Abstract:
A guide or tensioner arm including a bracket made from a formed sheet metal stamping. The bracket is formed of a body portion with a series of tabs formed along a bottom edge. The tabs are bent perpendicular to the body portion of the bracket in an alternating fashion. This forms a bracket having a T-shape providing a flat base for mounting a plastic shoe. Since the body portion is centered with respect to the alternating tabs a strong bracket for holding the plastic shoe is provided to guide or tension an associated strand of chain in a power transmission system.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a guide rail or tensioner arm for guiding or tensioning a drive chain and more particularly to a sheet metal bracket with tabs formed on one edge which are bent in alternate directions for engagement with a plastic shoe or wear face. The guide rails or tensioner arms of the preferred embodiment of the present invention are designed for use as chain guides or tensioner arms in power transmission systems and engine timing systems using chain to drivingly connect the elements of the system. 
     Conventional engine timing systems include a crankshaft and a corresponding sprocket system which operates an engine with either a single or dual overhead camshafts. The operation of the system is based upon a chain which extends from the crankshaft to the camshaft (or camshafts) and returns to the crankshaft in an endless loop. Rotation of the crankshaft and the chain causes the camshaft to rotate. 
     Examples of engine timing systems are shown in U.S. Pat. No. 5,427,580, which is incorporated herein by reference. As the chain extends in an endless loop between the driving and the driven sprockets, such as those located on a crankshaft (driving) and camshaft (driven), the chain forms a “tight” side and a “slack” side. The tight side is formed by the tension in the span of chain between the links entering the driving sprocket and the links leaving the driven sprocket. A slack side is formed on the other span of chain between the links leaving the driving sprocket and entering the driven sprocket. 
     The performance and action of the chain can differ dramatically between the tight and slack sides. A chain tensioner is conventionally used on the slack side of the chain. The tensioner acts to take up or eliminate the slack in the chain. As the engine accelerates or decelerates, the tensioner arm may move closer to the chain to maintain the tension, i.e., reduce the slack in the chain. The tensioner arm typically includes a convex surface to match the path of the chain. 
     In contrast, a chain guide is conventionally used on the tight side of the chain. Such a guide does not include a tensioner piece, as the chain portion remains tight between the two sprockets. Typically, the guide is fixed to a mounting surface, such as a side of the engine block. The guide serves to maintain the desired path of the chain between the sprockets. 
     Conventional guide rails of the prior art may be formed as a single piece but more typically include two components, a bracket or carrier and a plastic shoe or wear face, that are produced independently of one another and interconnected by some form of locking device. The bracket may be made of metal or plastic and the wear face or shoe is typically made of plastic. 
     U.S. Pat. No. 4,832,664 discloses a guide rail that includes a carrier formed of a first plastic material and a slideway lining body made of a second different plastic material. Each of these two components is formed in a mold. The carrier and slideway lining body are interconnected to one another by dovetail connections, and secured by bent end sections. In the chain guide shown in U.S. Pat. No. 4,832,664, the carrier and sliding guideway body are formed on complementary dovetail cross-sections, and interlocked by the bent end section, or a similar meshing arrangement, that prevent relative movement between the two portions. 
     U.S. Pat. No. 5,813,935 discloses a guide rail where the wear face is produced by an extrusion molding process. The extrusion molding process is used in place of injection molding to permit the use of dovetail connections and provide interlocking components. The carrier portion is substantially an I-shape in cross-section with an extending dovetail section. The dovetail section on the carrier fits a complementary dovetail cross-section formed in the wear face. The carrier portion may be manufactured of die cast aluminum or magnesium; injection molded nylon; steel stamping; steel casting; or, steel or aluminum weldment. 
     Prior art brackets for chain guides, when made of metal, have often been formed with the bracket mounted to the engine at a location away from the chain centerline. FIG. 1 shows such a chain guide. The bracket is L-shaped in cross-section One side of the bracket  12  is mounted to an engine block  14  and the other side of the bracket  12  includes an attached shoe  16  with a channel shaped wear face  18 . The chain  20  passes along the channel shaped wear face  18 . The load applied to the bracket  12  by the chain  20  acts through distance “X” applying a stress to the bracket. To prevent the bracket  12  from bending or failing due to the stress, a bracket of thick material is used or an expensive stronger material is used. 
     The guide or tensioner arm of the present invention includes a carrier or bracket made from a formed sheet metal stamping. On a longitudinal edge of the bracket a series of extending tabs are formed. The tabs are bent perpendicular to the main body of the bracket in an alternating fashion. This forms a bracket which has a T-shape providing a base for mounting a plastic shoe with a wear face for guiding a chain. 
     SUMMARY OF THE INVENTION 
     The present invention is primarily concerned with a bracket or carrier for a tensioner shoe. The carrier and shoe is used as a chain guide or pivoting tensioner arm and may be applied to a power transmission system or engine timing system using a chain to drivingly interconnect driving and driven members. 
     In accordance with one embodiment of this invention, a chain guide is formed of two main interlocking parts. A first part includes a bracket. The bracket is formed of an initially flat, elongated stamped metal plate. The bracket has a pair of spaced holes. 
     Along one longitudinal edge of the bracket are formed a row of extending tabs. The tabs are defined by a series of slots formed in the edge of the bracket. The slots may originate from a row of holes formed in the bracket and extend to the longitudinal edge of the bracket. After the plate is stamped, the tabs are bent to a position perpendicular to the plane of the main body of the bracket. The tabs are bent in an alternate manner to each side of the bracket to form a T-shaped carrier member. The present invention contemplates the formation of 20-40 tabs, i.e., 10-20 tabs on each side of the bracket centerline. 
     The second part includes a plastic shoe having a wear face. The wear face has a channel formed therein to engage an associated chain. Opposite the wear face is a side which is adapted to engage the bracket. A series of hook-shaped tabs engage the tabs on the bracket. A retaining hook engages an end tab on the bracket to keep the shoe fixed to the bracket. 
     The assembly of the carrier and the shoe forms a chain guide which is typically applied to the tight strand of a power transmission chain. 
     Similar to the chain guide described above, a second embodiment of the present invention includes a chain tensioner arm having two main interlocking parts. A first part is a bracket as described in the first embodiment which further includes a hole optionally fitted with a bushing which is rotatably attached to a fixed pivot pin. The pivot pin is attached to the engine. A plastic shoe or the like is attached to the bracket. A chain tensioner is positioned to bear upon the bracket to cause the tensioner arm to tension a slack strand of the chain. 
     For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment of the invention and to the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a prior art guide bracket and wear face illustrating the position of the chain and shape of the bracket. 
     FIG. 2 is a side view of the tensioner arm embodiment and the chain guide embodiment of the present invention in an engine between the crankshaft and one camshaft. 
     FIG. 3 is a sectional view of the guide bracket and wear face of the present invention illustrating the shape of the bracket and wear face along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a side view of the bracket of the present invention. 
     FIG. 5 is a bottom view of the bracket of FIG.  4 . 
     FIG. 6 is a cross sectional view of the bracket of FIG. 4 along line  6 — 6  showing the tab. 
     FIG. 7 is a side view of another embodiment of the bracket of the present invention. 
     FIG. 8 is a side view of a shoe shown oriented to fit to the bracket of FIG.  7 . 
     FIG. 9 is a bottom view of the wear face of the shoe of FIG.  8 . 
     FIG. 10 is a top view of the shoe of FIG. 8 showing the bracket engaging tabs. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings, FIG. 2 depicts two embodiments of the present invention as used in a representation of an engine timing system. The illustration shows only a single bank of an engine timing system. 
     The engine timing system includes chain  30 , chain tensioner system  32  and chain guide  34 . The engine chain  30  extends from the sprocket  36  mounted on the crankshaft  38  to the sprocket  40  mounted on the camshaft  42  in an endless loop. The movement of the crankshaft  38  causes the camshaft  42  to rotate. 
     The crankshaft sprocket  36  is the driving sprocket and thus the tight side  44  of the chain  30  is formed between the links entering the crankshaft sprocket  36  and leaving camshaft sprocket  40 . The slack side  46  is the opposite side of the chain  30  between the two sprockets  36 ,  40 . 
     The slack side  46  has a chain tensioner arm  32  and an actuator  50 , which may be a hydraulic tensioner or the like, to apply a force to the chain tensioner arm  32 . The tensioning arm and actuator are designed to act together to maintain the tension on the slack side  46  of the chain. The tight side  44  of the chain  30  has a chain guide  34  to keep the chain in position. The chain guide  34  is positioned so that its bottom side  48  is against the underside of the chain  30 . The chain  30  is forced into motion by the sprockets, resulting in its movement across the bottom of the chain guide. The chain tensioner arm  32  used in the chain tensioner system and chain guide  34  will be discussed in more detail below. 
     FIG. 3 depicts a cross section view of the chain guide  34  of the present invention having alternating tabs  60 A,  60 B for engaging a tensioner shoe  62  in use with a power transmission chain  30 . The chain guide  34  is mounted to the engine block  64  by a guide bracket  66 . The bracket has tabs  60 A,  60 B which are bent in an alternating manner perpendicular to the main body  68  of the bracket  66 . The plastic tensioner shoe  62  has a top side  72  with tabs  74 A,  74 B for engaging tabs  60 A,  60 B of the bracket  66 . Essentially, the tabs  74 A,  74 B on the tensioner shoe  62  form a channel into which the bottom portion of the bracket including the tabs may be inserted. Thus, the shoe  62  is retained in position on the bracket  66 . 
     The bottom side of the shoe  62  has a wear face  76  located thereon. The chain is positioned so that it runs across the wear face and is engaged and guided thereby. The wear face includes side rails  70 A,  70 B which are raised to help the chain maintain its position on the guide. The side rails are also shown in FIGS. 8 and 9. The bracket and tabs are shown in more detail in FIGS. 4-6. 
     As shown in FIG. 3, the bracket of the present invention is mounted to the engine block so that the chain is essentially centered over the main body of the bracket. The use of alternating tabs permits the centering of the chain over the main body of the bracket. By centering the chain, the torque or moment about the bracket main body is reduced, which permits use of a thinner main body formed of sheet metal. 
     FIG. 4 depicts the bracket  66  or carrier of the present invention. The main body  68  of the bracket  66  has a generally flat, elongated shape. A pair of spaced apart holes  80 ,  82  are formed in the bracket. When the bracket is being used as part of a chain guide, both holes may be used to rigidly mount the bracket to the engine or a similar mounting element. 
     The bottom edge  88  of the bracket  66  has a slight camber to match a curved length of chain. Extending along the entire length of the bottom edge  88  of the main body  68  is a row or series of tabs  90 . When the bracket  66  is first formed, by stamping for example, the tabs  90  are coplanar with the main body  68 . A subsequent manufacturing step causes the tabs  90  to be bent perpendicular to the plane of the main body portion  68  of the bracket  66  in an alternating manner. In other words, a first tab  90 A formed at one end of the bracket edge may be bent to a first side of the bracket perpendicular to the main body portion of the bracket. The following, or next tab  90 B would be bent to the opposite side or second side. A third tab  90 C would be bent to the first side, and so on. 
     The alternate pattern of the orientation of the tabs  90  is shown in FIG.  5 . FIG. 5 depicts the tabs  90  on the bottom edge of the bracket  66 . The tabs  90  are bent perpendicular to the main body of the bracket and form a flat surface for mounting a plastic tensioner or guide shoe. 
     FIG. 6 is a cross sectional view of the bracket  66  of FIG.  4 . In this view the main body portion  68  of the bracket  6  has a left-facing tab  90 B. Adjacent tabs (not shown) would be right facing. Thus, a flat surface is formed along the bottom edge of the bracket to fit a plastic shoe thereto. 
     FIG. 7 depicts an alternate embodiment of the present invention. The bracket  166  may have a pair of spaced holes as in the previous embodiment. However, only a single hole is required. The hole  180  is provided with a bushing  184 . The bracket  166  is pivotally mounted to a pivot pin  186  by way of the bushing  184 . Thus, the bracket  166 , when combined with a plastic shoe, may be used as a tensioner arm as shown in FIG.  2 . As described in FIGS. 4 and 5, the bracket has a row of tabs  190  along the bottom edge  188  of the main body portion  168  of the bracket  166 . The bottom edge  188  of the bracket  166  has a slight camber to match a curved length of chain. The tabs  190  are bent perpendicular to the plane of the bracket body in an alternating manner to form a flat shoe mounting surface  188  which is the same surface as the edge. As in the above embodiment, the shoe mounting surface  188  is centered with respect to the body portion  168  of the bracket  166 . 
     FIG. 8 depicts a plastic guide shoe or tensioner shoe  200  adapted for use with the bracket  166  shown in FIGS. 4 and 7. The shoe has an elongated flat shape which has a slight camber to match that of the bottom surface of the bracket  166 . The top side  202  of the shoe has a plurality of tabs  204  which, in effect, form a C-shaped groove into which the tabs  190  of the bracket  166  are inserted. The tabs  204  of the shoe  200  hold the shoe onto the bracket  166 . At one end of the shoe  200  an end wall  206  is formed which prevents the shoe  200  from sliding off of the bracket. A retaining hook  208  acts to prevent the shoe from sliding off of the bracket in the reverse direction by hooking one of the bracket tabs  190 . 
     The bottom surface  210  of the shoe  200  contains a wear face  212  described in more detail in FIG.  9 . The wear face  212  includes a sliding surface  214  and a pair of side walls  216 A,  216 B. The chain moves across the sliding surface  214  of the wear face  212  and is retained in place by the side walls  216 A,  216 B. 
     FIG. 10 depicts the top surface  202  of the shoe  200 . The plurality of shoe tabs  204  extend inwardly from the outside edges of the shoe  200 . The end wall  206  is positioned at one end of the top surface  202 . The retaining hook  208  extends from the end wall  206  and is positioned to clip a tab of the bracket and prevent movement in the reverse direction or disengaging of the shoe from the bracket. 
     While several embodiments of the invention are illustrated, it will be understood that the invention is not limited to these embodiments. Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention, particularly upon considering the foregoing teachings.