Abstract:
A blade-type chain tensioner includes a blade shoe having a chain sliding face, a blade spring biasing the blade shoe toward an associated chain, and a bracket to rotatably support the fixed end of the blade shoe. The length of the blade spring is shorter than that of the chain sliding face of the blade shoe. The first end of the blade spring is attached onto the fixed end of the blade shoe and slidably contacts the distal end of the bracket at a contact point located between the fixed and free ends of the shoe.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a blade-type tensioner having a blade shoe with a chain sliding face and a blade spring for application of spring force onto the blade shoe. 
     FIG. 6 shows one example of a conventional blade tensioner, used for tensioning an associated chain. As shown in the figure, conventional blade tensioner  100  includes a blade shoe  101  of resin that extends in a curved line form, multiple blade springs  102  that extend along blade shoe  101  and are attached onto the blade shoe, and a metal bracket  120  as the bracket member that supports blade shoe  101 . 
     Projection  110 , having curved face  110   a , is formed at the tip of blade shoe  101  and the projection  110  has concavity  111  that stores one end of blade spring  102 . A nearly triangular projection  112  is formed at the fixed end end of blade shoe  101  and a concavity  113 , that stores the other end of blade spring  102 , is formed in the projection  112 . 
     Holes for attaching,  121 ,  122 , are formed in bracket  120 . Sliding face  125 , on which projection  110  at blade shoe tip  101  can contact and slide, is formed at the tip of bracket  120 . One end of pin  130  is fixed at the center of bracket  120 . Projection  112 , as the fixed end side of blade shoe  101 , is inserted rotatably onto pin  130 . 
     During. operation of the chain, the chain runs on sliding face  101   a  of blade shoe  101  and the press-down load, due to blade shoe  101  and deformation of blade spring  102 , acts on the chain at such time. The conventional blade tensioner is used where the center-to-center distance of the chain is relatively short, such as a chain to drive the oil pump of an engine. On the other hand, because of the demand to lower the cost of the engine, it is desired to use a blade tensioner of relatively low manufacturing cost, for a cam chain that drives between the crankshaft and the camshaft. 
     In the case of a cam chain, the center distance is long, generally, so that the length of the blade tensioner needs to be long to match the center distance. However, when the total length of the blade tensioner is long, the resonant frequency becomes low due to its lower natural frequency and, as a result, the blade tensioner resonates within the rpm range of the engine and fatigue damage can occur. 
     This invention addresses such a conventional problem. The objective is to offer a blade tensioner that can prevent resonance in the rpm range and fatigue damage. 
     SUMMARY OF THE INVENTION 
     It is a first aspect of the invention to provide a blade tensioner which applies tension to a chain. The tensioner includes a blade shoe with a chain sliding face, a blade spring that applies the spring force to the blade shoe and a bracket upon which to attach the blade shoe. A fixed end, portion, or proximal end of the blade shoe is rotatably attached to the bracket. The blade spring contacts the tip or distal end of the bracket at a contact point located between the free end and the fixed end of the blade shoe. 
     In this invention, the chain runs on the chain sliding face of the blade shoe. Proper tension is applied to the chain by the action of the blade shoe activated by the force of the deformed blade spring. The natural frequency of the blade tensioner is determined by the location where the tip of the bracket and the blade spring come into contact. As the contact point between the spring and the bracket moves toward the tip of the blade shoe, the natural frequency of the shoe becomes lower. On the other hand, as the contact point moves toward the fixed end of the blade shoe, the natural frequency of the shoe and tensioner becomes higher. The objective is to raise the natural frequency of the blade tensioner higher than the frequency of vibrations generated by the engine. 
     In the present invention, the location of the contact point between the tip portion of the bracket and blade spring or blade shoe is located between the blade shoe tip or free end and its fixed end, so that the natural frequency of the blade tensioner is made relatively high. Thereby, the resonant frequency of the blade tensioner can be set relatively high compared to those frequencies generated by the engine and, as a result, the resonance of the blade tensioner within the rpm range of the engine can be prevented and fatigue damage due to resonance can be prevented. 
     It is a second aspect of the invention to provide a blade tensioner that applies tension force to the chain and includes a blade shoe with a chain sliding face, a blade spring that applies a spring force to the blade shoe, and a bracket to which the blade shoe is attached. The fixed end of the blade shoe is rotatably attached to the bracket. The length of the blade spring is shorter than the length of the sliding face of the blade shoe. A first end of the blade spring is attached to the fixed end of the blade shoe and the second end is located apart from the blade shoe and, at the same time, the second end slidably contacts the tip of the bracket. The overall length of the blade spring is shorter than the length of the sliding face of the blade shoe and the second end of the blade spring (i.e. the tip), located apart from the blade shoe, slides on the tip of the bracket. The tip of the bracket is in contact with the second end of the blade spring and the position of this contact point is located between the free and the fixed ends of the blade shoe and, in one example, it is offset from a mid position between the ends of the blade shoe and located nearer to the blade shoe tip. 
     In this manner, the resonance frequency of the blade tensioner can be set high and, as above, the resonance in the engine rpm range and fatigue damage due to resonance can be prevented. 
     It is a third aspect of the invention to provide a blade tensioner with a further or second blade spring that runs along the face opposite the chain sliding face of the blade shoe. Thus, the deformation per unit load is small. That is, a blade tensioner with a high spring constant is offered. 
     It is a fourth aspect of the invention to provide a blade tensioner with a free end or second end of the blade spring curved with the curved face slidably contacting the tip of the bracket. Thus, there is no interference with the bracket tip and deformation of the blade spring is smooth. 
     It is a fifth aspect of the invention to provide a blade tensioner to apply tension to the chain including a blade shoe with a chain sliding face and a blade spring that is provided on the side opposite the chain sliding face of the blade shoe. The blade spring applies the spring force onto the blade shoe. A bracket is provided on which to attach the blade shoe. The fixed end of the blade shoe is rotatably attached to the bracket. An outward projection is formed at the tip of the bracket or on the blade shoe, at a location approximately midway between the free end of the blade shoe and its fixed end. The projection is adapted to slide on the blade spring or the tip of the bracket depending on whether it is formed on the bracket or the blade shoe. 
     An outward projection is formed between the tip and fixed end of the blade shoe and the projection slidably contacts the blade spring or bracket tip. The projection at the bracket tip contacts the blade spring or the projection on the blade shoe side contacts the bracket tip and this contact point is located approximately midway between the blade shoe free end and its fixed end. Thereby, the resonance frequency of the blade tensioner can be set high and, as above, the resonance in the engine rpm range and fatigue damage due to the resonance can be prevented. 
     It is a sixth aspect of the invention to provide a blade tensioner with a projection. The projection has a curved face and the curved face slidably contacts the tip of the bracket or the blade spring. The projection formed on the blade shoe can have a curved face and this curved face slidably contacts the blade spring or bracket tip, thereby deformation of the blade spring can be smooth. 
     It is a seventh aspect of the invention to provide a blade tensioner which applies a force to the chain and includes a blade shoe with a chain sliding face, a blade spring to apply the spring force onto the blade shoe, and a bracket on which the blade shoe is rotatably attached. The blade spring includes a first blade spring that is provided on the side opposite to the chain sliding face of the blade shoe and a second blade spring which is shorter than the chain sliding face, a first end of which is attached to the fixed end of the blade shoe and the second end is positioned away from the blade shoe. At the same time, the other end of the second blade spring is attached to the projection that is provided to the bracket. 
     The projection of the bracket contacts the second or free end of the second blade spring and this point of contact is located between the blade shoe free end and its fixed end. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance in the engine rpm range and resulting fatigue damage are prevented. 
     It is an eighth aspect of the invention to provide a blade tensioner which has a projection on the bracket with a curved portion. The curved portion or face slidably contacts the first blade spring and the projection has an attachment portion or part to which the other end of the second blade spring can be slidably attached. 
     It should be understood that some embodiments of the present invention contemplate use of a protrusion formed on either the shoe or the bracket portion of the tensioner adapted to bear upon the other element. The protrusion can be located between the ends of the element (the shoe or bracket) upon which it is formed. The location of the protrusion defines the location of the point of contact between the shoe and the bracket. It can be seen that as the point of contact between the shoe and bracket is moved from a location near the middle of the shoe to the end of the shoe the free span of tensioner shoe thus created is lengthened and thus, the natural resonant frequency of the shoe becomes lower. It is therefore an object of the invention to locate the point of contact between the shoe and the bracket via the protrusion operating therebetween at a middle location between the ends of the shoe. Thus, the natural frequency of the shoe is maintained at a higher frequency relative to lower engine vibrations and reduces the susceptibility of the tensioner to damage from resonant vibrations originating from the engine and associated mechanisms. 
     For a more complete understanding of the invention, one should refer to the embodiments illustrated in greater detail in the drawings and described below by way of examples of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the blade tensioner of a first embodiment of this invention. 
     FIG. 2 is the sectional view along line II—II of FIG.  1 . 
     FIG. 3 is a side view of the blade tensioner of the second embodiment of this invention. 
     FIG. 4 is a side view of the blade tensioner of the third embodiment of this invention. 
     FIG. 5 is a side view of the blade tensioner of the fourth embodiment of this invention. 
     FIG. 6 is a side view of a conventional blade tensioner. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a side view of the blade tensioner of the first embodiment of this invention; FIG. 2 is its cross-section along II—II. As shown in FIG. 1, blade tensioner  1  includes a blade shoe  2  of resin which is curved in an arc form, a blade spring  3  that pushes blade shoe  2 , and a metal bracket  4  that acts as the bracket to attach blade shoe  2 . 
     As shown in FIG. 2, blade shoe  2  has a generally U-shaped cross-section and is composed of bottom wall  20  and side walls  21  that stand on both its sides. Outer face  20   a  of bottom wall  20  is a chain sliding face. 
     Fixed end  2   b  of blade shoe  2  is attached to bracket  4  rotatably via pin  5 . Blade spring  3  separates gradually from inside face  20   b  of bottom wall  20  of the blade shoe  2  from its rear part  3   b , which is in contact with inside face  20   b , to its tip  3   a  and it is curved in an arc form as a whole. The length of blade spring  3  is shorter than blade shoe  2 . 
     Rear part  3   b  of blade spring  3  is attached to boss  22  formed in fixed end  2   b  of blade shoe  2  and its tip  3   a  is placed away from blade shoe  2 . Curved face  31  is formed on tip  3   a  and said curved face  31  contacts tip  4   a  of bracket  4  slidably. Contact of the tip  4   a  of bracket  4  with tip  3   a  of blade spring  3  is made at a point C located between tip  2   a  and fixed end  2   b  of blade shoe  2 . 
     Bolt hole  40  in FIG. 1 is a bolt hole for attachment of bracket  4  onto the engine. Blade tensioner  1  is attached by an attachment bolt (not shown) inserted into the bolt hole and by pin  5  to the engine via bracket  4 . 
     FIG. 3 is a side view of the blade tensioner of a second embodiment of this invention and the same reference characters are assigned to the same or corresponding parts as in FIG.  1 . Here, the point of provision of the blade shoe and blade spring and the shape of the blade shoe are different from the first embodiment above. 
     As shown in FIG. 3, blade shoe  2  has a rectangular cross-section and blade spring  6  is mounted on inside face  20   b  opposite to chain sliding face  20   a  of blade shoe  2  along the inside face  20   b . Tip  6   a  of blade spring  6  is attached to concavity  23  formed at tip  2   a  of blade shoe  2  and its rear end  6   b  is attached to concavity  24  formed at fixed end  2   b  of blade shoe  2 . 
     In this second embodiment, too, contact between tip  4   a  of bracket  4  with tip  3   a  of blade spring  3  is located at a point C approximately midway between tip  2   a  of blade shoe  2  and its fixed end  2   b.    
     FIG. 4 is a side view of the blade tensioner of the third embodiment of this invention and the same or corresponding parts as FIG. 3 are assigned the same reference characters. Here, a projecting member, which is the contact point with the bracket tip, is provided on the side of the blade shoe. 
     As shown in FIG. 4, a projection  25  projecting toward bracket  4  is formed at the mid point between tip  2   a  and fixed end  2   b  of blade shoe  2 . Projection  25  has a curved face  25   a  and the curved face  25   a  contacts tip  4   a  of bracket  4  slidably. Bolt holes  40 ,  41  permit attachment of the bracket to the engine block. Projection  25  has a curved face  25   a  and the curved face  25   a  contacts tip  4   a  of bracket  4  slidably. 
     In this third embodiment, contact between tip  4   a  of bracket  4  with projection  25  is at point C located at the mid point between tip  2   a  and fixed end  2   b  of blade shoe  2 . Alternately, the projection can be formed at tip  4   a  of bracket  4 , the curved face can be formed on the projection towards blade shoe  2  and the curved face can contact blade spring  6  slidably. 
     FIG. 5 is a side view of the blade tensioner of the fourth embodiment of this invention and the same or corresponding parts as FIG. 4 are assigned the same reference characters. The projection is provided at the tip of the bracket and additional blade spring are provided. As shown in FIG. 5, projection  42  projecting toward blade shoe  2  is formed at tip  4   a  of bracket  4 . A curved face  42   a  is formed on projection  42  and the curved face contacts blade spring  6  mounted slidably on blade shoe  2 . 
     Blade spring  3  gradually separates in the lengthwise direction from its rear end  3   b  to its tip  3   a , from inside face  20   b , starting from its contact with inside face  20   b  of blade shoe  2  and it is in an arc-curved form as a whole. The length of blade spring  3  is shorter than the chain sliding face  2   a  of blade shoe  2 . Rear end  3   b  of blade spring  3  is attached to boss  22  at fixed end  2   b  of blade shoe  2  and tip  3   a  is placed away from blade shoe  2  and is attached slidably to through-hole  42   b  (attachment part) formed on projection  42 . Thereby, tip  3   a  of blade spring  3  is slidable against projection  42  of bracket  4 . Incidentally, a groove can be formed instead of through-hole  42   b  to slidably attach blade spring  3 . 
     In the fourth embodiment, contact of projection  42  of bracket  4  with blade spring  4  on the side of blade shoe  2  is at point C located at or near the mid point between tip  2   a  and fixed end  2   b  of blade shoe  2 . 
     When the chain is in operation, the chain runs on chain sliding face  20   a  of blade shoe  2  and proper tension is applied to the chain by blade shoe  2  as well as the elastic repulsive force of deformed blade springs  3 ,  6 . In such case, the natural frequency of blade tensioner  1  is determined by the position of contact point C. The closer the contact point C is to tip  2   a  of blade shoe  2 , the lower the natural frequency and, conversely, the closer the contact point C is to fixed end  2   b  of blade shoe  2 , the higher the natural frequency of the tensioner. 
     In the embodiments above, contact point C is located between tip  2   a  and fixed end  2   b  of blade shoe  2  and is closer to tip  2   a , so that the natural frequency of blade tensioner  1  is relatively high. Thereby, the resonance frequency of blade tensioner  1  can be set high and, as a result, the resonance of blade tensioner  1  in the engine rpm range and the resulting fatigue damage can be prevented. 
     In the embodiments above, one of two members that contact at contact point C has a curved face (see codes  31 ,  25   a ,  42   a ). Thereby, blade shoe  2  and blade springs  3 ,  6  do not interfere with other members and their deformation is smooth. As a result, the chain is tensioned properly during its operation. 
     As detailed above, the blade tensioner contact point of the tip of the bracket with the blade spring or blade shoe is at the mid point between the tip and fixed end of the blade shoe and, thereby, the resonance frequency of the blade tensioner can be set high. As a result, the resonance of the blade tensioner in the engine rpm range and the resulting fatigue damage can be prevented. 
     In one embodiment, the blade spring of the blade tensioner is shorter than the sliding face of the blade shoe and the other end of the blade spring (i.e. the tip), placed away from the blade shoe, is slidable against the tip of the bracket. The tip of the bracket is in contact with the other end of the blade spring and the contact point is located at the mid point between the tip and fixed end of the blade shoe. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance of the blade tensioner in the engine rpm range and resulting fatigue damage can be prevented. 
     In another embodiment, an additional blade spring is provided on the face opposite the chain sliding face of the blade shoe, therefore, the amount of deformation per unit load is small, that is, the spring constant of the blade tensioner is high. 
     In a further embodiment, the other end of the blade spring has a curved face and the curved face contacts the tip of the bracket slidably. In such case, the tip of the bracket does not interfere, so that the deformation of the blade spring is smooth and a proper tension is applied to the operating chain. 
     In a further embodiment, an outward projection is formed at the tip of the bracket or blade shoe at the mid point between the tip and fixed end of the blade shoe and the projection is provided slidably against the blade spring or bracket tip. The projection at the bracket tip contacts the blade spring or the projection on the side of the blade shoe contacts the bracket tip. This contact point is at the mid point between the tip and fixed end of the blade shoe. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance in the engine rpm range and resulting fatigue damage can be prevented. 
     In a further embodiment, the projection has a curved face and the curved face slidably contacts the blade spring or bracket tip. Therefore, deformation of the blade spring is made smooth. 
     In a further embodiment, the blade spring is composed of a first blade spring provided on the face opposite to the chain sliding face of the blade shoe and a second blade spring is provided, which is shorter than the chain sliding face and one end of which is attached to the fixed end of the blade shoe and the other end is located away from the blade shoe. The other end of the second blade spring is attached to the projection of the bracket. The projection of the bracket is attached to the other end of the second blade spring and the contact point is between the tip and the fixed end of the blade shoe. Thereby, similarly to the first embodiment, the resonance frequency of the blade tensioner can be set high and resonance in the engine rpm range and resulting fatigue damage can be prevented. 
     In a further embodiment, the projection of the bracket has a curved face and the curved face slidably contacts the first blade spring. The projection of the bracket has an attachment part to which the other end of the second blade spring can be slidably attached. Thereby, deformation of the blade spring is smooth. 
     Although specific embodiments and examples have been disclosed herein, it should be borne in mind that these have been provided by way of explanation and illustration and the present invention is not limited thereby. Certainly modifications which are within the ordinary skill in the art are considered to lie within the scope of this invention as defined by the following claims.