JP6737044B2 - Hydraulic drive of work machine - Google Patents

Description

The present invention relates to a hydraulic drive device provided in a work machine such as a hydraulic excavator, which includes a so-called split flow hydraulic pump.

BACKGROUND ART Conventionally, there is known a hydraulic drive device provided in a work machine, which includes a so-called split flow type hydraulic pump as a hydraulic power source. The split flow type hydraulic pump (hereinafter, abbreviated as “split flow type pump”) includes a single pump main body and a first discharge port that discharges hydraulic oil boosted by the pump main body independently of each other. And a second discharge port. Therefore, by connecting the first and second discharge ports to the first hydraulic circuit and the second hydraulic circuit, respectively, the split flow type pump can be connected to the first hydraulic circuit and the second hydraulic circuit by itself. It is possible to supply hydraulic oil individually.

However, even if the split flow type pump has a variable displacement function, it is not possible to individually adjust the discharge flow rate to the first hydraulic circuit and the discharge flow rate to the second hydraulic circuit. The hydraulic oil can be supplied to the first and second hydraulic circuits only at equal flow rates. Therefore, it is extremely difficult to supply hydraulic oil to both the first and second hydraulic circuits at an appropriate flow rate that individually corresponds to the operating state of each hydraulic circuit. For example, when only the control valve included in the first hydraulic circuit of the first and second hydraulic circuits is operated, if the discharge flow rate of the split flow type pump is increased corresponding to the operation, the control valve Must also be supplied to the second hydraulic circuit where the hydraulic oil is not operated and is returned to the tank as it is (without contributing to the driving of the hydraulic actuator). This results in a wasteful increase in the hydraulic oil supply flow rate to the second hydraulic circuit and a decrease in operating efficiency.

As means for suppressing such an inconvenience, Patent Document 1 discloses that when either one of two control valves connected to the first and second discharge ports of the split flow type pump is switched. A control for reducing the discharge flow rate of the split flow type pump is disclosed.

JP, 2005-143538, A

Since the control described in Patent Document 1 reduces the discharge flow rate of the split flow type pump only when either one of the two control valves is operated, the two control valves are simultaneously operated. Not applicable if manipulated. For example, even when there is a significant difference between the operation amounts of the two control valves, the control is not applied when both control valves are operated.

Further, when there is a significant difference between the operating pressure of the first hydraulic circuit connected to the first outlet and the operating pressure of the second hydraulic circuit connected to the second outlet, both hydraulic circuits The hydraulic oil cannot be supplied at a suitable flow rate. For example, when the operating pressure of the first hydraulic circuit reaches the relief pressure, while the operating pressure of the second hydraulic circuit is significantly lower than the relief pressure, the operating pressure of the first hydraulic circuit is set in consideration of engine horsepower. Therefore, since the capacity of the split flow type pump must be suppressed to a low level, the hydraulic oil is supplied only to a small flow rate to the second hydraulic circuit, which does not need to be regulated in flow rate due to low operating pressure. Therefore, the hydraulic actuator connected to the second hydraulic circuit cannot be moved at a high speed. On the other hand, in the first hydraulic circuit, excess hydraulic oil is returned to the tank through the relief valve, and its energy is discarded as heat, for example.

In view of the above circumstances, the present invention provides a split flow type hydraulic pump provided in a working machine and having first and second discharge ports, and a first hydraulic circuit connected to the first and second discharge ports, respectively. And a second hydraulic circuit, the device being capable of efficiently operating the first and second hydraulic circuits regardless of whether or not the first and second hydraulic circuits are operated. The purpose is to provide.

What is provided is a hydraulic drive device provided in a working machine, and a split flow having a pump main body that sucks hydraulic oil in a tank and raises the pressure, and a first discharge port and a second discharge port that are connected to the pump main body. a variable displacement hydraulic pump which can be a type of hydraulic pump independently of each other from the first discharge port and the second discharge port for discharging the hydraulic fluid, the first discharge port of the hydraulic pump A first pump line connected to the first discharge line, at least one first hydraulic actuator driven by hydraulic oil discharged from the first discharge port, and connected to the first discharge port via the first pump line, A first hydraulic pressure that includes at least one control valve interposed between the first discharge port and the at least one first hydraulic actuator and that guides hydraulic oil discharged from the first discharge port to the first hydraulic actuator. A circuit, a second pump line connected to the second outlet of the hydraulic pump, at least one second hydraulic actuator driven by hydraulic fluid discharged from the second outlet , and the second outlet An operation for discharging from the second discharge port, which includes at least one control valve interposed between the second discharge port and the at least one second hydraulic actuator connected to the second discharge line. A second hydraulic circuit that guides oil to the second hydraulic actuator is interposed between the first discharge port and the tank, and the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit is By opening a valve when a preset first relief pressure is reached, a part of the hydraulic oil discharged from the first discharge port is released to the tank without passing through the control valve of the first hydraulic circuit. A first relief valve and a first joining line arranged to join a part of the hydraulic oil discharged from the first discharge port with the hydraulic oil supplied to the second hydraulic circuit from the second discharge port. And an upstream end connected to a first branch point set in the middle of the first pump line, and a downstream end connected to a first junction point set in the middle of the second pump line, And allowing the first hydraulic oil flowing through the first pump line to branch from the first branch point and join the second hydraulic oil flowing through the second pump line at the first joining point. One converging line , switchable between a closed state of blocking the first converging line and an open state of opening the first converging line, and the first hydraulic circuit from the first discharge port. A first merging switching unit that is switched to the open state only when the pressure of the hydraulic oil supplied to the valve is equal to or higher than a first limiting pressure set in a range lower than the first relief pressure.

In this device, when the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit reaches the first limit pressure, the first merging switching unit is switched to the open state and the first merging switching unit is switched to the open state. By opening the first merging line, a part of the hydraulic oil discharged from the first discharge port can merge into the second hydraulic circuit, so that the operating pressure of the first hydraulic circuit is high. Even when the capacity of the split flow hydraulic pump is limited, the operating speed of the second hydraulic actuator can be increased.

Moreover, since the first limiting pressure is a pressure set in a range lower than the first relief pressure, the first merging switching unit is switched to the open state before the first relief valve is opened. It is possible to prevent the opening of the first relief valve. That is, it is possible to effectively prevent the hydraulic oil discharged from the first discharge port from being returned to the tank through the first relief valve. In other words, the flow rate of the hydraulic oil supplied to the second hydraulic actuator can be increased by effectively utilizing the hydraulic oil returned to the tank through the first relief valve in the related art. Also, the second hydraulic actuator can be moved with high efficiency.

The first merging switching unit is, for example, a pilot switching valve having a closed position that shuts off the first merging line and an open position that opens the first merging line, and when a pilot pressure above a certain level is input. wherein a first confluence switching valve is switched to the open position, the first combined only when the pressure of hydraulic fluid supplied to said first hydraulic circuit from said first discharge port is the first limit pressure or only It is preferable that the switching valve includes a first pilot operating section for inputting the pilot pressure above a certain level.

It is preferable that the pilot switching valve be switched to the open position when a pilot pressure higher than the first limit pressure is input, for example. In this case, the first pilot operating unit inputs, for example, the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit to the first merging switching valve as the pilot pressure. It is possible to appropriately switch the merging state by the first merging line with a simple configuration including only the above.

Alternatively, the first pilot operating portion may have a pilot hydraulic pressure source that generates the pilot pressure equal to or higher than a certain level, and a closed position that blocks introduction of pilot pressure generated by the pilot hydraulic pressure source into the first merging switching valve. A first pilot operation switching valve that has an open position that allows introduction of the pilot pressure to the merging switching valve, and is switched between the open position and the closed position by an input electric signal; and the first discharge valve. A first pressure detector that detects the pressure of the hydraulic oil supplied from the outlet to the first hydraulic circuit, and the first pressure detector only when the pressure detected by the first pressure detector is equal to or higher than the first limit pressure. And a first pilot switching control section for inputting the electric signal to the first pilot operation switching valve so as to switch the one pilot operation switching valve to the open position. The first merging switching unit can easily set and adjust (change) the first limiting pressure.

The device is further interposed between the second discharge port and the tank, and the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit is set to a preset second relief pressure. A second relief valve for opening a part of the hydraulic oil discharged from the second discharge port to the tank without passing through the control valve of the second hydraulic circuit when the valve reaches the second discharge valve, and the second discharge valve. A second merging line arranged so as to merge a part of the hydraulic oil discharged from the outlet with the hydraulic oil supplied to the first hydraulic circuit from the first discharge port , the second pump line At an upstream end connected to a second branch point set at a position upstream of the first confluence point in the middle of, and at a position downstream of the first branch point in the middle of the first pump line. And a downstream end connected to the set second confluence point, wherein the second hydraulic fluid flowing through the second pump line branches from the second branch point and flows through the first pump line. A second merging line that allows the oil to merge at the second merging point, a closed state that shuts off the second merging line, and an open state that opens the second merging line, and A second switch that is switched to the open state only when the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit is equal to or higher than a second limit pressure set in a range lower than the second relief pressure. A merging switching unit, a first merging check valve that is provided on the first merging line and that prevents a backflow of hydraulic oil from the first merging point to the first diverging point, and the second merging line, A second converging check valve that prevents the backflow of hydraulic oil from the second confluence point to the second converging point is provided between the first converging point and the second converging point. A first load check valve for preventing backflow to the first branch point and a backflow from the first branch point to the second branch point are provided between the second branch point and the first merge point. and a second load check valve, Ru equipped with.

According to this device, even when the operating pressure of the second hydraulic circuit is high and the operating pressure of the first hydraulic circuit is low, the opening of the second relief valve is suppressed and the discharge from the second discharge port is suppressed. It is possible to supply a part of the operating oil supplied to the first hydraulic circuit to increase the flow rate of the operating oil supplied to the first hydraulic actuator.

The first relief valve and the second relief valve may be configured as relief valves independent of each other, or a single relief valve may be used as both the first relief valve and the second relief valve. Good.

Like the first merging switching unit, the second merging switching unit is also a pilot switching valve that has a closed position that shuts off the second merging line and an open position that opens the second merging line. The second merging switching valve that is switched to the open position only when the pilot pressure is input, and the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit is equal to or higher than the second limit pressure. Only in such a case, it is preferable that the second merging switching valve includes a second pilot operating section for inputting the pilot pressure above the certain level.

It is preferable that the second merging switching valve is also switched to the open position when a pilot pressure equal to or higher than the second limiting pressure is input. In this case, the second pilot operating unit inputs the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit to the second merging switching valve as the pilot pressure of the second merging switching valve. With a simple configuration including only the second pilot line, it is possible to appropriately switch the merging state by the second merging line. Alternatively, the second pilot operating portion allows a closed position for preventing introduction of pilot pressure generated by the pilot hydraulic pressure source to the second merging switching valve and introduction of the pilot pressure to the merging switching valve. A second pilot operation switching valve, which has an open position and is switched between the open position and the closed position by an input electric signal; and a hydraulic oil supplied from the second discharge port to the second hydraulic circuit. A second pressure detector for detecting the pressure, and for switching the second pilot operation switching valve to the open position only when the pressure detected by the second pressure detector is equal to or higher than the second limit pressure. A second pilot switching control unit that inputs the electric signal to the second pilot operation switching valve may be included.

In the latter case, in the first and second pilot switching control units, the pressure detected by the first pressure detector is equal to or higher than the first limit pressure and the pressure detected by the second pressure detector is When the pressure is equal to or higher than the second limit pressure, that is, when the operating pressures of the first and second hydraulic circuits are both high and the merging is not necessary, the first merging switching valve and the second merging switching valve are operated. It is preferable to perform control for keeping each in the closed position. This control is performed by merging the hydraulic oil from the first discharge port to the second hydraulic circuit at the first limiting pressure, and merging the hydraulic oil from the second discharge port to the first hydraulic circuit at the second limiting pressure, By stopping both of the above, it is possible to expand the operating pressure range of the first and second hydraulic circuits to the first relief pressure and the second relief pressure that are higher than the first and second limiting pressures, respectively. enable.

As described above, according to the present invention, a split flow type hydraulic pump provided in a work machine and having first and second discharge ports, and a first hydraulic pressure connected to the first and second discharge ports, respectively. A hydraulic drive device including a circuit and a second hydraulic circuit, which enables efficient operation of the first and second hydraulic circuits regardless of whether or not the first and second hydraulic circuits are operated. A device is provided.

It is a circuit diagram which shows the hydraulic drive system of the working machine which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows the hydraulic drive system of the working machine which concerns on the 2nd Embodiment of this invention. It is a side view which shows the hydraulic excavator which is an example of the working machine which concerns on each said embodiment.

A preferred embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows a hydraulic excavator that is an example of a working machine provided with the hydraulic drive system according to the above-described embodiment. The hydraulic excavator includes a lower traveling body 10, an upper swing body 12, and an excavation attachment 14. The upper swing body 12 is mounted on the lower traveling body 10 so as to be swingable around a vertical axis X. The excavation attachment 14 is rotatably attached to the upper swing body 12, an arm 18 rotatably connected to the tip of the boom 16, and an arm 18 rotatably attached to the tip of the arm 18. The bucket 20, the boom cylinder 22 that is a hydraulic cylinder that expands and contracts to raise and lower the boom 16, the arm cylinder 24 that is a hydraulic cylinder that expands and contracts to rotate the arm 18, and the bucket 20 are rotated. Bucket cylinder 26, which is a hydraulic cylinder that expands and contracts as described above.

The working machine applied in the present invention is not limited to the hydraulic excavator. The hydraulic drive system according to the present invention can be provided in other hydraulic work machines such as cranes, crushers and other work machines.

FIG. 1 shows a hydraulic drive system according to a first embodiment of the present invention. This hydraulic drive system includes a main pump 28, at least one first hydraulic actuator (two first hydraulic actuators 30A and 32B in the example shown in FIG. 1), and at least one second hydraulic actuator (example shown in FIG. 1). Then, two second hydraulic actuators 30B and 32B), a first hydraulic circuit 34A, a second hydraulic circuit 34B, and a relief valve 36 are provided.

The main pump 28 is a so-called split flow type pump. That is, the main pump 28 has a single pump body 38 and the first discharge port 40A and the second discharge port 40B. The pump main body 38 is connected to and driven by an engine mounted on the hydraulic excavator, and thereby sucks the hydraulic oil in the tank to increase the pressure. The first discharge port 40A and the second discharge port 40B are arranged independently of each other, and the hydraulic oil pressurized by the pump main body 38 is independent from each other through the first discharge port 40A and the second discharge port 40B. It can be discharged.

The main pump 28 is of a variable displacement type and is capable of adjusting the displacement (displacement area) of the pump body 38. By adjusting the volume, it is possible to collectively change the flow rates of the hydraulic oil discharged from the first and second discharge ports 40A and 40B.

The first hydraulic actuators 30A and 32A operate by receiving the supply of hydraulic oil discharged from the first discharge port 40A, and the second hydraulic actuators 30B and 32B are discharged from the second discharge port 40B. It operates by receiving hydraulic oil. The first hydraulic actuators 30A, 32A and the second hydraulic actuators 30B, 32B are a plurality of hydraulic actuators included in the hydraulic excavator, specifically, the boom cylinder 22, the arm cylinder 24, the bucket cylinder 26, It is selected from other hydraulic actuators (eg, swing motor, hydraulic motor, optional cylinder, etc.).

The first hydraulic circuit 34A is connected to the first discharge port 40A of the main pump 28 via a first pump line 42A, and the hydraulic oil discharged from the first discharge port 40A is supplied to each of the first hydraulic actuators. Lead to 30A and 32A. Similarly, the second hydraulic circuit 34B is connected to the second discharge port 40B of the main pump 28 via a second pump line 42B, and the hydraulic oil discharged from the second discharge port 40B is supplied to each of the second hydraulic circuits 34B. 2 Lead to the hydraulic actuator 30B.

Specifically, the first hydraulic circuit 34A includes at least one control valve interposed between the first pump line 42A connected to the first discharge port 40A and each of the first hydraulic actuators 30A and 32A. (In the example shown in FIG. 1, two first control valves 44A and 46A) are included. Similarly, the second hydraulic circuit 34B includes at least one control valve (which is interposed between the second pump line 42B connected to the second discharge port 40B and each of the second hydraulic actuators 30B and 32B). The example shown in FIG. 1 includes two second control valves 44B and 46B). Each of the control valves 44A, 46A, 44B, 46B receives a pilot pressure from, for example, a remote control valve (not shown) and operates to open and close so as to control the supply and discharge of hydraulic oil to and from the corresponding hydraulic actuator.

The relief valve 36 is interposed between the first and second discharge ports 40A, 40B and the tank, and is supplied from the first discharge port 40A to the first hydraulic circuit 34A through the first pump line 42A. Of the pressure of the first hydraulic oil and the pressure of the second hydraulic oil supplied from the second discharge port 40B to the second hydraulic circuit 34B through the second pump line 42B are set in advance. By opening the valve when the relief pressure Pr is reached, the hydraulic oil having the higher pressure is released to the tank without passing through the control valve of the corresponding hydraulic circuit. For example, when the pressure of the first hydraulic oil is higher than the pressure of the second hydraulic oil and has reached the relief pressure Pr, the relief valve 36 causes a part of the first hydraulic oil to the first hydraulic pressure. The valve is opened so as to escape to the tank without passing through the first control valves 44A and 46A of the circuit 34A.

Specifically, the device according to this embodiment includes a tank line 50 that branches from the first and second pump lines 42A and 42B to reach the tank, and the relief valve 36 is provided in the middle of the tank line 50. Is provided. The first and second pump lines 42A, 42B are connected via first and second relief check valves 48A, 48B, respectively, and are provided with a common tank line 50 leading to a tank, and the tank line 50 is provided with the relief valve. 36 are provided. The first and second relief check valves 48A and 48B prevent the flow of hydraulic oil in the direction toward the first and second pump lines 42A and 42B, and the first and second relief check valves 48A and 48B flow through the first pump line 42A. Of the hydraulic oil and the second hydraulic oil flowing through the second pump line 42B, the hydraulic oil having a high pressure is opened to allow it to flow into the relief valve 36. For example, when the pressure of the first hydraulic oil is higher than the pressure of the second hydraulic oil, only the first relief check valve 48A of the first and second relief check valves 48A, 48B opens. And allows the first hydraulic oil to flow into the relief valve 36.

The relief valve 36 opens only when the pressure of the hydraulic oil introduced into the relief valve 36, that is, the primary pressure of the relief valve 36 reaches a preset relief pressure Pr, whereby the first The maximum pressure of the first and second hydraulic circuits 34A and 34B is defined as the relief pressure. In other words, the relief valve 36 according to the first embodiment has the first relief pressure set for the first hydraulic circuit 34A and the second relief pressure set for the second hydraulic circuit 34B. , Is also used as a relief valve for both the first and second hydraulic circuits 34A and 34B. That is, the first relief pressure and the second relief pressure according to the first embodiment are equal to each other, and the common relief pressure is equal to the pressure of either the first hydraulic oil or the second hydraulic oil. Is reached, the relief valve 36 opens.

The main pump 28 included in the hydraulic drive device is of a variable displacement type, and therefore can control the flow rates of the first hydraulic oil and the second hydraulic oil discharged from the first and second discharge ports 40A and 40B, respectively. Although possible, the flow rate of the first hydraulic oil and the flow rate of the second hydraulic oil cannot be individually adjusted (that is, the both flow rates can be different from each other). Therefore, the hydraulic drive system according to this embodiment has a first converging line 52A and a first converging line 52A as means for operating both the first and second hydraulic circuits 34A and 34B with high efficiency regardless of the circumstances. A confluence switching unit 54A, a second confluence line 52B, and a second confluence switching unit 54B are further provided.

The first merging line 52A is arranged so as to merge a part of the hydraulic oil discharged from the first discharge port 40A with the hydraulic oil supplied to the second hydraulic circuit 34B from the second discharge port 40B. To be done. Specifically, the first merging line 52A has an upstream end connected to a branch point 56A set in the middle of the first pump line 42A and a merging point 58B set in the middle of the second pump line 42B. And a downstream end connected to the first pump line 42A, the first hydraulic oil flowing in the first pump line 42A branches from the branch point 56A, and the second hydraulic oil flowing in the second pump line 42B merges with the second working oil 58B. Allow to join in. Similarly, the second merging line 52B is connected to an upstream end connected to a branch point 56B set in the middle of the second pump line 42B and a merging point 58A set in the middle of the first pump line 42A. And a downstream end to which the second hydraulic oil flows, which flows through the second pump line 42B and branches from the branch point 56B to the first hydraulic oil that flows through the first pump line 42A at the confluence point 58A. Allow to join.

As shown in FIG. 1, it is preferable that the first merging line 52A is provided with a first merging check valve 64A that prevents the backflow of the hydraulic oil from the merging point 58B to the branching point 56A. Similarly, it is preferable that the second merging line 52B be provided with a second merging check valve 64B that prevents the backflow of the hydraulic oil from the merging point 58A to the branching point 56B.

As shown in FIG. 1, the confluence points 58A are preferably provided at positions on the upstream side of the junction points 56A, respectively, and the junction points 58A to 58A are disposed between the junction points 58A and 58A. A first load check valve 66A that prevents backflow to the branch point 56A may be provided. Similarly, the converging points 58B are provided at positions upstream of the branching points 56B, respectively, and prevent backflow from the converging points 58B to the branching points 56B between the branching points 56B and the converging points 58B. A second load check valve 66A may be provided.

The first merging switching unit 54A can switch between a closed state in which the first merging line 52A is shut off and an open state in which the first merging line 52A is opened, and the first merging port 40A is connected to the first merging port 40A. The pressure of the first hydraulic oil supplied to the first hydraulic circuit 34A through the pump line 42A is the first relief pressure set for the first hydraulic circuit 34A (in the present embodiment, the first relief pressure is set for the relief valve 36). The open state is switched only when the pressure is equal to or higher than the first limit pressure PL1 set in a range lower than the relief pressure Pr). Similarly, the second merging switching unit 54B can switch between a closed state in which the second merging line 52B is shut off and an open state in which the second merging line 52B is opened, and from the second outlet 40B. The pressure of the second hydraulic oil supplied to the second hydraulic circuit 34B through the second pump line 42B is the second relief pressure set for the second hydraulic circuit 34B (in the present embodiment, the first relief pressure Similarly, it is switched to the open state only when the pressure is equal to or higher than the second limit pressure PL2 set in a range lower than the relief pressure Pr set in the relief valve 36.

Specifically, the first merging switching unit 54A according to the first embodiment has a first merging switching valve 60A and a first pilot line 62A. The first merging switching valve 60A is configured by a two-position pilot switching valve having a pilot port 60a, and opens the first merging line 52A and the closed position (the right side position in FIG. 1) that blocks the first merging line 52A. And an open position (left side position in FIG. 1). The first merging switching valve 60A holds the closed position when the pilot pressure of a certain level or more, that is, the first limiting pressure PL1 in this embodiment, is not input to the pilot port 60a, and the first merging switching valve 60A has a certain level of the pilot port 60a or more. Is switched to the open position only when the pilot pressure of, that is, the pressure equal to or higher than the first limit pressure PL1 in this embodiment is input. The first pilot line 62A supplies the pressure of the first hydraulic oil supplied to the first hydraulic circuit 34A through the first pump line 42A, preferably the pressure downstream of the confluence 58A, to the pilot port. By inputting the pilot pressure to 60a, a first pilot operating portion for switching the first merging switching valve 60A is configured.

Similarly, the second merging switching unit 54B according to the first embodiment has a second merging switching valve 60B and a second pilot line 62B. The second merging switching valve 60B is composed of a two-position pilot switching valve having a pilot port 60b, and opens the second merging line 52B and the closed position (the left side position in FIG. 1) that shuts off the second merging line 52B. And an open position (right side position in FIG. 1). The second merging switching valve 60B holds the closed position when the pilot pressure of a certain level or more, that is, the second limiting pressure PL2 in the present embodiment, is not input to the pilot port 60b, and the second merging switching valve 60B has a certain level of the pilot port 60b or more. Is switched to the open position only when the pilot pressure of, that is, the pressure of the second limit pressure PL2 or more in this embodiment is input. The second pilot line 62B supplies the pressure of the second hydraulic oil supplied to the second hydraulic circuit 34B through the second pump line 42B, preferably the pressure downstream of the confluence point 58B, to the second pressure line. By inputting the pilot pressure to the pilot port 60b of the merging switching valve 60B, a second pilot operating unit for switching the second merging switching valve 60B is configured.

The hydraulic drive system also includes a controller 80 as shown in FIG. The controller 80 changes the capacity of the main pump 28 by inputting a command signal to the regulator 78 attached to the main pump 28, whereby the first and second discharge ports 40A, 40B of the main pump 28 are changed. Controls the flow rate of hydraulic oil discharged from the pump (flow rate of pump discharge). The controller 80 is, for example, a so-called positive control for changing the pump discharge flow rate based on an operation given to the control valves 44A, 46A, 44B, 46B by an operator, or the first and second discharge ports 40A, 40B. Based on the pressure of the operating oil (pump discharge pressure), the horsepower control for keeping the horsepower required for driving the main pump 28 within a certain range is performed.

Next, the operation of this hydraulic drive system will be described.

The main pump 28 is driven by an engine (not shown) to discharge the first hydraulic oil and the second hydraulic oil from the first and second discharge ports 40A and 40B individually and at equal flow rates. The flow rates of the first and second hydraulic oils can be controlled by adjusting the capacity of the pump body 38 of the main pump 28.

The hydraulic oil discharged from the first and second discharge ports 40A and 40B is supplied to the first hydraulic circuits 34A and 34B through the first and second pump lines 42A and 42B, respectively. Here, of the control valves 44A, 46A, 44B, 46B included in the first and second hydraulic circuits 34A, 34B, for example, when the first control valve 44A is operated to open, the first hydraulic circuit 34A is supplied. At least a part of the generated first hydraulic oil moves the first hydraulic actuator 30A via the first control valve 44A and is supplied to the first hydraulic circuit 34A from the first discharge port 40A by the amount of the load. The pressure of the working oil (first working oil) increases.

When the pressure of the first hydraulic oil thus raised reaches the first limiting pressure PL1 (lower than the relief pressure Pr), the first limiting pressure is reached before the relief valve 36 connected to the first pump line 42A is opened. The first merging switching valve 60A that receives the input of PL1 is switched from the previously closed position to the open position, whereby a part of the hydraulic oil (first hydraulic oil) flowing through the first pump line 42A is first merged. It is allowed to join the second pump line 42B through the line 52A. This merging suppresses energy loss due to opening of the relief valve 36 and increases the flow rate of the hydraulic oil supplied to the second hydraulic circuit 34B, thereby increasing the operating speed of the second hydraulic actuators 30B and 32B. Allows you to maintain.

For example, in the case where the controller 80 performs horsepower control on the discharge flow rate of the main pump 28, if the pressure of the first hydraulic oil is significantly higher than the pressure of the second hydraulic oil, the first and second discharge ports are correspondingly increased. As a result of suppressing both the flow rates of the hydraulic oil discharged from 40A and 40B, the pressure of the second hydraulic oil is low and a large flow rate can be originally allowed, but the flow rate of the second hydraulic oil and thus the second hydraulic actuator. The operating speed of 30B and 32B can also be suppressed. However, in the device according to this embodiment, the flow rate of the second hydraulic oil supplied to the second hydraulic circuit 34B can be increased by merging part of the first hydraulic oil with the second hydraulic oil. Is.

In this way, when the pressure of the first hydraulic oil reaches the first limiting pressure PL1, the merging of the first hydraulic oil with the second hydraulic oil through the first merging line 52A is The energy loss is reduced by suppressing the pressure from reaching the relief pressure and the opening frequency of the relief valve 36, and the second hydraulic actuators 30B, 32B are secured by ensuring the flow rate of the hydraulic oil flowing through the second hydraulic circuit 34B. It is possible to secure the operating speed and achieve it at the same time.

This effect can also be obtained similarly when the pressure of the second hydraulic oil significantly rises to reach the second limit pressure PL2 as compared with the first hydraulic oil, contrary to the above. That is, in this case, the second merging switching valve 60B that has received the input pressure equal to or higher than the second limiting pressure PL2 is switched from the closed position to the open position until then, and the second pump line through the second merging line 52B. By allowing the second hydraulic oil to merge from 42B to the first pump line 42A, the frequency of opening the relief valve 36 due to the increase in the pressure of the second hydraulic oil is suppressed, and the second hydraulic oil is supplied to the first hydraulic circuit 34A. It is possible to simultaneously secure the flow rate of the first hydraulic oil and the operating speed of the first hydraulic actuators 30A and 32A.

In particular, the first and second merging switching valves 60A and 60B according to the first embodiment each have the open position when the pilot pressures equal to or higher than the first and second limiting pressures PL1 and PL2 are input. Therefore, the first and second pilot operating parts according to the first embodiment have a simple structure including only the first and second pilot lines 62A and 62B. It is possible to appropriately switch the merging state of the hydraulic oil by the second merging lines 52A and 52B.

The first and second limiting pressures PL1 and PL2 can be arbitrarily set in a range lower than the first and second relief pressures (the common relief pressure Pr in the above embodiment), respectively. Preferably, the relief pressure Pr is different from the first and second relief pressures by a degree that allows the first and second merging switching valves 60A and 60B to open reliably before the relief valve 36 opens. It is preferable to set the first and second limiting pressures PL1 and PL2 as high as possible while being applied between the two limiting pressures PL1 and PL2. Generally, it is preferable that the first and second limiting pressures PL1 and PL2 are set to about 80 to 90% of the relief pressure Pr. Further, the first and second limiting pressures PL1 and PL2 may be equal to each other or different from each other.

FIG. 2 shows a hydraulic drive system according to a second embodiment of the present invention.

While the first and second pilot operating parts according to the first embodiment are respectively configured by the first pilot lines 62A and 62B, the first pilot operating part according to the second embodiment is A pilot pump 68, a first pilot line 70A, a first pilot operation switching valve 72A, a first pressure detector 74A, and a first pilot switching controller 82A included in the controller 80. The second pilot operating unit according to the embodiment of the present invention includes a pilot pump 68, a second pilot line 70B, a second pilot operation switching valve 72B, a second pressure detector 74B, and a controller 80 included in the controller 80. And a 2-pilot switching control unit 82B.

The pilot pump 68 is a pilot hydraulic pressure source, and is driven by an engine (not shown) together with the main pump 28, and is sufficient to switch the first and second merging switching valves 60A and 60B to open positions. Generate pilot pressure. Unlike the first embodiment, the pilot pressure at which the first and second merging switching valves 60A and 60B are switched to the open position does not necessarily have to be equal to the first and second limiting pressures PL1 and PL2.

The first and second pilot lines 70A and 70B are piped so as to guide the pilot pressure output from the pilot pump 68 to the pilot ports 60a and 60b of the first and second merging switching valves 60A and 60B.

The first and second pilot operation switching valves 72A, 72B are provided in the middle of the first and second pilot lines 70A, 70B, respectively, and are closed positions for shutting off the first and second pilot lines 70A, 70B, respectively. And the open position where the first and second pilot lines 70A and 70B are opened respectively. The first and second pilot operation switching valves 72A, 72B according to the second embodiment are each configured by a two-position electromagnetic switching valve having solenoids 72a, 72b, and an electric signal is sent to the solenoids 72a, 72b. When it is not input, the closed position is maintained, and when an electric signal is input to the solenoids 72a and 72b, it is switched to the open position.

The first and second pressure detectors 74A and 74B are respectively supplied to the first and second hydraulic circuits 34A and 34B from the first and second discharge ports 40A and 40B, respectively. The oil pressure, preferably the pressure on the downstream side of the confluence points 58A and 58B, is detected and converted into a pressure detection signal which is an electric signal.

The first pilot switching control unit 82A stores the first limit pressure PL1, and the first pilot operation is performed only when the pressure detected by the first pressure detector 74A is equal to or higher than the first limit pressure PL1. An electric signal, that is, a valve opening command signal is input to the solenoid 72a of the first pilot operation switching valve 72A so as to switch the switching valve 72A to the open position. The second pilot switching controller 82B stores the second limit pressure PL2, and the second pilot operation is performed only when the pressure detected by the second pressure detector 74B is equal to or higher than the second limit pressure PL2. An electric signal, that is, a valve opening command signal is input to the solenoid 72b of the second pilot operation switching valve 72B so as to switch the switching valve 72B to the open position.

Also in the second embodiment, when the pressure of the first hydraulic oil supplied from the first discharge port 40A to the first hydraulic circuit 34A becomes equal to or higher than the first limit pressure PL1, the pressure from the first pressure detector 74A is increased. The first pilot switching control unit 82A receiving the detection signal inputs a valve opening command signal to the solenoid 72a of the first pilot operation switching valve 72A to switch the first pilot operation switching valve 72A to the open position. The merging of the first hydraulic oil to the second hydraulic oil supplied from the second discharge port 40B to the second hydraulic circuit 34B through the first merging line 52A is allowed. As a result, similarly to the first embodiment, the valve opening frequency of the relief valve 36 is suppressed by the increase in the pressure of the first hydraulic oil, the flow rate of the second hydraulic oil is secured, and the second hydraulic actuator 30B, Ensuring an operating speed of 32B is simultaneously achieved.

Similarly, when the pressure of the second hydraulic oil supplied from the second discharge port 40B to the second hydraulic circuit 34B becomes equal to or higher than the second limit pressure PL2, the second pressure detector 74B receives a pressure detection signal from the second pressure detector 74B. The 2 pilot switching control unit 82B inputs a valve opening command signal to the solenoid 72b of the second pilot operation switching valve 72B to switch the second pilot operation switching valve 72B to the open position, so that the first discharge port 40A moves to the first position. The merging of the second hydraulic oil into the first hydraulic oil supplied to the hydraulic circuit 34A through the second merging line 52B is allowed. Thereby, similarly to the second embodiment, the frequency of opening the relief valve 36 is suppressed by the increase in the pressure of the second hydraulic oil, the flow rate of the first hydraulic oil is secured, and the first hydraulic actuator 30A, Ensuring an operating speed of 32A is achieved at the same time.

In the second embodiment, the first and second limiting pressures PL1 and PL2 stored in the first and second pilot switching control sections 82A and 82B, respectively, are simply rewritten to perform the simple operation. 2 There is an advantage that the limiting pressures PL1 and PL2 can be easily changed and adjusted.

In the second embodiment, in the first and second pilot switching control units 82A and 82B, the pressure detected by the first pressure detector 74A is equal to or higher than the first limiting pressure PL1 and the second When the pressure detected by the pressure detector 74B is equal to or higher than the second limit pressure PL2, that is, when the operating pressures of the first and second hydraulic circuits 34A and 34B are both high and the merging is not necessary. It is preferable to perform control to keep the first merging switching valve 60A and the second merging switching valve 60B in closed positions. In this way, the first hydraulic fluid merges from the first discharge port 40A to the second hydraulic circuit 34B at the first limit pressure PL1, and the second discharge port 40B to the first hydraulic circuit 34A at the second limit pressure PL2. To stop both the joining of the hydraulic oil to the first and second hydraulic circuits 34A and 34B is higher than the first and second limiting pressures PL1 and PL2, respectively. It is also possible to increase the pressure to the second relief pressure (the common relief pressure Pr in the second embodiment).

The present invention is not limited to the embodiments described above. The present invention includes the following modes, for example.

In the first and second embodiments, the single relief valve 36 is shared by the first and second hydraulic circuits 34A and 34B. However, the first and second relief valves according to the present invention have the first hydraulic pressure. It may be separately provided in the circuit and the second hydraulic circuit. In this case, the first relief pressure set for the first relief valve and the second relief pressure set for the second relief pressure may be different from each other. Even when the first relief pressure and the second relief pressure are different, the first limiting pressure is set in a range lower than the first relief pressure, and the second limiting pressure is set in a range lower than the second relief pressure. Is good.

Further, the second merging line 52B and the second merging switching unit 54B according to the first and second embodiments can be appropriately omitted. For example, at least one first hydraulic actuator is driven by a high driving pressure (for example, a boom cylinder or an arm cylinder of a hydraulic excavator), while each second hydraulic actuator is driven by a relatively low driving pressure. In the case of a thing (for example, a bucket cylinder of a hydraulic excavator), the first merging line and the first merging switching unit may be provided only for the first hydraulic circuit.

Hereinafter, preferred embodiments of the present invention will be assumed.

As a first example, assume a hydraulic excavator in which at least one first hydraulic actuator includes an arm cylinder and at least one second hydraulic actuator includes a bucket cylinder. If the driving load on the arm cylinder increases and the first relief valve opens as in the conventional case during excavation work by the hydraulic excavator, a part of the hydraulic oil supplied to the first hydraulic circuit is returned to the tank. While the energy is dissipated as heat and is dissipated, the flow rate of the second hydraulic oil is also suppressed due to the increase in the drive load, and the drive speed of the bucket cylinder is reduced. However, before the pressure of the first hydraulic oil supplied to the first hydraulic circuit reaches the first limiting pressure lower than the first relief pressure set in the first relief valve, By allowing the merging with the hydraulic oil, the opening of the first relief valve can be suppressed, and the flow rate of the hydraulic oil supplied to the bucket cylinder can be secured while the driving pressure of the arm cylinder is secured. That is, it is possible to secure the speed of the excavation work using the bucket.

As a second embodiment, assume a crusher in which at least one first hydraulic actuator includes a crushing cylinder that opens and closes the crusher, and at least one second hydraulic actuator includes a boom cylinder. If the driving load of the crushing cylinder is increased and the first relief valve is opened as in the conventional case in order to clamp the object with a sufficient force by the crusher, the operation supplied to the first hydraulic circuit. A part of the oil is returned to the tank and its energy is dissipated as heat, and the flow rate of the second hydraulic oil is also suppressed due to the increase in the drive load, so that the drive speed of the boom cylinder is reduced. However, before the pressure of the first hydraulic oil supplied to the first hydraulic circuit reaches the first limiting pressure lower than the first relief pressure set in the first relief valve, By allowing the merging with the hydraulic oil, the opening of the first relief valve can be suppressed, and the flow rate of the hydraulic oil supplied to the boom cylinder can be controlled while the driving pressure of the crushing cylinder is ensured. It is possible to secure the speed, that is, to secure the speed of the hoisting motion of the boom.

30A, 32A 1st hydraulic actuator 30B, 32B 2nd hydraulic actuator 34A 1st hydraulic circuit 34B 2nd hydraulic circuit 36 Relief valve 38 Pump main body 40A 1st discharge port 40B 2nd discharge port 44A, 46A 1st control valve 44B, 46B Second control valve 50 Tank line 52A First merging line 52B Second merging line 54A First merging switching part 54B Second merging switching part 60A First merging switching valve 60B Second merging switching valve 62A First pilot line 62B Second pilot Line 68 Pilot pump (pilot hydraulic source)
70A 1st pilot line 70B 2nd pilot line 72A 1st pilot operation switching valve 72B 2nd pilot operation switching valve 74A 1st pressure detector 74B 2nd pressure detector 80 controller 82A 1st pilot switching control part 82B 2nd pilot switching Control unit

Claims (8)

A hydraulic drive device provided in a work machine,
A split-flow type hydraulic pump having a pump main body for sucking and increasing the pressure of hydraulic oil in a tank, and a first discharge opening and a second discharge opening connected to the pump main body, wherein the first discharge opening and the second discharge opening are provided. A variable displacement hydraulic pump capable of discharging the hydraulic oil independently of each other,
A first pump line connected to the first outlet of the hydraulic pump;
At least one first hydraulic actuator moved by hydraulic fluid discharged from the first discharge port;
The first discharge port includes at least one control valve that is connected to the first discharge port through the first pump line and that is interposed between the first discharge port and the at least one first hydraulic actuator. A first hydraulic circuit for guiding hydraulic fluid discharged from the first hydraulic actuator to the first hydraulic actuator;
A second pump line connected to the second outlet of the hydraulic pump;
At least one second hydraulic actuator that is moved by hydraulic fluid discharged from the second discharge port;
The second discharge port includes at least one control valve connected to the second discharge port via the second pump line and interposed between the second discharge port and the at least one second hydraulic actuator. A second hydraulic circuit that guides hydraulic fluid discharged from the second hydraulic actuator to the second hydraulic actuator;
A valve that is interposed between the first discharge port and the tank and opens when the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit reaches a preset first relief pressure. A first relief valve that allows a part of the hydraulic oil discharged from the first discharge port to escape to the tank without passing through the control valve of the first hydraulic circuit,
A first confluence line disposed so as to merge some of the hydraulic fluid discharged from the first discharge port to the hydraulic fluid supplied to said second hydraulic circuit from said second discharge port, wherein An upstream end connected to a first branch point set in the middle of the first pump line, and a downstream end connected to a first junction point set in the middle of the second pump line, A first merging line that allows the first hydraulic oil flowing through the first pump line to branch from the first branch point and join the second hydraulic oil flowing through the second pump line at the first merging point ;
It is possible to switch between a closed state in which the first merging line is blocked and an open state in which the first merging line is opened, and the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit is the above-mentioned. A first merging switching unit that is switched to the open state only when the pressure is equal to or higher than a first limit pressure set in a range lower than the first relief pressure;
It is interposed between the second discharge port and the tank, and opens when the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit reaches a preset second relief pressure. A second relief valve that allows a part of the hydraulic oil discharged from the second discharge port to escape to the tank without passing through the control valve of the second hydraulic circuit,
A second merging line arranged to join a part of the hydraulic oil discharged from the second discharge port with the hydraulic oil supplied to the first hydraulic circuit from the first discharge port. An upstream end connected to a second branch point set at a position upstream of the first confluence point in the middle of the second pump line, and downstream of the first branch point in the middle of the first pump line. A downstream end connected to a second confluence point set at a side position, and the second hydraulic fluid flowing through the second pump line branches from the second branch point to the first pump line. A second merging line that permits merging with the flowing first hydraulic oil at the second merging point;
It is possible to switch between a closed state in which the second merging line is blocked and an open state in which the second merging line is opened, and the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit is the above. A second merging switching section that is switched to the open state only when the second limiting pressure set in a range lower than the second relief pressure is equal to or higher than the second limiting pressure;
A first merging check valve which is provided in the first merging line and which prevents a backflow of hydraulic oil from the first merging point to the first divergence point;
A second merging check valve which is provided in the second merging line and which prevents a backflow of the hydraulic oil from the second merging point to the second divergence point;
A first load check valve that is provided between the first branch point and the second junction point and prevents a backflow from the second junction point to the first junction point;
A second load check valve that is provided between the second branch point and the first junction point and prevents a backflow from the first junction point to the second junction point;
A hydraulic drive device for a working machine, comprising: The hydraulic drive system for a working machine according to claim 1, wherein the first merging switching unit has a closed position that shuts off the first merging line and an open position that opens the first merging line. And a first merging switching valve that is switched to the open position only when a pilot pressure above a certain level is input, and the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit is A hydraulic drive system for a working machine, comprising: a first pilot operating section for inputting the pilot pressure of a certain level or more to the first merging switching valve only when the pressure is one limit pressure or more. The hydraulic drive system for a working machine according to claim 2, wherein the first merging switching valve is switched to the open position when a pilot pressure equal to or higher than the first limiting pressure is input. The first pilot operation unit includes a first pilot line that inputs the pressure of the hydraulic oil supplied from the first discharge port to the first hydraulic circuit as the pilot pressure to the first merging switching valve, and the hydraulic pressure of the working machine. Drive. A hydraulic drive system for a working machine according to claim 2, wherein the first pilot operating unit has a front Symbol pilot hydraulic source for generating a certain level of pilot pressure, the pilot pressure generated by the pilot hydraulic source The open position and the closed position have a closed position for preventing introduction into the first merge switching valve and an open position for allowing introduction of the pilot pressure into the first merge switching valve. And a first pilot operation switching valve, a first pressure detector for detecting the pressure of the hydraulic fluid supplied from the first discharge port to the first hydraulic circuit, and a first pressure detector for detecting the pressure of the hydraulic oil. First pilot switching control for inputting the electric signal to the first pilot operation switching valve so that the first pilot operation switching valve is switched to the open position only when the pressure to be applied is equal to or higher than the first limit pressure. And a hydraulic drive unit for the working machine including the unit. The hydraulic drive system for a working machine according to claim 1 , wherein the second merging switching unit has a closed position that shuts off the second merging line and an open position that opens the second merging line. And a second merging switching valve that is switched to the open position only when a pilot pressure above a certain level is input, and the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit is A hydraulic drive system for a working machine, comprising: a second pilot operating section for inputting the pilot pressure of a certain level or more to the second merging switching valve only when the pressure is two or more limiting pressures. The hydraulic drive system for a work machine according to claim 5 , wherein the second merging switching valve is switched to the open position when a pilot pressure equal to or higher than the second limiting pressure is input. The 2nd pilot operation part inputs the pressure of the working oil supplied from the 2nd discharge port to the 2nd hydraulic circuit to the 2nd merging changeover valve as the pilot pressure of the 2nd merging changeover valve. Hydraulic drive for work machines, including. The hydraulic drive system for a work machine according to claim 5 , wherein the second pilot operation part includes a pilot hydraulic pressure source that generates the pilot pressure equal to or higher than the certain level, and the pilot pressure source that generates the pilot pressure. 2 has a closed position for preventing introduction into the second merging switching valve and an open position for allowing introduction of the pilot pressure into the second merging switching valve, and the open position and the closed position according to an input electric signal. To the second pilot operation switching valve, a second pressure detector for detecting the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit, and the second pressure detector. A second pilot switching control unit for inputting the electric signal to the second pilot operation switching valve so that the second pilot operation switching valve is switched to the open position only when the pressure is equal to or higher than the second limit pressure. And a hydraulic drive for the work machine, including. The hydraulic drive system for a work machine according to claim 4 , wherein the second merging switching unit has a closed position that shuts off the second merging line and an open position that opens the second merging line. And a second merging switching valve that is switched to the open position only when a pilot pressure above a certain level is input, and the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit is A second pilot operating portion for inputting the pilot pressure of the constant or more to the second merging switching valve only when the pressure is equal to or higher than two limiting pressures, the second pilot operating portion including the pilot hydraulic pressure source; It has a closed position for preventing the pilot pressure generated by the pilot hydraulic pressure source from being introduced into the second merging switching valve and an open position for allowing the pilot pressure to be introduced into the second merging switching valve. Second pilot operation switching valve that is switched between the open position and the closed position by an electric signal that is generated, and a second pressure detector that detects the pressure of the hydraulic oil supplied from the second discharge port to the second hydraulic circuit. And to the second pilot operation switching valve so as to switch the second pilot operation switching valve to the open position only when the pressure detected by the second pressure detector is equal to or higher than the second limit pressure. A second pilot switching control section for inputting an electric signal, wherein the first pilot switching control section and the second pilot switching control section are such that the pressure detected by the first pressure detector is the first limiting pressure. a control to keep at it and wherein the case is pressure detected at the second limit pressure or the second pressure detector, respectively the closed position the first confluence switching valve and the second confluence switching valve or The hydraulic drive of the working machine.

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