Belt for continuously variable transmission

Details Belt for continuously variable transmission Belt for continuously variable transmission

2000-06-30

2003-09-30

Joyce, William C (Department: 3682)

Endless belt power transmission systems or components

Friction drive belt

Including plural interconnected members each having a drive...

C474S201000

Reexamination Certificate

active

06626782

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission, which is comprised of metal ring assemblies each having a plurality of endless metal rings laminated one on another, and a plurality of metal elements each having ring slots into which the metal ring assemblies are fitted, the belt being wound around a drive pulley and a driven pulley to transmit a driving force between the pulleys.
2. Description of the Related Art
For explaining how forces generally act on a belt and its components during operation of a continuously variable transmission, reference is now made to
FIGS. 7
,
8
,
10
A and
10
B which are part of the drawings illustrating an embodiment of the invention.
As shown in
FIG. 8
, when a metal element
32
supported with a ring slot
35
thereof fitted over a metal ring assembly
31
is inclined forwards in a direction of advancement, a rear end a (in the direction of advancement) of a saddle surface
44
is brought into abutment against an inner surface of the metal ring assembly
31
. This causes a problem that a large stress &sgr;H (a hertz-stress) is produced at the rear end a which exerts a deleterious effect on the durability of the metal ring assembly
31
. The forward (in the direction of advancement) inclination of the metal element
32
is caused by a tangent frictional force F which the metal element
32
receives on its pulley contact surface, and an urging force E provided between the metal elements
32
. This tendency is particularly significant in an exit region of the driven pulley. The reason will be described below.
As can be seen from
FIG. 7
, a moment generated in the direction of an arrow M by the tangent frictional force F acts to lower the metal element
32
forwards in the direction of advancement about the swinging center C. On the other hand, a radial frictional force &mgr;E generated by the urging force E provided between the metal elements
32
generates a moment in the direction of an arrow M′ on the metal element
32
. This moment acts to lower the metal element
32
backwards in the direction of advancement about the swinging center C.
It is known that the tangent frictional force F, which the metal element
32
receives from a drive pulley
6
or a driven pulley
11
, is increased in an exit region of the pulley
6
or
11
, as shown in
FIG. 10A
, and such tangent frictional force F reaches four times the value provided when it is assumed that the tangent frictional force F has been distributed averaged over the entire wound region of the pulley
6
,
11
, for example, for the reason that the pulleys
6
,
11
are deformed, whereby the axial thrust is concentrated. In addition, as shown in
FIG. 10B
, the urging force E between the metal elements
32
assumes a large value in the exit region of the drive pulley
6
, but assumes 0 (zero) in the exit region of the driven pulley
11
. Therefore, the metal element
32
is liable to be inclined forwards in the direction of advancement to the maximum extent in a location where the tangent frictional force F inclining the metal element
32
forwards in the direction of advancement is the maximum and the urging force E inhibiting the forward (in the direction of advancement) inclination of the metal element
32
assumes 0 (zero), i.e., in the exit region of the driven pulley
11
.
When the metal element
32
is greatly inclined forward in the direction of advancement in the exit region of the driven pulley
11
for the above-described reason, the following problem is encountered: A rear end a (in the direction of advancement) of a saddle surface
44
of the ring slot
35
in the metal element
32
is brought into strong abutment against an inner circumferential surface of the metal ring assembly
31
(see FIG.
8
), whereby the fatigue life of the metal ring assembly
31
is shortened by the stress &sgr;H generated at the rear end a.
There are conventional known metal elements which are described in Japanese Utility Model Applications Laid-Open Nos. 59-79653 and 63-17353, Japanese Patent Application Laid-Open No. 6-10993 and Japanese Utility Model Application Laid-Open No. 60-107444, and which have a feature in the shape of a saddle surface against which an inner circumferential surface of a metal ring assembly abuts.
In the metal element described in Japanese Utility Model Application Laid-Open No. 59-79653, opposite ends of the saddle surface of the metal element in the direction of advancement are chamfered smoothly., In the metal element described in Japanese Utility Model Application Laid-Open No. 63-17353, a stepped projection is formed at a central (in the direction of advancement) portion of the saddle surface of the metal element, and an arcuate surface having a radius equal to a minimum wound radius of a metal ring assembly is formed at a top surface of the projection. The object of such arrangement is not described in the publication, but it is believed that the inventors have intended to moderate the strong abutment of the opposite (in the direction of advancement) ends of the saddle surface against the inner circumferential surface of the metal ring assembly in a region where a belt for a continuously variable transmission is wound around a pulley. In these metal elements, it is difficult to effectively moderate a hertz stress generated by the abutment of the rear (in the direction of advancement) end of the saddle surface against the inner circumferential surface of the metal ring assembly in an exit region of a driven pulley, because the shape of the saddle surface is symmetrical about its center in the direction of advancement.
In the metal elements described in Japanese Patent Application Laid-Open No. 6-10993 and Japanese Utility Model Application Laid-Open No. 60-107444, the saddle surface of the metal element is formed into an asymmetrical shape such that a rear (in the direction of advancement) portion of the saddle surface is lower in level than a front portion of the saddle surface. The object of such arrangement is to prevent the metal element from falling forwards and backwards by a pitching moment. These metal elements suffer a problem that the shape of the saddle surface is complicated, resulting in an increased processing cost.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to prevent a reduction in the durability of the metal ring assembly due to the inclination of the metal element, without increasing of the processing cost of the metal element.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a belt for a continuously variable transmission having a drive pulley and a driven pulley, comprising metal ring assemblies each having a plurality of endless metal rings laminated one on another, and a plurality of metal elements each having ring slots into which the metal ring assemblies are fitted. The belt is wound around the drive pulley and the driven pulley to transmit a driving force between both the pulleys, wherein a saddle surface of the ring slot, against which an inner circumferential surface of the metal ring assembly abuts, is formed so that the radius of a rear corner is larger than that of a front corner in a direction of advancement of the metal elements.
With the above arrangement, when the metal element moved away from the driven pulley, falls forwards in the direction of advancement, the comer of the saddle surface of the ring slot located on the rear side in the direction of advancement and having the larger radius is urged against the inner circumferential surface of the metal ring assembly. Therefore, it is possible to maintain the hertz stress generated on the inner circumferential surface of the metal ring assembly to the minimum to enhance the durability of the metal ring assembly.
According to a second aspect and feature of the present invention, each of the metal elements is formed by punching from a metal plate material,-and the rear comer in the direction

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