1. Field of the Invention
The present invention relates to the field of mechanical power transmission systems, which systems include a mechanism for the transmission of power between grooved pulleys wherein the transmission system includes at least one endless belt having a plurality of transverse links positioned thereon. Such systems include flexible elements, or belts, that operate by dry adherence, that is, without externally provided lubrication between the grooved pulleys. The transmission belt may include an interior V-shaped endless loop with a plurality of thrust links positioned thereon. The grooved pulleys may have fixed cheeks or flanges, or also, as is often used in variable speed transmissions, the pulleys may have movable cheeks or flanges. Both types of pulleys and/or transmissions are encountered in automotive applications and on agricultural and industrial equipment.
2. Background Information
Power transmission V-belts may be found in several families of products. The V-belts employed in such families of products may have similar external geometric shapes. Such belts were first used, and the majority of such belts are still used, for numerous industrial applications. The term "V-belt" applies, more precisely, to a composite material formed of traction cables. The cables, most often, are arranged in layers. The layers of cables form a longitudinal traction armature that may be embedded in an elastomer material. The elastomer material may be rubber or synthetic rubber. The transmission of forces by such V-belts takes place by frictional contact of the lateral, oblique surfaces of the belts with the metal walls of the conically shaped flanges of the pulleys around which the belts ar disposed.
There are two generations, or families, of such V-belts. The two families of belts differ from each other in terms of the surface of the oblique, lateral faces of the belts. The older generation of belts are surrounded by fine fabric. The fabric provides wear resistance and improves the quality of mechanical adherence between the belts and the flanges of the pulleys about which the belts are disposed. Another competing design of belts has appeared more recently. This more recent design of belts is provided for the same use as the older generation of belts. However, with the newer generation of belts, the formation of the oblique belt surfaces that contact the flanges of the pulleys is accomplished by the mechanical cutting of the belt material itself. This type of belt and pulley arrangement is termed a "raw-edge" arrangement since the surfaces of such belts are not covered by fabric.
Performance improvements over these conventional belt technologies are desirable to increase the resistance of the belts to the "wedge effect." The "wedge effect" is a phenomena wherein the transversal compression of the belts by the flanges of the pulleys causes a lateral deflection of the transverse rigidity elements of the belts. The transverse rigidity elements provide rigidity to the belts to prevent the belts from being crushed.
Patent publications, such as French Patent Publication No. 2,437,531, assigned to Varitrac AG, and European Patent Publication Nos. 0,242,263 and 0,305,227, both assigned to Hutchinson, each disclose belts with rigid transversal reinforcement elements. The reinforcement elements may be made of metal. The reinforcement elements cooperate together and also cooperate with a longitudinal traction armature. The reinforcement elements and the armature may be embedded in the elastomer base material of the belt.
These belts are generally wide V-belts that are used in mechanical devices for industrial or agricultural use. This type of belt, however, does not possess adequate performance characteristics for use in the field of automobile propulsion.
The severe demands placed on power transmissions and the desire to use such power transmissions for automobile propulsion have resulted in the production of belts whose geometry is the same as those described above, but whose operation is altogether different from those described above. Such belts are grouped, or identified, under the general category of "thrust link belts."
Numerous patent publications, in particular several assigned to Van Doorne, such as U.S. Pat. No. 3,720,113; French Patent Publication No. 2,089,587; and European Patent Publication Nos. 0,000,802; 0,014,013 and 0,014,492, disclose solid belt assemblies that are mounted on a guide element. This guide element is frequently made of metal and provides alignment to the belt assembly. However, theoretically, the guide element does not participate in the transmission of mechanical power between the pulleys to which the belts are connected. Rather, this transmission of mechanical power between pulleys is accomplished, generally, by the thrust between the adjacent, individual and aligned links that are connected to the guide element. The force transmitted through such adjacent links is then transmitted, from the links to the flanges of the pulleys, by the mechanical adherence, or friction.
The concentration of stresses in such thrust link belts can be so localized that if the belt components are constructed exclusively of metal, the operation of the belt must be conducted in a lubricated environment. This is the case even when the belt components are made of metals that have been specially treated to increase their hardness. Such thrust link belts cannot be made of currently available elastomers or plastomers due to the stresses present in the belts under operating conditions.
Nevertheless, a variant of such belts employs reinforced plastic rigid riders, or staples, that act as thrust links and operate without lubrication. Such belts are disclosed in French Patent Publication Nos. 2,536,486; and 2,527,723 and its Certificate of Continuation, French Patent Publication No. 2,536,487, all of which are assigned to Michelin. Additional variants of the belts described above are also disclosed in French Patent Publication No. 2,625,783, assigned to Caoutchouc Manufacture Et Plastiques. All of the links, or riders, disclosed in these publications are supported by flat, composite belts. However, the links, or riders, are likely to move on such composite belts due to rocking and relative slip.
The improvement of contact between the two types of independent solid materials that form the links, or riders, and the belts has been the object of numerous refinements in belt technology. Such refinements are disclosed in West German Patent Publication No. 2,557,724, assigned to Heynau; French Patent Publication No. 2,540,953, assigned to Regie Nationale Des Usines Renault et Compagnie Des Produits Industriels De L'Ouest; European Patent Publication No. 0,073,962, assigned to Nissan Motor Company, Limited; U.S. Pat. No. 4,433,965 to Hattori, assigned to Nippondenso, Co. Ltd.; and U.S. Pat. No. 4,610,648 to Miranti, assigned to Dayco Corporation. All of these publications relate to flat belts, or thin straps, that are equipped with rigid links, or riders. The rigid links, or riders are made of plastic and reinforced with fibers. The mechanical power transfer capabilities of the belts disclosed in these publications are, nevertheless, limited.
The prior art does not disclose a transmission belt that operates by dry, mechanical adherence and which is also capable of mechanically transferring the very high power levels required for automobile propulsion and for agricultural and industrial machines. Also, the prior art does not disclose a belt having a significantly long service life due to the capability of the belt to distribute stresses over all of the components of the belt.