HYDRAULIC CIRCLE FOR CONSTRUCTION MACHINE

Abstract

Task: A hydraulic circuit for a construction machine with good energy efficiency is provided. Means of solution: A hydraulic circuit (2) includes a motor generator (4), a pump motor (6) connected to the motor generator (4), a boom cylinder (8), a rod-side pipe (10) connecting the pump motor (6) and a rod-side port (8c) of the boom cylinder (8), a cover-side pipe (12) connecting the pump motor (6) and a cover-side port (8d) of the boom cylinder (8), an operating device (18) that outputs a signal to operate the boom cylinder (8), and a controller (20) that performs circuit control based on a signal output by the operating device (18).In a case where a rod extension signal for the boom cylinder (8) is issued by the operating device (18), hydraulic oil flows from the rod-side pipe (10) to the cover-side pipe (12) via the pump motor (6). In a case where a rod retraction signal for the boom cylinder (8) is issued by the operating device (18), hydraulic oil flows from the cover-side pipe (12) to the rod-side pipe (10) via the pump motor (6).

Description

Technical area

[0001] The present invention relates to a hydraulic circuit for a construction machine with a boom. State of the art

[0002] A hydraulic excavator, a typical example of a boom-type construction machine, includes a lower body, an upper swing body supported by the lower body, and a front attachment attached to the upper swing body. The front attachment includes a boom pivotally supported by the upper swing body, an arm pivotally supported at the tip end of the boom, and a bucket pivotally supported at the tip end of the arm.

[0003] A hydraulic circuit for a hydraulic excavator includes a hydraulic pump, a hydraulic actuator (such as a boom cylinder, an arm cylinder, and a bucket cylinder) operated by oil discharged from the hydraulic pump, an operating device that outputs a signal to operate the hydraulic actuator, and a directional control valve for switching the supply direction of hydraulic oil from the hydraulic pump to the hydraulic actuator based on a signal output from the operating device.

[0004] In the hydraulic excavator, the oil discharged from the hydraulic pump is supplied to the hydraulic actuator via the directional control valve based on the signal output from the operating device, and the hydraulic actuator is operated to swing the front attachment (see, for example, Patent Document 1). Prior art documentPATENT DOCUMENT

[0005] Patent Document 1: JP-A-2013-23821 Brief description of the inventionProblem the invention is intended to solve

[0006] However, in state-of-the-art hydraulic excavators, the pressure loss in the directional control valve is large, and there is potential for improvement in energy efficiency.

[0007] When the bucket is off the ground, the weight of the boom, arm, and bucket acts on the boom cylinder. Thus, when the boom is lowered, the pressure required to operate the boom cylinder (retracting a piston rod of the boom cylinder into a cylinder tube) is lower than the pressure required to operate the arm cylinder and bucket cylinder.

[0008] Thus, when operating other hydraulic actuators, such as an arm cylinder, together with the boom cylinder, although it is necessary to increase the discharge pressure of the hydraulic pump to the extent that other hydraulic actuators can be operated, the pressure of the hydraulic oil supplied to the boom cylinder is reduced by the boom directional control valve. Accordingly, there is a problem that a large pressure loss occurs in the directional control valve, and an improvement in energy efficiency is desired.

[0009] It is an object of the present invention to provide a hydraulic circuit for a construction machine with good energy efficiency. Means to solve the problem

[0010] According to the present invention, a hydraulic circuit for a construction machine is provided that solves the above-mentioned problems as follows. That is, the following is provided: “a hydraulic circuit for a construction machine having a boom, the hydraulic circuit comprising a motor generator, a bidirectional variable displacement pump motor connected to the motor generator, a boom cylinder for operating the boom, a rod-side pipe connecting the pump motor and a rod-side connection of the boom cylinder, a cover-side pipe connecting the pump motor and a cover-side connection of the boom cylinder, an operating device that outputs a signal to operate the boom cylinder, and a controller that performs circuit control based on a signal output from the operating device, wherein, in a case where a rod push-out signal for the boom cylinder is output from the operating device, hydraulic oil flows from the rod-side piping to the cover-side piping via the pump motor, and In a case where a rod retraction signal for the boom cylinder is output from the operation device, hydraulic oil flows from the cover-side piping to the rod-side piping via the pump motor.

[0011] Preferably, the hydraulic circuit further includes a cover-side pressure sensor that detects pressure in the cover-side piping, and in a case where the rod retraction signal for the boom cylinder is output from the operating device, the controller causes the motor generator to drive the pump motor when the pressure detected by the cover-side pressure sensor is less than a predetermined value, and allows the motor generator to be driven by the pump motor when the pressure detected by the cover-side pressure sensor is equal to or higher than the predetermined value.

[0012] The hydraulic circuit may further include a rod-side return piping connecting the rod-side piping and a hydraulic oil tank, and an electromagnetic on-off proportional valve disposed in the rod-side return piping, and when the rod retraction signal for the boom cylinder is output from the operating device, the controller may open the electromagnetic on-off proportional valve to discharge excess hydraulic oil from the rod-side return piping.

[0013] It is preferable that the controller adjusts an opening degree of the electromagnetic on-off proportional valve according to the signal output from the operating device and controls an amount of excess hydraulic oil discharged from the rod-side return piping.

[0014] The hydraulic circuit may further include a cover-side return piping connecting the cover-side piping and a hydraulic oil tank, and an electromagnetic relief proportional valve disposed in the cover-side return piping, and when the rod retraction signal for the boom cylinder is output from the operating device, the controller may reduce relief pressure of the electromagnetic relief proportional valve to discharge excess hydraulic oil from the cover-side return piping.

[0015] It is desirable that the hydraulic circuit further includes a rod-side supply piping connected to the rod-side piping, a rod-side check valve arranged in the rod-side supply piping, a cover-side close-thrust piping connected to the cover-side piping, and a cover-side check valve arranged in the cover-side supply piping, and in a case where the rod push-out signal for the boom cylinder is output from the operating device, the rod-side check valve opens to fill the rod-side piping with hydraulic oil, or the cover-side check valve opens to fill the cover-side piping with hydraulic oil.

[0016] The cover-side piping is provided with a drift reduction valve that allows flow from the pump motor to the cover-side port and blocks flow from the cover-side port to the pump motor, and in a case where the rod retraction signal for the boom cylinder is output from the operating device, the controller may open the drift reduction valve to allow flow from the cover-side port to the pump motor.

[0017] It is preferable that the controller adjusts a rotational speed of the motor generator and a displacement of the pump motor according to the signal output from the operating device. Advantage of the invention

[0018] In the hydraulic circuit for a construction machine according to the present invention, in a case where a rod push-out signal for the boom cylinder is output from the operating device, hydraulic oil flows from the rod-side piping to the cover-side piping via the pump motor, and in a case where a rod push-out signal for the boom cylinder is output from the operating device, hydraulic oil flows from the cover-side piping to the rod-side piping via the pump motor. Thus, a directional control valve for switching the operating direction of the boom cylinder is not required. Accordingly, no pressure loss occurs in the directional control valve, and good energy efficiency is achieved. Brief description of the drawings Fig. 1 is a circuit diagram illustrating a hydraulic circuit of the present invention. Fig. Figure 2 is a schematic diagram of a hydraulic excavator equipped with a hydraulic circuit arranged in Fig. 1 (state where an external force acts on a boom cylinder in a rod retraction direction). Fig. Fig. 3 is a circuit diagram illustrating the flow of hydraulic oil in a case where a rod push-out signal is output, in the state shown in Fig. 2 is illustrated. Fig. Fig. 4 is a circuit diagram illustrating the flow of hydraulic oil in a case where a rod retraction signal is output in the state shown in Fig. 2 is illustrated. Fig. Fig. 5 is a schematic diagram illustrating a state in which the hydraulic excavator used in Fig. 2, tilts a machine body using a front attachment (state in which an external force acts on a boom cylinder in a rod pushing-out direction). Fig. Fig. 6 is a circuit diagram illustrating the flow of hydraulic oil in a case where a rod push-out signal is outputted in the state shown in Fig. 5 is illustrated. Fig. Fig. 7 is a circuit diagram illustrating the flow of hydraulic oil in a case where a rod retraction signal is output in the state shown in Fig. 5 (when an electromagnetic on-off proportional valve is open). Fig. Fig. 8 is a circuit diagram illustrating the flow of hydraulic oil in a case where a rod retraction signal is output in the state shown in Fig. 5 (when an electromagnetic overpressure proportional valve is open). Best mode for carrying out the invention

[0019] An embodiment of a hydraulic circuit for a construction machine according to the present invention will be described below with reference to the accompanying drawings. Hydraulic circuit 2

[0020] A hydraulic circuit 2, illustrated in Fig. 1, can be mounted on a construction machine with a boom (for example, a hydraulic excavator). The hydraulic circuit 2 includes a motor generator 4, a bidirectional variable displacement pump motor 6 connected to the motor generator 4, and a boom cylinder 8 for operating the boom. Motor generator 4, pump motor 6

[0021] A battery (not illustrated) is connected to the motor generator 4. In a case where electric power is supplied to the motor generator 4 from the battery, the motor generator 4 functions as an electric motor, and the pump motor 6 driven by the motor generator 4 functions as a hydraulic pump.

[0022] When the motor generator 4 rotates forward to cause the pump motor 6 to rotate forward, low-pressure hydraulic oil is sucked from a first port 6a of the pump motor 6, and high-pressure hydraulic oil is discharged from a second port 6b of the pump motor 6. On the other hand, when the motor generator 4 rotates reversely to cause the pump motor 6 to rotate reversely, low-pressure oil is sucked from the second port 6b, and high-pressure oil is discharged from the first port 6a.

[0023] Further, in a case where the motor generator 4 functions as a generator, the pump motor 6 acts as a hydraulic motor to drive the motor generator 4.

[0024] When high-pressure oil flows into the first port 6a of the pump motor 6 and low-pressure oil flows out of the second port 6b, the pump motor 6 rotates forward to cause the motor generator 4 to rotate forward. On the other hand, when high-pressure oil flows into the second port 6b of the pump motor 6 and low-pressure oil flows out of the first port 6a, the pump motor 6 rotates reversely to cause the motor generator 4 to rotate reversely. Electric energy generated by the forward or reverse rotation of the motor generator 4 is stored in the battery.

[0025] Note that oil drained from the pump motor 6 is supplied only to the boom cylinder 8, and the hydraulic actuators (arm cylinder, bucket cylinder, and the like) other than the boom cylinder 8 are supplied with hydraulic oil from other hydraulic pumps besides the pump motor 6. Other hydraulic pumps are driven by drive sources other than the motor generator 4 (electric motor, engine, and the like). Thus, in the hydraulic circuit 2, there is no interference between the circuit of the boom cylinder 8 and the circuit of other hydraulic actuators, and the operability is excellent. Boom cylinder 8, rod-side pipe 10, cover-side pipe 12

[0026] The boom cylinder 8 includes a cylinder tube 8a and a piston rod 8b. A rod-side port 8c of the boom cylinder 8 is connected to the first port 6a of the pump motor 6 via a rod-side pipe 10. A cover-side port 8d of the boom cylinder 8 is connected to the second port 6b of the pump motor 6 via a cover-side pipe 12.

[0027] A rod-side pressure sensor 14, which detects the pressure in the rod-side piping 10, is provided in the rod-side piping 10. A cover-side pressure sensor 16, which detects the pressure in the cover-side piping 12, is provided in the cover-side piping 12.

[0028] As in Fig. 1, the hydraulic circuit 2 includes an operating device 18 that outputs a signal to operate the boom cylinder 8, and a controller 20 that performs circuit control based on the signal output from the operating device 18. Operating device 18

[0029] The operating device 18 may include an input device (e.g., a joystick or a slide switch) that increases the output intensity of an electrical signal as the amount of operation increases. The operating device 18 may output a signal for operating the boom cylinder 8 as well as a signal for operating a hydraulic actuator other than the boom cylinder 8. Control 20

[0030] The controller 20 includes a computer with a processing device and a storage device. As shown in Fig. As illustrated in Figure 1, the operating device 18 and the motor generator 4 are electrically connected to the controller 20. Although not illustrated, the pump motor 6, the rod-side pressure sensor 14, and the cover-side pressure sensor 16 are also electrically connected to the controller 20.

[0031] The hydraulic circuit 2 of the illustrated embodiment includes a rod-side return pipe 24 connecting the rod-side pipe 10 and the hydraulic oil tank 22, an electromagnetic on-off proportional valve 26 disposed in the rod-side return pipe 24, a cover-side return pipe 28 connecting the cover-side pipe 12 and the hydraulic oil tank 22, and an electromagnetic relief proportional valve 30 disposed in the cover-side return pipe 28.

[0032] The rod-side return piping 24 and the cover-side return piping 28 converge in front of the hydraulic oil tank 22 and are connected to the hydraulic oil tank 22 via a confluence return piping 32. Another return piping 34 for returning hydraulic oil discharged from hydraulic actuators other than the boom cylinder 8 to the hydraulic oil tank 22 is connected to the confluence return piping 32. Furthermore, the confluence return piping 32 is provided with a back pressure check valve 36 for assembling.

[0033] Although not illustrated, the electromagnetic on-off proportional valve 26 and the electromagnetic relief proportional valve 30 are electrically connected to the controller 20. The electromagnetic on-off proportional valve 26 closes the oil passage in a case where no signal is output from the controller 20, and opens the oil passage when the signal is sent from the controller 20. The opening degree of the electromagnetic on-off proportional valve 26 is adjusted according to a signal from the controller 20. Furthermore, the relief pressure of the electromagnetic relief proportional valve 30 is maintained at the initial value in a case where no signal is output from the controller 20, and is changed from the initial value according to the signal from the controller 20.

[0034] As in Fig. 1, the hydraulic circuit 2 further includes a rod-side supply pipe 38 connected to the rod-side pipe 10, a rod-side check valve 40 disposed in the rod-side supply pipe 38, a cover-side supply pipe 42 connected to the cover-side pipe 12, and a cover-side check valve 44 disposed in the cover-side supply pipe 42.

[0035] The rod-side supply line 38 connects the rod-side line 10 and the hydraulic oil tank 22. The rod-side check valve 40 allows flow from the hydraulic oil tank 22 to the rod-side line 10 and blocks flow from the rod-side line 10 to the hydraulic oil tank 22.

[0036] The cover-side supply line 42 in the illustrated embodiment is connected to the cover-side return line 28 in a manner that bypasses the electromagnetic relief pressure proportional valve 30, and the cover-side check valve 44 and the electromagnetic relief pressure proportional valve 30 are arranged in parallel. The cover-side check valve 44 allows flow from the cover-side supply line 42 to the cover-side pipe 12 and blocks flow from the cover-side pipe 12 to the cover-side supply line 42.

[0037] In the illustrated embodiment, the cover-side piping 12 is provided with a drift reduction valve 46. The drift reduction valve 46 allows flow from the second port 6b of the pump motor 6 to the cover-side port 8d of the boom cylinder 8 and essentially blocks flow from the cover-side port 8d to the second port 6b.

[0038] Although not illustrated, the drift reduction valve 46 is electrically connected to the controller 20. The controller 20 opens the drift reduction valve 46 in a case where a rod retraction signal of the boom cylinder 8 is output from the operating device 18 to allow flow from the cover-side port 8d to the second port 6b.

[0039] Fig. 2 illustrates a hydraulic excavator 50 as an example of a construction machine on which the hydraulic circuit 2 described above is mounted. The hydraulic excavator 50 includes a lower traveling body 52, an upper swing body 54 rotatably supported by the lower traveling body 52, and a front attachment 56 attached to the upper swing body 54.

[0040] The front attachment 56 includes a boom 58 pivotally supported by the upper swing body 54, an arm 60 pivotally supported at the tip end of the boom 58, and a bucket 62 pivotally supported at the tip end of the arm 60. In addition, the front attachment 56 is provided with the boom cylinder 8 for pivoting the boom 58, an arm cylinder 64 for pivoting the arm 60, and a bucket cylinder 66 for pivoting the bucket 62.

[0041] The base end of the cylinder tube 8a of the boom cylinder 8 is connected to the upper swing body 54, and the tip end of the piston rod 8b is connected to the boom 58. Then, when the piston rod 8b is pushed out of the cylinder tube 8a, the boom 58 swings in the direction indicated by a solid arrow A in Fig. 2. Furthermore, when the piston rod 8b is retracted into the cylinder tube 8a, the boom 58 swings in the direction indicated by a dotted arrow B in Fig. 2 is specified.

[0042] Next, the operation of the hydraulic circuit 2 for a construction machine as described above will be described.

[0043] In a case where the operating device 18 is not operated, no signal is output from the operating device 18 to the controller 20. In this case, the motor generator 4 and the pump motor 6 are not operated, and the hydraulic oil in the rod-side piping 10 and the cover-side piping 12 does not flow. Thus, the boom cylinder 8 is not operated.

[0044] When the boom cylinder 8 is stopped and the bucket 62 is above the ground, as shown in Fig. As illustrated in Figure 2, the weight of the front attachment 56 acts on the boom cylinder 8, i.e., the external force acts on the boom cylinder 8 in the rod retraction direction. Thus, the pressure in the cover-side pipe 12 increases.

[0045] However, in the illustrated embodiment, the drift reduction valve 46 blocks the flow from the cover-side port 8d to the second port 6b of the pump motor 6 unless the operating device 18 issues a rod retraction signal. Thus, the position of the piston rod 8b of the boom cylinder 8 is maintained, and the natural lowering of the boom 58 is prevented. In the above-mentioned state, no pressure builds up in the rod-side piping 10. 1. Pushing out the rod when external force acts in the rod retraction direction

[0046] In the state that Fig. 2, there is no pressure in the rod-side piping 10, and the pressure detected by the rod-side pressure sensor 14 becomes lower than a predetermined value. Then, when a rod push-out signal for the boom cylinder 8 is output from the operating device 18, the controller 20 supplies electrical power from the battery to the motor generator 4 to rotate the motor generator 4 forward. This causes the pump motor 6 to rotate forward. In other words, the motor generator 4 functions as an electric motor, and the pump motor 6 acts as a hydraulic pump.

[0047] Then, as in Fig. 3, low-pressure hydraulic oil in the rod-side pipe 10 is sucked into the first port 6a of the pump motor 6, and high-pressure hydraulic oil is discharged from the second port 6b to the cover-side pipe 12. That is, hydraulic oil flows from the rod-side pipe 10 to the cover-side pipe 12 via the pump motor 6. In Fig. 3, the flow of high-pressure hydraulic oil is indicated by a thick black line and the flow of low-pressure hydraulic oil is indicated by a thick gray line. Furthermore, the same applies to Fig. 4 and 6 to 8.

[0048] Furthermore, since hydraulic oil flows out of the rod-side port 8c of the boom cylinder 8 into the rod-side piping 10 and hydraulic oil flows into the cover-side port 8d from the cover-side piping 12, the piston rod 8b is pushed out of the cylinder tube 8a. Accordingly, the boom 58 swings (rises) in the direction indicated by the solid arrow A in Fig. 2 is specified.

[0049] As described above, since the drift reducing valve 46 allows the flow from the second port 6b of the pump motor 6 to the cover-side port 8d, when the discharge pressure of the pump motor 6 exceeds the pressure of the cover-side port 8d, the drift reducing valve 46 opens.

[0050] In a case where the piston rod 8b is pushed out of the cylinder tube 8a, the amount of hydraulic oil flowing out of the rod-side port 8c is less than the amount of hydraulic oil flowing into the cover-side port 8d by the volume of the piston rod 8b. Thus, the pressure in the rod-side pipe 10 becomes lower than the pressure in the hydraulic oil tank 22, and as shown in Fig. 3, the rod-side check valve 40 is opened, and the rod-side pipe 10 is filled with hydraulic oil from the hydraulic oil tank 22 via the rod-side supply pipe 38. Accordingly, cavitation is prevented. 2. Retraction of the rod when external force acts in the rod retraction direction

[0051] In the state that Fig. As illustrated in Figure 2, the pressure in the cover-side piping 12 increases as described above, so that the pressure detected by the cover-side pressure sensor 16 becomes equal to or higher than the predetermined value. Thus, when the rod retraction signal for the boom cylinder 8 is output from the operating device 18, the controller 20 allows the motor generator 4 to be driven by the pump motor 6.

[0052] In addition, the controller 20 opens the drift reduction valve 46 to allow the hydraulic oil to flow from the cover-side port 8d to the second port 6b of the pump motor 6. Consequently, as shown in Fig. As illustrated in Figure 4, when high-pressure hydraulic oil flows from the cover-side piping 12 into the second port 6b, the pump motor 6 rotates reversely, and low-pressure hydraulic oil is discharged from the first port 6a. That is, hydraulic oil flows from the cover-side piping 12 to the rod-side piping 10 via the pump motor 6. At this time, the pump motor 6 acts as a hydraulic motor to drive the motor generator 4. Furthermore, the motor generator 4 functions as a generator to generate electricity.

[0053] Then, hydraulic oil flows out from the cover-side port 8d of the boom cylinder 8 into the cover-side piping 12, and hydraulic oil flows into the rod-side port 8c from the rod-side piping 10. Accordingly, the piston rod 8b is retracted into the cylinder tube 8a, and the boom 58 swings (lowers) in the direction indicated by the dotted arrow B in Fig. 2 is specified.

[0054] In a case where the piston rod 8b is retracted into the cylinder tube 8a, the amount of outflow from the cover-side port 8d is larger than the amount of inflow to the rod-side port 8c by the volume of the piston rod 8b. Thus, in a case where the rod retraction signal for the boom cylinder 8 is output from the operating device 18 as shown in Fig. 4, the controller 20 opens the electromagnetic on-off proportional valve 26 to discharge excess hydraulic oil from the rod-side return pipe 24 to the hydraulic oil tank 22.

[0055] It is desirable that the controller 20 adjusts the opening degree of the electromagnetic on-off proportional valve 26 according to the signal output from the operating device 18 and controls the amount of excess hydraulic oil discharged from the rod-side return piping 24 to the hydraulic oil tank 22. Thus, the pressure in the rod-side piping 10 is adjusted, and the retraction speed of the piston rod 8b can be appropriately controlled according to the signal from the operating device 18. Machine stroke

[0056] In the hydraulic excavator 50, as in Fig. As illustrated in Figure 5, there is a case where the bucket 62 is pressed against the ground to tilt the machine body (the lower traveling body 52 and the upper swing body 54) (sometimes called machine lifting). In such a case, an external force acts on the boom cylinder 8 in the rod-pushing direction, and the pressure in the rod-side piping 10 increases. 3. Pushing out the rod when external force acts in the rod pushing out direction

[0057] In the state that Fig. 5, the pressure in the rod-side piping 10 increases, so that the pressure detected by the rod-side pressure sensor 14 becomes equal to or higher than a predetermined value. The predetermined value of the pressure detected by the rod-side pressure sensor 14 at this time may not be equal to the predetermined value of the pressure detected by the cover-side pressure sensor 16 (a predetermined value for allowing the motor generator 4 to be driven by the pump motor 6 in a case where the rod retraction signal is output).

[0058] Then, in the state that Fig. As illustrated in Figure 5, when a rod push-out signal for the boom cylinder 8 is output from the operating device 18, the controller 20 supplies electrical power from the battery to the motor generator 4 to rotate the motor generator 4 forward. Consequently, the pump motor 6 rotates forward, and hydraulic oil flows into the first port 6a of the pump motor 6 and flows out of the second port 6b. In other words, hydraulic oil flows from the rod-side piping 10 to the cover-side piping 12 via the pump motor 6.

[0059] Furthermore, since hydraulic oil flows from the rod-side port 8c of the boom cylinder 8 into the rod-side piping 10 and hydraulic oil flows into the cover-side port 8d from the cover-side piping 12, the piston rod 8b is pushed out of the cylinder tube 8a. Accordingly, the machine body (the lower traveling body 52 and the upper swing body 54) swings in the direction indicated by a solid arrow C in Fig. 5 is specified.

[0060] As described above, in the condition described in Fig. 5, the pressure in the rod-side piping 10 is increased, so the hydraulic oil flowing into the first port 6a is at high pressure. Accordingly, when the pump motor 6 rotates forward and a flow is generated from the rod-side piping 10 to the cover-side piping 12, the controller 20 can stop the supply of electric power from the battery to the motor generator 4, can cause the pump motor 6 to rotate forward by the high-pressure hydraulic oil flowing into the first port 6a, and can rotate the motor generator 4 forward by the rotation of the pump motor 6.

[0061] That is, in a case where an external force acts in the rod push-out direction (in a case where the pressure detected by the rod-side pressure sensor 14 is equal to or higher than a predetermined value), when the rod push-out signal is output, the controller 20 first causes the motor generator 4 to drive the pump motor 6 as a hydraulic pump, and after a predetermined period of time has passed since the pump motor 6 started to be driven, the controller 20 may switch the pump motor 6 to a hydraulic motor and cause the motor generator 4 to generate power.

[0062] As described above, in a case where the piston rod 8b is pushed out from the cylinder tube 8a, the amount of outflow from the rod-side port 8c is smaller than the amount of inflow into the cover-side port 8d by the volume of the piston rod 8b, but when an external force acts in the rod-push-out direction, the pressure in the rod-side piping 10 becomes higher than the pressure in the hydraulic oil tank 22. Thus, the rod-side check valve 40 does not open.

[0063] However, in the illustrated embodiment, since the back pressure check valve 36 is provided in the confluence return pipe 32 connected to the cover-side return pipe 28, the pressure in the cover-side pipe 12 becomes lower than the pressure in the cover-side return pipe 28, the cover-side check valve 44 is provided as in Fig. 6 illustrates that the cover-side pipe 12 is opened, and the cover-side supply pipe 42 is filled with hydraulic oil. Accordingly, cavitation is prevented. 4. Retraction of the rod when external force acts in the rod pushing out direction

[0064] In the state that Fig. 5, there is no pressure in the cover-side piping 12, and the pressure detected by the cover-side pressure sensor 16 becomes lower than a predetermined value. Thus, when a rod retraction signal for the boom cylinder 8 is output from the operating device 18, the controller 20 supplies electrical power from the battery to the motor generator 4 to rotate the motor generator 4 in reverse. This causes the pump motor 6 to rotate in reverse. In this way, the motor generator 4 functions as an electric motor, and the pump motor 6 acts as a hydraulic pump.

[0065] In addition, the controller 20 opens the drift reduction valve 46 to allow the hydraulic oil to flow from the cover-side port 8d to the second port 6b of the pump motor 6. Consequently, as shown in Fig. As illustrated in Figure 7, low-pressure hydraulic oil in the cover-side piping 12 is sucked into the second port 6b, and high-pressure hydraulic oil is discharged from the first port 6a to the rod-side piping 10. That is, hydraulic oil flows from the cover-side piping 12 to the rod-side piping 10 via the pump motor 6.

[0066] Consequently, hydraulic oil flows out from the cover-side port 8d of the boom cylinder 8 into the cover-side piping 12, and hydraulic oil flows into the rod-side port 8c from the rod-side piping 10. Accordingly, the piston rod 8b is retracted into the cylinder tube 8a, and the machine body (the lower traveling body 52 and the upper swing body 54) swings in the direction shown by a dotted arrow C in Fig. 5 is specified.

[0067] Furthermore, in a case where a rod retraction signal for the boom cylinder 8 is output from the operating device 18, the controller 20 opens the electromagnetic on-off proportional valve 26 in the same manner as when an external force acts on the boom cylinder 8 in the rod retraction direction. This drains excess hydraulic oil from the rod-side return pipe 24 to the hydraulic oil tank 22.

[0068] Furthermore, in this case, it is desirable for the controller 20 to adjust the opening degree of the electromagnetic on-off proportional valve 26 according to the signal output from the operating device 18 and control the amount of excess hydraulic oil discharged from the rod-side return piping 24 to the hydraulic oil tank 22. Thus, the pressure of the hydraulic oil flowing into the rod-side port 8c is adjusted, and the retraction speed of the piston rod 8b can be appropriately controlled according to the signal from the operating device 18.

[0069] Alternatively, in a case where an external force acts on the boom cylinder 8 in the rod pushing-out direction and a rod retraction signal for the boom cylinder 8 is output from the operating device 18, the controller 20 may reduce the relief pressure of the electromagnetic relief proportional valve 30 to discharge excess hydraulic oil from the cover-side return piping 28 to the hydraulic oil tank 22, as shown in Fig. 8. This can reduce the amount of inflow from the cover-side piping 12 to the pump motor 6 and suppress energy loss. At this time, the electromagnetic on-off proportional valve 26 can be opened or closed.

[0070] In addition, the controller 20 adjusts the rotational speed of the motor generator 4 and the displacement of the pump motor 6 according to the signal output from the operating device 18, regardless of whether the rod push-out signal or the rod retraction signal is output. Thus, the push-out speed or retraction speed of the piston rod 8b of the boom cylinder 8 can be appropriately controlled.

[0071] As described above, in the hydraulic circuit 2, in a case where a rod push-out signal for the boom cylinder 8 is output from the operation device 18, hydraulic oil flows from the rod-side piping 10 to the cover-side piping 12 via the pump motor 6, and in a case where a rod push-out signal for the boom cylinder 8 is output from the operation device 18, hydraulic oil flows from the cover-side piping 12 to the rod-side piping 10 via the pump motor 6. Thus, a directional control valve for switching the operating direction of the boom cylinder 8 is not required. Accordingly, no pressure loss occurs in the directional control valve, and good energy efficiency is achieved. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP-A-2013-23821

[0005]

Claims

[1] Hydraulic circuit for a construction machine with a boom, the hydraulic circuit comprising: a motor generator; a bidirectional variable displacement pump motor connected to the motor generator; a boom cylinder for operating the boom; a rod-side pipe connecting the pump motor and a rod-side port of the boom cylinder; a cover-side pipe connecting the pump motor and a cover-side port of the boom cylinder; an operating device that outputs a signal to operate the boom cylinder; and a controller that performs circuit control based on a signal output from the operating device, wherein, in a case where a rod push-out signal for the boom cylinder is output from the operating device, hydraulic oil flows from the rod-side piping to the cover-side piping via the pump motor, and In a case where a rod retraction signal for the boom cylinder is output from the operation device, hydraulic oil flows from the cover-side piping to the rod-side piping via the pump motor. [2] A hydraulic circuit for a construction machine according to claim 1, further comprising: a cover-side pressure sensor that detects pressure in the cover-side pipeline, wherein, in a case where the rod retraction signal for the boom cylinder is output from the operating device, the controller causes the motor generator to drive the pump motor when the pressure detected by the cover-side pressure sensor is less than a predetermined value, and allows the motor generator to be driven by the pump motor when the pressure detected by the cover-side pressure sensor is equal to or higher than the predetermined value. [3] A hydraulic circuit for a construction machine according to claim 1, further comprising: a rod-side return piping connecting the rod-side piping and a hydraulic oil tank; and an electromagnetic on-off proportional valve arranged in the rod-side return pipe, wherein, When the rod retraction signal for the boom cylinder is output from the operating device, the controller opens the electromagnetic on-off proportional valve to discharge excess hydraulic oil from the rod-side return piping. [4] A hydraulic circuit for a construction machine according to claim 3, wherein the controller adjusts an opening degree of the electromagnetic on-off proportional valve according to the signal output from the operating device and controls an amount of excess hydraulic oil discharged from the rod-side return piping. [5] A hydraulic circuit for a construction machine according to claim 1, further comprising: a cover-side return pipe connecting the cover-side pipe and a hydraulic oil tank; and an electromagnetic overpressure proportional valve arranged in the cover-side return pipe, wherein, When the rod retraction signal for the boom cylinder is output from the operating device, the controller reduces the relief pressure of the electromagnetic relief proportional valve to discharge excess hydraulic oil from the cover-side return piping. [6] A hydraulic circuit for a construction machine according to claim 1, further comprising: a rod-side supply piping connected to the tube-side piping; a rod-side check valve arranged in the tube-side supply piping; a cover-side supply pipeline connected to the cover-side pipeline; and a cover-side check valve arranged in the cover-side supply pipe, wherein, in a case where the rod push-out signal for the boom cylinder is output from the operation device, the rod-side check valve opens to fill the rod-side piping with hydraulic oil, or the cover-side check valve opens to fill the cover-side piping with hydraulic oil. [7] A hydraulic circuit for a construction machine according to claim 1, wherein the cover-side piping is provided with a drift reduction valve that allows flow from the pump motor to the cover-side port and blocks flow from the cover-side port to the pump motor, and, in a case where the rod retraction signal for the boom cylinder is output from the operating device, the controller opens the drift reducing valve to allow flow from the cover-side port to the pump motor. [8] A hydraulic circuit for a construction machine according to claim 1, wherein the controller adjusts a rotational speed of the motor generator and a displacement of the pump motor according to the signal output from the operating device.

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