1. Field of the Invention
This invention relates to power transmission V-belts and, more particularly, to a belt that is particularly adaptable for use with stepless speed variation pulleys and which is constructed to resist a) side face and tensile/load-carrying cord degradation, b) peeling of adjacent layers, and c) fly-out of the load-carrying cords by reason of the outer portion of the drive/driven side faces being forcibly engaged by cooperating pulley parts during operation.
2. Background Art
V-belts are constructed with laterally oppositely facing drive/driven faces which effect pulley rotation utilizing a wedging action between the belt and cooperating pulley surfaces. The lateral pressure on the belt side faces may be very substantial during operation, particularly in speed variable systems. Normally, V-belts used in speed variable systems are constructed with wide outside surfaces to resist this high lateral pressure.
It is also known, to rigidify such V-belts in the lateral direction, to employ a STIFLEX.TM. layer having short staple reinforcing fibers embedded therein and oriented in generally a lateral direction in that portion of the belt that is the most heavily compressed by the pulley parts. Nonetheless, such belts, over time, become substantially deformed as they are engaged by the speed variation pulleys. This deformation may occur early in the belt life in systems in which the pulley parts repetitively squeeze and release the side faces of the belt during normal operation.
Aside from the problem of belt deformation, V-belts used in speed variation pulley systems are prone to cracking, particularly at the outside region of the belt.
A further problem is that the pulleys, by severely squeezing the outside region of the side faces of the V-belt, tend to effect fly-out of the load-carrying cords from the belt rubber layer in which they are embedded and/or peeling of the rubber layer, in which the load-carrying cords are embedded, from an adjacent layer.
A still further problem with the prior art belts is that the repeated opening and closing of the pulley pieces, defining the variable speed pulley, may result in premature and excessive wear on the side faces of the belt. For example, as the pulley pieces move closer together to increase the effective diameter of the pulley, the side surfaces are squeezed with a force substantial enough to wedge the belt outwardly, which causes considerable frictional wear on the belt side faces. Eventually, the wear becomes significant enough that the effective width of the belt is decreased which results in a change in the speed variation ratio. Consequently, over time, the operation of the overall system, in which the belt operates, changes and becomes unpredictable.
To eliminate the above problems, the assignee of the present invention devised a speed variation V-belt, as disclosed in Japanese Patent Laid-Open No. 164840/1989. As shown in that publication, at least one, and preferably a plurality, of sheets/layers of reed cord screen-like material are provided with the reed cords extending substantially parallel to each other and laterally of the belt.
The structure shown in Japanese Patent Laid-Open No. 164840/1989 is a cogged belt with longitudinally spaced cogs/teeth and U-shaped valleys between adjacent cogs/teeth formed from HRH-compound rubber. Load-carrying cords are embedded in an adhesive rubber layer. One reed cord screen-like sheet/layer is embedded in the compression section of the belt so as to bisect the distance between the load-carrying cords and the base of the valleys. The reed cord screen-like sheet/layer assumes a wave-like pattern during manufacture to generally follow the contour of the cogs/teeth. It is preferred that the thickness of the reed cords be in the range of 0.20 to 0.45 times as large as the distance between the bottom edge of the load-carrying cords and the base of the valley. A canvas layer is placed on the inside and/or outside rubber surfaces of the belt.
While the above belt construction has proven very successful, there have been two associated problems. The first is a result of the method of manufacturing the cogged belt. The cogged belt is manufactured by first forming the cogs/teeth and then vulcanizing the belt. In forming the cogs/teeth, the reed cord screen-like sheet/layer is bent in a wave form to generally follow the cog/tooth shape. During belt formation, the adhesive rubber layer tends to gather at the cogged portion of the belt. The result of this may be that the reed cords come into direct contact with the load-carrying cords in the vicinity of the valleys. This problem is aggravated by the thinness of the adhesive rubber layer. The result of this is that, during operation, the engaged load-carrying and reed cords tend to abrade each other, which may ultimately cause rupture of the load-carrying cord(s) and thereby reduce the belt capacity.
The second problem is that the lateral pressure exerted by the pulleys on the side faces of the V-belt causes belt deformation, particularly at the outer portion of the belt. Aside from the deformation that occurs, there is a tendency of a) the adjacent belt layers to peel and, more particularly, for the adhesive layer with the load-carrying cords to peel from the remainder of the belt and b) the load-carrying cords to "fly out" of the rubber layer in which they are embedded. These problems are attributable to the fact that the reed cords are substantially rigid and the adhesive rubber layer is relatively flexible in the lateral direction. As the belt deforms under the forces produced by the pulleys, the reed cords remain relatively stationary and the adhesive layer bends and tends to be peeled back towards the middle of the belt. This may release the load-carrying cords from the rubber layer in which they are embedded and/or separate the rubber layer in which the load-carrying cords are embedded from an adjacent layer. This problem is aggravated in environments in which the deformation is repetitive during system operation.