Tensioning and absorbing element

Details Tensioning and absorbing element Tensioning and absorbing element

2001-01-16

2002-12-03

Hannon, Thomas R. (Department: 3682)

Endless belt power transmission systems or components

Means for adjusting belt tension or for shifting belt,...

C474S109000

Reexamination Certificate

active

06488602

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a tensioning and damping element consisting of an elastomeric material for chain drives, especially a tensioning and damping element for the secondary chain drive of a motorcycle exhibiting temporary alteration of the distance between the centers of the sprocket wheels.
BACKGROUND OF THE INVENTION
In motorcycles having a secondary chain drive and a rear wheel swinging arm, there is the problem of the temporary alteration of the distance between the centers of the sprocket wheels during the swinging movement away from the middle position of the swinging arm, which is used as the position for adjusting the slack of the chain and the distance between the centers of the sprocket wheels, in the phases of the upper, deflected end position of the swinging arm and the lower, rebound end position of the swinging arm. Upon deflection and rebounding of the swinging arm, therefore, the distance between the centers of the sprocket wheels is also always reduced, with the effect that the chain slack in the non-loaded strand becomes greater. The cause of this is the position of the sprocket wheel at the gearbox output which is determined by the design and which does not coincide with the pivot of the rear wheel swinging arm but lies in front of the pivot in the direction of travel.
The temporary alteration of the distance between the centers is combined at the same time with an enforced rotation of the rear wheel, since the rear wheel is rolling along the roadway when the distance of the center point of the wheel from the sprocket wheel at the gearbox output changes. The same rotational movement as the rear wheel is performed, therefore, by the sprocket wheel on the rear wheel and, at a suitable gear ratio, also by the sprocket wheel at the gearbox output. The temporary alteration of the distance between the centers and the enforced rotation of the rear wheel by the rolling movement during deflection and rebounding exacerbate other and impair the driving stability of the motorcycle.
When there is a large amount of slack in the non-loaded strand, oscillations and shocks furthermore occur in the non-loaded strand, which have an adverse effect on the driving characteristics of the motorcycle. To avoid that disadvantage, therefore, a spring-loaded chain tensioning device directed towards the non-loaded strand is usually provided.
In the transition phases from acceleration to braking or during gear-changing, there will also be phases in which the loaded strand also is not loaded. One also speaks in this context of “double non-loaded strand phases” in which also the loaded strand briefly runs under no load. Those phases are especially dangerous, since they may cause the circulating, temporarily overlong, chain which is loaded only by centrifugal force to ride up on the sprocket wheel at the gearbox end, which may result in indifferent changing of the gear ratio of the secondary chain drive and/or in skipping of the chain.
The alteration of the distance between the centers, the enforced rotation of the rear wheel and the double non-loaded strand phases result in indifferent phases of the vertical dynamics of the vehicle which are affected by springing, damping and tire resilience and in indifferent phases of the longitudinal dynamics (shifting of the center of gravity and pitching motion) of the motorcycle. When cornering with changing load caused by braking or acceleration and when there is a large amount of slack in the non-loaded strand in the lower, rebound end position of the swinging arm, the contact surface of the tires may be so greatly reduced that it is no longer possible to control the motorcycle and a fall is inevitable.
A tensioning and damping element for chain drives is known from DD 275 166 A3. In that specification, the element is an axleless ring of elastic material which mates with the chain and which is elastically deformable between the shape of a concentric ring and the shape of a Cassini curve having an ellipse-like configuration. That tensioning and damping element is arranged between strands of the chain drive and engages therein by its toothed rim, automatically securing its position in the chain drive and tensioning diametrically.
A tensioning and damping element is also known from DE 43 17 033 C1, which will be described in more detail below with reference to
FIGS. 2 and 3
using, as an example, a secondary chain drive of a motorcycle exhibiting temporary alteration of the distance between the centers of the sprocket wheels.
The chain drive shown in
FIGS. 2 and 3
has a sprocket wheel
1
at the gearbox end, a rear wheel sprocket wheel
2
and a circulating chain consisting of a loaded strand
5
and a non-loaded strand
6
. Arranged between the non-loaded strand and the loaded strand is a tensioning and damping element
7
which assumes an ellipse-like shape in this stressed, installed state. That tensioning and damping element comprises an elastically deformable ring part and a toothed rim arranged at the periphery thereof, the ring part being circular in the stress-free, uninstalled state. In the installed state, the toothed rim engages with the non-loaded strand and the loaded strand, whereby a tensioning force caused by the ellipse-like deformation of the ring part is transmitted to the two strands.
The rear wheel sprocket wheel
2
is fastened to one end of a rear wheel swinging arm
4
which, at the other end, can be pivoted about a swinging arm pivot
3
from the middle position shown in
FIG. 2
into a deflected and a rebound end position of the swing. In
FIG. 3
, the deflected end position of the swinging arm is shown.
Owing to the fact that the swinging arm pivot
3
and the pivot of the sprocket wheel
1
at the gearbox end do not coincide, temporary alteration of the distance between the centers of the two sprocket wheels
1
,
2
occurs upon movement of the rear wheel swinging arm
4
. In the middle position shown in
FIG. 2
, a maximum distance between centers a
max
is produced and, in the two end positions, see
FIG. 3
, a minimum distance a
min
. As a result of the distance between the centers being reduced, the chain slack in the non-loaded strand
6
increases.
The biased, installed tensioning and damping element always strives to attain its stress-free state in which it has a circular shape. The tensioning and damping element is so dimensioned that it never assumes its stress-free state in the installed state. That ensures that, even in the deflected end position shown in
FIG. 3
, in which greater chain slack occurs, a tensioning force will still be transmitted to the two strands by the tensioning and damping element. The tensioning and damping element therefore changes its shape in dependence upon the distance between the centers of the two sprocket wheels
1
,
2
, as can be seen especially from
FIGS. 2 and 3
. In the state shown in
FIG. 2
, the distance between the minor axis extremities N
1
, N
2
of the tensioning and damping element deformed into an ellipse-like shape is smaller than in the state shown in FIG.
3
. In addition to compensating for chain slack, the tensioning and damping element also damps deflections of the chain which may arise, for example, as a result of polygonal and over-running shocks and the effects of gravity and/or centrifugal force.
The tensioning force and the damping increase with increasing ellipse-like deformation of the tensioning and damping element as a result of dynamically elastic and plastic deformation parameters. In addition, the tensioning force is at the same time increased by static deformation parameters.
That means, however, that during driving operation, the tensioning and damping element
7
is dynamically loaded to a greater extent in the phases in which the rear wheel swinging arm
4
is in the middle position shown in
FIG. 2
, and in which the amount of chain slack is consequently smaller, than it is in the deflected end position of the rear wheel swinging arm shown in FIG.
3
.
During operation of the chain drive, the tensioning and damping e

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