JP7670535B2 - Hydraulic circuits for construction machinery - Google Patents

Description

The present invention relates to a hydraulic circuit for a construction machine equipped with a work tool such as a hydraulic hammer.

A hydraulic excavator, a typical example of construction machinery, comprises a lower traveling body, an upper rotating body supported for free rotation 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 connected to the upper rotating body for free swinging, and an arm connected to the tip of the boom for free swinging.

Many hydraulic excavators have a bucket for excavation work attached to the end of the arm as a work tool, but various work tools other than a bucket can also 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.

When using a hydraulic hammer as a work tool, the back pressure of the hydraulic hammer must be kept below a specified value in order for the hydraulic hammer to perform at its required capacity. For this reason, a circuit is sometimes used that returns hydraulic oil from the work tool to the hydraulic oil tank without passing through a control valve (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 8-128076

However, when 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 the surge pressure that occurs when the hydraulic hammer is used. On the other hand, if the return oil from the hydraulic hammer does not pass through an oil cooler, there is a risk that the temperature of the hydraulic oil may rise excessively while the hydraulic hammer is in operation.

In light of the above, the objective of the present invention 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.

According to the present invention, there is provided the following hydraulic circuit for a construction machine that solves the above-mentioned problems: That is, the hydraulic circuit for 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 the 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 off 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, and a control valve and an oil cooler disposed in the bypass line downstream of the bypass valve. a return pipeline for returning hydraulic oil from the work tool to the hydraulic oil tank without passing through a cooler; and 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 not fully closed and smaller than the first opening when the work tool operating device is operated, wherein 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 that is smaller than the second opening when the temperature of the hydraulic oil is below the adjustment start temperature.

When the work tool operating device is being operated, the controller preferably adjusts the opening of the bypass valve to the second opening, and then adjusts the opening of the bypass valve to the third opening when the temperature of the hydraulic oil becomes equal to or lower than the end-of-adjustment temperature.

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

It is preferable that the controller controls the discharge volume of the hydraulic pump so that when the opening of the bypass valve is adjusted to the second opening, the same amount of hydraulic oil is supplied to the work tool as when the opening of the bypass valve is adjusted to the third opening.

The hydraulic circuit of the construction machine of the present invention is equipped 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 occurs during use of the work tool.

The hydraulic circuit of the construction machine of the present invention is also equipped with a controller that adjusts the opening of the bypass valve to a first opening when the work tool operating device is not being 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 being operated. Therefore, during operation of the work tool, a portion 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.

1 is a circuit diagram showing a hydraulic circuit of a construction machine configured according to the present invention.

Below, an embodiment of a hydraulic circuit for a construction machine configured according to the present invention will be described with reference to the drawings.

The hydraulic circuit, generally designated by the reference symbol 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.

In addition to the work tool 8, the hydraulic circuit 2 includes other hydraulic actuators that are operated by the oil discharged from the hydraulic pump 6. If 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 drives the hydraulic excavator, a rotation motor that rotates the upper rotating body relative to the lower traveling body, etc.

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

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. The hydraulic circuit 2 also includes other operating devices (configurations having levers or pedals) for operating hydraulic actuators other than the work tool 8.

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

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

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

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

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.

As shown in FIG. 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 the hydraulic oil tank 18. The hydraulic oil sucked from the hydraulic oil tank 18 by the hydraulic pump 6 is discharged into the pump line 16. In addition, the pump line 16 is provided with a pressure sensor 22 that detects the pressure of the pump line 16, and the pressure detected by the pressure sensor 22 is sent to the controller 14. The hydraulic oil tank 18 is provided with a temperature sensor 24 that detects the temperature of the hydraulic oil in the hydraulic oil tank 18, and the temperature detected by the temperature sensor 24 is sent to the controller 14.

The bypass line 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 downstream of the bypass valve 26 in the bypass line 20 (on the hydraulic oil tank 18 side).

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

Next, we will explain the operation of the hydraulic circuit 2 of the construction machine as described above.

When the work tool operating device 10 or other operating devices other than the work tool operating device 10 are not being operated, no signal is output from the work tool operating device 10, etc. In this case, the oil passage to the work tool 8 and other actuators is closed by the control valve 12, so that the discharge oil from the hydraulic pump 6 is not supplied to the work tool 8, etc., and the work tool 8, etc. does not operate.

When the work tool operating device 10 or the like is not being operated, the controller 14 adjusts the opening of the bypass valve 26 to the first opening. This allows the discharge oil from the hydraulic pump 6 to return to the hydraulic oil tank 18 through the bypass line 20, and the pressure in the pump line 16 is maintained at a predetermined pressure.

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 operates the control valve 12 to open the oil passage leading from the hydraulic pump 6 to the work tool 8. This causes the oil discharged from the hydraulic pump 6 to be supplied to the work tool 8, causing the work tool 8 to operate.

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 line 16 into the bypass line 20 and is cooled in the oil cooler 28.

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 discharge oil from the hydraulic pump 6 flows into the bypass line 20 and is cooled by the oil cooler 28, so that the temperature of the hydraulic oil can be prevented from rising excessively during operation of the work tool 8.

The second opening of the 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 of the hydraulic pump 6 can flow into the bypass line 20 while the work tool 8 is in operation. In addition, the second opening may be constant, or may be changed according to the temperature of the hydraulic oil (for example, the temperature of the hydraulic oil in the hydraulic oil tank 18).

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

Conversely, the smaller the second opening, the smaller the reduction in the amount of hydraulic oil supplied to the work tool 8, and therefore the less impact it has on the operation of the work tool 8; however, the less hydraulic oil passes through the oil cooler 28, which increases the risk of the hydraulic oil overheating.

Therefore, it is preferable that the second opening of the bypass valve 26 is large enough to distribute a flow rate that can effectively prevent overheating of the hydraulic oil to the bypass line 20, and to supply a flow rate that can exert the required capacity of the work tool 8 to the work tool 8.

As described above, the controller 14 is configured to adjust the opening degree of the bypass valve 26 to the second opening degree when the work tool operating device 10 is operated, but the controller 14 may also be configured to adjust the opening degree of the bypass valve 26 to the second opening degree when other conditions are satisfied in addition to the work tool operating device 10 being operated.

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 opening of the bypass valve 26 to a second opening when the temperature of the hydraulic oil is equal to or higher than the adjustment start temperature, and adjust the opening of the bypass valve 26 to a third opening smaller than the second opening when the temperature of the hydraulic oil is less than the adjustment start temperature.

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 the temperature at which there is concern about overheating of the hydraulic oil. The third opening of the bypass valve 26 can 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).

The hydraulic oil that flows from the pump line 16 into the bypass line 20 is not used to operate the work tool 8 and is returned to the hydraulic oil tank 18. Therefore, even if the 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 the bypass valve 26 can be adjusted to a third opening smaller than the second opening to reduce the amount of hydraulic oil that flows from the pump line 16 into the bypass line 20 and suppress energy loss.

As described above, when the work tool operating device 10 is operated, the temperature of the hydraulic oil can determine whether the controller 14 adjusts the opening of the bypass valve 26 to the second opening. Furthermore, the temperature of the hydraulic oil can also determine whether the controller 14 terminates the control of adjusting the opening of the bypass valve 26 to the second opening.

In other words, the controller 14 may adjust the opening of the bypass valve 26 to the second opening while the work tool operating device 10 is being operated, and then adjust the opening of the bypass valve 26 to the third opening when the temperature of the hydraulic oil becomes equal to or lower than the end-of-adjustment temperature. In other words, the controller 14 may adjust the opening of the bypass valve 26 to the third opening while the work tool operating device 10 is being operated if the concern about overheating of the hydraulic oil is resolved. This makes it possible to reduce the amount of hydraulic oil unloaded from the discharge oil of the hydraulic pump 6.

The end-of-adjustment temperature can be set arbitrarily as long as there is no risk of overheating the hydraulic oil. However, it is desirable for the end-of-adjustment temperature to be a temperature lower than the start-of-adjustment temperature and capable of preventing chattering (for example, a temperature approximately 10 to 15°C lower than the start-of-adjustment temperature).

Conversely, once the opening degree of the bypass valve 26 has been 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.

As described above, while the opening of the bypass valve 26 is adjusted to the second opening, a portion of the oil discharged from the hydraulic pump 6 flows into the bypass line 20. Therefore, if the discharge amount of the hydraulic pump 6 is constant both when it is adjusted to the second opening and when it is adjusted to the third opening, which is smaller than the second opening, the amount of hydraulic oil flowing into the bypass line 20 will be greater when it is adjusted to the second opening than when it is adjusted to the third opening, and the amount of hydraulic oil used to operate the work tool 8 will be less.

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.

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

As a result, while the work tool 8 is in operation, a constant amount of hydraulic oil can be supplied to the work tool 8 regardless of the opening of the bypass valve 26 (whether it is the second opening or the third opening), allowing the work tool 8 to stably exert its capabilities. In addition, the second opening can be increased without impairing the capabilities of the work tool 8, increasing the amount of hydraulic oil flowing into the bypass line 20, allowing the hydraulic oil to be cooled more effectively.

The discharge volume 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.

As described above, the hydraulic circuit 2 in the illustrated embodiment includes a 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 surge pressure occurs when the work tool 8 is used.

The hydraulic circuit 2 also includes a controller 14 that adjusts the opening of the bypass valve 26 to a first opening when the work tool operating device 10 is not being operated, and adjusts the opening of the bypass valve 26 to a second opening that is smaller than the first opening and is not fully closed when the work tool operating device 10 is being operated. 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.

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

Claims (4)

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. 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. 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. 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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