JPH0320373Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a working machine hydraulic circuit for a construction machine equipped with a bucket.

In general, construction machines equipped with a bucket belt such as a dozer shovel are capable of leveling work such as dozing and back grading, and these operations are performed while moving the bucket up and down depending on the unevenness of the leveled surface. In addition, the hydraulic circuit of the above working machine is as follows:
Conventionally, a circuit shown in FIG. 1 has been adopted. That is, by supplying the hydraulic pressure discharged from the hydraulic pump a to the dump cylinder c via the dump operation valve b, the bucket can be dumped, and by supplying it to the lift cylinder e via the lift operation valve d, the bucket can be moved up and down. For example, the head side circuit of dump cylinder c is loaded with 305 kg/kg.
There is a relief valve f that provides relief at ^cm2 , and a relief valve g that provides relief at 250Kg/ ^cm2 in the bottom circuit.
are connected to each other.

That is, due to the structure of the working machine, a larger force acts on the dump cylinder c during back grading work, so the relief pressure in the head side circuit of the dump cylinder c is increased. However, in the above hydraulic circuit, when the bucket is raised in a dumped state, when the tilt lever comes into contact with the dump stopper during the ascent of the bucket, a force is applied in the direction of extension of the dump cylinder c, and the head side of the dump cylinder c becomes under high pressure. However, since the relief pressure in the relief pressure circuit of the head side circuit is higher than the relief pressure of the relief valve h provided on the discharge side of the hydraulic pump a, the lift cylinder e side loses, and no more There was a problem where the bucket could not rise.

This idea was made with the purpose of improving this problem, and the head side circuit of the dump cylinder is
By providing multiple relief valves with different relief pressures,
By providing a working machine hydraulic circuit for construction machinery in which these relief valves are selected according to the work content,
This is an attempt to solve the problems of the past.

This invention will be described in detail below with reference to an embodiment shown in FIG. 2 and subsequent figures. FIG. 2 schematically shows a construction machine such as a dozer shovel. Reference numeral 1 denotes a vehicle body that can move freely by a track-type suspension 2, and a work implement 3 is attached to the front part of the vehicle body 1. The work equipment 3 includes a lift arm 5 whose base end is pivotally attached to the front part of the vehicle body 1 and can be moved up and down by a lift cylinder 4, and a bucket 6 pivoted at the tip of the lift arm 5.
Brackets 5b project obliquely forward from a horizontal rod 5a that connects approximately the middle portions of the lift arm 5, and the middle portion of the tilt lever 7 is pivotally supported at the tips of these brackets 5b. One end of the tilt lever 7 is connected to the rear surface of the bucket 6 via a link 20, and the other end of the tilt lever 7 is connected to the tip of a piston rod 8a of a dump cylinder 8 whose base end is pivotally connected to the vehicle body 1. It is pivoted to.

The lift cylinder 4 and dump cylinder 8 are provided with hydraulic piping as shown in FIG.

That is, 10 is a hydraulic pump, and the hydraulic pressure discharged from this hydraulic pump 10 is supplied to the dump cylinder 8 via the dump operation valve 11, and a part is supplied to the lift cylinder 4 via the lift operation valve 12. . A relief valve 14 that provides relief at, for example, 250 kg/cm ² is connected to the bottom side circuit 13 of the dump cylinder 8, and a switching valve 16 such as a solenoid valve is connected to the head side circuit 15 of the dump cylinder 8. A plurality of relief valves, for example two relief valves 17 and 18, each having a different set pressure, are connected through the valve. The above-mentioned switching valve 16 has a dump stopper 7a provided on the tilt lever 7 which is connected to the side rod 5 of the lift arm 5
When it comes into contact with the tilt lever 7, the limit switch 19 is operated by an operating portion 7b provided on the tilt lever 7, thereby selecting the relief valves 17 and 18 as follows.

However, when performing leveling work such as back grading, the bucket cart 6 is dumped to the position shown in the imaginary line in Figure 2, the vehicle body 1 is moved backwards, and the leveling work is performed using the tip of the bucket cart 6. At this time, the switching valve 16
is in position 16 ₁ , high pressure side relief valve 1
7 is selected, and therefore, even if the head side of the dump cylinder 8 becomes high pressure during leveling work, the relief valve 17 does not relieve, thereby making it possible to perform back grading work.

Next, when the bucket 6 is raised in the dumped state, the dump stopper 7a of the tilt lever 7 comes into contact with the lift arm 5 (see the solid line in FIG. 4), and at the same time, the limit switch 19 is activated and the switching valve 16 is moved to the position 16 ₂ Switch to low pressure side release
Select the valve 18. As a result, the relief pressure on the head side of the dump cylinder 8 becomes lower than the set pressure of the relief valve 19 that determines the relief pressure of the lift cylinder 4.
However, since it does not lose to dump cylinder 8,
Furthermore, the bucket 6 can be raised.

In the above embodiment, the switching valve 16 for selecting the relief valves 17 and 18 is switched by the limit switch 19, but it may of course be switched manually.

As described in detail above, this idea is based on providing a plurality of relief valves in the head side circuit of the dump cylinder.
Since these relief valves are selected depending on the content of the work, leveling work such as back grating can be performed efficiently with a high set pressure. In addition, when lifting a bucket after dumping, the low-pressure side relief valve is selected, so the lift cylinder loses control to the dump cylinder.
Problems such as difficulty in raising the bucket can also be resolved.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional hydraulic circuit, Figure 2 is a side view of a construction machine that is an embodiment of this invention.
FIG. 3 is a hydraulic circuit diagram of the same, and FIG. 4 is an enlarged view of the limit switch portion. 3 is a working machine, 4 is a lift cylinder, 6 is a bucket, 8 is a dump cylinder, 10 is a hydraulic pump, 1
1 is a dump operation valve, 12 is a lift operation valve, 15 is a head side circuit, 16 is a switching valve, and 17 and 18 are relief valves.

Claims (1)

[Scope of utility model registration request] The bucket 6 of the working machine 3 is dumped by supplying the hydraulic pressure discharged from the hydraulic pump 10 to the dump cylinder 8 via the dump operation valve 11 and a part of it to the lift cylinder 4 via the lift operation valve 12. In addition, in a device that moves up and down, a construction in which a plurality of relief valves 17, 18 with different set pressures and a switching valve 16 for selecting these relief valves 17, 18 are connected to the head side circuit 15 of the dump cylinder 8. Machine work equipment hydraulic circuit.