Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
2000-10-24
2002-09-17
Hurley, Kevin (Department: 3611)
Motor vehicles
Steering gear
With fluid power assist
C180S442000, C251S035000
Reexamination Certificate
active
06450286
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a rack and pinion power steering system with variable damping characteristics and more particularly, to a rack and pinion power steering system with variable damping characteristics which includes a variable orifice valve which allows the damping characteristics of the steering system to be selectively and controllably altered based upon the speed and steering wheel angle of the vehicle.
BACKGROUND OF THE INVENTION
Rack and pinion power steering systems include a hydraulic cylinder which selectively provides forces to the rack, effective to assist the driver in steering the vehicle. Particularly, these power steering systems utilize a control valve to selectively pressurize the hydraulic fluid or oil within the left and/or right chambers of the cylinder. This pressurization is based upon the rotary motion of the steering wheel and is converted by the cylinder into an assisting force which acts on the rack and which intensifies the steering force exerted by the driver.
Hydraulic cylinders used within rack and pinion power steering systems provide some amount of damping against forces that are transmitted to the steering wheel that may result from irregularities in the road surface. However, because the flow of fluid in and out of the cylinder is not properly limited to enhance damping, the damping capabilities of these cylinders are relatively limited.
Some steering systems include damper assemblies which provide a desired amount of damping. These damper assemblies provide a damping force which varies based upon the velocity of the damper according to a certain function, relationship or curve. However, these conventional damper assemblies have several drawbacks. Particularly, conventional damper assemblies typically have a single force versus velocity function or curve which does not vary based upon vehicle speed or other parameters. As a result, conventional damper assemblies have either a relatively high force/velocity curve which provides high damping of impacts while compromising steering effort, or have a relatively low force/velocity curve which maintains power steering effort at a desirable level, but does not substantially reduce steering “shimmy” and “nibble”. Moreover, these damper assemblies undesirably add to the cost of the vehicle.
There is therefore a need for a rack and pinion power steering system having variable damping characteristics which overcomes the drawbacks of prior steering systems and assemblies.
SUMMARY OF THE INVENTION
A first advantage of the invention is that it provides a rack and pinion power steering system having variable damping characteristics which overcomes some or all of the previously delineated drawbacks of prior steering systems and assemblies.
A second advantage of the invention is that it provides a rack and pinion power steering system having variable damping which does not require the use of additional damping assemblies.
A third advantage of the present invention is that it provides a rack and pinion power steering system which utilizes a variable orifice valve which controls the flow of fluid in and out of the system's steering cylinder in a manner which allows the cylinder to provide variable self-damping to impacts and vibration based upon vehicle speed and steering wheel angle.
A fourth advantage of the present invention is that it provides a rack and pinion power steering system having variable damping characteristics which provides relatively high damping at high vehicle speeds and high power steering effort at low vehicle speeds and during parking maneuvers.
According to a first aspect of the present invention, a power steering system is provided. The power steering system includes a rack and pinion assembly; a hydraulic cylinder which is operatively coupled to the rack and pinion assembly and which selectively provides a steering assist force to the rack and pinion assembly; and a variable orifice valve which is fluidly coupled to the hydraulic cylinder and which allows a certain amount of pressurized fluid to flow in and out of the hydraulic cylinder, the variable orifice valve having a variable volume fluid flow passage which is effective to selectively increase and decrease the fluid flow in and out of the hydraulic cylinder, thereby selectively altering the damping characteristics of the hydraulic cylinder.
According to a second aspect of the present invention, a valve assembly is provided. The valve assembly includes a housing having an interior cavity and at least one conduit which forms at least one fluid flow path; and a member slidably disposed within the interior cavity and having at least one tapered channel which cooperates with the at least one conduit to form the at least one fluid flow path, the member being selectively movable from a first position in which the at least one tapered channel causes the at least one fluid flow path to have a first volume, to a second position in which the at least one tapered channel causes the at least one fluid flow path to have a second volume.
According to a third aspect of the present invention, a method is disclosed for providing damping within a power steering system of the type including a rack and pinion assembly and a hydraulic cylinder which is coupled to the rack and pinion assembly and which provides an assist force to the rack and pinion assembly. The method includes the steps of providing at least one fluid flow path to the hydraulic cylinder for selectively communicating pressurized fluid to the hydraulic cylinder, effective to selectively cause the hydraulic cylinder to provide the assist force; and selectively varying the volume of the at least one fluid flow path.
These and other objects, aspects, features, and advantages of the present invention will become apparent from a consideration of the following specification and the attached drawings.
REFERENCES:
patent: 3896908 (1975-07-01), Petrak
patent: 4566477 (1986-01-01), Barker et al.
patent: 4705132 (1987-11-01), Tsuchiya
patent: 4949802 (1990-08-01), Gage
patent: 5261637 (1993-11-01), Curnow
patent: 5293952 (1994-03-01), Ledamoisel et al.
patent: 5435698 (1995-07-01), Phillips
patent: 5544715 (1996-08-01), Phillips
patent: 5600955 (1997-02-01), Sahinkaya
patent: 6148853 (2000-11-01), Wang
patent: 6164320 (2000-12-01), Hamano et al.
patent: 2001/0045318 (2001-11-01), Wang
patent: 58-139867 (1983-08-01), None
patent: 6067266 (1985-04-01), None
patent: 61159283 (1986-10-01), None
Offerle Timothy Gerard
Rui Yuting
Walsh Thomas J.
Wang Dexin
Ford Global Tech. Inc.
Ford Global Tech., Inc.
Hurley Kevin
Yeagley Daniel
LandOfFree
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