Belt

Details Belt Belt

2001-12-28

2004-03-16

Charles, Marcus (Department: 3682)

Endless belt power transmission systems or components

Friction drive belt

Including plural interconnected members each having a drive...

C474S201000, C474S272000

Reexamination Certificate

active

06705963

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a belt for a continuously variable transmission.
DETAILED DESCRIPTION OF THE RELATED ART
Such a belt, generally known as a “push belt” and in this particular design alternatively denoted single package push belt, is generally known from a plurality of publications. One early publication of a so-called single package belt is U.S. Pat. No. 3,720,113. The single package push belt is highly desired for practical application compared to a double package belt as known from later publications like EP-A 0000802, but suffers from costly technical measures at providing separate retaining means to keep the carrier and transverse elements of the belt as a whole, in other words to prevent the elements from falling apart from the carrier and to maintain its structural coherence. This maintaining of the integrity of the belt particularly is an issue while the belt is in operation, but is also a consideration at simply maintaining the integrity of a belt assembly.
The prior art shows several ways of solving the above-mentioned problem. In particular, several types of carrier receiving recesses of the transverse element are shown. Amongst these are the provision of one or more axially extending slots, the provision of element parts for hooking the carrier, and the provision of retaining means for locking the carrier receiving recess such as closure pins.
In the belt disclosed by the said US publication, radially extending limb parts of the element are bent axially inwardly with respect to the recess, thereby creating a hook like part, so that the carrier, in addition to it being surrounded along its lateral and its radial inner sides, is at least partly surrounded along its radial outer side too. This construction of hooking of the carrier by the transverse element is favourable for it's relatively low weight. However, the construction suffers from manufacturing difficulties in that the inward bending of the transverse element provides for a relatively complicated blanking shape and in that at assembly specific effort is required to insert the carrier in the desired position relative to the transverse elements. In particular, the carrier can not be inserted freely, i.e. without deformation thereof. Such deformation may be an initiator of carrier breakage when under severe tensile load during operation. Another construction of such kind is disclosed in EP-A 0095257, where the carrier is relatively tightly hooked into a contacting position with the element.
A construction, which overcomes the latter insertion problem, is known from EP-A 0135237. In this known construction an element shows a so-called slot, being a laterally oriented recess in the element having an opening towards an upper corner of the element. At least part of the radial outer side of the carrier is contacted by a radial outer, or upper element part, and the elements are to be inserted in an alternating sequence. Belts comprising such elements come with a relatively high weight, thus limiting the performance in terms of transmittable torque. Also the alternating sequence requirement brings along a manufacturing complication in that the elements have to be assembled into the belt alternatingly positioned, i.e. mirrored about the longitudinal direction of the belt.
An alike earlier construction showing a favourably more simple slot construction is known from EP-A 0073962. This document discloses elements with a more or less straight slot having an opening towards an axial side of the element. For preventing the risk of the carrier coming into contact with a pulley face while the belt is in operation, also with this construction the elements have to be fitted mirrored. The complication of mirrored adjacent elements is suggested to be overcome by producing the lower, tapered element part with a two sided tapering so that, expectedly at the expense of some production difficulty and cost, only one element orientation need be applied.
Another known single package design shows a separate element type for maintaining belt integrity at operation of the belt. Such element type is provided with a retaining means in the form of locking element, e.g. a pin or a locking ring, closing of the carrier receiving recess after assembly thereof. Such a construction may render a secured integrity of the belt, both in operation and as a separate part, but is relatively unfavourable due to weight and manufacturing cost, while the robustness in many designs can not be guaranteed when somewhat larger torque levels are to be transmitted, such as e.g. typically required for automotive application. Of this belt design, one such pin construction is disclosed in EP-A 0122064, and one such ring construction is disclosed in U.S. Pat. No. 5,123,880.
SUMMARY OF THE INVENTION
The present invention principally, but not exclusively, aims at realising a single package belt design without above mentioned cost raising disadvantages, which is composed of only a single element type, which has a relatively uncomplicated shape and a relatively low weight so as to maximise the amount of torque transmittable by the belt, while still responding in a good manner to the various functional demands for a belt. Such a belt is according to the invention is discussed below.
A belt of the invention may be produced easily since in principle no carrier retaining means is required during operation. Surprisingly, in the design according to the invention the function of the retaining means of maintaining belt integrity may be achieved by favourably utilising and adapting some geometric features inherently present within a belt. Here setting a specific ratio between a circumference length of the belt, i.e. its longitudinal dimension when measured at the radially inner side of the carrier, and the height of the upper element part of the transverse elements.
The solution is based on the insight that at a slack in between pulleys part of the belt's trajectory when applied in a transmission, which is considered the most critical part in view of disintegration of the belt by the invention, the elements may block one another in a stable end position in which the relevant belt part is concavely shaped. The solution takes account of the experience and insight that such slack trajectory part has a tendency to buckle radially inward as a result of a clamping action on the belt by the pulleys, which tends to counteract the belt exiting the pulleys and urging the belt to continue to rotate in the pulley.
According to the invention the current design feature may favourably be applied to the double package belt designs. For the double package design this feature enables a different design of the element with respect to the known art. In particular the transverse width of the T-shaped upper element part may be reduced, since it no longer serves to limit the radial play between carrier and element. Moreover, the feature aids in securing or optimising the belt's functional lifetime, because the carrier is loaded less during operation of the belt. There e.g. no longer needs to be an interaction between the radial outer side of carrier and the element, which in the belt according to the known art occurs at the location where the elements exit a pulley. In this area the, due to elastic deformation of the pulley, the elements are clamped between the sheaves of the pulley very effectively such that they tend to keep rotating along with the pulley. In the known belt, the elements are pulled away from the pulley sheaves by the carrier interacting with the retaining means, such as the T-shaped upper element part or the locking pin, putting an additional load on those components. In the belt according to the invention, the elements of the belt are kept firmly in contact also in the slack trajectory part, so that a force for pulling the elements away from the pulley may be transmitted from one element to the other.
Alternatively, with the solution according to the invention favourably large values of a total end play, being the summation of

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