WO1997026178A1

WO1997026178A1 - Steering system for a motorcycle's front wheel with in-hub kingpin

Info

Publication number: WO1997026178A1
Application number: PCT/GR1997/000003
Authority: WO
Inventors: Athanassiós LEFAS; Dionyssios Ohoidas
Original assignee: Lefas Athanassios; Choidas Dionyssios
Priority date: 1996-01-16
Filing date: 1997-01-16
Publication date: 1997-07-24
Also published as: GR1002722B

Abstract

Steering system for a motorcycle's front wheel with in-hub kingpin, mounted on a telescopic suspension system whose the sliding members so called sliders (8) extend through both ends of the supports (9) and at the lower end the sliders (8) have the wheel's composite axle (1) attached and at the upper end the sliders (8) are interconnected rigidly by a bridge (24) acting as a moving carrier of a part of the steering mechanism.

Description

STEERING SYSTEM FOR A MOTORCYCLE'S FRONT WHEEL. WITH

IN-HUB KINGPIN

This application refers to a steering system for the front wheel of a motorcycle. This steering system in integrated into a syspension consisting of members moving in a straight line and a front wheel incorporating the kingpin inside the hub.

The basic idea of such a concept is presented in another (ours,also) application (950100441/12.12.1995 - GR) with the title: "Telescopic system of syspension for a motorcycle's front wheel with hub-steering". This system consists of an "Upside Down" front fork, a wheel with kingpin ("incorporated inside the hub) and a steering transmission linkage.

This setup proved itself as inferior to the conventional front forks because: the simplification of the motor- cycle's frame and the small upgradation of the overall rigitity were not enough to compensate for the complexi¬ ty of the necessary steering mechanisms and the pro¬ duction difficulties. This is also the reason that simi¬ lar systems (also been applied for patent by various inventors) failed to prove their usefulness in the testing field and,finally in production.

Our point is that the complexity of the steering mecha¬ nism can be compensated only by a system that offers enormous gains in rigidity compared to weight. And the Upside-Down forks (with conventional steering or with hub steering) cannot provide enough torsional rigidity because their construction is composed by two separate parts (one moving, the other mounted on the frame) with a variable amount of overlapping between them, according to the "up and down" movement of the front wheel. Another problem of the "Upside Down Forks/Hub Steering" installa¬ tions, is that the steering linkage extends from the top of the upper (not moving) part of the fork to the bottom of the lower (moving) part of the fork, where it is connected to the "in-hub steering" wheel. The result is that the flexibility between the top of the upper part of the fork and the bottom of the lower part of the fork affects the relative distances between the interconnected parts of the steering transmission as- sembly. The result is a relative uncertainty of the position of the front wheel and the feeling of instabili¬ ty.

Our application goes further than conventional Upside Down Forks connected to a "hub-steer" wheel. In our case, we have a telescopic system whose sliding members do not "end" inside the stationary members. On the contrary, the sliding members continue through the top of the stationary members and their (the sliding mem¬ bers' ) upper extensions are interconnected via a rigid member (a "bridge"). This "bridge" is part of the steering system as a moving (up and down) carrier of certain steering transmission components. The benefits of our approach can be recognized from

1 the schematic prosentation of drawing . Here, the steering mechanism and the wheel are omitted for reasons of simplicity.

In drawing 1 we can see, from the front, our "bridged sliders'" concept with hub steering. The hub (4) of the wheel can move to the right and to the left around the kingpin (2) and the kingpin (2) is incorporated (or, simply, connected to) the "composite axle" (1 ) of the wheel. The composite axle (1) is conncected to the sliders (8). he sliders (8) have the freedom to move in a straight line through the supports (9) and the supports (9) are mounted rigidly to the frame (20) of the motorcycle.In their upper end, the sliders(8) are interconnected by a transverse member,the bridge(24). It is obvious that the orthogonal parallelogram con¬ sisting from the composite axle (1), the sliders 98) and the bridge (24) is a very stiff unit (according to weight) being able to withstand to large amounts of twisting or bending moments. The concept is that this parallelogram has,in whole, only one degree of freedom. Its motion is restricted by the supports(9) in a straight line and the composite axle (1 ) is always parallel to itself, during the up and down motion of the wheel.

It is important to mention here that we do not consider the pairs of sliders (8) and supports (9) as "shock absorbers". During our experiments we decided that the "shock absorption" is optimised by a separate damping unit (or pair of units) activated by a linkage pro¬ viding a variable leverage.

The "hub-steering wheel" is a known concept for at least

20 years with a number of commercial applications, especially with the "leading arm" type of motorcycle

(front) syspension.

In drawing 2 we can see two different kingpin (2) confi- figurations according to its friction-free connection to the hub. The bearing can be either of the bushing type or the "rollers" type.

In drawing 3 there is a simplified cut-out of the centre of the front wheel.The composite axle (1) can be moved only parallel to itself. he hub (4) can be moved around the kingpin (2) according to the "steering messages" passing via the hub terminal (6). Between composite axle (1 ) and hub (4) there are anti-friction bushings(3).

Between hub (4) and wheel (5) there are antifriction

(roller) bearings (7).

Our present request refers to an integrated steering/ syspension system. A side view of a certain application of this system can be seen in drawing 4.

The 6 angular motion of the handlebar (17) during the steering motion is transmitted by the shaft (12). This shaft (12) is connected to the lower arm (13) and trans- its to it its angular motion. The lower arm (13) can be rotated around the axis of the shaft bushing (15). The connection between the lower arm (13) and the hub terminal (6) of the hub (4) is being materialized by the lower link (14) as can be seen, also, in drawing 5. Thus, the angular motion of the shaft (12) can be transmitted to the hub (4) to obtain the desired steering effect.

In drawing 5 we can see, from another point of view (almost vertically to the ground) the connection between shaft (12), lower arm (13), lower link (14), hub termi- nal (6) and (the half of) the hub (4).

Notice: here we can see a certain application where the geometrical axis of the kingpin (2),to the slider (8) and shaft (12) are parallel. This configuration is been chosen just for the understanding of the concept in its simplest form.

To understand how the handlebar (17) activates the shaft (12) we have to go back to drawing 4.

The handlebar (17) rotates the handlebar plate (18) around the geometrical axis of the handlebar bushing (19), while the handlebar bushing (19) is mounted rigidly to the frame (20) of the motorcycle.

The handlebar plate (18) is connected (via a hinge) to the hinged yoke (30) and the hinged yoke (30) is composed by upper member (31) and the lower member (32) (drawing 6). Between the upper member (31) and lower member (32) there is a hinge. The lower member (32) is connected (drawing 5), via a hinge ,with the bridge plate (33) and the bridge plate (33) can turn around the geometrical axis of the bridge bushing (34) while the bridge bushing (34) is mounted on the bridge (24). The reason behind all this linkage is simple: The hinged yoke (30) transmits steering angular motion from the handlebar plate (18) to the bridge plate (33) while the bridge plate (33) is moving up and down according to the syspension movement of the wheel. Thus, the angu¬ lar "displacement" of the motion of the bridge plate (33) is equal to the angular displacement (steering input (of the handlebal plate (18) and the handlebar (17) itself.

In drawing 7 there is a shematic representation of the linkage over the bridge (24).

We can see the symmetrical half of the bridge plate (33) connected to the upper arm (22) via the upper link (21). The upper arm (22) transmits its angular motion to the (rotating) shaft (12). The shaft (12) transmits its angular motion to the hub (4) as already explained. In drawing 7 we can also notice the hinged connection between bridge plate (33) and the lower member (32) of the hinged yoke.

The equal angular displacements of the handlebar and the hub can be achieved by selecting equal (geometri¬ cally) parts in the linkages and arms connected to the bridge plate and ub respectively assuming that the bridge plate is "geometrically" equal to the hub. The "equality" of the relative dimensions for the upper (bridge) and lower (hub) mechanisms is not a necessity for the equal angular motion of the handlebar and the hub. his angular equality can be obtained also by a geometrical "similari¬ ty".

In practice, and during our full-scale experiments we achieved a better behaviour of the motorcycle by avoiding the "equality" of angular displacements (of handlebar and hub, respectively) in favour of a "proportional" transmission ratio.

In drawing 8 we can see the symmetrical half of the handlebar plate (18), rigidly connected with the handle¬ bar (17) and hinged to the upper member (31) of the hinged yoke (30).

The placing of the shafts (12) relative to the sliders

(8) is not obligatory as the one presented on drawing 4. We had the best results (according to the "working flexibility" of the sliders) with the shafts (12) passing through the inside of the sliders (8). This configuration protects, also, the shafts (12) from damage in case of an accident. It is obvious that when we have "similarity" and not "equality" of the relative geometrical shapes of the mechanisms in bridge and hub, respectively, the shafts (12) can e positioned as non-parallel to the sliders(8). For reasons of simplicity we assumed, to this point, that the geometrical axis of the kingpin and the geo- metrical axis of the sliders are parallel. In our experi¬ ments we had better results when the angle between the sliders and the vertical was bigger than the castor angle of the kingpin. This enabled the motorcycle to be quick in steering responce but also stable over road bumps because of the "friendly" angle of attack of the sliders relatively to the surface of the road.

Claims

1. We claim a steering system for a motorcycle's front wheel with in-hub kingpin (2), with the kingpin (2) mounted rigidly on the composite axle (1), this composite axle (1) is rigidly connected to two parallel sliders (8), the sliders (8) can move axially inside supports (9) mounted rigidly on the frame (20) of the motorcycle and this steering system is characterized by the fact that the composite axle (1) can be moved only in parallel positions to itself, by the fact that the sliders (8) are interconnected rigidly in their upper part by a transverse member, the bridge (24),where, the bridge (24) supports a rotating bridge plate (33), where the bridge plate (33) is connected with the handlebar plate (18) via a hinged yoke (30) and this steering system is also characterized by the fact that the steering variations of the directional angle of the wheel, re¬ lative to the steering input of the handlebar (17), is "produced" by the angular motion of the handlebar (17) which is transmitted to the handlebar plate (18) and of the handlebar plate (18) to the, mounted on the bridge (24), bridge plate (33) via the hinged yoke (30: from the bridge plate (33) to the upper arm (22) via the upper link (21), from the upper arm (22) to the lower arm (13) via the shaft (12) and, finally, from the lower arm (12) to the hub (4) via the lower link (14) whose the other end is connected to the hub termi¬ nal (6).

2. We claim a steering system for a motorcycle's front wheel with in hub kingpin (2), according to claim (1), characterized by the fact that during the action of the steering system, the geometrical axis of every point of the upper arm (22) and the lower arm (13) is a circle's arc positioned in a plane vertical to the geometrical axis of the shaft (12) and the center of each circle is positioned on the geometrical axis of the shaft (12).

3. We claim a steering system fora motorcycle's front wheel, according to claim 1, characterized by the fact that, for safety reasons, it can be consisted of two steering mechanisms of same type, positioned on each side of the wheel, and each one mechanism is composed from an uperlink (21), an upper arm (22), a shaft (12), a:lower arm (13) and a lower link (14).

4. We claim a steering system for a motorcycle's front wheel, according to claim 1, characterised by the fact that the handlebar bushing (19) of the handlebar (17), the kingpin (2) and the bridge bushing (34), have their geometrical axis belonging to the same straight line.

5. We claim a steering system for a motorcycle's front wheel, according to claims 1,2 and 4, characterized by the fact that the equal angular displacement between wheel and handlebar demands the equality of active lenght between the upper link (21) and the lower link (14) the equality of active radius between upper arm (22) and lower arm (13) and the equality between distance A and distance B, where A is the distance between the geometrical axis of the bridge bushing (34) and the joint between bridge plate (33) and upper arm (22) and B is the distance between the geometrical axis of kingpin (2) and the joint at hub terminal (6).