Construction Machinery

Abstract

The object of the present invention is to provide an engineering machine capable of efficiently driving a hydraulic cylinder using an accumulator. Therefore, in an engineering machine having a hydraulic cylinder, a first accumulator storing return oil from the hydraulic cylinder at a first set pressure, an oil tank storing working oil, a first hydraulic pump discharging the working oil sucked from the oil tank, a hydraulic actuator driven by the first hydraulic pump, and a second accumulator storing return oil from the hydraulic actuator at a second set pressure, the first control valve is arranged in a first oil circuit connecting the first accumulator and the hydraulic cylinder; and a second control valve is arranged in a second oil circuit connecting the second accumulator and the hydraulic cylinder, and the second set pressure is set to a value higher than the first set pressure.

Description

Technical Field

[0001] The present invention relates to engineering machinery such as hydraulic excavators. Background Art

[0002] According to Patent Document 1, when the boom is lowered, the bottom side of the boom hydraulic cylinder is connected to the rod side, and the bottom side is connected to the accumulator, so that the return oil from the boom hydraulic cylinder can be pressurized and stored in the accumulator. In Patent Document 2, the pressure oil stored in the accumulator is supplied to the boom hydraulic cylinder, and the flow rate from the slave pump to the boom hydraulic cylinder is reduced, so that the oil consumption can be reduced.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-275769

[0006] Patent Document 2: Japanese Patent Application Publication No. 2009-275771 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the structure of Patent Document 1 or 2, the accumulator is stored at a constant pressure, while the bottom pressure of the boom hydraulic cylinder changes according to the movement of the front part including the arm and the bucket. Therefore, when the bottom pressure of the boom hydraulic cylinder is low, a large pressure loss occurs when the pressure oil is supplied from the accumulator to the bottom side, and the energy stored in the accumulator may not be effectively used.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a construction machine capable of efficiently driving a hydraulic cylinder using an accumulator.

[0010] Means for solving problems

[0011] In order to achieve the above-mentioned purpose, the present invention provides a construction machinery comprising: a hydraulic cylinder; a first accumulator, which accumulates return oil from the hydraulic cylinder at a first set pressure; an oil tank, which stores working oil; a first hydraulic pump, which discharges the working oil sucked from the oil tank; a hydraulic actuator, which is driven by the first hydraulic pump; and a second accumulator, which accumulates return oil from the hydraulic actuator at a second set pressure, wherein the construction machinery is characterized in that it comprises: a first control valve, which is arranged in a first oil circuit connecting the first accumulator and the hydraulic cylinder; and a second control valve, which is arranged in a second oil circuit connecting the second accumulator and the hydraulic cylinder, and the second set pressure is set to a value higher than the first set pressure.

[0012] According to the present invention configured as above, by opening either the first control valve or the second control valve, either the first accumulator on the low-pressure side or the second accumulator on the high-pressure side can be connected to the hydraulic cylinder. Thus, the pressure loss when the pressure oil is supplied from the first accumulator 4 or the second accumulator 21 to the hydraulic cylinder 1 can be suppressed, so the hydraulic cylinder 1 can be driven efficiently.

[0013] Effects of the Invention

[0014] According to the construction machine of the present invention, the hydraulic cylinder can be driven efficiently using the accumulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a side view of the hydraulic excavator according to the embodiment of the present invention.

[0016] Figure 2 It is installed on Figure 1 The circuit diagram of the hydraulic drive device of the hydraulic excavator shown.

[0017] Figure 3 Is based on Figure 2 The diagram shows the control flow of the controller driving the boom hydraulic cylinder.

[0018] Figure 4 Is based on Figure 2 A diagram showing a control flow of a controller related to a regenerative operation of a swing electric motor.

[0019] Figure 5 Is based on Figure 2 FIG. 2 is a diagram of a control flow related to the pressure accumulation operation of the accumulator on the low-pressure side of the controller shown.

[0020] Figure 6 Is based on Figure 2 FIG. 2 is a diagram of a control flow related to the pressure accumulation operation of the accumulator on the high-pressure side of the controller shown. DETAILED DESCRIPTION

[0021] Hereinafter, a hydraulic excavator will be described as an example of a construction machine according to an embodiment of the present invention with reference to the accompanying drawings. In addition, in each figure, the same reference numerals are attached to the same components, and repeated descriptions are omitted as appropriate.

[0022] Figure 1 It is a side view of the hydraulic excavator according to the present embodiment.

[0023] like Figure 1As shown, the hydraulic excavator 100 includes: a traveling body 101; a revolving body 102 which is rotatably arranged on the traveling body 101 and constitutes a vehicle body; and a working device 103 which is mounted on the revolving body 102 so as to be rotatable in the vertical direction and performs sand excavation work, etc. The revolving body 102 is driven by a revolving motor 22.

[0024] The working device 103 includes a boom 105 mounted on the revolving body 102 in a manner that allows it to rotate in the vertical direction, an arm 106 mounted on the front end of the boom 105 in a manner that allows it to rotate in the vertical direction, and a bucket 107 mounted on the front end of the arm 106 in a manner that allows it to rotate in the vertical direction. The boom 105 is driven by a boom hydraulic cylinder 1, the arm 106 is driven by an arm hydraulic cylinder 108, and the bucket 107 is driven by a bucket hydraulic cylinder 109.

[0025] A cab 110 is provided at the front position of the revolving body 102, and a counterweight 111 for ensuring weight balance is provided at the rear position. A machine room 112 is provided between the cab 110 and the counterweight 111. The machine room 112 accommodates an engine, a hydraulic pump, a control valve 113, etc. The control valve 113 controls the flow of the hydraulic oil supplied from the hydraulic pump to each actuator.

[0026] Figure 2 This is a circuit diagram of a hydraulic drive device mounted on the hydraulic excavator 100 .

[0027] The accumulator 4 is a hydraulic device that accumulates return oil from the bottom side of the boom hydraulic cylinder 1 and supplies pressure oil when the boom hydraulic cylinder 1 is extended. The accumulator 4 is connected to the bottom side oil chamber 1a of the boom hydraulic cylinder 1 via oil passages 41 and 42, and a control valve 2 is arranged in the oil passage 41. The control valve 2 receives a control signal from the controller 6 to connect or cut off the oil passage 41. A pressure sensor 30 for detecting the pressure of the accumulator 4 is provided in the oil passage 42, and the signal of the pressure sensor 30 is input to the controller 6.

[0028] The rod-side oil chamber 1b of the boom cylinder 1 is connected to the oil tank 40 via an oil passage 43, and a control valve 3 is disposed in the oil passage 43. The control valve 3 receives a control signal from the controller 6 to connect or block the oil passage 43.

[0029] The oil circuit portion connecting the bottom side oil chamber 1a and the control valve 2 in the oil circuit 41 is connected to the oil circuit portion connecting the rod side oil chamber 1b and the control valve 3 via the oil circuit 44 and the oil circuit 43, and the control valve 7 is arranged in the oil circuit 44. The control valve 7 receives a control signal from the controller 6 to connect or cut off the oil circuit 44. When the boom lowering operation signal is input from the boom operating lever 5, the controller 6 switches the control valve 7 to the connecting position, so that the bottom side of the boom hydraulic cylinder 1 is connected to the rod side, thereby increasing the pressure on the bottom side.

[0030] In addition, the oil circuit portion connecting the bottom oil chamber 1a and the control valve 2 in the oil circuit 41 is connected to the accumulator 21 via the oil circuits 45 and 46, and the control valve 19 is arranged in the oil circuit 45. The control valve 19 receives a control signal from the controller 6 to connect or disconnect the oil circuit 45. A pressure sensor 9 for detecting the bottom pressure of the boom hydraulic cylinder 1 is provided in the oil circuit portion connecting the control valve 19 and the oil circuit 41 in the oil circuit 45, and the signal of the pressure sensor 9 is input to the controller 6. The controller 6 switches the control valves 2, 3, and 19 to the connection position or the disconnection position respectively according to the operation signal (boom raising operation signal or boom lowering operation signal) input from the boom operating lever 5 and the bottom pressure of the boom hydraulic cylinder 1 detected by the pressure sensor 9.

[0031] The swing motor 22 is connected to the hydraulic pump 13 and the oil tank 40 via the directional control valve 14. The directional control valve 14 receives a control signal from the controller 6 and switches from the neutral position to any left or right position. When the directional control valve 14 is switched to any left or right position, the discharge oil of the hydraulic pump 13 flows into one port of the swing motor 22, and the working oil discharged from the other port of the swing motor 22 returns to the oil tank 40. As a result, the swing motor 22 is driven, and the swing body 102 rotates in any left or right direction. The controller 6 switches the directional control valve 14 from the neutral position to any left or right position according to the operation signal input from the swing operating lever 18.

[0032] The oil passages 47 and 48 connecting the directional control valve 14 and the swing motor 22 are connected to the oil passage 49 via the check valves 23 and 24, and the pressure oil on the high-pressure side of the oil passages 47 and 48 flows into the oil passage 49. The oil passage 49 is connected to the oil passage 46, and the control valve 20 is arranged in the oil passage 49. The pressure sensor 25 is provided in the oil passage portion connecting the check valves 23 and 24 and the control valve 20 in the oil passage 49, and the signal of the pressure sensor 25 is input to the controller 6. The controller 6 switches the control valve 20 to the connection position or the disconnection position according to the pressure of the oil passage 49 detected by the pressure sensor 25 (the pressure on the high-pressure side of the oil passages 47 and 48). The accumulator 21 accumulates the return oil of the swing motor 22 via the control valve 20, and supplies the accumulated pressure oil to the boom hydraulic cylinder 1 via the control valve 19.

[0033] Here, the set pressures of the accumulators 4 and 21 are described. The accumulator 4 is mainly used to recover the return oil of the boom hydraulic cylinder 1, and the accumulator 21 is mainly used to recover the return oil of the swing motor 22. In order to suppress the pressure loss when the return oil of the boom hydraulic cylinder 1 flows into the accumulator 4 and improve the energy recovery efficiency, the set pressure of the accumulator 4 is set to a value close to the bottom pressure of the boom hydraulic cylinder 1. Similarly, in order to suppress the pressure loss when the return oil of the swing motor 22 flows into the accumulator 21 and improve the energy recovery efficiency, the set pressure of the accumulator 21 is set to a value close to the return pressure of the swing motor 22. In addition, since the return pressure of the swing motor 22 is higher than the bottom pressure of the boom hydraulic cylinder 1, the set pressure of the accumulator 21 becomes higher than the set pressure of the accumulator 4.

[0034] The hydraulic pump 27 is mainly a hydraulic device for accumulating pressure in the accumulator 4, and the discharge port of the hydraulic pump 27 is connected to the accumulator 4 via the control valve 26 and the oil circuit 42. The control valve 26 receives a control signal from the controller 6 and switches from the unloading position 26a to the loading position 26b. When the control valve 26 is at the unloading position 26a, the discharge oil of the hydraulic pump 27 is discharged to the oil tank 40, and when the control valve 26 is switched to the loading position 26b, the discharge oil of the hydraulic pump 27 is accumulated in the accumulator 4. A pressure sensor 30 for detecting the pressure of the accumulator 4 is provided in the oil circuit 42, and the signal of the pressure sensor 30 is input to the controller 6. The controller 6 switches the control valve 26 to the unloading position 26a or the loading position 26b according to the pressure of the accumulator 4 detected by the pressure sensor 30.

[0035] The hydraulic pump 29 is mainly a hydraulic device for accumulating pressure in the accumulator 21, and the discharge port of the hydraulic pump 29 is connected to the accumulator 21 via the control valve 28 and the oil circuit 46. The control valve 28 receives a control signal from the controller 6 and switches from the unloading position 28a to the loading position 28b. When the control valve 28 is at the unloading position 28a, the discharge oil of the hydraulic pump 29 is discharged to the oil tank 40, and when the control valve 28 is switched to the loading position 28b, the discharge oil of the hydraulic pump 29 is accumulated in the accumulator 21. A pressure sensor 31 for detecting the pressure of the accumulator 21 is provided in the oil circuit 46, and the signal of the pressure sensor 31 is input to the controller 6. The controller 6 switches the control valve 28 to the unloading position 28a or the loading position 28b according to the pressure of the accumulator 21 detected by the pressure sensor 31.

[0036] Next, use Figure 3 to Figure 5 The processing contents of the controller 6 will be described. Figure 3 represents the control flow related to the drive of the boom hydraulic cylinder 1, Figure 4 The control flow related to the regenerative operation of the rotary electric motor 22 is shown. Figure 5 1 shows the control flow involved in the pressure accumulation operation of the accumulator 4 on the low-pressure side. Figure 6 1 and 2 show control flows related to the pressure accumulation operation of the high-pressure-side accumulator 21. These control flows are started, for example, when a key switch (not shown) is turned on, and are executed simultaneously and in parallel.

[0037] First, refer to Figure 3 , a control flow involved in driving the boom hydraulic cylinder 1 will be described.

[0038] The controller 6 first determines whether a boom raising operation signal is input from the boom operating lever 5 (step S101 ).

[0039] When it is determined as YES in step S101 (the boom raising operation signal is input), it is determined whether the bottom pressure of the boom cylinder 1 detected by the pressure sensor 9 is higher than a predetermined pressure set1 (step S102 ).

[0040] If it is determined to be "yes" in step S102 (the bottom pressure of the boom hydraulic cylinder 1 is higher than the predetermined pressure set1), the control valves 3 and 19 are opened while the control valves 2 and 7 are closed (step S103), and the process returns to step S101. As a result, the hydraulic oil is supplied from the accumulator 21 on the high-pressure side to the bottom side of the boom hydraulic cylinder 1, and the hydraulic oil on the rod side is discharged to the oil tank 40, and the boom hydraulic cylinder 1 performs an extension operation.

[0041] If it is determined to be "No" in step S102 (the bottom pressure of the boom hydraulic cylinder 1 is less than the predetermined pressure set1), the control valves 2 and 3 are opened while the control valves 7 and 19 are closed (step S104), and the process returns to step S101. As a result, the hydraulic oil is supplied from the accumulator 4 on the low-pressure side to the bottom side of the boom hydraulic cylinder 1, and the hydraulic oil on the rod side is discharged to the oil tank 40, and the boom hydraulic cylinder 1 performs an extension operation.

[0042] When it is determined as NO in step S101 (the boom raising operation signal is not input), it is determined whether a boom lowering operation signal is input from the boom operating lever 5 (step S105 ).

[0043] If it is determined to be "yes" in step S105 (the boom lowering operation signal is input), the control valves 2 and 7 are opened while the control valves 3 and 19 are closed (step S106), and the process returns to step S101. As a result, part of the pressure oil discharged from the bottom side of the boom hydraulic cylinder 1 is accumulated in the accumulator 4 via the control valve 2, and the remaining part is supplied to the rod side of the boom hydraulic cylinder 1 via the control valve 7, and the boom hydraulic cylinder 1 performs a contraction operation.

[0044] If the determination in step S105 is "NO" (the boom lowering pilot pressure Pd is not detected), the control valves 2, 3, 7, and 19 are closed (step S107), and the process returns to step S101. As a result, all the oil passages supplying and discharging the hydraulic oil to the boom cylinder 1 are cut off, so that the boom cylinder 1 remains stationary.

[0045] Through the above control process, when the bottom pressure of the boom hydraulic cylinder 1 is low, the accumulator 4 on the low-pressure side is connected to the bottom side, and when the bottom pressure is high, the accumulator 21 on the high-pressure side is connected to the bottom side. Therefore, the pressure loss when the pressure oil is supplied from the accumulators 4 and 21 to the bottom side of the boom hydraulic cylinder 1 can be suppressed, and the boom hydraulic cylinder 1 can be efficiently extended.

[0046] Next, refer to Figure 4 , the control flow involved in the regenerative action of the rotary electric motor 22 is described.

[0047] The controller 6 first determines whether the pressure of the swing motor 22 detected by the pressure sensor 25 (swing motor pressure) is higher than a predetermined pressure set2 (step S201). The predetermined pressure set2 is set to a value greater than a set pressure set4 of the accumulator 21 described later.

[0048] If the determination in step S201 is "yes" (the swing motor pressure is higher than the predetermined pressure set2), the control valve 20 is opened (step S202), and the process returns to step S201. Thus, the return side of the swing motor 22 is connected to the accumulator 21, and the energy of the swing body 102 during deceleration is regenerated.

[0049] When the determination result in step S201 is “NO” (the swing electric motor pressure is equal to or lower than the predetermined pressure set2 ), the control valve 20 is closed (step S203 ), and the process returns to step S201 .

[0050] Next, refer to Figure 5 , a control flow related to the pressure accumulation operation of the accumulator 4 on the low-pressure side will be described.

[0051] The controller 6 first determines whether the pressure of the accumulator 4 detected by the pressure sensor 30 (accumulator pressure) is lower than a predetermined pressure set3 (step S301). The predetermined pressure set3 here is a set pressure of the accumulator 4, which is set to a value lower than a set pressure set4 of the accumulator 21 described later.

[0052] If the judgment in step S301 is "yes" (the accumulator pressure is lower than the predetermined pressure set3), the control valve 26 is switched to the loading position 26b to connect the discharge port of the hydraulic pump 27 to the accumulator 4 (step S302), and the process returns to step S301. As a result, the discharge oil of the hydraulic pump 27 is accumulated in the accumulator 4, and the pressure of the accumulator 4 is maintained at or above the predetermined pressure set3.

[0053] If the determination result in step S301 is "No" (the accumulator pressure is greater than the predetermined pressure set3), the control valve 26 is switched to the unloading position 26a and the discharge port of the hydraulic pump 27 is connected to the oil tank 40 (step S303), and the process returns to step S301. As a result, the accumulator 4 is not pressurized by the hydraulic pump 27 to a level greater than necessary, thereby suppressing unnecessary energy consumption.

[0054] Next, refer to Figure 6 A control flow related to the pressure accumulation operation of the accumulator 21 will be described.

[0055] The controller 6 first determines whether the pressure of the accumulator 21 detected by the pressure sensor 31 (accumulator pressure) is lower than a predetermined pressure set4 (step S401). The predetermined pressure set4 is a set pressure of the accumulator 21 and is set to a value higher than the set pressure set3 of the accumulator 4.

[0056] If the judgment in step S401 is "yes" (the accumulator pressure is lower than the predetermined pressure set4), the control valve 28 is switched to the loading position 28b and the discharge port of the hydraulic pump 29 is connected to the accumulator 21 (step S402), and the process returns to step S401. As a result, the discharge oil of the hydraulic pump 29 is accumulated in the accumulator 21, and the pressure of the accumulator 21 is maintained at or above the predetermined pressure set4.

[0057] If the determination result in step S401 is "No" (the accumulator pressure is greater than the predetermined pressure set4), the control valve 28 is switched to the unloading position 28a and the discharge port of the hydraulic pump 29 is connected to the oil tank 40 (step S403), and the process returns to step S401. As a result, the accumulator 21 is not pressurized by the hydraulic pump 29 to a level greater than necessary, thereby suppressing unnecessary energy consumption.

[0058] (action)

[0059] Reference Figure 2 , the operation of the hydraulic drive device 200 will be described.

[0060] First, the operation of the rotary body 102 will be described.

[0061] When the swing operating lever 18 is operated, the controller 6 determines which direction to swing to, right or left, and switches the directional control valve 14 from the neutral position to any left or right position. The hydraulic pump 13 supplies pressure oil to the swing motor 22 via the directional control valve 14, so that the swing body 102 swings. When the swing operating lever 18 returns to the neutral position, the directional control valve 14 returns to the neutral position, thereby increasing the pressure on the return side of the swing motor 22 and slowing down the swing body 102. At this time, the return oil of the swing motor 22 flows into the oil circuit 49 via the check valve 23 or the check valve 24. And, when the pressure of the oil circuit 49 detected by the pressure sensor 25 exceeds the predetermined pressure set2, the controller 6 opens the control valve 20. As a result, the return oil of the swing motor 22 is accumulated in the accumulator 21, and the braking energy of the swing body 102 is recovered.

[0062] Next, the lowering operation of the boom 105 (retraction operation of the boom cylinder 1) will be described.

[0063] When the boom operating lever 5 is operated in the boom lowering direction, the controller 6 opens the control valve 7 to connect the bottom side of the boom hydraulic cylinder 1 with the rod side to increase the pressure. At the same time, the controller 6 opens the control valve 2, whereby the return oil from the bottom side of the boom hydraulic cylinder 1 is accumulated in the accumulator 4. As a result, the boom hydraulic cylinder 1 contracts, the boom 105 moves downward, and the potential energy of the boom 105 is regenerated.

[0064] Next, the raising operation of the boom 105 (extension operation of the boom cylinder 1) will be described.

[0065] When the boom operating lever 5 is operated in the boom raising direction, the controller 6 opens the control valve 3 to connect the rod side of the boom hydraulic cylinder 1 to the oil tank 40, and opens one of the control valves 2 and 19 according to the bottom pressure of the boom hydraulic cylinder 1. Specifically, the control valve 2 is opened when the bottom pressure is less than the predetermined pressure set1, and the control valve 19 is opened when the bottom pressure is higher than the predetermined pressure set1. As a result, when the bottom pressure is less than the predetermined pressure set1, the accumulator 21 on the low pressure side is connected to the bottom side, and when the bottom pressure is higher than the predetermined pressure set1, the accumulator 4 on the high pressure side is connected to the bottom side. And, by supplying pressure oil from the accumulators 4 and 21 to the bottom side of the boom hydraulic cylinder 1, the boom hydraulic cylinder 1 is extended, and the boom 105 performs a rising action. As described above, by switching the connection between the accumulators 4 and 21 and the boom hydraulic cylinder 1 according to the bottom pressure of the boom hydraulic cylinder 1, it is possible to suppress the pressure loss when the pressure oil is supplied from the accumulators 4 and 21 to the boom hydraulic cylinder 1, so that the boom hydraulic cylinder 1 can be driven efficiently. Furthermore, since the accumulators 4 and 21 are maintained at a set pressure or higher by the hydraulic pumps 27 and 29 , respectively, the boom cylinder 1 can be driven at an arbitrary timing.

[0066] (Effect)

[0067] In the present embodiment, in an engineering machine 100 including a hydraulic cylinder 1, a first accumulator 4 for accumulating return oil from the hydraulic cylinder 1 at a first set pressure set3, an oil storage tank 40 for storing working oil, a first hydraulic pump 13 for discharging the working oil sucked from the oil storage tank 40, a hydraulic actuator 22 driven by the first hydraulic pump 13, and a second accumulator 21 for accumulating return oil from the hydraulic actuator 22 at a second set pressure set4, a first control valve 2 is arranged in a first oil circuit 41 connecting the first accumulator 4 and the hydraulic cylinder 1, and a second control valve 19 is arranged in a second oil circuit 45 connecting the second accumulator 21 and the hydraulic cylinder 1, and the second set pressure set4 is set to a value higher than the first set pressure set3.

[0068] According to the present embodiment configured as above, by opening either the first control valve 2 or the second control valve 19, either the first accumulator 4 on the low-pressure side or the second accumulator 21 on the high-pressure side can be connected to the hydraulic cylinder 1. Thus, it is possible to suppress the pressure loss when the pressure oil is supplied from the first accumulator 4 or the second accumulator 21 to the hydraulic cylinder 1, so that the hydraulic cylinder 1 can be driven efficiently.

[0069] In addition, the engineering machinery 100 of the present embodiment comprises: a first pressure sensor 9, which detects the pressure of the hydraulic cylinder 1; and a controller 6, which inputs a pressure signal from the first pressure sensor 9 and outputs a control signal to the first control valve 2 and the second control valve 19. The controller 6 controls the first control valve 2 and the second control valve 19 according to the pressure of the hydraulic cylinder 1.

[0070] With this configuration, the accumulators 4 and 21 connected to the hydraulic cylinder 1 can be selected according to the pressure of the hydraulic cylinder 1. This can suppress pressure loss when supplying pressurized oil from the accumulators 4 and 21 to the boom hydraulic cylinder 1, so the boom hydraulic cylinder 1 can be driven efficiently.

[0071] In addition, the controller 6 in this embodiment is controlled in the following manner: when the pressure of the hydraulic cylinder 1 is higher than the first set pressure set3, the first control valve 2 is closed and the second control valve 19 is opened; when the pressure of the hydraulic cylinder 1 is lower than the first set pressure set3, the second control valve 19 is closed and the first control valve 2 is opened.

[0072] With this configuration, when the pressure of the hydraulic cylinder 1 is lower than the first set pressure set3, the first accumulator 4 on the low-pressure side is connected to the hydraulic cylinder 1, and when the pressure of the hydraulic cylinder 1 is higher than the first set pressure set3, the second accumulator 21 on the high-pressure side is connected to the hydraulic cylinder 1. Thus, it is possible to suppress the pressure loss when the pressure oil is supplied from the accumulators 4 and 21 to the boom hydraulic cylinder 1, so that the boom hydraulic cylinder 1 can be driven efficiently.

[0073] In addition, the engineering machinery 100 of the present embodiment comprises: a second hydraulic pump 27; a second pressure sensor 30, which detects the pressure of the first accumulator 4; and a third control valve 26, which can be switched to a loading position 26b connecting the discharge port of the second hydraulic pump 27 to the first accumulator 4 and an unloading position 26a connecting the discharge port of the second hydraulic pump 27 to the oil tank 40 according to a control signal from the controller 6, and the controller 6 controls in the following manner: when the pressure of the first accumulator 4 is lower than the first set pressure set3, the third control valve 26 is switched to the loading position 26b, and when the pressure of the first accumulator 4 is greater than the first set pressure set3, the third control valve 26 is switched to the unloading position 26a.

[0074] With this configuration, the pressure of the first accumulator 4 can be maintained at or above the first set pressure set 3. In addition, since the first accumulator 4 is not pressurized more than necessary by the second hydraulic pump 27, unnecessary energy consumption can be suppressed.

[0075] In addition, the engineering machinery 100 of the present embodiment comprises: a third hydraulic pump 29; a third pressure sensor 31, which detects the pressure of the second accumulator 21; and a fourth control valve 28, which can be switched to a loading position 28b connecting the discharge port of the third hydraulic pump 29 to the second accumulator and an unloading position 28a connecting the discharge port of the third hydraulic pump 29 to the oil tank 40 according to a control signal from the controller 6, and the controller 6 controls in the following manner: when the pressure of the second accumulator 21 is lower than the second set pressure set4, the fourth control valve 28 is switched to the loading position 28b, and when the pressure of the second accumulator 21 is greater than the second set pressure set4, the fourth control valve 28 is switched to the unloading position 28a.

[0076] With this configuration, the pressure in the second accumulator 21 can be maintained at or above the second set pressure set4. In addition, since the second accumulator 21 is not pressurized more than necessary by the third hydraulic pump 29, unnecessary energy consumption can be suppressed.

[0077] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments and includes various modifications. For example, the above embodiments are described in detail to explain the present invention in an easy-to-understand manner and are not limited to all the structures described.

[0078] Description of Reference Numerals

[0079] 1… Boom hydraulic cylinder (hydraulic cylinder), 2… Control valve (first control valve), 3… Control valve, 4… Accumulator (first accumulator), 5… Boom operating lever, 6… Controller, 7… Control valve, 9… Pressure sensor (first pressure sensor), 13… Hydraulic pump (first hydraulic pump), 14… Direction control valve, 18… Swing operating lever, 19… Control valve (second control valve), 20… Control valve, 21… Accumulator (second accumulator), 22… Swing motor (hydraulic actuator), 23… Check valve, 24… Check valve, 25… Pressure sensor, 26… Control valve (third control valve), 26a… Unloading position, 26b… Loading position, 27… Hydraulic pump (second hydraulic pump), 28… Control valve (fourth control valve), control valve), 28a…unloading position, 28b…loading position, 29…hydraulic pump (third hydraulic pump), 30…pressure sensor (second pressure sensor), 31…pressure sensor (third pressure sensor), 40…oil tank, 41…oil circuit (first oil circuit), 42-44…oil circuit, 45…oil circuit (second oil circuit), 46-49…oil circuit, 100…hydraulic excavator (construction machinery), 101…traveling body, 102…slewing body, 103…working device, 105…boom, 106…arm, 107…bucket, 108…arm hydraulic cylinder, 109…bucket hydraulic cylinder, 110…operating room, 111…counterweight, 112…machine room, 113…control valve, 200…hydraulic drive device.

Claims

1. A construction machine, comprising: a hydraulic cylinder; a first accumulator that accumulates return oil from the hydraulic cylinder at a first set pressure; an oil tank that stores working oil; a first hydraulic pump that discharges the working oil sucked from the oil tank; a hydraulic actuator that is driven by the first hydraulic pump; and a second accumulator that accumulates return oil from the hydraulic actuator at a second set pressure, It is characterized in that The engineering machine includes: a first control valve disposed in a first oil passage connecting the first accumulator and the hydraulic cylinder; and a second control valve disposed in a second oil circuit connected to an oil circuit portion of the first oil circuit that connects the hydraulic cylinder to the first control valve, connects the second accumulator to the hydraulic cylinder, and supplies pressurized oil from the second accumulator to the hydraulic cylinder; The second set pressure is set to a value higher than the first set pressure.

2. The construction machinery according to claim 1, characterized in that: The engineering machinery has: a first pressure sensor that detects the pressure of the hydraulic cylinder; and a controller which inputs a pressure signal from the first pressure sensor and outputs a control signal to the first control valve and the second control valve, The controller controls the first control valve and the second control valve according to the pressure of the hydraulic cylinder, thereby connecting the hydraulic cylinder to the first accumulator or connecting the hydraulic cylinder to the second accumulator.

3. The construction machinery according to claim 2, characterized in that: The controller performs control in the following manner: when the pressure of the hydraulic cylinder is higher than the first set pressure, the first control valve is closed and the second control valve is opened; when the pressure of the hydraulic cylinder is lower than the first set pressure, the second control valve is closed and the first control valve is opened.

4. The construction machinery according to claim 2, characterized in that: The engineering machinery has: A second hydraulic pump; a second pressure sensor that detects the pressure of the first accumulator; and a third control valve capable of switching between a loading position in which the discharge port of the second hydraulic pump is connected to the first accumulator and an unloading position in which the discharge port of the second hydraulic pump is connected to the oil tank according to a control signal from the controller, The controller controls the third control valve to be switched to the loading position when the pressure of the first accumulator is lower than the first setting pressure, and switches the third control valve to the unloading position when the pressure of the first accumulator is equal to or higher than the first setting pressure.

5. The construction machine according to claim 2, characterized in that: The engineering machinery has: A third hydraulic pump; a third pressure sensor that detects the pressure of the second accumulator; and a fourth control valve capable of switching between a loading position in which the discharge port of the third hydraulic pump is connected to the second accumulator and an unloading position in which the discharge port of the third hydraulic pump is connected to the oil tank according to a control signal from the controller, The controller controls the fourth control valve to be switched to the loading position when the pressure of the second accumulator is lower than the second setting pressure, and switches the fourth control valve to the unloading position when the pressure of the second accumulator is equal to or higher than the second setting pressure.

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