated to start the open-loop control, if the opening area of the bypass valve with respect to the operation input of the operation lever is set in advance, there may be a difference and discontinuity between the opening area of the bypass valve during the closed-loop control and the opening area of the bypass valve at the time of starting the open-loop control at the time of switching from the closed-loop control to the open-loop control. Thus, there is a problem that the pump pressure may suddenly fluctuate at the discontinuous point, resulting in deterioration of operability. Further, if the opening area of the bypass valve in the open-loop control is set in advance in correspondence with the operation input of the operation lever. However, since conditions such as the hydraulic oil temperature and the individual difference of the hydraulic equipment are not reflected in the set value, there is a problem that the pump pressure cannot be controlled based on the opening area of the bypass valve in consideration of these conditions, and there is a problem to be solved by the present invention.

[ means for solving the problems ]

The present invention has been made in view of the above circumstances to solve these problems. The hydraulic control circuit of a work machine according to claim 1 of the present invention comprises: a variable displacement type hydraulic pump, a hydraulic actuator that drives a hydraulic pump as a hydraulic supply source, a control valve for performing control for supplying/discharging oil to/from the hydraulic actuator based on an operation of an operation lever, a bypass oil passage formed by branching from a discharge line of the hydraulic pump and extending to a tank, a bypass valve having a variable open area for controlling a flow rate of the bypass oil passage, and a controller for controlling a displacement changing device of the hydraulic pump and the bypass valve, wherein the controller performs closed-loop control to maintain a pump flow rate constant and controls an open area of the bypass valve so that the pump pressure is maintained at a set pressure during non-operation of the operation lever, and on the other hand performs open-loop control to increase the pump flow rate according to an operation input of the operation lever and to decrease the open area of the bypass valve according to the operation input of the operation lever during operation of the operation lever, and wherein the controller includes a correction means for correcting a correspondence relationship between an operation input of the operation lever in the open-loop control and the opening area of the bypass valve based on the opening area of the bypass valve during the closed-loop control.

The hydraulic control circuit of a work machine according to claim 2 of the present invention is the hydraulic control circuit of a work machine according to claim 1, wherein the correcting means controls the opening area of the bypass valve at the time of starting the open-loop control so that the opening area of the bypass valve does not become discontinuous at the time of switching from the closed-loop control to the open-loop control.

The hydraulic control circuit of a work machine according to claim 3 of the present invention is the hydraulic control circuit of a work machine according to claim 1 or 2, wherein the correction means includes a standard map indicating a correspondence relationship between an operation input of the operation lever in the open-loop control and an opening area of the bypass valve, and corrects the standard map based on the opening area of the bypass valve during the closed-loop control.

The hydraulic control circuit of a working machine according to claim 4 of the present invention is the hydraulic control circuit of a working machine according to claim 1 or 2, wherein the correcting means obtains a relationship between the pump flow rate, the pump pressure, and the open area of the bypass valve during the closed-loop control, and corrects the open area of the bypass valve corresponding to the operation input of the operation lever during the open-loop control based on the relationship.

[ advantageous effects of the invention ]

According to claim 1 of the present invention, the transition from the closed-loop control to the open-loop control can be smoothly performed, and the open area control of the bypass valve in the open-loop control can be performed as control that takes into account the conditions of each time, such as the hydraulic oil temperature and the individual difference of the hydraulic equipment, similar to the closed-loop control, and thereby the pump pressure control based on the open area of the bypass valve can be performed as high-precision control that is not affected by the conditions of each time.

According to claim 2 of the present invention, it is possible to eliminate fluctuations in pump pressure caused by the opening area of the bypass valve becoming discontinuous at the time of switching from closed-loop control to open-loop control, which contributes to improvement in operability.

According to claim 3 or 4 of the present invention, the open area control of the bypass valve in the open-loop control can be performed as control considering the condition of each time similar to the closed-loop control.

Drawings

Fig. 1 is a hydraulic control circuit diagram of a work machine.

Fig. 2 is a block diagram showing the input/output of the controller.

Fig. 3 is a diagram showing a relationship between an operation input of the operation lever and an opening area of a supply valve passage/an opening area of a bypass valve/a pump pressure of a pump flow rate/control valve.

Fig. 4 is a diagram showing a relationship between the operation input of the operation lever and the opening area of the bypass valve/pump pressure in a case where the correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve is set in advance in the open-loop control.

Fig. 5 is a diagram showing the relationship between the operation input of the operation lever and the opening area of the bypass valve/pump pressure in correction example 1.

Fig. 6A is a diagram showing the relationship between the operation input of the operation lever and the pump pressure in correction example 2, and fig. 6B is a flowchart showing the control procedure in correction example 2.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a diagram showing a hydraulic control circuit provided in a working machine such as a hydraulic excavator. In fig. 1, reference numeral 1 denotes an engine mounted to a working machine, and 2 denotes a variable displacement type hydraulic pump driven by the engine 1, 2a denotes a pump displacement changing device (displacement changing device of the hydraulic pump 2) for making a displacement of the hydraulic pump 2 variable in accordance with a control signal from a controller 9 described below, 3 denotes a discharge line of the hydraulic pump 2, 4 denotes an oil tank, 5 denotes a plurality of hydraulic actuators that drive the hydraulic pump 2 as a hydraulic pressure supply source, and 6 denotes a control valve for performing control for supplying/discharging oil to/from each hydraulic brake 5, respectively, based on an operation of a corresponding operation lever 7. Three hydraulic brakes 5 are shown in fig. 1 as a plurality of hydraulic brakes, but it goes without saying that they are not limited thereto. For example, in a hydraulic excavator, a plurality of hydraulic brakes such as left and right traveling motors, a rotary motor, a boom cylinder, an arm cylinder, a bucket cylinder, and the like are provided.

The control valve 6 is a spool valve equipped with pilot bores 6a, 6 b. When the pilot pressure is not input to the pilot holes 6a, 6b, the control valve 6 is located at the neutral position N where the control of supplying/discharging the oil to/from the hydraulic brake 5 is not performed. However, by inputting the pilot pressure to the pilot holes 6a, 6b, the control valve 6 is shifted to the operation position X or Y in the shift direction and shift amount corresponding to the pilot pressure, and the supply valve passage 6c for supplying the discharge oil of the hydraulic pump 2 to the hydraulic brake 5 is opened, so that the discharge oil of the hydraulic pump 2 is supplied to the hydraulic brake 5 in a state where the directional control and flow control have been affected.

Reference numerals 8a, 8b also denote electromagnetic proportional pilot valves for outputting pilot pressure to pilot holes 6a, 6b of the control valve 6. The pilot valves 8a, 8b output a pilot pressure corresponding to an operation input of the operation lever 7 based on a control signal output from the controller 9. Then, control of supplying/discharging oil to/from the hydraulic brake 5 corresponding to the operation of the operation lever 7 is performed by the control valve 6 shifted in the shift direction by the shift amount corresponding to the pilot pressure output from the pilot valves 8a, 8 b. A pilot valve 8a, 8b is provided to each control valve 6, respectively. In fig. 1, only the pilot valves 8a, 8b for outputting the pilot pressure to one control valve 6 (the right-hand control valve 6) are shown, and the pilot valves for the other control valves 6 are omitted.

Reference numeral 10 denotes a bypass oil passage formed by branching from the discharge line 3 of the hydraulic pump 2 and extending to the oil tank 4. In the bypass oil passage 10, a bypass valve 11 for controlling the flow rate of the bypass oil passage 10 is provided. The bypass valve 11 is configured such that the opening area is variably controlled based on a control signal from the controller 9 from a fully open position where the bypass oil passage 11 is fully opened to a fully closed position where the bypass oil passage is fully closed.

Reference numeral 12 also denotes a pressure reducing valve of a pilot pressure source connected to the discharge line 3 of the hydraulic pump 2. The pressure reducing valve 12 of the pilot pressure source reduces the discharge pressure of the hydraulic pump 2 to a predetermined pressure, and outputs it to the pilot pressure supply oil passage 13. The pilot pressure supply oil passage 13 is an oil passage that serves as a pilot pressure supply source for the pilot valves 8a, 8b and the bypass valve 11. An accumulator 14 for maintaining the pilot pressure supply oil passage 13 at a predetermined pressure is connected to the pilot pressure supply oil passage 13. Of course, the pilot pressure supply source can be constituted even by a circuit using a common pilot pump.

On the other hand, as shown in the block diagram of fig. 2, on the input side, the controller 9 is connected to an operation detection device 15 for detecting the operation direction and operation input of each operation lever 7 and a pressure sensor 16 for detecting the discharge pressure of the hydraulic pump 2 and the like. Meanwhile, on the output side, the controller 9 is connected to a bypass valve 11, a pump displacement changing device 2a, pilot valves 8a, 8b for respective control valves, and the like. The controller 9 is configured to perform various controls such as a pump control for outputting a control signal to the bypass valve 11 and the pump displacement changing device 2a to control the flow rate and pressure of the hydraulic pump 2 based on the input signal, and a hydraulic brake control for outputting a control signal to the pilot valves 8a, 8b to control the operation of the hydraulic brake 5.

Next, the pump control performed by the controller 9 will be described with reference to fig. 3.

First, the controller 9 determines non-operation or operation of the operation lever 7 based on a detection signal from the operation detection device 15. Then, when it is determined as the non-operation of the operation lever 7, the controller 9 outputs a control command to the pump displacement varying device 2a to set the flow rate of the hydraulic pump 2 to the minimum flow rate, and the controller 9 outputs a control signal to vary the opening area so as to maintain the discharge pressure of the hydraulic pump 2 at the set pressure set in advance by returning the detection value of the pressure sensor 16 to the bypass valve 11. Therefore, a closed-loop flow control will be performed in which, during non-operation of the operation lever 7, the opening area of the bypass valve 11 is controlled so that the pump flow rate is maintained at the minimum flow rate, and the pump pressure is maintained at the set pressure. As a result, since the pressure of the discharge line 3 is maintained at the set pressure, it is possible to achieve a reduction in fuel consumption, and it is possible to achieve an improvement in responsiveness at the start of operation of the operation lever 7.

In the present embodiment, in determining the non-operation or operation of the operation lever 7, the controller 9 not only determines the case where the operation lever 7 is not actually operated (operation input of the operation lever "0" shown in fig. 3) but also includes the operation within the dead band D of the operation lever 7 as the non-operation of the operation lever 7. In this case, the dead zone D of the operation lever 7 refers to the operation range of the operation lever 7 even in a state where the control valve 6 is located near the neutral position N and the supply valve passage 6c is closed when the operation lever 7 is operated. As shown in fig. 3, by the operation of the operating lever 7 beyond the dead zone D, the supply valve passage 6c of the control valve 6 is opened and the supply of pressure oil to the hydraulic actuator 5 is started, and the opening area of the supply valve passage 6c is increased in accordance with the increase of the operation input of the operating lever 7, and thereby the amount of pressure oil supplied to the hydraulic actuator 5 is increased.

On the other hand, when it is determined that the operation lever 7 has been operated (operation beyond the dead zone D as described above), the controller 9 outputs a control command to the pump-displacement varying device 2a to obtain a pump flow rate corresponding to the operation input of the operation lever 7 (operation input of the operation lever), that is, to increase the pump flow rate in accordance with an increase in the operation input of the operation lever 7, and outputs a control command to execute open-loop control to decrease the opening area of the bypass valve 11 in accordance with an increase in the operation input of the operation lever 7 to the bypass valve 11. Therefore, the pump flow rate is increased in accordance with an increase in the operation input of the operation lever 7, and the pump pressure is increased due to a decrease in the opening area of the bypass valve 11, and thus the pump flow rate and the pump pressure can be increased corresponding to an increase in the amount of pressure oil supplied to the hydraulic actuator 5 with an increase in the operation input of the operation lever 7, and thus an improvement in the operating efficiency can be achieved.

In addition, the controller 9 is equipped with a correction device 17, and when a control signal is output to the bypass valve 11 in the closed-loop control, the correction device 17 corrects the correspondence relationship between the operation input of the operation lever 7 and the opening area of the bypass valve 11 based on the opening area of the bypass valve 11 during the open-loop control. In a state where the correction by the correction device 17 has been performed during the open-loop control, a control signal is output to the bypass valve 11.

In other words, in the closed-loop control, since the opening area of the bypass valve 11 is variably controlled so that the discharge pressure of the hydraulic pump 2 is maintained at the set pressure, the opening area of the bypass valve 11 takes a different value each time due to the temperature of the hydraulic oil and the individual difference of the hydraulic devices. On the other hand, the opening area of the bypass valve will be determined in accordance with the operation input of the operation lever 7 during the open-loop control, but in this case, if the opening area of the bypass valve 11 during the open-loop control is a set value that has been set in advance with respect to the operation input of the operation lever, as shown in fig. 4, a difference may be generated between the actual opening area (actual value) of the bypass valve 11 during the closed-loop control and the opening area of the bypass valve 11 at the time of starting the open-loop control, and the opening area may become discontinuous. When the opening area of the bypass valve 11 becomes discontinuous in this way, the pump pressure suddenly fluctuates at the discontinuous point, which becomes a factor that deteriorates operability. Further, if the opening area of the bypass valve 11 in the open-loop control corresponding to the operation input of the operation lever is a set value that has been set in advance regardless of conditions such as the temperature of hydraulic oil and individual differences of hydraulic equipment, the opening area control of the bypass valve 11 in consideration of the conditions of each time will not be achieved. Therefore, the correspondence relationship between the operation input of the operation lever in the open-loop control and the opening area of the bypass valve 11 is corrected by the correction means 17 based on the opening area of the bypass valve 11 in the closed-loop control. Thereby, it is possible to avoid the occurrence of discontinuity of the opening area of the bypass valve 11 at the time of switching from the closed-loop control to the open-loop control, and it is possible to realize the opening area control of the bypass valve 11 in consideration of the condition of each time in the open-loop control.

Next, the correction performed by the correction device 17 will be described, but the correction varies depending on how the relationship between the operation input of the operation lever 7 and the opening area of the bypass valve 11 is set in the open-loop control. Therefore, as correction example 1, correction in the case where the relationship between the operation input of the operation lever and the opening area of the bypass valve 11 is set to the unique relationship will be described, and as correction example 2, correction in the case where the relationship between the operation input of the operation lever and the opening area of the bypass valve 11 is set to obtain the pump pressure set in accordance with the operation input of the operation lever will be described.

First, correction example 1 will be described with reference to fig. 5. Correction example 1 is a case where the relationship between the operation input of the operation lever in the open-loop control and the opening area of the bypass valve 11 (hereinafter, the opening area of the bypass valve 11 is also referred to as the bypass opening degree) is set to a unique relationship. Specifically, a standard value "As" of the bypass opening for maintaining the pump pressure at the set pressure is set in advance. In addition, assuming that the criterion value "As" is an initial value of the bypass opening degree at the time of starting the open-loop control, a relationship between the operation input of the lever and the bypass opening degree in the open-loop control, that is, a relationship in which the bypass opening degree decreases in accordance with an increase in the operation input of the lever is set in advance As the criterion map "MAs". If such a standard mapping "MAs" is set, the correction is performed as follows: a ratio R (R ═ An/As) between An actual value An of the opening area of the bypass valve for maintaining the pump pressure at the set pressure in the closed-loop control and a standard value As is first obtained, and then a value of a correction map MAn (MAn ═ C × MAs) is obtained by multiplying the value of the standard map MAs by the ratio R. In the open-loop control, the bypass valve 11 is controlled to have an open area corresponding to the operation input of the operation lever using the correction map MAn thus created. As a result, the opening area of the bypass valve 11 at the time of starting the open-loop control becomes equal to the opening area of the bypass valve 11 during the closed-loop control, and the occurrence of discontinuity of the bypass opening degree at the time of switching from the closed-loop control to the open-loop control can be avoided, and in the open-loop control, the opening area control of the bypass valve 11 corresponding to the condition at each time can also be realized similarly to the closed-loop control.

Next, correction example 2 will be described. Correction example 2 is a case where the correspondence relationship between the operation input of the operation lever and the pump pressure in the open-loop control is set in advance as a map MPs (see fig. 6A), and is set to control the opening area of the bypass valve 11 based on the map MPs and the pump flow rate. With such setting, in order to correct the opening area of the bypass valve 11 corresponding to the operation input of the operation lever in the open-loop control, first, the pump pressure Pp corresponding to the operation input of the operation lever, which is input from the operation detecting device 15, is obtained by using the map MPs indicating the relationship between the operation input of the operation lever and the pump pressure, as shown in the flowchart of fig. 6A (step S1).

Next, a coefficient Cr to be used in equation (2) described below is obtained by inputting the pump flow rate (minimum pump flow rate in the present embodiment) Qmin, the pump pressure (set pressure) Ps, and the actual value An of the bypass opening degree during closed-loop control into equation (1) below (step S2).

Qmin＝Cr×An×(Ps)1/2 (1)

The coefficient Cr obtained using the above equation (1) is a coefficient calculated using an actual value in closed-loop control, and is obtained as a variable including a change in the hydraulic oil density.

Next, by inputting the pump pressure Pp corresponding to the operation input of the operation lever obtained in step S1, the coefficient Cr obtained in step S2, and the pump flow rate Q corresponding to the operation input of the operation lever to the following equation (2), the opening area a of the bypass valve 11 corresponding to the operation input of the operation lever during the open-loop control is obtained (step S3).

Q＝Cr×A×(Pp)1/2 (2)

A control signal is output to the bypass valve 11 so as to be equal to the opening area obtained by using the above equation (2) (step S4).

As a result, the bypass opening degree during the open-loop control takes a value corrected under the conditions during the closed-loop control (the pump flow rate (minimum flow rate), the pump pressure (set pressure), and the actual value of the bypass opening degree during the closed-loop control), it is possible to avoid the occurrence of discontinuity of the bypass opening degree at the time of the shift from the closed-loop control to the open-loop control, and in the open-loop control, the open area control of the bypass valve 11 can be realized according to the conditions at each time, similarly to the case during the closed-loop control.

The values of the pump flow rates Qmin and Q in the above equations (1) and (2) are pump flow rate values used when a control signal from the controller 9 is output to the pump displacement changing device 2 a. The pump pressure Pp in equation (2) is also used as the differential pressure before and after the bypass valve 11Assuming that the tank pressure is substantially zero

Meanwhile, the hydraulic control circuit of the working machine is provided with a hydraulic lock device, although not shown. The hydraulic lock device is used to introduce a hydraulic lock state in which pressure oil is not supplied to the hydraulic brake 5 even when the operation lever 7 is operated (the hydraulic brake 5 is not operated) unless the hydraulic lock device is released. For example, the hydraulic lock device is configured to use a hydraulic lock lever (not shown) provided in the operation chamber and an unload valve that brings the pilot pressure supply oil passage 13 into an unloaded state based on an operation of the hydraulic lock lever. If the hydraulic lock device is not released, i.e., in a hydraulic lock state in which the hydraulic brake 5 does not operate even when the operation lever 7 is operated, the controller 9 outputs a control signal that restricts the flow rate of the hydraulic pump 2 to the minimum flow rate to the pump displacement varying device 2a, and outputs a control signal to the bypass valve 11 so as to be located at a fully open position in which the bypass oil passage 10 is fully open. As a result, since the pump flow rate is maintained at the minimum flow rate, the pump discharge pressure is lowered, and the bypass oil passage 10 through which the discharge oil of the hydraulic pump 2 flows into the oil tank 4 is fully opened. Therefore, low fuel consumption in the hydraulically locked state can be achieved. The operation and non-operation portion of the operation lever in the present invention includes the operation and non-operation of the operation lever 7 in the hydraulic lock state.

In the present embodiment configured as described above, the hydraulic control circuit of the working machine includes the variable displacement type hydraulic pump 2; a hydraulic brake 5 that drives the hydraulic pump 2 as a hydraulic pressure supply source; a control valve 6 for performing control of supplying/discharging oil to/from the hydraulic brake 5 based on an operation of the operation lever 7; a bypass oil passage 10 formed by branching from the discharge line 3 of the hydraulic pump 2 and extending to the oil tank 4; a bypass valve 11 having a variable opening area to control the flow rate of the bypass oil passage 10; and a controller 9 for controlling the displacement changing device 2a of the hydraulic pump 2 and the bypass valve 11, and during non-operation of the operation lever 7 (including operation within the dead zone D of the lever 7), the controller 9 performs closed-loop control to maintain the pump flow rate constant (minimum flow rate), and controls the opening area of the bypass valve so that the pump pressure is maintained at the set pressure, and on the other hand, during operation of the operation lever 7 (operation exceeding the dead zone D of the operation lever 7), performs open-loop control to increase the pump flow rate in accordance with the operation input of the operation lever 7, and to decrease the opening area of the bypass valve in accordance with the operation input of the operation lever. As a result, in a steady state during non-operation of the operation lever 7, the pump pressure is maintained at the set pressure, and thus low fuel consumption can be achieved, and on the other hand, during operation of the operation lever 7, the pump flow rate and the pump pressure are increased in accordance with the operation input of the operation lever, and thus improvement in work efficiency can be achieved. Further, in the hydraulic control unit, the controller 9 is equipped with a correction device 17 for correcting the correspondence relationship between the operation input of the operation lever in the open-loop control and the opening area of the bypass valve, based on the opening area of the bypass valve 11 during the closed-loop control.

As described above, in the present embodiment, during non-operation of the operation lever 7, the controller 9 performs closed-loop control of the opening area of the bypass valve 11, the bypass valve 11 performs flow control of the bypass oil passage 10 formed by branching from the discharge line 3 of the hydraulic pump 2 and extending to the tank 4 so that the pump pressure is maintained at the set pressure, and on the other hand, during operation of the operation lever 7, performs open-loop control so that the opening area is increased corresponding to the operation input of the operation lever, and thereby low fuel consumption and improved work efficiency can be achieved. Nevertheless, during the closed-loop control, the correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve 11 can be corrected based on the opening area of the bypass valve 11 by the correction device 17. As a result, the transition from the closed-loop control to the open-loop control can be smoothly performed, and the open area control of the bypass valve 11 in the open-loop control can be performed as a control that takes into account conditions similar to those during the closed-loop control, that is, conditions of each time such as the hydraulic oil temperature and the individual difference of the hydraulic equipment, and therefore, the pump pressure control based on the open area of the bypass valve 11 can be performed as a highly accurate control that is not affected by the conditions of each time.

In the hydraulic control unit, the correcting device 17 is configured to control the opening area of the bypass valve 11 at the time of starting the closed-loop control so that the opening area of the bypass valve 11 does not become discontinuous at the time of switching from the closed-loop control to the open-loop control. As a result, it is possible to eliminate fluctuations in pump pressure due to the opening area of the bypass valve 11 becoming discontinuous when switching from closed-loop control to open-loop control, which contributes to improvement in operability.

Further, in the hydraulic control unit, when the correspondence relationship between the operation input of the operation lever in the open-loop control and the opening area of the bypass valve 11 is corrected by the correction device 17, the correction device 17 is provided with a standard map MAs indicating the correspondence relationship between the operation input of the operation lever in the open-loop control and the opening area of the bypass valve 11, and is configured to correct the standard map MAs based on the opening area of the bypass valve 11 during the closed-loop control, and thereby the opening area control of the bypass valve 11 in the open-loop control can be executed as control that takes into account the conditions each time, similar to the closed-loop control.

Further, the correction device 17 can be configured to obtain a relationship between the pump flow rate, the pump pressure, and the opening area of the bypass valve during the closed-loop control, and correct the opening degree of the bypass valve corresponding to the operation input of the operation lever during the open-loop control based on the relationship. Even with this configuration, the open area control of the bypass valve 11 in the open-loop control can be executed as control considering the conditions each time similar to the closed-loop control.

Industrial applicability

The present invention can be applied to a hydraulic control circuit of a working machine such as a hydraulic excavator.