Fluid handling – Systems – Supply and exhaust
Patent
1983-11-03
1986-03-11
Michalsky, Gerald A.
Fluid handling
Systems
Supply and exhaust
91451, 13759617, F15B 1306
Patent
active
045748381
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a means for saving energy in a hydraulic circuit in which pressurized oil supplied by a hydraulic pump is used to activate various functions with the aid of one or several valves controlling these functions. Such a hydraulic circuit is especially suited for use in agricultural tractors. A tractor usually incorporates a system in which the hydraulic control circuit of the differential lock, the power take-off shaft, the high-speed gear or another equivalent hydraulically operated clutch has been connected to the lubricating circuit of the tractor's mechanical shifting gear. The pressurized oil to such a circuit comes from a hydraulic pump driven by the engine.
Since in such an arrangement the coupling elements require a pressure on the order of 1.5 MPa, and only a liquid flow sufficient to fill the operating cylinder, while for the lubrication of the shift gears is required a sizeable flow at a pressure not higher than 0.4 MPa, there must be some kind of throttling point in the system before the gear lubricating circuit, to raise the pressure to be proper for the said coupling means. A 1.5 MPa pressure regulating valve, for instance, is proper to be used to do this. However, this entails that the lubricating oil for the shift gears has to be driven against 1.6 MPa back pressure all the time, and this involves unnecessary waste of energy as well as need to cool the oil.
To overcome this drawback, a pressure-controlled free circulation valve by-passing the pressure regulating valve has been used, said valve being switched into action with the aid of the pressure rising in the circuit in question when none of the coupling valves is in operation. A solution of this type however requires a pressure accumulator operating in the range of 1.6 to 2.0 MPa. This accumulator is an expensive piece of equipment and susceptible to damage.
It is also conventional to employ three-way directional valves which have been dimensioned liberally enough to enable oil to be driven through them continuously. No separate free circulation valve is then needed because the directional valve can be set in the free circulated position. This design is however bulky and costly.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a hydraulic circuit of the type described above with a means for achieving energy savings and which is free of the drawbacks mentioned above. The invention is mainly characterized in that the means for saving energy is a free circulation valve associated with the hydraulic circuit and connected to cooperate with the valves controlling various functions in such manner that whenever at least one of the function-controlling valves is open the free circulation valve is closed and that the free circulation valve is open only when all function-controlling valves are closed. In this manner the free circulation valve requires no pressure accumulator and operates under a control which is separate from the hydraulic circuit.
According to an advantageous embodiment, solenoids for controlling the free circulation valve and the various function-controlling valves are provided, the switches of the solenoids' circuits being so cross-connected that the solenoid of the free circulation valve is without current when at least one special function has been switched on or coupled, whereby no oil will pass through the free circulation valve, and that the solenoid of the free circulation valve is energized when all special functions are switched off, whereby the oil will flow through the free circulation valve.
In this way is obtained a means which is highly reliable in operation and simple in construction being composed of inexpensive standard components. The arrangement taught by the invention provides efficient control of the free circulation valve, by the aid of which it is possible to save the wasted power caused by throttling at a pressure limiting valve and the need of a cooling means resulting from the oil-heating effect of this valve.
DETAILED
REFERENCES:
patent: 3150685 (1964-09-01), Lohbauer et al.
patent: 3709103 (1973-01-01), Dukhovny et al.
Ilmoniemi Juha
Manttari Erkki
Michalsky Gerald A.
Valmet Oy
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