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Belt for continuously variable transmission and manufacturing method of the sameRelated Patent Categories: Endless Belt Power Transmission Systems Or Components, Friction Drive Belt, Including Plural Interconnected Members Each Having A Drive Surface Facing In A Common Direction, Belt Has Oppositely Facing Side Drive Surfaces (e.g., "v-belt", Etc.)Belt for continuously variable transmission and manufacturing method of the same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060135306, Belt for continuously variable transmission and manufacturing method of the same. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] Apparatuses and methods consistent with the present invention relate to a belt for a continuously variable transmission which is wound across a primary pulley and a secondary pulley each composed of a pair of sheaves and, more specifically, to a belt for a continuously variable transmission whose noise is reduced by using V blocks having different thickness for the large number of V blocks that abut against the pulleys. [0003] 2. Description of Related Art [0004] A belt type continuously variable transmission (hereinafter abbreviated as CVT) is generally used for power transmission systems of cars and the like. Belts for the CVTs typically include V blocks that are continuously attached to an endless body. In terms of the endless body, there is a push-type endless body that uses a ring composed of a plurality of laminated metal plates that transmits power by exerting a compression force on the V blocks, and a pull-type endless body that uses a chain in which link plates are linked alternately by pins and that transmits power by a tensile force acting on the chain. Although the present invention has been developed for the push-type endless body, it is also applicable to the pull-type endless body. [0005] Belts for CVTs generate an abutment sound when the V blocks (elements) abut against the pulleys. The sound becomes irritating to human ears at a peak frequency when the thicknesses of the V blocks are the same. [0006] Conventionally, belts have provided a lower noise by dispersing the peak frequency, described above, by randomly disposing a plurality of types of blocks having different thicknesses, as disclosed in Japanese Patent Publication No. 1994-21605 and Japanese Patent Laid-Open No. 2000-274492, for example. Although the belt in which the blocks, having different thickness, are attached at random (hereinafter referred to as a randomly mixed belt) can lower the frequency peak by dispersing the noise, its effect is not enough and a noise is still produced that irritates human ears. [0007] As shown in FIG. 6, a belt 1.sub.1 assembled by 400 blocks (elements) 3 having a thickness of only 1.5 mm generates noise having a very narrow peak on a bite-in order of the blocks to the pulley. [0008] Although a randomly mixed belt 1.sub.2, in which the same number (200) of blocks (elements) having a thickness of 1.4 mm and blocks (elements) having a thickness of 1.5 mm are mixed and arranged at random, can lower the frequency peak by white noise centering on an order equivalent to 1.45 mm, which is the mean value between 1.4 mm and 1.5 mm as shown in FIG. 7, noise is still generated that is irritating to human ears. BRIEF SUMMARY OF THE INVENTION [0009] It is an aspect of the invention to provide a belt for a CVT that disperses a peak of the frequency and lowers noise by forming a plurality of block groups having different ratios of blocks with different thicknesses. [0010] According to a first exemplary aspect of the invention, there is provided a belt for continuously variable transmission (CVT) in which a number of V blocks are attached to an endless body, wherein the V blocks include a plurality of types of blocks having different thickness. The V blocks, which may constitute a large number, comprise a series attached to the endless body and are divided into a plurality of V block groups, in which combination ratios of the different types of V blocks are different. [0011] That is, multiple V blocks are attached to the endless body and include a plurality of types of V blocks having different thickness. The V blocks are divided into a plurality of V block groups in which a ratio of different types of V blocks is different. The V blocks attached to the endless body form a series composed of the plurality of V block groups. [0012] The different types of V blocks may be arranged at random in the V block group. The different types of V blocks may also be arranged with a specified and predetermined order in the V block groups. In addition, a number of each different type of the V blocks may be almost equal in the series of the V blocks. [0013] In an exemplary embodiment, the V blocks comprise two types, including first V blocks and second V blocks whose thicknesses are different. The plurality of V block groups is composed of first and second V block groups respectively having a different ratio of the first V blocks to the second V blocks. The ratios of the first to second V blocks may be inversive in the first and second V block groups. Also, the endless body may be a ring in which a plurality of metal sheets is laminated, for example. [0014] According to a second exemplary aspect of the invention, there is provided a method for manufacturing a belt for a CVT, comprising forming a plurality of V block groups respectively having a different ratio of different types of V blocks and forming a series of V blocks by attaching a large number of the V blocks, comprising the plurality of V block groups, to an endless belt. [0015] The forming of the V block groups may include dividing the V blocks into the plurality of V block groups, respectively having a different ratio of different types of V blocks and specifying an arrangement of the V blocks. The operation of specifying the arrangement may comprise assembling a series of belts, including the V block groups, on a computer, and simulating a state in which the assembled belts are wound across pulleys to calculate noise levels of the individual belts, so as to analyze the calculated noise level of each belt to determine an optimum belt configuration. [0016] According to a further exemplary aspect of the invention, the method for manufacturing the belt for a CVT comprises dividing V blocks into a plurality of V block groups respectively having a different ratio of different types of V blocks, and specifying a large number of arrangements of the V blocks in the V block groups to assemble a series of belts for simulation on a computer. The belts are simulated in a state in which a large number of the belts are individually wound across pulleys to calculate noise levels on the computer, so as to calculate the noise level of each belt to determine an optimum belt configuration. [0017] Since the belts for a CVT of the present invention are composed of a plurality of V block groups having a different combination ratio of V blocks, they can disperse noise further when compared to the traditional randomly mixed belt and can reduce a rasping noise which is otherwise disturbing to human ears. The belt may be readily assembled by randomly arranging the V blocks in the V block groups. The noise may be reduced further by arranging the V blocks in the V block groups with a predetermined order that even further reduces the noise level. [0018] The belt may be readily assembled with fewer types of V blocks and its cost lowered by forming the V block groups with two types of V blocks having different thicknesses and by forming the series of belts using two V block groups. [0019] The number of different types of V blocks used may be equalized, thus improving efficiency in assembly and yield by equalizing the number of V blocks in the series or by inverting the ratios of the combinations of the V blocks in the two V block groups. [0020] As will be appreciated, the invention may be suitably applied to a belt whose endless body is a metal ring, such that the V blocks are attached successively to reduce noise. [0021] Further, the inventive belt manufacturing method enables an optimum arrangement of V blocks, causing less of a noise level, which can be analyzed through computer simulation, for example. 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