Construction machine

Abstract

Provided is a construction machine comprising: a double-tilting first hydraulic pump / motor that is connected to a first hydraulic actuator in a closed circuit; a prime mover that drives the first hydraulic pump / motor; an accumulator that accumulates pressure oil discharged from a second hydraulic actuator; an assist valve that opens and closes a connection oil path between the accumulator and the first hydraulic pump / motor; and a pressure accumulation pressure sensor that detects a pressure of the accumulator. When the first hydraulic pump / motor is not in the pumping operation and the pressure of the accumulator is equal to or higher than a set pressure, a controller calculates a target assist power to be input to the prime mover in accordance with the load of the prime mover, and outputs a control signal that controls the tilting of the first hydraulic pump / motor in accordance with the target assist power, and that commands an opening operation of the assist valve. This enables further improvement of energy efficiency in the construction machine by utilizing regenerative energy

Description

Construction machinery

[0001] The present invention relates to construction machinery such as hydraulic excavators.

[0002] In a hydraulic drive device used in construction machinery such as a hydraulic excavator, fuel efficiency may be improved by utilizing regenerative energy. For example, in the hydraulic circuit disclosed in Patent Document 1, the regenerative energy during the boom lowering operation is stored in an accumulator, and the assist motor (hydraulic motor) directly connected to the engine is driven by the energy stored in the accumulator, thereby reducing the load on the engine and improving fuel efficiency.

[0003] Japanese Patent Application Laid-Open No. 2019-94608

[0004] However, in the hydraulic circuit of Patent Document 1, although a dedicated assist motor is provided for energy regeneration, pressure oil is not always supplied from the accumulator to the assist motor during the operation of the construction machinery. Therefore, in a state where pressure oil is not supplied from the accumulator, the assist motor increases the drag loss and rather becomes a load on the engine. As a result, the effect of improving energy efficiency by utilizing regenerative energy is partially offset.

[0005] An object of the present invention is to provide a construction machinery that can further improve energy efficiency by utilizing regenerative energy.

[0006] To achieve the above objective, the present invention provides a construction machine comprising: a first hydraulic actuator for driving a first driven member; a second hydraulic actuator for driving a second driven member; a double-tilting type first hydraulic pump motor connected in a closed circuit to the first hydraulic actuator; a prime mover for driving the first hydraulic pump motor; an accumulator for storing pressurized oil discharged from the second hydraulic actuator; a first operating lever for outputting an operating signal for commanding the operation of the first driven member; and a controller for controlling the first hydraulic pump motor in accordance with the operating signal of the first operating lever, wherein the present invention provides an assist valve for opening and closing the oil passages connecting the accumulator and the first hydraulic pump motor, and the accumulator The present invention provides a construction machine comprising a pressure accumulator sensor for detecting the pressure of a data point, wherein the controller determines whether the first hydraulic pump motor is operating based on the operation signal of the first operating lever, determines whether the pressure of the accumulator detected by the pressure accumulator is equal to or greater than a set pressure, and if the first hydraulic pump motor is not operating and the pressure of the accumulator is equal to or greater than the set pressure, calculates a target assist power to be input to the prime mover by the motor operation of the first hydraulic pump motor according to the load of the prime mover, controls the tilting of the first hydraulic pump motor according to the target assist power, and outputs a control signal to command the assist valve to open.

[0007] According to the present invention, energy efficiency can be further improved in construction machinery by utilizing regenerative energy.

[0008] Figure 2 is a side view of a hydraulic excavator, an example of a construction machine according to the first embodiment of the present invention. Figure 3 is a hydraulic circuit diagram of the main part of the hydraulic system provided in the construction machine according to the first embodiment of the present invention. Figure 4 is an explanatory diagram illustrating the flow of pressurized oil during regenerative operation in the hydraulic circuit of Figure 2. Figure 5 is a block diagram showing the main part of the function of the controller provided in the construction machine according to the first embodiment of the present invention. Figure 6 is a block diagram relating to the engine load signal calculation function of the controller provided in the construction machine according to the first embodiment of the present invention. Figure 7 is a hydraulic circuit diagram of the main part of the hydraulic system provided in the construction machine according to the second embodiment of the present invention. Figure 8 is a hydraulic circuit diagram of the main part of the hydraulic system provided in the construction machine according to the third embodiment of the present invention. Figure 9 is a block diagram relating to the engine load signal calculation function of the controller provided in the construction machine according to the third embodiment of the present invention.

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] <First Embodiment> -Construction Machinery- Figure 1 is a side view of a hydraulic excavator as an example of construction machinery according to the first embodiment of the present invention. In the following embodiments, the left side in Figure 1 is the front of the rotating body 12 of the hydraulic excavator 1. Although Figure 1 illustrates a so-called large or extra-large hydraulic excavator, in this embodiment the present invention can also be applied to hydraulic excavators of smaller size. The hydraulic excavator 1 shown in Figure 1 is a crawler type, but the present invention can also be applied to wheeled construction machinery. Furthermore, the present invention can be applied to other types of construction machinery used in various operations such as civil engineering work, construction work, and demolition work, such as wheel loaders and cranes.

[0011] The hydraulic excavator 1 shown in Figure 1 is composed of a vehicle body 10 and a front work implement 20. The vehicle body 10 is composed of a traveling body 11 and a rotating body 12.

[0012] The hydraulic excavator in this embodiment is a crawler type, and the running body 11 is equipped with left and right crawlers (running gear) 16, each having an idler wheel 13 and a drive tumbler 14 with a continuous track 15 wrapped around them. The drive tumblers 14 are driven by left and right running motors (not shown), and the continuous track 15 wrapped around the idler wheel 13 and drive tumbler 14 rotates and circulates, causing the hydraulic excavator 1 to move. Hydraulic motors are used as running motors. Depending on the size of the vehicle, the running body 11 can also be a wheel type.

[0013] The slewing body 12 is mounted on the upper part of the traveling body 11 via a slewing device (not shown) so as to be able to slewing left and right. The slewing device connecting the slewing body 12 to the traveling body 11 includes a slewing motor 27 (Figure 2), and by driving the slewing motor 27, the slewing body 12 rotates counterclockwise or clockwise in a plan view relative to the traveling body 11. A hydraulic motor is used for the slewing motor 27. An operator's cab 18 is provided at the front of the slewing body 12 (front left side in this embodiment) where the operator sits. The slewing body 12 is also equipped with a prime mover, hydraulic system, etc.

[0014] The front work implement 20 is a multi-jointed arm-type work device for performing tasks such as excavating earth and sand, and is attached to the front of the slewing body 12 (to the right of the driver's cab 18 in this embodiment). This front work implement 20 consists of a boom 21, an arm 22, and a bucket 23.

[0015] The boom 21 is connected by a pin to the base frame of the slewing body 12, called the slewing frame, and rotates up and down relative to the slewing body 12, driven by the boom cylinder 24. Both ends of the boom cylinder 24 are rotatably connected to the boom 21 and the slewing body 12 by pins. The arm 22 is connected by a pin to the tip of the boom 21 and rotates forward and backward relative to the boom 21, driven by the arm cylinder 25. Both ends of the arm cylinder 25 are rotatably connected to the arm 22 and the boom 21 by pins. The bucket 23 is connected by a pin to the tip of the arm 22 and rotates up and down relative to the arm 22, driven by the bucket cylinder 26. Both ends of the bucket cylinder 26 are rotatably connected to the boom 21 and the bucket 23 by pins.

[0016] - Hydraulic System - Figure 2 is a hydraulic circuit diagram of the main parts of a hydraulic system provided in a construction machine according to the first embodiment of the present invention. The hydraulic system shown in Figure 2 illustrates the circuits of the boom cylinder 24, arm cylinder 25, and slewing motor 27, but the circuit of the bucket cylinder 26 is the same as the circuit of the boom cylinder 24. In this embodiment, the boom cylinder 24, arm cylinder 25, bucket cylinder 26, and slewing motor 27 each constitute a closed-circuit system driven by a dedicated double-tilting hydraulic pump motor connected in a closed circuit.

[0017] The system includes a hydraulic pump motor 31-33, a charge pump Pc, a relief valve Vr, makeup valves 41a, 41b, 42a, 42b, 43a, 43b, relief valves 51a, 51b, 52a, 52b, 53a, 53b, flushing valves 61-63, an accumulator 70, a regenerative valve 75, an assist valve 76, and switching valves 77a, 77b.

[0018] -Actuator Circuit- Figure 2 shows the circuits for the boom cylinder 24, the arm cylinder 25, and the slewing motor 27 as actuator circuits, but below we will explain the circuit for the slewing motor 27 as a representative example. The explanations for the boom cylinder 24 and the arm cylinder 25 circuits are the same as the explanation for the slewing motor 27 circuit, so we will omit the explanation. However, the explanation for the boom cylinder 24 circuit can be replaced by changing the last digit of the two-digit code from "1" to "2" and reading the slewing motor 27 as boom cylinder 24 in the explanation of the slewing motor 27 circuit below. Similarly, the explanation for the arm cylinder 25 circuit can be replaced by changing the last digit of the two-digit code from "1" to "3" and reading the slewing motor 27 as arm cylinder 25 in the explanation of the slewing motor 27 circuit below.

[0019] The hydraulic pump-motor 31 is a double-tilting type pump driven by the prime mover, engine E. An electric motor can also be used as the prime mover instead of engine E. Power transmission between engine E and hydraulic pump-motor 31 is performed via a power transmission device TM. The hydraulic pump-motor 31 has a double-tilting slanted plate mechanism with a pair of input / output ports, and a regulator R that adjusts the tilt angle of the double-tilting slanted plates, and is configured to switch the direction of intake and discharge of hydraulic fluid from the input / output ports. Furthermore, the intake and discharge direction and flow rate of the hydraulic pump-motor 31 are controlled by a control signal from controller 80 that is input to regulator R via signal line Ls. Oil passages La and Lb are connected to the two input / output ports of the hydraulic pump-motor 31, respectively. Oil passage La is connected to the first port of the slewing motor 27, and oil passage Lb is connected to the second port of the slewing motor 27. In other words, the first port of the swing motor 27 is connected to the first input / output port of the hydraulic pump motor 31 via the oil passage La, and the second port of the swing motor 27 is connected to the second input / output port of the hydraulic pump motor 31 via the oil passage Lb, so that the swing motor 27 and the hydraulic pump motor 31 are connected in a closed circuit. The direction of operation of the swing motor 27 is determined by the discharge direction of the hydraulic fluid of the hydraulic pump motor 31. Since the hydraulic pump motor 31 is a closed-circuit hydraulic pump motor, it can perform not only pump operation but also motor operation. Furthermore, a pressure sensor 31Sa is provided in the oil passage La to detect the pressure at one port of the swing motor 27. Similarly, a pressure sensor 31Sb is provided in the oil passage Lb to detect the pressure at the other port of the swing motor 27.

[0020] The flushing valve 61 is a valve that replaces the hydraulic fluid flowing through the closed circuit (oil passages La and Lb) of the hydraulic pump motor 31, and opens and closes the oil passage Lx, which is an oil passage connecting the closed circuit of the hydraulic pump motor 31 to the hydraulic fluid tank T. Oil passages Lc and Ld branch off from oil passages La and Lb, which are connected to the hydraulic pump motor 31, respectively. The flushing valve 61 is a pilot-driven three-position directional control valve with switching positions A-C, and connects oil passages Lc and Ld to oil passage Lx, and is connected to the hydraulic fluid tank T via oil passage Lx. The spool of the flushing valve 61 is biased by springs on both sides, and when either oil passage La or Lb is below the set pressure defined by the springs, it is in switching position C (neutral position), blocking the connection between oil passages Lc and Ld and oil passage Lx. For example, when the pressure in oil passage La exceeds the set pressure, the flushing valve 61 switches to switching position A, connecting oil passage La to oil passage Lx via oil passage Lc, and excess pressurized oil is discharged from oil passage La to oil passage Lx. Conversely, when the pressure in oil passage Lb exceeds the set pressure, the flushing valve 61 switches to switching position B, connecting oil passage Lb to oil passage Lx via oil passage Ld, and excess pressurized oil is discharged from oil passage Lb to oil passage Lx.

[0021] Oil passages La and Lb are connected to oil passage Lx via oil passages Le and Lf, respectively. Relief valves 51a and 51b are provided in oil passages Le and Lf, respectively. Relief valves 51a and 51b are pressure control valves that define the upper limit pressure of the closed circuit (oil passages La and Lb) of the hydraulic pump motor 31. When the pressure in oil passages La and Lb exceeds the upper limit pressure, they open, discharging hydraulic fluid from oil passages La and Lb to the hydraulic fluid tank T via oil passage Lx to protect the closed circuit. The relief pressure (upper limit pressure of the closed circuit of the hydraulic pump motor 31) by the relief valves 51a and 51b is defined by the spring force of the relief valves 51a and 51b.

[0022] Oil passages La and Lb are also connected to oil passage Lx via makeup oil passages Lg and Lh, respectively. Makeup valves 41a and 41b are provided in makeup oil passages Lg and Lh, respectively. Makeup valves 41a and 41b are check valves that restrict the flow direction of hydraulic fluid in makeup oil passages Lg and Lh from the hydraulic fluid tank T towards oil passages La and Lb, and prevent hydraulic fluid from being discharged from makeup oil passages Lg and Lh to the hydraulic fluid tank T. For example, when oil passage La becomes negative pressure, or when the flow rate of hydraulic fluid in oil passage La becomes insufficient, the makeup valve 41b opens and hydraulic fluid is drawn from the hydraulic fluid tank T into oil passage La. Similarly, when oil passage Lb becomes negative pressure, the makeup valve 41a opens and hydraulic fluid is drawn into oil passage Lb. The makeup valves 41a and 41b suppress the occurrence of cavitation within the closed circuit.

[0023] The oil passage Lx is connected to the discharge port of the charge pump Pc and also to the hydraulic fluid tank T via a relief valve Vr, and its internal pressure is kept constant. The charge pump Pc is driven by the power of the engine E, which is input via a power transmission device TM. The internal pressure of the oil passage Lx (relief pressure of the relief valve Vr) is lower than the relief pressure of the relief valves 51a and 51b in the closed circuit of the hydraulic pump motor 31 and the set pressure specified by the flushing valve 61. Also, the set pressure specified by the flushing valve 61 is lower than the relief pressure of the relief valves 51a and 51b.

[0024] -Regenerative Circuit- The hydraulic system of the hydraulic excavator 1 is equipped with a regenerative circuit. This regenerative circuit utilizes the first hydraulic pump motor, which is part of the closed circuit of the first hydraulic actuator that drives the first driven member, as an assist motor. When the first hydraulic pump motor is not operating, the regenerative circuit activates the first hydraulic pump motor to input assist power to the engine E. The pressurized oil that drives the first hydraulic pump motor is supplied from the accumulator 70. The accumulator 70 stores the pressurized oil discharged when the second hydraulic actuator, which drives the second driven member and is different from the first hydraulic actuator, is operating. However, it is also possible to store the pressurized oil discharged when the first hydraulic actuator is operating in the accumulator 70. In this embodiment, the case in which the first driven member is the slewing body 12, the second driven member is the boom 21, the first hydraulic actuator is the slewing motor 27, the second hydraulic actuator is the boom cylinder 24, and the first hydraulic pump motor is the hydraulic pump motor 31 will be explained as an example. However, this is just one example, and it is also possible to use hydraulic pump motors 32 and 33 as assist motors, or to store pressurized oil discharged from the arm cylinder 25 and the swing motor 27 in the accumulator 70.

[0025] The regenerative circuit includes a regenerative valve 75, an accumulator 70, and an assist valve 76. In this embodiment, in the boom cylinder 24 circuit, the oil passage Lb connected to the bottom port of the boom cylinder 24 and the accumulator 70 are connected via an oil passage Lm. The regenerative valve 75 is provided in the oil passage Lm connecting the boom cylinder 24 and the accumulator 70, and is driven by a control signal output from the controller 80 to open and close the oil passage Lm. The oil passage Lm also branches between the accumulator 70 and the regenerative valve 75 and is connected to the assist valve 76. In addition, oil passages Li and Lj branch off from oil passages La and Lb in the slewing motor 27 circuit, respectively. The assist valve 76 is an electromagnetically driven three-position control valve having switching positions a-c. It connects oil passages Li and Lj to oil passage Lm, and connects the boom cylinder 24 and accumulator 70 to the closed circuit (oil passages La and Lb) of the swing motor 27 via oil passage Lm. The spool of the assist valve 76 is biased by springs on both sides, and when both solenoids are demagnetized, it is in switching position c (neutral position), blocking the connection between oil passage Lm and oil passages Li and Lj. When the assist valve 76 is switched to switching position a by a control signal from the controller 80, the oil passage La of the swing motor 27 circuit and the accumulator 70 are connected via oil passages Lm and Li. Conversely, when the assist valve 76 is switched to switching position b by a control signal from the controller 80, the oil passage Lb of the swing motor 27 circuit and the accumulator 70 are connected via the oil passages Lm and Lj. In this way, the assist valve 76 opens and closes the connecting oil passage between the accumulator 70 and the hydraulic pump motor 31.

[0026] Furthermore, the oil passage Lm is equipped with an accumulator pressure sensor S for detecting the pressure of the accumulator 70. The accumulator pressure sensor S is located in the oil passage Lm between the accumulator 70, the regenerative valve 75, and the assist valve 76.

[0027] Furthermore, in this embodiment, the first switching valve 77a is provided in the oil passage La connecting the first port of the swing motor 27 and the first input / output port of the hydraulic pump motor 31, and opens and closes this oil passage La. The second switching valve 77b is provided in the oil passage Lb connecting the second port of the swing motor 27 and the second input / output port of the hydraulic pump motor 31, and opens and closes this oil passage Lb. These switching valves 77a and 77b are located closer to the swing motor 27 than the branching point of the oil passage Lc-Lj in the oil passages La and Lb. When the switching valves 77a and 77b are closed, the oil passages La and Lb are blocked and the swing motor 27 is held in place, preventing the swing motor 27 from operating unintentionally when, for example, pressurized oil is supplied from the accumulator 70 to the hydraulic pump motor 31.

[0028] -Basic Operation- The controller 80 is a computer equipped with a processing unit such as a CPU and a storage device such as RAM, ROM, HDD, SSD, and has a control function for the hydraulic system, including the function of controlling the hydraulic pump motors 31-33 in response to the operation signals of the operation levers X1-X3. The operation levers X1-X3 are some of the operation devices provided in the operator's cab 18 of the hydraulic excavator 1 (or the remote control device if the hydraulic excavator 1 supports remote control). In the example in Figure 2, operation lever X1 is assumed to be an electric lever device that outputs an operation signal to command the movement of the slewing body 12 (i.e., the movement of the hydraulic pump motor 31). Similarly, operation levers X2 and X3 are assumed to be electric lever devices that output operation signals to command the movement of the boom 21 and arm 22 (i.e., the movement of the hydraulic pump motors 32 and 33).

[0029] For example, when an operation signal is input to the operating lever X2 for raising the boom, the controller 80 controls the tilt (regulator R) of the hydraulic pump motor 32 in accordance with the operation signal from the operating lever X2. As a result, pressurized oil is supplied to the bottom port of the boom cylinder 24, the boom cylinder 24 extends, and the boom 21 rises.

[0030] When an operation signal is input to the operating lever X2 in conjunction with the boom lowering operation, the controller 80 outputs a control signal to the regenerative valve 75 to command it to open. As a result, the pressurized oil pushed out from the bottom port of the boom cylinder 24 by the weight of the front work implement 20 flows into the accumulator 70 and is stored in the accumulator 70. This causes the boom cylinder 24 to contract and the boom 21 to descend.

[0031] When an operation signal is input from the operating lever X3 in conjunction with the arm cloud operation, the controller 80 controls the tilt (regulator R) of the hydraulic pump motor 33 in accordance with the operation signal from the operating lever X3. As a result, pressurized oil is supplied to the bottom port of the arm cylinder 25, the arm cylinder 25 extends, and the arm 22 performs the cloud operation.

[0032] When an operation signal is received from the operating lever X3 in conjunction with the arm dump operation, the controller 80 controls the tilt (regulator R) of the hydraulic pump motor 33 in accordance with the operation signal from the operating lever X3. As a result, pressurized oil is supplied to the port on the rod side of the arm cylinder 25, causing the arm cylinder 25 to contract and the arm 22 to perform a dumping operation.

[0033] When an operation signal is input corresponding to a leftward rotation of the operating lever X1, the controller 80 controls the tilt (regulator R) of the hydraulic pump motor 31 in accordance with the operation signal from the operating lever X1. As a result, pressurized oil discharged from the hydraulic pump motor 31 into the oil passage La is supplied to the first port of the slewing motor 27, causing the slewing body 12 to rotate to the left.

[0034] When an operation signal is input corresponding to a rightward rotation of the operating lever X1, the controller 80 controls the tilt (regulator R) of the hydraulic pump motor 31 in accordance with the operation signal from the operating lever X1. As a result, pressurized oil discharged from the hydraulic pump motor 31 into the oil passage Lb is supplied to the second port of the slewing motor 27, causing the slewing body 12 to rotate to the right.

[0035] -Regenerative Operation- In this embodiment, similar to the pressure sensors 31Sa and 31Sb described above, the oil passage La of the boom cylinder 24 circuit is provided with a pressure sensor 32Sa for detecting the pressure at the rod-side port of the boom cylinder 24, and the oil passage Lb is provided with a pressure sensor 32Sb for detecting the pressure at the bottom-side port of the boom cylinder 24. The oil passage La of the arm cylinder 25 circuit is provided with a pressure sensor 33Sa for detecting the pressure at the rod-side port of the arm cylinder 25, and the oil passage Lb is provided with a pressure sensor 33Sb for detecting the pressure at the bottom-side port of the arm cylinder 25. The controller 80 has a function to control the regenerative circuit and the hydraulic pump motor 31 in response to the operation signals of the operating levers X1-X3, as well as the detection signals of the accumulating pressure sensor S and the pressure sensors 31Sa, 31Sb, 32Sa, 32Sb, 33Sa, and 33Sb.

[0036] Specifically, the controller 80 determines whether the hydraulic pump motor 31 is operating, that is, discharging pressurized oil to drive the swing motor 27, based on the operation signal of the operating lever X1 related to the swing operation. The controller 80 also determines whether the pressure of the accumulator 70 is equal to or greater than the set pressure P1, based on the pressure of the accumulator 70 detected by the pressure accumulation sensor S. The execution order of these determination processes is not limited and may be simultaneous. If, as a result of these determinations, the hydraulic pump motor 31 is not operating and the pressure of the accumulator 70 is equal to or greater than the set pressure P1, the controller 80 calculates the target assist power Wt to ​​be input to the engine E by the motor operation of the hydraulic pump motor 31, according to the load of the engine E. Motor operation of the hydraulic pump motor 31 refers to the state in which the hydraulic pump motor 31 is driven as a hydraulic motor by the supplied pressurized oil. The controller 80 controls the tilt of the hydraulic pump motor 31 according to the calculated target assist power Wt, and outputs a control signal to the assist valve 76 to open (switching to switching position a or b). The tilt of the hydraulic pump motor 31 required for the hydraulic pump motor 31 to output the target assist power Wt is calculated by the controller 80 based on the target assist power Wt and the pressure of the accumulator 70 detected by the pressure sensor S. When the assist valve 76 opens, the hydraulic pump motor 31 for driving the swing motor 27 is driven by the pressurized oil supplied from the accumulator 70, and assist power is input from the hydraulic pump motor 31, which normally receives power from the engine E, to the engine E, thereby assisting the engine E.

[0037] As the hydraulic pump motor 31 operates, the pressure in the closed circuit of the hydraulic pump motor 31 increases due to the pressurized oil injected from the accumulator 70, causing the flushing valve 61 to open. As a result, the excess pressurized oil supplied from the accumulator 70 to the closed circuit and used to drive the hydraulic pump motor 31 is discharged into the hydraulic oil tank T via the flushing valve 61.

[0038] Furthermore, when the controller 80 drives the hydraulic pump motor 31, it outputs a control signal to the switching valves 77a and 77b to command them to close. This holds the swing motor 27 in place, and the pressurized oil supplied to the closed circuit from the accumulator 70 prevents the swing motor 27 from operating unintended.

[0039] Furthermore, if the hydraulic pump motor 31 is operating, or if the pressure in the accumulator 70 is less than the set pressure P1, the controller 80 outputs a control signal to the assist valve 76 to close (set to switching position c), and also outputs control signals to the switching valves 77a and 77b to open. If the operating lever X1 is operated, the controller 80 controls the tilt of the hydraulic pump motor 31 according to the operating signal of the operating lever X1, and controls the discharge flow rate of the hydraulic pump motor 31 that drives the slewing motor 27. Also, as mentioned above, the controller 80 outputs a control signal to the regenerative valve 75 to open when the boom cylinder 24 is retracting (when the boom is lowered). As a result, the pressurized oil discharged from the bottom port of the boom cylinder 24 is stored in the accumulator 70. The pressurized oil thus stored in the accumulator 70 is used to drive the hydraulic pump motor 31 as described above. However, since the regenerative valve 75 opens during boom lowering operation regardless of the operating state of the hydraulic pump / motor 31 or the pressure of the accumulator 70, there is a possibility that both the assist valve 76 and the regenerative valve 75 may be open. In this case, the pressurized oil discharged from the boom cylinder 24 can bypass the accumulator 70 and be supplied directly to the hydraulic pump / motor 31.

[0040] Under this control, for example, when the assist valve 76 is switched to switching position b as shown in Figure 3, the pressurized oil discharged from the accumulator 70 flows through the oil passage Lm and the assist valve 76 into the closed-circuit oil passage Lb of the swing motor 27, as indicated by the arrow in the figure, and is supplied to the second port of the hydraulic pump motor 31. Consequently, the oil passage Lb is pressurized and the flushing valve 61 is switched to switching position B. The pressurized oil that drove the hydraulic pump motor 31 is discharged from the first port of the hydraulic pump motor 31 into the oil passage La, and then through the oil passage Lc and the flushing valve 61 to the oil passage Lx. As a result, the oil passage Lx is pressurized and the relief valve Vr opens, and the pressurized oil is discharged from the oil passage Lx to the hydraulic oil tank T.

[0041] -Controller- Figure 4 is a block diagram showing the main functions of the controller 80. A specific example of control related to regenerative operation will be explained using Figure 4.

[0042] The controller 80 includes function generators 81a, 81b, 81c, 81d, an AND gate 82, a multiplier 83, a divider 84, an adder 85, gain generators 86a, 86b, 86c, and output conversion units 87a, 87b, 87c, 87d, 87e. These may be implemented as hardware elements such as electrical circuits, or as software elements.

[0043] The function generator 81a receives an operation signal output from the operation lever X2 according to the amount of boom lowering operation. Based on the operation signal input from the operation lever X2, the function generator 81a calculates and outputs a control command value that sets the opening degree of the regenerative valve 75 to a value corresponding to the amount of boom lowering operation, for example, according to a control map. The control command value output by the function generator 81a is converted into a control signal by the output conversion unit 87a (for example, a D / A converter) and output to the solenoid of the regenerative valve 75. As a result, the opening area of ​​the regenerative valve 75 is controlled according to the amount of boom lowering operation, and the boom 21 descends at a speed corresponding to the amount of boom lowering operation.

[0044] The operation signals output from the operation lever X1 are input to the function generators 81b and 81c according to the left-turn operation amount. For the sake of simplicity of explanation, in the example of FIG. 4, the case where the left-turn operation is performed by the operation lever X1 will be described. However, the same processing is executed when the right-turn operation is performed. The function generator 81b calculates and outputs a control command value for tilting the hydraulic pump-motor 31 that rotates the turning motor 27 at a speed corresponding to the left-turn operation amount based on the operation signal input from the operation lever X1.

[0045] The function generator 81c calculates, for example, according to a control map, a determination value as to whether the hydraulic pump-motor 31 for turning can be used for assisting the engine E based on the operation signal of the operation lever X1. In this function generator 81c, when no operation signal is input from the operation lever X1 (when the operation signal is less than a preset value), it is estimated that the hydraulic pump-motor 31 is not in the pump operation and the hydraulic pump-motor 31 can be used for assisting the engine E, and the determination value "1" is output. On the contrary, when an operation signal is input from the operation lever X1 (when the operation signal is greater than or equal to the preset value), it is estimated that the hydraulic pump-motor 31 is in the pump operation according to the operation of the operation lever X1 and the hydraulic pump-motor 31 cannot be used for assisting the engine E, and the function generator 81c outputs the determination value "0".

[0046] The pressure of the accumulator 70 detected by the accumulator pressure sensor S is input to the function generator 81d. The function generator 81d calculates, for example, according to a control map, a determination value as to whether the pressure oil of the accumulator 70 can be used for assisting the engine E based on the pressure of the accumulator 70. In this function generator 81d, when the pressure of the accumulator 70 is equal to or higher than the set pressure, it is estimated that the pressure oil of the accumulator 70 can be used for assisting the engine E, and the determination value "1" is output. On the contrary, when the pressure of the accumulator 70 is less than the set pressure, it is estimated that the pressure oil of the accumulator 70 cannot be used for assisting the engine E, and the function generator 81d outputs the determination value "z".

[0047] The AND gate 82 receives the judgment values ​​from the function generators 81c and 81d. Based on the judgment values ​​from the function generators 81c and 81d, the AND gate 82 calculates and outputs a judgment value indicating whether the accumulator 70 will drive the hydraulic pump motor 31 to assist the engine E. Specifically, if both the judgment values ​​from the function generators 81c and 81d are "1", the hydraulic pump motor 31 is not operating, and the pressure in the accumulator 70 is above the set pressure, then it is estimated that the accumulator 70 can drive the hydraulic pump motor 31 to assist the engine E, and the AND gate 82 outputs a judgment value of "1". Conversely, if at least one of the judgment values ​​of the function generators 81c and 81d is "0", and the hydraulic pump motor 31 is operating or the pressure of the accumulator 70 is below the set pressure, it is presumed that the accumulator 70 is not in a state to drive the hydraulic pump motor 31 and assist the engine E, and the AND circuit 82 outputs a judgment value of "0".

[0048] The determination value of the AND circuit 82 is input to the gain generators 86a - 86c and the multiplier 83. In the gain generators 86a - 86c, if the input determination value is "1", control command values for operating the hydraulic pump - motor 31 as a motor are calculated and output to the assist valve 76 and the switching valves 77a, 77b. Conversely, if the input determination value is "0", the gain generators 86a - 86c calculate and output control command values for making the hydraulic pump - motor 31 capable of operating as a pump to the assist valve 76 and the switching valves 77a, 77b. Specifically, in the gain generator 86a, a control command value for switching the assist valve 76 to the switching position a or b according to the determination value "1" is calculated, and in the gain generators 86b, 86c, control command values for closing the switching valves 77a, 77b according to the determination value "1" are calculated. Conversely, in the gain generator 86a, a control command value for switching the assist valve 76 to the switching position c according to the determination value "0" is calculated, and in the gain generators 86b, 86c, control command values for opening the switching valves 77a, 77b according to the determination value "0" are calculated. The control command values calculated by the gain generators 86a - 86c are respectively converted into control signals by output converters 87c - 87e (for example, D / A converters) and output to the solenoids of the corresponding valves.

[0049] Note that the switching position of the assist valve 76 corresponding to the determination value "1" can be either a or b, but for example, it can be considered to be determined according to the positive or negative of the current swashplate tilt of the hydraulic pump - motor 31. For example, if the current swashplate tilt of the hydraulic pump - motor 31 is in the positive direction (for example, the direction of discharging pressure oil to the oil passage La), the assist valve 76 is set to the switching position b, and if the current swashplate tilt of the hydraulic pump - motor 31 is in the negative direction (for example, the direction of discharging pressure oil to the oil passage Lb), the assist valve 76 is set to the switching position a.

[0050] The multiplier 83 receives the judgment value of the AND gate 82 and the engine load signal as inputs. The engine load signal is the current required assist power for engine E, and corresponds to, for example, the current load power of engine E. Therefore, if the judgment value of the AND gate 82 is "1", the multiplier 83 outputs a required assist power equal to the engine load signal, and if the judgment value of the AND gate 82 is "0", it outputs a required assist power of 0. The calculation of the engine load signal will be described later.

[0051] The divider 84 receives the requested assist power output by the multiplier 83 and the pressure of the accumulator 70 detected by the pressure sensor S. Based on these input values, the divider 84 calculates and outputs a control command value for the tilt of the hydraulic pump motor 31 so that the hydraulic pump motor 31 outputs the requested assist power at a supply flow rate of pressurized oil corresponding to the pressure of the accumulator 70. However, the tilt of the hydraulic pump motor 31 is limited by its mechanical structure, and the pressure of the accumulator 70 is not always sufficient, so it is not always possible for the hydraulic pump motor 31 to input the requested assist power to the engine E. However, from a control perspective, the assist power input from the hydraulic pump motor 31 to the engine E will not exceed the requested assist power. In other words, the requested assist power functions as a limiting value for the power input from the hydraulic pump motor 31 to the engine E.

[0052] The adder 85 adds the control command value for tilting the hydraulic pump motor 31 calculated by the divider 84 and the control command value for tilting the hydraulic pump motor 31 calculated by the function generator 81b, and outputs the final control command value for tilting the hydraulic pump motor 31. However, at least one of the control command values ​​calculated by the divider 84 and the function generator 81b will be 0 depending on whether the operation lever X1 is operated or not. Therefore, the control command value output by the adder 85 is 0 if both the control command values ​​calculated by the divider 84 and the function generator 81b are 0, and if either one is not 0, it will be a value other than 0. The control command value output by the adder 85 is converted into a control signal by the output conversion unit 87b (for example, a D / A converter) and output to the regulator R of the hydraulic pump motor 31. As a result, the hydraulic pump motor 31 discharges a flow rate according to the operation of the operation lever X1 or outputs assist power according to the load of the engine E.

[0053] -Engine Load Signal- Figure 5 is a block diagram relating to the engine load signal calculation function of the controller 80. A specific example of engine load signal calculation will be explained using Figure 5. The engine load signal is the sum of the power requirements of each device driven by the engine E, and specifically, it is the sum of the power requirements of the hydraulic pump motors 31-33 and auxiliary equipment (fan, pilot pump, air conditioner, etc.) including the charge pump Pc over real time. In this embodiment, the engine load signal is calculated as the basis for calculating the assist power by the hydraulic pump motor 31, so the engine load signal is calculated when the hydraulic pump motor 31 is not operating (the operating lever X1 is not operated). In Figure 5, an example of calculating the sum of the power requirements of the hydraulic pump motors 32 and 33 and the power requirements of the auxiliary equipment will be explained.

[0054] The controller 80 includes function generators 81e, 81f, multipliers 83b, 83c, adders 85a, 85b, and a gain generator 86d. These may be implemented as hardware elements such as electrical circuits, or as software elements.

[0055] The function generator 81e receives the operation signal of the operation lever X2 related to boom operation. The function generator 81e calculates the target discharge flow rate of the hydraulic pump motor 32 (the required flow rate of the boom cylinder 24) from the input operation signal, for example, according to a control map. The target discharge flow rate calculated by the function generator 81e is input to the multiplier 83b along with the pressure of the hydraulic pump motor 32 (the maximum output of the pressure sensors 32Sa and 32Sb). The multiplier 83b multiplies the input target discharge flow rate and pressure of the hydraulic pump motor 32 to calculate the required power of the hydraulic pump motor 32.

[0056] The function generator 81f receives the operation signal of the operating lever X3 related to arm operation. The function generator 81f calculates the target discharge flow rate of the hydraulic pump motor 33 (the required flow rate of the arm cylinder 25) from the input operation signal, for example, according to a control map. The target discharge flow rate calculated by the function generator 81f is input to the multiplier 83c along with the pressure of the hydraulic pump motor 33 (the maximum value of the pressure sensors 33Sa and 33Sb). The multiplier 83c multiplies the input target discharge flow rate and pressure of the hydraulic pump motor 33 to calculate the required power of the hydraulic pump motor 33.

[0057] The power requirements of the hydraulic pumps and motors 32 and 33, calculated by the multipliers 83b and 83c, are input to the adder 85a and added together. The total power requirements of the hydraulic pumps and motors 32 and 33 are input to the gain generator 86d. The gain generator 86d calculates the total shaft power of the hydraulic pumps and motors 32 and 33 by dividing the total power requirements of the hydraulic pumps and motors 32 and 33 by the pump efficiency (e.g., 0.9). The total shaft power of the hydraulic pumps and motors 32 and 33 is input to the adder 85b along with the auxiliary power (constant) which is set in advance and stored in the memory of the controller 80, and is added together with the auxiliary power and output as an engine load signal. The engine load signal corresponds to the current shaft power of engine E.

[0058] -Effects- (1) According to this embodiment, by supplying the pressurized oil from the accumulator 70, which has been regenerated, to the closed-circuit hydraulic pump motor 31 and driving the hydraulic pump motor 31 as a hydraulic motor, assist power is input from the hydraulic pump motor 31 to the engine E, thereby reducing the load on the engine E and lowering fuel consumption. In particular, the hydraulic pump motor 31 is not exclusively for engine assist, but is originally a closed-circuit hydraulic pump motor for the swing motor 27. The pressurized oil from the accumulator 70 is used for engine assist only when the hydraulic pump motor 31 is not operating, and is used for its original role of driving the swing motor 27 when the operating lever X1 is operated. In addition, when the hydraulic pump motor 31 is not operating as an assist motor, it is used for its original role, and unlike a dedicated assist motor, the occurrence of unnecessary drag losses when not in use is suppressed. In this way, the frequency of use of the hydraulic pump motor 31 is increased, and the hydraulic pump motor 31 can be used more effectively. Accordingly, energy efficiency can be further improved by utilizing the regenerated energy obtained from the accumulator 70.

[0059] In this embodiment, since the assist power from the hydraulic pump motor 31 is calculated according to the load of the engine E, it is possible to suppress the input of excessive assist power from the hydraulic pump motor 31 to the engine E.

[0060] (2) As the hydraulic pump motor 31 operates, the flushing valve 61 opens, and the pressurized oil supplied from the accumulator 70 to the closed circuit of the hydraulic pump motor 31 and used to drive the hydraulic pump motor 31 is discharged to the hydraulic oil tank T via the flushing valve 61. The flushing valve 61 can also be configured to be electromagnetically driven and controlled by the controller 80 together with the assist valve 76, but in this embodiment, the flushing valve 61 is pilot driven so that the flushing valve 61 operates automatically as the pressure in the closed circuit increases due to the injection of pressurized oil from the accumulator 70. Therefore, the control when driving the hydraulic pump motor 31 as an assist motor can be simplified.

[0061] (3) In this embodiment, when the hydraulic pump motor 31 is driven, the controller 80 outputs a control signal to the switching valves 77a and 77b to command them to close. This prevents the swing motor 27 from operating unintentionally due to pressurized oil flowing from the accumulator 70 into the closed circuit of the hydraulic pump motor 31.

[0062] (4) In a closed circuit in which the two input / output ports of the hydraulic pump / motor 31 and the two ports of the slewing motor 27 are connected by oil passages La and Lb, the flow rate supplied to the slewing motor 27 is basically controlled entirely by the tilt of the hydraulic pump / motor 31. Therefore, there is no need for a valve to control the flow rate supplied to the slewing motor 27, and the pressure loss due to valves in the hydraulic circuit is reduced, allowing the slewing motor 27 to be driven efficiently. In this embodiment, a closed circuit is used not only for the slewing motor 27 but also for the hydraulic actuators of the front work equipment 20 such as the boom cylinder 24, allowing the hydraulic actuators to be driven efficiently as a whole hydraulic system.

[0063] (5) In this embodiment, the return oil from the boom cylinder 24 is stored in the accumulator 70, and the pressurized oil stored in the accumulator 70 is used to drive the swing motor 27, which is a hydraulic actuator different from the boom cylinder 24. For example, in the case of a large hydraulic excavator operating in a mine, the power required for the boom cylinder 24 is greater than the power required for other hydraulic actuators such as the swing motor 27. Also, since swinging operations are generally not performed during excavation, as in this embodiment, when the boom is lowered, the pressurized oil that is actively discharged from the boom cylinder 24 is stored in the accumulator 70 and regenerated, and this is used to drive the swing hydraulic pump motor 31, which requires less power than the boom cylinder 24, thereby rationally utilizing the regenerated energy.

[0064] <Second Embodiment> Figure 6 is a hydraulic circuit diagram of the main part of a hydraulic system provided in a construction machine according to the second embodiment of the present invention. Figure 6 corresponds to Figure 2 of the first embodiment. Elements that are the same as or corresponding to elements of the embodiments described in Figure 6 are denoted by the same reference numerals as in the previously shown drawings, and their descriptions are omitted as appropriate.

[0065] The difference between this embodiment and the first embodiment is that, in the first embodiment, the assist valve 76 was composed of one three-position control valve, whereas in this embodiment, the assist valve 76 is composed of two two-position control valves 76a and 76b. In this embodiment, the oil passage Lm is connected to the oil passage Li via one of the two-position control valves 76a, and the accumulator 70 is connected to one of the oil passages La in the closed circuit via the two-position control valve 76a. The oil passage Lm is also connected to the oil passage Lj via the other two-position control valve 76b, and the accumulator 70 is connected to the other oil passage Lb in the closed circuit via the two-position control valve 76b. The other configurations of this embodiment are the same as those of the first embodiment. The same effects as those of the first embodiment can be obtained with the configuration of this embodiment as well.

[0066] In the first embodiment, the second embodiment, and the third embodiment described later, an example is shown in which the oil passage Lm of the accumulator 70 is selectively connected to either the oil passages La or Lb of the closed circuit of the hydraulic pump motor 31 when the hydraulic pump motor 31 is driven by the motor. However, the configuration is not necessarily limited to this, and for example, one of the oil passages Li or Lj can be omitted, and the path of the pressurized oil flowing from the accumulator 70 to the hydraulic oil tank T when the hydraulic pump motor 31 is driven by the motor can be uniquely determined. In this case, the assist valve 76 can be a two-position switching valve.

[0067] <Third Embodiment> Figure 7 is a hydraulic circuit diagram of the main part of a hydraulic system provided in a construction machine according to the third embodiment of the present invention. Figure 7 corresponds to Figure 2 of the first embodiment. Elements that are the same as or corresponding to elements of the embodiments described in Figure 7 are denoted by the same reference numerals as in the previously shown drawings, and their descriptions are omitted as appropriate.

[0068] The difference between this embodiment and the first embodiment is that the boom cylinder 24 has an open circuit, and is equipped with an open-circuit hydraulic pump 91 connected to the boom cylinder 24, and a directional control valve 92 that controls the flow of pressurized oil from the hydraulic pump 91 to the boom cylinder 24 in accordance with the operation of the operating lever X2. In this embodiment, the slewing motor 27 has a closed circuit, as in the first embodiment, and the boom cylinder 24 and arm cylinder 25 have open circuits. The boom cylinder 24 and arm cylinder 25 are driven by pressurized oil discharged by a common hydraulic pump 91.

[0069] The open circuit 90 shown in Figure 7 includes a hydraulic pump 91, a pilot pump (not shown), directional control valves 92 and 93, etc. In addition, although not shown, the open circuit 90 also includes a main relief valve that defines the upper limit of the pressure in the discharge oil passage Lp of the hydraulic pump 91, a pilot relief valve that defines the upper limit of the pressure in the discharge oil passage of the pilot pump, and multiple solenoid valves that generate pilot pressure to be input from the discharge oil of the pilot pump to the pilot chambers of the directional control valves 92 and 93.

[0070] The hydraulic pump 91 is a variable displacement pump driven by the engine E, similar to the hydraulic pump motor 31 of the swing motor 27. This hydraulic pump 91 pumps hydraulic fluid drawn in from the hydraulic fluid tank T and supplies it to the boom cylinder 24 and arm cylinder 25 via the directional control valves 92 and 93. In this embodiment, a variable displacement hydraulic pump is used for the hydraulic pump 91, but a fixed displacement hydraulic pump can also be used for the hydraulic pump 91. A pressure sensor Sp is provided in the discharge oil passage Lp of the hydraulic pump 91.

[0071] The directional control valve 92 is a center bypass type directional control valve and has a switching position 92a for retracting the boom cylinder 24, a neutral switching position 92c (neutral position) that connects the hydraulic pump 91 and the hydraulic oil tank T to return the hydraulic oil directly to the hydraulic oil tank T, and a switching position 92b for extending the boom cylinder 24. The directional control valve 92 switches to one of the switching positions 92a-92c by the stroke of an internal spool in response to the pilot pressure acting on each of the pair of pressure-receiving chambers. This controls the flow rate and direction (flow) of the hydraulic oil supplied from the hydraulic pump 91 to the boom cylinder 24.

[0072] The directional control valve 93, like the directional control valve 92, is a center bypass type directional control valve and has a switching position 93a that retracts the arm cylinder 25, a switching position 93c (neutral position) that connects the hydraulic pump 91 and the hydraulic fluid tank T to return the hydraulic fluid directly to the hydraulic fluid tank T, and a switching position 93b that extends the arm cylinder 25. Similar to the directional control valve 92, the directional control valve 93 switches to one of the switching positions 93a-93c by the stroke of an internal spool in response to the pilot pressure acting on each of the pair of pressure-receiving chambers. This controls the flow rate and direction (flow) of the hydraulic fluid supplied from the hydraulic pump 91 to the arm cylinder 25.

[0073] The pilot pressure acting on the pressure-receiving chambers of the directional control valves 92 and 93 is generated by the above-mentioned plurality of solenoid valves. Each solenoid valve is driven by a command signal output from the controller 80 in response to the operation signals of the operating levers X2 and X3.

[0074] As described above, in this embodiment, where the boom cylinder 24 and other circuits are open circuits, the assist valve 76 provided in the slewing motor 27 circuit, the bottom port of the boom cylinder 24, and the accumulator 70 are connected by an oil passage Lm, similar to the first embodiment. The slewing motor 27 circuit is the same as in the first embodiment. The controller 80 outputs a control signal to the regenerative valve 75 to open when the boom cylinder 24 is operating (when the boom is lowered). As a result, the pressurized oil discharged from the boom cylinder 24 is stored in the accumulator 70. The pressurized oil stored in the accumulator 70 is used to drive the hydraulic pump motor 31, similar to the first embodiment. The control at that time is the same as the control described in Figure 4 of the first embodiment. However, because the configuration of the boom cylinder 24 and other circuits is different from the first embodiment, the calculation of the engine load signal is slightly different.

[0075] Figure 8 is a block diagram relating to the engine load signal calculation function of the controller 80 in this embodiment. Figure 8 corresponds to Figure 5 of the first embodiment. Elements in Figure 8 that are the same as or corresponding to elements of embodiments already described are denoted by the same reference numerals as in the previously shown drawings, and their descriptions are omitted as appropriate.

[0076] In this embodiment, the controller 80 includes function generators 81e, 81f, a multiplier 83d, adders 85b, 85c, and a gain generator 86d. These may be implemented as hardware elements such as electrical circuits, or as software elements.

[0077] In this embodiment, since the boom cylinder 24 and the arm cylinder 25 share the hydraulic pump 91, the required flow rates of the boom cylinder 24 and the arm cylinder 25, calculated by the function generators 81e and 81f, are added together by the adder 85c. This total required flow rate is multiplied by the pressure of the hydraulic pump 91 (output of pressure sensor Sp) by the multiplier 83d to calculate the required power of the hydraulic pump 91. Subsequently, as in the first embodiment, the required power of the hydraulic pump 91 is divided by the pump efficiency (for example, 0.9) in the gain generator 86d to calculate the shaft power of the hydraulic pump 91, and auxiliary power is added to this to output as an engine load signal.

[0078] The other configurations are the same as in the first embodiment. In this embodiment as well, the assist valve 76 may be configured as a two-position switching valve, as in the second embodiment.

[0079] As in this embodiment, even if the pressurized oil discharged from an open-circuit hydraulic actuator (boom cylinder 24 in this embodiment) is stored in an accumulator 70 and used to drive a closed-circuit hydraulic pump motor (hydraulic pump motor 31 in this embodiment), the same effects as in the first embodiment can be obtained.

[0080] Furthermore, since multiple hydraulic actuators share the hydraulic pump 91, the number of valves used in the hydraulic pumps and circuits that drive the hydraulic actuators can be reduced, allowing for a simpler hydraulic circuit configuration.

[0081] As mentioned above, the boom cylinder 24 requires more power than other hydraulic actuators, and a large amount of regenerative energy can be obtained by storing the pressurized oil discharged from the boom cylinder 24 in the accumulator 70 when the boom is lowered, for example. In particular, the amount of energy that can be recovered when the boom is lowered is large in large hydraulic excavators operating in mines and the like. Also, generally, when an open circuit is used in the circuit of the hydraulic actuator of the front work equipment such as the boom cylinder, the slewing motor circuit is often also incorporated into an open circuit. The hydraulic excavator 1 according to this embodiment has the special feature that, while the hydraulic actuators of the front work equipment 20 (boom cylinder 24, arm cylinder 25, etc.) share an open circuit to simplify the circuit configuration, a closed circuit is deliberately used for the slewing motor 27 circuit, and the hydraulic pump motor 31 for that closed circuit can be used as an assist motor.

[0082] 1...Hydraulic excavator (construction machine), 11...Traction body, 12...Slewing body (first driven member), 20...Front work implement, 21...Boom (second driven member), 24...Boom cylinder (second hydraulic actuator), 27...Slewing motor (first hydraulic actuator), 31...Hydraulic pump / motor (first hydraulic pump / motor), 32...Hydraulic pump / motor (second hydraulic pump / motor), 61...Flushing valve, 70...Accumulator, 75...Regenerative valve, 76...Assist valve, 77a...Switching valve (first switching valve), 77b...Switching valve (second switching valve), 80...Controller, 92...Directional control valve, E...Engine (prime mover), La-Lj, Lm, Lx...Oil passage, S...Pressure accumulator sensor, T...Hydraulic oil tank, X1...Operating lever (first operating lever), X2...Operating lever (second operating lever)

Claims

1. A construction machine comprising: a first hydraulic actuator for driving a first driven member; a second hydraulic actuator for driving a second driven member; a double-tilting type first hydraulic pump motor connected in a closed circuit to the first hydraulic actuator; a prime mover for driving the first hydraulic pump motor; an accumulator for storing pressurized oil discharged from the second hydraulic actuator; a first operating lever for outputting an operating signal to command the operation of the first driven member; and a controller for controlling the first hydraulic pump motor in accordance with the operating signal of the first operating lever, wherein the controller comprises: an assist valve for opening and closing the connecting oil passage between the accumulator and the first hydraulic pump motor; and a pressure accumulator sensor for detecting the pressure of the accumulator, wherein the controller determines whether the first hydraulic pump motor is operating based on the operating signal of the first operating lever, and determines whether the pressure of the accumulator detected by the pressure accumulator is equal to or greater than a set pressure, A construction machine characterized in that, when the first hydraulic pump motor is not operating and the pressure of the accumulator is equal to or greater than a set pressure, the machine calculates a target assist power to be input to the prime mover by the motor operation of the first hydraulic pump motor according to the load of the prime mover, controls the tilting of the first hydraulic pump motor according to the target assist power, and outputs a control signal to command the assist valve to open.

2. A construction machine according to claim 1, wherein the controller calculates the tilt of the first hydraulic pump motor to output the target assist power based on the target assist power and the pressure of the accumulator detected by the pressure sensor.

3. A construction machine according to claim 1, further comprising a flushing valve that opens and closes an oil passage connecting the closed circuit of the first hydraulic pump motor and a hydraulic oil tank, wherein the flushing valve opens in conjunction with the motor operation of the first hydraulic pump motor, and the pressurized oil supplied from the accumulator to the closed circuit to drive the first hydraulic pump motor is discharged to the hydraulic oil tank via the flushing valve.

4. A construction machine according to claim 3, comprising: a first switching valve for opening and closing an oil passage connecting a first port of the first hydraulic actuator and a first input / output port of the first hydraulic pump motor; and a second switching valve for opening and closing an oil passage connecting a second port of the first hydraulic actuator and a second input / output port of the first hydraulic pump motor, wherein the controller outputs a control signal commanding the first switching valve and the second switching valve to close when the first hydraulic pump motor is driven.

5. A construction machine according to claim 3, comprising: a second hydraulic pump motor of the double-tilting type connected in a closed circuit to the second hydraulic actuator; and a second operating lever that outputs an operating signal for commanding the operation of the second driven member, wherein the controller controls the second hydraulic pump motor in accordance with the operating signal of the second operating lever.

6. A construction machine according to claim 5, wherein a regenerative valve is provided in an oil passage connecting the second hydraulic actuator and the accumulator, and the controller outputs a control signal that commands the regenerative valve to open when the second hydraulic actuator is operating.

7. A construction machine according to claim 3, comprising: a second hydraulic pump motor connected in an open circuit to the second hydraulic actuator; a second operating lever that outputs an operating signal for commanding the operation of the second driven member; and a directional control valve that controls the flow of pressurized oil from the second hydraulic pump motor to the second hydraulic actuator in accordance with the operation of the second operating lever.

8. A construction machine according to claim 7, wherein a regenerative valve is provided in an oil passage connecting the second hydraulic actuator and the accumulator, and the controller outputs a control signal that commands the regenerative valve to open when the second hydraulic actuator is operating.

9. A construction machine according to claim 8, comprising: a traveling body; a slewing body rotatably mounted on the upper part of the traveling body; and a front work machine attached to the slewing body, wherein the first driven member is the slewing body; the second driven member is the boom of the front work machine; the first hydraulic actuator is a slewing motor that drives the slewing body; and the second hydraulic actuator is a boom cylinder that drives the boom.

Images