Hydraulic circuit for construction machine

Abstract

[Problem] To provide a hydraulic circuit of a construction machine that can supply hydraulic oil to a closed circuit even without a charge pump. [Solution] An opening circuit of a hydraulic circuit includes a hydraulic pump, a hydraulic actuator operated by hydraulic oil discharged from the hydraulic pump, a direction switching valve switching a flow direction of the hydraulic oil from the hydraulic pump to the hydraulic actuator, a return line connecting the direction switching valve and a hydraulic oil tank, and a return check valve provided on the return line. A closed circuit of the hydraulic circuit includes a bidirectional hydraulic pump having a first port and a second port, a hydraulic motor operated by hydraulic oil discharged from the bidirectional hydraulic pump, a first line connecting the first port of the bidirectional hydraulic pump and the hydraulic motor, and a second line connecting the second port of the bidirectional hydraulic pump and the hydraulic motor. A charge line connecting the return line and the first line via a first check valve and connecting the return line and the second line via a second check valve is provided between the open circuit and the closed circuit.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydraulic circuit of a construction machine including an open circuit and a closed circuit. BACKGROUND

[0002] In a hydraulic circuit of a hydraulic excavator or a wheel loader, a closed circuit closed by a bidirectional hydraulic pump and a hydraulic actuator can be adopted. In the closed circuit, a charge pump for supplying hydraulic oil to the closed circuit is generally provided to supplement an insufficient amount of oil when the hydraulic actuator is stopped, to cool the hydraulic oil in the closed circuit, and the like (for example, see Patent Literature 1).

[0003]

PRIOR ART DOCUMENTS

[0004]

PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. 2001-173025 SUMMARY

[0006]

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] When the closed circuit is adopted, problems such as an increase in the cost of the hydraulic circuit and energy waste can occur. In general, when the charge pump is provided, an external filter is recommended to be used, and thus not only the cost of the charge pump but also the cost of the external filter is included in the cost of the entire hydraulic circuit. In addition, the charge pump is driven by a driving source such as an engine, and thus even when the hydraulic oil is not required to be charged into the closed circuit, the hydraulic oil is driven all the time when the driving source is operated, and thus the driving time of the charge pump is wasted, and energy is wasted.

[0008] The present application has been made to solve the above-described problems, and an object of the present application is to provide a hydraulic circuit of a construction machine which can supply hydraulic oil to a closed circuit without a charge pump.

[0009]

MEANS FOR SOLVING THE PROBLEMS

[0010] According to the present application, the following hydraulic circuit of a construction machine which solves the above-described problems is provided. That is, a hydraulic circuit of a construction machine is provided which includes an open circuit and a closed circuit,

[0011] the open circuit includes:

[0012] a variable displacement hydraulic pump which discharges hydraulic oil taken from a hydraulic oil tank;

[0013] a hydraulic actuator which is operated by the hydraulic oil discharged from the hydraulic pump;

[0014] a directional switching valve which switches a flow direction of the hydraulic oil from the hydraulic pump to the hydraulic actuator;

[0015] a pump line connecting the hydraulic pump and the directional switching valve;

[0016] a return line connecting the directional switching valve and the hydraulic tank;

[0017] a return check valve provided in the return line;

[0018] a bypass line connecting the pump line and the return line; and

[0019] an electromagnetic proportional bypass valve provided in the bypass line;

[0020] the closed circuit comprises:

[0021] a variable displacement bidirectional hydraulic pump having a first port and a second port;

[0022] a hydraulic motor operated by hydraulic oil discharged by the bidirectional hydraulic pump;

[0023] a first line connecting the first port of the bidirectional hydraulic pump and the hydraulic motor; and

[0024] a second line connecting the second port of the bidirectional hydraulic pump and the hydraulic motor,

[0025] the open circuit and the closed circuit are provided with a charging line connecting an upstream side portion of the return check valve of the return line and the first line via a first check valve and connecting an upstream portion of the return check valve of the return line and the second line via a second check valve.

[0026] the closed circuit can comprise a first safety valve for releasing hydraulic oil of the first line to the second line via the second check valve and a second safety valve for releasing hydraulic oil of the second line to the first line via the first check valve.

[0027] Preferably, a throttle valve is provided between the first safety valve and the second check valve and between the second safety valve and the first check valve, and a third safety valve is provided between the first safety valve and the hydraulic tank and between the second safety valve and the hydraulic tank, wherein a set pressure of the third safety valve is smaller than a set pressure of the first safety valve and smaller than a set pressure of the second safety valve.

[0028] the closed circuit can comprise a first safety valve for releasing hydraulic oil of the first line to the hydraulic tank and a second safety valve for releasing hydraulic oil of the second line to the hydraulic tank.

[0029] The first check valve and the second check valve can be mounted to a housing of the bidirectional hydraulic pump, and the charge line can be connected to the housing. Alternatively, the first check valve and the second check valve can be mounted to a housing of the hydraulic motor, and the charge line can be connected to the housing.

[0030] Preferably, the hydraulic circuit of the present application includes a pressure sensor for detecting a pressure on an upstream side of the backflow check valve in the backflow line, and a controller for increasing a discharge amount of the hydraulic pump when the pressure detected by the pressure sensor is lower than a required pressure.

[0031] Preferably, the controller sets the required pressure based on an operation amount of a motor operator that outputs a signal for operating the hydraulic motor of the closing circuit. The controller can set the required pressure based on a rotational speed of an operation object operated by the hydraulic motor of the closing circuit.

[0032] The hydraulic circuit of the present application can include a regulator that controls a discharge amount and a discharge direction of the bidirectional hydraulic pump, an electromagnetic proportional regulator switching valve that switches a flow direction of hydraulic oil with respect to the regulator, a pilot line that branches from the pump line and extends to the regulator switching valve, and a pressure reducing valve provided in the pilot line.

[0033] In the hydraulic circuit of the present application, a charge line is provided between an opening circuit and a closing circuit, the charge line connects an upstream side portion of the backflow check valve of the backflow line and the first line via the first check valve, and connects the upstream side portion of the backflow check valve of the backflow line and the second line via the second check valve, so that hydraulic oil can be supplied to the closing circuit without a charge pump. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a hydraulic circuit diagram according to a first embodiment of the present application;

[0035] Figure 2 is a flowchart of control performed by Figure 1 the controller shown.

[0036] Figure 3 is a hydraulic circuit diagram according to a second embodiment of the present application;

[0037] Figure 4 is a hydraulic circuit diagram according to a third embodiment of the present application;

[0038] Figure 5 is a hydraulic circuit diagram according to a fourth embodiment of the present application; DETAILED DESCRIPTION

[0039] (First Embodiment)

[0040] First, a first embodiment of a hydraulic circuit of a construction machine according to the present application will be described with reference to the drawings.

[0041] (Hydraulic Circuit 2, Open Circuit 2a)

[0042] Figure 1 A hydraulic circuit 2 according to the first embodiment is shown. The hydraulic circuit 2 includes an open circuit 2a and a closed circuit 2b. The open circuit 2a includes a hydraulic pump 4, a hydraulic actuator 6, a directional switching valve 8, a return line 10, and a return check valve 12.

[0043] (Hydraulic Pump 4)

[0044] The hydraulic pump 4 has a suction port 4a and a discharge port 4b to suck hydraulic oil in a hydraulic oil tank 14 from the suction port 4a and discharge the hydraulic oil from the discharge port 4b to a pump line 16. The hydraulic pump 4 is driven by a driving source 18 such as an engine or an electric motor, and the hydraulic oil is always discharged from the hydraulic pump 4 to the pump line 16 when the driving source 18 is running. However, the hydraulic pump 4 is variable capacity, and the amount of the hydraulic oil discharged to the pump line 16 can be appropriately changed according to the operating conditions of the construction machine in which the hydraulic circuit 2 is installed.

[0045] (Hydraulic Actuator 6)

[0046] The hydraulic actuator 6 is operated by the hydraulic oil discharged from the hydraulic pump 4. Although Figure 1 A hydraulic cylinder is shown as the hydraulic actuator 6, but the hydraulic actuator 6 can be a hydraulic motor. In addition, the number of the hydraulic actuator 6 is optional. For example, as the hydraulic actuator 6 of the open circuit 2a, a plurality of hydraulic cylinders and a plurality of hydraulic motors can be included.

[0047] (Directional Switching Valve 8)

[0048] The directional switching valve 8 switches the flow direction of the hydraulic oil from the hydraulic pump 4 to the hydraulic actuator 6. The directional switching valve 8 is connected to the hydraulic pump 4 through the pump line 16 and to the hydraulic oil tank 14 through the return line 10. The directional switching valve 8 is also connected to the hydraulic actuator 6 through a pair of lines 20a, 20b. Note that the directional switching valve 8 can be of an electromagnetic proportional type or a hydraulic pilot type. In addition, a plurality of directional switching valves 8 corresponding to the number of the hydraulic actuator 6 can be provided.

[0049] When the direction switching valve 8 is opened, the pump line 16 communicates with either of a pair of lines 20a, 20b, and the other of the pair of lines 20a, 20b communicates with the return line 10. Thus, the hydraulic actuator 6 is operated. Further, when the direction switching valve 8 is closed, the pump line 16 and the return line 10 are blocked from communicating with the pair of lines 20a, 20b, and the operation of the hydraulic actuator 6 is stopped.

[0050] (return line 10, return check valve 12)

[0051] The return line 10 is a line connecting the direction switching valve 8 and the hydraulic oil tank 14. The return check valve 12 installed on the return line 10 generates a back pressure on the return line 10. The back pressure generated by the return check valve 12 rises as the amount of hydraulic oil passing through the return line 10 (return flow rate) increases. Further, the return line 10 is provided with a pressure sensor 22 that detects the pressure on the upstream side of the return check valve 12 in the return line 10.

[0052] (bypass line 24, bypass valve 26)

[0053] The open circuit 2a is provided with a bypass line 24 connecting the pump line 16 and the return line 10. The bypass line 24 is provided with an electromagnetic proportional bypass valve 26 that adjusts the amount of hydraulic oil flowing from the pump line 16 to the return line 10.

[0054] (closed circuit 2b)

[0055] The closed circuit 2b includes a bidirectional hydraulic pump 28, a hydraulic motor 30, a first line 32, and a second line 34.

[0056] (bidirectional hydraulic pump 28)

[0057] The bidirectional hydraulic pump 28 has a first port 28a and a second port 28b, and sucks hydraulic oil from the first port 28a and discharges hydraulic oil from the second port 28b, or sucks hydraulic oil from the second port 28b and discharges hydraulic oil from the first port 28a. That is, in the bidirectional hydraulic pump 28, the first port 28a becomes a suction port and the second port 28b becomes a discharge port, and conversely, the second port 28b becomes a suction port and the first port 28a becomes a discharge port. Note that, since the closed circuit 2b is a closed circuit by the bidirectional hydraulic pump 28 and the hydraulic motor 30, unlike the hydraulic pump 4 of the open circuit 2a, the bidirectional hydraulic pump 28 does not suck and discharge hydraulic oil in the hydraulic oil tank 14.

[0058] The bidirectional hydraulic pump 28 is driven by the drive source 18 similar to the hydraulic pump 4 of the open circuit 2a. Therefore, the bidirectional hydraulic pump 28 is always rotated when the drive source 18 is operated. However, since the bidirectional hydraulic pump 28 has a variable capacity, and the discharge amount (capacity) and the discharge direction are controlled by the regulator 36, the hydraulic oil can not be discharged from either of the first port 28a and the second port 28b even if the bidirectional hydraulic pump 28 is rotated.

[0059] The regulator 36 of the bidirectional hydraulic pump 28 is of a hydraulic pilot type, and the flow direction of the hydraulic oil with respect to the regulator 36 is switched by an electromagnetic proportional regulator switching valve 38. The regulator switching valve 38 is connected to the pump line 16 through a pilot line 40. The pilot line 40 is provided with a pressure reducing valve 42 for reducing the hydraulic oil in the pump line 16 to a predetermined pressure.

[0060] Note that the housing 28c of the bidirectional hydraulic pump 28 is shown in dotted line in Figure 1 . It is assumed that the configurations (e.g., the first check valve 46 and the second check valve 48, the first safety valve 50 and the second safety valve 52, described below) provided in the rectangular region separated by the dotted line are installed in the housing 28c of the bidirectional hydraulic pump 28.

[0061] (Hydraulic motor 30, first line 32 and second line 34)

[0062] The hydraulic motor 30 is operated by the hydraulic oil discharged from the bidirectional hydraulic pump 28. The hydraulic motor 30 has a first port 30a and a second port 30b. The first port 30a of the hydraulic motor 30 is connected to the first port 28a of the bidirectional hydraulic pump 28 via the first line 32. Further, the second port 30b of the hydraulic motor 30 is connected to the second port 28b of the bidirectional hydraulic pump 28 via the second line 34.

[0063] (Charge line 44)

[0064] The charge line 44 is provided between the open circuit 2a and the closed circuit 2b for supplying the hydraulic oil from the open circuit 2a to the closed circuit 2b. The open circuit 2a side of the charge line 44 is connected to the upstream portion of the backflow check valve 12 in the backflow line 10. On the other hand, the closed circuit 2b side of the charge line 44 is connected to the first line 32 via the first check valve 46, and is connected to the second line 34 via the second check valve 48. Further, the closed circuit 2b side of the charge line 44 is connected to the housing 28c of the bidirectional hydraulic pump 28.

[0065] (First safety valve 50 and second safety valve 52)

[0066] The closed circuit 2b of the first embodiment includes a first safety valve 50 for releasing hydraulic oil of the first line 32 to the second line 34 via the second check valve 48 and a second safety valve 52 for releasing hydraulic oil of the second line 34 to the first line 32 via the first check valve 46. The set pressure of the first safety valve 50 and the second safety valve 52 can be, for example, 30 MPa to 40 MPa.

[0067] The hydraulic circuit 2 further includes an actuator manipulator 54, a motor manipulator 56, and a controller 58.

[0068] (The actuator manipulator 54, the motor manipulator 56)

[0069] The actuator manipulator 54 outputs a signal for actuating the hydraulic actuator 6. The motor manipulator 56 outputs a signal for operating the hydraulic motor 30. The actuator manipulator 54 and the motor manipulator 56 can have an input device (for example, a lever operable in a front-rear direction, a joystick operable in a cross direction, a slide switch, a pedal, or the like) whose output signal increases in strength as the amount of operation increases. Although Figure 1 An example is shown in which each of the manipulators 54, 56 outputs an electric signal, but each of the manipulators 54, 56 can be configured to output a hydraulic signal.

[0070] (The controller 58)

[0071] The controller 58 performs circuit control based on the signals output from each of the manipulators 54, 56. The controller 58 includes a computer having a processing device and a storage device. Note that when the signals output from each of the manipulators 54 and 56 are hydraulic signals, the output hydraulic signals are detected by a pressure sensor (not shown), and the detection results of the pressure sensor are input to the controller 58.

[0072] (Action of the hydraulic circuit 2)

[0073] Next, the action of the hydraulic circuit 2 as described above, particularly the supply of hydraulic oil from the open circuit 2a to the closed circuit 2b, will be described. First, the supply of pilot hydraulic oil to the regulator 36 of the closed circuit 2b will be described, and then the replenishment of hydraulic oil to the first line 32 and the second line 34 of the closed circuit 2b will be described. It will be explained below that the direction switching valve 8 is electromagnetic proportional, and that the direction switching valve 8 is controlled by an electric signal from the controller 58.

[0074] (Supply of pilot hydraulic oil to the regulator 36)

[0075] The regulator 36 of the bidirectional hydraulic pump 28 can be supplied with pilot hydraulic oil from the hydraulic pump 4 of the open circuit 2a. As described above, the regulator 36 is connected to the hydraulic pump 4 of the open circuit 2a through the pump line 16 and the pilot line 40. In addition, when the drive source 18 is running, hydraulic oil is continuously discharged from the hydraulic pump 4 to the pump line 16. Therefore, in the first embodiment, the pilot hydraulic oil can be supplied to the regulator 36 of the closed circuit 2b without a charge pump.

[0076] However, when the motor manipulator 56 is operated, the pilot hydraulic oil is actually supplied to the regulator 36 of the bidirectional hydraulic pump 28. When the motor manipulator 56 is operated, a signal is output from the motor manipulator 56 according to the operation amount. Then, in response to the signal output from the motor manipulator 56, the controller 58 opens the regulator switching valve 38 and adjusts the opening degree of the regulator switching valve 38. Therefore, the hydraulic oil discharged from the hydraulic pump 4 to the pump line 16 is supplied to the regulator 36 as pilot hydraulic oil that has been depressurized to a predetermined pressure by the pressure reducing valve 42 of the pilot line 40. Thus, according to the operation direction of the motor manipulator 56, hydraulic oil is discharged from the first port 28a or the second port 28b of the bidirectional hydraulic pump 28, and an amount of hydraulic oil corresponding to the operation amount of the motor manipulator 56 is discharged from the bidirectional hydraulic pump 28. Therefore, the hydraulic motor 30 rotates in a rotational direction corresponding to the operation direction of the motor manipulator 56, and the hydraulic motor 30 rotates at a rotational speed corresponding to the operation amount of the motor manipulator 56.

[0077] On the other hand, if the motor manipulator 56 is not operated, the pilot hydraulic oil is not supplied to the regulator 36. When the motor manipulator 56 is not operated, the motor manipulator 56 does not output a signal. In this case, the controller 58 positions the regulator switching valve 38 at the closed position to block the pilot line 40 by the regulator switching valve 38, and thus the pilot hydraulic oil is not supplied to the regulator 36. Therefore, no hydraulic oil is discharged from the bidirectional hydraulic pump 28, and the hydraulic motor 30 does not run.

[0078] (Supplementing hydraulic oil to the first line 32 and the second line 34)

[0079] Now, supplementing hydraulic oil to the first line 32 and the second line 34 of the closed circuit 2b will be described.

[0080] In the hydraulic circuit 2, when the actuator operator 54 is operated, the hydraulic actuator 6 is operated. When the actuator operator 54 is operated, a signal is output from the actuator operator 54 depending on the amount of operation. Then, in response to the signal output from the actuator operator 54, the controller 58 increases the pressure of the pump line 16 by adjusting the discharge amount of the hydraulic pump 4 and the opening degree of the bypass valve 26. The controller 58 opens the direction switching valve 8 and adjusts the opening degree of the direction switching valve 8 in response to the signal output from the actuator operator 54. This supplies hydraulic oil from the hydraulic pump 4 to the hydraulic actuator 6 through the pump line 16 and returns hydraulic oil from the hydraulic actuator 6 to the hydraulic tank 14 through the return line 10. Thus, the hydraulic actuator 6 is operated.

[0081] When the hydraulic actuator 6 is operated, hydraulic oil is discharged from the hydraulic actuator 6 to the return line 10, and thus a back pressure is generated in the return line 10 by the return check valve 12. By this, a pressure greater than or equal to a predetermined value also acts on the charging line 44 that branches and extends from the return line 10. Thus, hydraulic oil can be replenished from the charging line 44 to the first line 32 through the first check valve 46, or hydraulic oil can be replenished from the charging line 44 to the second line 34 through the second check valve 48. Thus, in the first embodiment, even without a charging pump, hydraulic oil can be supplied from the open circuit 2a to the closed circuit 2b through the charging line 44.

[0082] On the other hand, if the actuator operator 54 is not operated, the hydraulic actuator 6 is not operated, and hydraulic oil is not discharged from the hydraulic actuator 6 to the return line 10. When the actuator operator 54 is not operated, no signal is output from the actuator operator 54. In this case, the controller 58 positions the direction switching valve 8 at the closed position. Thus, no hydraulic oil is supplied from the pump line 16 to the hydraulic actuator 6, and no hydraulic oil is discharged from the hydraulic actuator 6 to the return line 10.

[0083] However, even if hydraulic oil is not discharged from the hydraulic actuator 6 to the return line 10, hydraulic oil is delivered to the return line 10. If the actuator operator 54 is not operated, the controller 58 adjusts the discharge amount of the hydraulic pump 4 to a relatively small standby flow rate and adjusts the opening degree of the bypass valve 26 to a predetermined opening degree that is not fully closed. This keeps the pressure of the pump line 16 at a predetermined standby pressure (for example, 3 to 4 MPa). Hydraulic oil discharged from the hydraulic pump 4 to the pump line 16 is also delivered to the return line 10 through the bypass line 24.

[0084] Therefore, a pressure greater than or equal to the predetermined value is also acted on the charging line 44 branched and extended from the return line 10, so that hydraulic oil can be replenished from the charging line 44 to the first line 32 or the second line 34. Therefore, in the first embodiment, even if hydraulic oil is not discharged from the hydraulic actuator 6 to the return line 10, hydraulic oil can be supplied from the open circuit 2a to the closed circuit 2b via the charging line 44.

[0085] (Adjustment of pressure of return line 10)

[0086] When the pressure of the return line 10 detected by the pressure sensor 22 is lower than the required pressure, the controller 58 needs to increase the discharge amount of the hydraulic pump 4. This is because, depending on the operating conditions of the construction machine, the pressure of the return line 10 can not rise to the value (required pressure) required to replenish hydraulic oil to the closed circuit 2b.

[0087] When the hydraulic actuator 6 is not operated, the discharge amount (standby flow rate) of the hydraulic pump 4 is smaller than the discharge amount of the hydraulic pump 4 when the hydraulic actuator 6 is operated, to suppress energy consumption. That is, when the hydraulic actuator 6 is not operated, the flow rate of the return line 10 is smaller than the flow rate of the return line 10 when the hydraulic actuator 6 is operated. Therefore, when the hydraulic actuator 6 is not operated, the pressure of the return line 10 is smaller than the pressure of the return line 10 when the hydraulic actuator 6 is operated. Therefore, depending on the operating conditions of the construction machine, when the hydraulic actuator 6 is not operated, the pressure of the return line 10 can not rise to the required pressure. However, even when the hydraulic actuator 6 is operated, depending on the operating conditions of the construction machine, the pressure of the return line 10 can not rise to the required pressure.

[0088] Therefore, when the pressure of the return line 10 detected by the pressure sensor 22 is lower than the required pressure, the controller 58 needs to increase the discharge amount of the hydraulic pump 4 to raise the pressure of the return line 10 to the required pressure, regardless of whether the hydraulic actuator 6 is operated. This makes it possible to supply hydraulic oil to the closed circuit 2b regardless of the operating conditions of the construction machine.

[0089] Regarding the above-described "required pressure", the controller 58 preferably sets the required pressure based on the operation amount of the motor operator 56.

[0090] When the motor operator 56 is returned to the neutral position (non-operation position) after the motor operator 56 is operated and the hydraulic motor 30 is operated, the supply of hydraulic oil from the bidirectional hydraulic pump 28 to the hydraulic motor 30 is cut off. If the motor operator 56 is returned to the neutral position, the controller 58 stops discharging hydraulic oil from the bidirectional hydraulic pump 28 through the regulator switching valve 38 because the signal from the motor operator 56 is interrupted. Therefore, the supply of hydraulic oil from the bidirectional hydraulic pump 28 to the hydraulic motor 30 is cut off.

[0091] However, even if the supply of hydraulic oil to the hydraulic motor 30 is cut off, the operation of the hydraulic motor 30 can continue, in which case cavitation can occur. Even if the supply of hydraulic oil to the hydraulic motor 30 is cut off, the operation of the hydraulic motor 30 can continue due to the inertia of the operation object operated by the hydraulic motor 30 (for example, in a hydraulic excavator, the upper swing body rotated by the hydraulic swing motor). In this case, the actuation of the hydraulic motor 30 acts as a pump. That is, the hydraulic motor 30 discharges hydraulic oil drawn from one of the first port 30a and the second port 30b from the other of the first port 30a and the second port 30b. Therefore, the line on the side that draws hydraulic oil (the first line 32 or the second line 34) can cavitate.

[0092] To prevent cavitation from occurring, a required pressure must be applied to the return line 10. This required pressure varies depending on the inertial force of the operation object. That is, the greater the inertial force of the operation object, the greater the required pressure, and the smaller the inertial force of the operation object, the smaller the required pressure. The inertial force of the operation object depends on the rotational speed of the hydraulic motor 30 immediately before stopping. The rotational speed of the hydraulic motor 30 immediately before stopping depends on the amount of hydraulic oil supplied from the bidirectional hydraulic pump 28 to the hydraulic motor 30. Then, the amount of hydraulic oil supplied from the bidirectional hydraulic pump 28 to the hydraulic motor 30 is controlled by the controller 58 in accordance with the operation amount of the motor manipulator 56. Therefore, the controller 58 preferably sets the required pressure based on the operation amount of the motor manipulator 56.

[0093] Reference will now be made to Figure 2 The role of the controller 58 in controlling the required pressure on the actuation return line 10 will be described.

[0094] (Step S1)

[0095] First, the controller 58 performs Step S1, that is, obtains the amount of hydraulic oil supplied from the bidirectional hydraulic pump 28 to the hydraulic motor 30 (the flow rate of the hydraulic motor 30) based on the signal output by the motor manipulator 56 in accordance with the operation amount of the motor manipulator 56. A first map showing the relationship between the operation amount of the motor manipulator 56 and the flow rate of the hydraulic motor 30 is registered in advance in the controller 58. Therefore, the controller 58 refers to the first map to obtain the flow rate of the hydraulic motor 30 in accordance with the signal output by the motor manipulator 56.

[0096] (Step S2)

[0097] After executing step S1, the controller 58 executes step S2 of obtaining the rotational speed of the hydraulic motor 30 in accordance with the flow rate of the hydraulic motor 30 determined in step S1. A second map showing the relationship between the flow rate of the hydraulic motor 30 and the rotational speed of the hydraulic motor 30 is pre-registered in the controller 58. Therefore, with reference to the second map, the controller 58 obtains the rotational speed of the hydraulic motor 30 in accordance with the flow rate of the hydraulic motor 30.

[0098] (Step S3)

[0099] After executing step S2, the controller 58 executes step S3 of obtaining the required pressure to be applied to the return line 10 in accordance with the rotational speed of the hydraulic motor 30 obtained in step S2. A third map showing the relationship between the rotational speed of the hydraulic motor 30 and the required pressure to be applied to the return line 10 is pre-registered in the controller 58. The third map takes into account the rotational speed of the operation object operated by the hydraulic motor 30, the mass of the operation object, and the like. Then, the controller 58 obtains the required pressure to be applied to the return line 10 based on the rotational speed of the hydraulic motor 30 with reference to the third map.

[0100] (Step S4)

[0101] After executing step S3, the controller 58 executes step S4 of determining whether the pressure of the return line 10 is less than the required pressure. The pressure of the return line 10 is input to the controller 58 as the detection result of the pressure sensor 22. The required pressure is the pressure obtained in step S3. Then, if the pressure of the return line 10 is less than the required pressure (if the determination result of step S4 is YES), the process proceeds to step S5. On the other hand, if the pressure of the return line 10 is greater than the required pressure (if the determination result of step S4 is NO), the process returns to step S1.

[0102] (Step S5)

[0103] If the process proceeds to step S5 from step S4, the controller 58 obtains the actual return flow rate in accordance with the detection result of the pressure sensor 22. As described above, the return line 10 is provided with the return check valve 12 that generates back pressure, and the back pressure generated by the return check valve 12 increases as the amount of hydraulic oil passing through the return line 10 (the return flow rate) increases. A fourth map created based on the characteristics of such a return check valve 12 is pre-registered to the controller 58. The fourth map is a map showing the relationship between the flow rate passing through the return line 10 (the return flow rate) and the back pressure generated by the return check valve 12 in the return line 10. Then, the controller 58 obtains the actual return flow rate in accordance with the detection result of the pressure sensor 22 (the actual pressure of the return line 10) with reference to the fourth map.

[0104] (Step S6)

[0105] After executing step S5, the controller 58 executes step S6 of obtaining the backflow flow rate corresponding to the required pressure obtained in step S3 with reference to the fourth map. Note that step S6 can be executed before step S5, or steps S5 and S6 can be executed in parallel.

[0106] (Step S7)

[0107] After executing step S6, the controller 58 obtains the correction flow rate using the following Equation 1 from the actual backflow flow rate (pre-correction flow rate) obtained in step S5 and the backflow flow rate corresponding to the required pressure obtained in step S6.

[0108] Equation 1 Correction flow rate = backflow flow rate corresponding to required pressure - actual backflow flow rate (step S8)

[0109] After executing step S7, the controller 58 executes step S8 of obtaining the correction current corresponding to the correction flow rate obtained in step S7. A fifth map indicating the relationship between the current delivered to the hydraulic pump 4 and the discharge amount of the hydraulic pump 4 is registered in advance in the controller 58. Then, the controller 58 refers to the fifth map to obtain the correction current corresponding to the correction flow rate.

[0110] (Step S9)

[0111] After executing step S8, the controller 58 executes step S9 of correcting the discharge amount of the hydraulic pump 4 based on the correction current obtained in step S8. Specifically, the correction current obtained in step S8 and the current delivered to the hydraulic pump 4 before correction are added to the current delivered to the hydraulic pump 4. Thus, the flow rate added to the discharge amount of the hydraulic pump 4 before correction is discharged from the hydraulic pump 4. Therefore, the pressure of the backflow line 10 is raised to the required pressure, and the required amount of hydraulic oil to close the circuit 2b can be replenished through the charging line 44, thereby preventing the occurrence of cavitation. Note that when the discharge amount of the hydraulic pump 4 is corrected, an adjustment current as a safety margin can be added to the current before correction together with the correction current.

[0112] Therefore, the controller 58 sets the required pressure based on the operation amount of the motor manipulator 56, and when the pressure of the backflow line 10 detected by the pressure sensor 22 is lower than the required pressure, it is desired to increase the discharge amount of the hydraulic pump 4 to raise the pressure of the backflow line 10 to the required pressure.

[0113] Alternatively, the controller 58 can set the required pressure based on a rotational speed of an operation object operated (rotated) by the hydraulic motor 30 of the closing circuit 2b. The rotational speed of the operation object is associated with an inertial force of the operation object, and the inertial force of the operation object is associated with the required pressure acting on the return line 10. That is, the required pressure depends on the rotational speed of the operation object. Therefore, the controller 58 can set the required pressure based on the rotational speed of the operation object.

[0114] If the controller 58 sets the required pressure based on the rotational speed of the operation object, a rotational speed detection device (for example, a rotational angle sensor that detects a rotational angle of the operation object) for detecting the rotational speed of the operation object is provided, and a detection result of the rotational speed detection device is transmitted to the controller 58. Further, a sixth map indicating a relationship between the rotational speed of the operation object and the required pressure is pre-registered in the controller 58. Then, the controller 58 can refer to the sixth map, set the required pressure according to the rotational speed of the operation object, and increase the discharge amount of the hydraulic pump 4 to raise the pressure of the return line 10 to the required pressure when the pressure of the return line 10 detected by the pressure sensor 22 is lower than the required pressure.

[0115] As described above, in the first embodiment, the hydraulic oil can be replenished to the first line 32 from the charging line 44 through the first check valve 46, or the hydraulic oil can be replenished to the second line 34 from the charging line 44 through the second check valve 48. That is, in the first embodiment, even without the charging pump, the hydraulic oil can be supplied from the opening circuit 2a to the closing circuit 2b via the charging line 44.

[0116] Therefore, in the first embodiment, the charging pump, the external filter to be connected to the charging pump, the piping member for integrating the charging pump and the external filter into the hydraulic circuit 2 are not required, so that the cost of the hydraulic circuit 2 is not increased. Further, by reducing the number of components, the maintenance work becomes easier. Further, in the first embodiment, the hydraulic oil (oil return) of the return line that does not use the work of the driving source is utilized to replenish the hydraulic oil to the closing circuit 2b, so that the work consumption of the driving source can be reduced. In other words, the energy consumption can be suppressed.

[0117] (Second Embodiment)

[0118] Next, a second embodiment of the hydraulic circuit of the construction machine according to the present application will be described with reference to Figure 3 The second embodiment of the hydraulic circuit of the construction machine according to the present application will be described with reference to

[0119] As Figure 3As shown, a throttle valve 60 is provided between the first safety valve 50 and the second check valve 48 and between the second safety valve 52 and the first check valve 46. Further, a third safety valve 62 is provided between the first safety valve 50 and the hydraulic oil tank 14 and between the second safety valve 52 and the hydraulic oil tank 14. The set pressure of the third safety valve 62 is smaller than the set pressure of the first safety valve 50 and smaller than the set pressure of the second safety valve 52. Further, the charge line 44 is provided with a third check valve 64 which allows flow from the open circuit 2a to the closed circuit 2b and prevents flow from the closed circuit 2b to the open circuit 2a.

[0120] In the second embodiment, if the pressure of the first line 32 exceeds the set pressure of the first safety valve 50, the hydraulic oil of the first line 32 flows to the second line 34 through the throttle valve 60 and the second check valve 48 and, after passing through the first safety valve 50, to the hydraulic oil tank 14 through the third safety valve 62. Similarly, if the pressure of the second line 34 exceeds the set pressure of the second safety valve 52, the hydraulic oil of the second line 34, after passing through the second safety valve 52, flows to the first line 32 via the throttle valve 60 and the first check valve 46 and to the hydraulic oil tank 14 via the third safety valve 62.

[0121] Thus, in the second embodiment, a part of the hydraulic oil released from the first line 32 and the second line 34 is allowed to flow into the hydraulic oil tank 14. Therefore, in the second embodiment, the amount of the hydraulic oil supplemented from the open circuit 2a to the closed circuit 2b is increased. That is, in the second embodiment, the hydraulic oil in the closed circuit 2b is easily replaced. Generally, the hydraulic oil temperature in the closed circuit is more likely to increase than the hydraulic oil temperature in the open circuit, but in the second embodiment, since the hydraulic oil in the closed circuit 2b is easily replaced, excessive increase in the hydraulic oil temperature is suppressed. It should be noted that, in the second embodiment, as in the first embodiment, the hydraulic oil can be supplied from the open circuit 2a to the closed circuit 2b through the charge line 44 even without the charge pump.

[0122] (Third Embodiment)

[0123] Next, a third embodiment of the hydraulic circuit of the construction machine according to the present application will be described with reference to Figure 4 In the third embodiment, components identical to those of the first and second embodiments can be given the same reference numerals as those of the first and second embodiments, and the description thereof will be omitted.

[0124] The closed circuit 2b of the third embodiment includes a first safety valve 50' which releases the hydraulic oil of the first line 32 to the hydraulic oil tank 14 and a second safety valve 52' which releases the hydraulic oil of the second line 34 to the hydraulic oil tank 14. As with the first and second embodiments, the first safety valve 50' and the second safety valve 52' are provided with a relief valve 54' and a relief valve 56', respectively. Figure 4It will be appreciated that, unlike the first safety valve 50 of the first and second embodiments, the first safety valve 50' of the third embodiment is not connected to the second check valve 48. Furthermore, unlike the second safety valve 52 of the first and second embodiments, the second safety valve 52' of the third embodiment is not connected to the first check valve 46.

[0125] In the third embodiment, all hydraulic oil that passes through the first and second safety valves 50', 52' flows into the hydraulic oil tank 14. Therefore, in the third embodiment, since the hydraulic oil in the closed circuit 2b is more easily replaced than in the second embodiment, a temperature rise in the hydraulic oil is further suppressed. It should be noted that in the third embodiment, as in the first and second embodiments, hydraulic oil can be supplied from the open circuit 2a to the closed circuit 2b via the charging line 44 even without a charging pump.

[0126] (Fourth embodiment)

[0127] Finally, refer to Figure 5 In the fourth embodiment, the same components as those of the first to third embodiments may be given the same reference numerals as those of the first to third embodiments, and their description will be omitted.

[0128] In the fourth embodiment, the first check valve 46 and the second check valve 48 are connected to the housing 30 c of the hydraulic motor 30 , and the charging line 44 is also connected to the housing 30 c of the hydraulic motor 30 .

[0129] In the fourth embodiment, for example, when the hydraulic circuit 2 is installed in a hydraulic excavator and the hydraulic motor 30 of the closed circuit 2b is a rotary motor that rotates the upper rotating body of the hydraulic excavator, the layout of the charging line 44 connecting the open circuit 2a and the closed circuit 2b becomes easier. Typically, in a hydraulic excavator, the rotary motor is closer to the directional control valve than the hydraulic pump. Therefore, connecting the charging line 44 to the housing 30c of the hydraulic motor 30 (the rotary motor) as in the fourth embodiment is easier than connecting the charging line 44 to the housing 28c of the bidirectional hydraulic pump 28 as in the third embodiment. It should be noted that in the fourth embodiment, as in the first to third embodiments, hydraulic oil can be supplied from the open circuit 2a to the closed circuit 2b via the charging line 44 even without a charging pump.

[0130] Description of Reference Numerals

[0131] 2: Hydraulic circuit

[0132] 2a: Opening the circuit

[0133] 2b: Closing the loop

[0134] 4: Hydraulic pump

[0135] 6: Hydraulic actuator

[0136] 8: Directional switching valve

[0137] 10: Return line

[0138] 12: Backflow check valve

[0139] 14: Hydraulic oil tank

[0140] 16: Pump line

[0141] 22: Pressure sensor

[0142] 24: Bypass route

[0143] 26: Bypass valve

[0144] 28: Bidirectional hydraulic pump

[0145] 28a: Bidirectional hydraulic pump first port

[0146] 28b: Bidirectional hydraulic pump second port

[0147] 28c: Housing of bidirectional hydraulic pump

[0148] 30: Hydraulic motor

[0149] 30a: Hydraulic motor first port

[0150] 30b: Second port of hydraulic motor

[0151] 30c: Hydraulic motor housing

[0152] 32: First Pipeline

[0153] 34: Second pipeline

[0154] 36: Regulator

[0155] 38: Regulator switching valve

[0156] 40: Guide pipeline

[0157] 42: Pressure reducing valve

[0158] 44: Filling line

[0159] 46: First check valve

[0160] 48: Second check valve

[0161] 50: First safety valve (first and second embodiments)

[0162] 50': First safety valve (third and fourth embodiments)

[0163] 52: second safety valve (first and second embodiments)

[0164] 52': second safety valve (third and fourth embodiments)

[0165] 56: motorized actuator

[0166] 58: controller

[0167] 60: throttle valve

[0168] 62: third safety valve

Claims

1. A hydraulic circuit for a construction machine, comprising an opening circuit and a closing circuit, The open loop includes: a variable capacity hydraulic pump that discharges hydraulic oil drawn from a hydraulic oil tank; a hydraulic actuator operated by hydraulic oil discharged from the hydraulic pump; a direction switching valve that switches the flow direction of hydraulic oil from the hydraulic pump to the hydraulic actuator; a pump line connecting the hydraulic pump and the directional switching valve; a return line connecting the directional switching valve and the hydraulic oil tank; a backflow check valve disposed in the backflow line; a bypass line connecting the pump line and the return line; as well as an electromagnetic proportional bypass valve disposed in the bypass line; The closed loop includes: a variable capacity, bi-directional hydraulic pump having a first port and a second port; a hydraulic motor operated by hydraulic oil discharged from the bidirectional hydraulic pump; a first pipeline connecting the first port of the bidirectional hydraulic pump and the hydraulic motor; a second pipeline connecting the second port of the bidirectional hydraulic pump and the hydraulic motor; A charging line is provided between the open circuit and the closed circuit, the charging line connecting a portion of the return line upstream of the return check valve and the first line via a first check valve, and connecting a portion of the return line upstream of the return check valve and the second line via a second check valve.

2. The hydraulic circuit for construction machinery according to claim 1, wherein: The closed loop includes: a first safety valve that releases the hydraulic oil of the first pipeline to the second pipeline via the second check valve; and a second safety valve that releases the hydraulic oil of the second pipeline to the first pipeline via the first check valve.

3. The hydraulic circuit for construction machinery according to claim 2, wherein: The throttle valve is arranged between the first safety valve and the second check valve and between the second safety valve and the first check valve; a third safety valve disposed between the first safety valve and the hydraulic oil tank and between the second safety valve and the hydraulic oil tank; A setting pressure of the third safety valve is lower than a setting pressure of the first safety valve and lower than a setting pressure of the second safety valve.

4. The hydraulic circuit for construction machinery according to claim 1, wherein: The closed loop includes: a first safety valve that releases the hydraulic oil of the first pipeline to the hydraulic oil tank; and a second safety valve for releasing the hydraulic oil of the second pipeline to the hydraulic oil tank.

5. The hydraulic circuit for construction machinery according to claim 1, wherein: The first check valve and the second check valve are mounted to a housing of the bidirectional hydraulic pump, and the charging line is connected to the housing.

6. The hydraulic circuit for construction machinery according to claim 1, wherein: The first check valve and the second check valve are mounted to a housing of the hydraulic motor, and the charging line is connected to the housing.

7. The hydraulic circuit for a construction machine according to claim 1, comprising: a pressure sensor that detects pressure on an upstream side of the return check valve of the return line; as well as A controller increases a discharge volume of the hydraulic pump when the pressure detected by the pressure sensor is lower than a required pressure.

8. The hydraulic circuit for construction machinery according to claim 7, wherein: The controller sets the required pressure based on an operation amount of a motor operator that outputs a signal for operating the hydraulic motor of the closed circuit.

9. The hydraulic circuit for construction machinery according to claim 7, wherein: The controller sets the required pressure based on a rotation speed of an operation object operated by the hydraulic motor of the closed circuit.

10. The hydraulic circuit for a construction machine according to claim 1, comprising: a regulator for controlling the discharge volume and discharge direction of the bidirectional hydraulic pump; as well as an electromagnetic proportional regulator switching valve that switches and directs the flow direction of hydraulic oil relative to the regulator; a pilot line branching from the pump line and extending to the regulator switching valve; A pressure reducing valve is provided on the guide pipeline.

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