JPH0674050B2 - Hydraulic circuit of tractor - Google Patents

Description

The present invention relates to a hydraulic circuit for a tractor.

(Prior Art) As shown in FIG. 4, a tractor includes a hydraulic device 40 such as a hydraulic cylinder for a working machine, a hydraulic clutch interposed in a power transmission system that transmits the power of an engine 41 to wheels and a PTO shaft, and the like. Hydraulic system 42 and full hydraulic power steering hydraulic system
It is equipped with various hydraulic systems such as 43.

Since the respective hydraulic devices 40, 42, 43 have different operating pressures and different hydraulic oil supply amounts, individual hydraulic pumps 44, 45,
The prescribed hydraulic oil was supplied from 46. The filters 47, 48 and the oil coolers 49, 50 are provided for each hydraulic circuit.

(Problems to be Solved by the Invention) In the conventional hydraulic circuit, since a plurality of hydraulic pumps must be mounted in the vicinity of the engine, the number of hydraulic pumps is large, the cost is increased, and the hydraulic pumps are mounted. There was a problem that an extra space had to be secured.

Further, a filter and an oil cooler must be provided for each hydraulic circuit, which causes a problem that piping is complicated and cost is increased.

Therefore, in order to solve the above-mentioned problem, the number of hydraulic pumps may be reduced and the hydraulic oil may be supplied from one hydraulic pump to a plurality of hydraulic devices. Since the characteristics are different, how to integrate which hydraulic system was a very difficult problem to solve. And if it integrates, various new problems will arise.

The present invention solves such a difficult problem.

(Means for Solving the Problems) In the present invention, the hydraulic pump for power steering is also used for the hydraulic clutch to reduce the cost, and at the same time, it is not necessary to secure a mounting space. The problem that arises is solved, and the feature is that a priority valve is provided to flow a fixed amount of hydraulic oil from the sub-hydraulic pump to the main circuit, and the rest to the surplus flow circuit. A control valve for power steering is connected, a return circuit of the control valve is connected to a hydraulic clutch, and a first relief valve for maintaining the return circuit at a predetermined pressure is provided, and a main relief circuit is provided between the main circuit and the return circuit. A second relief valve is provided for maintaining the circuit pressure above the return circuit pressure, and
The surplus flow circuit is connected to the suction port of the main hydraulic pump so that the oil in the surplus flow circuit flows to the main hydraulic pump without returning to the sub hydraulic pump.

(Operation) According to the present invention, the hydraulic oil from the sub-hydraulic pump is diverted by the priority valve such that a constant flow rate flows in the main circuit and an excess flow flows in the excess flow circuit.

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

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

When the steering handle is operated, the control valve for power steering moves and hydraulic oil is supplied to the steering cylinder.
Steering wheels steer.

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 operates due to the differential pressure.

Moreover, since the relief pressure of the first relief valve is constantly applied to the low pressure side of the steering cylinder, for example, when the steering wheel comes into contact with an obstacle and an external force acts in the operating direction of the steering cylinder, The relief pressure acts as a resistance of the cylinder, the steering wheel is not “stripped”, and the steering operation is very stable.

Even during the steering operation, the oil on the low pressure side of the steering cylinder is sent to the return circuit, so that the operation of the hydraulic clutch is not hindered.

By the way, when the main circuit and the return circuit are maintained at a predetermined pressure by the relief valve, the bubbles sucked by the sub-hydraulic pump remain in the main circuit and the return circuit and are difficult to escape from the circuit. Therefore, by connecting the surplus flow circuit to the suction port of another main hydraulic pump, air bubbles are forcibly flown on the surplus flow to be eliminated and do not enter the main circuit and return circuit. It does not worsen the operation.

(Example) Hereinafter, the Example of this invention is described based on drawing.

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 a rear portion of an engine 2 of a tractor 1, and a working oil of a lubricating oil / hydraulic device is stored in the transmission case 3.

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

The main and sub hydraulic pumps 8 and 9 are driven by the engine 2, and the oil discharged from the main hydraulic pump 8 is supplied to the hydraulic device 12 of the working machine at the rear through the pipe 10 and the auxiliary control valve 11. On the other hand, it is supplied to the working machine lifting hydraulic device 14 via the 3P control valve 13.

The working machine lifting hydraulic device 14 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 working machine lifting hydraulic device 14.

The discharge oil of the sub hydraulic pump 9 is supplied to the priority valve 15,
The fixed amount flows into the main circuit 16, and the surplus flow flows into the surplus flow circuit 17. The surplus flow circuit 17 is connected to the suction port of the main hydraulic pump 8. An oil cooler 18 is interposed in the middle of this surplus flow circuit 17. The oil cooler 18 is arranged in the vicinity of a radiator fan 19 for cooling the engine, and the cooling air of the fan 19 is applied thereto.

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

A return circuit 25 is connected to the return oil port of the control valve 20, a high / low speed switching hydraulic clutch 27 is connected to the return circuit 25 via a high / low speed switching valve 26, and a front wheel drive switching is performed via a front wheel drive switching valve 28. Hydraulic clutch 29 and PTO valve 30
PTO variable speed hydraulic clutches 31 are connected to each other via. These hydraulic clutches 27, 29, 31 are internally provided 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 the relief valve 32 is a high / low speed switching hydraulic clutch 27 and a PTO gear shift. It is used as lubricating oil for the clutch 31.

A second relief valve 33 is interposed between the main circuit 16 and the return circuit 25 to maintain the pressure in the main circuit 16 higher than the pressure in the return circuit 25.

The present invention is not limited to the above embodiment.

According to the present invention, by providing the first and second relief valves, the power steering hydraulic device and the hydraulic clutch can be driven by the hydraulic oil from one hydraulic pump. Therefore, the number of hydraulic pumps can be reduced,
The cost is reduced and it is not necessary to secure a space for the hydraulic pump.

Also, by providing a relief valve to increase the circuit pressure,
The difficulty in removing bubbles can be solved by providing a priority valve to allow the excess flow to flow into the excess flow circuit, and connecting the excess flow circuit to the suction port of another hydraulic pump.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention, FIG. 2 is an external view of the same 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, 16 ... Main circuit, 17 ... Excess flow circuit, 20 ... Control valve, 25 ... Return circuit , 27,29,31 …… hydraulic clutch, 32 …… first relief valve, 33 …… second relief valve.

Claims (1)

[Claims] Claim: What is claimed is: 1. A priority valve (15) for supplying a fixed amount of hydraulic oil from an auxiliary hydraulic pump (9) to a main circuit (16) and the rest to an excess flow circuit (17). 16) is connected to a control valve (20) for power steering, and the control valve (20)
Is connected to a hydraulic clutch (27, 29, 31), a first relief valve (32) for maintaining the return circuit (25) at a predetermined pressure is provided, and the main circuit (16) and A second relief valve (33) for maintaining the pressure in the main circuit (16) higher than the pressure in the return circuit (25) is provided between the return circuits (25), and the excess flow circuit (17) The surplus flow circuit (17) is connected to the suction port of the main hydraulic pump (8) so that oil flows to the main hydraulic pump (8) without returning to the sub hydraulic pump (9). Hydraulic circuit of the tractor.