Hydraulic circuits for construction machinery

Abstract

To provide a hydraulic circuit of a construction machine which can prevent damage to an oil cooler and an excessive rise of a temperature of hydraulic oil.SOLUTION: A hydraulic circuit 2 includes: a work tool operation device 10 for outputting a signal for operating a work tool 8 by operated by an operator; a bypass valve 26 arranged in a bypass pipeline 20; a return pipeline 30 for returning hydraulic oil to a hydraulic oil tank 18 from the work tool 8 not via a control valve 12 and an oil cooler 28; and a controller 14 for adjusting the opening of the bypass valve 26 to a first opening when the work tool operation device 10 is not operated, and adjusting the opening of the bypass valve 26 to a non-full close second opening smaller than the first opening when the work tool operation device 10 is operated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hydraulic circuit for a construction machine equipped with a work tool such as a hydraulic hammer. [Background technology]

[0002] A hydraulic excavator, which is a typical example of a construction machine, includes a lower traveling body, an upper rotating body rotatably supported on the lower traveling body, and a front working machine attached to the upper rotating body. The front working machine of the hydraulic excavator includes a boom swingably connected to the upper rotating body, and an arm swingably connected to the tip of the boom.

[0003] In many hydraulic excavators, a bucket for excavation work is attached to the end of the arm as a work tool, but various work tools other than the bucket can be attached to the end of the arm. An example of a work tool other than a bucket is a hydraulic hammer (hydraulic breaker) for breaking up concrete, rocks, etc.

[0004] When using a hydraulic hammer as a work tool, the back pressure of the hydraulic hammer must be kept below a certain value in order for the hydraulic hammer to perform at its required capacity. Therefore, a circuit is sometimes used to return hydraulic oil from the work tool to the hydraulic oil tank without passing through a control valve (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-128076 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the hydraulic oil is returned from the hydraulic hammer to the hydraulic oil tank without passing through the control valve, if the return oil from the hydraulic hammer passes through an oil cooler, there is a problem that the oil cooler may be damaged by surge pressure that occurs with the use of the hydraulic hammer.On the other hand, if the return oil from the hydraulic hammer does not pass through the oil cooler, there is a risk that the temperature of the hydraulic oil may rise excessively during operation of the hydraulic hammer.

[0007] The object of the present invention, made in consideration of the above facts, is to provide a hydraulic circuit for a construction machine that can prevent damage to the oil cooler and prevent the temperature of the hydraulic oil from rising excessively. [Means for solving the problem]

[0008] According to the present invention, there is provided the following hydraulic circuit for a construction machine which solves the above problems. That is, the hydraulic circuit of a construction machine includes a hydraulic pump, a work tool operated by hydraulic oil discharged by the hydraulic pump, a work tool operating device that outputs a signal for operating the work tool when operated by an operator, a control valve that allows supply of hydraulic oil from the hydraulic pump to the work tool based on the signal output by the work tool operating device, a pump line connecting the hydraulic pump and the control valve, a bypass line branching from the pump line and extending to a hydraulic oil tank, a bypass valve disposed in the bypass line, an oil cooler disposed in the bypass line downstream of the bypass valve, a return line for returning hydraulic oil from the work tool to the hydraulic oil tank without passing through the control valve and the oil cooler, and a controller that adjusts an aperture of the bypass valve to a first aperture when the work tool operating device is not operated, and adjusts an aperture of the bypass valve to a second aperture that is not fully closed and smaller than the first aperture when the work tool operating device is operated. When the work tool operating device is operated, the controller adjusts the opening of the bypass valve to the second opening when the temperature of the hydraulic oil is equal to or higher than an adjustment start temperature, and adjusts the opening of the bypass valve to a third opening smaller than the second opening when the temperature of the hydraulic oil is lower than the adjustment start temperature. A hydraulic circuit for a construction machine is provided.

[0010] It is preferable that, in a state in which the work tool operating device is being operated, the controller adjusts the aperture of the bypass valve to the second aperture, and then, when the temperature of the hydraulic oil becomes equal to or lower than an adjustment end temperature, adjusts the aperture of the bypass valve to the third aperture.

[0011] It is desirable that the controller controls the discharge volume of the hydraulic pump when the opening degree of the bypass valve is adjusted to the second opening degree so that the discharge volume of the hydraulic pump is greater than the discharge volume of the hydraulic pump when the opening degree of the bypass valve is adjusted to the third opening degree.

[0012] It is convenient for the controller to control the discharge volume of the hydraulic pump such that, when the aperture of the bypass valve is adjusted to the second aperture, the same amount of hydraulic oil is supplied to the work tool as the amount of hydraulic oil supplied to the work tool when the aperture of the bypass valve is adjusted to the third aperture. Effect of the Invention

[0013] The hydraulic circuit of the construction machine of the present invention is provided with a return line for returning hydraulic oil from the work tool to the hydraulic oil tank without passing through the control valve and oil cooler, so that the oil cooler will not be damaged even if surge pressure is generated due to use of the work tool.

[0014] Furthermore, the hydraulic circuit of the construction machine of the present invention is equipped with a controller that adjusts the opening of the bypass valve to a first opening when the work tool operating device is not operated, and adjusts the opening of the bypass valve to a second opening that is smaller than the first opening and is not fully closed when the work tool operating device is operated. Therefore, during operation of the work tool, some of the hydraulic oil discharged by the hydraulic pump flows from the pump line into the bypass line and is cooled in the oil cooler, preventing the temperature of the hydraulic oil from rising excessively. [Brief description of the drawings]

[0015] [Figure 1]1 is a circuit diagram showing a hydraulic circuit of a construction machine configured according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a hydraulic circuit for a construction machine configured according to the present invention will be described with reference to the drawings.

[0017] The hydraulic circuit generally designated by reference numeral 2 in Fig. 1 includes a variable displacement hydraulic pump 6 driven by an engine 4, and a work tool 8 operated by hydraulic oil (discharged oil) discharged by the hydraulic pump 6. A construction machine in which the hydraulic circuit 2 is used is, for example, a hydraulic excavator, and examples of the work tool 8 of the hydraulic excavator include the hydraulic hammer mentioned above, as well as a harvester used for felling and de-limbing in forestry work.

[0018] In addition to the work tool 8, the hydraulic circuit 2 also includes other hydraulic actuators that are operated by oil discharged from the hydraulic pump 6. When the hydraulic circuit 2 is for a hydraulic excavator, the hydraulic actuators other than the work tool 8 may include, although not shown, a boom cylinder that swings the boom, an arm cylinder that swings the arm, a travel motor that travels the hydraulic excavator, a swing motor that swings the upper swing body relative to the lower traveling body, and the like.

[0019] As shown in FIG. 1 , hydraulic circuit 2 further includes a work tool operating device 10 that outputs a signal for actuating work tool 8 when operated by an operator, and a control valve 12 that allows the supply of hydraulic oil from hydraulic pump 6 to work tool 8 based on the signal output by work tool operating device 10.

[0020] The work tool operating device 10 may be configured to have a pedal that is operated by stepping on it, or a push button switch. The push button switch may be attached to a joystick (not shown) for operating a boom cylinder or an arm cylinder, for example. Note that the hydraulic circuit 2 includes other operating devices (configurations having a lever or pedal) for operating hydraulic actuators other than the work tool 8.

[0021] When an appropriate operation such as stepping or pushing is performed on the work tool operating device 10, the work tool operating device 10 outputs an electric signal or a hydraulic signal. Fig. 1 shows a form in which the work tool operating device 10 outputs an electric signal. The electric signal output from the work tool operating device 10 is sent to the control valve 12 via the controller 14.

[0022] Unlike the illustrated embodiment, the work tool operating device 10 may output a hydraulic pressure signal to the control valve 12. In this case, the hydraulic pressure signal output from the work tool operating device 10 is detected by a pressure sensor (not shown), and the detection result of this pressure sensor is input to the controller 14.

[0023] When work tool operating device 10 outputs a signal, control valve 12 opens the oil passage leading from hydraulic pump 6 to work tool 8, allowing the oil discharged from hydraulic pump 6 to be supplied to the work tool 8. On the other hand, when work tool operating device 10 does not output a signal, control valve 12 closes the oil passage leading from hydraulic pump 6 to work tool 8, preventing the oil discharged from hydraulic pump 6 from being supplied to the work tool 8.

[0024] Furthermore, control valve 12 also opens and closes other oil passages leading from hydraulic pump 6 to hydraulic actuators other than work tool 8 in response to signals output from operating devices other than work tool operating device 10 .

[0025] The controller 14 is composed of a computer having a processing device and a storage device. The controller 14 controls the operation of the control valve 12 and the discharge volume of the hydraulic pump 6 based on signals output from the work tool operating device 10 and signals output from operating devices other than the work tool operating device 10.

[0026] 1, the hydraulic circuit 2 has a pump line 16 that connects the hydraulic pump 6 and the control valve 12, and a bypass line 20 that branches off from the pump line 16 and extends to a hydraulic oil tank 18. Hydraulic oil sucked from the hydraulic oil tank 18 by the hydraulic pump 6 is discharged to the pump line 16. In addition, a pressure sensor 22 that detects the pressure of the pump line 16 is provided in the pump line 16, and the pressure detected by the pressure sensor 22 is sent to the controller 14. A temperature sensor 24 that detects the temperature of the hydraulic oil in the hydraulic oil tank 18 is provided in the hydraulic oil tank 18, and the temperature detected by the temperature sensor 24 is sent to the controller 14.

[0027] The bypass pipeline 20 is provided with a bypass valve 26 for returning (unloading) a portion of the oil discharged from the hydraulic pump 6 to the hydraulic oil tank 18 without supplying it to a hydraulic actuator such as the work tool 8, and an oil cooler 28 for cooling the hydraulic oil. The opening degree of the bypass valve 26 is controlled by the controller 14, as will be described in detail later. The oil cooler 28 is disposed in the bypass pipeline 20 downstream of the bypass valve 26 (on the hydraulic oil tank 18 side).

[0028] 1, hydraulic circuit 2 includes a return line 30 for returning hydraulic oil from work tool 8 to hydraulic oil tank 18 without passing through control valve 12 and oil cooler 28. Therefore, even if surge pressure occurs when work tool 8 is used, hydraulic oil returning from work tool 8 to hydraulic oil tank 18 does not pass through oil cooler 28, so oil cooler 28 will not be damaged. Note that, although not shown, return oil from hydraulic actuators other than work tool 8 returns to hydraulic oil tank 18 via control valve 12 and oil cooler 28 but without passing through bypass valve 26.

[0029] Next, the operation of the hydraulic circuit 2 of the construction machine as described above will be described.

[0030] When the work tool operating device 10 or an operating device other than the work tool operating device 10 is not being operated, no signal is output from the work tool operating device 10, etc. In this case, the oil passages to the work tool 8 and other actuators are closed by the control valve 12, so that the oil discharged from the hydraulic pump 6 is not supplied to the work tool 8, etc., and the work tool 8, etc. do not operate.

[0031] Furthermore, when the work tool operating device 10, etc. is not being operated, the controller 14 adjusts the opening of the bypass valve 26 to the first opening, whereby the oil discharged from the hydraulic pump 6 passes through the bypass line 20 and returns to the hydraulic oil tank 18, and the pressure in the pump line 16 is maintained at a predetermined pressure.

[0032] On the other hand, when the work tool operating device 10 is operated, a signal is output from the work tool operating device 10. In response, the controller 14 actuates the control valve 12 to open the oil passage leading from the hydraulic pump 6 to the work tool 8. As a result, the oil discharged from the hydraulic pump 6 is supplied to the work tool 8, and the work tool 8 is operated.

[0033] Furthermore, when the work tool operating device 10 is operated, the controller 14 adjusts the opening of the bypass valve 26 to a second opening that is smaller than the first opening and is not fully closed. As a result, a portion of the oil discharged from the hydraulic pump 6 flows from the pump pipe 16 into the bypass pipe 20 and is cooled in the oil cooler 28.

[0034] In the illustrated embodiment, the return line 30 connecting the work tool 8 and the hydraulic oil tank 18 does not pass through the oil cooler 28, so the hydraulic oil passing through the return line 30 (return oil from the work tool 8) returns to the hydraulic oil tank 18 without being cooled by the oil cooler 28. However, when the work tool operating device 10 is operated, the controller 14 adjusts the opening of the bypass valve 26 to a second opening that is not fully closed. As a result, a portion of the oil discharged from the hydraulic pump 6 flows into the bypass line 20 and is cooled by the oil cooler 28, so that it is possible to prevent the temperature of the hydraulic oil from excessively increasing while the work tool 8 is in operation.

[0035] The second opening of bypass valve 26 can be set to any opening smaller than the first opening, but does not include a completely closed state (fully closed) in the second opening so that a portion of the discharge oil from hydraulic pump 6 can flow into bypass line 20 while work tool 8 is in operation. In addition, the second opening may be constant, or may be changed depending on the temperature of the hydraulic oil (for example, the temperature of the hydraulic oil in hydraulic oil tank 18).

[0036] The larger the second opening of bypass valve 26, the more hydraulic oil flows into bypass line 20 and passes through oil cooler 28, reducing concerns about overheating of the hydraulic oil. However, the larger the second opening, the greater the reduction in the amount of hydraulic oil used to operate work tool 8, which increases the impact on the operation of work tool 8.

[0037] Conversely, as the second opening degree becomes smaller, the reduction in the amount of hydraulic oil supplied to the work tool 8 becomes smaller, and therefore the impact on the operation of the work tool 8 becomes less. However, since the amount of hydraulic oil passing through the oil cooler 28 becomes smaller, there is a greater concern about the hydraulic oil overheating.

[0038] Therefore, the second opening of bypass valve 26 is preferably large enough to distribute a flow rate capable of effectively preventing overheating of the hydraulic oil to bypass line 20, while supplying a flow rate capable of exerting the required capacity of work tool 8 to work tool 8.

[0039] As described above, the controller 14 is configured to adjust the aperture of the bypass valve 26 to the second aperture when the work tool operating device 10 is operated. However, the controller 14 may be configured to adjust the aperture of the bypass valve 26 to the second aperture when other conditions are satisfied in addition to the work tool operating device 10 being operated.

[0040] For example, another condition may be that the temperature of the hydraulic oil is equal to or higher than the adjustment start temperature. That is, when the work tool operating device 10 is operated, the controller 14 may adjust the aperture of the bypass valve 26 to the second aperture when the temperature of the hydraulic oil is equal to or higher than the adjustment start temperature, and may adjust the aperture of the bypass valve 26 to a third aperture smaller than the second aperture when the temperature of the hydraulic oil is lower than the adjustment start temperature.

[0041] The temperature of the hydraulic oil can be the temperature output by the temperature sensor 24 to the controller 14 (the temperature of the hydraulic oil in the hydraulic oil tank 18), but it does not necessarily have to be the temperature in the hydraulic oil tank 18. The adjustment start temperature can be set arbitrarily as a temperature at which there is concern about overheating of the hydraulic oil. The third opening of the bypass valve 26 may be any opening smaller than the second opening, but from the viewpoint of reducing fuel consumption, it is preferable that it is in a completely closed state (fully closed).

[0042] The hydraulic oil that flows from pump line 16 into bypass line 20 is not used to operate work tool 8 and returns to hydraulic oil tank 18. Therefore, even when work tool operating device 10 is operated, if the temperature is below the adjustment start temperature (if there is no concern about overheating of the hydraulic oil), the opening of bypass valve 26 can be adjusted to a third opening smaller than the second opening, thereby reducing the amount of hydraulic oil that flows from pump line 16 into bypass line 20 and suppressing energy loss.

[0043] As described above, when the work tool operating device 10 is operated, whether or not the controller 14 adjusts the aperture of the bypass valve 26 to the second aperture can be determined based on the temperature of the hydraulic oil. Furthermore, whether or not the controller 14 ends the control of adjusting the aperture of the bypass valve 26 to the second aperture may also be determined based on the temperature of the hydraulic oil.

[0044] That is, while the work tool operating device 10 is being operated, the controller 14 may adjust the aperture of the bypass valve 26 to the second aperture, and then adjust the aperture of the bypass valve 26 to the third aperture when the temperature of the hydraulic oil becomes equal to or lower than the adjustment end temperature. That is, while the work tool operating device 10 is being operated, if the concern about overheating of the hydraulic oil is eliminated, the controller 14 may adjust the aperture of the bypass valve 26 to the third aperture. This makes it possible to reduce the amount of hydraulic oil unloaded from the oil discharged from the hydraulic pump 6.

[0045] The adjustment end temperature can be set arbitrarily as a temperature at which there is no risk of overheating the hydraulic oil. However, it is preferable that the adjustment end temperature is a temperature lower than the adjustment start temperature and at which chattering can be prevented (for example, a temperature about 10 to 15°C lower than the adjustment start temperature).

[0046] Conversely, once the opening degree of the bypass valve 26 is adjusted to the second opening degree, the opening degree of the bypass valve 26 may be maintained at the second opening degree until the operation of the work tool operating device 10 is released.

[0047] Incidentally, while the aperture of bypass valve 26 is adjusted to the second aperture, as described above, a portion of the oil discharged from hydraulic pump 6 flows into bypass line 20. For this reason, if the discharge amount of hydraulic pump 6 is constant both when adjusted to the second aperture and when adjusted to a third aperture smaller than the second aperture, the amount of hydraulic oil flowing into bypass line 20 will be greater when adjusted to the second aperture than when adjusted to the third aperture, and the amount of hydraulic oil used to operate work tool 8 will be less.

[0048] For this reason, it is preferable that the controller 14 controls the discharge volume of the hydraulic pump 6 when the opening degree of the bypass valve 26 is adjusted to the second opening degree so that the discharge volume of the hydraulic pump 6 is greater than the discharge volume of the hydraulic pump 6 when the opening degree of the bypass valve 26 is adjusted to the third opening degree.

[0049] Specifically, it is advantageous for the controller 14 to control the discharge rate of the hydraulic pump 6 such that, when the opening degree of the bypass valve 26 is adjusted to the second opening degree, the same amount of hydraulic oil is supplied to the work tool 8 as the amount of hydraulic oil supplied to the work tool 8 when the opening degree of the bypass valve 26 is adjusted to the third opening degree.

[0050] As a result, while work tool 8 is in operation, a constant amount of hydraulic oil can be supplied to work tool 8 regardless of the opening of bypass valve 26 (whether it is the second opening or the third opening), allowing work tool 8 to stably demonstrate its capacity. Also, since the amount of hydraulic oil flowing into bypass pipeline 20 can be increased by increasing the second opening without impairing the capacity of work tool 8, the hydraulic oil can be cooled more effectively.

[0051] The discharge amount of the hydraulic pump 6 may be controlled by changing the capacity of the hydraulic pump 6 or by changing the rotation speed of the engine 4.

[0052] As described above, the hydraulic circuit 2 in the illustrated embodiment includes the return line 30 for returning hydraulic oil from the work tool 8 to the hydraulic oil tank 18 without passing through the control valve 12 and the oil cooler 28, so that the oil cooler 28 will not be damaged even if a surge pressure is generated due to use of the work tool 8.

[0053] Furthermore, the hydraulic circuit 2 is provided with a controller 14 that adjusts the aperture of the bypass valve 26 to a first aperture when the work tool operating device 10 is not operated, and adjusts the aperture of the bypass valve 26 to a second aperture that is smaller than the first aperture and is not fully closed when the work tool operating device 10 is operated. Therefore, during operation of the work tool 8, a portion of the hydraulic oil discharged by the hydraulic pump 6 flows from the pump line 16 into the bypass line 20 and is cooled in the oil cooler 28, preventing the temperature of the hydraulic oil from rising excessively. [Explanation of symbols]

[0054] 2: Hydraulic circuit 6: Hydraulic pump 8: Work tools 10: Work tool operating device 12: Control valve 14: Controller 16: Pump pipe 18: Hydraulic oil tank 20: Bypass pipeline 26: Bypass valve 28: Oil cooler 30: Return pipe

Claims

1. A hydraulic circuit of a construction machine, comprising: A hydraulic pump; a work tool operated by the hydraulic oil discharged by the hydraulic pump; a work tool operating device that, when operated by an operator, outputs a signal for actuating the work tool; a control valve that allows supply of hydraulic oil from the hydraulic pump to the work tool based on a signal output from the work tool operating device; a pump line connecting the hydraulic pump and the control valve; a bypass line branching off from the pump line and extending to a hydraulic oil tank; a bypass valve disposed in the bypass line; an oil cooler disposed downstream of the bypass valve in the bypass pipe; a return line for returning hydraulic oil from the work tool to the hydraulic oil tank without passing through the control valve and the oil cooler; a controller that adjusts an opening degree of the bypass valve to a first opening degree when the work tool operating device is not operated, and adjusts an opening degree of the bypass valve to a second opening degree that is smaller than the first opening degree and is not fully closed when the work tool operating device is operated, When the work tool operating device is operated, the controller When the temperature of the hydraulic oil is equal to or higher than an adjustment start temperature, the opening degree of the bypass valve is adjusted to the second opening degree, A hydraulic circuit for a construction machine, which adjusts the opening of the bypass valve to a third opening smaller than the second opening when the temperature of the hydraulic oil is lower than the adjustment start temperature.

2. 2. The hydraulic circuit for a construction machine according to claim 1, wherein, in a state in which the work tool operating device is operated, the controller adjusts the opening of the bypass valve to the second opening, and then, when a temperature of the hydraulic oil becomes equal to or lower than an adjustment end temperature, adjusts the opening of the bypass valve to the third opening.

3. 3. The hydraulic circuit for a construction machine according to claim 1, wherein the controller controls the discharge volume of the hydraulic pump when the opening degree of the bypass valve is adjusted to the second opening degree so that the discharge volume of the hydraulic pump is greater than the discharge volume of the hydraulic pump when the opening degree of the bypass valve is adjusted to the third opening degree.

4. 4. The hydraulic circuit for a construction machine according to claim 3, wherein, when an opening degree of the bypass valve is adjusted to the second opening degree, the controller controls the discharge amount of the hydraulic pump such that an amount of hydraulic oil supplied to the work tool is the same as an amount of hydraulic oil supplied to the work tool when the opening degree of the bypass valve is adjusted to the third opening degree.

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