Abstract:
Attenuation of transmission of noise along a clutch linkage for a manual transmission clutch is achieved by providing a segmented linkage. A clutch pedal side segment has a substantially greater mass than does the clutch lever side segment. Bi-directional force between the clutch lever side segment and he clutch pedal side segment is through compressible bearings located inside a coupler between the segments.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The invention relates to a clutch linkage for a manual transmission and more particularly to a clutch linkage for isolating the cab from vibration originating in a vehicle&#39;s clutch from transmission to the clutch pedal and for attenuating vibration. 
   2. Description of the Problem 
   Operator comfort and the perception of quality in any motor vehicle is enhanced by the diminution of noise and vibration in the passenger cabin. One source of noise and vibration in vehicles, particularly medium and heavy duty trucks equipped with standard transmissions, has been the clutch. A particular issue concerns vibration of the clutch lever on the transmission bell housing. Noise and vibration, particularly at high engine RPMs, has been transmitted from the clutch lever to the clutch pedal along the clutch linkage. This problem has been partially addressed in the past by increasing the mass of the linkage so that it operates as a filter to attenuate the high frequency vibration. 
   Rubber isolators and non-linear springs are known for vibration isolation for vehicle chassis iso-mounts and engine mounts. Typically these springs have progressive stiffness, that is, under higher loads they hit a snubber or through design they become stiffer. This limits large motions due to hard cornering or hitting bumps and potholes. Rubber isolators are not known to have been used in a segmented clutch linkage. 
   SUMMARY OF THE INVENTION 
   According to the invention there is provided a vibration attenuating bi-directional linkage for a clutch assembly. The vibration attenuating bi-directional linkage comprises clutch pedal side and clutch lever side segments. The clutch lever side segment is coupled to vibration sources. The clutch pedal side segment carries a weight giving that segment a substantially greater mass than the clutch lever side segment. The weight may take the form of a coupler attached to the clutch pedal segment and fitted around the clutch lever side segment. The coupler provides internal surfaces perpendicular to the directions of reciprocating movement of the linkage against which first and second compressible bearings supported on the clutch lever side segment impinge for transmitting force. A thrust washer backs the second compressible bearing for assuming loading from the second compressible bearing upon sufficient compression of the second compressible bearing. 
   Additional effects, features and advantages will be apparent in the written description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a heavy duty truck with which the present invention is advantageously used. 
       FIG. 2  is a plan view of a truck chassis illustrating a motor vehicle driver train in a high level block diagram. 
       FIG. 3  is a side view of a simplified clutch actuation linkage. 
       FIG. 4  is an exploded view of a linkage or control rod in constructed accordance with the present invention. 
       FIG. 5  is a cross sectional view of the linkage or control rod illustrated in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the figures and in particular to  FIG. 1 , where a truck  100  is illustrated. Truck  100  represents the class of vehicles with which the vibration attenuating control rod of the present invention is advantageously utilized. 
     FIG. 2  is a plan view of truck chassis  102  illustrating major components of the vehicle and invention and their approximate spatial relationship to one another. Chassis  102  includes an engine  60  the output of which is coupled to rear end differentials  80  and rear axles  84  by a clutch  12 , a gear box  11  and a propeller shaft  82 . Clutch  12  is selectively engaged and disengaged to allow change in selection of a desired gear ratio in gear box  11 . Engagement of clutch  12  is controlled by the operator&#39;s use of a clutch pedal  14 , which is connected to the clutch  12  by a linkage  16 . 
     FIG. 3  illustrates a standard transmission  10  which includes a clutch  12  and a gear box  11 . Clutch linkage geometry can be arranged to be either a “pull” type clutch linkage or a “push” type clutch linkage. A pull type linkage is illustrated in  FIG. 3 . Clutch  12  is moved between engaged and unengaged states by movement of clutch release lever  18 . Clutch release lever  18  is part of a linkage assembly  16 , which includes a pull link  122  connected between the clutch lever and a clutch pedal support linkage  20 . Clutch pedal  14  is attached to one end of clutch pedal support linkage  20 . When clutch pedal  14  is depressed, as indicated by arrow “A”, the lower end of pedal support linkage  20  moves away from clutch  12 , as indicated by arrow “B”, pulling link  122  in the same direction. Link  122  is placed under tension as indicated by arrow “C”. Clutch lever  18  is always in direct contact with the clutch throw-out bearing, (not shown), which is a component of the clutch. The clutch throw-out bearing is in turn attached to the engine flywheel (not shown). The lack of complete disengagement of clutch lever  18  from the clutch is one source of vibration, a condition which is inherent to this type of clutch assembly. 
   Clutch release lever  18  readily transmits vibration from clutch  12  to push linkage  122 , hereafter referred to as the control rod or, particularly in the claims, as a clutch linkage. A combination mass/coupler  40  is illustrated installed on control rod/push linkage  122 . Control rod  122  comprises two major, elongated linkage segments  42  and  44  which are termed the clutch pedal segment and clutch lever segment, respectively. 
   Referring to  FIGS. 4 and 5 , a control rod  122  is depicted in exploded and cross sectional views. Control rod  122  comprises two major, elongated segments, a first or clutch pedal segment  42  and a second or clutch lever segment  44 . Clutch pedal segment  42  terminates in an attachment hook  46  for connection to whatever clutch pedal linkage arrangements have been provided. Clutch lever segment  44  terminates in an attachment hook  96  for coupling the clutch lever segment to a clutch lever  18 . Thus clutch lever segment  44  is subjected vibration originating in clutch  12  and potentially other drive train components. 
   Clutch pedal segment  42  carries a substantially greater mass than does clutch lever segment  44 . The high mass carried by clutch pedal segment  42  relative to clutch lever segment  44  allows the clutch pedal segment to operate as a filtering impedance to high frequency, low amplitude vibration. In an unloaded condition the high mass on clutch pedal segment  42  is only loosely coupled to the vibration source, as described below. 
   Clutch pedal segment  42  is attached to weight/coupler  40  using a plug  48 . In the preferred embodiment of the invention most of the mass of control rod  122  is in weight/coupler  40 . Thus clutch pedal segment  42  is rigidly attached to weight/coupler  40 . Weight/coupler  40  (also referred to in the claims as a mass or vibration filtering mass) is a cylindrical mass having a axial, central bore  51  consisting of a narrow diameter section  57  and a large diameter section  52 . The larger diameter section  52  of central bore  51  has an opening  50  onto a first end  54  of the weight/coupler  40 . The narrow diameter section  57  opens out to a second end  75  of the weight/coupler  40 . Attachment of the pedal segment  42  to weight/coupler  40  is effected using a plug  48  which is inserted by one end into a cooperatively threaded portion of the large diameter section  52 . Clutch pedal segment  42  is likewise inserted into a threaded bore  58  within plug  48 . The principal axis of clutch pedal segment  42  is thus aligned with the central axis of central bore  51  and weight/coupler  40 , plug  48  and the clutch pedal segment function as a single unit. 
   The coupling of clutch lever segment  44  to weight/coupler  40  is more complex. It may be accurate to describe one end of clutch lever segment  44  as being positioned and retained in the central bore  51 . Clutch lever segment  44  is shaped by several radial substructures which provide points for mounting three rubber bearings  62 ,  66  and  68  and a rigid thrust washer  64 . These bearings and the washer in turn impinge against the interior surfaces of central bore  51 , particularly under loading. They also keep the principal axis of clutch lever segment aligned with the principal axis of clutch pedal segment  42  which is coincident with the principal axis of the central bore  51 . Rubber bearing  62  is radially disposed around the stem of segment  44  on the side of a radial shoulder  92  closer to plug  48 . Plug  48 , by closing the large diameter section  52 , provides a shoulder  55  against which bearing  62  fits. A nylon or PTFE (polytetrafluoroelethylene) thrust washer  64  is disposed around the stem of segment  44  and nestles against the opposite face of shoulder  92  as does rubber bearing  62 . On the same side of the shoulder  92  as the thrust washer  64  but spaced from the shoulder  92  by the thrust washer is the second rubber bearing  66 . Rubber bearing  62  and rubber bearing  66  lie nestled against shoulders  55  and  53  formed in the inserted end of plug  48  and the transition zone from large diameter section  52  to narrow diameter section  57 . Rubber bearing  66  further lies in an a radial indentation  90  in clutch lever segment  44  which better positions the bearing. Under unloaded conditions radial shoulder  92  is spaced from plug  48  by an air gap  132 . Thrust washer  64  is spaced from the shoulder  53  by an air gap  136 . Under loading one of these air gaps disappears as either of rubber bearings  62 ,  66  is compressed. A radial air gap  134  appears around the perimeter of radial shoulder  92  and thrust washer  64  is of greater diameter than radial shoulder, extending radially outwardly into near contact with the inner surface of large section  52 . 
   Rubber bearings  62 ,  66  and  68  are compressible and provide, respectively, for cushioning clutch pedal segment  42  from small amplitude movement of clutch lever segment  44  to and fro along the principal axes of segments  42 ,  44  and from movement of clutch lever segment  44  perpendicular to its direction of elongation (i.e. its principal axis) relative to the weight/coupler  40 . 
   A third rubber bearing  68  is positioned in a trough  70  spaced from shoulder  92  and located, in the assembled structure, in the narrow section  57  of central bore  51 . Bearing  68  resists movement of clutch lever segment  44  off of alignment from the principal axis of the central bore  51 . Only an end portion of clutch lever segment  44  lies held within central bore  51 , and, as can be readily seen, must be inserted into, and substantially passed through the bore, from opening  50  in face  54  and out of the opening in face  75  for assembly. 
   The entire assembly weights about 3 pounds with about 2.5 pounds being rigidly linked to the clutch pedal segment. During normal driving, the linkage is lightly loaded, and the clutch pedal segment is well isolated by rubber bearing resulting in little vibration reaching the passenger cab through the linkage. When the driver depresses the clutch pedal to disengage the clutch the assembly is loaded (either in tension or in compression). The rubber bearings deflect, and the rod segments bottom out. Contact load for disengagement is carried by the hard elastomer thrust washer which prevents buzzing noise at the point of contact. Normally engine RPMs are reduced during clutching with the result that there is less high frequency noise (above 300 Hz) to be transmitted. The linkage exhibits non-linear stiffness under tension loading such that after a short extension of approximately 1.5 mm (provided by the air gaps), the assembly becomes very stiff. A vehicle driver should not be able to perceive the gap through his shoes, foot and leg leaving clutch feel unchanged. The device also exhibits good dimensional stability, there should be no sag and the device should appear rigid. 
   While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.