JP3681549B2 - Hydraulic circuit for boom cylinder of hydraulic excavator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic circuit for a boom cylinder of a hydraulic excavator, and more particularly, to a hydraulic circuit for a boom cylinder of a hydraulic excavator that has improved safety when the engine is started in a vehicle body lifted state.
[0002]
[Prior art]
Japanese Unexamined Patent Publication No. 8-68078 discloses a hydraulic circuit for a boom cylinder of a hydraulic excavator according to the prior art. An outline of the circuit is shown in FIG.
[0003]
In the figure, 1 is an engine that drives a hydraulic pump 2 and an auxiliary hydraulic pump 7, 2 is a hydraulic pump that supplies pressure oil to a boom cylinder hydraulic circuit, and 3 is a switch that supplies oil discharged from the hydraulic pump 2 to a boom cylinder 4. The direction switching valve 4 is a boom cylinder for driving a boom (not shown) of the hydraulic excavator, and 5 is for controlling the maximum value of the hydraulic pressure in the rod side oil chamber 41 of the boom cylinder 4 and is normally set on the high pressure side and set pressure. A relief valve that is set to the low pressure side when pressure oil is supplied to the oil chamber 131 of the variable portion 13, 6 is a relief valve that controls the maximum value of the hydraulic pressure in the bottom side oil chamber 42 of the boom cylinder 4, and 7 is a relief valve. 5 is an auxiliary hydraulic pump that supplies pressure oil to the oil chamber 131 of the set pressure variable section 13 via the electromagnetic switching valve 9, 8 is a relief valve that controls the discharge pressure of the auxiliary hydraulic pump 7, and 9 is a control In accordance with a command signal from the device 10, an electromagnetic switching valve for switching the supply or outflow of the pressure oil to or from the oil chamber 131 of the set pressure variable unit 10 is based on signals from the set pressure switch 11 and the direction switching valve operation detection unit 12 The control device 11 that outputs a switching signal to the electromagnetic switching valve 9 outputs a command signal for switching the relief set pressure to the low pressure side when closed, and the relief set pressure to high pressure when opened. A set pressure changeover switch 12 for outputting is a direction for detecting that the direction changeover valve 3 has been switched to a contraction side position 31 for operating the rod of the boom cylinder 4 to the contraction side or an expansion side position 33 for operating the rod to the expansion side. A switching valve operation detecting unit, 13 is provided with an oil chamber 131, and a set pressure variable unit for controlling the set pressure of the relief valve 5 to high pressure or low pressure, 14 is a boom cylinder A rod-side hydraulic circuit between the rod-side oil chamber 41 and the directional control valve 3.
[0004]
This boom cylinder hydraulic circuit is instructed to switch the relief set pressure of the relief valve 5 to a low pressure by the set pressure changeover switch 11 during excavation work, and the direction changeover valve operation detector 12 is on the contraction side of the direction changeover valve 3. When it is detected that the position has been switched to the position 31 or the extension side position 33, a switching signal is output from the control device 10 to the electromagnetic switching valve 9, and the electromagnetic switching valve 9 is supplied from the auxiliary hydraulic pump 7 to the oil chamber 131 of the set pressure variable unit 13. Switch to the pressure oil supply side. As a result, since the relief set pressure of the relief valve 5 is switched to a low pressure, the hydraulic pressure in the rod side oil chamber 41 of the boom cylinder 4 can only rise to the relief set pressure that is the low pressure of the relief valve 5, and a large excavation force is generated. When acted on, the boom swings upward, and a bucket (not shown) can be automatically moved upward, so that it is not necessary to operate the bucket upward by an operator operation when the excavation load is large. On the other hand, when the command for switching the relief valve 5 to the high pressure side is output by the set pressure switching switch 11, a switching signal is output from the control device 10 to the electromagnetic switching valve 9. It switches to the side where pressure oil flows out from the oil chamber 131 to the tank. As a result, the relief set pressure of the relief valve 5 becomes high, so that the oil pressure in the rod side oil chamber 41 of the boom cylinder 4 can be increased and the vehicle body can be lifted. A strong excavation force can also be obtained. Further, when the direction switching valve 3 is switched to the neutral position 32 while the vehicle body is lifted, the direction switching valve operation detecting unit is operated even if the set pressure switching switch 11 is operated to switch the relief valve 5 to the low relief set pressure. 12 does not detect the contraction side position 31 or the expansion side position 33 of the direction switching valve 3, so the signal for switching to the low pressure side is not output from the control device 10, so the electromagnetic switching valve 9 is not switched and the relief valve 5 is relieved. The set pressure is maintained at a high level, and the vehicle body is held in a lifted state.
[0005]
[Problems to be solved by the invention]
However, the above prior art is operated so that the relief set pressure of the relief valve 5 is switched to the low pressure side by the set pressure changeover switch 11 for some reason when the engine 1 is stopped and the vehicle body is lifted. After that, when the engine 1 is started and the operation lever is positioned at the contraction side position 31 or the expansion side position 33 of the direction switching valve 3 by the operation of the operator, the vehicle body falls unintentionally. In such a case, it is very dangerous if there are people around the excavator.
[0006]
In view of the above problems, an object of the present invention is to start an engine in a state where the relief set pressure is switched from a stopped state of the engine to a low pressure side in a state where the vehicle body is lifted, and an operator It is an object of the present invention to provide a hydraulic circuit for a boom cylinder of a hydraulic excavator that does not unintentionally drop the vehicle body even when operation is started.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention employs the following means.
[0008]
A boom cylinder having a rod-side oil chamber and a bottom-side oil chamber, and swinging a boom of a hydraulic excavator up and down; a direction switching valve for switching and supplying discharge oil of a hydraulic pump driven by an engine to the boom cylinder; A relief valve capable of switching a relief set pressure between a high pressure and a low pressure in a rod side hydraulic circuit connecting the rod side oil chamber and the direction switching valve; and the relief set of the relief valve which has been switched to the high pressure when the engine is stopped. In a boom cylinder hydraulic circuit of a hydraulic excavator provided with a switching control means capable of switching the pressure to the low pressure side after the engine is driven, the switching control means is provided with a switch means for switching to the high pressure side or the low pressure side. In addition, switching prevention for preventing switching of the switch means to the low pressure side when the engine is stopped. Characterized in that a stage.
[0009]
2. The boom cylinder hydraulic circuit for a hydraulic excavator according to claim 1, wherein the switching control means includes at least an auxiliary hydraulic pump driven by the engine and a discharge oil of the auxiliary hydraulic pump provided in the relief valve. A set pressure variable portion that switches the relief set pressure to the low pressure side, and a switching valve that is provided between the auxiliary hydraulic pump and the set pressure variable portion to supply or discharge pressure oil to the set pressure variable portion And a control unit for outputting a switching signal for switching the relief set pressure to the high pressure or the low pressure to the switching valve by a switching command on the high pressure side or the low pressure side from the switch means when the engine is driven. It is characterized by that.
[0010]
Further, in the boom cylinder hydraulic circuit for a hydraulic excavator according to any one of claims 1 to 2, the switching prevention means detects a driving state of the engine, and the engine is driven. The switching prevention function is canceled when the engine is stopped, and the switching prevention function is exhibited when the engine is stopped.
[0011]
Further, in the boom cylinder hydraulic circuit of the hydraulic excavator according to claim 2, the switching prevention means detects a discharge pressure of the auxiliary hydraulic pump, and releases the switching prevention function when the discharge pressure is high, The switching prevention function is exhibited when the discharge pressure is low.
[0012]
A directional switching valve that switches and supplies discharge oil of a hydraulic pump driven by an engine to a rod side oil chamber and a bottom side oil chamber of a boom cylinder that swings a boom of a hydraulic excavator up and down; and the rod side oil chamber wherein the directional control valve switchable relief set pressure to a high pressure or low pressure to the rod side hydraulic circuit which connects a relief valve, the relief set pressure of the relief valve has been switched to the high pressure when the engine is stopped, engine driven In a hydraulic circuit for a boom cylinder of a hydraulic excavator provided with a switching control means that can be switched to the low pressure side later, switch means for switching the high pressure side and the low pressure side to the switching control means, and when the engine is started The engine start detecting means for detecting the engine and the switch means are switched to the low pressure side when the engine is started. When that has been gills is characterized in that a switching means switching means for switching said switch means to said high-pressure side.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
First, a first embodiment of the present invention will be described with reference to FIG.
[0014]
FIG. 1 is a diagram illustrating a configuration of a boom cylinder hydraulic circuit of a hydraulic excavator according to the present embodiment.
[0015]
In the figure, 15 is a generator driven by the engine 1 and generates an induced voltage during engine rotation, and 16 includes a solenoid 162 that is excited by the induced voltage of the generator 15, and the set pressure changeover switch 11 when the engine is stopped. Is an electric switch release means for fixing the switch to the high pressure side (open side) and making it impossible to switch to the low pressure side (closed side), 161 is an upper spring, 162 is a solenoid, and 163 is a pressing portion.
[0016]
Other configurations are the same as those shown in FIG.
[0017]
The operation of the boom cylinder hydraulic circuit according to this embodiment will be described with reference to FIG.
[0018]
Here, when the control device 10 is instructed to (1) switch the relief set pressure to the low pressure side by the set pressure switch 11, (2) the direction switch valve operation detector 12 operates the direction switch valve 3. Thus, when it is detected that it is at the contraction side position 31 or the expansion side position 33, a switching signal is output to the electromagnetic switching valve 9 so as to switch to a low pressure relief set pressure.
[0019]
First, when the engine 1 is stopped, since the generator 15 does not output an induced voltage, the solenoid 162 of the electric switch release means 16 is not excited, and the upper spring 16 moves the pressing portion 163 downward in the figure to switch the set pressure. The switch 11 is fixed to the open side, that is, the high voltage side. In this state, for example, even if the set pressure changeover switch 11 is erroneously switched to the low pressure side, it will not be switched. Next, even if the engine 1 is started and the operator operates the operation lever, the set pressure changeover switch 11 is open, that is, on the high pressure side at this time, and the set pressure of the relief valve 5 is maintained at a high pressure. Even if the car body is lifted up, there will be no unintentional fall of the car body. Further, when the engine 1 is started, the solenoid 162 is excited by the induced voltage of the generator 15, so that the pressing portion 163 moves upward in the figure against the upper spring 161, and the set pressure changeover switch 11 is closed. That is, it becomes possible to switch to the low pressure side. Therefore, after that, if the operator switches the set pressure changeover switch 11 to the closed side, that is, the low pressure side, the set pressure of the relief valve 5 is switched to the low pressure side, and the vehicle body is lifted during work that does not require high digging force. Work can be done without
[0020]
Thus, according to the present embodiment, when the engine 1 is stopped, the set pressure changeover switch 11 cannot be switched to the low pressure side, so the engine 1 is started and the operator operates the operation lever. However, at that time, the set pressure changeover switch 11 is open, that is, on the high pressure side, and the set pressure is maintained at a high pressure, so that there is no inadvertent drop of the vehicle body.
[0021]
Next, a second embodiment of the present invention will be described with reference to FIG.
[0022]
FIG. 2 is a diagram showing a configuration of a hydraulic circuit for a boom cylinder of the hydraulic excavator according to the present embodiment.
[0023]
In the figure, 17 has a piston 172 that is pressed by the discharge oil guided from the auxiliary hydraulic pump 7 to the opposite side of the upper spring 171 chamber, and when the engine is stopped, the set pressure changeover switch 11 is set to the high pressure side (open side). A hydraulic switch release means that is fixed and cannot be switched to the low pressure side (closed side), 171 is an upper spring, 172 is a piston, and 173 is a pressing portion.
[0024]
This embodiment is different in that a hydraulic switch release means is used instead of the electric switch release means of the first embodiment, and the other configuration is substantially the same as that shown in FIG. To do.
[0025]
The operation of the boom cylinder hydraulic circuit according to this embodiment will be described with reference to FIG.
[0026]
The control device 10 of this embodiment has the same function as the control device 10 of the first embodiment. When the engine 1 is stopped, the discharge pressure of the auxiliary hydraulic pump 7 is low, and the piston 172 is pushed by the upper spring 171 and moves downward in the figure, so the set pressure changeover switch 11 is open, that is, on the high pressure side. The set pressure of the relief valve 5 is kept high. Therefore, the vehicle body does not fall when the vehicle body is lifted. When the engine 1 is started, the piston 172 moves upward in the figure against the upper spring 171 by the discharge oil of the auxiliary hydraulic pump 7, and the pressing portion 173 also moves upward accordingly, so the set pressure changeover switch 11 is closed. It becomes possible to switch to the formation side, that is, the low pressure side. Therefore, after that, if the operator switches the set pressure changeover switch 11 to the closed side, that is, the low pressure side, as in the first embodiment, the work can be performed without lifting the vehicle body when the work does not require high digging force. It can be performed.
[0027]
As described above, this embodiment can achieve the same effects as those of the first embodiment.
[0028]
Next, a third embodiment of the present invention will be described with reference to FIGS.
[0029]
FIG. 3 is a diagram illustrating a configuration of a boom cylinder hydraulic circuit of the hydraulic excavator according to the present embodiment.
[0030]
In the same figure, 18 is an engine drive state detection means capable of detecting each of the start, drive, and stop states of the engine 1, 19 is a set pressure changeover switch 11, a direction switching valve operation detector 12 and an engine drive state detection. A control device 20 that outputs a switching signal to the electromagnetic switching valve 9 based on each signal from the means 18, and a set pressure switch 20 that receives a command from the control device 19 switches the set pressure switch 11 from the low pressure side to the high pressure side. Switch switching means.
[0031]
In this embodiment, instead of the electrical switch release means of the first embodiment and the hydraulic switch release means of the second embodiment, the set pressure changeover switch 11 is switched to the low pressure side when the engine is started. Is different in that a set pressure changeover switch switching means forcibly switching to the high pressure side is provided, and the other configuration is substantially the same as that shown in FIG.
[0032]
FIG. 4 is a flowchart showing a processing procedure in the control means 19.
[0033]
Next, the operation of the boom cylinder hydraulic circuit according to this embodiment will be described with reference to FIGS. 3 and 4.
[0034]
First, when the engine 1 is started from the stop state of the engine 1, the start of the engine 1 is detected by the engine drive state detection means 18 in step 1, and in step 2, the set pressure changeover switch 11 sets the relief set pressure to the high pressure side. When it is determined that the valve is open so as to command the operation, the process proceeds to step 5 where the control device 19 continuously outputs a switching signal for switching the relief set pressure to the high pressure side with respect to the electromagnetic switching valve 9. do. If NO in step 2, it is determined in step 3 whether or not the set pressure changeover switch 11 is set to switch the relief set pressure to the low pressure side (closed side). The set pressure changeover switch 11 is forcibly switched to the open side to bring the relief set pressure to the high pressure side with respect to the set pressure changeover switch 11. After the determination in step 2 again, the process proceeds to step 5 and a switching signal for switching the relief set pressure to the high pressure side is continuously output from the control device 19 to the electromagnetic switching valve 9. Here, by performing the processing of step 3 and step 4, even if the set pressure changeover switch 11 is accidentally closed so as to command the relief set pressure to the low pressure side when the engine 1 is stopped, it is forcibly opened. It is possible to prevent the low-pressure side command from being output.
[0035]
Further, when the engine 1 is stopped, in step 6, the engine drive state detection means 18 detects the state, and the processing of step 2 to step 4 is executed in the same manner as when the engine start of step 1 is detected. In step 5, the control device 19 outputs a switching signal for switching the relief set pressure to the high pressure side to the electromagnetic switching valve 9.
[0036]
When the engine 1 is being driven, if the engine drive state detector 18 detects that the engine 1 is being driven in step 7, the direction switching valve 3 is further controlled in step 8 by operating the operation lever. When the direction switching valve operation detecting unit 12 detects the contraction side position 31 or the expansion side position 33 of the direction switching valve 3, the set pressure changeover switch 11 further instructs the relief set pressure to the high pressure side in step 9. In the case of YES, the process proceeds to step 5, and a switching signal for switching the relief set pressure to the high pressure side is output from the control device 19 to the electromagnetic switching valve 9. If NO in step 9, it is determined in step 10 whether the set pressure changeover switch 11 is closed so as to command the relief set pressure to the low pressure side. If YES, in step 11, the control device 19 A switching signal for switching the relief set pressure to the low pressure side is output to the electromagnetic switching valve 9. By the processing of Step 10 and Step 11, the work efficiency can be improved without lifting the vehicle body at the time of work that does not require high excavation force.
[0037]
Further, according to the present embodiment, the engine 1 is started in a state in which the set pressure changeover switch 11 is operated so that the relief set pressure is switched to the low pressure side from the stopped state of the engine 1 with the vehicle body lifted. Even so, the set pressure changeover switch 11 is controlled to detect the start of the engine 1 and forcibly switch the relief set pressure to the high pressure side, so that the vehicle body falls even if the operator operates the operation lever. Can be prevented.
[0038]
【The invention's effect】
As described above, according to the present invention, the switching control means is provided with the switch means for switching the relief set pressure between the high pressure and the low pressure, and the switching prevention means for preventing the switch means from being switched to the low pressure side when the engine is stopped. Therefore, when the vehicle body is lifted up, the engine is started in a state where the switch means is operated to switch to the low pressure side from the engine stop state, and the vehicle body is inadvertent even if the operator operates the operation lever. Can be prevented from falling.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a hydraulic circuit for a boom cylinder of a hydraulic excavator according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a boom cylinder hydraulic circuit of a hydraulic excavator according to a second embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of a hydraulic circuit for a boom cylinder of a hydraulic excavator according to a third embodiment of the present invention.
4 is a flowchart showing a processing procedure in the control device 19 shown in FIG. 3;
FIG. 5 is a diagram illustrating a configuration of a hydraulic circuit for a boom cylinder of a hydraulic excavator according to a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 2 Hydraulic pump 3 Directional switching valve 4 Boom cylinder 5 Relief valve 7 Auxiliary hydraulic pump 9 Electromagnetic switching valve 10 Controller 11 Set pressure switching switch 12 Directional switching valve operation detection unit 13 Set pressure variable unit 14 Rod side hydraulic circuit 15 Power generation Machine 16 Electric switch release means 17 Hydraulic switch release means 18 Engine drive state detection means 19 Control device

Claims (5)

A boom cylinder having a rod-side oil chamber and a bottom-side oil chamber, and swinging a boom of a hydraulic excavator up and down; a direction switching valve for switching and supplying discharge oil of a hydraulic pump driven by an engine to the boom cylinder; A relief valve capable of switching a relief set pressure between a high pressure and a low pressure in a rod side hydraulic circuit connecting the rod side oil chamber and the direction switching valve; and the relief set of the relief valve which has been switched to the high pressure when the engine is stopped. In a hydraulic circuit for a boom cylinder of a hydraulic excavator provided with switching control means capable of switching the pressure to the low pressure side after the engine is driven,
The switching control means is provided with switching means for switching to the high pressure side or the low pressure side, and switching prevention means for preventing switching of the switching means to the low pressure side when the engine is stopped. Hydraulic circuit for excavator boom cylinder. In the description of claim 1,
The switching control means includes at least an auxiliary hydraulic pump driven by the engine, and a set pressure variable unit that is provided in the relief valve and switches the relief set pressure to the low pressure when the discharge oil of the auxiliary hydraulic pump is supplied. A switching valve provided between the auxiliary hydraulic pump and the set pressure variable section for supplying or discharging pressure oil to the set pressure variable section, and a switching command of the high pressure or the low pressure from the switch means when the engine is driven. A boom cylinder hydraulic circuit for a hydraulic excavator, wherein the switching valve is provided with a control unit that outputs a switching signal for switching the relief set pressure to the high pressure side or the low pressure side. In any one of claims 1 to 2,
The switching prevention means detects a driving state of the engine, releases the switching prevention function when the engine is driven, and exhibits the switching prevention function when the engine is stopped. A hydraulic circuit for a boom cylinder of a hydraulic excavator. In the description of claim 2,
The switching prevention means detects a discharge pressure of the auxiliary hydraulic pump, releases the switching prevention function when the discharge pressure is higher than a predetermined pressure, and releases the switching prevention function when the discharge pressure is lower than the predetermined pressure. A hydraulic circuit for a boom cylinder of a hydraulic excavator characterized by exhibiting A direction switching valve that switches and supplies discharge oil of a hydraulic pump driven by an engine to a rod side oil chamber and a bottom side oil chamber of a boom cylinder that swings a boom of a hydraulic excavator up and down; the rod side oil chamber; A relief valve capable of switching the relief set pressure between a high pressure and a low pressure in a rod side hydraulic circuit connected to the direction switching valve, and the relief set pressure of the relief valve that has been switched to the high pressure when the engine is stopped after the engine is driven . In the hydraulic circuit for a boom cylinder of a hydraulic excavator provided with a switching control means switchable to the low pressure side,
The switching control means includes a switching means for switching to the high pressure side or the low pressure side, an engine start detection means for detecting when the engine is started, and the switch means is switched to the low pressure side when the engine is started. And a switch means switching means for switching the switch means to the high pressure side.

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