Hydraulic control system

Abstract

To reduce energy loss of a pressure reduction valve that reduces a pump pressure to a set pilot primary pressure Pp when a hydraulic pump, which is a pressurized oil supply source for a hydraulic actuator, is also used as a pressure oil supply source for a pilot primary pressure generation circuit that supplies pilot primary pressure to a pilot valve.SOLUTION: A hydraulic control system is provided with a pilot hydraulic source control unit 30 that selects, from among a plurality of hydraulic pumps 1 to 3 which serve as supply sources for hydraulic actuators, a hydraulic pump whose pump pressure is the lowest, equal to or higher than a set pilot primary pressure Pp, as a hydraulic pump which serves as a pressure oil supply source for a pilot primary pressure generation circuit 15, and that connects the selected hydraulic pump to the pilot primary pressure generation circuit 15.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of hydraulic control systems for work machines such as hydraulic excavators. [Background technology]

[0002] Among hydraulic systems installed in working machines such as hydraulic excavators, there are those equipped with a plurality of hydraulic actuators, a plurality of variable displacement hydraulic pumps serving as hydraulic supply sources for these hydraulic actuators, a plurality of pilot-operated control valves for controlling the supply of oil from the hydraulic pumps to the hydraulic actuators, and a plurality of pilot valves for supplying pilot pressure to the control valves based on the operation of an operating tool for the hydraulic actuators. In such hydraulic systems, as a pilot hydraulic source for supplying pilot primary pressure to the pilot valves, a fixed displacement pump, such as a gear pump, which is provided separately from the hydraulic pump serving as the hydraulic supply source for the hydraulic actuators and is driven by an engine, has been conventionally used. However, when such a fixed displacement pump is used as a pilot hydraulic source, there is a problem that energy is wasted because the fixed displacement pump constantly discharges pilot oil while the engine is running, even when all the operating tools for the hydraulic actuators are not operated and the pilot valves are not outputting pilot pressure to the control valves. In addition, a fixed displacement pump is required as a dedicated pump for the pilot hydraulic source, separate from the hydraulic pump serving as the hydraulic supply source for the hydraulic actuators, which hinders cost reduction and space saving. Therefore, conventionally, there is known a technique in which a hydraulic pump that serves as a hydraulic supply source for a hydraulic actuator is also used as a hydraulic pump for a pilot hydraulic source (see, for example, Patent Documents 1 and 2). These techniques can eliminate the need for a dedicated pump for the pilot hydraulic source, thereby reducing costs and eliminating the energy loss caused by the dedicated pump that is constantly consumed while the engine is running. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Publication No. 6-21971 [Patent Document 2] JP 2001-20903 A Summary of the Invention [Problem to be solved by the invention]

[0004] In general, a work machine such as a hydraulic excavator may be provided with a plurality of hydraulic pumps as a hydraulic supply source for a hydraulic actuator. Patent documents 1 and 2 also describe a case where a plurality of hydraulic pumps are provided as a hydraulic supply source for a hydraulic actuator. In this case, a high-pressure hydraulic pump is selected from the plurality of hydraulic pumps by a shuttle valve or a check valve, and the pump pressure of the selected high-pressure hydraulic pump is reduced by a pressure reducing valve to be used as a pilot primary pressure. However, when the pump pressure of the hydraulic pump is reduced to the pilot primary pressure by the pressure reducing valve, there is a problem that the higher the pump pressure, the greater the energy loss caused by the pressure reducing valve. In addition, even when the hydraulic actuator operating tool is not operated and the hydraulic pump is not supplying pressure oil to the hydraulic actuator, it is preferable to maintain the pump pressure of the hydraulic pump serving as the pilot hydraulic source at about the pilot primary pressure in order to ensure the responsiveness of the control valve when the hydraulic actuator operating tool is operated. However, when a plurality of hydraulic pumps are provided, there is a problem that maintaining the pump pressure of all of these hydraulic pumps at about the pilot primary pressure is a waste of energy, and these are the problems to be solved by the present invention. [Means for solving the problem]

[0005] The present invention has been created in view of the above-mentioned circumstances and with the objective of solving these problems. The invention of claim 1 relates to a hydraulic control system including a plurality of hydraulic actuators, a plurality of variable displacement hydraulic pumps serving as hydraulic supply sources for these hydraulic actuators, a plurality of pilot operated control valves for controlling the supply of oil from the hydraulic pumps to the hydraulic actuators, and a plurality of pilot valves for supplying pilot pressure to the control valves based on the operation of an operating tool for the hydraulic actuator. In providing a pilot primary pressure generating circuit for generating pilot primary pressure to be supplied to the pilot valves, the pilot primary pressure generating circuit is The hydraulic control system is characterized in that any one of the hydraulic pumps serves as a hydraulic supply source, and is equipped with a pressure reducing valve that reduces the pump pressure of the hydraulic pump serving as the hydraulic supply source to a preset set pilot primary pressure, while the hydraulic control system is provided with pilot hydraulic source control means that selects a hydraulic pump that serves as a hydraulic supply source for the pilot primary pressure generation circuit from among the plurality of hydraulic pumps and connects the selected hydraulic pump to the pilot primary pressure generation circuit, and the pilot hydraulic source control means selects the hydraulic pump with the lowest pressure from among the hydraulic pumps whose pump pressure is equal to or higher than the set pilot primary pressure, as the hydraulic supply source for the pilot primary pressure generation circuit when any of the hydraulic actuator operating tools is operated. The invention of claim 2 is a hydraulic control system according to claim 1, characterized in that the pilot primary pressure generating circuit is controlled by a pilot hydraulic source control means and includes a selector valve that switches to selectively connect one of a plurality of hydraulic pumps to the pilot primary pressure generating circuit. The invention of claim 3 is a hydraulic control system characterized in that, in claim 1, the pilot hydraulic source control means sets one of the hydraulic pumps as a non-operated pilot hydraulic source pump when none of the hydraulic actuator operating tools are operated, connects the set non-operated pilot hydraulic source pump to a pilot primary pressure generating circuit, and controls the pump pressure of the non-operated pilot hydraulic source pump to be equal to or higher than the set pilot primary pressure, while controlling the pump pressure of the hydraulic pumps other than the non-operated pilot hydraulic source pump to be a low pressure lower than the set pilot primary pressure. The invention of claim 4 is a hydraulic control system according to claim 1, characterized in that the pilot primary pressure generating circuit is provided with a hydraulic lock valve capable of cutting off the oil supply from the pilot primary pressure generating circuit to all pilot valves, and when the hydraulic lock valve is in a cut-off state, the pump pressures of all hydraulic pumps are controlled to be low pressures lower than the set pilot primary pressure. The invention of claim 5 is a hydraulic control system according to any one of claims 1 to 4, characterized in that the hydraulic control system includes, for each hydraulic pump, a bypass oil passage branched off from a discharge line upstream of a control valve and leading to an oil tank, and a bypass valve disposed in the bypass oil passage for increasing or decreasing a bypass amount flowing from the hydraulic pump to the oil tank, and the pump pressure of each hydraulic pump is controlled by increasing or decreasing the bypass amount controlled by the bypass valve. Effect of the Invention

[0006] By adopting the invention of claim 1, it is possible to eliminate the need for a pump dedicated to the pilot hydraulic source, thereby reducing costs and energy loss, and also to reduce energy loss due to the pressure reducing valve installed in the pilot primary pressure generation circuit as much as possible, thereby contributing to energy conservation. According to the invention as defined in claim 2, the hydraulic pump selected as the hydraulic supply source for the pilot primary pressure circuit can be easily connected to the pilot primary pressure circuit by switching the selector valve. By adopting the invention of claim 3, even when none of the operating devices for the hydraulic actuators are operated, pressurized oil at or above the set pilot primary pressure is supplied to the pilot primary pressure generating circuit from the hydraulic pump set as the non-operated pilot hydraulic source pump, thereby ensuring good responsiveness of the control valve when any of the operating devices for the hydraulic actuators is operated, while the pump pressures of the hydraulic pumps other than the non-operated pilot hydraulic source pump are controlled to be low pressures below the set pilot primary pressure, thereby contributing to further energy savings. By adopting the invention of claim 4, when the hydraulic lock lever is in the locked position and there is no need to operate the hydraulic actuators immediately, the pump pressure of all hydraulic pumps becomes a low pressure lower than the set pilot primary pressure, thereby achieving further energy savings. According to the invention as defined in claim 5, the pump pressure of the hydraulic pump can be controlled independently regardless of the operating state of the hydraulic actuator operating tool. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a hydraulic circuit diagram of the work machine. [Diagram 2] FIG. 4 is a block diagram showing inputs and outputs of a pilot hydraulic power source control unit. [Diagram 3] FIG. 4 is a flowchart showing a control procedure of a pilot hydraulic source control unit. [Figure 4] FIG. 11 is a table showing pump pressures according to the operating position of the hydraulic lock lever and according to whether or not an operating tool is operated. [Diagram 5] FIG. 11 is a hydraulic circuit diagram of a main portion according to a second embodiment. [Figure 6] FIG. 11 is a hydraulic circuit diagram of a main portion according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a hydraulic circuit of a hydraulic excavator which is an example of a working machine, in which 1, 2, 3 are first, second and third variable displacement hydraulic pumps driven by a prime mover, 1a, 2a, 3a are displacement varying means of the first, second and third hydraulic pumps 1, 2 and 3, respectively, 4, 5, 6 are discharge lines of the first, second and third hydraulic pumps 1, 2 and 3, respectively, 7 is an oil tank, 8 is a hydraulic actuator using at least one of the first, second and third hydraulic pumps 1, 2 and 3 as a hydraulic supply source, 9 is a pilot-operated control valve (corresponding to the control valve of the present invention) which controls the oil supply to the hydraulic actuator 8, and 10A and 10B are a pair of electromagnetic proportional pressure reducing valves (corresponding to the pilot valve of the present invention) which output pilot pressure to operate the control valve 9 based on the operation of an operating tool (not shown) for each hydraulic actuator. Incidentally, a hydraulic excavator is provided with various hydraulic actuators such as a swing motor, left and right travel motors, a boom cylinder, a stick cylinder, a bucket cylinder, etc., and each hydraulic actuator is provided with a control valve and each control valve is provided with an electromagnetic proportional pressure reducing valve. However, as representatives of these hydraulic actuators, control valves, and electromagnetic proportional pressure reducing valves, FIG. 1 only illustrates one hydraulic actuator (hydraulic cylinder) 8 which uses a first hydraulic pump 1 as a pressure oil supply source, a control valve 9 which controls the oil supply to the hydraulic actuator 8, a pair of electromagnetic proportional pressure reducing valves 10A, 10B which output pilot pressure to the control valve 9, and six other control valves 9 which control the oil supply to hydraulic actuators (not shown) which use the first, second, and hydraulic pumps 1, 2, and 3 as pressure oil supply sources.

[0009] The control valve 9 is a closed center type spool valve, and has a pair of pilot ports 9a, 9b connected to a pair of electromagnetic proportional pressure reducing valves 10A, 10B, respectively. The control valve 9 is located in a neutral position N where oil is not supplied to or discharged from the hydraulic actuator 8 when pilot pressure is not input to both pilot ports 9a, 9b, but is switched to a first operating position X when pilot pressure is input to one pilot port 9a, and controls the supply flow rate from the first hydraulic pump 1 to one oil chamber 8a of the hydraulic actuator 8 and the discharge flow rate from the other oil chamber 8b to the oil tank 7. Also, when pilot pressure is input to the other pilot port 9b, the control valve 9 is switched to a second operating position Y where the supply flow rate from the first hydraulic pump 1 to the other oil chamber 8b of the hydraulic actuator 8 and the discharge flow rate from the one oil chamber 8a to the oil tank 7 are controlled. In this embodiment, each control valve 9 is connected in parallel to the first, second and third hydraulic pumps 1, 2 and 3, and each control valve 9 is connected to the first, second and third hydraulic pumps 1, 2 and 3 via a check valve 11 for maintaining the load pressure of the hydraulic actuator 8. In addition, in this embodiment, a pair of electromagnetic proportional pressure reducing valves 10A, 10B are used as the pilot valves that output pilot pressure to the control valve 9, but the present invention is not limited to this and any pilot valve that outputs pilot pressure based on the operation of a hydraulic actuator operating tool may be used.

[0010] On the other hand, the electromagnetic proportional pressure reducing valves 10A, 10B output pilot pressure to pilot ports 9a, 9b of the control valve 9 based on a control signal from the controller 12. In this case, the controller 12 controls the pilot pressure output from the electromagnetic proportional pressure reducing valves 10A, 10B to increase or decrease according to the operation amount of the hydraulic actuator operating tool, and increases or decreases the spool displacement amount of the control valve 9 according to the increase or decrease in the pilot pressure, thereby controlling the increase or decrease in the supply flow rate and discharge flow rate to the hydraulic actuator 8.

[0011] 1, 15 denotes a pilot primary pressure generating circuit for generating a pilot primary pressure, and in the pilot primary pressure generating circuit 15, a selector valve 16 (to be described later), a pressure reducing valve 17 for reducing the pressure of the hydraulic oil supplied from the selector valve 16 to generate a predetermined pilot primary pressure, a check valve 18 for holding the pilot primary pressure, an accumulator 19 for smoothing the pilot primary pressure, and a hydraulic lock valve 20 (to be described later) are arranged in this order from the upstream side (selector valve 16 side), and the electromagnetic proportional pressure reducing valves 10A and 10B are connected to the downstream side of the hydraulic lock valve 20. The electromagnetic proportional pressure reducing valves 10A and 10B reduce the pilot primary pressure supplied from the pilot primary pressure generating circuit 15 based on a control signal output from the controller 12, and output the reduced pressure to the pilot ports 9a and 9b of the control valve 9. The value of the predetermined pilot primary pressure generated by the pressure reducing valve 17 is preset to be a value slightly larger than the maximum pilot pressure output from the electromagnetic proportional pressure reducing valves 10A and 10B, and is hereinafter referred to as a set pilot primary pressure Pp.

[0012] The selector valve 16 is a three-position switching valve that switches to connect any one of the first, second and third hydraulic pumps 1, 2 and 3 to the pilot primary pressure generating circuit 15, and includes first, second and third ports 16a, 16b and 16c connected to the first, second and third hydraulic pumps 1, 2 and 3, respectively, an output port 16d connected to the pilot primary pressure generating circuit 15, and a pair of pilot ports 16e and 16f to which pilot pressures output from a pair of selector valve solenoid valves 40A and 40B are input. In the neutral position N where pilot pressure is not input to both pilot ports 16e and 16f, the selector valve 16 communicates between the first port 16a and the output port 16d, that is, connects the first hydraulic pump 1 and the pilot primary pressure generating circuit 15. However, based on a control signal from the controller 12, the pilot pressure output from one of the selector valve solenoid valves 40A is input to one of the pilot ports 16e, so that the selector valve 16 is switched to a first switching position X to communicate between the second port 16b and the output port 16d, that is, connects the second hydraulic pump 2 and the pilot primary pressure generating circuit 15. Also, the pilot pressure output from the other selector valve solenoid valve 40B is input to the other pilot port 16f, so that the selector valve 16 is switched to a second switching position Y to communicate between the third port 16c and the output port 16d, that is, connects the third hydraulic pump 3 and the pilot primary pressure generating circuit 15.

[0013] On the other hand, the hydraulic lock valve 20 is an electromagnetic valve that is switched based on the operation of a hydraulic lock lever (not shown, but provided near the driver's seat where the operator sits) that can be displaced between a locked position and an unlocked position, and when the hydraulic lock lever is in the locked position, the hydraulic lock valve 20 is in a blocking position N that blocks the supply of pilot primary pressure from the pilot primary pressure generating circuit 15 to the electromagnetic proportional pressure reducing valves 10A, 10B, but is configured to switch to a communicating position X based on the hydraulic lock lever being operated to the unlocked position, allowing the supply of pilot primary pressure from the pilot primary pressure generating circuit 15 to the electromagnetic proportional pressure reducing valves 10A, 10B. Thus, when the hydraulic lock lever is in the locked position, the supply of pilot primary pressure to the electromagnetic proportional pressure reducing valves 10A, 10B is blocked by the hydraulic lock valve 20 in the blocking position N, and pilot pressure is not output from the electromagnetic proportional pressure reducing valves 10A, 10B to the control valve 9 even if the hydraulic actuator operating tool is operated, and thus the operation of the hydraulic actuator 8 is locked. On the other hand, when the hydraulic lock lever is operated to the unlocked position, the hydraulic lock valve 20 is located in the communication position X, allowing the supply of pilot primary pressure to the electromagnetic proportional pressure reducing valves 10A, 10B, and pilot pressure is output from the electromagnetic proportional pressure reducing valves 10A, 10B to the control valve 9 based on the hydraulic actuator operating tool, thereby operating the hydraulic actuator 8. 1 shows only a pair of electromagnetic proportional pressure reducing valves 10A, 10B downstream of the hydraulic lock valve 20, but various pilot valves (electromagnetic proportional pressure reducing valves) that output pilot pressure to the control valve 9 based on the operation of a hydraulic actuator operating tool are connected downstream of the hydraulic lock valve 20. All of the pilot valves arranged downstream of the hydraulic lock valve 20 are configured so that when the hydraulic lock lever is in the lock position, that is, when the hydraulic lock valve 20 is in the cut-off position N, the supply of pilot primary pressure is cut off and the output of pilot pressure is prohibited.

[0014] 1, 21, 22, 23 are first, second, and third bypass oil passages that are branched off from the discharge lines 4, 5, and 6 on the upstream side of the control valve 9 and lead to the oil tank 7, and the first, second, and third bypass oil passages 21, 22, and 23 are provided with first, second, and third bypass valves (bleed valves) 24, 25, and 26 that control the bypass amount (bleed amount) flowing from the first, second, and third hydraulic pumps 1, 2, and 3 to the oil tank 7 via the first, second, and third bypass oil passages 21, 22, and 23. The first, second, and third bypass valves 24, 25, and 26 each include inlet ports 24a, 25a, and 26a connected to the first, second, and third hydraulic pumps 1, 2, and 3, respectively, outlet ports 24b, 25b, and 26b connected to the oil tank 7, and pilot ports 24c, 25c, and 26c connected to solenoid proportional valves 27, 28, and 29 for the first, second, and third bypass valves, respectively.

[0015] Here, since the first, second and third bypass valves 24, 25 and 26 are similar to each other, the operation of the first bypass valve 24 will be described by taking the first bypass valve 24 as an example. The first bypass valve 24 is located in an initial position N when no pilot pressure is input to the pilot port 24c, and is set to open with an initial opening area intermediate between fully closed and fully open in the initial position N. On the other hand, when pilot pressure is output from the first bypass solenoid proportional valve 27 to the pilot port 24c based on a control signal from the controller 12, the first bypass valve 24 is continuously displaced from a fully closed position X where the opening area is fully closed to a fully open position Y where the opening area is maximum, according to the pilot pressure. In this case, when an operating tool for a hydraulic actuator to which pressure oil is supplied from the first hydraulic pump 1 is operated, the controller 12 controls the first bypass valve 24 so that the opening area becomes smaller (including fully closed) as the operation amount of the operating tool increases, that is, so that the bypass amount flowing from the first hydraulic pump 1 to the oil tank 7 is reduced and the pump pressure increases, thereby controlling the relationship between the operation amount of the operating tool for the hydraulic actuator and the pump pressure to have a pressure characteristic that is set in advance. Furthermore, in this embodiment, when an operating tool for a hydraulic actuator that uses the first hydraulic pump 1 as a hydraulic supply source is operated, the opening area of ​​the first bypass valve 24 is set to be equal to or smaller than a set opening area that is slightly smaller than the opening area when fully open, and with an opening area equal to or smaller than the set opening area, the pump pressure of the first hydraulic pump 1 is controlled to be equal to or higher than the set pilot primary pressure Pp. On the other hand, when an operating tool for a hydraulic actuator that uses the first hydraulic pump 1 as a hydraulic supply source is not operated, and an operating tool for a hydraulic actuator that uses a hydraulic pump other than the first hydraulic pump 1 as a hydraulic supply source is operated, the opening area of ​​the first bypass valve 24 is set to be wide, and as a result, the pump pressure of the first hydraulic pump 1 is controlled to be a low pressure that is less than the set pilot primary pressure Pp.

[0016] On the other hand, the controller 12 performs various controls such as oil supply and discharge control for each hydraulic actuator 8, discharge flow rate (pump flow rate) control and discharge pressure (pump pressure) control for the first, second and third hydraulic pumps 1, 2 and 3 based on the operation of the hydraulic actuator operating tool, and furthermore, the controller 12 is provided with a pilot hydraulic source control section 30 (corresponding to the pilot hydraulic source control means of the present invention) that performs control related to the pilot hydraulic source. As shown in the block diagram of FIG. 2, the pilot hydraulic power source control unit 30 is configured to input signals from operation detection means 31 which detects the operation of each hydraulic actuator operating tool (not shown), first, second and third pressure sensors 32, 33 and 34 which detect the pressures (pump pressures) of the first, second and third hydraulic pumps 1, 2 and 3, respectively, hydraulic lock detection means 35 which detects the operation position of a hydraulic lock lever, and to output control signals to the first, second and third bypass valve solenoid proportional valves 27, 28 and 29, the selector valve solenoid valves 40A and 40B, the capacity varying means 1a, 2a and 3a of the first, second and third hydraulic pumps 1, 2 and 3, etc., based on these input signals.

[0017] Here, among the various controls performed by the controller 12, a control that is not performed by the pilot hydraulic source control unit 30 but is related to the pilot hydraulic source control will be described. The controller 12 determines whether the hydraulic lock lever is in the locked position or the unlocked position based on a detection signal input from the hydraulic lock detection means 35, and controls the hydraulic lock valve 20 to be in the blocked position N when the hydraulic lock lever is in the locked position, and to be in the communicating position X when the hydraulic lock lever is in the unlocked position. As a result, as described above, when the hydraulic lock lever is in the locked position, the output of pilot pressure to the control valve 9 is prohibited even if the hydraulic actuator operating tool is operated, and the operation of the hydraulic actuator 8 is locked, whereas when the hydraulic lock lever is in the unlocked position, pilot pressure is output to the control valve 9 in response to the operation of the hydraulic actuator operating tool, and the hydraulic actuator 8 is operated. Furthermore, when the hydraulic lock lever is in the locked position, the controller 12 controls the engine speed to a preset first idling speed (e.g., 1000 rpm).On the other hand, when the hydraulic lock lever is in the unlocked position and none of the hydraulic actuator operating tools are operated, the controller 12 controls the engine speed to a second idling speed (e.g., 1200 rpm) that is slightly higher than the first idling speed.Furthermore, when the hydraulic lock lever is in the unlocked position and any of the hydraulic actuator operating tools is operated, the controller 12 controls the engine speed to be the engine speed set by the engine speed setting operating tool (accelerator dial or accelerator lever, not shown) and in accordance with the work load. Furthermore, when the hydraulic lock lever is in the locked position, the controller 12 controls the capacity varying means 1a, 2a, 3a so that the discharge flow rates of the first, second, and third hydraulic pumps 1, 2, and 3 are minimum flow rates. On the other hand, when the hydraulic lock lever is in the unlocked position and any of the hydraulic actuator operating tools is operated, discharge flow rate control is performed to increase or decrease the discharge flow rates of the first, second, and third hydraulic pumps 1, 2, and 3, which serve as hydraulic supply sources for the operated hydraulic actuator 8, in accordance with the operating amount of the operating tool. Furthermore, the controller 12 controls the pilot pressure output from the electromagnetic proportional pressure reducing valves 10A, 10B to the control valve 9 based on the amount of operation of the hydraulic actuator operating tool. As a result, as described above, the supply flow rate and discharge flow rate to the hydraulic actuator 8 are increased or decreased in accordance with the amount of operation of the hydraulic actuator operating tool. Furthermore, the controller 12 controls the pilot pressures output from the first, second and third bypass solenoid proportional valves 27, 28 and 29 to the first, second and third bypass valves 24, 25 and 26 based on the operational position of the hydraulic lock lever and the operational amount of the hydraulic actuator operating tool, thereby controlling the opening areas of the first, second and third bypass valves 24, 25 and 26. In this case, for example, when the hydraulic lock lever is in the locked position, the first, second and third bypass valves 24, 25 and 26 are all controlled to be in the initial position N. Furthermore, when any of the hydraulic actuator operating tools is operated with the hydraulic lock lever in the unlocked position, the opening areas of the first, second and third bypass valves 24, 25 and 26 connected to the first, second and third hydraulic pumps 1, 2 and 3 serving as the hydraulic supply sources for the operated hydraulic actuator 8 are increased or decreased in accordance with the amount of operation of the hydraulic actuator operating tool, thereby controlling the pump pressures of the first, second and third hydraulic pumps 1, 2 and 3, and although the pump pressures in this case depend on the operating conditions of the hydraulic actuators, they are controlled to be generally equal to or higher than the set pilot primary pressure Pp. Furthermore, the pump pressures of hydraulic pumps other than the hydraulic pump serving as the hydraulic supply source for the operated hydraulic actuator 8 are controlled to be low pressures lower than the set pilot primary pressure Pp, as described above.

[0018] Next, the control performed by the pilot hydraulic power source control unit 30 will be described based on the flowchart of Fig. 3. When the engine starts and the system starts, the pilot hydraulic power source control unit 30 first judges whether the hydraulic lock lever is in the lock position or the unlock position (step S1). If the hydraulic lock lever is in the lock position, the process returns to the judgment of step S1. When the hydraulic lock lever is in the lock position, the hydraulic lock valve 20 is placed in the shutoff position N by the control performed by the controller 12 described above, the engine speed becomes the first idling speed, the discharge flow rate of the first, second and third hydraulic pumps 1, 2 and 3 becomes the minimum flow rate, and the first, second and third bypass valves 24, 25 and 26 are controlled to be placed in the initial position N, but in this state, the pump pressure of the first, second and third hydraulic pumps 1, 2 and 3 is a low pressure lower than the set pilot primary pressure Pp.

[0019] On the other hand, when it is determined in step S1 that the hydraulic lock lever is in the unlocked position, it is then determined whether any of the hydraulic actuator operating tools is being operated (step S2). Then, when the determination in step S2 is "NO", that is, when it is determined that all of the hydraulic actuator operating tools are not being operated, one of the first, second, and third hydraulic pumps 1, 2, and 3 is set as a hydraulic pump that serves as a pilot hydraulic source when all of the hydraulic actuator operating tools are not being operated (hereinafter, referred to as a non-operation pilot hydraulic source pump) (step S3). The non-operation pilot hydraulic source pump may be set arbitrarily in advance by the operator using, for example, a monitor device or the like provided in the operator's cab, but when a hydraulic pump (the first hydraulic pump 1 in this embodiment) connected to the pilot primary pressure generating circuit 15 by the selector valve 16 in the neutral position N is set as the non-operation pilot hydraulic source pump, the processing in step S4 described below can be omitted. When the hydraulic lock lever is in the unlocked position, the engine speed is controlled by the controller 12 to a second idling speed that is slightly higher than the first idling speed when the hydraulic lock lever is in the locked position.

[0020] Next, the pilot hydraulic source control section 30 controls the selector valve 16 via the selector valve solenoid valves 40A, 40B so that the non-operated pilot hydraulic source pump set in step S3 is connected to the pilot primary pressure generating circuit 15 (step S4). That is, when the non-operated pilot hydraulic source pump is the first hydraulic pump 1, the selector valve 16 is controlled to be positioned at the neutral position N, when the non-operated pilot hydraulic source pump is the second hydraulic pump 2, the selector valve 16 is controlled to be positioned at the first switching position X, and when the non-operated pilot hydraulic source pump is the third hydraulic pump 3, the selector valve 16 is controlled to be positioned at the second switching position Y. In the following description, for convenience, the non-operated pilot hydraulic source pump connected to the pilot primary pressure generating circuit 15 will be described as the first hydraulic pump 1, and the pumps other than the non-operated pilot hydraulic source pump will be described as the second and third hydraulic pumps 2 and 3.

[0021] Next, the pilot hydraulic source control unit 30 sets the target pump pressure of the first hydraulic pump 1, which is the non-operated pilot hydraulic source pump, to the set pilot primary pressure Pp (step S5). Then, based on the detected pump pressure of the first hydraulic pump 1 input from the first pressure sensor 32, feedback control is performed so that the pump pressure of the first hydraulic pump 1 becomes the set pilot primary pressure Pp (step S6). In this case, the capacity of the first hydraulic pump 1 is kept constant (the control signal output from the controller 12 to the capacity varying means 1a of the first hydraulic pump 1 is kept constant) and the opening area of ​​the first bypass valve 24 is feedback controlled (the control signal output from the controller 12 to the first bypass solenoid proportional valve 27 is feedback controlled), or the opening area of ​​the first bypass valve 24 is kept constant and the capacity of the first hydraulic pump 1 is feedback controlled. Note that the target pump pressure of the non-operated pilot hydraulic source pump may be a pressure equal to or higher than the set pilot primary pressure Pp, but from the viewpoint of reducing energy loss, the lower the pressure, the more preferable. Therefore, in this embodiment, the target pump pressure is set to the set pilot primary pressure Pp.

[0022] Furthermore, the pilot hydraulic source control section 30 controls, via the second and third bypass solenoid proportional valves 28 and 29, so as to widely open the opening areas of the second and third bypass valves 25 and 26 connected to the second and third hydraulic pumps 2 and 3, which are hydraulic pumps other than the pilot hydraulic source pump when not in operation (step S7). As a result, the pump pressures of the second and third hydraulic pumps 2 and 3 are controlled to be low pressures that are lower than the set pilot primary pressure Pp. After the processing of step S7, the process returns to the judgment of step S1.

[0023] On the other hand, if the determination in step S2 is "YES", that is, if it is determined that any of the hydraulic actuator operating tools is being operated, first it is determined whether or not a non-operation pilot hydraulic source pump is set (step S8). Then, if the determination in step S8 is "YES", that is, if a non-operation pilot hydraulic source pump is set, the setting of the non-operation pilot hydraulic source pump and the setting of the target pump pressure are released, and the feedback control performed on the non-operation pilot hydraulic source pump is terminated (step S9).

[0024] Also, when the determination in step S8 is "NO", that is, when the non-operation pilot hydraulic source pump is not set, or after the processing in step S9, the pump pressures of the first, second, and third hydraulic pumps 1, 2, and 3 detected by the first, second, and third pressure sensors 32, 33, and 34 are read, and one of the pumps to be the pilot hydraulic source is selected from the first, second, and third hydraulic pumps 1, 2, and 3 based on these pump pressures (step S10). In this case, the hydraulic pump with the lowest pump pressure among the hydraulic pumps whose pump pressure is equal to or higher than the set pilot primary pressure Pp is selected as the pilot hydraulic source pump. Note that when the hydraulic lock lever is in the unlocked position and any of the hydraulic actuator operating tools is operated, the pump pressure of the hydraulic pump that is the hydraulic supply source of the operated hydraulic actuator 8 is controlled to be equal to or higher than the set pilot primary pressure Pp by the control of the controller 12 described above, and the pump pressure of the hydraulic pump that is the hydraulic supply source of the hydraulic actuator 8 other than the operated one is controlled to be a low pressure lower than the set pilot primary pressure Pp. For example, when the hydraulic actuator 8 using the first hydraulic pump 1 as its hydraulic supply source and the hydraulic actuator 8 using the third hydraulic pump 3 as its hydraulic supply source are operated, and the hydraulic actuator 8 using the second hydraulic pump 2 as its hydraulic supply source is not operated, the pump pressures of the first and third hydraulic pumps 1, 3 will be equal to or greater than the set pilot primary pressure Pp, and the pump pressure of the second hydraulic pump 2 will be less than the set pilot primary pressure Pp. In this case, the lower-pressure hydraulic pump out of the first and third hydraulic pumps 1, 3 is selected as the pilot hydraulic source pump.

[0025] Next, the pilot hydraulic source control section 30 controls the selector valve 16 via the selector valve solenoid valves 40A, 40B so that the pilot hydraulic source pump selected in step S10 is connected to the pilot primary pressure generating circuit 15 (step S11). That is, when the pilot hydraulic source pump is the first hydraulic pump 1, the selector valve 16 is controlled to be positioned at the neutral position N, when the pilot hydraulic source pump is the second hydraulic pump 2, the selector valve 16 is controlled to be positioned at the first switching position X, and when the pilot hydraulic source pump is the third hydraulic pump 3, the selector valve 16 is controlled to be positioned at the second switching position Y. Then, after the processing of step S11, the process returns to the judgment of step S1.

[0026] Thus, by the control performed by the controller 12 and the pilot hydraulic source control unit 30 provided in the controller 12, when the hydraulic lock lever is in the locked position, the pump pressures of all the hydraulic pumps 1, 2, 3 are controlled to be low pressures less than the set pilot primary pressure Pp. On the other hand, when the hydraulic lock lever is in the unlocked position and none of the hydraulic actuator operating tools are operated, one hydraulic pump from among the first, second, and third hydraulic pumps 1, 2, 3 is set as a non-operated pilot hydraulic source pump, and the non-operated pilot hydraulic source pump is connected to the pilot primary pressure generating circuit 15, and the pump pressure of the non-operated pilot hydraulic source pump is feedback-controlled to be the set pilot primary pressure Pp. In addition, the hydraulic pumps other than the non-operated pilot hydraulic source pump are controlled to be low pressures less than the set pilot primary pressure Pp. On the other hand, when the hydraulic lock lever is in the unlocked position and any of the hydraulic actuator operating tools is operated, the pump pressure of the hydraulic pumps serving as the hydraulic supply source for the operated hydraulic actuator becomes equal to or higher than the set pilot primary pressure Pp, but among these, the hydraulic pump with the lowest pump pressure is selected as the pilot hydraulic source pump and connected to the pilot primary pressure generating circuit 15. In addition, the hydraulic pumps serving as the hydraulic supply source for hydraulic actuators other than the operated hydraulic actuator are controlled to have a low pressure lower than the set pilot primary pressure Pp. 4 shows the pump pressures of the first, second and third hydraulic pumps 1, 2 and 3 according to the operating position of the hydraulic lock lever and whether or not the operating tool for the hydraulic actuator is operated, but here, a case is shown in which the first hydraulic pump 1 is set as a non-operated pilot hydraulic source pump that serves as a pilot hydraulic source when none of the operating tools for the hydraulic actuator are operated. Also, as shown in FIG. 4, when the operating tools for the hydraulic actuators that use the first and third hydraulic pumps 1 and 3 as hydraulic supply sources are operated with the hydraulic lock lever in the unlocked position, the pump pressures of the first and third hydraulic pumps 1 and 3 are equal to or higher than the set pilot pressure Pp, but among these, the hydraulic pump with the lower pump pressure is selected as the pilot hydraulic source pump and connected to the pilot primary pressure generating circuit 15.

[0027] In the embodiment configured as described above, the hydraulic control system of the working machine is configured to include a plurality of hydraulic actuators 8, a plurality of variable displacement hydraulic pumps 1-3 (first, second and third hydraulic pumps 1, 2 and 3) which serve as hydraulic supply sources for these hydraulic actuators 8, a plurality of pilot operated control valves (control valves 9) which control the supply of oil from the hydraulic pumps 1-3 to the hydraulic actuators 8, and a plurality of pilot valves (electromagnetic proportional pressure reducing valves 10A and 10B) which supply pilot pressure to the control valves based on the operation of a hydraulic actuator operating tool. In providing the pilot primary pressure generating circuit 15 that generates the pilot primary pressure Pp, the pilot primary pressure generating circuit 15 has one of the hydraulic pumps 1 to 3 that serve as a hydraulic supply source for the hydraulic actuator 8 as a hydraulic supply source, and is provided with a pressure reducing valve 17 that reduces the pump pressure of the hydraulic pump that serves as the hydraulic supply source to a preset pilot primary pressure Pp. Meanwhile, the hydraulic control system is provided with a pilot hydraulic source control unit 30 that selects a hydraulic pump that serves as a hydraulic supply source for the pilot primary pressure generating circuit 15 from among the hydraulic pumps 1 to 3, and controls the selected hydraulic pump to be connected to the pilot primary pressure generating circuit 15. When any of the hydraulic actuator operating tools is operated, the pilot hydraulic source control unit 30 selects the lowest-pressure hydraulic pump from among the hydraulic pumps whose pump pressure is equal to or higher than the set pilot primary pressure Pp, as the hydraulic supply source for the pilot primary pressure generating circuit 15.

[0028] In this manner, in this embodiment, the hydraulic pump serving as the hydraulic supply source for the pilot primary pressure generating circuit 15 is selected from among the hydraulic pumps 1 to 3 serving as the hydraulic oil supply source for the hydraulic actuator 8, which makes it possible to eliminate the need for a fixed displacement pump dedicated to the pilot hydraulic source, thereby reducing costs and eliminating the energy loss caused by the fixed displacement pump that was constantly consumed during engine operation. In this configuration, when any of the hydraulic actuator equipment is operated, the hydraulic pump with the lowest pressure among the hydraulic pumps 1 to 3 whose pump pressure is equal to or higher than the set pilot primary pressure Pp is selected as the hydraulic supply source for the pilot primary pressure generating circuit 15 and connected to the pilot primary pressure generating circuit 15. As a result, the energy loss caused by the pressure reducing valve 17, which is arranged in the pilot primary pressure generating circuit 15 and reduces the pump pressure of the hydraulic pump to the set pilot primary pressure Pp, can be reduced as much as possible, which contributes to energy saving.

[0029] In this system, the pilot primary pressure generating circuit 15 includes a selector valve 16 that is controlled by a pilot hydraulic source control unit 30 and switches to selectively connect any one of the plurality of hydraulic pumps 1 to 3 to the pilot primary pressure generating circuit 15. Thus, by the switching operation of the selector valve 16, the hydraulic pump selected as the hydraulic supply source for the pilot primary pressure circuit 15 can be easily connected to the pilot primary pressure circuit 15.

[0030] Furthermore, in this device, when none of the hydraulic actuator operating tools are operated, the pilot hydraulic source control unit 30 sets one of the hydraulic pumps as a non-operation pilot hydraulic source pump, connects the set non-operation pilot hydraulic source pump to the pilot primary pressure generating circuit 15, and controls the pump pressure of the non-operation pilot hydraulic source pump to be equal to or higher than the set pilot primary pressure Pp, while controlling the pump pressure of the hydraulic pumps other than the non-operation pilot hydraulic source pump to be a low pressure less than the set pilot primary pressure Pp. As a result, even when none of the hydraulic actuator operating tools are operated, pressure oil equal to or higher than the set pilot primary pressure Pp is supplied from the non-operation pilot hydraulic source pump to the pilot primary pressure generating circuit 15, thereby ensuring good responsiveness of the switching operation of the control valve 9 when any of the hydraulic actuator operating tools is operated from a state in which all of the hydraulic actuator operating tools are not operated, while the pump pressure of the hydraulic pumps other than the non-operation pilot hydraulic source pump is controlled to be a low pressure less than the set pilot primary pressure Pp, which contributes to energy conservation.

[0031] Furthermore, in this device, the pilot primary pressure generating circuit 15 is equipped with a hydraulic lock valve 20 capable of cutting off the oil supply from the pilot primary pressure generating circuit 15 to all pilot valves (electromagnetic proportional pressure reducing valves 10A, 10B which output pilot pressure to the control valve 9), and is configured so that when the hydraulic lock valve 20 is in a cut-off state, the pump pressures of all the hydraulic pumps 1-3 are controlled to a low pressure less than the set pilot primary pressure Pp. As a result, when the hydraulic lock lever is in the locked position and there is no need to operate the hydraulic actuator 8 immediately, the pump pressures of all the hydraulic pumps 1-3 are low pressures less than the set pilot primary pressure Pp, thereby achieving further energy savings.

[0032] Furthermore, the hydraulic control system of the work machine is provided with bypass oil passages 21-23 (first, second and third bypass oil passages 21, 22, 23) corresponding to the hydraulic pumps 1-3, which are branched off from the discharge lines 4-6 upstream of the control valve (control valve 9) and lead to the oil tank 7, and bypass valves 24-26 (first, second and third bypass valves 24, 25, 26) arranged in the bypass oil passages 21-23 and control the increase and decrease of the bypass amount flowing from the hydraulic pumps 1-3 to the oil tank 7, while the pump pressure of each hydraulic pump 1-3 is controlled by controlling the increase and decrease of the bypass amount by the bypass valves 24-26. This allows the pump pressure of the hydraulic pumps 1-3 to be controlled independently regardless of the operating state of the hydraulic actuator operating tool.

[0033] Of course, the present invention is not limited to the above embodiment (first embodiment). In the first embodiment, three hydraulic pumps, namely, a first, a second and a third hydraulic pumps, are provided as hydraulic pumps that serve as hydraulic supply sources for the hydraulic actuator, and any one of these three hydraulic pumps is selected as the pilot hydraulic source pump or the pilot hydraulic source pump when not in operation. However, of course, the present invention can be implemented in a similar manner even if two or four or more hydraulic pumps are provided.

[0034] 5, the selector valve 16 may be provided with a cut-off position Z for cutting off the supply of pressure oil from all hydraulic pumps (first, second and third hydraulic pumps 1, 2 and 3) to the pilot primary pressure generating circuit 15 in addition to the neutral position N, first switching position X and second switching position Y as in the first embodiment, and a pilot pressure sensor 41 for detecting the pressure downstream of the check valve 18 of the pilot primary pressure generating circuit 15 may be provided, and the detected pressure of the pilot pressure sensor 41 may be input to the controller 12 for monitoring, thereby controlling the switching operation of the selector valve 16. In this case, when the pressure of the pilot primary pressure generating circuit 15 input from the pilot pressure sensor 41 is equal to or higher than the threshold value Pt, the selector valve 16 is positioned at the cut-off position Z, and controlled so that pressure oil is not supplied to the pilot primary pressure generating circuit 15 from any hydraulic pump. The threshold value Pt is set to, for example, a pressure (maximum value + α) obtained by adding a margin to the maximum value of the output pilot pressure of the electromagnetic proportional pressure reducing valves 40A, 40B required according to the operation amount of the hydraulic actuator operating tool. On the other hand, when the pressure of the pilot primary pressure generating circuit 15 is less than the threshold value Pt, the selector valve 16 is controlled in the same manner as in the first embodiment described above. In this way, the selector valve 16 is provided with a cut-off position Z at which pressure oil is not supplied from any of the hydraulic pumps to the pilot primary pressure generating circuit 15, and the selector valve 16 is switched to the cut-off position Z according to the pressure of the pilot primary pressure generating circuit 15, thereby contributing to further reduction of energy loss. In FIG. 5, the same reference numerals are used for the same parts as in the first embodiment. In the second embodiment, the selector valve 16 is provided with the cut-off position Z, but a valve capable of cutting off the connection between all the hydraulic pumps and the pilot primary pressure generating circuit 15 may be provided separately from the selector valve 16.

[0035] Also, a swash plate type axial piston pump is generally used as a variable displacement hydraulic pump that serves as a hydraulic supply source for a hydraulic actuator. Fig. 6 is a hydraulic circuit diagram of a third embodiment showing a circuit configuration of regulators (variable displacement means) 1a, 2a when first and second hydraulic pumps 1, 2 made of swash plate type axial piston pumps are provided as hydraulic pumps that serve as hydraulic supply sources for a hydraulic actuator. In this embodiment, the regulators 1a, 2a are configured using an electromagnetic proportional valve 42 that outputs a control pressure based on a control signal from a controller, a spool valve 43 that receives the control pressure output from the electromagnetic proportional valve 42 and controls the supply pressure to a piston 44, and a piston 44 that changes the inclination angle of the swash plates 1b, 2b by receiving the supply pressure from the spool valve 43 and the pump pressure. In the regulators 1a and 2a configured as described above, the self-pressure (pump pressure) of the first and second hydraulic pumps 1 and 2 is required to move the swash plates 1b and 2b. However, if the pump pressure of the hydraulic pumps other than the non-operating pilot hydraulic source pump is controlled to be low when the hydraulic lock lever is in the unlocked position and all the hydraulic actuator operating tools are not operated as in the first embodiment, when the hydraulic actuator operating tool using the hydraulic pump other than the non-operating pilot hydraulic source pump as the pressure oil supply source is operated, the self-pressure for moving the swash plates 1b and 2b is low, so the response of the regulators 1a and 1b is reduced. Therefore, as shown in FIG. 6, a shuttle valve 45 is provided to select the high-pressure side of the first and second hydraulic pumps 1 and 2, and the output pressure of the shuttle valve 45 is configured to be led to the regulators 1a and 2a, so that the pump pressure of the non-operating pilot hydraulic source pump is also led to the regulators of the hydraulic pumps other than the non-operating pilot hydraulic source pump, thereby avoiding a drop in the response of the regulators. [Industrial Applicability]

[0036] INDUSTRIAL APPLICABILITY The present invention can be utilized in a hydraulic control system of a work machine such as a hydraulic excavator when the hydraulic pump that serves as a hydraulic supply source for a hydraulic actuator is also used as a pilot hydraulic source. [Explanation of symbols]

[0037] 1, 2, 3 First, second and third hydraulic pumps 7 Oil Tank 8 Hydraulic Actuators 9. Control Valve 10A, 10B Solenoid proportional pressure reducing valve 12 Controller 15 Pilot primary pressure generating circuit 16 Selector valve 17 Pressure reducing valve 20 Hydraulic lock valve 21, 22, 23 First, second, and third bypass oil passages 24, 25, 26 First, second, and third bypass valves 30 Pilot hydraulic power source control section

Claims

1. In a hydraulic control system including a plurality of hydraulic actuators, a plurality of variable displacement hydraulic pumps serving as hydraulic supply sources for these hydraulic actuators, a plurality of pilot operated control valves for controlling the supply of oil from the hydraulic pumps to the hydraulic actuators, and a plurality of pilot valves for supplying pilot pressure to the control valves based on the operation of an operating tool for the hydraulic actuator, when providing a pilot primary pressure generating circuit for generating a pilot primary pressure to be supplied to the pilot valves, The pilot primary pressure generating circuit has a hydraulic pump among a plurality of hydraulic pumps serving as hydraulic supply sources for the hydraulic actuator as a hydraulic supply source, and includes a pressure reducing valve that reduces the pump pressure of the hydraulic pump serving as the hydraulic supply source to a preset set pilot primary pressure, The hydraulic control system is provided with a pilot hydraulic source control means that selects a hydraulic pump to be a hydraulic supply source for the pilot primary pressure generation circuit from among the plurality of hydraulic pumps and connects the selected hydraulic pump to the pilot primary pressure generation circuit, and the pilot hydraulic source control means selects, when any of the hydraulic actuator operating tools is operated, a hydraulic pump with the lowest pressure from among the hydraulic pumps whose pump pressure is equal to or higher than the set pilot primary pressure, as the hydraulic supply source for the pilot primary pressure generation circuit.

2. 2. The hydraulic control system according to claim 1, wherein the pilot primary pressure generating circuit is controlled by a pilot hydraulic source control means and includes a selector valve that switches to selectively connect one of a plurality of hydraulic pumps to the pilot primary pressure generating circuit.

3. The hydraulic control system according to claim 1, wherein the pilot hydraulic source control means, when none of the hydraulic actuator operating tools are operated, sets any one of the hydraulic pumps as a non-operated pilot hydraulic source pump, connects the set non-operated pilot hydraulic source pump to the pilot primary pressure generating circuit, and controls the pump pressure of the non-operated pilot hydraulic source pump to be equal to or higher than the set pilot primary pressure, while controlling the pump pressure of the hydraulic pumps other than the non-operated pilot hydraulic source pump to be a low pressure lower than the set pilot primary pressure.

4. 2. The hydraulic control system according to claim 1, wherein the pilot primary pressure generating circuit is provided with a hydraulic lock valve capable of cutting off oil supply from the pilot primary pressure generating circuit to all pilot valves, and wherein, when the hydraulic lock valve is in a cut-off state, the pump pressures of all hydraulic pumps are controlled to be low pressures lower than a set pilot primary pressure.

5. The hydraulic control system according to any one of claims 1 to 4, further comprising: a bypass oil passage branched off from a discharge line upstream of a control valve and leading to an oil tank, corresponding to each hydraulic pump; and a bypass valve disposed in the bypass oil passage for increasing or decreasing a bypass amount flowing from the hydraulic pump to the oil tank, and the hydraulic control system controls the pump pressure of each hydraulic pump by controlling the increase or decrease of the bypass amount by the bypass valve.

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