Abstract:
A clearance damping element for use with a telescoping shaft assembly including a shaft having a shaft outer diameter and a tube configured to receive the shaft therein. The clearance damping element comprises a tube engaging portion and a shaft engaging portion. The tube engaging portion is adapted to fixedly receive the tube and the shaft engaging portion has a body extending from the second end of the tube engaging portion. The shaft engaging portion body includes a plurality of flexible fingers with inward extending projections that define an inner diameter less than the shaft outer diameter.

Description:
BACKGROUND  
       [0001]     The present invention relates to an extendable shaft, for example, an intermediate shaft used in a steering apparatus of an automobile or the like.  
         [0002]     It has hitherto been widely practiced that an expandable/contractible intermediate shaft is provided midway of a steering apparatus in order to prevent a steering wheel from thrusting a driver&#39;s body up in the event of a collision accident. This expandable/contractible intermediate shaft diminishes an entire length if a front portion of the automobile is crashed subsequent to a so-called primary impact in which the automobile collides with other automobile. Such an expandable/contractible intermediate shaft is constructed by making a serration or spline engagement between one end of an outer tube member and one end of a solid inner shaft member.  
         [0003]      FIG. 1  shows one example of an automobile steering apparatus incorporating an intermediate shaft according to the present invention. A steering apparatus for an automobile involves the use of a mechanism, as schematically shown in  FIG. 1 , for transmitting a motion of a steering wheel to a steering gear. Referring to  FIG. 1 , a steering wheel  102  is fixed to a steering shaft  101  rotatably inserted through within a steering column  103 . The steering column  103  is fixed to a schematically shown car body  106  through members  104 ,  105 . Rotations of the steering shaft  101  are transmitted to a shaft  111  of an unillustrated steering gear portion via a steering intermediate shaft constructed of universal joints  107 ,  110  and shaft members  108 ,  109 .  
         [0004]     It is generally known that, in the thus constructed steering apparatus, the shaft member of the steering intermediate shaft is constructed as a mechanism for absorbing, when collided, an impact energy and a movement and a deformation of the steering apparatus by an entire length shrinking upon receiving an impact in order to protect a driver from a damage just when a vehicle collision happens. What is widely used as this mechanism is that the steering intermediate shaft is structured so that an outer tube member and a solid inner shaft member are combined with each other by a spline or serration engagement enough to permit a relative movement in the axial direction therebetween. To give an explanation with reference to  FIG. 1 , an upper portion  108  of the shaft member of the intermediate shaft is formed as a tube member the inner surface of which is formed with a serration or a spline, while a lower portion  109  is formed as a solid inner shaft member the outer surface of which is formed with the serration or the spline. Then, this solid inner shaft member is inserted into the tube member, thus making the serration or spline engagement.  
         [0005]     It is, as described above, useful also when assembling the steering apparatus to give a degree of freedom of the axial movement to the intermediate shaft. When the vehicle is assembled, normally the steering gear portion for changing a direction of the wheel is at first fixed to a car body chassis, while the intermediate shaft portion is fixed to the body side integrally with the steering column, and these components are assembled afterward. This is a procedure of how the apparatus is assembled. To describe it referring to  FIG. 1 , the shaft  111  of the steering gear apparatus exists on the side of the chassis, and the portions higher than the universal joint  110  exist on the body side. When in the assembling process, it follows that the shaft  111  is joined to the joint  110 . It is therefore necessary and useful for the intermediate shaft including the inner shaft member and the outer tube member to have the degree of freedom of the movement (expansion and contraction) in the axial direction.  
         [0006]     Further, as disclosed in Japanese Utility Model Post-Exam Publication No. 63-17862, there has hitherto been known a structure for reducing backlash in the engaging portions between one end of the outer tube member and one end of the inner shaft member.  
         [0007]      FIG. 2  shows an expandable/contractible intermediate shaft disclosed in this Japanese publication. An inner peripheral surface of an outer tube member P 1  is formed with a female spline P 2 , and an outer peripheral surface of a solid inner shaft member P 3  is formed with a male spline P 4  engaging with the female spline P 2 . Further, slits P 5 , P 5  each opening at one edge of the outer tube member P 1  are formed in a plurality of positions in a circumferential direction of one end of the outer tube member P 1 . Moreover, a ring-like fastening member P 6  is externally fitted to one end of the outer tube member P 1 . This ring-like fastening member P 6  elastically fastens an inner peripheral surface of one end of the outer tube member P 1  onto the outer peripheral surface of the solid inner shaft member in a state where the inner shaft member P 3  is inserted into the outer tube member P 1 . Then, a backlash in engaging portions between the female and male splines P 2 , P 4  is thereby prevented irrespective of a minute gap existing between the female spline P 2  and the male spline P 4 .  
         [0008]     While such an assembly has allowed for reduced lash and noise in the steering shaft assembly, such an assembly requires significant modification of the intermediate shaft outer tube. Such modification is generally costly and impractical based on the numerous variations of outer tubes utilized in various vehicles. A modification to the production process for each of these various tubes would be required. Furthermore, the ring-like fastening member P 6  is a loose member which may be lost during production. Additionally, the ring-like fastening member P 6  requires an extra assembly step, which if forgotten by assembly personnel will leave the ring-like fastening member to move and shake during vehicle operation and will further fail to provide the desired damping.  
       SUMMARY  
       [0009]     The present invention provides a clearance damping element for use with a telescoping shaft assembly including a shaft having a shaft outer diameter and a tube configured to receive the shaft therein. The clearance damping element comprises a tube engaging portion and a shaft engaging portion. The tube engaging portion is adapted to fixedly receive the tube. The shaft engaging portion has a body extending from the second end of the tube engaging portion body. The shaft engaging portion body has a plurality of radially spaced axial slots therealong to define a plurality of flexible fingers, at least two of the fingers having inward extending projections that define an inner diameter less than the shaft outer diameter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a side elevation view of a prior art steering shaft assembly.  
         [0011]      FIG. 2  is a side elevation view of a prior art telescoping shaft assembly.  
         [0012]      FIG. 3  is a front isometric view of a clearance damping element of a first embodiment of the present invention.  
         [0013]      FIG. 4  is a rear isometric view of the clearance damping element of  FIG. 3 .  
         [0014]      FIG. 5  is a side elevation view of the clearance damping element of  FIG. 3  positioned between a shaft and corresponding tube.  
         [0015]      FIG. 6  is a side elevation view similar to  FIG. 5  with the clearance damping element and the tube shown in cross-section.  
         [0016]      FIG. 7  is a side elevation view similar to  FIG. 6  with the clearance damping element positioned on the shaft.  
         [0017]      FIG. 8  is a side elevation view similar to  FIG. 7  with the tube positioned within the clearance damping element.  
         [0018]      FIG. 9 a  front isometric view of a clearance damping element of a second embodiment of the present invention.  
         [0019]      FIG. 10  is a cross-section taken along the line  10 - 10  in  FIG. 9 .  
         [0020]      FIG. 11  shows a hysteresis curve for a telescoping shaft assembly without a damping element.  
         [0021]      FIG. 12  shows a hysteresis curve for a telescoping shaft assembly with a clearance damping element of the present invention positioned between the shaft and tube. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     The present invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for example, “top”, “bottom”, “right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and “rearward”, is used in the following description for relative descriptive clarity only and is not intended to be limiting.  
         [0023]     Referring to  FIGS. 3-6 , a clearance damping element  10  that is a first embodiment of the present invention will be described. The clearance damping element  10  includes a tube engaging portion  12  and a shaft engaging portion  20 . The tube engaging portion  12  of the present embodiment generally comprises a cylindrical body  14  having an open end  16  and terminating in a shoulder  18  at the opposite end. As shown in  FIG. 6 , the cylindrical body  14  preferably has an inner diameter d 1  that is substantially equal to or slightly smaller than the outer diameter t 2  of the tube  108 . As such, the tube  108  fits within the cylindrical body  14  with an interference fit. While an interference fit is preferred, other engaging means, for example, welding, shrink fitting, adhesive or the like may be utilized.  
         [0024]     The shaft engaging portion  20  of the clearance damping element  10  has a cylindrical body  22  that extends from the tube engaging portion  12  cylindrical body  14 . As can be seen in  FIG. 6 , the cylindrical body  22  has an inner diameter d 2  that is less than the tube outer diameter t 2  such that the cylindrical body  22  defines the shoulder  18  of the tube engaging portion  12 . The cylindrical body  22  inner diameter d 2  is approximately equal to the tube inner diameter t 1  such that the shaft  109  can be received through the cylindrical body  22  and into the tube  108 , as will be described hereinafter.  
         [0025]     Referring to  FIG. 3 , the cylindrical body  22  has a plurality of radially spaced axial slots  24  such that a plurality of fingers  26  are defined at the forward end of the cylindrical body  22 . The slots  24  preferably have an axial length approximately three-quarters the axial length of the cylindrical body  22  such that the fingers  26  have some radial flexibility. The present embodiment is shown with four axial slots  24  and four corresponding fingers  26 , however, more or fewer slots  24  and fingers  26  may be provided.  
         [0026]     As shown in  FIGS. 3 and 6 , each finger  26  preferably includes an inwardly extending projection  28  adjacent the forward end of the respective finger  26 . While all fingers  26  preferably have a projection  28 , less than all may be provided with such. The inwardly extending projections  28  provide a reduced diameter d 3  at the forward end of the shaft engaging portion  20 , the reduced diameter d 3  being less than the outer diameter s 1  of the shaft  109  such that the projections  28  engage the shaft  109  as will be described hereinafter. The projections  28  are illustrated as flat pads, but may have other configurations.  
         [0027]     Referring to  FIGS. 7 and 8 , assembly of the clearance damping element  10  with the shaft  109  and tube  108  will be described. Referring to  FIG. 7 , the shaft  109  is extended through the shaft engaging portion  20  and out through the open end  16  of the tube engaging portion  12 . As the shaft  109  is extended through the shaft engaging portion  20 , the projections  28  contact the larger diameter shaft  109  such that the fingers  26  are flexed outward. The flexing of the fingers  26  causes a cantilever effect on the fingers  26 , causing the fingers  26  and associated projections  28  to exert an inward force upon the shaft  109 . As shown in  FIG. 8 , with the clearance damping element  10  in a generally desired position on the shaft  109 , the tube  108  is slid over the shaft  109  and into the open end  16  of the tube engaging portion  12 . As explained above, the tube engaging portion  12  has an interference fit with respect to the tube  108  or is otherwise secured relative to the tube  108 . With the tube engaging portion  12 , and thereby the clearance damping element  10 , fixed to the tube  108 , the inward force of the fingers  26  and projections  28  against the shaft  109 , the relative radial movement between the shaft  109  and tube  108  is minimized, reducing the play or lash in the shaft assembly.  
         [0028]     The size and number of the axial slots  24  and fingers  26 , the material and material thickness, and the projection  28  size, configuration and depth are chosen such that the projections  28  provide a desired damping force against the shaft  109 . The force is preferably such that the shaft  109  and tube  108  may still be moved axially relative to each other to allow some flexibility during assembly. Additionally, while it is described to assemble the clearance damping element  10  to the shaft  109  first, it is also possible to affix the clearance damping device to the tube  108  first.  
         [0029]     The clearance damping element  10  is preferably manufactured from a polymer, but may also be manufactured from other materials. While the tube engaging portion body  14  and the shaft engaging portion body  22  are each described as cylindrical, other shapes, for example, oval or square, may be utilized to correspond to the shapes of the shaft  109  and tube  108 .  
         [0030]     Referring to  FIGS. 9 and 10 , a clearance damping element  50  that is a second embodiment of the present invention is shown. The clearance damping element  50  includes a tube engaging portion  52  and a shaft engaging portion  60 . The tube engaging portion  52  includes a body  54  having an open end  56  and having a diameter d 1  configured to interference fit about the tube  108 . The shaft engaging portion  60  has a body  62  that is generally an extension of the tube engaging portion body  54 , being coplanar on the inner and outer surfaces therewith. A phantom line is provided in  FIGS. 9 and 10  to distinguish the portions, although they are generally formed of a single cylinder or other desired shape. As in the previous embodiment, a plurality of axial slots  64  extend into the shaft engaging portion body  62  such that a plurality of fingers  66  are defined. A projection  68  extends inwardly at the forward end of each finger  66  to define an area of reduced diameter d 3 . Again, diameter d 3  is less than the outside diameter s 1  of the shaft  109 . In the present embodiment, each of the projections  68  includes a series of splines  70  for engaging with the splined surface of the shaft  109 . However, splines are not required on the projection or on the shaft  109 .  
         [0031]     As in the previous embodiment, the shaft  109  is extended through the shaft engaging portion  50  such that the projections  68  contact the larger diameter shaft  109 . The fingers  66  are flexed outward with a resultant cantilever effect on the fingers  66 , causing the fingers  66  and associated projections  68  to exert an inward force upon the shaft  109 . The size and number of the axial slots  64  and fingers  66 , the material and material thickness, and the projection  68  size, configuration and depth are chosen such that the projections  68  provide a desired damping force against the shaft  109 . While the tube engaging portion body  54  and the shaft engaging portion body  62  are each described as cylindrical, other shapes, for example, oval or square, may be utilized to correspond to the shapes of the shaft  109  and tube  108 .  
         [0032]     Referring to  FIGS. 11 and 12 , the effect of the clearance damping element  10 ,  50  is observed by comparing the two graphs. The graph of  FIG. 10  is a hysteresis curve showing torque versus deflection for a steering shaft assembly that does not utilize a clearance damping element. The graph of  FIG. 11  is a hysteresis curve showing torque versus deflection for a steering shaft assembly utilizing a clearance damping element according to the present invention. Comparison shows that the clearance damping element serves to alter the deflection characteristic of the shaft assembly such that the slope of the deflection curve is maintained as the applied torque from a clockwise direction passes through zero to a counterclockwise direction. Maintaining a slope through this “zone” results in a lower impact energy potential as the components begin to transmit torque during rapid direction change.