Hydraulic system for a mobile work device, in particular a wheel

Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy

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60494, F16D 3102

Patent

active

058028471

DESCRIPTION:

BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION

The present invention is based on a hydraulic system which is used for a mobile work device, particularly a wheel loader.
From Federal Republic of Germany 39 09 205 C1, it is known to dampen the pitching oscillations of wheel loaders which take place, particularly with the loading shovel full and a high speed of travel, by means of a damping system which is part of the hydraulic system of the wheel loader. For the damping of the oscillation, the, in general, two hydraulic lift cylinders for the raising and lowering of the loading shovel can be connected by a shut-off valve to a hydraulic accumulator which can be loaded by a hydraulic pump via a filling line. The shut-off valve which is arranged between the hydraulic accumulator and the lift cylinders is closed as long as the loading shovel is being used and it can be opened manually by the driver or automatically as soon as pitching oscillations occur upon travel or as soon as the speed of travel exceeds a given value of, for instance, 6 km/hour. A hydraulic control system of a wheel loader comprises, as is also known from Federal Republic of Germany 39 09 205 C1, several directional control valve devices one of which serves to supply the lift cylinders with pressurized fluid for the raising and lowering of the loading shovel. In accordance with Federal Republic of Germany DE 39 09 205 C1, this directional control valve also has a switch position in which the two pressure chambers of each lift cylinder are connected to the tank. In this switch position of the directional control valve, the loading shovel rests with its weight on the ground and can be pulled or pushed over the ground in order to level it. It floats, so to speak, on the ground, for which reason the corresponding switch position of the directional control valve is also known as the "floating" switch position. The "floating" function can--as can be noted from Federal Republic of Germany 41 29 509 A1--also be obtained by an additional directional control valve which, in one switch position, connects the two pressure chambers of each lift cylinder to each other and to the tank.


SUMMARY OF THE INVENTION

The object of the present invention is further to develop such a hydraulic control device in such a manner that a compact, space-saving construction is possible, that the expense for piping is reduced; and that the cost of manufacture can be favorable.
This object is achieved in accordance with the invention by a hydraulic system whenever, the shut-off valve is so integrated in the directional control valve by which the two pressure chambers of the hydraulic cylinder can be separately pressurized and/or jointly connected to the tank that the hydraulic accumulator and the first pressure chamber of the hydraulic pump can be connected to each other via the control slide of the directional control valve. In a hydraulic system in accordance with he invention therefore, in addition to the directional control valves there is not only also present an additional shut-off valve. Rather, one of the directional control valves also serves the function of the shut-off valve. In this way, the expense for the piping is less, the manner of construction is compact and space-saving, and the cost is reduced.
Advantageous developments of a hydraulic system in accordance with the invention.
During a connection of the first pressure chamber with the hydraulic accumulator the second pressure chamber is at the same time connected to the tank. Thus, no pressure can be produced in the second pressure chamber and the piston of the hydraulic cylinder can oscillate without cavitation.
In agreement with the hydraulic system of Federal Republic of Germany 41 29 509 A1, a first directional control valve via which the two pressure chambers of the hydraulic cylinder can be connected alternately to a hydraulic pump and to the tank, and a second directional control valve via which the two pressure chambers can be connected jointly to the tank and by which, therefore, the "floating" function i

REFERENCES:
patent: 4096878 (1978-06-01), Adams
patent: 4240515 (1980-12-01), Kirkwood
patent: 4995517 (1991-02-01), Saotome
patent: 5116188 (1992-05-01), Kurohashi et al.
patent: 5520499 (1996-05-01), Ufheil et al.

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