Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1996-08-09
1998-02-24
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60445, F16D 3102
Patent
active
057201684
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a control device for a hydraulic pump. In accordance with claim 1, by means of this control device, the hydraulic pump, which has a hydraulic displacement device is to be displaceable, by control of the flow as required for the supplying of hydraulic fluid to a first hydraulic apparatus and by pressure control for the supplying of hydraulic fluid to a second hydraulic apparatus, in which connection the pressure set and the setting of a servo-valve associated with the second hydraulic apparatus can, in the second case, be controlled jointly by a command signal.
The control of the flow of a variable-displacement hydraulic pump as required is also known as load-sensing control. This type of control is characterized by the fact that the pump pressure rises by a given .DELTA.p above the highest load pressure of all hydraulic apparatus which are controlled in this manner in parallel to each other. The pump pressure drops to the load pressure over an adjustable aperture which is associated with the apparatus having in each case the highest load pressure. Depending on the cross section of the aperture, the amount of fluid delivered by the pump must be greater or smaller in order to maintain the predetermined pressure difference. For this load-sensing control of the hydraulic pump a control device associated with it has a control valve which can be acted on in the direction of larger displacement volume by the highest load pressure and by a spring, and in the direction of small displacement volume by the pump pressure.
From Federal Republic of Germany 43 08 004 A1, a control for a variable-displacement hydraulic pump is known which is a pressure control. In that case, the pressure to be controlled and the adjustment of a servo-valve which is associated with a hydraulic apparatus which is supplied with hydraulic fluid by a hydraulic pump controlled in this manner can be programmed jointly by a command signal. The command signal can, for instance, be a pilot pressure which is set by means of a pre-control device and acts in the direction of larger displacement volume on the slide of the servo-valve and on the control piston of a control valve associated with the variable-displacement pump. In the direction of smaller displacement volume, the pump pressure can act on the control piston of the control valve, in which case, by a difference in size of the areas acted on by the pressures, a control position of the control piston is possible. Furthermore, the pilot pressure can be increased to the level of the pump pressure by means of a copying valve, so that equally large actuation areas on the control piston are possible. In the case of a control in accordance with Federal Republic of Germany 43 08 004 A1, a given pump pressure is established and the slide of a servo-valve is brought into a given position in which the servo-valve can also already be open. If the pre-established pump pressure is less than the pressure necessary in order to move the apparatus, the apparatus remains at rest despite the fact that the servo-valve is open. Only when the pump pressure reaches the apparatus pressure by an increase in the command signal does the apparatus start to move. This movement therefore commences at a cross section of the opening of the servo-valve which is greater the higher the load is.
From Federal Republic of Germany 43 08 004 A1, it is also known to adjust a variable displacement hydraulic pump which supplies several hydraulic apparatus with hydraulic fluid by load-sensing control for first apparatus and by pressure control for second apparatus. Whether a reported maximum load pressure of the first apparatus or the predetermined command signal requires a higher pump pressure depends on what type of control is used. For this purpose, the highest load pressure or a pressure generated from the command signal by means of a nozzle and a displaceable pressure-limiting valve is connected via a shuttle valve to a control space of a control valve of the v
REFERENCES:
patent: 5493861 (1996-02-01), Friedrichsen
patent: 5528911 (1996-06-01), Roth et al.
Oilhydraulic and Pneumatik, vol. 38, No. 5, Jan. 1, 1994 pp. 250-252, 255, XP 000195276 "Grundlagen der hydraulischen Schaltungstechnik".
Oilhydraulic and Pneumatik, vol. 38, No. 8, Jan. 1, 1994, pp. 473-478, 480, XP 000195316, Esders H "Elektrohydraulisches Load-Sensing Fur Die Mobilhydraulik".
Farber Martin A.
Lopez F. Daniel
Mannesmann Rexroth GmbH
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