Patent Number: 6,254,358

Title: Positive-displacement pump

Abstract: A positive-displacement pump for conveying a pressure medium from a container to a consumer, in particular a power steering system includes, a pump package (2); the pump package includes a rotor (3), a cam ring (4) and several operating slides (5) has been inserted into the interior of a housing (1). A bypass flow control valve (11) with a piston (11A) is used for controlling an actual flow. A throttle of the bypass flow control valve (11) is formed by an orifice (12), which is fixed in place on the housing and has an adjustable cross-sectional surface. The cross-sectional surface of the orifice (12) is increased in case of an increasing pressure being applied to the orifice (12). The orifice (12) is arranged so it cannot be displaced in relation to the housing (1). By use of a pressure occurring at the orifice (12), the piston is exclusively displaced against the force of the spring (15), so that the cross-sectional surface of the orifice (12) can be changed as a function of the pressure. The piston is usefully designed as a control pin (13) which is displaceable, independently of the piston (11A) of the bypass flow control valve (11), in relation to the orifice (12). Because of this a regulation of the flow rate can already occur at low numbers of revolutions.

Inventors: Merz; Johann (Schwabisch Gmund, DE)

Assignee: ZF Friedrichshafen AG

International Classification: F04B 49/06 (20060101); F04B 049/00 ()

Expiration Date: 07/03/2018