Abstract:
In a sliding contact guide for a flexible power transmission medium such as a chain or belt, the guide body includes a shoe and a plate-receiving portion integrally molded as a unit from a synthetic resin. A reinforcing plate is inserted into a slot in the plate-receiving portion. A surface of the reinforcing plate is of a concavo-convex shape. The concavo-convex shape enhances the strength of the reinforcing plate without increasing the overall weight of the guide. By controlling the spacing of the bend lines forming the concavo-convex configuration, the strength of the guide can be controlled in accordance with strength requirements for different regions of the guide.

Description:
FIELD OF THE INVENTION 
   This invention relates to a sliding contact guide for a power transmission utilizing an endless, circulating, flexible power transmission medium. It relates, for example, to a guide in a chain drive transmission, in which a chain transmits power from a driving sprocket to a driven sprocket, or to a guide in a belt drive transmission, in which a belt transmits power from a driving pulley to a driven pulley. 
   BACKGROUND OF THE INVENTION 
   In general, as shown in  FIG. 9 , a chain or belt transmission device for valve timing in an internal combustion engine, or for transmitting rotational power in another drive mechanism, includes a chain or belt CH, which transmits power from a driving sprocket or pulley S 1  to one or more driven sprockets or pulleys S 2 . The transmission includes a pivotally mounted, movable sliding contact guide Ga, which cooperates with a tensioner, and a fixed sliding contact guide Gb. The movable guide and the fixed guide are attached to a frame E of the engine or other drive mechanism by suitable pins P or by bolts, or similar mountings. The guides make sliding contact with the chain or belt CH, and prevent vibration of the chain or belt both in the plane of its traveling path (which is usually vertical), and in the transverse direction. The pivoting guide Ga cooperates with a tensioner T to maintain tension in the chain or belt. 
     FIG. 7 , is an exploded side view of a movable guide (i.e., a tensioner lever)  30  for use with a chain, as disclosed in Japanese Patent No. 3253951.  FIG. 8  is bottom plan view of the guide. The guide  30  comprises a guide body including a shoe  31  on a surface of which chain CH travels in sliding contact. A plate-receiving portion  32  is provided on a back of the shoe  31 , and extends along the longitudinal direction of the guide. The plate-receiving portion and the shoe are integrally molded as a unit from a synthetic resin. A reinforcing plate  40 , composed of a rigid material, is fitted into a slot  32   a  in an edge of the plate-receiving portion. This slot opens in a direction facing away from the shoe, and extends along the longitudinal direction of the guide. The plate-receiving portion  32  is provided with a mounting hole  32   b  adjacent one end thereof, for mounting the guide body on a frame of an engine, or other machine. A mounting hole  41  is provided adjacent one end of the reinforcing plate  32  at a position such that it comes into register with the mounting hole  32   b  when the reinforcing plate  40  is fitted into slot  32   a . This allows the guide body and reinforcing plate to be fastened together on a pivot means such as a mounting bolt, a mounting pin or the like. 
   Since the shoe  31  and the plate-receiving portion  32  are integrally molded as a unit from a synthetic resin, it is not necessary to provide a separate shoe. Thus, the number of parts, and the number of production steps are reduced. Further, since the reinforcing plate  40  is received in slot  32   a  in the plate-receiving portion  32  the strength of the guide in its pivoting direction is increased, and its bending rigidity, toughness and strength are significantly improved. The use of this type of guide has increased rapidly due to the demand for low cost and high reliability. 
   However, in order to increase the strength of the guide, it is necessary to increase the thickness in the reinforcing plate. The increase in thickness results in an undesirable increase in the weight of the reinforcing plate and in the overall weight of the guide. Moreover, when reinforcing plates are formed by punching a rolled metallic sheet or by molding a fiber-reinforced resin, production difficulties are encountered when increased plate thickness is desired. Furthermore, some regions in the reinforcing plate require higher strength than others. For example the region surrounding the mounting hole, and the region adjacent the part that contacts the plunger of a tensioner, require higher strength than other regions. However, it was not easy to vary the strength of a conventional reinforcing plate to meet the requirements for added strength only in the regions where additional strength is needed. Accordingly, to meet these regional strength requirements, it was conventional practice to make the entire reinforcing plate thicker, and the result was an increase in the weight of the reinforcing plate and in the overall weight of the guide body. 
   Accordingly a general object of the invention is to solve one or more of the above-mentioned problems of conventional sliding contact guides. Another object of the invention is to provide a sliding contact guide having enhanced strength without increasing the weight guide. Still another object is to provide a simple way to control strength distribution in a guide, according to the strength requirements of respective regions of the guide body. 
   BRIEF SUMMARY OF THE INVENTION 
   The sliding contact guide in accordance with the invention comprises an elongated shoe composed of synthetic resin, an elongated plate-receiving portion, and a reinforcing plate. The shoe has front and back sides and a surface extending longitudinally on the front side for sliding contact with a flexible power transmission medium. The elongated plate-receiving portion, which is also composed of synthetic resin, is integrally molded as a unit with the shoe on the back side thereof. The plate-receiving portion extends longitudinally along the back side of the shoe and has a longitudinally extending slot. The slot has opposed walls disposed in perpendicular relation to the transmission medium-contacting surface. A body mounting hole extends through the plate-receiving portion adjacent one end of the guide and intersecting the slot. The reinforcing plate, for reinforcing the guide, fits in the slot and has opposite surfaces respectively in opposed relationship to the opposed walls of the slot, and a through hole in register with the body mounting hole. In accordance with the invention, at least one of the opposite surfaces of the reinforcing plate has a concavo-convex shape. 
   The concavo-convex shape can be formed by bends along lines extending parallel to the opposed walls of the slot and transverse to the direction of elongation of the shoe. Alternatively, the concavo-convex shape can be formed by at least one bend extending substantially parallel to the direction of elongation of the shoe. At regions requiring increased strength, the bend lines can be closer together than the bend lines in other regions. 
   The materials, which form a guide body in the invention, are not significantly limited. However, since the sliding contact surface of the guide body functions as a shoe, the materials of the guide body are preferably so-called engineering plastics such as polyamide resin and the like, having high durability and superior lubricating properties. Suitable materials include nylon 6, nylon 66, all aromatic nylons and the like. Furthermore, fiber reinforced plastics may be used alone, or in combination with other materials, depending on requirements such as bending strength and the like. 
   Provided that the materials of the reinforcing plates have sufficient bending rigidity and strength, they are also not limited significantly. However, the materials of the reinforcing plates are preferably iron-based metals such as cast iron, stainless steel and the like, non-ferrous metals containing aluminum, magnesium, titanium or the like as the main component, engineering plastics such as polyamide resin, fiber-reinforced plastics, and the like. 
   By virtue of the concavo-convex shape of the reinforcing plate, the plate has an improved load-supporting capability over that of a conventional reinforcing plate composed of the same material. The sliding contact guide exhibits a significantly higher strength compared to that of a flat reinforcing plate having the same thickness. 
   When the concavo-convex shape is formed by bend lines parallel to the opposed walls of the slot and transverse to the direction of elongation of the shoe, the guide has improved strength to withstand loads exerted in the direction perpendicular to its shoe, for example impact loads exerted by the plunger of a tensioner cooperating with the guide. 
   On the other hand, when the concavo-convex shape is formed by one or more bend line extending in the longitudinal direction of the reinforcing plate, higher strength is exerted in longitudinal directional, so that the guide is better able to withstand longitudinal loads, such as vibration due to the pivoting of the guide or the like. 
   The density of the concavo-convex portions of the reinforcing plate can be varied by selecting the spacing of the bend lines, and accordingly the strength of the plate can be selectively enhanced in regions where larger loads are applied, such as the portion engaged by a plunger of the tensioner, or the portion surrounding the mounting hole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view showing a movable guide according to a first embodiment of the invention; 
       FIG. 2  is a bottom plan view of the movable guide shown in  FIG. 1 ; 
       FIG. 3  is an exploded view of a cross-section of the movable guide taken on the plane —III—III— in  FIG. 1 , the exploded view also showing a mounting pin; 
       FIGS. 4(   a ),  4 ( b ) and  4 ( c ) are bottom plan views, corresponding to  FIG. 2 , of guides in accordance with further embodiments of the invention, showing alternative shapes for the reinforcing plate; 
       FIG. 5  is an exploded perspective view showing a mova0ble guide according to still another embodiment of the invention; 
       FIG. 6  is a cross sectional view taken on plane —VI—VI— in  FIG. 5 ; 
       FIG. 7  is an exploded side view of a conventional movable guide 
       FIG. 8  is a bottom plan view of the conventional movable guide shown in  FIG. 7 ; 
       FIG. 9  is an elevational view showing sliding contact guides in the valve timing transmission of an internal combustion engine; and 
       FIG. 10  is a bottom plan view corresponding to  FIG. 2 , showing bend lines near the ends of a reinforcing plate that are closer together than the bend lines in a central portion of the plate. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a plastic movable guide  10  is formed by incorporating a reinforcing plate  20  into a guide body in the direction of the arrow. 
   This guide body is a plastic body integrally molded as a unit from synthetic resin, and comprises a shoe  11  having a surface on one side for sliding contact with a traveling chain, and a plate-receiving portion  12  provided on the back side of the shoe  11  and extending along the longitudinal direction of the guide. The guide body includes a flange  12   f  formed at an edge of the plate-receiving portion  12  remote from the shoe  11 , and a boss  12   c  having a mounting hole  12   b  for pivotally mounting the guide body on the frame of an engine, or other machine incorporating a flexible transmission medium. The plate-receiving portion  12  has truss-shaped reinforcing ribs  12   e , and a slot  12   a  opening at flange  12   f , facing away from the shoe, and extending along the longitudinal direction of the guide. 
   To reinforce the guide body, a reinforcing plate  20 , having a mounting hole  21 , is fitted into the slot  12   a . Holes  22  are locking holes for engagement with locking pieces  12   g  of the guide body when the reinforcing plate  20  is inserted into the guide body, in order to secure the reinforcing plate  20  to the guide body. 
   A plunger-receiving portion  12   d  is provided adjacent the pivoting front-end portion of the guide body for engagement with the plunger of a tensioner. The shape of the plunger-receiving portion  12   d  is not limited especially. For example, to prevent the plunger from becoming dislodged from the plunger-receiving portion  12   d  by transverse vibration, a protruding portion (not shown) is preferably formed at the edge of the flange  12   a , for preventing transverse shift of the plunger. 
   With the reinforcing plate  20  fitted into it, the movable guide is attached to the frame of an engine, or other machine, by a mounting pin or mounting bolt such as the shoulder bolt  13  shown in  FIG. 3 . The mounting bolt has a pivot portion  13 A which is received in the holes  12   b  and  21  of the guide body and reinforcing plate, respectively. The mounting bolt not only establishes a pivot, but also assists holes  22  and locking pieces  12   g  in fastening the guide body  10  and the reinforcing plate  20  together. 
   The reinforcing plate  20  is molded in a bent shape by pressing a metallic rolled sheet using a wave-shaped mold such that the bending lines of the plate are parallel to the walls of slot  12   a , but transverse to the shoe, as shown in  FIG. 1 . The thickness of the material from which the reinforcing plate is formed is approximately one-half the width in the slot  12   a . However, by virtue of the concavo-convex configuration of the reinforcing plate, it can fill the slot  12   a  as can be seen in  FIG. 2 . The reinforcing plate, bent as shown in  FIGS. 1 and 2 , can withstand large loads directed in the pivoting direction of the guide, and the guide exhibits a strength that is the same as or greater than that of a flat reinforcing plate having a thickness the same as the slot width. 
   Although the reinforcing plate  20  was molded into a bent shape by pressing a rolled metallic sheet, the concavo-convex shape on the surface of the reinforcing plate can be also obtained by a die casting process, using a die casting mold having a concavo-convex shape. A fiber-reinforced resin can also be formed into the concavo-convex shape 
   The concavo-convex shapes of the surface of the reinforcing plate are not limited to the shape shown in  FIG. 2 . Alternatively, a wave type shape such as shown in  FIG. 4(   a ) can be adopted. Likewise, a bent shape, as shown in  FIG. 4(   b ), having no longitudinally extending flat portions can be used. As a further alternative, a shape in which ribs  20   a  are formed on both surfaces of a reinforcing plate, as shown in  FIG. 4(   c ), may be used. In the embodiments shown in  FIGS. 2 and 4(   a ) to  4 ( c ), a regular concavo-convex shape is formed, in which the bends are disposed at equal intervals. However, a more dense configuration of bend lines can be used to enhance the strength of the reinforcing plate. Thus, the concavo-convex shape in portions positioned at regions where a large load is applied, such as a region near the tensioner receiving portion  12   d , and/or a region near the boss  12   c , can be formed with a bend line density greater than that in other regions of the reinforcing plate formed than in other regions so that the strength of the guide can be selectively improved. 
   The embodiment shown in  FIGS. 5 and 6 , is substantially the same as the embodiments of  FIGS. 1–4(   c ) except that the reinforcing plate  20  is formed so that the bending lines extend along the longitudinal direction of the reinforcing plate, and enhances the strength on the load in the longitudinal direction of the guide. 
   In the embodiments described so far, each of the guides is a movable guide, supported for pivotal movement on a mounting pin, bolt or the like. However, the invention can be applied to a fixed guide attached to a frame of an engine or the like by two mounting pins or bolts. 
   The most important advantages of the invention may be summarized as follows. 
   First, the concavo-convex shape of the reinforcing plate, provides the plate with an improved load-supporting capability. The sliding contact guide exhibits a significantly higher strength compared to that of a flat reinforcing plate having the same thickness. As a result the weight of the guide can be decreased, which contributes to improved fuel economy in the case of an engine. 
   When the concavo-convex shape is formed by bend lines parallel to the opposed walls of the slot and transverse to the direction of elongation of the shoe, the guide has improved strength to withstand loads exerted in the direction perpendicular to its shoe, for example impact loads exerted by the plunger of a tensioner cooperating with the guide. 
   On the other hand, when the concavo-convex shape is formed by one or more bend line extending in the longitudinal direction of the reinforcing plate, higher strength is exerted in longitudinal directional, so that the guide is better able to withstand longitudinal loads, such as vibration due to the pivoting of the guide or the like. 
   The density of the concavo-convex portions of the reinforcing plate can be varied by selecting the spacing of the bend lines, and accordingly the strength of the plate can be selectively enhanced in regions where larger loads are applied, such as the portion engaged by a plunger of the tensioner, and/or the portion surrounding the mounting hole. Thus, the bend lines can be formed close together at and near the ends of the reinforcing plate, and farther apart in the central portion of the plate as shown in  FIG. 10 . 
   The sliding contact guide according to the invention can be produced simply by changing the molds, dies or the like used to reproduce the reinforcing plate. Thus, production cost is not increased. Moreover the material cost is reduced. Therefore, the invention has significant industrial value.