Land vehicles – Wheeled – Running gear
Reexamination Certificate
2002-08-02
2004-11-16
Fleming, Faye M. (Department: 3616)
Land vehicles
Wheeled
Running gear
C280S090000
Reexamination Certificate
active
06817620
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to vehicle steering systems and more particularly to a centering device for controlling the steerable wheels of a vehicle such as a motor home, bus, truck, automobile or the like so that a center steering position is selected and maintained in spite of spurious steering inputs, such as those caused by variable crosswinds, crown curvature or slant of the highway, or other factors tending to adversely affect vehicle steering by the driver.
BACKGROUND OF THE INVENTION
The steering systems of highway vehicles and the like are designed primarily for driver control. In these systems, the steering force required on the steering wheel and the ratio between steering wheel movement and movement of the steerable ground wheels depend upon the characteristics of the particular vehicle and the conditions under which it will usually be operated. A wide variety of extraneous forces can act on a vehicle steering system and spurious steering inputs caused by these forces must be dealt with satisfactorily in order to provide stable and controllable steering of a vehicle. As vehicle speed increases, the effects of any spurious steering inputs are magnified, making it necessary for the driver to exercise more precise and careful driving control.
Vehicles with steering systems having positive caster generally track relatively straight ahead and generally resist normal steering inputs away from center, including those of the driver. Intentional turning maneuvers by the driver therefore require sufficient turning force to overcome this positive resistance to movement away from center. When the driver relaxes the turning force applied to the steering wheel, a positive caster system has a definite tendency to return to its straight ahead position, although it may overshoot the neutral or center position if the steering wheel is entirely released.
While positive caster is desirable in some respects, it is not without compromises over the full steering spectrum. For example, the adverse effects of strong gusty cross winds are usually more pronounced with positive caster. As its name would imply, the vehicle tends to caster towards the side of the roadway to which it is being pushed by the wind. Similarly, a high crown at the center of the roadway or a slanted roadway can cause vehicles to turn toward the edge of the roadway, that is, in the downhill direction. In addition, generous positive caster provides significant resistance to small radius turns, which can make city driving quite fatiguing. These three adverse effects are some of the negative aspects of achieving steering stability through generous amounts of positive caster.
Another drawback of prior art steering systems is that spurious inputs transmitted from the roadway through the steerable wheels affect substantially the entire steering assembly before encountering any stabilizing resistance from the steering wheel. The negative action of the steerable wheels is caused by spurious steering inputs from crosswinds, slanted or crown roads, bad road surfaces, and other adverse dynamic steering forces. Inherent geometric steering characteristics may also be responsible for spurious steering inputs.
The transmission of these various inputs between the steerable wheels and the steering wheel causes the interconnecting components of the steering system to repeatedly oscillate between states of tension and compression. Such oscillations cause wear and slack in ball joints and other connections and have long been considered a primary source of stress fatigue which can lead to premature failure of various steering system components. Mechanical slack due to worn parts can also be a cause of steering system oscillations and vehicle wandering that require constant corrections and therefore produce driver fatigue.
The ideal driving situation is therefore one where the steering system inherently causes the vehicle to travel in an unswerving straight line unless the driver intentionally turns the vehicle in another direction. Thus, the ideal steering system would require relatively little attention from the driver as the vehicle progresses along a straight line path down the roadway. From a steering standpoint, the vehicle should not respond to anything but the driver's steering commands and these must be of sufficient magnitude to overcome a significant resistance to turning away from center. In the absence of a steering input by the driver, the vehicle should literally do nothing but progress straight ahead.
SUMMARY OF THE INVENTION
The invention provides improved on-center control of the steerable wheels, and significantly reduces driver fatigue because it results in a major reduction in driver steering inputs. This is accomplished by allowing the driver to easily make small adjustments in the centered position of the steering system to fine tune steering of the vehicle during its operation. Such fine tuning is made while driving, and makes driving more pleasurable and less fatiguing.
The invention thus comprises a precision steer wheel control system having a center position which is remotely adjustable to permit the driver of a vehicle to change and reset the center position of the vehicle's steering system to compensate for new or changed steering forces which would otherwise cause the vehicle to deviate from its straight ahead course.
In addition, the control system of the invention provides remotely adjustable levels of resistance force for opposing off-center steering movements and of centering force for returning the steering system to its center position after a turning movement. The adjustment means also provides for different levels of steering force to initiate or breakaway into a steering movement away from center. This level of force is sometimes referred to in this specification as the “break away resistance”. Different levels of break away resistance and of resistance force may be appropriate to compensate for different steering system characteristics on the same or different types of vehicles and/or for changes in the forces acting upon the vehicle. The level of break away resistance and of resistance force opposing movement away from center may be remotely adjusted either by a control mechanism operable by the driver or by a microprocessor responsive to the speed of the vehicle.
The return force for returning the steering system to center may also be remotely adjusted either by a control mechanism operable by the driver or by a microprocessor responsive to the speed of the vehicle. Both the resistance force and the return force provided by the control system are increased or decreased to provide a level of force sufficient to overcome any spurious steering inputs and to suit driver road feel, particularly a feel of the steering wheel that lets the driver know when the steered wheels are beginning to move away from center and are closely approaching return to center.
The control system may be left on continuously because it will automatically turn off with the ignition and come back on when the engine is started. With any malfunction of the vehicle's power steering, an automatic disabling feature of the invention shuts the control system completely off.
The invention also provides a distinctive feel when approaching or leaving the center position. Thus, the sense of touch is added to the visual sense to aid control of the vehicle and reduce driver fatigue. The turning resistance selected should satisfy the road feel desired by the driver and be sufficient to overcome anticipated spurious inputs.
In the absence of the invention, spurious inputs to and/or mechanical slack in the steering assembly require almost constant manipulation of the steering wheel by the driver and make it almost impossible for the driver to hold the vehicle on a true straight ahead course. Use of the invention therefore permits a substantial reduction or elimination of the caster angle for vehicles previously requiring positive caster, thereby significantly reducing the crosswind effect and providing the dri
Belser, Jr. Townsend M.
Fleming Faye M.
Nexsen Pruet Adams Kleemeier LLC
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