Abstract:
A rotary damper for use in an automotive vehicle. The rotary damper includes an outer casing having a main chamber and a pair of piston orifices, the main chamber and the piston orifices being filled with a damping fluid, a pivotable cam located in the main chamber and attached to an arm for transferring the rotary movement of the arm to the cam. The damper also includes a pair of pistons, each located in its own orifice, and connected to opposite sides of the cam. When the ami transfers the rotary movement to the cam, each piston is moved in opposite directions in its respective piston orifice to damp the rotary movement of the arm.

Description:
TECHNICAL FIELD 
     The present invention relates to vibration damping devices, and more particularly, to rotary dampers for use in automotive vehicle shock absorbing systems. 
     BACKGROUND OF THE INVENTION 
     Automobiles and other vehicles utilize shock absorbers to dissipate shock and vibrational forces sustained by the vehicle wheels. The vehicles typically use conventional, linear-style shock absorbers. Such shock absorbers include a pair of telescoping cylindrical sleeves oriented generally vertically in the vehicle. A piston is attached to one of the sleeves and travels in a fluid-filled cylinder associated with the other sleeve. One of the sleeves is coupled to a wheel support structure of the associated vehicle and the other sleeve is attached to the frame of the vehicle. When shock or vibrational forces displace the associated vehicle wheel relative to the associated vehicle, the force drives the piston along the cylinder, thereby forcing fluid through an orifice in the piston, which resists such motion with a force proportional to the shock force. In conventional shock absorbers, the shock absorber must extend between the vehicle body and wheel support structure, and must be oriented along the direction of travel of the wheel support structure in response to a shock load. Therefore, the conventional linear-style shock absorber is limited in its spatial orientation. 
     Rotary shock absorbers, or rotary dampers, have been developed to replace linear-style shock absorbers. Rotary shock absorbers have several advantages over conventional linear-style shock absorbers and operate by converting shock forces into rotary motion, and then damping the rotary motion. For example, rotary shock absorbers are not limited in spatial orientation relative to the vehicle body to oppose shock forces, as are linear-type shock absorbers. Rotary dampers may be oriented generally horizontally, and thereby extend underneath the body of the associated vehicle. Furthermore, because the rotary damper is more isolated from the vehicle frame than conventional linear-type type shock absorbers, shock and vibrational forces (including noise) are not transmitted from the shock absorber to the vehicle body to the same extent as prior art linear-style shock absorbers. 
     Rotary dampers typically include a shaft, arm, or cam which transmits shock forces from the wheel to one or more components that are forced through a fluid filled chamber to damp the shock forces. However, existing rotary dampers can be relatively large, lack durability, and be expensive to manufacture. Accordingly, there is a need for a rotary damper that is compact, durable, and inexpensive. 
     SUMMARY OF THE INVENTION 
     The present invention is a rotary damper, suitable for use in an automotive vehicle shock absorbing system, which is compact, robust and relatively inexpensive to fabricate. The rotary damper of the present invention includes a rotatable cam coupled to a pair of pistons, each mounted in its own fluid-filled orifice and coupled to opposite sides of the cam such that rotation of the cam causes the pistons to move within their respective piston orifice. The movement of the pistons in the piston orifices in response to movement of the cam forces the fluid through a set of valves, which damps the applied forces. 
     In a preferred embodiment, the damper includes an outer casing enclosing a main chamber and a pair of piston orifices filled with a damping fluid. A pivotable cam is located in the main chamber and is attached to an arm which typically is connected to a wheel support structure. The damper also includes a pair of pistons, each located in one of the pair of orifices and connected to opposed sides of the cam. The arm is connected to pivot about its connection to the cam. Movement of the arm pivots the cam within the main chamber, which moves each piston in opposite directions in its respective piston orifice. Displacement of the piston forces fluid through orifices in the pistons which damps the rotary movement of the arm. 
     Other objects and advantages of the present invention will be apparent from the following description, the accompanying drawing and the appended claims. 
    
    
     SUMMARY OF THE DRAWINGS 
     FIG. 1 is a perspective view of a suspension system of a vehicle incorporating a preferred embodiment of the rotary damper of the present invention; 
     FIG. 2 is a perspective cross section of the damper of FIG. 1; 
     FIG. 3 is a perspective, exploded view of the damper of FIG. 1; 
     FIG. 4 is a perspective, exploded view of the upper housing portion of the damper of FIG. 1; 
     FIG. 5 is a top plan view in section of the lower housing portion of the damper shown in FIG. 3; 
     FIG. 6 is a side elevational view in section of the upper housing portion of the damper shown in FIG. 3; 
     FIG. 7 is a perspective, exploded view of a piston and piston valve of the damper shown in FIG. 2; 
     FIG. 8 is a perspective, exploded view of a chamber valve of the damper shown in FIG. 2; 
     FIG. 9 is a perspective view showing an assembly for coupling a trailing arm to the rotary damper of FIG. 2; 
     FIG. 10 is a side elevation in section of the trailing arm and rotary damper of FIG. 9; and 
     FIG. 11 is a detail showing, the trailing arm and rotary damper of FIG.  10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, the rotary damper  10  of the present invention may be used in a suspension system, generally designated  12 , for a vehicle. The suspension system  12  includes a disc and hub assembly  14  upon which a wheel (not shown) may be mounted. A trailing arm  16  extends generally rearwardly from the disc and hub assembly  14 , and is coupled to the rotary damper  10  and a torsion spring  18  at the axis A. When shock or vibrational forces are applied to the wheel and the disc and hub assembly  14 , the disc and hub assembly  14  is vertically displaced relative to the associated vehicle frame  20 . This displacement causes the trailing arm  16  to pivot about the axis A. The torsion spring  18  resists the rotation of the trailing arm  16 , and the rotary damper  10  damps the rotation of the trailing arm  16 . The rotary damper  10  includes an eye  21  and is mounted to a raised boss  22  on the frame  20  of the vehicle by a bolt  23 . 
     The rotary damper  10  is shown in greater detail in FIG. 2, and includes an outer casing  24  having a main chamber  26  and a pair of piston orifices  28 ,  30 . The inner volume of the outer casing  24 , including the main chamber  26  and the piston orifices  28 ,  30 , is filled with a damping fluid (not shown in FIG.  2 ). A cam  32  is pivotably mounted in the main chamber  26  such that the cam pivots about the axis A. A pair of pistons  34 ,  36  are slidably mounted in the piston orifices  28 ,  30 . The piston orifices  28 ,  30  closely receive, and generally form a seal with, the respective pistons  34 ,  36 . 
     The pistons  34 ,  36  each include a pin  40 ,  42 , respectively. Springs  44 ,  46  are coupled to opposite sides of the cam  32  and to the pils  40 ,  42  to couple the cam to the pistons  34 ,  36 . Each piston  34 ,  36  also includes a roller  48 ,  50  that is pulled into engagement with a lower or cam surface  52  of the cam  32  by the springs  44 ,  46 . The springs  44 ,  46  are preferably constant length springs, and maintain the alignment between the cam  32  and the pistons  34 ,  36 . The springs  44 ,  46  also maintain contact between the cam  32  and the rollers  48 ,  50 . The rollers  48 ,  50  are preferably made of a self-lubricating material. 
     As shown in FIG. 3, the damper housing  24  includes upper housing and lower housing portions  54 ,  56 . A pair of O-rings or seals  58  are located between the upper housing portion  54  and the lower housing portion  56 . A cover assembly  60  is mounted over the main chamber  26  and is attached to the upper housing portion  54  by a pair of flat head screws  62  located on top of a pair of seal washers  64  and a pair of O-rings  66 . A second set of screws  68  further attach the cover assembly  60  to the upper housing portion  54 . 
     As shown in FIG. 4, the upper housing portion  54  receives the cam  32 . Roller bearings  70 ,  72  arc mounted on a pair of cylindrical ends  74 ,  76  of the cam to guide the rotation of the cam  32 . A pair of O-rings  78 ,  80  are also mounted on the cylindrical ends  74 ,  76  of the cam  32 . Each of the pistons  34 ,  36  has a piston valve  82 ,  84 , respectively, at its bottom, and a pair of bands  86 ,  88  are seated on annular grooves  75 ,  77  on the pistons. The bands  86 ,  88  help to form a seal between the pistons  34 ,  36  and their piston orifices  28 ,  30 . The bands preferably are made of a self-lubricating material to facilitate the sliding of the pistons. 
     With reference to FIG. 5, the lower housing portion  56  includes a pair of laterally extending orifices  90 ,  92  that are in fluid communication with the piston orifices  28 ,  30 . The laterally extending orifices  90 ,  92  connect to a single longitudinal passage  94 , which is in fluid communication with a longitudinal passage  96  in the upper housing portion  54 , as seen in FIG. 6; and the longitudinal passage  96  in the upper housing portion  54  is in fluid communication with the main chamber  26 . In this manner, the laterally extending orifices  90 ,  92  and longitudinally extending orifices  94 ,  96  form a return path  98  that couples the piston orifices  28 ,  30  to the main chamber  26 . As seen in FIG. 6, the upper housing portion  54  may also include an instrument port  157  to receive sensors for measuring the temperature, pressure, viscosity, or other qualities of the damping fluid. 
     As shown in FIG. 5, the rotary damper  10  includes an accumulator  100  that is in fluid communication with the laterally extending orifice  92  via a connecting orifice  102 . The accumulator  100  receives excess fluid that is not located in the main chamber  26 , the piston orifices  28 ,  30  or the return path  98 . The accumulator  100  also accommodates thermal expansion of the fluid. A movable gas cup  104  (FIG. 2) is located in the accumulator  100  to maintain the pressure of the fluid in the accumulator  100  and to maintain the fluid-gas separation. The lower housing portion  56  also includes fill ports  103 ,  105  through which fluid may be added to the damper  10  (FIG.  5 ). 
     Returning to FIG. 2 and 4, the piston valves  82 ,  84  in pistons  34 ,  36  control the flow of fluid from the main chamber  26  to the respective piston orifices  28 ,  30 . The piston valves  82 ,  84  are biased in the closed position such that the flow of fluid from the main chamber  26  to the respective piston orifices  28 ,  30  is normally blocked. However, when the pressure in the main chamber  26  exceeds the pressure in the respective piston orifice  28 ,  30  by a predetermined value, the piston valves  82 ,  84  open and allow fluid to flow from the main chamber  26  to the respective piston orifices  28 ,  30 . The piston valves  82 ,  84  do not allow fluid to flow through the valves from the piston orifices  28 ,  30  to the main chamber  26 . 
     Chamber valves  106 ,  108  are located at the bottom of the piston orifices  28 ,  30  and control the flow of fluid from the piston orifices  28 ,  30  to the main chamber  26  via the return path  98 . The chamber valves  106 ,  108  are biased in the closed position such that fluid flow from the piston orifices  28 ,  30  to the respective laterally extending orifices  90 ,  92  (and thereby the main chamber  26 ) is normally blocked. However, when the pressure in the piston orifices  28 ,  30  exceeds the pressure in the main chamber  26  by a predetermined value, the chamber valves  106 ,  108  open and allow fluid to flow from the piston orifices  28 ,  30  to the main chamber  26  (via the return path  98 ). The chamber valves  106 ,  108  do not allow fluid to flow through the valves from the main chamber  26  to the piston orifices  28 ,  30 . 
     The piston valves  82 ,  84  and chamber valves  106 ,  108  may take a variety of forms, but in a preferred embodiment they include a disk that is spring biased against a seat. For example, FIG. 7 illustrates a piston  34  and its piston valve  82 , the construction and operation of the piston  36  and its piston valve  84  being substantially identical. The piston  34  has a plurality of holes  81  located in its bottom surface, or valve seat  83 . A disk  85  is biased against the valve seat  83  to block flow through the holes  81 . The disk  85  is biased against the valve seat  83  by a spring  87 . A screw  91  is passed through a hole  79  in the bottom of the piston  34 , and is threaded into a valve nut  59  to hold the valve assembly  82  together. When the pressure upstream of the disk  85  (i.e. pressure in the main chamber  26 ) reaches a sufficient level relative the pressure downstream of the disk (i.e. pressure in the piston orifice  28 ), the disk  85  is moved away from the seat  83 , compressing the spring  87 . This allows fluid to flow through the holes  81  and into the piston orifice  28 . When the pressure differential drops to a sufficient level, the disk  85  is pressed against the seat  83  by the spring  87 , thereby closing the valve  82 . 
     The operation and construction of the chamber valves  106 ,  108  is similar to that of the piston valves  82 ,  84 . The chamber valve  106  is shown in FIG. 8, the operation and construction of the chamber valve  108  being substantially identical. The chamber valve  106  includes a valve base  95  having a plurality of holes. A number of valve disks  93  are biased against the valve base  95  to selectively block flow through the holes  97  in the manner know to those skilled in vehicle suspension damper design. The valve disks  93  are located adjacent a spring seat  99 , which receives a rebound or coil spring  101 . The valve assembly  106  is held together by a valve bolt  103  that is threaded into a shoulder nut  121 . A gasket  107  is located between the valve bolt  103  and the valve base  95 . 
     In operation, when pressure in the piston orifice  28  exceeds the pressure in the main chamber  26  by a sufficient level, the disks  93  and spring scat  99  are moved away from the valve base  95  such that fluid can flow through the holes  97 . When sufficient pressure in the piston orifice  18  is released, the disks  93  are pressed against the valve base  95  by the spring  101  to close the valve  106 . The number and thickness of the valve disks  93 , as well as the spring constant in the rebound spring  101 , may be changed to vary the damping characteristics of the damper  10  as desired. Three valve disks  93  are shown, although the number of valve disks may be varied as desired to change the characteristics of the valve  106 . 
     When shock or vibrational forces are applied to the trailing arm  16  (FIG.  1 ), the trailing arm rotates about central axis A. Because the trailing arm  16  is coupled to the cam  32  and torsion spring  18 , the cam  32  and torsion spring  18  arc rotated about axis A. When the cam  32  rotates about axis A (FIG.  2 ), the rotation of the cam causes the pistons  34 ,  36  to move in opposite directions in the piston orifices  28 ,  30 . For example, referring to FIG. 2, when the cam  32  is rotated counterclockwise, the cam surface  52  bears against the roller  48  of the piston  34 , and thereby urges the piston  34  up and to the left of its position shown in FIG.  2 . This increases the pressure of the fluid in the piston orifice  28 . When the pressure differential between the piston orifice  28  and the main chamber  26  reaches the cracking pressure for the chamber valve  106 , the chamber valve  106  opens. When the chamber valve  106  opens it allows fluid to flow into the laterally extending orifice  90  of the return path  98 , and the fluid then flows through the return path  98  and into the main chamber  26 . 
     Simultaneously, the spring  46  on the opposite side of the cam  32  pulls the piston  36  down and to the right of its position as shown in FIG. 2, which decreases the pressure of the fluid in the piston orifice  30  relative to the main chamber  26 . When the pressure in the piston orifice  30  is reduced sufficiently compared to the pressure in the main chamber  26 , the piston valve  84  opens and allows fluid to flow from the main chamber into the piston orifice  30 . The flow of fluid through the restricted orifices of the piston valve  84 , chamber valve  106 , and return path  98 , as well as the pressurization of the fluid, damps the rotational motion of the cam  32 , and thereby damps the motion of the trailing arm  16 . 
     Similarly, when the trailing arm  16  is urged in the opposite direction (i.e. clockwise in FIG.  1 ), the cam  32  of FIG. 2 is moved in the clockwise direction in FIG.  2 . This increases the pressure in the piston orifice  30  and causes the chamber valve  108  to open, and reduces the pressure in the piston orifice  28  and causes the piston valve  82  to open. The flow of fluid through the restricted orifices of the piston valve  82 , chamber valve  108 , and return path  98 , as well as the pressurization of the fluid, damps the rotational movement of the cam  32  and trailing arm  16 . 
     The cam surface  52  is preferably shaped as an involute curve so that the rate of rotation of the cam  32  is proportionally translated into linear movement of the pistons  34 ,  36 . In this embodiment, the damper  10  provides generally uniform damping) for a given angular displacement of the trailing arm  16 , regardless of the position of the trailing arm  16 . However, the shape of the cam surface  52  may be varied to provide differing damping characteristics depending upon the location of the trailing arm  16  and the disk and hub assembly  14 . For example, in order to help control the movement of the vehicle wheel when the wheel is located near the limits of its (vertical) travel, the cam surface  52  may be shaped to increase the damping forces when the wheel is located at these extreme positions. In this case, when the trailing arm  16  (and therefore the wheel and hub assembly  14 ) is outside normal operating conditions, any additional angular displacement of the trailing arm outside normal operating conditions may cause increased displacement of the pistons  34 ,  36  (and therefore additional damping) as compared to the damping that the trailing arm would experience for the same angular displacement if the trailing arm were within normal operating conditions. In this manner the cam surface  52  may be shaped to provide softer damping when the trailing arm  16  (and therefore the disk and hub assembly  14 ) is in normal operating conditions, and firmer damping when the trailing arm  16  is located outside normal operating conditions. 
     The damping forces applied by the damper  10  may also be varied as a function of the displacement of the wheels caused by a load carried by the vehicle. Finally, the cam surface  52  may provide different damping forces when the disk and hub assembly  14  is rising (jounce) as opposed to downward movement of the disk and hub assembly  14  (rebound). Of course, the shape of the cam surface  52  may be varied in a number of other manners beyond those discussed herein to vary the performance of the damper  10 . 
     A preferred method for attaching a trailing arm to a rotary damper is shown in FIGS. 9-11. The trailing arm  16 ′ and rotary damper  10 ′ shown in FIGS. 9-11 differ slightly from the trailing arm  16  and rotary damper  10  discussed above, but the structure for coupling the trailing arm  16 ′ to the rotary damper  10 ′ shown in FIGS. 9-11 and described below may be used in nearly any rotary damper, including the rotary damper  10  discussed above. As shown in FIG. 9, the trailing arm  16 ′ includes a shoulder pin  120  extending from an upper end  122  of the trailing arm  16 ′. The shoulder pin  120  is preferably eccentric or non-circular in cross section, and in the illustrated embodiment the shoulder pin is square in cross section. The cam  32 ′ of the rotary damper  10 ′ includes a through hole  124  that is shaped to closely receive the shoulder pin  120 , which means that, in this embodiment, it is also square. The shoulder pin  120  includes a threaded hole  126 , and the pin includes a set of longitudinal slots  128  that extend through the pin  120  to the threaded hole  126 . The slots  128  define a set of arms  132  that are located adjacent the end of the shoulder pin  120  that is received in the hole  124  of the cam  32 ′. 
     In order to couple the trailing arm  16 ′ to the cam  32 ′, the shoulder pin  120  is inserted into the hole  124  of the cam  32 ′. The eccentric shape of the shoulder pin  120  and hole  124  ensures that any rotary movement of the trailing arm  16 ′ is transferred to the cam  32 ′. Next, a screw  130  is threaded into the threaded hole  126 . As the screw  130  is received in the hole  126 , the arms  132  are urged radially outwardly and into contact with the walls  125  of the hole  124  of the cam  32 ′ (FIGS.  10 - 11 ). When the screw  130  is tightened down, the frictional forces between the arms  132  and the walls  125  of the hole  124  couple the shoulder pin  120 , and thereby the trailing arm  16 ′, to the cam  32 ′. The angles of the threads of the hole  126  may be formed such that the arms  132  are urged radially outwardly with greater force as the screw  130  is driven deeper into the hole  126 . 
     The screw  130  is preferably a flathead screw, and the hole  124  in the cam  32 ′ includes countersinks  136  to enable the screw  130  to be located flush with or recessed below the outer face of the cam  32 ′. Furthermore, the shoulder pin  120  and cam  32 ′ are shaped such that the trailing arm  16 ′ can be attached to either side of the rotary damper  10 ′ using this attachment assembly. Compared to the prior art assemblies for attaching a trailing arm to a cam, this assembly has a reduced part count, reduces the need for precise manufacturing methods, and is relatively compact. Furthermore, after the trailing arm  16 ′ is coupled to the damper  10 ′, all of the parts of the attachment assembly are visible, which enables inspectors to ensure the trailing arm  16 ′ is properly attached to the damper  10 ′.