Abstract:
An asymmetric damping mechanism for use in a belt tensioner. The damping mechanism comprises two parts having substantially similar arcuate shapes for engaging a tensioner. The first part is in contact with the second part at a pivotable point of contact. The point of contact position is determined according to the desired asymmetric damping factor. The first part is also in contact with a spring. The second part is in contact with a tensioner arm. The damping mechanism also comprises two damping shoes, each having a damping band. The damping band is joined to the damping shoe by a plurality of vertical grooves on the damping shoe cooperating with a plurality of grooves on the damping band. The damping mechanism has an asymmetric damping factor in the range of approximately 1.5 to 5.

Description:
FIELD OF THE INVENTION 
     The invention relates to a damping mechanism, and more particularly, to an asymmetric damping mechanism for a tensioner. 
     BACKGROUND OF THE INVENTION 
     Belt tensioners are used to impart a load on a belt. Typically the belt is used in an engine application for driving various accessories associated with the engine. For example, an air conditioning compressor and alternator are two of the accessories that may be driven by a belt drive system. 
     A belt tensioner comprises a pulley journaled to an arm. A spring is connected between the arm and a base. The spring may also engage a damping mechanism. The damping mechanism comprises frictional surfaces in contact with each other. The damping mechanism damps an oscillatory movement of the arm caused by operation of the belt drive. This in turn enhances a belt life expectancy. 
     Representative of the art is U.S. Pat. No. 5,632,697 to Serkh (1997) which discloses a spring activated damping mechanism which provide a normal force greater than a spring force applied to a brake shoe that engages a cylindrical member. 
     Reference is also made to co-pending U.S. patent application Ser. No. 09/861,338 filed May 18, 2001 which discloses a tensioner having a damping mechanism. 
     Reference is also made to co-pending U.S. patent application Ser. No. 09/864,536 filed 24, May 2001 which discloses an asymmetric damping tensioner belt drive system. 
     What is needed is a damping mechanism having an asymmetric damping factor in the range of approximately 1.5 to 5.0. What is needed is a tensioner having a damping mechanism comprising two members having a pivotal connection. The present invention meets these needs. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the present invention is to provide a damping mechanism having an asymmetric damping factor in the range of 1.5 to 5.0. 
     Another aspect of the invention is to provide a tensioner having a damping mechanism comprising two members having a pivotal connection. 
     Other aspects of the invention will be pointed out or made apparent by the following description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of an inventive damping mechanism. 
         FIG. 2  is a cross-section view of an inventive damping mechanism at line  2 — 2  in  FIG. 1 . 
         FIG. 3  is a top perspective view of an inventive damping mechanism. 
         FIG. 4  is a cross-section view of an inventive damping mechanism at line  4 — 4  in  FIG. 3 . 
         FIG. 5  is a top perspective view of a locking mechanism on the damping shoe of an inventive damping mechanism. 
         FIG. 6  is a top perspective view of a locking mechanism on the damping band of an inventive damping mechanism. 
         FIG. 7  is a top perspective view of a prior art damping mechanism. 
         FIG. 8  is a top perspective view of a prior art damping mechanism damping shoe. 
         FIG. 9  is a top perspective view of a prior art damping mechanism damping band. 
         FIG. 10  is a diagram of forces acting on a damping mechanism. 
         FIG. 11  is a cross-sectional view of forces acting on a tensioner at line  11 — 11  in  FIG. 12 . 
         FIG. 12  is a plan view of forces acting on a tensioner. 
         FIG. 13  is a diagram of forces acting on a damping mechanism. 
         FIG. 14  is a cross-sectional view of forces acting on a tensioner at line  14 — 14  in  FIG. 15 . 
         FIG. 15  is a plan view of forces acting on a tensioner. 
         FIG. 16  is an exploded view of a tensioner having a damping mechanism. 
         FIG. 17  is an exploded view of a tensioner having a damping mechanism. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  is a top perspective view of an inventive damping mechanism. The inventive damping mechanism is utilized in a belt tensioner, see  FIG. 17 . The belt tensioner engages a belt through a pulley journaled to a lever arm. The tensioner is used to apply a preload to the belt and to damp oscillatory movements of the belt. 
     The damping mechanism damps oscillatory movements of a tensioner lever arm. The lever arm generally experiences a bi-directional or oscillatory motion caused by changes in the operating status of a belt drive, for example by load changes. Damping is necessary to remove energy from the belt system, thereby ensuring proper operation of the tensioner in order to maximize belt life and operational efficiency. 
     More particularly, an inventive damping mechanism is shown in  FIG. 1 . Damping mechanism  100  comprises damping band  102 . Damping band  102  is connected to an outer arcuate surface  104  of damping shoe  101 . Spring, or biasing member, receiving portion  103  comprises a slot in damping shoe  101 . Receiving portion  103  receives an end tang (not shown, see  500  in  FIG. 15 ) of a coil spring. Surface  105  engages a coil of a spring to provide support during operation. 
     Damping band  102  comprises a lubricated plastic such as nylon, PA and PPA, and their equivalents. 
       FIG. 2  is a cross-section view of an inventive damping mechanism at line  2 — 2  in  FIG. 1 . Ring cut  106  extends about an outer perimeter of outer arcuate surface  104 . Rim or protrusion  107  extends about a partial circumference of damping shoe  101 . Ring cut  106  in combination with protrusion  107  serve to mechanically attach damping band  102  to damping shoe  101 . 
       FIG. 3  is a top perspective view of an alternate damping mechanism. Inventive damping mechanism  200  comprises a first arcuate member  210  and a second arcuate member  220 . First arcuate member  210  has a spring receiving portion  211  into which a spring end tang may be inserted, see  FIG. 12 . A wall of the spring receiving portion has maximum thickness  211   a  at the spring contact area. Wall  211   a  may be tapered from the contact area in one direction or in both directions as it extends in both directions. By comparison, a like wall of the previous art has uniform thickness. 
     First arcuate member  210  comprises a damping band  213  attached to a damping shoe  212 . Second arcuate member  220  comprises a damping band  215  attached to a damping shoe  214 . 
     First arcuate member  210  is in pivotal contact with the second arcuate member  220  at a point of contact  216 . Point of contact  216  comprises end  228  of damping shoe  212  and end  219  of damping shoe  214 . Point of contact  216  may vary from a minimum radius to a maximum radius across a width W of each damping shoe with respect to a lever arm axis of rotation R—R, see  FIG. 11 . 
     In order to achieve the desired asymmetric damping factor, point of contact  216  is located at a predetermined radial distance from a lever arm axis of rotation R—R. A minimum radius location for point of contact  216 , shown in  FIG. 3 , results in the highest asymmetric damping factor for the damping mechanism in operation in a tensioner. Point of contact  216  may be disposed at an outer radius  288  which produces a reduced asymmetric damping factor as compared to the foregoing minimum radius location. 
     In an alternate arrangement, end  218  of first arcuate member  210  is in contact with the second arcuate member end  217 . In this alternate embodiment, a spring (not shown) having a coil direction opposite that used for the embodiment in  FIG. 3  is used. Therefore, by switching the point of contact from one end of the first arcuate member and second arcuate member to another end, either a left hand or right hand spring can be used. 
     Damping band  213 ,  215  are made of frictional material such as plastics, phenolics and metallics. A working surface  230 ,  231  of damping band  213 ,  215  respectively is slideably engaged under pressure with a tensioner base or arm by operation of a spring, see  FIG. 12  and  FIG. 15 . A frictional damping force is generated when the damping band slides on the base or arm. 
     Damping shoes  212 ,  213  are each made of structural material such as steel, molded plastic or equivalents thereof. Each damping shoe can be manufactured by utilizing a powder metal process, a die cast process, injection molding or similar processes. Materials that can be used include steel, aluminum (for low load parts), thermoplastics with various fillers, and equivalents thereof. 
     Damping band  215  of the second arcuate member has a material thickness less than the damping band  213  of the second portion. This has two advantages, first, increased spring hook-up size can be realized therefore a larger spring can be used. Second, due to the fact of that the second portion  220  of the damping mechanism has higher load than the first portion  210 , a reduced thickness of the first damping band  213  will equalize durability life of both parts. 
       FIG. 4  is a cross-section view of an alternate damping mechanism at line  4 — 4  in  FIG. 3 . Ring cut  221  extends about an outer perimeter of damping shoe  212 . Protrusion  222  extends about a partial circumference of damping shoe  212 . Ring cut  223  extends about an outer perimeter of damping shoe  214 . Protrusion  224  extends about a partial circumference of damping shoe  214 . Each ring cut  221 ,  223  in combination with each protrusion  222 ,  224  serve to mechanically attached each damping band  213 ,  215  to each damping shoe  212 ,  214  respectively. 
       FIG. 5  is a top perspective view of a locking mechanism on the damping shoe of an inventive damping mechanism. Locking mechanism  300  joins damping shoe  101  to damping band  102 , see  FIG. 6 . Locking mechanism  300  comprises a plurality of vertical grooves  110  on an arcuate outer engaging surface  111  of damping shoe  101 . Ring cut  112  is included to a top edge of the arcuate outer surface  111  to enhance the interconnection of the damping band  102  to the damping shoe  101 . Accordingly, lip portion  227  on damping band  102  engages over ring cut  112 . The disclosed multiple groove locking mechanism provides an improved, strong and uniform connection between the damping shoe and damping band. The connection distributes a frictional load imparted to the damping band  102  during operation, thereby extending an operational life over the prior art. 
       FIG. 6  is a top perspective view of a locking mechanism on the damping band of an inventive damping mechanism. The damping band portion of locking mechanism  300  comprises a plurality of spaced vertical ribs  120  on an arcuate inner engaging surface  121  of damping band  102 . Ribs  120  of damping band  102  cooperatively engage grooves  110  of damping shoe  101 . Protrusions  228  extend from a lower portion  229  of damping band  102 . Protrusions  228  engage cooperating recesses or dimples  231  in a base of damping shoe  101  to further affix damping band  102 . 
     The inventive locking mechanism significantly reduces weakening of the damping shoe, therefore, the inventive damping mechanism is much stronger than those in prior art. Loading conditions on the damping shoe/damping band are also much improved due to an improved load distribution across the damping shoe realized by the force distributive nature of the locking mechanism. 
       FIG. 7  is a top perspective view of a prior art damping mechanism. Prior art damping band DB is connected to prior art damping shoe DS. Tabs T mechanically connect the damping band DB, see  FIG. 9 , to the damping shoe DS, see  FIG. 8 . 
       FIG. 8  is a top perspective view of a prior art damping mechanism damping shoe. Damping shoe DS comprises slots S. Slots S receive tabs T in order to mechanically connect damping band DB to damping shoe DS, see  FIG. 9 . 
       FIG. 9  is a top perspective view of a prior art damping mechanism damping band. Damping band DB comprises tabs T. Each of tabs T mechanically cooperate with corresponding slots S in order to connect damping band DB to damping shoe DS. 
       FIG. 10  is a diagram of forces acting on a damping mechanism. The damping mechanism depicted is the embodiment described in  FIG. 3  and  FIG. 4 . Forces F 1  are spring contact reaction forces caused by contact of spring end  500  with the spring receiving portion  211 . Spring end  500  contacts the spring receiving portion  211  at two points, creating a pair of reaction forces F 1 . F 2  is a normal reaction force on the damping surface  230 . F 3  is a tangent friction force on the damping surface  230 . F 8  is a normal reaction force on the damping surface  231 . F 9  is a tangent friction force on the damping surface  231 . F 4  is the normal reaction force on damping mechanism arcuate member  220  imparted by a contact of damping shoe  214  with a lever arm  1030 , see  FIG. 16 . 
     The asymmetric damping factor is a function of a difference in frictional forces F 3  and F 9  for a movement of the lever arm  1030 . In operation, a normal reaction force F 8  on damping surface  231  is larger than normal reaction force F 2  on damping surface  230 . More particularly, when the lever arm  1030  moves in the +A direction the vectors for the friction forces, F 3  and F 9  operate as shown in  FIG. 10 . As the lever arm moves in a direction −A, friction force vectors F 3  and F 9  reverse direction. The change of direction of frictional force vectors F 3  and F 9  causes a resultant force on each damping surface  230 ,  231  to change. As a result, when lever arm moves in the −A direction, a normal reaction force on damping mechanism F 4  is larger than when the lever arm moves in direction +A. Proportionally, the torque generated on the lever arm in reference to the lever arm axis of rotation R—R by the force F 4  is larger when the lever arm moves in the −A direction than when the lever arm moves in the direction +A. The value of the torque on the lever arm when the arm moves in the direction −A is larger than the value of torque generated by the pair of forces F 1 . The difference between the two values of torque is defined as the damping torque in the direction −A. The value of the torque on the lever arm when the arm moves in the direction +A is smaller than the value of torque generated by the pair of forces F 1 . The difference between the two values of torque is defined as the damping torque in the direction +A. The ratio between the value of the damping torque in the direction −A and the value of the damping torque in the direction +A represents the asymmetric damping factor. 
     The asymmetric damping factor is adjustable depending upon the radial location of point of contact  216  described in  FIG. 3  and  FIG. 4 . The asymmetric damping factor will be increased as the point of contact  216  is placed radially closer to an axis of rotation of the lever arm  1030 . In the alternative, the asymmetric damping factor will be decreased as the point of contact  216  is placed radially farther from an axis of rotation of the lever arm  1030 . By radially moving point of contact  216  the asymmetric damping factor can be varied in the range of approximately 1.5 to 5. 
       FIG. 11  is a cross-sectional view of forces acting on a tensioner at line  11 — 11  in  FIG. 12 . Force F 7  is a normal reaction force acting on the arm at the damping mechanism contact point. Force F 7  has the same magnitude as force F 4  acting on the damping mechanism. F 6  is a pivot bushing reaction force acting at the interface between bushing  1040  and lever arm  1030 . F 5  is a hub load caused by a load on a belt B, see  FIG. 12 . 
       FIG. 12  is a plan view of forces acting on a tensioner. Depicted in  FIG. 12  is a plan view of the forces described in  FIG. 11 . 
       FIG. 13  is a diagram of the forces acting on a damping mechanism. The damping mechanism is that depicted in  FIG. 1  and  FIG. 2 . Forces F 11  are spring contact reaction forces caused by contact of the end  500  with the spring receiving portion  103 . One can see that spring end  500  contacts the spring receiving portion at two points creating a pair of reaction forces F 11 . F 12  is a normal reaction force on the damping surface  109 . F 13  is a tangent friction force on the damping surface  109 . F 14  is the reaction force on damping mechanism portion  102  imparted by a contact with a lever arm  2030 , see  FIG. 17 . 
     The asymmetric damping factor is realized by a difference in frictional force F 13  for a movement of the lever arm  2030 . More particularly, when lever arm  2030  moves in the +A direction, F 13  operates as shown in  FIG. 13 . As the lever arm moves in the −A direction, F 13  operates in the reverse direction. The change in direction in F 13  causes a resultant force on damping surface  109  to change. As a result when lever arm  2030  moves in the +A direction, a force F 14  on the damping mechanism is larger than when the lever arm moves in direction −A. Proportionally, the torque generated on the lever arm in reference to the lever arm axis of rotation R—R by the force F 14  is larger when the lever arm moves in the +A direction than when the lever arm moves in the direction −A. The value of the torque on the lever arm when the arm moves in the direction +A is larger than the value of torque generated by the pair of spring forces F 11 . The difference between the two values of torque is defined as the damping torque in the direction +A. The value of the torque on the lever arm when the arm moves in the direction −A is smaller than the value of torque generated by the pair of spring forces F 11 . The difference between the two values of torque is defined as the damping torque in the direction −A. The ratio between the value of the damping torque in the direction +A and the value of the damping torque in the direction −A represents the asymmetric damping factor. 
       FIG. 14  is a cross-sectional view of forces acting on a tensioner at line  14 — 14  in  FIG. 15 . Force F 17  is a normal reaction force acting on the damping mechanism contact point. F 16  is a pivot bushing reaction force acting at the interface between bushing  1040  and lever arm  1030 . F 15  is a hub load caused by a load on a belt B. 
       FIG. 15  is a plan view of the forces acting on a tensioner. Depicted in  FIG. 15  is a plan view of the forces described in  FIG. 14 . 
       FIG. 16  is an exploded view of a tensioner having a damping mechanism. Damping mechanism  200  engages lever arm  1030  at tab  1031 . Biasing member or spring  1020  has one end connected to base  1010  and the other end connected to damping mechanism spring receiving portion  211  as described elsewhere in this specification. Lever arm  1030  is pivotably connected to base  1010  through bushing  1040 . Dust seal  1050  prevents foreign material from entering the tensioner during operation. Pulley  1060  is journaled to lever arm  1030  through bearing  1070 . A belt (not shown) engages pulley surface  1061 . 
     Bearing  1070  is connected by a fastener such as bolt  1080 . Damping mechanism surfaces  230 ,  231  are in sliding engagement with an inner surface  1011  of tensioner base  1010 . 
     Tab  1031  engages damping shoe  212  during operation, thereby causing a movement of base inner surface  1011  across damping mechanism surface  230 . 
       FIG. 17  is an exploded view of a tensioner having a damping mechanism. Damping mechanism  100  is engaged with lever arm  2030  at tab  2031 . Biasing member or spring  2020  has one end connected to base  2010  and the other end connected to damping mechanism spring receiving portion  103  as described elsewhere in this specification. Lever arm  2030  is pivotably connected to base  2010  through bushing  2040 . Dust seal  2050  prevents foreign material from entering the tensioner during operation. Pulley  2060  is journaled to lever arm  2030  through bearing  2070 . A belt (not shown) engages pulley surface  2061 . 
     Bearing  2070  is connected by a fastener such as bolt  2080 . Damping mechanism surface  109  is in sliding engagement with an inner surface  2011  of tensioner base  2010 . 
     Tab  2031  engages damping mechanism  100  during operation, thereby causing a movement of base inner surface  2011  across damping mechanism surface  109 . 
     Although a single form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.