JPS63312267A - Hydraulic circuit for tractor - Google Patents

Abstract

PURPOSE:To make it possible to drive both hydraulic power steering device and hydraulic clutch with the use of hydraulic oil fed from only one hydraulic pump by providing first and second relief valves. CONSTITUTION:A return circuit 25 connected to a return oil port of a control valve 20 is connected to a hydraulic high and low speed change-over clutch 27 through a high and low change-over valve 26, to a hydraulic front wheel drive change-over clutch 26 through a front drive change-over valve 28 and to a hydraulic PTO speed change clutch 31 through a PTO valve 30. First relief valve 32 whose drainage is used as lubrication oil for the hydraulic high and low speed change-over clutch and the PTO speed change clutch 31, for maintaining the pressure of the return circuit 25 at a predetermined value is disposed in one end part of the return circuit 25. Further, a second relief valve 33 is disposed between a main circuit 16 and a return circuit 25, thereby it is possible to make the pressure of a main circuit higher than the pressure of the return circuit.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a hydraulic circuit for a tractor.

(Prior art) As shown in FIG.
Various hydraulic devices are installed, such as a hydraulic device 42 such as a hydraulic clutch interposed in the power transmission system for transmitting data to the TO shaft, and a hydraulic device 43 for a fully hydraulic power steering system.

Since each of the hydraulic devices 40, 42, and 43 has a different operating pressure and a different amount of hydraulic fluid supplied, a predetermined hydraulic fluid is supplied from individual hydraulic pumps 44, 45, and 46. Filters 47, 48 and oil coolers 49, 50 were provided for each hydraulic circuit.

(Problems to be Solved by the Invention) In the conventional hydraulic circuit, a plurality of hydraulic pumps must be installed near the engine, resulting in a large number of hydraulic pumps, which increases costs. The problem was that extra space had to be secured for the

In addition, a filter and an oil cooler must be provided for each hydraulic circuit, resulting in complicated piping and increased costs.

Therefore, in order to solve the above problem, the number of hydraulic pumps can be reduced and hydraulic oil can be supplied from one hydraulic pump to multiple hydraulic equipment, but as mentioned above, each hydraulic equipment has Because of their different characteristics, it has been an extremely difficult problem to decide which hydraulic devices should be integrated and how. And if they are integrated, various new problems will arise.

The present invention solves these difficult problems.

(Means for Solving the Problems) The present invention allows a hydraulic pump for power steering to be used also for a hydraulic clutch, thereby reducing costs and eliminating the need to secure installation space. This solution solves the problems caused by the hydraulic pump, and its feature is that the hydraulic fluid from the hydraulic pump is divided into a main circuit and a surplus flow circuit via a priority valve, and the main circuit is used to control the power steering. A first relief valve is connected to the control valve, the return circuit of the control valve is connected to a hydraulic clutch, and maintains the return circuit at a predetermined pressure. A first relief valve is provided between the main circuit and the return circuit to return the pressure of the main circuit. A second relief valve is provided to maintain a pressure higher than the circuit pressure, and the surplus flow circuit is connected to the inlet of another hydraulic pump.

(Function) According to the present invention, the hydraulic oil from the hydraulic pump is divided by the priority valve so that a constant flow flows into the main circuit, and a surplus flow flows into the surplus flow circuit.

When the power steering control valve is in neutral, the hydraulic oil in the main circuit flows into the return circuit and is returned to the tank from the first relief valve. At this time, since the return circuit is maintained at a predetermined pressure by the first relief valve, the hydraulic clutch can be controlled to be turned on and off by turning on and off the clutch control valve.

In this case, since the hydraulic oil for the hydraulic clutch is sent through the priority valve, the amount of oil is always constant, and therefore the feeling when connecting the hydraulic clutch is stable.

When the steering wheel is operated, the power steering control valve moves and hydraulic oil is supplied to the steering cylinder.
The steering wheel steers.

At this time, since the main circuit is maintained at a higher pressure than the return circuit by the second relief valve, the steering cylinder is operated by the differential pressure.

In addition, since the relief pressure of the first relief valve is always applied to the low pressure side of the steering cylinder, for example, if the steering wheel comes into contact with an obstacle and an external force is applied in the direction of operation of the steering cylinder, the The relief pressure acts as a resistance in the cylinder, preventing the steering wheel from becoming ``unlocked,'' making the steering operation extremely stable.

Even during the steering operation, the oil on the low pressure side of the steering cylinder is sent to the return circuit, so it does not interfere with the operation of the hydraulic clutch.

By the way, if the main circuit and return circuit are maintained at a predetermined pressure by the relief valve, the air bubbles sucked by the hydraulic pump will
It stays in the main circuit and return circuit and is difficult to remove from the circuit, so
By connecting the surplus flow circuit to the suction port of another hydraulic pump, air bubbles are forced to flow away on the surplus flow and are eliminated.
Since it does not enter the main circuit or return circuit, the operation of the steering device and hydraulic clutch will not be deteriorated.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram of the tractor, and FIG. 2 is an external view of piping.

In these drawings, a transmission case 3 is connected to the rear of an engine 2 of a tractor 1, and a lubricating oil and working oil for a hydraulic system is stored in the transmission case 3.

A hydraulic oil outlet 4 is provided at the lower rear portion of the transmission case 3, and a suction pipe 5 is connected to the outlet 4. An oil filter 6 is interposed in this suction pipe 5. This suction pipe 5 is branched via a Y-shaped connector 7 as shown in FIG. 3, and is connected to the suction ports of a main hydraulic pump 8 and a sub-hydraulic pump 9. The reason why the Y-shaped connector 7 is used in this manner is to prevent cavitation from occurring at the bent portion when the pipe is bent at right angles.

The main and auxiliary hydraulic pumps 8.9 are driven by the engine 2, and the oil discharged from the main hydraulic pump 8 passes through a pipe 10.
It is supplied to the hydraulic system 12 of the rear work machine through the auxiliary control valve 11, and is supplied to the hydraulic system 14 for lifting and lowering the work machine through the 3P control valve 13.

This hydraulic device 14 for lifting and lowering the working machine is mounted on the rear upper surface of the transmission case 3, and the 3P control valve 13 and the auxiliary control valve 11 are attached to the side surface of the hydraulic device I4 for lifting and lowering the working machine.

The oil discharged from the auxiliary hydraulic pump 9 is supplied to a priority valve 15, a certain amount of which flows into a main circuit 16, and a surplus flow into a surplus flow circuit 17. This surplus flow circuit 17 is connected to the inlet of the main hydraulic pump 8. An oil cooler 18 is interposed in the middle of this surplus flow circuit 17. This oil cooler 18 is arranged near a radiator fan 19 for cooling the engine, and is exposed to cooling air from the fan 19.

The main circuit 16 is connected to a control valve 20 for power steering. This control valve 20 is connected to a metering pump 21 and a power steering hydraulic cylinder 22, and the control valve 20 and metering pump 21 are connected to a steering handle 23.
is linked to. The power steering hydraulic cylinder 22 is operatively connected to a steering device for the front wheels 24.

A return circuit 25 is connected to the return oil date of the control valve 20,
This return circuit 25 is connected to a high/low speed switching hydraulic clutch 27 via a high/low speed switching valve 26, a front wheel drive switching hydraulic clutch 29 via a front wheel drive switching valve 28, and a PTO shift hydraulic pressure via a PTO valve 30. clutch 3
1 are connected to each other. Each of these hydraulic clutches 27.
29 and 31 are contained in the mission case 3.

A first relief valve 32 for maintaining the pressure of the return circuit 25 at a constant value is interposed at the end of the return circuit 25, and the drain of this relief valve 32 is connected to the high/low speed switching hydraulic clutch 27 and the PTO transmission. It is used as lubricating oil for the clutch 31.

A second relief valve 3 is provided between the main circuit 16 and the return circuit 25.
3 is interposed to maintain the pressure in the main circuit 16 higher than the pressure in the return circuit 25.

Note that the present invention is not limited to the above embodiments.

(Effects of the Invention) According to the present invention, by providing the first and second relief valves, the power steering hydraulic system and the hydraulic clutch can be driven with hydraulic fluid from one hydraulic pump. Therefore, the number of hydraulic pumps can be reduced,
This reduces costs and eliminates the need to secure space for a hydraulic pump.

In addition, by installing a relief valve and increasing the circuit pressure,
The difficulty in removing air bubbles can be solved by connecting the surplus flow circuit to the suction port of another hydraulic pump.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention, FIG. 2 is an external view of the piping, FIG. 3 is a perspective view of a Y-type connector, and FIG. 4 is a conventional hydraulic circuit diagram. 8... Main hydraulic pump (other hydraulic pump), 9... Sub-hydraulic pump, 15... Priority valve, Work 6... Main circuit, 1
7... Surplus flow circuit, 20... Control valve, 25... Return circuit, 27, 29. 31... Hydraulic clutch, 32...
... 1st relief valve, 33... 217th leaf valve.

Claims (1)

[Claims] (1) Hydraulic oil from the hydraulic pump is divided into a main circuit and a surplus flow circuit via a priority valve, the main circuit is connected to a control valve for power steering, and the return circuit of the control valve is connected to a hydraulic clutch. A first relief valve connected thereto is provided to maintain the return circuit at a predetermined pressure, and a second relief valve is provided between the main circuit and the return circuit to maintain the pressure in the main circuit at a higher pressure than the pressure in the return circuit. A hydraulic circuit for a tractor, wherein the surplus flow circuit is connected to a suction port of another hydraulic pump.