Abstract:
A power transmission belt comprising a belt body having a length and defining at least one elongate rib, the rib having an exposed surface that engages a cooperating pulley, the exposed rib surface having at least one longitudinal groove formed therein which reduces transverse modulus of the surfaces engaging the cooperating pulley and thereby reduce noise accompanying running of the belt.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates to power transmission belts and, more particularly, to a power transmission belt having at least one rib with a longitudinal groove formed therein that reduces noise accompanying the running of the belt. 
     2. Background Art 
     V-belts and V-ribbed belts are used in a wide range of environments. V-ribbed belts are preferred for their high power transmission capability, which is attributable to the large in contact area between the ribs on the belt and the flank on the cooperating pulleys. 
     In operation, there is a tendency for V-belts and V-ribbed belts to emit noise; a common complaint, especially on automotive drives. Belt noise is predominately the result of pulley engagement and disengagement noise arising as the ribs on the belt enter into and exit from the pulley grooves or arising from excessive rotational slip of the pulley relative to the belt. Rotational slip occurs during rapid acceleration or deceleration of the drive such as is encountered during shifting, engine startup or engine shutdown or due to excessive loading or insufficient wrapping around the pulleys. 
     Previous attempts to reduce belt noise have utilized materials substitutions and have focused on interfacial characteristics between the pulley and the belt flanks without affecting the forces normal to the belt flanks. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to reduce the noise which accompanies the use of V-ribbed belts and V-belts. 
     According to the present invention, a power transmission belt is provided comprising an endless belt body having a length, a tension section, a load-carrying section, and a compression section and defining at least one elongate rib, the rib having an exposed surface that engages a cooperating pulley, the exposed rib surface having at least one longitudinal groove formed therein. 
     More particularly, the invention provides a multiribbed power transmission belt comprising an outer portion or tension section, a load-carrying section having a plurality of transversely spaced, longitudinally extending tensile cords embedded therein, a fabric cover on the outer surface of the outer portion of the belt, and a compression section extending inwardly from said outer portion and defining a plurality of laterally spaced, longitudinally extending ribs, each rib having an inner portion formed of a rubber material, inwardly converging planar opposite side surfaces for engaging complementary pulley groove side surfaces, and having an exposed rib surface having at least one longitudinal groove therein. 
     The longitudinal groove formed in the external rib surface(s) is believed to reduce noise by reducing the transverse compression modulus of the belt flanks. This reduces the tendency for noise by facilitating lateral deflection of the rib flanks near the rib tips during engagement with the pulley flanks such that the normal force to the rib flanks progressively increases along the height of the rib flank from the tip to the base of the rib, reducing the normal force at the tip during engagement where relative motion with the pulley flank is the greatest. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating one exemplary embodiment of a V-ribbed belt in accordance with the present invention. 
         FIG. 2  is a sectional view along the line  2 - 2  of  FIG. 1 . 
         FIG. 2A  is a fragmentary sectional view along the line  2 - 2  for an exemplary embodiment having a lesser groove depth. 
         FIG. 2B  is a fragmentary sectional view along the line  2 - 2  for an exemplary embodiment having a greater groove depth and a greater groove width. 
         FIGS. 3 and 4  are schematic diagrams illustrating the flank force distribution for a conventional V-belt ( FIG. 3 ) and a belt in accordance with one embodiment of the invention ( FIG. 4 ). 
         FIGS. 5 and 6  are schematic diagrams illustrating flank force distribution for a conventional belt and for a belt in accordance with one embodiment of the invention when there is an angle mismatch between the belt and the pulley 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment is described below with reference to the accompanying drawings. While the various features of this invention are hereinafter illustrated and described as being particularly adapted to provide an endless power transmission V-ribbed belt construction, it is to be understood that the various features of this invention can be utilized singularly or in various combinations thereof to provide other belt constructions such as round or V-belt constructions useful in automotive and/or industrial applications. 
     As shown in  FIGS. 1 and 2 , a V-ribbed belt  10  comprises a tension layer  12 , a load-carrying section  13  having cords  14  and a compression section  16 , which in this example includes four ribs  18  formed therein extending in parallel along the longitudinal axis of the belt under the load carrying section  13 . In each rib  18  is at least one groove  20 . A cover fabric  22  may be provided above the tension layer  12 . The number of ribs in the belt will vary with the application. In automotive applications, the number of ribs will typically be about 3 to 10. However, for other applications belts having 20 or more ribs are known. When the belt includes more than one rib, i.e., in multiribbed belts, grooves may be provided in all or fewer than all the ribs. In one embodiment, groove(s) may be provided in the outside rib surfaces but not in the inner rib surfaces. Alternatively, grooves may be provided in the inner rib surfaces but not in the outside rib surfaces. 
     This is only one example of a belt construction in accordance with one embodiment of the invention. Those skilled in the art will recognize that the present invention can be used in conjunction with substantially any ribbed belt or V-belt. V-ribbed belts in accordance with certain embodiments of the invention may come in any of several cross-sectional sizes, referred to as (US) PVH, PVJ, PVK, PVL, and PVM, (ISO) PH, PJ, PK, PL, and PM, in ascending order of pitch between the ribs. 
     The grooves  20  are shown as being V-shaped, however, a person skilled in the art will recognize that other groove shapes can be used including U-shaped or a square groove. Parabolic and curvilinear variations are included. The groove  20  reduces noise by reducing the transverse force required to deflect the flanks of the belt and providing smooth engagement and minimization of interference upon engagement or disengagement with the pulley. In terms of the rib width, the grooves in each rib surface can be from about 3% to about 95%, more particularly from about 15% to about 70% of the width of the rib for a V-ribbed belt and from about 3% to about 100%, more particularly from about 15% to about 70%, of the width of the rib for a V-belt. The grooves can extend to a depth which is up to just less than the depth of the cords  14  in load carrying section  13 . In terms of the rib height, as measured from the root of the groove between the belt ribs and the innermost surface of the belt rib, the grooves can range from about 10% to about 120%, more particularly from about 25% to about 100%, of the rib height for a V-ribbed belt and from about 10% to about 95%, more particularly from about 25% to about 75%, of the rib height for a V-belt. 
     Specific dimensions will vary with the belt cross-section. For example, in a PK section belt, the rib is about 2 mm deep and the groove in certain embodiments is from about 0.5 mm to 2.0 mm, more particularly about 1.0 mm, deep and from about 0.25 mm to about 0.75 mm, more particularly about 0.40 mm, wide. In the case of a PL section belt the rib is about 3.5 mm deep and the depth of the groove is about 1.75 mm. 
     More than one longitudinal groove may be provided in each rib if desired. As a general rule, however, space will limit the number of grooves to one or two. The grooves may be formed in the belt by grinding the groove into the rib surface or by molding the groove into the rib, by cutting with a sabre-type or rotating knife, by flycutting or other machining operation, or by any other means known in the art, as may be used for also cutting the ribs. The ribs may be formed, and the grooves may be formed by different means, as permitted or desired in the manufacturing process. For a discussion of forming the surface of ribs by grinding see U.S. Pat. No. 5,492,507. 
     The materials used to form the belt, for example, the rubber compounds, fabrics and cords, can be selected from among those materials that are known in the art as being useful for this purpose. 
     One theory for the noise reduction achieved in accordance with the present invention is illustrated in  FIGS. 3-6 .  FIGS. 3 and 4  are schematic diagrams illustrating the flank force distribution for a conventional V-belt ( FIG. 3 ) and a V-belt in accordance with one embodiment of the invention ( FIG. 4 ). With reference to  FIG. 3 , the pulley flanks are schematically identified by lines  30  and  32  and the tensioning force is identified by arrow  33 . The belt is defined by the trapezoidal area  34 . As shown in  FIG. 3 , in a conventional belt, the flank force lines  36  are approximately equal along both flanks of the belt  34 . With reference to  FIG. 4 , the V-belt  34  includes a groove  35 . When the belt is seated in the pulley defined by flanks  30  and  32 , the forces on the flanks  38  of the belt are distributed as shown in  FIG. 4 . Specifically, the groove  35  allows transverse deflection such that the force in area  40  at the tip of the rib is relatively low and the force gradually increases in the region of the upper flank surface  42 . 
       FIGS. 5 and 6  illustrate the flank force distribution when there is an angle mismatch between the V-belt and the pulley, which commonly occurs in practice due to deformation of the compression section of the belt when bending to small diameter pulleys. As shown in  FIG. 5 , the inner surface  50  (indicated at its original position by a dotted line) of a conventional V-belt deforms as shown by line  52  and the flank force is high in the region  54  adjacent the inner surface  50  and decreases from the inner surface  50  to the point  56  in which the V-belt is no longer in contact with the pulley surfaces  30  and  32 . 
     By comparison, as shown in  FIG. 6 , when the V-belt  34  includes a groove  35  in accordance with the present invention, deformation that accompanies angle mismatch of the belt and pulley does not occur significantly at the outer surface  50  but rather occurs along the groove  35 . The sides of the groove are designated by the dotted lines  57  prior to deformation and by solid lines  35  after deformation. Because deformation of the belt occurs principally in the groove  35 , the V-belt  34  is able to seat evenly on the pulley flanks  30  and  32  and provide a fairly uniform flank force distribution as indicated by the force lines  60  and  62 . 
     Another advantage associated with the present invention is that the presence of the groove  35  and the ability of the groove to deform when there is an angle mismatch with the pulley promote complete seating of the V-belt  34  on the pulley flanks as indicated by the distance  64 . By contrast, as shown in  FIG. 5 , the conventional V-belt fails to completely seat when there is an angle mismatch with the pulley as indicated by distance  66 . 
     By comparison, as shown in  FIG. 6 , when the V-belt  34  includes a groove  35  in accordance with the present invention, deformation that accompanies angle mismatch of the belt and pulley does not occur significantly at the inner surface  50  but rather occurs along the groove  35 . The sides of the groove are designated by the dotted lines  57  prior to deformation and by solid lines  35  after deformation. Because deformation of the belt occurs principally in the groove  35 , the V-belt  34  is able to seat evenly on the pulley flanks  30  and  32  and provide a fairly uniform flank force distribution as indicated by the force lines  60  and  62 . 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that numerous modifications and variations are possible without departing from the spirit of the invention as defined by the following claims.