JPS5874902A - Hydraulic circuit for working machine - Google Patents

Abstract

PURPOSE:To protect a front member from damage, by restricting the pressurized oil for a bucket cylinder depending on a signal of detection of relative position of a boom and an arm to limit the load upon the front member. CONSTITUTION:A directional control valve 11 is shifted by operating a control lever 14, to connect a hydraulic pump 12 and an oil tank 13 to a hydraulic circuit to supply cylinders with pressurized oil to drive a front section. The maximum pressure of the pressurized oil for the cylinders is limited by overload relief valves 23. A signal from a signal generator 19 is applied through a switch 18 to an overload relief valve 20 at the bottom side of a bucket cylinder 6 to set relief pressure. When an arm cylinder 4 is driven to the most contracted state, the switch 18 is shifted by the output of an arm angle detector 21 so that the relief pressure for the overload relief valve 20 is set by the output of a function generator 16.

Description

[Detailed Description of the Invention] This invention includes a plurality of cylinders connected to a hydraulic pump,
The present invention relates to a hydraulic circuit for a working machine, including a pressure control means for setting a maximum pressure in a hydraulic conduit.

For example, a hydraulic excavator with a loader front equipped with a conventional pressure control means is shown in FIGS. 1 to 6. Fig. 1 is a characteristic diagram, Fig. 2 is a side view showing the state of the front part of the excavator at the end of the stroke on the most retracted side of the am cylinder, and Fig. 3 is a schematic side view of the entire hydraulic excavator and the diagram for driving the front part. A hydraulic circuit diagram is shown. First, the configuration of the hydraulic excavator will be explained based on FIGS. 2 and 3. Reference numeral 1 is a part of the front section, which is connected to a frame 9 described later, and is driven by a boom cylinder 2 described below. is connected to the boom 1 and the frame 9 described later,
A boom cylinder 3 is connected to the boom 1 and a bucket (bucket) 6, which will be described later, and is driven by the operation of a control lever 14, which will be described later.
The arm driven by the arm cylinder 4 below, the above 4
is connected to boom 1 and arm λ, and operated as described below...-1
The arm cylinder is driven by the operation of 4, the above 5 is connected to the arm 3, and the packet is driven by the below packet cylinder 6 via the boom cylinder 2, arm cylinder 4, link 7. A packet cylinder which connects 1 and packet 5 and is driven by the operation of a control lever 14 which will be described later; 7 is a link which connects arm 6 and packet cylinder 6 and link 8 below; 8 is a link between packet 5, packet cylinder 6 and link There are 5 links connecting 7. Then, 9 connects the poom 1 and the poom cylinder 2, and swings to the top of the track 10 below.

The frame 10 can be attached to the frame 9, indicating a track connected to the frame 9 for running motion. Next, the configuration of the hydraulic circuit will be explained with reference to FIG. There are two.

One of the directional control valves 11 switches the flow direction of the pressure oil supplied to the arm cylinder 4 by the hydraulic pump 12 that generates supply pressure oil by operating one of the two operating levers 14. 13 is the hydraulic pump 12
15 is an IJ valve that sets the maximum pressure of the supply pressure oil generated by the hydraulic pump 12;
3 is an overload relief valve that sets the overload relief pressure of the arm cylinder 4, respectively. The remaining one of the directional control valves 11 is a hydraulic pump 1 different from the above.
2 is used to switch the flow direction of the pressure oil supplied to the bucket cylinder B by going up an operation lever 14 different from the above, and the above and another 23 are respectively connected to the packet cylinder 6.
13 and 15 are an oil tank and a relief valve provided separately from the above, respectively, and the connection of these parts is the same as the connection explained for the arm cylinder 4 above. is the same as

Since the above-mentioned conventional type is configured in this way, when each cylinder is not at the end of its stroke at the front of the loader, the pressure supplied to each cylinder acts to limit the load. Alternatively, each cylinder is hydraulically limited by the overload relief pressure of the force it receives as a cylinder reaction force, so each cylinder and each front member must be designed for strength under the relief pressure or overload relief pressure conditions. It had been done. However, at the front of the loader, when the arm cylinder 4 attempts to excavate at the stroke end on the forging side, that is, to perform front excavation, 5. A load larger than the limit load F1 (see FIG. 1) may be applied to the arm cylinder 4 and the arm 3.

In other words, in FIG. 1, even if the set value of the keratin relief pressure P is changed as shown in P1, P2, P3 (P, >P2>P3), A load much larger than the limit load F1 is applied to the arm cylinder 4.The same is true at the end of the stroke on the arm cylinder weight line side (at the hydraulic pressure point bell) (at the Tsukuho front).

As mentioned above, with conventional front excavators, when working in the limited front position of the stroke end of the cylinder, each part of the front has a relief pressure that is limited by the hydraulic circuit, an overload, and a pressure that exceeds the relief pressure. Due to the force applied, there is a problem that either the front member lacks strength or the front part must be designed to have the strength to withstand this force, ignoring economical considerations.

This invention was made for the purpose of solving the above-mentioned problems, and will be explained below based on the drawings. FIG. 4 shows a schematic side view of the entire hydraulic excavator that is the same as that shown in FIG. 3, and a hydraulic circuit diagram of an embodiment of the present invention. In addition, the same reference numerals are given to the middle part of each figure or equivalent parts.

First, only the points different from the conventional hydraulic circuit shown in FIG. 3 will be described regarding the hydraulic circuit. The point is that the circuit described below is connected to one of the two overflow 2 relief valves 26 of the packet cylinder 6.

That is, the packet angle detector 22, the function generator 16, and the amplifier 17 are connected to the B terminal of the electrical changeover switch 18.
The changeover switch 18 with the signal generator 19 connected to the A terminal is connected to the overload relief valve 20 connected to the bottom side of the packet cylinder 6.
This is connected to the switching setting value adjustment section. The packet angle detector 22 detects a packet angle that has a numerical relationship with the packet cylinder stroke and outputs a signal α3, and the function generator 16 receives this signal and has a functional relationship with this. Outputs signal VR. The amplifier 17 is
The signal generator 19 inputs the signal vR and outputs a signal IR2, and outputs a current signal IR1 for setting the relief pressure of the overload relief valve 2o to a predetermined value. Also, selector switch 18ti, arm angle detector 2
The arm angle detector 21 switches the A1B terminal by inputting the signal α output from 1. double signal,
This outputs the following.

Next, the effect will be explained. By operating the operating lever 14, the directional switching valve 11 is switched, and the hydraulic pump 12 is switched.
An oil tank 13 is connected to a hydraulic circuit and supplies pressure oil to each cylinder to drive the front section. The maximum pressure of the pressure oil applied to each cylinder is limited by an overload relief valve 23, and on the bottom side of the packet cylinder 6, an overload relief valve 20 passes the signal IR1 from the signal generator 19 to the changeover switch 18. The relief pressure is set by inputting through the A terminal. When the arm cylinder 4 is driven by operating the operating lever 14 and reaches the most retracted stroke end, the arm angle detector 21 outputs a signal α□ and switches the changeover switch 18 to the B terminal side. At this time, the overload relief valve 20 receives the signal 8 degrees from the changeover switch 18 and sets a relief pressure that changes with respect to the stroke position of the packet cylinder 6. The set relief pressure is arm cylinder forging side +1
In the case of stroke end, bucket cylinder.

The load applied to the front member depending on the position of the troller is
This is a value that does not exceed the limit load of the front member, and the arm cylinder 4 set as shown in the solid line in FIG. When the state of contraction side stroke end is released, arm angle detector 2
The signal α output from 1 becomes 0, and the “changeover switch 1
8 is switched to the A terminal again, and the relief pressure of the overload relief valve 20 becomes the value set by the signal generator 19. Note that the most retracted stroke end of the arm cylinder 4 can be directly detected by attaching a limit switch to the arm cylinder 4 instead of using the arm angle detector 21.

FIG. 5 shows another embodiment of the invention. In this example,
In the first embodiment shown in FIG. 4, when receiving the signal α from the arm angle detector 21 and switching the changeover switch 18 from the A terminal to the B terminal, the output signal α3 of the packet angle detector 22 is set as a function. Instead of receiving the signal vR from the generator 1.16 and outputting a signal vR having a functional relationship, inputting this signal to the amplifier 17JC and outputting the current signal IR2, a changeover switch 180 is used.
1. A signal generator 24 is connected to the B terminal. After the changeover switch 18 is switched from the A terminal to the B terminal, the relief pressure of the overload relief valve 20 is set to a predetermined value by the current signal R3 outputted from the signal generator 24. At this time, the relief pressure is set to a value that maintains the strength of the front member and does not cause insufficient digging force, for example, as shown by the solid line in Fig. 8, which shows an example of an overload relief pressure that is set according to the packet cylinder stroke. .

As described above, according to FIGS. 4 and 5, by changing the relief set pressure of the overload relief valve 20 according to the arm cylinder stroke end, the pressure oil applied to the cylinder 6 is restricted. However, front excavation can be performed within a range that does not exceed the strength of the front member.

Next, FIG. 6 shows a third embodiment. This is a circuit in which the following circuit is provided in place of the circuit of the hydraulic pump 12 and relief valve 15 of the directional control valves 1 and 11 in the conventional hydraulic circuit shown in FIG. That is, the variable hydraulic pump 29
and a cut-off valve 27 for setting the maximum oil pressure discharged by the variable hydraulic pump 29, based on the signal from the arm angle detector/small device 21.

a pressure reducing valve 28 having a changeover switch 18 that switches the output of the signal generator 25, an oil tank 13, and a hydraulic pump 26;
and connect the pressure reducing valve 28 to the cut-off valve 2.
This configuration is connected to a cylinder 30 that is connected to a cylinder 7.

Next, the effect will be explained. If the operating lever 14 is operated when the arm cylinder 4 is not at the stroke end on the dose line side, the directional control valve 11 is switched and the pressure oil discharged from the variable hydraulic pump 29 that generates supply pressure oil is supplied to the packet cylinder 6, A packet 5 not shown here is driven. The pressure oil discharged from the variable hydraulic pump 29 is limited by a cut-off valve 27 that sets the maximum pressure of the supply pressure oil discharged by the variable hydraulic pump 29, and when the discharge pressure becomes higher than the set pressure of the cut-off valve 27, The cutoff valve 27 is switched, and the pressure oil discharged from the hydraulic pump 26 that generates supply pressure oil is applied to the swash plate portion of the variable hydraulic pump 29, and the swash plate portion controls the discharge flow rate of the variable hydraulic pump 29. When the discharge pressure becomes equal to the set pressure of the cut-off valve 27, the cut-off valve 27 returns to its original position, the swash plate position becomes constant, and the discharge pressure of the variable hydraulic pump 29 reaches the set pressure of the cut-off valve. The pressure is maintained so as not to exceed the set pressure of 27. Next, when the stroke end of the arm cylinder forging side is reached, the arm angle detector 21 detects this and outputs a detection signal α. The changeover switch 18 is set by a signal generator 25 that receives the detection signal α□, switches the changeover switch 18 from the A terminal to the B terminal, and outputs a signal to reduce the pressure of the supply pressure oil discharged by the hydraulic pump 26. The pressure reducing valve 28 is driven by the signal (2). The pressure reducing valve 28 inputs the signal I and reduces the supply pressure of the hydraulic pump 26.
The supply pressure oil of the hydraulic pump 26 applied through the pressure reducing valve 28 is applied to the sill 30, lowering the set pressure of the cut-off valve 27 (r), and reducing the set pressure of the variable hydraulic pump 29.
Reduce the discharge pressure. At this time, the set pressure of the cut-off valve 27 set by the signal generator 25 is set to a value that maintains the strength of the front member and does not cause insufficient digging force when performing front excavation at the arm cylinder forging side stroke end. do. Note that the arm cylinder forging side stroke end can also be detected by attaching a limit switch to the arm cylinder 4. Also, in Fig. 6, the signal generator 2
5, the packet angle signal α3 having a functional relationship with the packet cylinder stroke is detected as shown in the first embodiment in FIG. The pressure oil applied to the packet cylinder 6 can also be restricted by changing the pressure oil according to the packet cylinder stroke position, reducing the pressure oil supplied to the hydraulic pump 26, and changing the set pressure of the cut-off valve 27. As explained above, according to FIG. 6, the cutoff valve 27 at the arm cylinder forging side stroke end
By changing the set pressure, the maximum discharge pressure of the variable hydraulic pump 29 is limited, and the pressure oil applied to the packet cylinder 6K is limited, so that front excavation can be performed within a range that does not exceed the strength of the front member.

Note that the means for limiting the pressure applied to the packet cylinder 6 is not limited to that shown in the above embodiment.

As explained above, this inventor has provided a detection means for detecting the relative position of the boom and the arm, and a subsidiary that limits the pressure oil applied to the packet cylinder based on the signal from the detection means. Since it is possible to limit the load applied to the front member during excavation in the cylinder forging side stroke end state, designers can economically design the strength of the front member under relief pressure or overload relief pressure conditions. Furthermore, even an inexperienced operator can easily perform excavation without considering damage to the front member.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the packet cylinder stroke and the load applied to the nano cylinder at the stroke end of the arm cylinder forging side, and Figure 2 is a characteristic diagram of the front part of the oil store excavator at the end of the stroke of the arm cylinder forging side. FIG. 3 is a side view schematically showing the entire hydraulic excavator according to the prior art and a hydraulic circuit diagram, and FIG. 4 is a side view schematically showing the entire hydraulic excavator same as that shown in FIG. A hydraulic circuit diagram of an embodiment of the invention, FIG.
Fig. 6 is a schematic side view of the entire hydraulic excavator and a hydraulic circuit diagram of a second embodiment of the present invention, and Fig. 6 is a hydraulic circuit diagram of a third embodiment of the invention. 7 and 8 are characteristic diagrams each showing an example of the overload relief pressure set according to the bucket cylinder stroke in the present invention. Explanation of symbols 1゛°boom 2...Boom cylinder 5.
...Arm 4...Arm cylinder 5...
・Bucket 6...Packet cylinder 7.8
... Link 9 ... Frame 10 ... Track 11 ... Directional control valve 12.26.29.
... Hydraulic pump 16 ... Oil tank 14 ... Operation lever 15
...IJ IJ-fu valve 16...Function generator 17
...Amplifier 18...Switching device 19.
24.25...Signal generator 20.26...Overload relief valve 21...Arm angle detector 22...Bucket angle detector 27...
Cut-off valve 28...Reducing valve 30...Cylinder Patent attorney Junnosuke Nakamura-1- IF5 diagram t3 Figure 1P4 Figure 1-5 Figure 1P6 diagram Off view? 8 figure straw 7

Claims (1)

[Claims] A boom cylinder that drives a boom, an arm cylinder that drives an arm, and a packet cylinder that drives a packet, which are connected to a hydraulic pump, and a pressure control means that sets a maximum pressure in a conduit connecting the packet cylinder and the hydraulic pump. In the hydraulic circuit of a work machine equipped with a hydraulic circuit, at least one signal generating device is connected to the pressure control means via a signal selection means, and the signal selection means detects the relative position of the boom and the arm. A hydraulic circuit for a working machine, characterized in that the signal from the signal generator is selected based on the signal from the detection means, and the signal is guided to the pressure control means.