Pumps – With condition responsive pumped fluid control – Pressure responsive relief or bypass valve
Reexamination Certificate
2000-04-27
2001-07-10
Walberg, Teresa (Department: 3742)
Pumps
With condition responsive pumped fluid control
Pressure responsive relief or bypass valve
C137S119090
Reexamination Certificate
active
06257841
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a regulating device for positive-displacement pumps, in particular vane cell and roller cell pumps having a pressure chamber, which is connected with a pressure duct connected to an outlet via a bore, in which a regulating piston can be displaced against the force of a spring. The regulating piston controls the outlet cross section of a throttle duct as a function of the number of revolutions of the pump, or respectively of the flow rate. The regulating piston has a control edge for this purpose, by means of which, and in connection with the opening of the throttle duct, the open cross-sectional surface of the throttle duct is reduced in the course of the movement of the regulating piston in the direction toward the spring chamber. In addition, a flow control valve with a control piston charged by the force of a spring is provided in a housing bore.
BACKGROUND OF THE INVENTION
Such a regulating device is known from WO-A1-96/09475. (also DE 44 38 398.9 or U.S. Pat. No. 5,810,565) The descending characteristic curve of the flow rate is attained with this regulating device. In order to make possible different shapes of the characteristic flow rate curve, it is necessary to use different springs and different piston diameters. If, however, a characteristic flow rate curve of an unsteady course is desired, for example of a stepped course, such a characteristic curve can only be realized with an increased outlay, for example by using two successively acting springs.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is based on providing a regulating device for any arbitrary descending characteristic flow rate curves, among them also descending ones, which have an unsteady course, with the least possible structural outlay. It should be easily possible to represent different shapes of the characteristic curve.
This object is achieved by the regulating device of the present invention. The regulating piston has at least one control edge by means of which, together with the opening of the throttle duct, the cross-sectional surface of the throttle circuit is reduced during a movement of the regulating piston in the direction toward the spring chamber. Moreover, the regulating piston has at least one further control edge, by means of which, together with the opening of the throttle duct, the cross-sectional surface of the throttle circuit is increased during a movement of the regulating piston in the direction toward the spring chamber. It is possible by means of such an embodiment that the characteristic flow rate curve of the positive-displacement pump shows a descending course starting at the point at which the first control edge begins to cover the opening of the throttle duct, and in this way to reduce the open cross-sectional surface of the throttle duct. The flow delivered to the consumer is reduced by this. Starting at a second point, where the second control edge enters the area of the opening of the throttle duct, the open cross-sectional surface of the throttle duct in this area is increasingly enlarged. This results in an unsteady point in the course of the characteristics flow rate curve, for example to the effect that from this point on the characteristics curve descends less steeply or not at all anymore. The amount regulated away by the first control edge is definitely regulated back by the second control edge.
Advantageous and useful embodiments of the invention are recited hereinbelow. The control edges can be embodied particularly easily if the first control edge is constituted by a cut between the front face of the regulating piston facing the spring chamber and the cylindrical circumferential face of the regulating piston. The further control edge then is designed as a limit edge of an annular groove arranged on the cylindrical circumferential surface of the regulating piston.
In a second exemplary embodiment, both control edges are constituted by respective limit edges of two annular grooves arranged on the cylindrical circumferential surface of the regulating piston. It is possible by means of this to set the characteristic flow rate curves with greater variety. For example, a characteristic flow rate curve results as a function of viscosity, which has particularly good cold-starting properties.
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Fastovsky Leonid
Larson & Taylor PLC
Walberg Teresa
ZF Friedrichshafen AG
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