Hydraulic systems for construction machinery

Abstract

A hydraulic system (2) for a construction machine according to one embodiment includes an electric motor (21) supplied with electric power from a battery (13), a hydraulic pump (33) driven by the electric motor (21), and a circulation pump (71) that causes cooling water to be circulated in a circulation path (7) passing through the battery (13) and a radiator (76). Furthermore, the hydraulic system (2) includes a heat exchanger (24) connected to the circulation path (7) in parallel with the radiator (76), a first switching valve (52) that switches whether or not hydraulic oil discharged from the hydraulic pump (33) is supplied to the heat exchanger (24), and a second switching valve (74) that switches whether the cooling water passing through the battery (13) is supplied to the radiator (76) or supplied to the heat exchanger (24).

Description

Technical Field

[0001] The present disclosure relates to a hydraulic system of a construction machine.

Background Art

[0002] Construction machines such as hydraulic excavators are equipped with a hydraulic system that supplies hydraulic oil from a hydraulic pump to a plurality of hydraulic actuators. For example, Patent Document 1 discloses a hydraulic system of a construction machine including a hydraulic pump driven by an engine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, a hydraulic system of a construction machine in which an electric motor is adopted instead of an engine has been under development. In this case, electric power is supplied from a battery to the electric motor. However, in cold regions, the performance of the battery significantly deteriorates.

[0005] Therefore, an object of the present disclosure is to provide a hydraulic system of a construction machine that can raise the temperature of a battery.

Means for Solving the Problems

[0006] This disclosure provides a hydraulic system for construction machinery, comprising: an electric motor powered by a battery; a hydraulic pump driven by the electric motor; a circulation pump for circulating coolant through a circulation path via the battery and a radiator; a heat exchanger connected in parallel with the radiator to the circulation path for heat exchange between the coolant and hydraulic oil; a first switching valve for switching whether or not to supply the hydraulic oil discharged from the hydraulic pump to the heat exchanger; and a second switching valve for switching whether or not to supply the coolant that has passed through the battery to the radiator or to the heat exchanger. [Effects of the Invention]

[0007] According to this disclosure, a hydraulic system for construction machinery is provided that can raise the temperature of a battery. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a hydraulic system for a construction machine according to one embodiment. [Figure 2] This is a plan view showing the internal structure of the slewing body of a hydraulic excavator equipped with the aforementioned hydraulic system. [Figure 3] This is a side view showing the internal structure of the rotating body of the hydraulic excavator. [Figure 4] This is a plan view from the position of line IV-IV in Figure 3. [Figure 5] This is a schematic diagram illustrating the configuration of a hydraulic system for a modified construction machine. [Modes for carrying out the invention]

[0009] Figure 1 shows a hydraulic system 2 for a construction machine according to one embodiment. The hydraulic system 2 is mounted on a construction machine 1 as shown in Figure 2. In this embodiment, the construction machine 1 is a hydraulic excavator 1A. However, the hydraulic system 2 may be mounted on a construction machine 1 other than a hydraulic excavator, such as a crane or a wheel loader.

[0010] As shown in Figures 2 and 3, the hydraulic excavator 1A includes a slewing body 11 and a boom 14 that moves up and down relative to the slewing body 11. If the hydraulic excavator 1A is self-propelled, the slewing body 11 is supported on the vehicle so as to be rotatable. The slewing body 11 is provided with a driver's cab 12 on the side of the boom 14.

[0011] As shown in Figure 1, the hydraulic system 2 supplies hydraulic fluid from at least one hydraulic pump 33 to multiple hydraulic actuators 15 shown in Figure 3. Note that Figure 3 shows only the boom cylinder 15A among the multiple hydraulic actuators 15. Other hydraulic actuators include the slewing motor, arm cylinder, and bucket cylinder.

[0012] Specifically, the hydraulic system 2 includes a hydraulic oil tank 31 for storing hydraulic fluid, at least one hydraulic pump 33 connected to the hydraulic oil tank 31 by hydraulic piping 32, an electric motor 21 for driving at least one hydraulic pump 33, and a control valve unit 4 connected to at least one hydraulic pump 33 by hydraulic piping 35 and also connected to the hydraulic oil tank 31 by hydraulic piping 47. In Figure 3, the pump unit including the hydraulic pump 33 and electric motor 21 is installed horizontally, but the pump unit may be installed vertically.

[0013] In this embodiment, the hydraulic system 2 includes two hydraulic pumps 33. However, the hydraulic system 2 may include only one hydraulic pump 33, or it may include three or more hydraulic pumps 33. Also, in this embodiment, each hydraulic pump 33 is a variable displacement pump, and the capacity of each hydraulic pump 33 is changed by a regulator 34. For example, each hydraulic pump 33 is an axial piston pump, such as a swashplate pump or a slanted shaft pump.

[0014] In this embodiment, as shown in Figure 3, two hydraulic pumps 33 are arranged coaxially to form a tandem pump. The rotating shafts of the tandem pumps are connected to the output shaft of the electric motor 21 by a coupling. However, the two hydraulic pumps 33 may also be arranged side by side to form a parallel pump.

[0015] Returning to Figure 1, in this embodiment, each regulator 34 is controlled by the control device 9. Note that in Figure 1, some signal lines are omitted for the sake of simplifying the drawing. For example, if the hydraulic pump 33 is a swash plate pump, the regulator 34 may electrically change the hydraulic pressure acting on the servo piston connected to the swash plate of the hydraulic pump 33, or it may be an electric actuator connected to the swash plate of the hydraulic pump 33.

[0016] However, each regulator 34 does not necessarily need to be controlled by the control device 9, and may operate by the pressure of the hydraulic fluid. For example, each regulator 34 may be a negative control type or a load sensing type. Alternatively, each hydraulic pump 33 may be a fixed-displacement pump, and the discharge flow rate may be changed according to the rotational speed.

[0017] The driver's seat 12 is equipped with multiple operating devices, such as a boom operating device, an arm operating device, and a bucket operating device. In this embodiment, an electric motor 21 drives a hydraulic pump 33 at a constant rotational speed. The control device 9 maintains the capacity of the hydraulic pump 33 at a minimum when none of the operating devices are being operated. On the other hand, when any of the operating devices are operated, the control device 9 increases the capacity of the hydraulic pump 33 that supplies hydraulic fluid to the hydraulic actuator 15 corresponding to the operated operating device, as the amount of operation of the operating device increases.

[0018] The hydraulic oil tank 31 is located inside the slewing body 11. The hydraulic oil tank 31 is located on the opposite side of the boom 14 from the driver's seat 12. A battery 13 is also located inside the slewing body 11. The battery 13 is located behind the driver's seat 12 and the boom 14. Power is supplied to the electric motor 21 from the battery 13.

[0019] When any of the above-described operating devices is operated, the control valve unit 4 supplies the hydraulic oil discharged from the hydraulic pump 33 to the hydraulic actuator 15 corresponding to the operated operating device, and returns the hydraulic oil discharged from the hydraulic actuator 15 to the hydraulic oil tank 31.

[0020] Specifically, the control valve unit 4 includes a plurality of control valves respectively corresponding to the hydraulic actuators 15. In the control valve unit 4, two pump passages 41 respectively communicating with the hydraulic oil pipe 35 and a tank passage 46 communicating with the hydraulic oil pipe 47 are formed, and each control valve is connected to one pump passage 41 and the tank passage 46. Further, a pair of supply / discharge passages are formed for each control valve in the control valve unit 4. The control valve unit 4 is connected to the hydraulic actuator 15 by the hydraulic oil pipe 48 shown in FIG. 2 communicating with the supply / discharge passage. The control valve unit 4 is disposed between the boom 14 and the battery 13 in the swivel body 11.

[0021] Furthermore, as shown in FIG. 1, the control valve unit 4 is formed with a relief passage 44 provided with a relief valve 45, and a relay passage 42 connecting each pump passage 41 and the relief passage 44 is formed. A check valve 43 that allows the flow from the pump passage 41 to the relief passage 44 but prohibits the flow from the relief passage 44 to the pump passage 41 is provided in each relay passage 42.

[0022] The control valve unit 4 is connected to the first switching valve 52 by a hydraulic oil pipe 51. The above-described relief passage 44 communicates with the hydraulic oil pipe 51. That is, the relief valve 45 is interposed between the first switching valve 52 and the hydraulic pump 33.

[0023] The first switching valve 52 is connected to the oil cooler 54 by a hydraulic oil pipe 53, and the oil cooler 54 is connected to the hydraulic oil tank 31 by a hydraulic oil pipe 55. The hydraulic oil pipe 55 is equipped with a check valve 56 that allows flow from the oil cooler 54 to the hydraulic oil tank 31 but prohibits flow from the hydraulic oil tank 31 to the oil cooler 54. Note that the check valve 56 is not shown in Figures 2 and 3.

[0024] The oil cooler 54 cools the hydraulic fluid discharged from the hydraulic pump 33 and passing through the relief valve 45. In other words, the hydraulic fluid pipes 51, 53, 55, the first switching valve 52, and the oil cooler 54 constitute the cooling passage 5. In this embodiment, the oil cooler 54 is air-cooled, with air blown from the fan motor 22, but the oil cooler 54 may also be water-cooled.

[0025] A heat exchanger 24 is connected in parallel with the oil cooler 54 to the cooling passage 5. The heat exchanger 24 performs heat exchange between the hydraulic oil and the cooling water. More specifically, the heat exchanger 24 is connected to the first switching valve 52 by hydraulic oil piping 61 and to the hydraulic oil tank 31 by hydraulic oil piping 62. A check valve 63 is provided in the hydraulic oil piping 62, which allows flow from the heat exchanger 24 to the hydraulic oil tank 31 but prohibits flow from the hydraulic oil tank 31 to the heat exchanger 24. Note that the check valve 63 is not shown in Figures 2 and 3.

[0026] The first switching valve 52 is switched between a cooling position in which the hydraulic oil piping 51 is connected to the hydraulic oil piping 53 and a non-cooling position in which the hydraulic oil piping 51 is connected to the hydraulic oil piping 61. In other words, the first switching valve 52 switches whether to supply the hydraulic oil that has passed through the relief valve 45 to the heat exchanger 24 or to the oil cooler 54, or in other words, whether to supply the hydraulic oil discharged from the hydraulic pump 33 to the heat exchanger 24 or not. The first switching valve 52 is controlled by the control device 9.

[0027] Furthermore, this embodiment employs a configuration for cooling the battery 13. Specifically, the hydraulic system 2 includes a radiator 76 and a circulation pump 71 that circulates cooling water through a circulation path 7 that passes through the battery 13 and the radiator 76. In this embodiment, the radiator 76 is air-cooled, with air blown from a fan motor 23, but the radiator 76 may also be water-cooled.

[0028] The circulation pump 71 is connected to the battery 13 by a cooling water pipe 72, and the battery 13 is connected to the second switching valve 74 by a cooling water pipe 73. The battery 13 has an internal passage 13a, which communicates with the cooling water pipes 72 and 73. However, a jacket may be used instead of the internal passage 13a. In addition, a cooling water tank may be provided in the circulation path 7 (for example, the cooling water pipe 77 upstream of the circulation pump 71, which will be described later).

[0029] The second switching valve 74 is connected to the radiator 76 by a cooling water pipe 75, and the radiator 76 is connected to the circulation pump 71 by a cooling water pipe 77. The cooling water pipe 77 is equipped with a check valve 78 that allows flow from the radiator 76 to the circulation pump 71 but prohibits flow from the circulation pump 71 to the radiator 76. Note that the check valve 78 is not shown in Figures 2 and 3.

[0030] A heat exchanger 24 is connected in parallel with the radiator 76 in the circulation path 7. More specifically, the heat exchanger 24 is connected to the second switching valve 74 by a cooling water pipe 81, and is also connected to the portion of the cooling water pipe 77 downstream of the check valve 78 by a cooling water pipe 82.

[0031] In this embodiment, a heater 83 is provided in the cooling water piping 81, but the heater 83 is optional. The cooling water piping 82 is provided with a check valve 84 that allows flow from the heat exchanger 24 to the cooling water piping 77, but prohibits flow from the cooling water piping 77 to the heat exchanger 24. Note that the check valve 84 is not shown in Figures 2 and 3.

[0032] The second switching valve 74 switches between a cooling position in which the cooling water pipe 73 is connected to the cooling water pipe 75, and a heating position in which the cooling water pipe 73 is connected to the cooling water pipe 81. In other words, the second switching valve 74 switches whether the cooling water that has passed through the battery 13 is supplied to the radiator 76 or to the heat exchanger 24. The second switching valve 74 is controlled by the control device 9.

[0033] With respect to the control device 9, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor, which is considered a type of circuit, then the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or the processor.

[0034] The control device 9 is electrically connected to a temperature sensor 91 located in the hydraulic oil tank 31 and a temperature sensor 92 located in the battery 13. The temperature sensor 91 detects the temperature of the hydraulic oil stored in the hydraulic oil tank 31, and the temperature sensor 92 detects the temperature of the battery 13. However, the temperature sensor 91 may be located in one of the hydraulic oil pipes, and the temperature sensor 92 may be located in one of the cooling water pipes.

[0035] The control device 9 displays the hydraulic fluid temperature detected by the temperature sensor 91 on a display device installed in the driver's seat 12. When the hydraulic fluid temperature is low, the driver performs a warm-up operation to reduce the viscosity of the hydraulic fluid. The control device 9 switches the first switching valve 52 to the non-cooled position when the hydraulic fluid temperature detected by the temperature sensor 91 is lower than a predetermined value α, and switches the first switching valve 52 to the cooled position when the hydraulic fluid temperature detected by the temperature sensor 91 is higher than a predetermined value α. For example, the predetermined value α is in the range of 10°C to 40°C.

[0036] For example, the operator tilts the operating lever of the boom control device to its maximum extent to shorten the boom cylinder 15A to its stroke end, and then maintains the tilted position of the operating lever. As a result, the hydraulic fluid discharged from the hydraulic pump 33 at maximum flow rate passes through the relief valve 45, generating heat.

[0037] Furthermore, the control device 9 switches the second switching valve 74 to the cooling position when the temperature of the battery 13 detected by the temperature sensor 92 is higher than a predetermined value β, and switches the second switching valve 74 to the heating position when the temperature of the battery 13 detected by the temperature sensor 92 is lower than a predetermined value β. For example, the predetermined value β is in the range of 10°C to 40°C.

[0038] As described above, in the hydraulic system 2 of this embodiment, the first switching valve 52 supplies the hydraulic fluid discharged from the hydraulic pump 33 and passed through the relief valve 45 to the heat exchanger 24, and the second switching valve 74 supplies the cooling water that has passed through the battery 13 to the heat exchanger 24. As a result, the cooling water circulating through the battery 13 is heated by the hydraulic fluid. Therefore, the temperature of the battery 13 can be increased.

[0039] Furthermore, in this embodiment, as shown in Figures 2 to 4, the electric motor 21, hydraulic pump 33, oil cooler 54, first switching valve 52, heat exchanger 24, circulation pump 71, radiator 76, and second switching valve 74 are arranged in the space enclosed by the side 11a of the slewing body 11 on the hydraulic oil tank 31 side, the battery 13, the control valve unit 4, and the hydraulic oil tank 31, so that the hydraulic oil piping and cooling water piping can be laid out with short lengths.

[0040] <Variation> This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure.

[0041] For example, the warm-up operation does not need to be performed by the operator, but may be performed automatically by the control device 9 when the power to the construction machine 1 is turned on. In this case, the battery 13 may be continuously heated after the temperature of the hydraulic fluid has risen above a predetermined value α due to the warm-up operation.

[0042] Furthermore, as shown in the modified hydraulic system 2A in Figure 5, a check valve 49 with a slightly higher cracking pressure may be provided in the hydraulic fluid piping 47, and the tank passage 46 may communicate with the relief passage 44 downstream of the relief valve 45. In this case, the oil cooler 54 cools the hydraulic fluid discharged from the multiple hydraulic actuators 15 through the control valve unit 4. With this configuration, not only the hydraulic fluid that has passed through the relief valve 45 but also the hydraulic fluid discharged from the hydraulic actuators 15 can be cooled. Note that the hydraulic fluid returned from the hydraulic actuators 15 and the hydraulic fluid that has passed through the relief valve 45 basically flow through the oil cooler 54, but if the pressure of the hydraulic fluid increases due to a problem with the oil cooler 54 or a large amount of hydraulic fluid returning, it will flow into the hydraulic fluid piping 47.

[0043] Alternatively, the relief passage 44 and the oil cooler 54 may be directly connected by the hydraulic oil piping 53, the first switching valve 52 may be made into a simple on / off valve, a branch passage may be formed in the control valve unit 4 that branches off from the pump passage 41, and the hydraulic oil piping 51 extending from the first switching valve 52 may be connected to the aforementioned branch passage.

[0044] However, with the configuration described above, the temperature of the hydraulic fluid can be increased as it passes through the relief valve 45. Moreover, when heating of the cooling water is not required, the hydraulic fluid that has passed through the relief valve 45 can be cooled by the oil cooler 54.

[0045] <Summary> In a first aspect, the present disclosure provides a hydraulic system for construction machinery comprising: an electric motor powered by a battery; a hydraulic pump driven by the electric motor; a circulation pump for circulating coolant through a circulation path via the battery and a radiator; a heat exchanger connected in parallel with the radiator to the circulation path for heat exchange between the coolant and hydraulic oil; a first switching valve for switching whether or not to supply hydraulic oil discharged from the hydraulic pump to the heat exchanger; and a second switching valve for switching whether or not to supply coolant that has passed through the battery to the radiator or to the heat exchanger.

[0046] With the above configuration, the first switching valve supplies the hydraulic fluid discharged from the hydraulic pump to the heat exchanger, and the second switching valve supplies the cooling water that has passed through the battery to the heat exchanger. As a result, the cooling water circulating through the battery is heated by the hydraulic fluid. Therefore, the temperature of the battery can be increased.

[0047] In a second embodiment, the hydraulic system in the first embodiment further comprises a relief valve interposed between the hydraulic pump and the first switching valve, and an oil cooler for cooling the hydraulic fluid that has passed through the relief valve, wherein the first switching valve may switch between supplying the hydraulic fluid that has passed through the relief valve to the heat exchanger or to the oil cooler. With this configuration, the temperature of the hydraulic fluid can be increased when it passes through the relief valve. Moreover, when heating of the cooling water is not required, the hydraulic fluid that has passed through the relief valve can be cooled by the oil cooler.

[0048] In a third embodiment, in the second embodiment, for example, the hydraulic system may further include a hydraulic fluid tank connected to the hydraulic pump and a control valve unit connected to the hydraulic pump and a plurality of hydraulic actuators.

[0049] In a fourth embodiment, in the third embodiment, the oil cooler may cool the hydraulic fluid discharged from the plurality of hydraulic actuators through the control valve unit. With this configuration, not only the hydraulic fluid that has passed through the relief valve but also the hydraulic fluid discharged from the hydraulic actuators can be cooled.

[0050] In a fifth embodiment, in the third or fourth embodiment, the construction machine is a hydraulic excavator including a slewing body, a boom that moves up and down relative to the slewing body, and a driver's seat provided on the slewing body on the side of the boom, wherein within the slewing body, the hydraulic oil tank is located on the opposite side of the boom from the driver's seat, the battery is located behind the driver's seat and the boom, the control valve unit is located between the boom and the battery, and the electric motor, the hydraulic pump, the oil cooler, the first switching valve, the heat exchanger, the circulation pump, the radiator and the second switching valve may be arranged in the space enclosed by the side of the slewing body on the hydraulic oil tank side, the battery, the control valve unit and the hydraulic oil tank. With this configuration, the hydraulic oil piping and cooling water piping can be laid out with short lengths.

Claims

1. An electric motor powered by a battery, A hydraulic pump driven by the aforementioned electric motor, A circulation pump that circulates coolant through the aforementioned battery and radiator circulation path, A heat exchanger connected in parallel with the radiator to the circulation path, which performs heat exchange between the cooling water and the hydraulic oil, A first switching valve that switches whether or not to supply the hydraulic fluid discharged from the hydraulic pump to the heat exchanger, A second switching valve that switches whether the coolant that has passed through the battery is supplied to the radiator or to the heat exchanger, A hydraulic system for construction machinery that includes the following features.

2. A relief valve interposed between the hydraulic pump and the first switching valve, The system further includes an oil cooler for cooling the hydraulic fluid that has passed through the relief valve, The hydraulic system for a construction machine according to claim 1, wherein the first switching valve switches whether the hydraulic fluid that has passed through the relief valve is supplied to the heat exchanger or to the oil cooler.

3. A hydraulic oil tank connected to the aforementioned hydraulic pump, The hydraulic system for a construction machine according to claim 2, further comprising the hydraulic pump and a control valve unit connected to a plurality of hydraulic actuators.

4. The hydraulic system for a construction machine according to claim 3, wherein the oil cooler cools the hydraulic fluid discharged from the plurality of hydraulic actuators through the control valve unit.

5. The aforementioned construction machine is a hydraulic excavator including a slewing body, a boom that moves up and down relative to the slewing body, and a driver's cab provided on the slewing body to the side of the boom. Within the rotating body, the hydraulic oil tank is located on the opposite side of the boom from the driver's seat, the battery is located behind the driver's seat and the boom, and the control valve unit is located between the boom and the battery. A hydraulic system for a construction machine according to claim 3 or 4, wherein the electric motor, the hydraulic pump, the oil cooler, the first switching valve, the heat exchanger, the circulation pump, the radiator, and the second switching valve are arranged in a space enclosed by the side of the rotating body on the hydraulic oil tank side, the battery, the control valve unit, and the hydraulic oil tank.

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