Motor vehicles – Special wheel base – Having only two wheels
Patent
1994-05-10
1996-04-02
Focarino, Margaret A.
Motor vehicles
Special wheel base
Having only two wheels
280660, 280673, 280 963, B62K 2102
Patent
active
055032443
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a motorcycle having a stub-axle steering for the front wheel of the motorcycle. Such stub-axle steerings have been known for a while. In contrast to steering mechanisms suspended on the steering head, the stub-axle steering allows the wheel guiding elements and the spring/absorber elements to be suspended on the main frame such that they are not pivoted with the wheel in the course of steering movements.
The advantage of a stub-axle steering resides inter alia in that the moments of inertia about the steering axis are reduced and the construction height of the motorcycle is decreased while maintaining sufficient space for spring deflection.
Every motorcycle has two critical modes of oscillation. The first mode of oscillation is the shimmy, i.e. an oscillation of the front wheel and the steering system about the steering axis. The shimmy can be obviated by increasing the trail. The trail is defined as the distance between the vertical projection of the wheel axis onto the driving ground and the extension of the steering axis to the ground. On the other hand, the trail must not be made too long, since otherwise the motorcycle becomes difficult to steer. The second critical mode of oscillation is the pendulum motion, representing a complex intercoupled oscillation of the front and rear wheel system, during which the motorcycle is subject to a steering, yawing and rolling oscillation. This oscillation can be obviated by a rake angle of the steering axis as flat (i.e. small) as possible, i.e. by an angle as small as possible between the ground and the steering axis about which the front wheel can be pivoted. Thus, the optimum is a relatively small rake angle of the steering axis in combination with a trail that is not too great. These design constraints are difficult to meet, as in conventional constructions a small rake angle of the steering axis results in too great a trail rendering the motorcycle difficult to control. The stub-axle steering probably best known is the so-called "Diffazio steering" according to which the front wheel is suspended through a stub axle on a large forked swinging arm and can be pivoted about a stub-axle pin whose longitudinal axis thus represents the steering axis as well. This steering axis extends through the center of the wheel, causing an undesirably great trail while yielding an acceptable rake angle of the steering axis. Hence, the motorcycle is difficult to steer. Moreover, the angle of steering lock is relatively tightly limited, as a result of which this type of steering has not been able to gain general acceptance for the road traffic; in Germany, for example, a possible angle of steering of at least 30.degree. to both sides is required for obtaining administrative approval.
A further exemplary stub-axle steering is known from racing sports in the form of the "Elf-X" prototypes. Such a stub-axle steering is disclosed in the German patent specification no. 29 05 776, in which the front wheel is provided with a pivot bearing offset laterally from the center plane of the wheel and guided in a relatively complicated manner by two swinging arms arranged on one side. The steering axis formed by the pivot bearing is offset from the wheel axis towards the rear of the vehicle so that the trail does not get too long. Pivoting of the front wheel takes place by means of a relatively complicated construction comprising a track rod and lever.
A drawback of this construction resides in that the steering axis is laterally offset (in a plan view) from the longitudinal axis of the motorcycle and, thus, from the center plane of the wheel, whereby the longitudinal forces acting on the front wheel cause a steering torque which the driver has to compensate for by counter-steering.
In order to at least reduce this steering torque, attempts have been made to place the steering axis as close as possible to the center plane of the wheel. To this end, the wheel spokes were formed such as to curve arcuately at one side towards the wheel side having no swinging arm. However,
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Focarino Margaret A.
Zeender F.
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