US 5,435,698 A · Bootstrap power steering systems

Abstract

Methods and devices for enhancing bootstrap hydraulic systems for use in vehicular power steering systems are disclosed. Improved pressure dividing networks are provided for enabling balanced operation of supply pressure control function when valve input shaft and sleeve are in relative centered positions or for enabling a first method of providing speed sensitive control of steering assist. Control valves utilizing a combination of open-center and closed-center flow control orifices are provided for reducing parasitic pressure losses. An improved variable displacement pump is provided for enabling volumetric flow rate efficient operation of bootstrap systems. A vehicular speed dependent command signal for a servo motor powered bootstrap hydraulic system is utilized in another method of providing speed sensitive control of steering assist. Control valves using parasitic and bypass slots having decreasing overall flow resistance over a meaningful portion of nominally closing motion of a host control valve are disclosed wherein methods of providing nominally linear control valve pressure-effort characteristics of the meaningful portion of nominally closing motion of the host control valve are comprised. Finally, various power steering systems utilizing selected combinations of these methods and devices for enhancing bootstrap hydraulic systems are disclosed.

Claims10

Dependent claims

A pressure unbalanced variable displacement pump for use with a control valve having a first and second output pressure, said pump comprising:

a housing having a main chamber with an inner peripheral surface and a control pressure chamber, said housing further having a inlet port spaced part from delivery port;
reaction member mounted within said main chamber abutting said peripheral surface;
a cam ring mounted within said main chamber, said cam ring having a bore and an outer periphery, said outer periphery being in rolling contact with said inner peripheral surface of said exterior chamber, said outer periphery of said cam member adapted to reciprocally roll on said inner peripheral surface to vary the displacement of said pump, said cam ring movable towards and away from said pressure chamber, said cam ring further having means for sealingly contacting said inner peripheral surface of said main chamber, said means for sealing diametrically opposed to said reaction surface;
means for biasing said cam ring in a direction towards said control chamber, said means biasing opposing pressure in said control chamber to position said cam ring with respect to inlet and delivery ports;
a rotor having a plurality of pumping chambers mounted for rotation within said main chamber;
and
means for connecting a lower pressure of said first and second output pressures to said pressure control chamber.

4 more elements

Dependencies are inferred from the claim text.

Bootstrap power steering systems

Life of this patent

Bootstrap power steering systems

Life of this patent

Abstract

Claims10