JPH0329397Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a hydraulic control device for a front loader.
The purpose is to eliminate the possibility that the hydraulic cylinder may operate erratically due to back pressure from the hydraulic system side of the tractor.

A front loader is attached to a tractor equipped with a hydraulic system for lifting and lowering work equipment, and the front loader is equipped with a boom cylinder that swings the boom up and down, and a bucket cylinder that moves up and down a bucket that is pivotally supported at the tip of the boom. Some tractors are equipped with a hydraulic pump that supplies pressure oil to the hydraulic system and hydraulic cylinder.

By the way, in the above-mentioned system, as shown in FIG.
, a bucket cylinder control valve 5 that controls the bucket cylinder 4, and a hydraulic system 6 of the tractor are connected in series in the above order, and the boom cylinder control valve 3 controls the bucket cylinder at each operating position. Pressure oil is supplied to the valve 5, and the bucketed cylinder control valve 5 is also adapted to supply pressure oil to the hydraulic device 6 at each operating position.

However, in the conventional system described above, due to the influence of back pressure from the hydraulic system 6 side, the hydraulic system side oil passage 7, which connects the hydraulic system 6 and the bucket cylinder control valve 5,
8 and intermediate oil passages 9 and 1 that connect both control valves 3 and 5.
0 oil pressure may become abnormally high, but if you operate each cylinder 2, 4 in such a case,
There was a problem in that each cylinder 2, 4 operated erratically under the influence of abnormally high pressure.

The present invention solves the above problems, and its characteristics are that a front loader equipped with a hydraulic cylinder is attached to a tractor equipped with a hydraulic system, and a hydraulic pump and a hydraulic cylinder control valve that controls the hydraulic cylinder are installed on a tractor equipped with a hydraulic system. and a hydraulic system are connected in series in the above order, and the oil pressure in the oil path connecting the hydraulic cylinder control valve and the hydraulic system is abnormally high due to back pressure from the hydraulic system side. The point is that a relief valve is installed to prevent this from happening.

Hereinafter, one embodiment of the present invention will be explained based on the drawings of FIGS. 2 and 3. In FIG. etc. can be detachably attached, and a working machine lifting/lowering hydraulic system 5 is mounted. The hydraulic device 15 has an operating lever 1
The control valve 17 is equipped with a control valve 17 with a 6-type control valve, and by operating the control valve 17, the work equipment etc. can be raised and lowered.

Reference numeral 18 denotes a bucket-type front loader for mounting on a tractor, which includes a pair of left and right booms 20 that are pivotally supported on a mounting frame 19 of the tractor 13, and a pair of left and right boom cylinders 21 that swing the booms 20 up and down.
It is comprised of a working part 22, exemplified by a bucket that is pivotally supported at the tip of the boom 20, and a pair of left and right working part cylinders 23 that move the working part 22 up and down.

FIG. 2 shows the hydraulic control circuit of the front loader 18, which includes a hydraulic pump 24 provided in the tractor 13, a boom cylinder control valve 25 that controls the boom cylinder 21, and a working section cylinder that controls the working section cylinder 23. Control valve 26 and hydraulic system 1
5 are connected in series in the above order. Reference numeral 27 denotes a first relief valve on the loader side, which limits the pressure of the pressure oil supplied from the hydraulic pump 24 to within a predetermined pressure.
28 and 29 are check valves.

The boom cylinder control 25 is a 6-port 3-position manual switching valve having an operating lever 30, and is connected to the hydraulic pump 24 via a hydraulic pump side oil passage 31. Moreover, the boom cylinder control valve 25 is
With respect to the working part cylinder control valve 26, a first supplying pressure oil to the working part cylinder control valve 26 at a neutral position;
The boom cylinder control valve 25 connects the return oil from the boom cylinder 21 to the first intermediate oil via the second intermediate oil path 33 in the ascending operation position and the descending operating position. 32. Therefore, the boom cylinder control valve 25 supplies pressure oil to the working section cylinder control valve 26 at each operating position, and both cylinders 21 and 23 can be operated simultaneously.

The working part cylinder control valve 26 is connected to the operating lever 34
It is a 6-port, 3-position manual switching valve. The working part cylinder control valve 26 is connected to the hydraulic device 15.
The working part cylinder control valve 26 is connected to the hydraulic system 15 at a neutral position via a first hydraulic system side oil passage 35 that supplies pressure oil to the hydraulic system 15 at a neutral position, and the working part cylinder control valve 26 is in an upward rotation operation position and a downward rotation operation position. Then, the return oil from the working part cylinder 23 is supplied to the first hydraulic device side oil path 35 via the second hydraulic device side oil path 36. Therefore, the working part cylinder control valve 26 supplies pressure oil to the hydraulic device 15 at each operating position, and both cylinders 21, 2
3 and the hydraulic system 15 can be operated simultaneously.

Reference numeral 37 denotes a return oil passage, which connects the second hydraulic system side oil passage 36 and the tank.

39 is a loader-side second valve installed in the return oil passage 37.
This is a relief valve that prevents the oil passages 35 and 36 on the hydraulic equipment side and the intermediate oil passages 32 and 33 from becoming abnormally high pressure due to back pressure from the side of the hydraulic equipment 15, and the oil passage on the first hydraulic equipment side. It is urged to the open operation position by the pilot pressure from 35, and is urged to the closed operation position by the elastic force of the bomb 39. When the hydraulic device 15 raises the working machine, etc., each hydraulic device side oil passage 35, 36 and each intermediate oil passage 32, 3
Even if the pressure of the oil in No. 3 becomes high, the elastic force of the bomb 39 is set so that the second relief valve 38 does not reach the open operation position due to this pressure.
The set pressure value of the relief valve 38 is determined by adding an appropriate pressure value to the above pressure value.

Reference numeral 40 denotes a chatter prevention circuit for preventing chattering of the second relief valve 38, which is interposed between the confluence part of the first hydraulic system side oil passage 35 with the second hydraulic system side oil passage 36 and the pilot pressure take-off part. .
The prevention circuit 40 is constructed by connecting a check valve 41 and a throttle valve 42 in parallel. The check valve 41 allows oil to flow to the hydraulic device 15 side.

According to the embodiment configured as described above, by operating each control valve 17, 25, 26, the hydraulic system 15 and each cylinder 21, 23 can be controlled in the same way as in the conventional example.

By the way, when the three-point linkage mechanism 14 is equipped with a work implement, a balance weight, etc. and is held in the raised position, if the tractor bounces due to an uneven ground surface, etc., the hydraulic system 15 side Due to the back pressure, the oil passages 35, 36 on the hydraulic equipment side and the intermediate oil passages 32, 33 attempt to rise to abnormally high pressure, but at this time, the second relief valve 38 is in the open operation position, and the pressure on each hydraulic equipment side Since the oil passages 35 and 36 are communicated with the tank, the oil passages 35 and 36 on the hydraulic equipment side and the intermediate oil passages 32 and 33 do not become abnormally high pressure due to the influence of back pressure from the hydraulic equipment 15 side.

Therefore, even if the cylinders 21 and 23 are operated at the time described above, the cylinders 21 and 23 will not operate erratically.

Further, between the second relief valve 38 and its pilot pressure take-off part, there is provided a chattering prevention circuit 40 comprising a check valve 41 and a throttle valve 42 connected in parallel.
Since the second relief valve 38 is interposed therebetween, the second relief valve 38 does not cause any chattering phenomenon when the second relief valve 38 operates as described above.

In the embodiment, the front loader is equipped with a boom cylinder and a working part cylinder, but the present invention can also be applied to a front loader equipped with only a boom cylinder.

As detailed above, the present invention provides a relief valve for the oil passage connecting the hydraulic cylinder control valve and the hydraulic system to prevent the oil pressure in the oil passage from becoming abnormally high due to back pressure from the hydraulic equipment side. Since this is installed, the pressure of the oil in the oil passage does not become abnormally high due to the influence of back pressure from the hydraulic system side, and there is no risk that the hydraulic cylinder will operate erratically when the hydraulic cylinder is operated. The present invention has the various advantages mentioned above and is of great practical benefit.

FIG. 4 shows a hydraulic control circuit for a front loader different from that of the present invention, in which the second intermediate oil passage 33 is connected to the first oil pressure control circuit.
It is communicated with the tank via a return oil passage 43.
Further, the working section cylinder control valve 26 supplies pressure oil to the hydraulic device 15 via the hydraulic device side oil passage 44 only in the neutral position, and the return oil from the working section cylinder 23 is supplied to the hydraulic device 15 through the oil passage 44 on the hydraulic device side only in the neutral position. 2 Return oil path 4
5 to the first return oil path 43.

Reference numeral 46 denotes a return control valve, which is interposed closer to the second intermediate oil passage 33 than the confluence part with the second return oil passage 45 in the first return oil passage 43 . Return control valve 46
has an open operating position and a closed operating position, is biased to the open operating position by a bullet 47, and is provided with a solenoid 48 for operating to the closed operating position.

Limit switches 49 and 50 are operated by the operating lever 34, and each switch 49 and 50 is turned ON when the working section cylinder control valve 26 is in the ascending operating position and the descending operating position.

Reference numeral 51 denotes a limit switch operated by the operating lever 16, which is turned ON only when the supply of pressure oil to the hydraulic system 15 is required, that is, when the control valve 17 is in the upward operating position.

And the limit switch 49, 50, 5
When even one of them is in the ON state, the solenoid 48 is activated and the return control valve 46 is placed in the open operation position.

According to the above, each control valve 17, 25, 2
6, the hydraulic system 15 and each cylinder 21, 2
3 can be controlled as before, and when the hydraulic device 15 is not in use, pressure oil is not supplied to the hydraulic device 15 side, and the second intermediate oil path 33 and the first return oil path 43
and is returned to the tank by the return control valve 46 or by the second return oil path 45, so each cylinder 2
When the cylinders 1 and 23 are operated, the cylinders 21 and 23 will not operate erratically due to the influence of back pressure from the hydraulic system 15 side.

[Brief explanation of drawings]

Figure 1 is a hydraulic control circuit diagram showing an example of a conventional system;
3 and 3 show one embodiment of the present invention, FIG. 2 is an overall side view, FIG. 3 is a hydraulic control circuit diagram, and FIG. 4 is a hydraulic control circuit diagram different from the present invention. 13...Tractor, 15...Hydraulic device for lifting and lowering the work machine, 18...Front loader, 20...Boom, 21...Boom cylinder, 22...Work machine,
23...Working part cylinder, 24...Hydraulic pump,
25... Boom cylinder control valve, 26... Working part cylinder control valve, 29, 38... First and second relief valves, 32, 33... First and second intermediate oil passages, 3
5, 36...First and second hydraulic device side oil passages.

Claims (1)

[Scope of utility model registration request] A front loader equipped with a hydraulic cylinder is attached to a tractor equipped with a hydraulic system, and a hydraulic pump and
a hydraulic cylinder control valve that controls the hydraulic cylinder;
In a case where the hydraulic system is connected in series in the above order, the oil pressure in the oil path connecting the hydraulic cylinder control valve and the hydraulic system becomes abnormally high due to back pressure from the hydraulic system side. A hydraulic control device for a front loader, characterized in that it is equipped with a relief valve that prevents.