Abstract:
A blade-type tensioner for chain drives which is suitable for use as a tensioner of the timing chain of a motor vehicle engine. The present invention is a chain tensioner particularly suited for use in confined spaces having a blade spring element mechanically interlocked with a plastic shoe. The shoe may be of rigid filled nylon and engages the chain to be tensioned. The spring element is interlocked to the plastic shoe by having ends inserted into grooves formed in the opposite ends of the shoe. The shoe is rotatably fixed to a base by way of a pin. The groove at the fixed end of the shoe extends towards the tip of the fixed end of the shoe past the pin attachment point. The groove at the free end of the shoe extends toward the tip of the free end of the shoe past the point at which the free end of the shoe bears upon a sliding surface formed on the base.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to a chain tensioner for chain drives which is particularly, though not exclusively, suitable for use as a tensioner on the timing chain of a motor vehicle engine. The present invention is a chain tensioner particularly suited for use in confined spaces having a flat blade spring element mechanically interlocked with a plastic shoe. The shoe may be of rigid filled nylon and engages the chain to be tensioned.  
           [0002]    Conventionally, a blade tensioner is used as the tensioner to apply tension force onto a chain. One form of prior art blade chain tensioner is shown in U.S. Pat. No. 3,490,302, which is incorporated herein by reference. Another example of a blade tensioner is shown in FIG. 4 and FIG. 5 herein.  
           [0003]    As shown in FIG. 4, the conventional blade tensioner  100  is composed of a shoe  101  made of resin that extends in an arc form, multiple blade springs  102  that extend along shoe  101  and are mounted on shoe  101 , and a metal base  120  that rotatably supports one end of shoe  101 .  
           [0004]    A first projecting portion  110  is formed at the tip or free end of shoe  101 . Distal groove  111 , for housing one end of blade spring  102 , is formed in the projecting portion  110 . A second projecting portion  112  is formed on the fixed end of shoe  101 . Proximal groove  113 , for housing the other end of blade spring  102 , is formed in the second projecting portion  112 .  
           [0005]    Attachment holes  121 ,  122  are formed on base  120 . Sliding surface  125 , the curved surface  110   a  of which is formed in projecting portion  110  at the free end of shoe  101 , and which can slide in contact, is formed at the tip of base  120 . One end of metal pin  130  is fixed at the center of base  120 . Pin  130  passes through projecting portion  112  on the fixed end of shoe  101  and a stop ring (not shown) for shoe  101  is mounted on the free end of the shoe. The shoe  101  is thus rotatable around pin  130 .  
           [0006]    In operation, the chain runs on sliding surface  101   a  of shoe  101 , and a pressure load from blade spring  102  (see FIG. 5) acts on the chain via shoe  101 . However, in the conventional blade tensioner, projecting portion  112  on the fixed end of the shoe moves in the direction of arrow a as shoe  101  deforms from a small radius curvature, shown in FIG. 4, to a large radius curvature, as shown in FIG. 5 in shoe  101 . As a result, the degree of opening of the proximal groove  113  increases. When the degree of opening of proximal groove  113  changes, the contact position of the end part of blade spring  102  with groove  113  changes and the operation of the blade shoe is adversely affected causing deterioration of the response of the blade tensioner.  
           [0007]    Similarly, for projecting portion  110  on the free end of shoe  101 , the contact position of the end part of blade spring  102  with distal groove  111  changes when the degree of opening of the open part of distal groove  111  changes due to deformation of shoe  101 . Accordingly, the operation of the blade shoe can be adversely affected.  
           [0008]    The stiffness of shoe  101  cannot be made high in automotive applications where the temperature change is large, because a large bending stress acts at the portion of shoe  101  shown at the arrow A when shoe  101  deforms.  
           [0009]    This invention addresses such conventional problems and offers a blade tensioner that provides reduced deterioration of tensioner response and improves durability.  
         SUMMARY OF THE INVENTION  
         [0010]    The blade tensioner of one embodiment of the present invention includes a blade tensioner that applies tension force to a chain. The blade tensioner has a base or bracket and a chain contacting surface over which the chain slides. The chain contacting surface is a surface portion of a resin or plastic shoe having an arcuate shape. The shoe is made of a material which will “creep.” “Creep” is the term used in the art to describe the tendency of the shoe to plastically deform in a gradual manner under elevated load and temperature. The fixed or proximal end of the shoe is rotatably mounted to a metal pin. The pin is fixed to the base The free end or distal part of the shoe slides freely on an adjacent slide surface formed on the base. A flat blade spring or multiple blade springs are positioned on the side of the shoe opposite the chain-contacting surface The springs have ends inserted into grooves, slots or housings formed in the ends of the shoe. The proximal groove which receives the blade springs in the fixed end of the shoe extends longitudinally toward the tip of the fixed end of the shoe beyond the point where the pin passes through the shoe  
           [0011]    The blade tensioner of a second embodiment includes a blade tensioner to apply tension force to a chain. The blade tensioner is mounted to a base and has a chain sliding surface over which the chain slides. The sliding surface forms a portion of a shoe and has an arcuate shape. The free end of the shoe slides on a slide surface formed in the base. The fixed end of the shoe is mounted rotatably around a metal pin that is fixed to the base. The shoe is kept under load by a blade spring, the ends of which are inserted in a proximal and distal groove formed in the fixed end and the free end of the blade shoe respectively. The distal groove on the free end of the shoe extends longitudinally toward the tip of the free end of the shoe beyond the contact point between the free end of the shoe and the sliding surface of the base.  
           [0012]    The blade tensioner of a third embodiment has blade springs whose ends contact a side of the proximal groove at a point which is located longitudinally beyond the attachment position of the pin in a direction toward the tip of the fixed end of the shoe.  
           [0013]    The blade tensioner of a fourth embodiment has blade springs whose ends contact a side of the distal groove at a point which is located longitudinally beyond the contact point between the free end of the shoe and the sliding surface of the base.  
           [0014]    The blade tensioner of a fifth embodiment, has a concave relief portion or channel formed in the proximal and distal grooves for preventing contact between the blade spring ends and the shoe.  
           [0015]    The blade tensioner of a sixth embodiment has a concave space or opening that extends across the width or transverse direction of the blade shoe formed in the fixed and the free ends of the shoe. The concave space may be filled with fiber-reinforced resin.  
           [0016]    The blade tensioner of a seventh embodiment has a guide portion that guides the free end of the blade shoe on the sliding surface. The guide portion extends from the edges of the sliding surface of the base. The guide part is provided on both sides in the width direction of the sliding surface and has convex curved members adjacent the blade shoe.  
           [0017]    In the present invention, in one or more embodiments, the proximal groove on the fixed end of the blade shoe opens past the pin attachment point and extends further toward the tip of the fixed end of the shoe. Thereby, the degree of opening of the groove opening does not change greatly when the blade shoe deforms and, as a result, the change of the contact point between the groove and the end of the blade spring is reduced. Furthermore, deterioration of the response of the blade tensioner is reduced in this manner. In this case, generation of excessive bending stress in the blade shoe is prevented so that the durability of the blade tensioner is improved.  
           [0018]    As for the distal groove on the free end of the blade shoe, it is also preferred that it extends past the contact point between the free end of the shoe and sliding surface or face on the base and extends further in a longitudinally outward direction. In this case, the change of the contact point between the tip of the blade spring and groove is reduced even when the degree of groove opening changes, so that an adverse effect on the operation of the blade shoe is reduced and deterioration of the response of the blade tensioner is reduced.  
           [0019]    It is preferable that the contact point of the blade spring with the groove in the fixed end of the shoe is closer to the tip of the fixed end than the pin attachment point. In this case, opening of the groove on the fixed end of the blade shoe can be reduced or eliminated.  
           [0020]    In addition, it is preferable, in the distal groove on the free end of the blade shoe, that the contact point between the blade spring and free end is located further toward the tip of the free end of the shoe than the contact point between the free end of the shoe and the sliding surface of the base. In this case, opening of the distal groove can be reduced or eliminated when the blade shoe deforms  
           [0021]    It is preferable to have a relief point or concavity formed in the shoe adjacent the ends of the blade springs. The concavity is a concave channel formed transversely across the grooves in both ends of the shoe. This concave relief channel prevents interference of the end of the blade spring with the blade shoe and defective operation of the blade spring during operation of the tensioner is prevented. Thereby, the deterioration of response of the blade tensioner can be prevented. In addition, in such a case, wear of the contact part of the blade shoe with the end of the blade spring is prevented, so that the durability of the tensioner is improved.  
           [0022]    Formation of a concave space or opening that extends in the width direction of the blade shoe at the fixed and free ends is preferable and the weight of the blade shoe is reduced by it and response of the tensioner is improved. In addition, filling of the concave space with fiber-reinforced resin is preferable, and improves the buckling strength of the ends of the blade shoe.  
           [0023]    It is preferable to provide a guide element that guides the sliding of the free end blade shoe on the sliding surface. The guide element is attached to the sides to the sliding surface of the base. It is preferable that this guide element be provided on both widthwise sides of the sliding surface and a convex curved surface be formed on the surface of each guide element adjacent the sides of the free end of the shoe. Thereby the sliding resistance between the guide element and the blade shoe is reduced and smooth movement of the blade shoe is realized.  
           [0024]    For a further understanding of the present invention and the objects thereof, attention is directed to the drawings and the following brief description thereof, to the detailed description of the preferred embodiments of the invention and to the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a side view of the blade tensioner of the present invention.  
         [0026]    [0026]FIG. 2 is a cross-sectional view along indicated line II of FIG. 1  
         [0027]    [0027]FIG. 3 is a side view the blade tensioner of the present invention.  
         [0028]    [0028]FIG. 4 is a side view of a prior art blade tensioner  
         [0029]    [0029]FIG. 5 is a side view of the blade tensioner of FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    The embodiment mode of this invention is explained below with the aid of the attached figures. FIG. 1 is a side view of a blade tensioner of the present invention. FIG. 2 is a view along the line described by arrow II of FIG. 1. FIG. 3 illustrates the operation of the blade tensioner.  
         [0031]    As shown in FIG. 1, blade tensioner  1  has a chain sliding surface  2   a  on which the chain slides, a shoe  2  having an arcuate form, multiple sheet spring-like blade springs  3  mounted along the curved direction of the blade shoe  2  on the side opposite to the chain sliding surface  2   a  of blade shoe  2 , and a metal base  4  that supports blade shoe  2 .  
         [0032]    A projecting portion  21  of the shoe is provided on the free end of the blade shoe  2  and an arcuate surface  21   s  is formed in the projecting part  21 . On the other hand, flat sliding surface  41  is formed at the tip of base  4  and the curved surface  21   s  of projecting part  21  of blade shoe  2  and the surface  21   s  is made so that curved surface  21   s  of projecting part  21  of blade shoe  2  can slide on sliding surface  41  while in contact with sliding surface  41  at a point  21   c.  Distal groove  21   a  is formed in projecting part  21 . The end of each blade spring  3  is inserted in distal groove  21   a  and it is in contact with the shoe inside the groove at point  21   g.    
         [0033]    Projecting portion  22  is provided on the fixed end (opposite the free end) of blade shoe  2  and proximal groove  22   a  is formed in the projecting portion  22 . The end of each blade spring  3  is inserted in groove  22   a  and it is in contact with proximal groove  22   a  at point  22   g.    
         [0034]    On the other hand, one end of pin  5  is fixed near the center of base  4  and pin  5  penetrates projecting portion  22  of blade shoe  2 . Blade shoe  2  is supported rotatably by this pin  5 . Stopper washer  6 , for blade shoe  2 , is fixed to the tip of pin  5  to prevent the shoe from becoming detached from the pin.  
         [0035]    Groove  22   a,  formed in projection part  22  on the base side of blade shoe  2 , goes over the attachment point of pin  5  and extends to the side of lip part  22   b  of projection part  22  that is the side of tip part  22   b  on the side of the other end of blade shoe  2 . Concave relief part  22   e  is formed in the groove  22   a  to avoid contact with rear end  3   b  of blade spring  3 . Between blade spring  3  and groove  22   a,  contact point  22   g  is located further on the side of tip part  22   b  of projection part  22  than the attachment point of pin  5 .  
         [0036]    Distal groove  21   a  formed in projecting portion  21  on the free end of blade shoe  2  extends to contact point  21   c  of projecting portion  21  and extends further in a longitudinal direction toward the tip part  21   b,  i.e., on the endmost portion of the free end of blade shoe  2 . A concave channel or relief part  21   e  is formed transversely across distal groove  21  a to avoid contact of tip  3   a  of blade spring  3  with distal groove  21   a.  Contact point  21   g,  between blade spring  3  and distal groove  21   a,  is located past a line drawn perpendicular to the longitudinal axis of the blade springs through the contact point  21   c  of projecting portion  21  with sliding surface  41 .  
         [0037]    Concave spaces  21   f,    22   f  that extend in the transverse or width direction of the blade shoe are formed in projection parts  21 ,  22  of blade shoe  2 . Formation of these concave spaces  21   f,    22   f  reduce the weight of blade shoe  2  and response of the tensioner is improved.  
         [0038]    Glass fiber reinforced resin FRP (Fiber Reinforced Plastic) can be filled into the concave spaces  21   f,    22   f.  In such a case, the buckling strength of projection parts  21 ,  22  can be improved further.  
         [0039]    As shown in FIG. 2, a pair of guides  42 , located at both widthwise sides of blade shoe  2 , are provided to sliding surface  41  of base  4 . These guides  42  guide the sliding of projecting portion  21  of blade shoe  2  on sliding surface  41 . In order to reduce the sliding resistance between the surface and blade shoe  2 , convex curved surface  42   a  is formed on the side of each guide  42  adjacent blade shoe  2 . Smooth movement of blade shoe  2  is realized by these convex curved surfaces  42   a  and the wear on these parts can be reduced because convex curved surface  42   a  contacts the tip of the blade spring  3 .  
         [0040]    When in operation, a chain (not shown) runs on the chain sliding surface  2   a  of blade shoe  2 . As shown in FIG. 3, chain sliding surface  2   a  of blade shoe  2  pressure-contacts the chain so that blade shoe  2  deforms to a flatter shape and thereby projecting portion  21  at the tip slides on sliding surface  41  of base  4 , while blade shoe  2  rotates around pin  5 . Each blade spring  3  deforms similarly when blade shoe  2  deforms and the elastic repulsive force of these blade springs acts  3  on the chain via blade shoe  2 .  
         [0041]    Proximal groove  22   a,  formed in projecting portion  22  on the fixed end blade shoe  2 , extends to the attachment point of pin  5  and further toward the tip  22   b  of projecting portion  22 . Thereby, the degree of opening of opening B of proximal groove  22   a  does not change greatly when blade shoe  2  deforms. As a result, change of the contact point between proximal groove  22   a  and blade spring  3  is reduced. In this manner, deterioration of response of blade tensioner  1  is reduced. In this case, generation of excessive bending stress in blade shoe  2  is prevented, so that the durability of blade tensioner  1  is improved.  
         [0042]    Distal groove  21   a,  formed in projecting portion  21  on the free end of blade shoe  2 , extends beyond contact point  21   c  of projecting portion  21  with sliding surface  41  to the tip part  21   b  of projecting portion  21 . Thereby, change of the contact point of end part  3   a  of blade spring  3  with groove  21  a reduced even when the degree of opening C of groove  21  on the tip side of blade shoe  2  changes. As a result, the adverse effect on the operation of blade shoe  2  is reduced and deterioration of response of blade tensioner  1  is reduced.  
         [0043]    In addition, the opening of opening B on the fixed end of proximal groove  22   a  of blade shoe  2  can be reduced when blade shoe  2  deforms because contact point  22   g  of blade spring  3 , with groove  22   a,  in groove  22   a,  that is formed in projecting portion  22  on the fixed end of blade shoe  2 , is located more toward the tip portion  22   b  of projecting portion  22  than the pin attachment point.  
         [0044]    Similarly, contact point  21   g,  of blade spring  3  with distal groove  21   a,  in groove  21   a,  that is formed in projecting portion  21  on the free end of blade shoe  2 , is located more toward the tip  21   b  of projecting portion  21  than contact point  21   c  of projecting portion  21  with sliding surface  41 . Therefore, the opening of opening C of groove  21   a  on the tip side of blade shoe  2  is reduced, when blade shoe  2  deforms.  
         [0045]    [0045]FIG. 3 includes lines E and F to illustrate defined points on the tensioner shoe beyond which the grooves extend in a longitudinal direction. In particular, line E is a line perpendicular to the chain-contacting surface  2   a  of the shoe  2  which passes through the center of pin  5 . The groove  22   a  extends past line E towards the tip of the shoe shown at  22   b.  Similarly, line F is a line perpendicular to the chain-contacting surface  2   a  of the shoe  2  which passes through point  21   c  where the free end of the shoe contacts the face  41  of the base  4 . The groove  21   a  extends past line F towards the tip of the shoe shown at  21   b.    
         [0046]    In addition, formation of concave relief parts  21   e,    22   e  in each groove  21   a,    22   a  of blade shoe  2  prevents interference of ends  3   a,    3   b  of blade spring  3  with blade shoe  2 . The concave relief parts are channels formed in the shoe ends transverse to the longitudinal direction of the shoe. Thereby, operation of blade spring  3  during operation of the blade tensioner  1  is improved and deterioration of response of the blade tensioner  1  is reduced. Also, in such case, wear on the contact point of blade shoe  2  with blade spring ends  3   a,    3   b  is prevented and, as a result, the durability of the blade tensioner  1  is improved.  
         [0047]    As detailed above, the proximal groove in the fixed end of the blade shoe extends beyond the pin attachment point toward the tip of the fixed end of the blade tensioner of this invention. Thus, the change in the degree of opening of the opening of the groove is reduced when the blade shoe deforms. As a result, deterioration of response of the blade tensioner is reduced and, in addition, in such a case, generation of excessive bending stress on the blade shoe is reduced to obtain improved durability of the blade tensioner.  
         [0048]    In the blade tensioner of the present invention, the distal groove on the free end of the blade shoe extends beyond the contact point between the free end and the sliding surface toward the tip of the shoe. Thus, the change of the contact point between the tip of the blade spring and the groove is reduced for the distal groove on the free end of the blade shoe, even when the degree of opening of the distal groove is changed. Thereby, an adverse effect on the operation of the blade shoe and deterioration of the response of the blade tensioner is reduced.  
         [0049]    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.