Land vehicles – Wheeled – Running gear
Reexamination Certificate
1998-11-06
2001-03-20
Swann, J. J. (Department: 3611)
Land vehicles
Wheeled
Running gear
C280S093511, C074S496000
Reexamination Certificate
active
06203038
ABSTRACT:
PRIOR ART
The invention relates to a vehicle steering mechanism (device used in steering a vehicle) of the type that allows the ratio of transmission between the controlling movement of a steering control device and the controlled movement of the components of the vehicle which are steered by the steering mechanism to be varied, with the variability of the transmission ratio being generated principally via the steering gear. A steering gear of this type encompasses a drive component and an output component, and translates movement of the drive component into movement of the output component, with the ratio of transmission being variable. The drive component of the steering gear is connected to the steering control device, wherein the ratio of transmission between the movement of the steering control device and that of the drive component remains basically constant. The output component of the steering mechanism is connected to the steered components of the vehicle, wherein, again, the ratio of transmission between the movement of the output component and that of the steered components of the vehicle remains basically constant.
The term “vehicle” will hereinafter be used to refer generally to any vehicle (land-based vehicle, watercraft, aircraft, space vehicle); however, for purposes of illustration, the most common example, that of an automobile, will be used to illustrate the steering mechanism and steering gear specified in the invention, as well those known-in-the-art assemblies assemblies. In a land-based vehicle, the steering control device is normally comprised of a assemblies wheel, and the components of the vehicle steered by it comprise the wheels of the vehicle. In the case of a boat, the steering control device and the components steered by it may be comprised of a steering wheel or rudder, and in the case of an aircraft, they may be comprised of a control stick or rudder unit.
When used in an automobile steering mechanism, the drive component of the steering gear—normally in the form of a steering shaft—is connected to a steering wheel. The output component of the steering gear is connected to the steered wheels of the vehicle, usually the front wheels, via a steering linkage. The steering linkage normally comprises tie rods, connecting rods, a steering arm, and/or other components. In the case of a rack-and-pinion steering mechanism, the steering gear is comprised of a pinion-steering rack mechanism, with the steering rack, which forms the output component of the steering gear, being connected to the steering linkage. In the case of a cam-and-roller steering mechanism and/or a ball-and-nut-type power steering mechanism, the output component of the steering gear is formed by a so-called steering roller shaft, to which a steering arm, which controls the steering linkage, is connected.
In the case of a land-based vehicle having a steering wheel and steered wheels, the angle of the steering wheel is designated as a and that of the steered wheels is designated as &bgr;. Then, the steering mechanism of the vehicle generally translates a rotation of the steering wheel by an angle of rotation d&agr; into a rotational movement of the steered wheels by a steering angle d&bgr;. In most commonly used steering mechanism, the transmission ratio between the rotational movement of the steering wheel and that of the steered wheels remains basically constant over the entire steering range from one steering stop of the steering mechanism to the other steering stop, in other words, there is a linear relationship between the angle of rotation d&agr; of the steering wheel and the steering angle d&bgr; of the steered wheels.
In terms of operation of the vehicle, however, a variable ratio of transmission between the rotation of the steering wheel and the rotation of the steered wheels is generally desirable. In addition, the requirements as to the characteristic curve of this transmission ratio may differ greatly depending upon the type of vehicle and/or the driving conditions. For example, for secure control of the vehicle at high speeds, in which the steering assembly is operated principally within a narrow range around the straight-ahead position, a high transmission ratio d&agr;/d&bgr; (ratio between the angle of rotation d&agr; of the steering wheel and the steering angle d&bgr; of the steered wheels) is desirable, in order that slight movements of the steering wheel do not result in an abrupt change in direction. However, when the vehicle is being maneuvered at low speeds, especially during parking, a low transmission ratio d&agr;/d&bgr; is desirable, in order that the steered wheels may be rapidly turned from one steering stop to the other steering stop.
When the transmission ratio d&agr;/&bgr;, (ratio between the angle of rotation d&agr; of the steering wheel and the steering angle d&bgr; of the steered wheels) of a neutral steering position for travel straight ahead decreases with rotation of the steering wheel to the right or left up to the steering stop, this is referred to as a progressive steering mechanism. With a progressive steering mechanism (that is, a steering mechanism for which the transmission ratio has a progressive characteristic curve) a rotation of the steering wheel around a certain angular increment d&agr; when the wheels are already turned thus effects a greater rotation d&bgr; of the steered wheels than when the wheels are in a straight position. A progressive steering mechanism is particularly advantageous for racing cars, as it enables precision steering on the straightaway at high speeds, while permitting rapid adjustments to the steering angle of the steered wheels should the vehicle go into a skid, thus permitting the car to pull out of the skid.
In contrast, one may speak of a degressive steering mechanism (that is, a steering mechanism whose transmission ratio has a degressive characteristic curve) when the transmission ratio d&agr;/d&bgr; (ratio between the angle of rotation d&agr; of the steering wheel and the steering angle d&bgr; of the steered wheels) of a neutral steering position for driving straight ahead increases with the rotation of the steering wheel to the right or left up to the steering stop. In the case of a degressive steering mechanism, a rotation of the steering wheel around a certain angular increment d&agr; when the wheels are turned out of the straight-ahead position effects a lesser rotation d&bgr; of the steered wheels than when the wheels are in a straight-ahead position. A degressive steering assembly may be used, for example, in cases in which it is desirable to omit a power or power-assisted support of the steering mechanism, while enabling the steering of heavy-duty vehicles at low speeds. In this case, a degressive steering assembly facilitates maneuvering, for example, during parking at low speeds, in that it operates more smoothly when the wheels are turned very far than when they are in the straight-ahead range.
One vehicle steering mechanism having a variable transmission ratio is offered, for example, by the firm “ZF Friedrichshafen AG” of Germany, in the form of a rack-and-pinion steering assembly having either a degressive or a progressive characteristic curve. The degressivity or progressivity of this steering mechanism is based upon a steering rack the toothing of which is manufactured using a different module and pressure angle. The difference between the largest and the smallest transmission of the steering rack amounts to a maximum of approximately 30%.
From DE 195 19 588 A1 (Honda) a steering gear having a progressive characteristic curve is known in the art. The variability of the transmission ratio in this steering gear is based upon the fact that the output shaft of the steering gear extends parallel to its input shaft, but offset from it somewhat (that is, eccentrically). To couple the input shaft with the output shaft, a connecting component is positioned between the two shafts, which performs the basic function of a thrust crank (rectilinear sliding pair combined with a hinge), transmitting the torque
Shriver J. Allen
Swann J. J.
Wandfluh Automotive AG
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