MEANS FOR SAVING ENERGY IN A HYDRAULIC CIRCUIT

Abstract: A means for saving energy in a hydraulic circuit where pressurized oil supplied by a hydraulic pump is used to activate various functions by the aid of one or several valves (2, 3, 4) controlling the function. A hydraulic circuit like this is in particular used in agricultural tractors, where the pressurized oil comes from a hydraulic pump driven by the engine. The problem is then that one is compelled to run the pressurized oil through a pressure regulating valve, thereby causing unnecessary waste of energy and need to cool the oil. This drawback is eliminated, as taught by the invention, in that to the hydraulic circuit has with a view to saving energy been connected a free circulation valve (1) which has been connected to cooperate with the valves (2, 3, 4) controlling the different functions in such manner that when one, even if only one, of the function-controlling valves (2, 3, 4) is open the free circulation valve (1) is closed and that when all function-controlling valves (2, 3, 4) are closed the free circulation valve (1) is open.

Description: Means for saving energy in a hydraulic circuit The present invention concerns a means for saving energy in a hydraulic circuit in which pressurized oil supplied by a hydraulic i pump is used to activate various functions with the aid of one or several valves controlling these functions. A hydraulic circuit 5 like this is in particular used 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 10 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 suffi- 15 cient 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 20 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 abolish this detriment, in prior art has been used a pressure- controlled free circulation valve by-passing the pressure regulat¬ ing valve, said valve being switched into action with the aid of the pressure rising in the circuit in question when none of the 30 coupling valves is in operation. A problem 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 a practice of prior art to employ three-way directional valves which have been dimensioned liberally enough to enable oil to be driven through them continuously. No separate free circula¬ tion valve is then needed because the directional valve can be set in the free circulated position. This design is however bulky and costly. The object of the present invention is to provide the hydraulic circuit presented with a means aiming at energy savings and which is free of the drawbacks mentioned above. The invention is mainly characterized in that the means intended to save energy is a free circulation valve associated with the hydraulic circuit and con¬ nected to cooperate with the valves controlling various functions in such manner that whenever one, even if only one, of the function-controlling valves is open the free circulation valve is closed and that the free circulation valve is open when all function-controlling valves are closed. Hereby the free circulation valve requires no pressure accumulator: it operates under a control separate from the hydraulic circuit. According to an advantageous embodiment, with the free circulation valve and the valves controlling various functions have been asso¬ ciated solenoids controlling the valves, the switches of the solen¬ oids' circuits being so cross-connected that the solenoid of the free circulation valve is without current when any special func¬ tion, be it even only one, 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 spe- cial 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 opera¬ tion and simple, 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— " BV_fR f cA(7 O PI heating effect of this valve. In the following, the invention shall be described with the aid of an example, with reference to the attached drawing, presenting a hydraulic functional diagram associated with a tractor. The pressurized oil arrives by the pipe 10 e.g. from a hydraulic pump driven by the tractor engine, and is divided among three pipes. The first of them goes to the valves 2,3 and 4, by which are coupled into action the tractor's power take-off shaft, differ¬ ential lock and high-speed gear. The second pipe goes over the pressure regulating valve 11 further to the shift gear lubrication. This pipe incorporates before the shift gears, a filter circuit where the oil passes through a filter 12 or, if this filter should become blocked, through a pressure relief valve 13 to the shift gears by the pipe 15. Furthermore, a pressure relief valve 14 has been provided before the shift gears to prevent excessive pressure build-up in the gear box. The third pipe goes to the free circula¬ tion valve 1, through which the oil has access to the shift gear lubricating circuit, by-passing the pressure regulator valve 11. The valves 1,2,3 and 4 are operated by the aid of solenoids 5,6,7 and 8, the electric circuits of these solenoids being controlled by the aid of a switching means 9. This switch has a design such that it switches on the circuit activating the free circulation valve 1 whenever none of the circuit activating special functions is energized. The figure illustrates that situation in which the tractor's engine is not running, whereby the valves are closed. The system operates as follows. As the ignition key is turned, the solenoid of the free circulation valve 1 is immediately energized and the free circula¬ tion valve opens. The free circulation valve is hereby already open in readiness when the tractor engine starts running. Thus the hydraulic pump will supply oil through the pipe 10, past the pressure regulating valve 11, into the gear box. Thus the power losses of the liquid flow are mainly made up only of the pressure OMPI , drops in the filter 12 and in the gear box, which are on the order of 0.1 MPa. But this pressure is not enough for the coupling means to engage the tractor's power take-off shaft or whatever. When one of these pieces of equipment is activated with the aid of the electric switch 9, this switch will interrupt the current of the solenoid 5 and the free circulation valve 1 will close. The liquid is now directed to the pressure regulating valve 11, of which the operating pressure is 1.6 MPa. Fluid under this pressure suffices to actuate the coupling means that has been activated. It is thus understood that during the coupling operation the oil going to lubricate the shift gears passes through the 1.6 MPa valve. When normal driving is once more resumed, that is when the valve 2,3 and 4 are inoperative, the valve 1 will place the free circulation in operation, and the oil going to the shift gears is conducted in an energy-conserving manner past the pressure regulating valve 11. The invention is naturally not exclusively confined to agricultural tractors nor to the use of the special functions enumerated here: it may also be applied more broadly, within the scope of the claims stated hereinbelow. I UREAI OMPI

Claims: Claims 1. A means for saving energy in a hydraulic circuit where pressurized oil produced by a hydraulic pump is used to activate various functions with the aid of one or several valves (2,3,4) controlling the functions, characterized in that the means intended to save energy is a free circulation valve (1) connected into the hydraulic circuit which has been connected to cooperate with the valves (2,3,4) controlling the different functions so that when one, even if only one, of the function-controlling valves (2,3,4) is open, the free circulation valve (1) is closed and that when all function-controlling valves (2,3,4) are closed, the free circulation valve is open. 2. Means according to claim 1, characterized in that with the free circulation valve (1) and with the valves (2,3,4) controlling various functions are associated solenoids (5,6,7,8) controlling the valves, the switches in the circuits of these solenoids being so connected that when one, even if only one, special function is activated, the solenoid (5) of the free circulation valve (1) is without current, whereby no oil passes through the free circulation valve and that when all special functions are deactivated, the solenoid (5) of the free circulation valve (1) is energized, whereby the oil flows through the free circulation valve. 3. Means according to claim 1 or 2, characterized in that when the tractor is not running, the solenoids (5,6,7,8) of all valves (1,2,3,4) are without current and the valves closed, and that when the tractor is started, switching on of the current also switches on the current to the solenoid (5) of the free circulation valve (1), causing the free circulation valve to open.

Inventors: ILMONIEMI JUHA, MAENTTAERI ERKKI, ILMONIEMI, JUHA, MAENTTAERI, ERKKI
Applicants: VALMET OY
Application year: 1983
Main classification: F15B13
IPC codes: F15B11