JP2511165Y2 - Relief pressure control device for power shovel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a device for controlling relief pressure in a hydraulic circuit of a power shovel.

[Conventional technology]

Hoisting work is performed at the power shovel. At this time, the arm and bucket of the work machine of the power shovel are fixed at fixed positions, and the drive control is performed so that only the boom rises. Although heavy loads are often lifted during lifting work, if the pressure in the hydraulic circuit remains low enough for normal excavation work, it is not suitable for lifting heavy loads, and work efficiency decreases. Invite.

Therefore, in the past, a heavy lift switch was provided, and when lifting work was performed and the boom was raised, this switch was turned on to increase the set relief pressure of the relief valve arranged in the hydraulic circuit, and to increase the pressure in the hydraulic circuit. It was at high pressure.

[Problems to be solved by the device]

However, during the excavation operation, not only the arm or bucket but also the boom is often driven together. For this reason, if the boom is raised and the heavy lift switch is still turned on, the pressure in the hydraulic circuit becomes high even during excavation work. For this reason, the load on the working machine becomes severe and each part of the hydraulic circuit is frequently exposed to high pressure, which causes deterioration of durability of the hydraulic equipment.

The present invention has been made in view of these circumstances,
An object of the present invention is to provide a device capable of increasing the pressure in the hydraulic circuit only during the lifting operation to eliminate the above inconvenience.

[Means for solving the problem]

Therefore, in the present invention, in the power shovel for operating the boom, the arm and the bucket by supplying the pressure oil discharged from the hydraulic pump to the actuator that drives the boom, the arm and the bucket via the working machine hydraulic circuit, the working machine hydraulic circuit is used. A variable relief valve that variably sets the internal pressure in two stages, high and low, detection means for detecting the operating states of the boom, arm, and bucket, respectively, and the detection means fixes the arm and bucket at fixed positions. In addition, when it is detected that the boom is rising, the variable relief valve is changed so that the pressure in the working machine hydraulic circuit becomes high.

[Action]

That is, according to such a configuration, when the arm or bucket of the work machine is operating, the set relief pressure of the relief valve is maintained at a low pressure even if the boom is driven to move upward. When the arm and bucket of the work machine are fixed at a fixed position and only the boom is driven to rise, the relief pressure set by the relief valve is maintained at a high pressure. As described above, the pressure in the hydraulic circuit is increased only during the lifting operation in which only the boom is operated.

〔Example〕

An embodiment of a relief pressure control device for a power shovel according to the present invention will be described below with reference to the drawings. The drawings conceptually show the configuration of the embodiment apparatus.

In the figure, the variable displacement hydraulic pump 1 is driven by an engine (not shown), and the discharge flow rate per rotation is changed by changing the tilt angle of the swash plate. The pressure oil discharged from the hydraulic pump 1 is supplied to the working machine hydraulic circuit 2. In the hydraulic circuit 2, the hydraulic fluid discharged from the hydraulic pump 1 is supplied to a manually operated valve (not shown), and is supplied to the cylinder chamber of the hydraulic cylinder 3 that drives the boom via the manually operated valve. As a result, the hydraulic cylinder 3 is driven and the boom operates. A variable relief valve 4 for holding the hydraulic pressure of the circuit 2 at a predetermined relief pressure is arranged at a predetermined position of the pipeline of the working machine hydraulic circuit 2. This variable relief valve 4 has two stages of high and low set relief pressures (for example, 360 kg / cm ² and 320 kg / c depending on the size of pilot pressure oil applied through the pilot passage 5).
m ² ). The pilot passage 5 is a pressure oil supply passage that connects the discharge side of the control pump 7 driven by the engine and the variable relief valve 4 via an electromagnetic switching valve 6 described later. Pilot passage 5
When the pilot pressure is not set at 1, the relief pressure of the variable relief valve 4 is set to low pressure (320 kg / cm ² ).
On the other hand, when the pilot pressure is rising in the pilot passage 5, the relief pressure of the variable relief valve 4 is high (360 k
g / cm ² ).

On the other hand, a heavy lift switch 8 is provided in, for example, the cab of the power shovel. This switch 8 is a switch operated when it is desired to lift a heavy load during a lifting operation. Further, a pressure switch 9 for detecting the pressure in the compression side cylinder chamber is arranged in the compression side cylinder chamber (boom rising direction) of the hydraulic cylinder 3 for driving the boom. The pressure switch 9 is turned on when the detected pressure exceeds a predetermined value. Here, the predetermined value is a threshold value for determining whether or not the boom is rising. When the pressure switch 9 is in the off state, the line 15 connecting the battery 12 and the terminal 14a of the relay 14 which will be described later is in an electrically disconnected state, and when the switch 9 is in the on state, the line 15 is in the conducting state and the voltage of the battery 12 is Applied to terminal 14a.

Pressure switches 10 and 11 similar to the pressure switch 9 are arranged in the cylinder chamber of the hydraulic cylinder that drives the arm and the cylinder chamber of the hydraulic cylinder that drives the bucket, respectively. It is turned on by detecting that each is operating. These switches 10 and 11 are arranged in parallel with the line 16 connecting the battery 13 and the coil 14d for energizing the relay 14, and when at least one of the switches 10 and 11 is turned on, the line 16 is brought into conduction, A current is passed through the coil 14d to energize the relay 14. The relay 14 connects the terminal 14b of the electric cable 17 connected to the solenoid of the electromagnetic switching valve 6 to the terminal 14a of the line 15 or the terminal 14b.
It is a relay that is switched and connected to 14c, and when the coil 14d is not energized and is in a deenergized state, the terminal 14b is connected to the terminal 14a, and when the coil 14d is energized and is in an energized state. The terminal 14b is connected to the terminal 14c.

To explain the operation of this configuration, it is assumed that the heavy lift switch 8 is still turned on. At this time, when the operator operates the arm or bucket with the predetermined operation lever and the boom is moved up (during excavation work), the pressure switches 10, 11
Is turned on. Therefore, a current flows from the battery 13 to the coil 14d, and the relay 14 is energized. Therefore, the terminal 14b is connected to the terminal 14c, no voltage is applied to the solenoid of the electromagnetic switching valve 6 through the electric cable 17, the solenoid is deenergized, and the switching position of the switching valve 6 is biased by the spring. The position where the pilot passage 5 is closed is set. Therefore, the discharge pressure oil is not supplied from the control pump 7 to the variable relief valve 4. Since the pilot pressure oil is not added to the variable relief valve 4, the relief pressure of the hydraulic circuit 2 is changed to a low pressure.

Therefore, even during the excavation work, even if the heavy lift switch is turned on, the hydraulic circuit 2 can be operated at a low pressure, the work machine is optimally driven, the load is prevented from increasing, and the hydraulic equipment is durable. It is possible to improve the sex.

On the other hand, the operator turns on the heavy lift switch 8 when he / she wants to perform the hanging work. During the hanging operation, the arm and the bucket are fixed to the normal position by a predetermined operation lever and the boom is operated so as to rise. As a result, both the pressure switches 10 and 11 are turned off. Therefore, no current flows from the battery 13 to the coil 14d, and the relay 14 is deenergized. As a result, terminal 14b becomes terminal 1
Connected to 4a.

On the other hand, the pressure switch 9 detects that the boom is rising, and the switch 9 is turned on. Since the heavy lift switch 8 is also turned on, the battery 12 to the terminal 14
a, and the terminal 14b connected to it, the electrical cable
A voltage is applied to the solenoid of the solenoid operated directional control valve 6 via 17. Therefore, the solenoid is urged to overcome the urging force of the spring, and the switching position of the switching valve 6 becomes the position for opening the pilot passage 5. Therefore, the discharge pressure oil is supplied from the control pump 7 to the variable relief valve 4. Since pilot pressure oil is added to the variable relief valve 4, the relief pressure of the hydraulic circuit 2 is changed to a high pressure.

Therefore, during the lifting operation, the hydraulic circuit 2 can be operated at a high pressure, and the boom is preferably driven to lift a heavy load. In the embodiment described above, the arm and the bucket are fixed at fixed positions,
When it is detected that the boom is rising, it is judged that the lifting operation is being performed, and the hydraulic circuit 2 is being pressurized. However, the present invention is not limited to the lifting operation, and the arm and the bucket are not fixed. Applicable if the work is fixed in position and the boom is under load. That is, when the arm and the bucket are fixed at fixed positions and it is detected that the boom is operating, the hydraulic circuit 2 can be set to a high pressure.

As described above, according to the embodiment, the pressure of the hydraulic circuit 2 becomes high only when the arm and the bucket are fixed at the fixed positions and only the boom is raised, so that the load on the working machine is reduced. As a result, each part of the hydraulic circuit is not frequently exposed to high pressure. As a result, the durability of hydraulic equipment is improved.

[Effect of device]

As described above, according to the present invention, the boosting of the hydraulic circuit is canceled during the normal excavation work, and the hydraulic circuit becomes a high pressure only during the lifting work. Each part is not frequently exposed to high pressure, and the durability of hydraulic equipment is greatly improved.

[Brief description of drawings]

1 is a view conceptually showing the configuration of an embodiment of a relief pressure control device for a power shovel according to the present invention. 1 ... Variable displacement hydraulic pump, 2 ... Working machine hydraulic circuit,
3 ... Boom hydraulic cylinder, 4 ... Variable relief valve, 5 ... Pilot passage, 6 ... Electromagnetic switching valve, 7 ...
… Control pump, 8 …… Heavy lift switch,
9, 10, 11 ... Pressure switch, 12, 13 ... Battery, 14
……relay.

Claims (1)

(57) [Scope of utility model registration request] 1. A power shovel for operating a boom, an arm and a bucket by supplying pressure oil discharged from a hydraulic pump to an actuator for driving the boom, the arm and the bucket via a working machine hydraulic circuit. A variable relief valve that variably sets the pressure in the circuit in two stages, high and low, a switch that selects the high pressure side of the set pressure of the variable relief valve, and detects the operating states of the boom, arm, and bucket, respectively. And a switch for selecting a high-pressure side set pressure, and the detecting means for fixing the arm and bucket to a fixed position and detecting that the boom is operating, the working machine. A means for changing the variable relief valve so that the pressure in the hydraulic circuit becomes high. Excavators relief pressure control device.