Abstract:
A motor vehicle includes a clutch linkage connected to a throw out lever which is operated by a clutch pedal or said control lever biased by a return spring to a clutch engaged position. A damper with a cylinder housing a piston and a piston rod delays excessively rapid engagement of the clutch by engaging the clutch linkage to provide a force opposed to pressure from the return spring. The damper functions to prevent mechanical damage to the motor vehicle and to avoid discomfort to passengers.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to motor vehicle clutches and more particularly to mechanical clutch actuating linkages for engaging and disengaging a clutch of a motor vehicle. 
         [0002]    In the past some inexperienced or poorly coordinated operators of manual transmissions of motor vehicles have experienced problems when removing foot pressure from the clutch pedal or when releasing manual pressure from the handle on a handle bar too quickly or too slowly causing unwanted jerking of the motor vehicle or causing damage to the clutch. In particular, excessively rapid engagement of a clutch in a motor vehicle can shock the drive train of the motor vehicle. By preventing drive train shock, satisfactory balance of the vehicle and handling characteristics are enhanced. It is well known that clutch engagement needs to occur at a certain rate to be efficient. Engaging a clutch too quickly can damage the drive train components of the motor vehicle including the transmission, differential, half shafts, axles, and CV joints. Engaging the drive train too slowly can damage the clutch friction disc by causing clutch slippage. 
         [0003]    Heretofore to achieve such a result a number of complicated designs have been employed. 
         [0004]    An object of this invention is to ameliorate or eliminate problems of jerking of the vehicle caused by operation of the clutch by an inexperienced or physically challenged operator with a minimal complication and with few additional parts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a partially schematic diagram showing a clutch pedal operated hydraulic clutch system in accordance with this invention for a motor vehicle incorporating dampers for retarding the return of the clutch to the fully engaged position. 
           [0006]      FIG. 2  is a partially schematic diagram showing a modification of  FIG. 1  which is a clutch pedal operated embodiment of this invention comprising a mechanical clutch system for a motor vehicle incorporating dampers for retarding the return of the clutch to the fully engaged position. 
           [0007]      FIG. 3  is a schematic perspective drawing of a clutch pedal operated embodiment of this invention comprising a hydraulic clutch system for a motor vehicle incorporating dampers with a clutch housing and a transmission. 
           [0008]      FIG. 4  is a schematic perspective drawing of a clutch pedal operated embodiment of this invention comprising a mechanical clutch system for a motor vehicle with a clutch housing and a transmission comprising a modification of  FIGS. 2 and 3  also incorporating dampers with the orientation of the clutch housing and a transmission reversed for convenience of illustration. 
           [0009]      FIG. 5A  is a schematic diagram showing a manually operated embodiment of this invention employing a control lever mounted by a perch on a handlebar for operation of the clutch throw-out fork of a motor vehicle.  FIG. 5A  is a modification of  FIG. 4  comprising a mechanical clutch system for a motorcycle type of vehicle incorporating dampers for retarding the return of the clutch to the fully engaged position. 
           [0010]      FIG. 5B  is an enlarged schematic perspective drawing of a modification of  FIG. 5A  with the control lever rotated to expose the shaft of a damper.  FIG. 5C  is a modification of  FIG. 5B  with a damper in the perch in contact with the control lever. 
           [0011]      FIG. 6  is a sectional view of a spring operated damper with a hollow damper cylinder containing a piston with a piston rod on the sealed end thereof extending through a cap bearing sealed by a bearing seal at the sealed end of the damper cylinder. 
           [0012]      FIG. 7A  is a perspective view of a spring operated damper including a damper cylinder and a piston rod extending through a cap bearing on the right end thereof.  FIG. 7B  is a side view of the damper of  FIG. 7A  with the piston rod extending from a cap bearing on the right end thereof.  FIG. 7C  is a left end view of the damper of  FIG. 7A  with a hole to access the needle valve adjustment screw for the (pressure or return) stroke of the damper (depending on manufacturer&#39;s design).  FIG. 7D  is a right end view of the damper of  FIG. 7A  with the piston rod  41  in the center of the cap bearing on the right end. 
           [0013]      FIG. 8A  is a perspective sectional view of a spring operated damper including a damper cylinder housing a damper piston from which the piston rod extends on the right through the center of a sealed cap bearing on the right end. A vent hole in the left end is formed in an orifice block.  FIG. 8B  is a sectional side view of the damper of  FIG. 8A .  FIG. 8C  is a sectional left end view of the damper of  FIG. 8A .  FIG. 8D  is a sectional right end view of the damper of  FIG. 8A . 
           [0014]      FIGS. 9A and 9B  are partially sectional views of a slow compression, faster expansion hydraulic damper in accordance with this invention comprising a hydraulic cylinder which houses a damper piston with a piston rod and a return coil spring. 
           [0015]      FIG. 9A  shows the slow return damper with the piston rod in its normally extended position awaiting compression thereof by deactivation of the clutch pedal to drive the piston rod and the piston into the retracted position shown in  FIG. 9B . 
           [0016]      FIG. 9B  shows the slow return damper with the piston rod and the damper piston in the fully shaft retracted position and with the damper spring fully compressed under external pressure previously exerted upon the piston rod. 
           [0017]      FIG. 10A  is a schematic drawing of a MagnetoRheological (MR) damper for use with a clutch actuating linkage.  FIG. 10B  is a schematic drawing of an electrical wiring circuit for increasing the viscosity of the MR fluid in the cylindrical housing in  FIG. 10A  by closing a normally open switch after a predetermined time delay. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]      FIG. 1  is a partially schematic diagram of an embodiment of the present invention showing a hydraulic clutch system for a motor vehicle incorporating dampers for retarding the return of the clutch to the fully engaged position. In  FIG. 1 , the hydraulic clutch system  7  includes a clutch housing  42 , a transmission  43  and a drive shaft  44  from the engine to the clutch (not shown) which is located within the clutch housing  42 . The hydraulic clutch system  7  has been modified in accordance with the present invention to overcome the problem of jerking of the vehicle during rapid clutch engagement in a low gear by incorporation of dampers  40 A- 40 C for the purpose of retarding the return of the clutch to the fully engaged position. The hydraulic clutch system  7  has been converted to operate with smooth clutch engagement by installation in accordance with the present invention of one or more hydraulic or spring operated dampers  40 A,  40 B and  40 C with each having a piston rod  41  to ameliorate or eliminate problems of jerking of the vehicle caused by operation of the clutch by an inexperienced or physically challenged operator starting out from an at rest or stopped condition. Only one damper may be needed to perform with the improved operation provided by the present invention. 
         [0019]    However to show alternative locations for a damper,  FIG. 1  shows three dampers  40 A- 40 C with shafts  41  pressing upon parts of the linkage to a clutch system to ameliorate or eliminate problems of jerking of the vehicle caused by clutch operation by an inexperienced or physically challenged operator starting out from an at rest or stopped condition. 
         [0020]    The pre-existing clutch system of  FIG. 1  includes a clutch pedal  8  mounted on the proximal end of a pedal arm  11  which is mounted extending radially from the distal end of a rotatable cross shaft  10  so that when the clutch pedal  8  a vehicle operator depresses pedal  8 , in the direction indicated by the arrow above the clutch pedal  8 , the rotatable cross shaft  10  turns clockwise. A metal bearing  32  (shown in phantom) is provided to support the cross shaft  10  for rotation. The metal bearing  32  is integral with a support  33  (also shown in phantom) which is secured to the frame of the motor vehicle, as will be understood by those skilled in the art. A first weld  21  bonds the proximal end of the rotatable cross shaft  10  to a downwardly depending pedal return lever  12  (depending downwardly from the cross shaft  10 .) The pedal return lever  12  is secured to the proximal end of a return spring  13  that returns the clutch pedal  8  to its normally disengaged position. To perform that function, the return spring  13  is secured at its distal end to a mounting bracket  9  secured to the body of the motor vehicle. The pedal return lever  12  supports an actuating rod  14  that is comparatively short which, when pedal  8  is depressed, drives a piston (not shown) into the master cylinder  15  the hydraulic clutch system  7 . The hydraulic fluid tube  16  from a hydraulic master cylinder  15  in turn energizes a smaller hydraulic slave cylinder  17 . When the slave cylinder  17  is energized a master cylinder piston therein (not shown) extends a slave cylinder piston rod  18  which is outwardly projecting with its free end seated in a cup-like abutment  19  formed on a clutch disengaging lever referred to hereinafter as a throw-out fork  20  of a clutch system in the clutch housing  44 . When the piston rod  18  is extended, it presses upon the throw-out fork  20  thereby disengaging the clutch in the clutch housing  42 . 
         [0021]    In accordance with this embodiment of the present invention, the three dampers  40 A- 40 C are shown for slowing reengagement of the clutch to ameliorate or eliminate problems of jerking of the vehicle caused by operation of the clutch by an inexperienced or physically challenged operator starting out from an at rest or stopped condition. A first damper  40 A is installed behind pedal arm  11 . A piston rod  41  actuated by the first damper  40 A pushes against the pedal arm  11  in the direction indicated by the arrow above the pedal  8  to slow down the return of the pedal  8  to its initial position prior to actuation, as shown in  FIG. 1 , thereby slowing down reengagement of the clutch. The piston rod  41  of the first damper  40 A pushes in the same direction as the arrow next to the pedal  8  which is opposite direction from the force exerted by the return spring  13 , to retard the return of the pedal  8  to its initial position, slowing clutch engagement. The piston rod  41  of a second damper  40 B pushes the pedal return lever  12  clockwise against the force exerted by the return spring  13  and the shaft of a third damper  40 C presses against the throw-out fork  20 , both working to slow clutch reengagement. 
         [0022]    In summary, with regard to the embodiment of the invention shown in  FIG. 1 , when the clutch pedal  8  is depressed in the direction indicated by the arrow adjacent thereto, the clockwise rotation of the cross shaft  10  against the force of the return spring  13  causes the actuating rod  14  to actuate the hydraulic master cylinder  15  by pushing its piston into it, thereby forcing hydraulic fluid out of line  16  from the hydraulic master cylinder  15  through the hydraulic fluid tube  16  into the input of the hydraulic slave cylinder  17  causing the slave cylinder piston therein to extend its slave cylinder piston drive rod  18  therefrom so that it presses the clutch throw-out fork  20  to disengage the clutch (not shown) located in the clutch housing  42 . Later, when the force on the clutch pedal  8  is removed by withdrawing the foot of the operator therefrom, the cross shaft  10  tends to return to its original position, thereby causing the actuating rod  14  to pull the piston in the master cylinder  15  towards its original position, returning hydraulic fluid from the slave cylinder  17  through hydraulic fluid tube  16  into the master cylinder  15 . As the hydraulic fluid returns from the slave cylinder  17  to the master cylinder  15  the piston therein withdraws the drive rod  18  to the right. As the drive rod  18  withdraws, it relaxes the force on the throw-out fork  20 . As the throw-out fork returns to its original position, a conventional clutch return spring (not shown) within the clutch housing  44  causes the clutch to re-engage. The operation of the clutch throw-out fork, and the actual structural configuration of the elements employed to achieve disengagement of the clutch are well known to those skilled in the art and has been illustrated and described here in a general fashion to facilitate an understanding of the use of the damper(s) of the present invention. 
         [0023]      FIG. 2  is a partially schematic diagram showing of an embodiment of the present invention which comprises a modification of  FIG. 1  in the form of a clutch pedal operated mechanical clutch system for a motor vehicle incorporating dampers for retarding the return of the clutch to the fully engaged position. In  FIG. 2 , a metal tube  34  is inserted onto the proximal end of the cross shaft  10  which is longer than in  FIG. 1  and which is secured thereto by a conventional set screw that is not visible at the angle shown in the drawing. A weld  35  secures the pedal return lever  12  to the metal tube  34  and thus to the cross shaft  10 . A weld  23  secures the proximal end of the metal tube  34  to a hole in the upper end of a crank  24 . The crank  24  comprises an elongated, rectangular metal plate. The weld  23  the tube  34  and the cross shaft  10  fill the hole in the crank  24 . As explained above, the crank  24  and the tube  34  are fixedly secured to cross shaft  10  for rotation therewith. 
         [0024]    The crank  24  depends downwardly from cross shaft  10  and is oriented in a plane transverse to the axis of rotation of both the cross shaft  10  and the tube  34 . Pivotal attachment holes  25  through the crank  24  are spaced respectively at different distances from the common rotational axis of tube  34  and the cross shaft  10 . A clevis  26  is provided with a clevis pin  27  that is shown passing through one of the attachment holes  25  and adapted to be retained in the selected hole for pivotal motion therein by means of a cotter pin (not shown) on the remote side of plate  24 . An elongated actuating rod  28  includes a threaded section  29  at one end thereof for thread engagement with the clevis  26 . Rod  28  is adapted to be screwed a selected distance into clevis  26  to adjust the effective length of rod  28 , and a jam nut  30  is provided for locking the rod  28  to clevis  26  at the selected adjusted length. Adjacent to the free end of rod  28 , a comparatively short length thereof is bent through an angle to the main direction of elongation of the rod to facilitate engagement of the free end of rod  28  with abutment  19  on the throw-out fork  20 . Thus it is assured that the free end of the rod  28  extends into the cup-like abutment  19  at substantially right angles to the plane of the throw-out fork  20  to disengage the clutch by pressing upon the throw-out fork  20 . 
         [0025]    In  FIG. 2 , in accordance with the present invention, as in  FIG. 1 , a first damper  40 A is shown installed behind pedal arm  11  with piston rod  41  of first damper  40 A pushing pedal arm  11  in the direction indicated by the arrow above the pedal  8  to slow down the return of the clutch pedal  8  to its initial position prior to actuation, as shown in  FIG. 1 . The pedal return lever  12  is secured to the proximal end of a return spring  13  that returns the clutch pedal  8  to its normally disengaged position. The piston rod  41  pushes in the same direction as the arrow next to the pedal  8 . That is the opposite direction from the force exerted by the return spring  13 , thereby retarding the return of the clutch pedal  8  to its initial position. As in  FIG. 1 , the shaft of a third damper  40 C presses against the throw-out fork  20 . In  FIG. 2 , a modification comprises using a fourth damper  40 D with its piston rod  41  pushing the plate  24  and the pedal return lever  12  clockwise against the force exerted by the return spring  13 . 
         [0026]    Thus return motion of clutch pedal  8  to its initial position slows as in  FIG. 1 . Also as in  FIG. 1 , piston rod  41  pushes in the same direction as the arrow next to pedal  8  which is opposite direction from the force exerted by return spring  13 , thereby retarding the return of the pedal  8  to its initial position. As in  FIG. 1 , piston rod  41  of second damper  40 B pushes pedal return lever  12  clockwise against the force exerted by return spring  13 . As in  FIG. 1 , the shaft of the third damper  40 C presses against the throw-out fork  20 . 
         [0027]      FIG. 3  is a schematic perspective drawing of a clutch pedal operated embodiment of this invention comprising a hydraulic clutch system  7  for a motor vehicle with a clutch housing  42  and a transmission  43 . As with  FIG. 1 , the hydraulic clutch system  7  has been converted to operate with smooth clutch engagement by installation in accordance with the present invention by incorporation of two hydraulic or spring operated dampers  40 A and  40 C, each of which has a piston rod  41 . As with  FIG. 1 , the pre-existing clutch system includes a clutch pedal  8  mounted on the proximal end of a pedal arm  11  which is mounted extending radially from the distal end of a rotatable cross shaft  10  so that when the clutch pedal  8  is depressed by the operator of the vehicle (in the direction indicated by the arrow above the clutch pedal  8 ,) the rotatable cross shaft  10  turns clockwise. A metal bearing  10 B secured to the vehicle body supports the cross shaft  10  for rotation. The pedal arm  11  is secured to the proximal end of a return spring  13  that returns the clutch pedal  8  to its normally disengaged position. The return spring  13  is fastened at its distal end to a mounting bracket  9  is secured to the body of the motor vehicle. In  FIG. 3 , an actuating rod  14  is connected to pedal arm  11  by a clevis  26  so that when clutch pedal  8  is depressed, actuating rod  14  drives a piston (not shown) into the hydraulic master cylinder  15  of the clutch system, and the hydraulic fluid tube  16  from the hydraulic master cylinder  15  in turn energizes a smaller hydraulic slave cylinder  17 . When the slave cylinder  17  is energized a master cylinder piston therein (not shown) drives a slave cylinder piston rod  18  which projects outwardly. Its free end presses directly on the clutch throw-out fork  20  of a clutch system in the clutch housing  44  to disengage the clutch or to reengage it as the clutch pedal  8  is released. The dampers  40 A and  40 C and the piston rods  41  thereof perform as described above on the pedal arm  11  and the clutch throw-out fork  20 . 
         [0028]      FIG. 4  is a schematic perspective drawing of a clutch pedal operated embodiment of this invention comprising a mechanical clutch system  7  for a motor vehicle with a clutch housing  42  and a transmission  43  comprising a modification of  FIGS. 2 and 3 , with the orientation of the clutch housing  42  and a transmission  43  reversed for convenience of illustration. The cross shaft  10  located below the clevis  26  so that the disengagement rod  28  is pushed to actuate the throw-out fork  20  to disengage the clutch. The pedal arm  11  is secured to the proximal end of a return spring  13  that returns the clutch pedal  8  to its normally disengaged position; and the return spring  13  that is fastened at its distal end to a mounting bracket  9  is secured to the body of the motor vehicle. The dampers  40 A and  40 C and the piston rods  41  thereof perform as described above on the pedal arm  11  and the clutch throw-out fork  20 . 
         [0029]      FIG. 5A  is a schematic perspective diagram showing a manually operated embodiment of this invention employing a lever mounted by a perch on a handlebar for operated which is a modification of  FIG. 4  comprising a mechanical clutch system for a motorcycle type of vehicle incorporating dampers for retarding the return of the clutch to the fully engaged position. A hand-operated control lever  22  is mounted by a perch  36  on a cylindrical handlebar  35  of a vehicle (not shown) such as a motorcycle, etc. The handlebar  35  is provided with a manually operated control lever  22  with a linkage, such as a cable linkage  37  or a rigid mechanical linkage (not shown) operated by reciprocation or in another manner well-known to those skilled in the art when the control lever  22  is actuated. Control lever  22  is secured to the handlebar  35  by a perch  36 , i.e. a handlebar mounting bracket. The perch  36  is clamped to the handlebar  35  in the conventional manner. The control lever  22  is pivotally secured to the perch  36  by a pivot axis screw/nut  22 N so that the control lever  22  pivots about the pivot axis screw/nut  22 N. A damper  40 A is inserted into the control lever with its piston rod  41  in contact with the perch  36 . The dampers  40 A and  40 C and the piston rods  41  thereof perform as described above on the pedal arm  11  and the clutch throw-out fork  20 . 
         [0030]      FIG. 5B  is an enlarged schematic perspective drawing of a modification of  FIG. 5A  with the control lever  22  rotated to expose the piston rod  41  of damper  40 A.  FIG. 5C  is a modification of  FIG. 5B  with a damper  40 E in the perch with the piston rod  41  of damper  40 E in contact with the control lever  22 . 
         [0031]      FIG. 6  is a sectional view of a spring operated hydraulic damper  40  with a hollow damper cylinder  45  containing a piston  50  with a piston rod  41  on the sealed end thereof extending through a cap bearing  48  sealed by a bearing seal  48 S at the sealed end of cylinder  45 . The damper  40  includes a damper return coil spring  46  tending to drive the piston rod  41  out of the cylinder  45 . An orifice block  71  is provided at the other end of the hollow damper cylinder  45 . The orifice block  71  is adjusted by an orifice adjustment screw  72 . Inside of the hollow damper cylinder  45  is a piston/spring liner  73 . The liner  73  may contain grooves or holes to regulate the flow of hydraulic fluid during the compression stroke. 
         [0032]      FIG. 7A  is a perspective view of a spring operated damper  40  with a damper cylinder  45 , a left end  39 , and a piston rod  41  extending through a cap bearing  48  on the right end.  FIG. 7B  is a side view of damper  40  of  FIG. 7A  with piston rod  41  extending from the right end of damper  40 .  FIG. 7C  is a left end view of damper  40  with an access hole  38  in the left end  39  for access to a needle screw valve (not shown, but see  FIG. 8B ) for adjustment of the (pressure or return) stroke of the damper (depending on manufacturer&#39;s design).  FIG. 7D  is a right end view of the damper  40  of  FIG. 7A  with piston rod  41  in the center of cap bearing  48  on the right end. 
         [0033]      FIG. 8A  is a perspective sectional view of a spring operated damper  40  including a damper cylinder  45  housing a damper piston  50  from which the piston rod  41  extends on the right through the center of sealed cap bearing  48  on the right end. The vent hole  38  in the left end  39  is formed in an orifice block  71 .  FIG. 8B  is a sectional side view of the damper  40  of  FIG. 8A  showing a needle valve adjustment screw  72 .  FIG. 8C  is a sectional left end view of the damper  40  of  FIG. 8A .  FIG. 8D  is a sectional right end view of the damper  40  of  FIG. 8A . 
         [0034]      FIGS. 9A and 9B  are partially sectional views of a hydraulic damper  65  in accordance with this invention. During a fast compression phase of operation, the damper  65  moves from the position shown in  FIG. 9A  to the position shown in  FIG. 9B . During a slow expansion phase of operation, the damper  65  moves from the position shown in  FIG. 9B  to the position shown in  FIG. 9A . The damper  65  includes a hydraulic cylinder  55  which houses a damper piston  70  with a piston rod  41  and a return coil spring  66 . Coil spring  66  is shown in the expanded position in  FIG. 9A  and compressed in  FIG. 9B . Hydraulic cylinder  55  has a closed end  49  on the left. On the right hydraulic cylinder  55  is closed by a cap bearing  48  which includes a sealed shaft hole  48 S through which the piston rod  41  extends for reciprocal motion therethrough. The return coil spring  66  presses on the left against the proximal, closed end  49  of the hydraulic cylinder  55  and on the right against the left surface of piston  70 . The piston rod  41  is affixed to the distal, right end of the piston  70 . A feature of the damper piston  70  is that it includes two check valves  51 / 61  extending therethrough between the spring end  53  on the left and the shaft end  54  on the right. Those check valves  51 / 61  comprise a fast compression check valve  61  and a slow expansion check valve  51 . The fast compression check valve  61  includes a large diameter compression orifice  62  through the piston  70  operated by a compression orifice ball  57 . The slow expansion check valve  51  includes a small diameter orifice  52  operated by the expansion orifice ball  56 . 
         [0035]    Piston  70  of  FIGS. 9A  / 9 B moves within the damper cylinder  55  in the presence of hydraulic fluid contained by cylinder  55  on both sides of the piston  70 . The slower flow orifice  52  of the slower flow expansion check valve  51  is somewhat smaller than faster flow orifice  62  of the faster flow compression check valve  61 . Slower flow orifice  52  is designed to assure a slow rate of expansion of coil spring  66  that causes extension of piston rod  41 . As a result, when clutch pedal  8  is released, piston rod  41  moves relatively slowly towards the position shown in  FIG. 9A  from the retracted position shown in  FIG. 9B . On the other hand the faster flow compression orifice  62  is designed to provide a fast rate of retraction of the piston rod  41  when the clutch pedal  8  is depressed thereby pressing the piston rod  41  against the force of the compression spring  66  from the position shown in  FIG. 9A  into the position shown in  FIG. 9B . 
         [0036]    Referring to  FIG. 9A , in operation of the hydraulic damper  65 , when spring  48  is forced to compress under pressure applied to the piston rod  41  by depression of the clutch pedal  8 , the hydraulic fluid flows rapidly through the faster flow compression check valve  61  from the left side to the right side of piston  70 . On the other hand, when the coil spring  66  is enabled to expand, as the pressure on the clutch pedal  8  is removed by the operator of the motor vehicle, the hydraulic fluid flows slowly through slower expansion check valve  51  to the left side from the right side of piston  70  In other words, because the orifice  62  of the faster flow compression check valve  61  is larger than the orifice  52  of the slower flow expansion check valve  51 , when foot pressure is applied to clutch pedal  8  thereby pressing the piston rod  41  to the left, the coil spring  66  contracts at a faster rate than it can expand since the hydraulic fluid is freely passing through the larger, faster flow compression orifice  62  of the fast compression check valve  61 . 
         [0037]    Referring to  FIG. 9B , the slow expansion phase of operation of the damper  65  follows the fast compression phase of operation of the damper  65  as described above. During the expansion phase, the damper coil spring  66  pushes on the piston  70  which restores the damper  40  to the uncompressed state over a period of time in preparation for providing slow engagement of the clutch after the pedal  8  is released. The damper piston rod  41  pushes directly on the pedal  8  (or indirectly on the linkage thereto) thereby slowing engagement of the clutch while slowing movement of the pedal  8  towards the released position thereof. Fluid within the damper cylinder  55  on the left side of the piston  70  is driven through expansion check valve  51  while applying considerable resistance to the action of the spring and tending to counteract the forces which would otherwise rapidly restore the pedal  8  to the released position. Assuming that the damper cylinder  55  contains a medium weight hydraulic oil then both orifices  52  and  62  would have to be nearly the same size with the compression orifice  62  being larger than the expansion orifice  52  so that the recovery under low pressure is as slow or slower as the compression speed is under high pressure forcing oil from left to right through compression orifice  62 . 
         [0038]      FIG. 9A  shows the slow return damper  65  with the piston rod  41  in its normally extended position awaiting withdrawal thereof by activation of the clutch pedal  8  which will drive the piston rod  41  and the piston  70  into the retracted position shown in  FIG. 9B . The slow return damper  60  is shown with the piston rod  41  fully extended because the coil spring  66  has pressed the piston  70  against the cap bearing  48  and little or no force is pressing upon the distal end  47  of the damper piston rod  41 . In other words, the piston  70  has been driven to the right end of the cylinder  32  by the force of the coil spring  66  so that the piston rod  41  is fully extended by the force of the coil spring  66  exerted upon the piston  70  which is also in its fully extended position. Thus piston rod  41  is fully extending the out through the cap bearing  48  of cylinder  45  in position to limit the rate of motion of an object, such as the mechanism linked to the clutch pedal  8  contacted by the distal end  47  of the piston rod  41 . The damper  65  can be employed with an embodiment with a clutch pedal  8 , as described in connection with  FIGS. 1-4  and a hand-operated control lever  22  on a handlebar as in  FIGS. 5A-5C . 
         [0039]      FIG. 9B  shows the slow return damper  65  with the piston rod  41  and the damper piston  70  in the fully shaft retracted position and with the damper spring  46  fully compressed under external pressure exerted upon the piston rod  41  in the direction of the arrow proximate to the piston rod  41  by a force such as that exerted upon a clutch pedal  8 , as described in connection with  FIGS. 1-4  and a hand-operated control lever  22  on a handlebar as in  FIGS. 5A-5C . 
         [0040]      FIG. 10A  is a schematic drawing of MagnetoRheological (MR) damper  116  which comprises a cylindrical housing  120  and a piston  130  with an attached hollow piston rod  132 . Housing  120  contains MR fluid  118 . The proximal end  122  of cylindrical housing  120  is closed, and it has an attachment eye  124  secured to proximal end  122 . At the distal end of cylindrical housing  120  a seal  128  retains MR fluid in the cylindrical housing  120 . The seal  128  has an opening for reciprocation of the piston shaft  132  therethrough. The piston rod  132  is secured to the wall  134  of the motor vehicle by mounting elements and a threaded nut  138  screwed onto the distal end of the piston shaft  132 . Wires  146  and  156  are connected through the distal end of the piston rod  132  to the piston  130  to energize an electromagnet  140  formed on the piston  130 . The electromagnet  140  is energized to raise the viscosity of the MR fluid, as will be well understood by those skilled in the MR damper art, to slow the movement of the piston  130  in the cylindrical housing  120  when the circuit  142  in  FIG. 10B  has been in the ON condition for a predetermined time delay of about two seconds. 
         [0041]      FIG. 10B  is a schematic electrical wiring diagram of a circuit  142  for increasing the viscosity of the MR fluid in the cylindrical housing  120  in  FIG. 10A  by closing a Normally Open (NO) switch  152  with a button  151  when the clutch is disengaged turning ON the output of circuit  142  to the electromagnet  140 . The negative terminal of a DC voltage source  145  connects to electrical conductor  146  and to ground  147 . Electrical conductor  146  is one of the lead lines to a terminal of the electromagnet  140  in the cylindrical housing  120 . The positive terminal of the DC voltage source  145  is connects by line  146  to on terminal of NO switch  152  which is adapted to be energized manually by operating button  151 . When NO switch  152  is closed, it connects voltage to node  153 . Node  153  connects both to one terminal of NO switch  154  and one terminal of time delay relay (TDS)  155 . TDS  155  is connected at its other terminal to ground. TDS  155  closes NO switch  154  after the predetermined time delay of about two seconds to energize the electromagnet  140  by current passing through line  156  to the other terminal of the electromagnet  140 . When electromagnet  140  is energized it increases the viscosity of the MR fluid in the cylindrical housing  120  to slow engagement of the clutch when the pedal  8  or the control lever  22  is released by the operator of the motor vehicle. The circuit of  FIG. 10B  enables the MR damper  116  after the time delay provided by the time delay switch actuator TDS 1   155  and later disables the MR damper  116  after the vehicle is in motion. 
         [0042]    In summary, referring to  FIG. 10B , when the time delay switch  151  is closed turning the circuit  142  ON, (with pedal/lever IN) the time delay relay TDS  155 waits for a predetermined time before closing switch  154  to power the electromagnet  140 . The activated electromagnet  140  thickens the fluid in the MR damper  116  and slows the engagement of the clutch. When the linkage reaches it&#39;s “rest” position (OUT/engaged), the switches  151  and  154  both open, allowing the system to function again without delay until switches  151  and  154  are both closed once more. The time delay of the relay TDS  155  prevents the damper  116  from working during normal operation because it does not turn on the damper  116  unless the pedal or lever is disengaged for a longer time period than it takes to perform a normal shift. All embodiments of dampers  40  described above should move slowly. The pistons  50 / 70  in the dampers  40 / 65  move slowly at a “slow in” rate when the clutch engages under the high pressure force of the clutch drive train return mechanism (pressure plate). Similarly the pistons  50 / 70  in the dampers  40 / 65  also move slowly in the low pressure state when the piston is under the influence of the internal return springs  46 / 66  in the dampers  40 / 65 . This is done with the proper sized valving (during extension) and/or channels in the piston sleeve (during compression). The MR type of damper  116  of  FIG. 10A  operates with a fixed delay controlled by the TDS relay  155 , as described above. 
         [0043]    The “slow out” damper movement is a principal feature of the present invention. After the vehicle is in motion, the damper does not have time to recover to the extended position and will not work. The advantage of this invention is that the device will not work to delay clutch reengagement in any normal driving situation other than starting out from a standing position. 
         [0044]    Therefore, all models except MR should be “slow in” as the clutch engages under the high pressure force of the clutch drive train return mechanism (pressure plate), and “slow out” in it&#39;s low pressure state as the piston is under the influence of it&#39;s internal return spring. This can be done with the proper sized valving (during extension) and/or channels in the piston sleeve (during compression). 
         [0045]    The “slow out” is the part that makes this invention useful. After the vehicle is in motion, the damper does not have time to recover to the extended position and will not work. The beauty of this device is that it will not work in any normal driving situation other than starting out. 
         [0046]    The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. While this invention is described in terms of the above specific exemplary embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims, i.e. changes can be made in form and detail, without departing from the spirit and scope of the invention. Accordingly, while the present invention is disclosed in connection with exemplary embodiments thereof, it should be understood that changes can be made to provide other embodiments which may fall within the spirit and scope of the invention and all such changes come within the purview of the present invention and the invention encompasses the subject matter defined by the following claims.