Abstract:
A hydraulic damper for providing fluid damping to a tensioner in a drive system that includes a damper cup, which is mounted to the tensioner and configured to rotate about a central axle in tandem with the tensioner, an end plate having an outer face and an inner face, which is attached to the damper cup forming a fluid chamber, a peg attached to the end plate and extending away from the inner face and toward the damping cup, a damping fluid, which is contained within the fluid chamber, a plurality of shear plates housed within the fluid chamber comprising alternating fixed plates engaged with a fixed component of the tensioner and rotatable plates engaged with a rotatable component of the tensioner where the peg extends through openings in each of the shear plates allowing for rotation of the rotatable plate with the rotation of the peg.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a damping mechanism for tensioners for a drive belt system and more particularly to a hydraulic damped tensioner utilizing a damping mechanism utilizing shear forces generated from rotating plates through a viscous fluid. 
     BACKGROUND 
     Belt tensioners use a system or mechanism to dampen tensioner movement which minimizes steady state vibrations or transient events that cause belt slip. The required magnitude of this damping depends on many drive factors including geometry, accessory loads, accessory inertia, engine duty cycle and others. For instance, drive systems that have higher torsional input or certain transient dynamic conditions may require higher damping to sufficiently control tensioner movement. Although higher damping is very effective at controlling arm movement, it can also be detrimental to other critical tensioner functions (e.g. slow or no response to slack belt conditions). In addition, variation or change in damping that occurs as a result of manufacturing variation, operating temperature and component break-in or wear can also result in undesirable tensioner responsiveness. 
     Damping derived by utilizing shear forces generated by rotating plates through a viscous fluid has been used with belt tensioners. One particular method involves a rotating plate and a fixed plate surrounded by a viscous fluid as in U.S. Pat. No. 4,838,839 to Watanabe. To achieve the fluid damping in Watanabe, the fixed plates are fixed directly to the fixed shaft, and the displaceable plates are fixed directly to an oscillation sleeve. 
     Other solutions using plates for hydraulic damping are found in U.S. Pat. Nos. 4,601,683 and 5,391,119 to Foster and Kondo respectively. These designs specifically manufacture the plates to attach directly to the rotating and fixed parts of the tensioner. This approach requires more complex manufacturing and assembly processes. 
     The aforementioned hydraulic damping mechanisms are not ideal. Accordingly, a new damping mechanism and tensioner design is desired. 
     SUMMARY 
     One aspect disclosed herein is a hydraulic damper for providing fluid damping to a tensioner in a drive system that includes a damper cup, which is mounted to the tensioner and configured to rotate about a central axle in tandem with the tensioner, an end plate having an outer face and an inner face, which is attached to the damper cup forming a fluid chamber, a pin attached to the end plate and extending away from the inner face and toward the damping cup, a damping fluid, which is contained within the fluid chamber, a rotatable plate having an opening configured to accept the pin through the rotatable plate and rotate about the central axle, and a fixed plate having an opening configured to accept the pin through the fixed plate, which is fixed to and does not rotate about the central axle. During wind-up and tensioning of the tensioner, a shear force is applied to the rotatable plate moving through the damping fluid to provide damping to the tensioner. 
     In another embodiment, the hydraulic damper includes a damper cup, which is mounted to the tensioner and configured to rotate about a central axle in tandem with the tensioner, an end plate having an outer face and an inner face, which has a central opening and is configured to accept the central axle and rotate about the central axle, and wherein the end plate is attached to the damper cup forming a fluid chamber, a ring configured to be mounted on the central axle and fit within the central opening of the end plate forming a fluid tight seal between the end plate and the central axle, a pin attached to the end plate and extending away from the inner face and toward the damping cup, a damping fluid, which is contained within the fluid chamber, a rotatable plate, which is mounted on a hub configured to be mounted on and rotate about the central axle, and the rotatable plate has an opening configured to accept the pin through the rotatable plate, and a fixed plate having an opening configured to accept the pin through the fixed plate, wherein the fixed plate is fixed to and does not rotate about the central axle. 
     The features, functions, and advantages discussed can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of an embodiment of the hydraulic damper. 
         FIG. 2  is a is a front view of an engine which utilizes an embodiment of a tensioner using the new hydraulic damper. 
         FIG. 3  is a cross sectional view of an embodiment of the hydraulic damper. 
         FIG. 4  is a front view of an embodiment of the hydraulic damper and tensioner assembly. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the invention or the application and uses of such embodiments. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     The hydraulic damper disclosed herein provides a tensioner with hydraulic damping. The tensioner is typically part of a power system, known as a Front End Accessory Drive (“FEAD”) system where the tensioner provides tension to an endless power transmitting element such as a belt, chain, or other continuous loop in a system driven by at least one source and that also drives at least one accessory. The endless power transmitting element and the tensioner operate in concert with the tensioner providing tension to the power transmitting element as needed and responding to dynamic conditions thereof. 
     Engines that utilize an endless power transmitting element for driving a plurality of driven accessories is well known in the art. Additionally belt tensioners utilized to provide a tensioning force on the endless power transmitting element are also well known in the art. 
     Referring now to  FIGS. 1 and 2 , in an embodiment, the hydraulic damper  100  of this invention is utilized to provide damping to a tensioner  124  utilized in continuous belt or chain drive systems in the manner described below. The tensioner  124  is configured to be fixed to an engine  200  using a mounting bracket  128 . The mounting bracket  128  is configured with a mounting peg  126  which is configured to be disposed within a designated opening in the engine  200 . The mounting peg  126  allows the mounting bracket  128  to be correctly aligned and oriented during operation of the engine  200 . The mounting bracket is secured to the engine with a bolt (not shown) passing through a pivot member  102 . The combination of the mounting bracket  128  and the pivot member  102  serve as the support structure for the tensioner  124 . Additionally, the pivot member  102  is configured to serve as a central axle about which the tensioner  124  rotates. Other methods may be used to secure the mounting bracket  128  to the engine, such as bolts, screws, welds, or any other suitable fastener known in the art that will hold the mounting bracket  128  in place during operation of the engine. Additionally, the mounting bracket  128  may be of any configuration and include any number of openings for receiving the fasteners to mount to the engine. 
     In an embodiment, the pivot member  102  extends axially away from the engine  200 , through and beyond the tensioner  124  providing support for the hydraulic damper  100 . The pivot member  102  is stationary and fixed to the engine  200  and the tensioner  124  rotates about the pivot member  102 . A damper cup  106 , having a closed end  120  and an open end  122  is mounted on the pivot member  102  through a central opening in the closed end  120  so that the closed end  122  abuts the tensioner  124 . The open end  122  has an inner wall  132  with a notch  134 . Once mounted on the pivot member  102 , the damper cup  106  is configured to rotate, in tandem with the tensioner  124 , about the pivot member  102 . An end cap  104  is secured to the pivot member  102  and configured to prevent the damper cup  106 /tensioner  124  combination from sliding off the end of the pivot member  102 . 
     Fixed plates  108  having a diameter less than the inner diameter of the open end  122  is mounted on a hub  118  though central opening  108   a . The fixed plate is secured to the hub  118  using lobes  108   d  and any means known in the art such that the fixed plates  108  remain stationary with respect to and does not rotate with the damper cup  106  and the tensioner  124 . The fixed plates  108  contain one or more curved openings  108   b  located between the central opening  108   a  and the outer edge of the plates  108 . Additionally, the fixed plates  108  contain one or more openings  108   c  located between the central opening  108   a  and the outer edge of the fixed plates  108 . The openings  108   c  allow a damping fluid  136  ( FIG. 3 ) to completely surround and immerse the fixed plates  108 . In another embodiment, the fixed plates  108  do not contain openings  108   c , and have a diameter less than the inner diameter of the open end  122  such that a gap exists between the diameter of the fixed plates  108  and the inner wall  132  to allow the damping fluid  136  to completely surround and immerse the fixed plates  108 . Openings  108   b  are elongated and at least one receives connecting peg  130  of end plate  112  and allows for the rotation of end plate  112  relative to the fixed plates  108 . 
     The hub  118  is mounted on pivot member  102  and configured to be fixed with pivot member  102 . Rotatable plates  110  having a diameter less than the inner diameter of the open end  122  are mounted on the hub  118  though central opening  110   a . The rotatable plates  110  are configured to rotate about the pivot member  102 . The rotatable plates  110  contain one or more circular openings  110   b  located between the central opening  110   a  and the outer edge of the rotatable plates  110 . Additionally, the rotatable plates  110  contain one or more openings  110   c  located between the central opening  110   a  and the outer edge of the rotatable plates  110 . The openings  110   c  allow the damping fluid  136  ( FIG. 3 ) to completely surround and immerse the rotatable plates  110 . In another embodiment, the rotatable plates  110  do not contain openings  110   c , and have a diameter less than the inner diameter of the open end  122  such that a gap exists between the diameter of the rotatable plates  110  and the inner wall  132  to allow the damping fluid  136  to completely surround and immerse the rotatable plates  110 . The rotatable plates  110  are driven by a connecting peg  130   
     An end plate  112  having an inner face  112   a , an outer face  112   b , an outer edge  112   c , and a notch  112   d  located on the outer edge  112   c . The connecting peg  130  is fixed to the inner face  112   a  and extends out away from the inner face  112   a  towards the tensioner  124 . The end plate  112  is disposed within the open end  122 . When placing the end plate  112  into the open end  122 , the assembler aligns notch  112   d  with notch  134  forming a small opening  138 . The end plate  112  is fixed to the inner wall  132  forming a fluid tight seal between the end plate  112  and the inner wall  132  except for the small opening  138 . In another aspect, the end plate  112  may be properly aligned with open  122  using a key located on end plate  112  that fits within a keyway located on the inner wall  132 . Additionally, any other method for aligning objects which is known in the art may also be used to properly align notch  112   d  with notch  134 . Once the end plate  112  is fixed to the inner wall  132 , a fluid chamber  140  is created between the closed end  120 , the inner face  112   a , and the inner wall  132 . Additionally, the end plate  112 , which is fixed to the inner wall  132  is configured to rotate in tandem with the damper cup  106  and the tensioner  124 . The end plate  112 , the rotatable plate  110 , and the fixed plate  108  are aligned such that connecting peg  130  passes through the circular opening  110   b  and the curved slot opening  108   b . In another embodiment, end plate  112  has a central opening  114 . A ring  116  having an inner diameter equal to the outer diameter of the hub  118  is mounted on the hub  118  forming a fluid tight seal between the ring  116  and the hub  118 . The ring  116  has an outer diameter equal to the diameter of the central opening  114 . The end plate  112  is mounted to the ring  116  via the central opening  114  such that a fluid tight seal is formed between the end plate  112  and the ring  116 . 
     In an embodiment, the fluid chamber  140  is filled with the damping fluid  136  through the small opening  138 . After filling the fluid chamber  140  with the damping fluid  136 , the small opening  138  is sealed using a plug, ball bearing, or any other method known in the art that would create a fluid tight seal. 
     Referring to  FIG. 3 , in an embodiment, protrusions  302  protrude from the surface of the fixed plates  108 . The protrusions  302  are configured to provide a space between the fixed plates  108  and the closed end  120  of the damper cup  106 . Additionally, protrusions  302  are configured to provide a space between the fixed plates  108  and the rotatable plates  110 . Protrusions  304  protrude from the surface of the rotatable plates  110  and are configured to provide a space between the rotatable plates  110  and adjacent fixed plates  108 . In an embodiment, a plurality of fixed plates  108  and rotatable plates  110  are mounted about hub  118  in an alternating manner. 
     In an embodiment, tensioning a slack power transmitting element is an unwinding of a wound-up tensioner which will be referred to herein as the tensioning direction T. In the opposite direction, referred to herein as the winding direction W, a winding up of the tensioner occurs in response to a prevailing force of the power transmitting element which is tightening in the span where the tensioner resides. The winding of the tensioner may have some potentially deleterious effects, so to mitigate these effects it is desirable to have a damper, for example a hydraulic damper, incorporated in the tensioner to resist the movement of the power transmitting element without adversely affecting movement of the tensioner, in particular its arm to tension the power transmitting element. This kind of damping is generally known as hydraulic damping. 
     Referring to  FIGS. 3 and 4 , in an embodiment, the hydraulic damper  100  achieves damping when the end plate  112  rotates in tandem with the damper cup  106  and tensioner  124  in either the tensioning direction T or winding direction W. There are limit stops  402 ,  404 , and  406 , which limit the travel of the tensioner  124 . When in a resting position, the tensioner  124  rests against limit stop  406 . As the tensioner  124  rotates in the winding direction W, the tensioner travels in that direction until either the belt force acting on the tensioner stops, or limit stop  402  meets limit stop  404 . When limit stops  402  and  404  come together, the tensioner  124  is prevented from moving further in the winding direction W. After winding, the tensioner  124  is biased to rotate in the tensioning direction T. When rotating in the tensioning direction T, the tensioner  124  continues to rotate in the tensioning direction until either the tensioner  124  is prevented from further rotation by the belt force or limit stop  406 . When the tensioner  124  reaches limit stop  406 , the tensioner  124  is prevented from rotating any further in the tensioning direction T. 
     As the rotatable plate  110  rotates through the surrounding damping fluid  136  a shear force is created between the rotatable plate  110  and the fixed plate  108 . This shear force acts in the opposite direction to the rotation of the rotatable plate  110 . This resistance by the shear force acts to dampen the movement of the tensioner  124  in either the tensioning direction T or winding direction W depending on the direction of rotation of the tensioner  124 . The shear force is generated each time the rotatable plate  110  rotates through the damping fluid  136  regardless of whether the rotation is in the tensioning direction T or winding direction W. Therefore, the hydraulic damper  100  provides damping to the tensioner  124  in both the tensioning direction T and the winding direction W. 
     In an embodiment, the hydraulic damper  100  may be assembled as a stand-alone unit, including all components and damping fluid  136 . The hydraulic damper  100  can then be inserted into the main body of tensioner  124 . 
     The components of the hydraulic damper  100  can be fabricated using a variety of techniques including forging, casting, die-casting, injection molding, sintering, or machining or fabricated in different components, or other techniques known to one of ordinary skill in the art and then joined together using a variety of methods such as sintering, welding, bonding, bolting, and even interference fits or other methods known to one of ordinary skill in the art. 
     The embodiments of this invention shown in the drawing and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is understood that numerous other configurations of the hydraulic damper  100  may be created taking advantage of the disclosed approach. In short, it is the applicant&#39;s intention that the scope of the patent issuing herefrom will be limited only by the scope of the appended claims.