Hydraulic circuit for construction machine

Abstract

To provide a hydraulic circuit for a construction machine that can effectively utilize the surplus flow rate of a first hydraulic pump.SOLUTION: In a hydraulic circuit 2, when signals are output from a first traveling operation device, a second traveling operation device, and an actuator operation device, hydraulic oil is supplied from a first hydraulic pump 28 to an actuator switching valve. In addition, hydraulic oil is supplied from a second hydraulic pump 30 to a first traveling switch valve 32 and a second traveling switch valve 34. Furthermore, an opening of a communication valve 64 is adjusted in response to the signal output from the actuator operation device, and the supply amount of hydraulic oil sent from a first pump line 38 to a second pump line 40 is controlled.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a hydraulic circuit of a construction machine for supplying hydraulic oil to a first traveling motor, a second traveling motor, and other hydraulic actuators.

Background Art

[0002] A hydraulic excavator, which is a typical example of a construction machine, includes a lower traveling body, an upper revolving body rotatably supported on the upper part of the lower traveling body, and a front working machine mounted on the upper revolving body. The lower traveling body includes a pair of left and right crawlers, a first traveling motor for driving one crawler, and a second traveling motor for driving the other crawler.

[0003] Generally, in the hydraulic circuit of a hydraulic excavator, hydraulic oil is supplied from two or more hydraulic pumps to hydraulic actuators. For example, when a straight traveling operation is performed, hydraulic oil is supplied from a first hydraulic pump to the first traveling motor, and hydraulic oil is supplied from a second hydraulic pump to the second traveling motor. Also, when a straight traveling operation and an operation of the front working machine are performed simultaneously, hydraulic oil is supplied from the first hydraulic pump to a hydraulic actuator for operating the front working machine, and the same amount of hydraulic oil is supplied from the second hydraulic pump to both the first and second traveling motors. Thereby, straightness during traveling is ensured (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the straight-ahead travel operation and the operation of the front working machine are performed simultaneously, there may be a surplus in the supply flow rate of the first hydraulic pump depending on the operating speed of the front working machine. However, this surplus flow rate has been wasted without being used.

[0006] An object of the present invention is to provide a hydraulic circuit for a construction machine that can effectively use the surplus flow rate of the first hydraulic pump.

Means for Solving the Problem

[0007] According to the present invention, there is provided a hydraulic circuit for a construction machine that solves the above problems. That is, "A hydraulic circuit for a construction machine for supplying hydraulic oil to a first travel motor, a second travel motor, and other hydraulic actuators, A variable displacement first hydraulic pump, A variable displacement second hydraulic pump, A first pump line through which the hydraulic oil discharged from the first hydraulic pump flows, A second pump line through which the hydraulic oil discharged from the second hydraulic pump flows, A first travel switching valve connected to the first pump line and the second pump line, for switching the flow direction of the hydraulic oil to the first travel motor, A second travel switching valve connected to the second pump line, for switching the flow direction of the hydraulic oil to the second travel motor, An actuator switching valve connected to at least the first pump line, for switching the flow direction of the hydraulic oil to the other hydraulic actuators, A first on-off valve provided between the first hydraulic pump and the first travel switching valve, A second on-off valve provided between the second hydraulic pump and the first travel switching valve, A communication line for communicating the first pump line and the second pump line, A communication valve provided on the communication line, A first travel operation tool for outputting a signal for operating the first travel motor, A second traveling operation tool that outputs a signal for operating the second traveling motor, an actuator operation tool that outputs a signal for operating the other hydraulic actuator, and a controller that executes circuit control based on signals output from the first traveling operation tool, the second traveling operation tool, and the actuator operation tool. The controller, when a signal is output from the first traveling operation tool and / or the second traveling operation tool and no signal is output from the actuator operation tool, opens the first on-off valve and closes the second on-off valve, thereby supplying hydraulic oil from the first hydraulic pump to the first traveling switching valve and / or supplying hydraulic oil from the second hydraulic pump to the second traveling switching valve and closing the communication valve. On the other hand, when signals are output from the first traveling operation tool, the second traveling operation tool, and the actuator operation tool, hydraulic oil is supplied from the first hydraulic pump to the actuator switching valve, the first on-off valve is closed, and the second on-off valve is opened, thereby supplying hydraulic oil from the second hydraulic pump to the first traveling switching valve and the second traveling switching valve and adjusting the opening degree of the communication valve according to the signal output from the actuator operation tool to control the supply amount of hydraulic oil sent from the first pump line to the second pump line. There is provided a hydraulic circuit for a construction machine.

[0008] Preferably, when signals are output from the first traveling operation tool, the second traveling operation tool, and the actuator operation tool, the controller sets the opening degree of the communication valve to a first opening degree when the signal output from the actuator operation tool is less than a predetermined value, and sets it to a second opening degree smaller than the first opening degree when the signal output from the actuator operation tool is greater than or equal to the predetermined value.

[0009] The first opening degree is preferably set to an opening degree such that the rotational speed of the first traveling motor does not fall below the required speed corresponding to the operation amount of the first traveling operation tool, and the rotational speed of the second traveling motor does not fall below the required speed corresponding to the operation amount of the second traveling operation tool. The first opening degree may be changed according to the signal of the actuator operation tool.

[0010] The second opening degree is preferably set to an opening degree such that the operating speed of the other hydraulic actuator does not fall below the required speed corresponding to the operation amount of the actuator operation tool. The second opening degree can be changed according to the signal of the actuator operation tool. The second opening degree may be fully closed.

[0011] When the controller sets the opening degree of the communication valve to the first opening degree, it is convenient to reduce the discharge amount of the second hydraulic pump to such an extent that the rotational speed of the first traveling motor does not fall below the required speed corresponding to the operation amount of the first traveling operation tool, and the rotational speed of the second traveling motor does not fall below the required speed corresponding to the operation amount of the second traveling operation tool.

[0012] The communication valve has a backflow prevention function, allows the flow of hydraulic oil from the first pump line to the second pump line, and can prevent backflow from the second pump line to the first pump line.

[0013] The actuator switching valve is connected to both the first pump line and the second pump line. A check valve is provided between the actuator switching valve and the first hydraulic pump, and a flow control valve may be provided between the actuator switching valve and the second hydraulic pump.

[0014] The actuator switching valve is connected to both the first pump line and the second pump line. A flow control valve is preferably provided between the actuator switching valve and the first hydraulic pump, and a poppet valve is provided between the actuator switching valve and the second hydraulic pump.

[0015] The actuator switching valve is connected to the first pump line and not connected to the second hydraulic pump line, and a check valve may be provided between the actuator switching valve and the first hydraulic pump.

Effects of the Invention

[0016] In the hydraulic circuit of the construction machine of the present invention, when signals are output from the first and second traveling operation tools and the actuator operation tool, hydraulic oil is supplied from the first hydraulic pump to the actuator switching valve, and hydraulic oil is supplied from the second hydraulic pump to the first and second traveling switching valves. At the same time, the supply amount of the hydraulic oil sent from the first pump line to the second pump line is controlled, so that the surplus flow rate of the first hydraulic pump is used for the operation of the first and second traveling motors. Therefore, according to the present invention, the surplus flow rate of the first hydraulic pump can be effectively used.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0018] Hereinafter, a preferred embodiment of the hydraulic circuit of the construction machine according to the present invention will be described with reference to the drawings.

[0019] (Hydraulic circuit 2) The hydraulic circuit 2 shown in FIG. 1 is an example of the hydraulic circuit according to the present invention and is mounted on a self-propelled construction machine. The hydraulic circuit 2 is a circuit for supplying hydraulic oil to a first travel motor, a second travel motor, and other hydraulic actuators other than the first and second travel motors.

[0020] The hydraulic circuit 2 can be mounted on, for example, the hydraulic excavator 4 shown in FIG. 2. The hydraulic excavator 4 includes a lower traveling body 6, an upper revolving body 8 rotatably supported by the lower traveling body 6, and a front working machine 10 attached to the upper revolving body 8. The lower traveling body 6 includes a pair of crawlers 12 (only one side is shown), a first travel motor 14 for driving one crawler 12, and a second travel motor (not shown) for driving the other crawler. The front working machine 10 includes a boom 16 swingably supported by the upper revolving body 8, an arm 18 swingably supported at the tip of the boom 16, a bucket 20 swingably supported at the tip of the arm 18, a boom cylinder 22 for swinging the boom 16, an arm cylinder 24 for swinging the arm 18, and a bucket cylinder 26 for swinging the bucket 20.

[0021] When the hydraulic circuit 2 is mounted on the hydraulic excavator 4 shown in FIG. 2, at least one of the boom cylinder 22, the arm cylinder 24, and the bucket cylinder 26 may correspond to the other hydraulic actuator. However, the other hydraulic actuator is not limited to at least one of the boom cylinder 22, the arm cylinder 24, and the bucket cylinder 26, and may be another hydraulic actuator (for example, a swing motor for swinging the upper revolving body 8).

[0022] The hydraulic circuit 2 will be described with reference to FIG. 1. The hydraulic circuit 2 includes a first hydraulic pump 28, a second hydraulic pump 30, a first travel switching valve 32, a second travel switching valve 34, and an actuator switching valve.

[0023] (First and second hydraulic pumps 28, 30) The first and second hydraulic pumps 28 and 30 are variable displacement type and are driven by a drive source (not shown) such as an engine or an electric motor. The first hydraulic pump 28 discharges the hydraulic oil sucked from the tank 36 into the first pump line 38. On the other hand, the second hydraulic pump 30 discharges the hydraulic oil sucked from the tank 36 into the second pump line 40. Note that a hydraulic pump other than the first and second hydraulic pumps 28 and 30 may be provided in the hydraulic circuit 2.

[0024] (First Travel Switching Valve 32) The first travel switching valve 32 controls the rotation direction of the first travel motor 14 by switching the flow direction of the hydraulic oil to the first travel motor 14. Further, the first travel switching valve 32 controls the supply amount of the hydraulic oil to the first travel motor 14 and also controls the discharge amount of the hydraulic oil guided from the first travel motor 14 to the tank 36 via the discharge line 42. The first travel switching valve 32 is an electromagnetic proportional type or a hydraulic pilot type. The first travel switching valve 32 is connected to both the first and second pump lines 38 and 40. However, as will be described later, the first travel switching valve 32 is supplied with hydraulic oil from either the first or second hydraulic pumps 28 and 30.

[0025] (Second Travel Switching Valve 34) The second travel switching valve 34 controls the rotation direction of the second travel motor by switching the flow direction of the hydraulic oil to the second travel motor. Further, the second travel switching valve 34 controls the supply amount of the hydraulic oil to the second travel motor and also controls the discharge amount of the hydraulic oil guided from the second travel motor to the tank 36 via the discharge line 42. The second travel switching valve 34 is, like the first travel switching valve 32, an electromagnetic proportional type or a hydraulic pilot type. The second travel switching valve 34 is connected to the second pump line 40 but not to the first pump line 38. Therefore, the second travel switching valve 34 is supplied with hydraulic oil from the second hydraulic pump 30 but not from the first hydraulic pump 28.

[0026] In FIG. 1, for the sake of convenience, a pair of pipelines connecting the first travel switching valve 32 and the first travel motor 14, and a pair of pipelines connecting the second travel switching valve 34 and the second travel motor are omitted.

[0027] (First and second on-off valves 44, 46) The first and second on-off valves 44, 46 are provided on the upstream side of the first travel switching valve 32. Specifically, the first on-off valve 44 is provided between the first hydraulic pump 28 and the first travel switching valve 32. The second on-off valve 46 is provided between the second hydraulic pump 30 and the first travel switching valve 32. Note that no on-off valve is provided on the upstream side of the second travel switching valve 34.

[0028] In this embodiment, poppet valves are used as the first and second on-off valves 44, 46. The poppet valve in this specification can be switched among three states: an open state, a closed state, and a check state by adjusting the pilot pressure acting on the spring chamber. In the open state, the upstream side (pump side) and the downstream side of the poppet valve are communicated with each other. In the closed state, the upstream side and the downstream side of the poppet valve are blocked. In the check state, the flow from the upstream side to the downstream side of the poppet valve is allowed, but the backflow from the downstream side to the upstream side of the poppet valve is prevented. Note that the first and second on-off valves 44, 46 may be electromagnetic or hydraulic pilot type two-position shut-off valves having an open position and a closed position.

[0029] (Actuator switching valve) The actuator switching valve is connected to at least the first hydraulic pump 28 and controls the operating direction of the other hydraulic actuators by switching the flow direction of the hydraulic oil to the other hydraulic actuators. In this embodiment, three actuator switching valves, namely, a boom switching valve 48, an arm switching valve 50, and a bucket switching valve 52 are provided. However, the actuator switching valve of the present invention is not limited to at least one of the boom switching valve 48, the arm switching valve 50, and the bucket switching valve 52, and other actuator switching valves may be used.

[0030] (Boom switching valve 48) The boom switching valve 48 controls the operating direction of the boom cylinder 22 by switching the flow direction of the hydraulic oil to the boom cylinder 22. The boom switching valve 48 is an electromagnetic proportional type or a hydraulic pilot type. As shown in FIG. 1, the boom switching valve 48 is connected to both the first and second pump lines 38 and 40. In the present embodiment, a boom check valve 54 is provided between the boom switching valve 48 and the first hydraulic pump 28. The boom check valve 54 prevents the backflow from the boom switching valve 48 to the first hydraulic pump 28. On the other hand, a boom flow control valve 56 is provided between the boom switching valve 48 and the second hydraulic pump 30. The boom flow control valve 56 is an electromagnetic proportional type and adjusts the amount of hydraulic oil supplied from the second hydraulic pump 30 to the boom switching valve 48. Further, the boom flow control valve 56 has a backflow prevention function and prevents the backflow from the boom switching valve 48 to the second hydraulic pump 30.

[0031] The hydraulic oil discharged from the first hydraulic pump 28 is supplied to the boom switching valve 48 via the boom check valve 54, and the hydraulic oil discharged from the second hydraulic pump 30 is supplied to the boom switching valve 48 via the boom flow control valve 56 as necessary. The flow rate of the hydraulic oil supplied from the second hydraulic pump 30 to the boom switching valve 48 is adjusted by the boom flow control valve 56. The boom switching valve 48 controls the total flow rate supplied to the boom switching valve 48 and sends it to the boom cylinder 22. Further, the boom switching valve 48 controls the discharge amount of the hydraulic oil led from the boom cylinder 22 to the tank 36 via the discharge line 42.

[0032] (Arm switching valve 50) The arm switching valve 50 controls the operating direction of the arm cylinder 24 by switching the flow direction of the hydraulic oil to the arm cylinder 24. The arm switching valve 50 is an electromagnetic proportional type or a hydraulic pilot type. As shown in FIG. 1, the arm switching valve 50 is connected to both the first and second hydraulic pumps 28 and 30. An arm flow control valve 58 is provided between the arm switching valve 50 and the first hydraulic pump 28. The arm flow control valve 58 is an electromagnetic proportional type and adjusts the amount of hydraulic oil supplied from the first hydraulic pump 28 to the arm switching valve 50. Further, the arm flow control valve 58 has a backflow prevention function and prevents backflow from the arm switching valve 50 to the first hydraulic pump 28.

[0033] Also, an arm poppet valve 60 is provided between the arm switching valve 50 and the second hydraulic pump 30. Similar to the poppet valve described above, the arm poppet valve 60 can be switched between three states: an open state, a closed state, and a check state. Specifically, when the arm poppet valve 60 is in the open state, the second hydraulic pump 30 and the arm switching valve 50 are communicated, and when the arm poppet valve 60 is in the closed state, the line connecting the second hydraulic pump 30 and the arm switching valve 50 is blocked. Further, when the arm poppet valve 60 is in the check state, the flow from the second hydraulic pump 30 to the arm switching valve 50 is allowed, but backflow from the arm switching valve 50 to the second hydraulic pump 30 is prevented.

[0034] The operating oil discharged from the second hydraulic pump 30 is supplied to the arm switching valve 50 via the arm poppet valve 60, and the operating oil discharged from the first hydraulic pump 28 is supplied via the arm flow control valve 58 as required. The flow rate of the operating oil supplied from the first hydraulic pump 28 to the arm switching valve 50 is adjusted by the arm flow control valve 58. The arm switching valve 50 controls the total flow rate supplied to the arm switching valve 50 and sends it to the arm cylinder 24. Further, the arm switching valve 50 controls the discharge amount of the operating oil led from the arm cylinder 24 to the tank 36 via the discharge line 42.

[0035] (Bucket switching valve 52) The bucket switching valve 52 controls the operating direction of the bucket cylinder 26 by switching the flow direction of the hydraulic oil to the bucket cylinder 26. Further, the bucket switching valve 52 controls the supply amount of the hydraulic oil to the bucket cylinder 26 and also controls the discharge amount of the hydraulic oil guided from the bucket cylinder 26 to the tank 36 via the discharge line 42. The bucket switching valve 52 is an electromagnetic proportional type or a hydraulic pilot type. As shown in FIG. 1, the bucket switching valve 52 is connected to the first pump line 38 but not to the second pump line 40. A bucket check valve 62 is provided between the bucket switching valve 52 and the first hydraulic pump 28. The bucket check valve 62 prevents the backflow from the bucket switching valve 52 to the first hydraulic pump 28.

[0036] In addition, in FIG. 1, for the sake of convenience, a pair of pipelines connecting the boom switching valve 48 and the boom cylinder 22, a pair of pipelines connecting the arm switching valve 50 and the arm cylinder 24, and a pair of pipelines connecting the bucket switching valve 52 and the bucket cylinder 26 are omitted.

[0037] The hydraulic circuit 2 further includes a communication valve 64, a first bypass valve 66, and a second bypass valve 68.

[0038] (Communication valve 64) The communication valve 64 is provided in a communication line 70 that communicates the first pump line 38 and the second pump line 40. The communication valve 64 is an electromagnetic proportional type and adjusts the supply amount of the hydraulic oil sent from the first pump line 38 to the second pump line 40. Further, the communication valve 64 has a backflow prevention function and allows the flow from the first pump line 38 to the second pump line 40 but prevents the backflow from the second pump line 40 to the first pump line 38.

[0039] (First bypass valve 66) The first bypass valve 66 is provided in a first bypass line 72 that branches from the first pump line 38 and extends to the tank 36. The first bypass valve 66 is an electromagnetic proportional type and adjusts the amount of hydraulic oil returning from the first pump line 38 to the tank 36.

[0040] (The second bypass valve 68) The second bypass valve 68 is provided in a second bypass line 74 that branches from the second pump line 40 and extends to the tank 36. The second bypass valve 68 is an electromagnetic proportional type and adjusts the amount of hydraulic oil returning from the second pump line 40 to the tank 36.

[0041] Referring to FIG. 3 for explanation, the hydraulic circuit 2 further includes a first travel operating tool 76, a second travel operating tool 78, an actuator operating tool, and a controller 80.

[0042] (The first and second travel operating tools 76, 78) The first travel operating tool 76 outputs a signal for operating the first travel motor 14. The second travel operating tool 78 outputs a signal for operating the second travel motor. In the present embodiment, as the actuator operating tool, a boom operating tool 82, an arm operating tool 84, and a bucket operating tool 86 are provided. The boom operating tool 82 outputs a signal for operating the boom cylinder 22. The arm operating tool 84 outputs a signal for operating the arm cylinder 24. The bucket operating tool 86 outputs a signal for operating the bucket cylinder 26. Note that the actuator operating tool is not limited to the boom operating tool 82, the arm operating tool 84, and the bucket operating tool 86.

[0043] Each of the operating tools 76, 78, 82, 84, 86 may be configured to have an input device (for example, a lever operable in the front-rear direction, a joystick operable in the cross direction, a slide switch, a pedal, etc.) in which the intensity of the signal output increases as the amount of operation increases. The signals output from each of the operating tools 76, 78, 82, 84, 86 are electrical signals or hydraulic signals. The electrical signal output is input to the controller 80. When the output signal is a hydraulic signal, the output hydraulic signal is detected by a pressure sensor (not shown), and the detection result of the pressure sensor is input to the controller 80.

[0044] (Controller 80) The controller 80 is composed of a computer having a processing device and a storage device. The controller 80 executes circuit control based on the signals output from each of the operating tools 76, 78, 82, 84, 86.

[0045] (Operation of the hydraulic circuit 2) Next, the operation of the hydraulic circuit 2 as described above will be described. Hereinafter, it will be described assuming that the first and second travel switching valves 32, 34 and the actuator switching valve are electromagnetic proportional valves and are controlled by an electrical signal from the controller 80.

[0046] (When the operating tool is not operated) First, the case where none of the operating tools 76, 78, 82, 84, 86 is operated will be described.

[0047] When none of the operating tools 76, 78, 82, 84, 86 is operated, no signal is output from each of the operating tools 76, 78, 82, 84, 86 to the controller 80. In this case, the controller 80 positions each of the switching valves 32, 34, 48, 50, 52 in the closed position, and shuts off the lines connecting the first and second pump lines 38, 40 and each of the hydraulic actuators 14, 22, 24, 26 by each of the switching valves 32, 34, 48, 50, 52. Therefore, hydraulic oil is not supplied to each of the hydraulic actuators 14, 22, 24, 26, and each of the hydraulic actuators 14, 22, 24, 26 does not operate.

[0048] Also, in the above case, the controller 80 adjusts the opening degrees of the first and second bypass valves 66 and 68 to a predetermined opening degree that is not fully closed. As a result, the hydraulic oil discharged from the first hydraulic pump 28 returns to the tank 36 through the first bypass line 72, and the pressure in the first pump line 38 is maintained at a predetermined standby pressure (for example, 3 to 4 MPa). Similarly, the hydraulic oil discharged from the second hydraulic pump 30 returns to the tank 36 through the second bypass line 74, and the pressure in the second pump line 40 is maintained at a predetermined standby pressure (for example, 3 to 4 MPa). Note that the boom flow control valves 56, the arm flow control valves 58, and the communication valve 64 are positioned in the closed position.

[0049] (When the first and second travel operation tools 76 and 78 are operated) Next, with reference to FIG. 4, a case where both the first and second travel operation tools 76 and 78 are operated and the actuator operation tools (boom operation tool 82, arm operation tool 84, bucket operation tool 86) are not operated will be described.

[0050] When the first and second travel operation tools 76 and 78 are operated, signals are output from the first and second travel operation tools 76 and 78 according to the operation amount. In this case, the controller 80 opens the first and second travel switching valves 32 and 34 and adjusts the opening degrees of the first and second travel switching valves 32 and 34 according to the signals output from the first and second travel operation tools 76 and 78.

[0051] Also, the controller 80 adjusts the pilot pressure acting on the spring chambers of the first and second on-off valves 44 and 46 by controlling an electromagnetic proportional valve (not shown). Specifically, by communicating the spring chamber of the first on-off valve 44 with the tank 36, the drain pressure is applied to the spring chamber of the first on-off valve 44 to open the first on-off valve 44. On the other hand, the higher pressure of either the first pump line 38 or the second pump line 40 is applied to the spring chamber of the second on-off valve 46 to close the second on-off valve 46.

[0052] Further, the controller 80 increases the discharge amounts of the first and second hydraulic pumps 28 and 30 according to the signals output from the first and second traveling operation tools 76 and 78, and makes the opening degrees of the first and second bypass valves 66 and 68 smaller than the predetermined opening degrees. As a result, the pressures in the first and second pump lines 38 and 40 rise to the required pressures (pressures higher than the standby pressure).

[0053] By the control of the controller 80 as described above, the first traveling switching valve 32 is supplied with the hydraulic oil discharged from the first hydraulic pump 28 via the first on-off valve 44, as shown by the thick gray line in FIG. 4. Then, the hydraulic oil is supplied from the first traveling switching valve 32 to the first traveling motor 14, and the first traveling motor 14 rotates. As described above, the supply amount and discharge amount of the first traveling motor 14 are controlled by the first traveling switching valve 32.

[0054] The second traveling switching valve 34 is supplied with the hydraulic oil discharged from the second hydraulic pump 30, as shown by the thick black line in FIG. 4. Then, the hydraulic oil is supplied from the second traveling switching valve 34 to the second traveling motor, and the second traveling motor rotates. As described above, the supply amount and discharge amount of the second traveling motor are controlled by the second traveling switching valve 34.

[0055] Here, the case where both the first and second traveling operation tools 76 and 78 are operated simultaneously has been described, but even when either one of the first and second traveling operation tools 76 and 78 is operated, the flow of the hydraulic oil is as shown in FIG. 4. That is, when only the first traveling operation tool 76 is operated, the hydraulic oil is supplied from the first hydraulic pump 28 to the first traveling switching valve 32. On the other hand, when only the second traveling operation tool 78 is operated, the hydraulic oil is supplied from the second hydraulic pump 30 to the second traveling switching valve 34.

[0056] In the above case, since no signal is output from the actuator operation tool, the actuator switching valves (boom switching valve 48, arm switching valve 50, bucket switching valve 52) remain positioned at the closed position. Also, as shown in FIG. 4, the boom flow control valve 56, arm flow control valve 58, and communication valve 64 also remain in the closed position.

[0057] (When the actuator operation tool is operated) Next, with reference to FIG. 5, the case where the actuator operation tools (boom operation tool 82, arm operation tool 84, bucket operation tool 86) are operated and neither of the first and second travel operation tools 76, 78 is operated will be described.

[0058] When the three of the boom operation tool 82, arm operation tool 84, and bucket operation tool 86 are simultaneously operated, signals are output from the respective operation tools 82, 84, 86 according to the operation amounts of the respective operation tools 82, 84, 86. In this case, the controller 80 opens the boom switching valve 48, arm switching valve 50, bucket switching valve 52, boom flow control valve 56, and arm flow control valve 58 according to the signals output from the respective operation tools 82, 84, 86, and adjusts the opening degrees of the respective switching valves 48, 50, 52 and the respective flow control valves 56, 58.

[0059] Also, the controller 80 puts the arm poppet valve 60 in a check state. Specifically, by controlling an electromagnetic proportional valve (not shown), the pressure on the downstream side of the arm poppet valve 60 is made to act on the spring chamber of the arm poppet valve 60. As a result, the arm poppet valve 60 becomes in a check state. That is, the flow from the second hydraulic pump 30 to the arm switching valve 50 is allowed, but the backflow from the arm switching valve 50 to the second hydraulic pump 30 is prevented.

[0060] Furthermore, the controller 80 increases the discharge amounts of the first and second hydraulic pumps 28 and 30 and reduces the opening degrees of the first and second bypass valves 66 and 68 to be smaller than the predetermined opening degree according to the signals output from the boom operation tool 82, the arm operation tool 84, and the bucket operation tool 86. As a result, the pressures in the first and second pump lines 38 and 40 rise to the required pressure (a pressure higher than the standby pressure).

[0061] By the control of the controller 80 as described above, the boom switching valve 48 is supplied with the hydraulic oil discharged from the first hydraulic pump 28 via the boom check valve 54, as shown by the thick gray line in FIG. 5. Further, the boom switching valve 48 is supplied with the hydraulic oil discharged from the second hydraulic pump 30 via the boom flow control valve 56, as shown by the thick black line in FIG. 5. Then, the hydraulic oil is supplied from the boom switching valve 48 to the boom cylinder 22, and the boom cylinder 22 operates. As described above, the supply amount and discharge amount of the boom cylinder 22 are controlled by the boom switching valve 48.

[0062] The arm switching valve 50 is supplied with the hydraulic oil discharged from the first hydraulic pump 28 via the arm flow control valve 58, as shown by the thick gray line in FIG. 5. Further, the arm switching valve 50 is supplied with the hydraulic oil discharged from the second hydraulic pump 30 via the arm poppet valve 60, as shown by the thick black line in FIG. 5. Then, the hydraulic oil is supplied from the arm switching valve 50 to the arm cylinder 24, and the arm cylinder 24 operates. As described above, the supply amount and discharge amount of the arm cylinder 24 are controlled by the arm switching valve 50.

[0063] The bucket switching valve 52 is supplied with the hydraulic oil discharged from the first hydraulic pump 28 via the bucket check valve 62, as shown by the thick gray line in FIG. 5. Then, the hydraulic oil is supplied from the bucket switching valve 52 to the bucket cylinder 26, and the bucket cylinder 26 operates. As described above, the supply amount and discharge amount of the bucket cylinder 26 are controlled by the bucket switching valve 52.

[0064] Here, the case where the boom operating tool 82, the arm operating tool 84, and the bucket operating tool 86 are simultaneously operated has been described. However, even when at least one of the boom operating tool 82, the arm operating tool 84, and the bucket operating tool 86 is operated, the hydraulic oil flow is as shown in Fig. 5. That is, the boom switching valve 48 and the arm switching valve 50 are supplied with hydraulic oil from the first and second hydraulic pumps 28 and 30, and the bucket switching valve 52 is supplied with hydraulic oil from the first hydraulic pump 28.

[0065] In the above case, since no signal is output from the first and second traveling operating tools 76 and 78, the first and second traveling switching valves 32 and 34 remain positioned in the closed position. Also, as shown in Fig. 5, the communication valve 64 also remains in the closed position.

[0066] (When the first and second traveling operating tools 76 and 78 and the actuator operating tool are operated) Next, with reference to Fig. 6, the case where the first and second traveling operating tools 76 and 78 and the actuator operating tool are simultaneously operated will be described. For the first and second traveling operating tools 76 and 78, it is assumed that the same operation amount is operated (i.e., the operation for the straight traveling of the lower traveling body 6).

[0067] When all of the first and second traveling operating tools 76 and 78, the boom operating tool 82, the arm operating tool 84, and the bucket operating tool 86 are simultaneously operated, signals are output from each of the operating tools 76, 78, 82, 84, and 86 according to the operation amounts of the respective operating tools 76, 78, 82, 84, and 86. In this case, the controller 80 opens the first and second traveling switching valves 32 and 34, the boom switching valve 48, the arm switching valve 50, and the bucket switching valve 52 according to the signals output from each of the operating tools 76, 78, 82, 84, and 86, and adjusts the opening degrees of the respective switching valves 32, 34, 48, 50, and 52.

[0068] Further, the controller 80 closes the first on-off valve 44 while opening the second on-off valve 46. That is, the higher pressure of either the first pump line 38 or the second pump line 40 is applied to the spring chamber of the first on-off valve 44 to close the first on-off valve 44. On the other hand, drain pressure is applied to the spring chamber of the second on-off valve 46 to open the second on-off valve 46.

[0069] Furthermore, the controller 80 closes the boom flow control valve 56, opens the arm flow control valve 58, and adjusts the opening degree. The arm poppet valve 60 is closed in the same manner as the first on-off valve 44.

[0070] Moreover, the controller 80 increases the discharge amounts of the first and second hydraulic pumps 28 and 30 according to the signals output from the respective operation tools 76, 78, 82, 84, and 86, and makes the opening degrees of the first and second bypass valves 66 and 68 smaller than the above-mentioned predetermined opening degrees. As a result, the pressures in the first and second pump lines 38 and 40 rise to the required pressure (a pressure higher than the standby pressure).

[0071] By the control of the controller 80 as described above, the same amount of hydraulic oil is distributed and supplied from the second hydraulic pump 30 to the first and second travel switching valves 32 and 34, as shown by the thick black line in FIG. 6. Then, the same amount of hydraulic oil is supplied from the first travel switching valve 32 to the first travel motor 14 and from the second travel switching valve 34 to the second travel motor. Therefore, since the first travel motor 14 and the second travel motor operate at the same rotational speed, the straight travel performance of the lower travel body 6 is ensured.

[0072] To the other party, boom switching valve 48, arm switching valve 50, and bucket switching valve 52, as shown by the thick gray line in Fig. 6, hydraulic oil is supplied from the first hydraulic pump 28. That is, in the above case, hydraulic oil is supplied to the actuator switching valve only from the first hydraulic pump 28. Then, hydraulic oil is supplied from the boom switching valve 48 to the boom cylinder 22, from the arm switching valve 50 to the arm cylinder 24, and from the bucket switching valve 52 to the bucket cylinder 26. As a result, by operating the boom cylinder 22, arm cylinder 24, and bucket cylinder 26, the required work is performed by the front work implement 10.

[0073] When such operations (the straight running operation of the lower traveling body 6 and the operation of the front work implement 10) are performed simultaneously, there may be a surplus in the supply flow rate of the first hydraulic pump 28 depending on the operating speed of the front work implement 10.

[0074] The case where a surplus occurs in the supply flow rate of the first hydraulic pump 28 is when the flow rate required by the front work implement 10 is relatively small. That is, when the required speed for the front work implement 10 is low. In this case, since the operation amount of the actuator operating tool is small, the signal output from the actuator operating tool becomes small.

[0075] On the other hand, the case where no surplus occurs in the supply flow rate of the first hydraulic pump 28 is when the flow rate required by the front work implement 10 is relatively large. That is, when the required speed for the front work implement 10 is high. In this case, since the operation amount of the actuator operating tool is large, the signal output from the actuator operating tool becomes large.

[0076] Therefore, when signals are output from the first and second traveling operating tools 76, 78 and the actuator operating tool (when the straight running operation of the lower traveling body 6 and the operation of the front work implement 10 are performed), the controller 80 adjusts the opening degree of the communication valve 64 according to the signal output from the actuator operating tool to control the supply amount of the hydraulic oil sent from the first pump line 38 to the second pump line 40.

[0077] As a result, as shown by the thick gray line in FIG. 6, the surplus flow rate of the first hydraulic pump 28 is equally distributed and supplied to the first and second travel switching valves 32 and 34. Then, the surplus flow rate of the first hydraulic pump 28 is supplied from the first travel switching valve 32 to the first travel motor 14 together with the hydraulic oil discharged from the second hydraulic pump 30 and is also supplied from the second travel switching valve 34 to the second travel motor. As a result, the surplus flow rate of the first hydraulic pump 28 is used for the operations of the first travel motor 12 and the second travel motor. Therefore, according to the present embodiment, the surplus flow rate of the first hydraulic pump 28 can be effectively used.

[0078] Regarding a preferred form, when signals are output from the first and second travel operation tools 76 and 78 and the actuator operation tool, the controller 80 sets the opening degree of the communication valve 64 to a first opening degree when the signal output from the actuator operation tool is less than a predetermined value, and sets it to a second opening degree smaller than the first opening degree when the signal output from the actuator operation tool is greater than or equal to the predetermined value.

[0079] Regarding the above-mentioned "signal output from the actuator operation tool", for example, it can be the total value of the signal intensities output from each of the boom operation tool 82, the arm operation tool 84, and the bucket operation tool 86. Further, the "signal output from the actuator operation tool" may be the value of the signal intensity of any one of the boom operation tool 82, the arm operation tool 84, and the bucket operation tool 86, or may be the total value of the signal intensities of any two of the boom operation tool 82, the arm operation tool 84, and the bucket operation tool 86.

[0080] Regarding the above-mentioned "first opening degree", it is desirable to set the opening degree such that the rotational speed of the first traveling motor 12 does not fall below the required speed corresponding to the operation amount of the first traveling operation tool 76, and the rotational speed of the second traveling motor does not fall below the required speed corresponding to the operation amount of the second traveling operation tool 78. If the first opening degree is too small, the pressure loss in the communication line 70 increases, so the pressure of the hydraulic oil discharged from the first hydraulic pump 28 increases. Then, the absorption torque of the first hydraulic pump 28 increases. By the way, in construction machines such as hydraulic excavators, generally, horsepower control is performed so that the maximum horsepower of the drive source is not exceeded by the pump absorption horsepower. When such horsepower control is performed, the absorption torque of the second hydraulic pump 30 may decrease as the absorption torque of the first hydraulic pump 28 increases. In such a case, since the discharge amount of the second hydraulic pump 30 decreases, the rotational speeds of the first traveling motor 14 and the second traveling motor may fall below the required speeds. Therefore, it is desirable to set the first opening degree to an opening degree (not too small an opening degree) such that the rotational speed of the first traveling motor 12 does not fall below the required speed corresponding to the operation amount of the first traveling operation tool 76, and the rotational speed of the second traveling motor does not fall below the required speed corresponding to the operation amount of the second traveling operation tool 78.

[0081] The first opening degree may be changed according to the signal of the actuator operation tool. For example, when the signal of the actuator operation tool is less than a predetermined value, the first opening degree may be increased as the signal of the actuator operation tool is smaller, and the first opening degree may be decreased as the signal of the actuator operation tool is larger. Thereby, an appropriate flow rate corresponding to the surplus flow rate generated can be supplied from the first pump line 38 to the second pump line 40.

[0082] Regarding the above-mentioned "second opening degree", it is preferable that the operating speed of other hydraulic actuators (boom cylinder 22, arm cylinder 24, bucket cylinder 26) is set to an opening degree such that it does not fall below the required speed corresponding to the operation amount of the actuator operating tool (boom operating tool 82, arm operating tool 84, bucket operating tool 86). When the required speed of the front working machine 10 is high, generally, the pressure in the first pump line 38 is higher than the pressure in the second pump line 40. Therefore, if the second opening degree is too large, hydraulic oil will escape from the first pump line 38 to the second pump line 40, and it will become impossible to supply the necessary flow rate to the boom cylinder 22, arm cylinder 24, and bucket cylinder 26. Therefore, it is preferable that the second opening degree is set to an opening degree (not too large an opening degree) such that the operating speed of other hydraulic actuators does not fall below the required speed corresponding to the operation amount of the actuator operating tool.

[0083] The second opening degree can be changed according to the signal of the actuator operating tool. For example, when the signal of the actuator operating tool is equal to or greater than a predetermined value, the second opening degree may be increased as the signal of the actuator operating tool becomes smaller, and the second opening degree may be decreased as the signal of the actuator operating tool becomes larger. This can more reliably prevent hydraulic oil from escaping from the first pump line 38 to the second pump line 40 and making it impossible to supply the necessary flow rate to the boom cylinder 22 or the like. Also, the second opening degree may be fully closed.

[0084] In addition, when the controller 80 sets the opening degree of the communication valve 64 to the first opening degree, it is convenient to reduce the discharge amount of the second hydraulic pump 30 to such an extent that the rotational speed of the first travel motor 14 does not fall below the required speed corresponding to the operation amount of the first travel operating tool 76, and the rotational speed of the second travel motor does not fall below the required speed corresponding to the operation amount of the second travel operating tool 78. Thereby, the energy consumption amount (fuel consumption amount when the drive sources of the first and second hydraulic pumps 28 and 30 are engines, and power consumption amount when the drive sources of the first and second hydraulic pumps 28 and 30 are electric motors) can be reduced.

[0085] Here, although the case where each of the operating tools 76, 78, 82, 84, and 86 is operated simultaneously has been described, even when any one of the actuator operating tools is operated together with both the first and second traveling operating tools 76 and 78, the hydraulic oil flow as shown in FIG. 6 is obtained. That is, the first and second traveling switching valves 32 and 34 are mainly supplied with hydraulic oil from the second hydraulic pump 30, and the surplus flow rate of the first hydraulic pump 28 can be supplied according to the signal output from the actuator operating tool. Further, the boom switching valve 48, the arm switching valve 50, and the bucket switching valve 52 are supplied with hydraulic oil only from the first hydraulic pump 28.

[0086] As described above, in the present embodiment, when the first and second traveling operating tools 76 and 78 and the actuator operating tool are operated simultaneously (when the straight traveling operation of the lower traveling body 6 and the operation of the front working machine 10 are performed simultaneously), according to the signal output from the actuator operating tool, the opening degree of the communication valve 64 is adjusted to control the supply amount of the hydraulic oil sent from the first pump line 38 to the second pump line 40. Therefore, together with the hydraulic oil discharged from the second hydraulic pump 30, the surplus flow rate of the first hydraulic pump 28 is supplied to the first traveling motor 14 and the second traveling motor via the first and second traveling switching valves 32 and 34, so that the surplus flow rate of the first hydraulic pump 28 can be effectively used.

[0087] In the present embodiment, the first and second traveling switching valves 32 and 34 and the actuator switching valve have been described as being electromagnetic proportional type and being controlled by an electric signal from the controller 80. However, the first and second traveling switching valves 32 and 34 and the actuator switching valve may be hydraulic pilot type. In this case, each of the switching valves 32, 34, 48, 50, and 52 is controlled by a hydraulic signal output from each of the operating tools 76, 78, 82, 84, and 86. Further, the output hydraulic signal is detected by a pressure sensor (not shown), and the detection result of the pressure sensor is input to the controller 80. Then, based on the detection result of the pressure sensor, the controller 80 can execute the above-described control on the first and second on-off valves 44 and 46 and the like.

Description of Reference Numerals

[0088] 2: Hydraulic circuit 14: First travel motor 22: Boom cylinder (other hydraulic actuator) 24: Arm cylinder (other hydraulic actuator) 26: Bucket cylinder (other hydraulic actuator) 28: First hydraulic pump 30: Second hydraulic pump 32: First travel switching valve 34: Second travel switching valve 38: First pump line 40: Second pump line 44: First on-off valve 46: Second on-off valve 48: Boom switching valve (actuator switching valve) 50: Arm switching valve (actuator switching valve) 52: Bucket switching valve (actuator switching valve) 54: Boom check valve 56: Boom flow control valve 58: Arm flow control valve 60: Arm poppet valve 62: Bucket check valve 64: Communication valve 70: Communication passage 76: First travel operating tool 78: Second travel operating tool 80: Controller 82: Boom operating tool (actuator operating tool) 84: Arm operating tool (actuator operating tool) 86: Bucket operating tool (actuator operating tool)

Claims

1. A hydraulic circuit for a construction machine for supplying hydraulic oil to a first traveling motor, a second traveling motor, and other hydraulic actuators, a variable displacement first hydraulic pump, a variable displacement second hydraulic pump, a first pump line through which the hydraulic oil discharged from the first hydraulic pump flows, a second pump line through which the hydraulic oil discharged from the second hydraulic pump flows, a first traveling switching valve connected to the first pump line and the second pump line and switching the flow direction of the hydraulic oil to the first traveling motor, a second traveling switching valve connected to the second pump line and switching the flow direction of the hydraulic oil to the second traveling motor, an actuator switching valve connected to at least the first pump line and switching the flow direction of the hydraulic oil to the other hydraulic actuators, a first on-off valve provided between the first hydraulic pump and the first traveling switching valve, a second on-off valve provided between the second hydraulic pump and the first traveling switching valve, a communication line communicating the first pump line and the second pump line, a communication valve provided in the communication line, a first traveling operation tool for outputting a signal for operating the first traveling motor, a second traveling operation tool for outputting a signal for operating the second traveling motor, an actuator operation tool for outputting a signal for operating the other hydraulic actuators, comprising a controller that executes circuit control based on signals output from the first traveling operation tool, the second traveling operation tool, and the actuator operation tool, the controller, when a signal is output from the first traveling operation tool and / or the second traveling operation tool and no signal is output from the actuator operation tool, opens the first on-off valve and closes the second on-off valve to supply hydraulic oil from the first hydraulic pump to the first traveling switching valve and / or supply hydraulic oil from the second hydraulic pump to the second traveling switching valve and closes the communication valve, When a signal is output from the other party, the first traveling operation tool, the second traveling operation tool, and the actuator operation tool, hydraulic oil is supplied from the first hydraulic pump to the actuator switching valve, and the first on-off valve is closed and the second on-off valve is opened, so that hydraulic oil is supplied from the second hydraulic pump to the first traveling switching valve and the second traveling switching valve, and the opening degree of the communication valve is adjusted according to the signal output from the actuator operation tool to control the supply amount of the hydraulic oil sent from the first pump line to the second pump line. A hydraulic circuit for a construction machine.

2. When a signal is output from the first traveling operation tool, the second traveling operation tool, and the actuator operation tool, the controller sets the opening degree of the communication valve to a first opening degree when the signal output from the actuator operation tool is less than a predetermined value, and sets the opening degree to a second opening degree smaller than the first opening degree when the signal output from the actuator operation tool is equal to or greater than the predetermined value. The hydraulic circuit for a construction machine according to claim 1.

3. The first opening degree is set to an opening degree such that the rotational speed of the first traveling motor does not fall below the required speed corresponding to the operation amount of the first traveling operation tool, and the rotational speed of the second traveling motor does not fall below the required speed corresponding to the operation amount of the second traveling operation tool. The hydraulic circuit for a construction machine according to claim 2.

4. The first opening degree is changed according to the signal of the actuator operation tool. The hydraulic circuit for a construction machine according to claim 2.

5. The second opening degree is set to an opening degree such that the operating speed of the other hydraulic actuator does not fall below the required speed corresponding to the operation amount of the actuator operation tool. The hydraulic circuit for a construction machine according to claim 2.

6. The second opening degree is changed according to the signal of the actuator operation tool. The hydraulic circuit for a construction machine according to claim 2.

7. The second opening degree is fully closed. The hydraulic circuit for a construction machine according to claim 2.

8. When the controller sets the opening degree of the communication valve to the first opening degree, the discharge amount of the second hydraulic pump is reduced to such an extent that the rotational speed of the first traveling motor does not fall below the required speed corresponding to the operation amount of the first traveling operation tool, and the rotational speed of the second traveling motor does not fall below the required speed corresponding to the operation amount of the second traveling operation tool. The hydraulic circuit for a construction machine according to claim 2.

9. The communication valve has a backflow prevention function, allows the flow of hydraulic oil from the first pump line to the second pump line, and prevents backflow from the second pump line to the first pump line. The hydraulic circuit of a construction machine according to claim 1.

10. The actuator switching valve is connected to both the first pump line and the second pump line. A check valve is provided between the actuator switching valve and the first hydraulic pump, and a flow control valve is provided between the actuator switching valve and the second hydraulic pump. The hydraulic circuit of a construction machine according to claim 1.

11. The actuator switching valve is connected to both the first pump line and the second pump line. A flow control valve is provided between the actuator switching valve and the first hydraulic pump, and a poppet valve is provided between the actuator switching valve and the second hydraulic pump. The hydraulic circuit of a construction machine according to claim 1.

12. The actuator switching valve is connected to the first pump line and not connected to the second hydraulic pump line, and a check valve is provided between the actuator switching valve and the first hydraulic pump. The hydraulic circuit of a construction machine according to claim 1.

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