Patent Publication Number: US-2005126328-A1

Title: Rack and pinion steering gear adjuster clearance enhancement

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. provisional patent application Ser. No. 60/530,004 for a RACK AND PINION STEERING GEAR ADJUSTER CLEARANCE ENHANCEMENT, filed on Dec. 16, 2003, and also claims the benefit of U.S. provisional patent application Ser. No. 60/560,663 for a RACK AND PINION STEERING GEAR ADJUSTER CLEARANCE ENHANCEMENT, filed on Apr. 8, 2004, both of which are hereby incorporated by reference in their entireties. This claim is made under 35 U.S.C. § 119(e); 37 C.F.R. § 1.78; and 65 Fed. Reg. 50093. 
    
    
     FIELD OF THE INVENTION  
      The invention relates to a rack and pinion steering assembly for a vehicle and, more specifically, the invention relates to the interaction between a rack bearing and an adjustment plug in the rack and pinion steering assembly.  
     BACKGROUND OF THE INVENTION  
      A rack and pinion steering assembly typically includes either a hydraulic steering valve or manual steering pinion, a rack and pinion housing assembly, a steering rack, a rack bearing, and an adjuster plug. The manual pinion or steering valve has one end positioned in the rack and pinion housing, while the gear end of the steering pinion engages with a steering rack. The steering rack in turn contacts the rack bearing. The interaction of the three components is basically as follows: The interaction between the steering rack and steering pinion is to convert rotational motion into linear movement. The rack bearing applies force to the back of the steering rack maintaining the proper mesh between the steering pinion&#39;s gear teeth and steering rack&#39;s rack teeth. The rack bearing&#39;s application of force is primarily utilized as a way to compensate for any dimensional discrepancies between the individual components. Therefore in the normal operation of the steering assembly the rack bearing reacts in a perpendicular manner relative to the steering rack&#39;s linear motion.  
      The steering rack and rack bearing are positioned in the housing between the steering pinion and the adjuster plug. A spring is positioned between the adjuster plug and the rack bearing. It is the spring&#39;s function to urge/force the rack bearing towards the steering rack and the steering rack towards the steering pinion. It is through this action that contact is maintained between the pinion teeth and the rack teeth. During assembly, the steering rack, the rack bearing, and the spring are inserted in their respective apertures defined by the R &amp; P housing. The aperture for the adjuster plug is defined by the threaded opening in the R &amp; P Housing, while the adjuster plug contains the mating threads. The adjuster plug engages via its threads with the opening of the aperture in the housing to compress the spring. The adjuster plug is rotated into the housing to a predetermined angular distance/force, to compress the spring and is then rotated in the reverse direction, a predetermined angular distance or clearance, to ensure that a predetermined gap is defined between the rack bearing and the adjuster plug. When the rack bearing and the adjuster plug contact one another during rotation of the steering rack, the rack bearing and the adjustment plug engage one another along opposing planar surfaces, especially around their perimeters. It is desirable to define a gap between the rack bearing and the adjustment plug to reduce the likelihood of frictional forces acting on the rack bearing that can result from sliding, relative contact between the adjustment plug and the rack bearing.  
      Currently, there are two primary methods used to set the adjuster plug back-off to establish the axial gap/clearance between the rack bearing and the adjuster plug. In the first method, the gear is assembled so that the following components are present in the housing: the steering rack, the hydraulic valve including a power pinion (or the manual pinion), the adjuster plug, the spring, and the rack bearing. The adjuster plug is then tightened in the aperture of the housing to compress the spring. The gear assembly is then “worn in” by manually stroking the gear to the full extent of its travel in both directions. The adjuster plug is then loosened and re-tightened to a predetermined amount of torque, usually 10 Nm. The adjuster plug is then rotated backwards or loosened by a predetermined angular amount. The turning torque of the gear is then tested.  
      In the second method used to set the adjuster plug back-off, the clearance is established using a direct measurement. The rack and pinion steering assembly is assembled so that the following components are present: the housing, the steering rack, the hydraulic valve including the power pinion assembly (or the manual pinion), the adjuster plug, the spring and the rack bearing. The adjuster plug is then tightened down and the gear assembly is worn in by manually stroking the gear to the full extent of its travel in both directions. The adjuster plug is then loosened. Next, a gauging device is attached directly to the housing, its indicator contacting either the steering rack or the rack bearing. The pinion is then torqued to a predetermined amount of torque and the total amount of displacement of the steering rack from its initial position is measured with the gauging device. If the amount of movement of the rack is not within a predetermined amount, the adjustment plug is readjusted to the proper clearance. The turning torque is then tested against a predetermined amount.  
     SUMMARY OF THE INVENTION AND ADVANTAGES  
      The invention provides a steering assembly including a first shaft having a first longitudinal axis. The steering assembly also includes a second shaft having a second longitudinal axis. The first and second longitudinal axis are transverse and offset with respect one another. The first and second shafts are engaged at an intersection such that the second shaft translates along the second longitudinal axis in response to rotation of the first shaft about the first longitudinal axis. The steering assembly also includes a bearing member contacting the second shaft. The bearing member is moveable along a bearing axis extending transverse to both of the first and second longitudinal axis at the intersection to support the second shaft. The steering assembly also includes an adjustment member adjustably spaced from the bearing member along the bearing axis. The adjustment member limits movement of the bearing member along the bearing axis. The steering assembly also includes a post disposed between the bearing member and the adjustment member along the bearing axis. The post prevents the bearing member and the adjustment member from contacting one another.  
      The present invention provides a post extending between the rack bearing and the adjuster plug to more accurately define the gap between the adjuster plug and the rack bearing. The length of the post is sized to ensure that a gap exists between the rack bearing and the adjustment plug. The post also defines the contact area between the rack bearing and the adjustment plug. The contact area can be minimized to reduce the frictional forces resulting from sliding, relative contact between the adjuster plug and the rack bearing. The post can be integral with either the rack bearing or the adjuster plug. Or the post can be assembled with respect to either of the two parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
       FIG. 1  is a cross-sectional view of a first embodiment of the invention wherein a power rack and pinion assembly having a valve assembly and includes a post according to the present invention;  
       FIG. 2  is a cross-sectional view of a second embodiment of the invention wherein a manual rack and pinion gear assembly includes a post according to the present invention;  
       FIG. 3  is a cross-sectional view of a third embodiment of the invention showing a rack bearing and centering post integrally formed with respect to one another; and  
       FIG. 4  is an exploded view of a fourth embodiment of the invention wherein the centering post is assembled to one of the rack bearing and the adjustment plug. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring now to  FIG. 1 , a steering assembly or power rack and pinion gear assembly  10  according to the exemplary embodiment of the invention includes a housing assembly  12  and a hydraulic valve and pinion assembly  14  received in the housing  12 . The valve and pinion assembly  14  can be supported for rotation in the housing assembly  12  by first bearing  16  and the second bearing  18 . The first bearing  16  can be an upper spool shaft bearing. The second bearing  18  can be a pinion bearing. A seal  20  and retaining clip  22  can be disposed at one end of the housing assembly  12  and a pinion nut  24  and dust cover  26  can be disposed at a second end of the housing assembly  12 . The valve and pinion assembly  14  can include a first shaft or steering pinion  28  disposed in the housing assembly  12  adjacent the pinion nut  24  and dust cover  26 . The first shaft  28  defines a first longitudinal axis  29 . A second valve and pinion assembly  30  can be disposed between the seal  20  and the second bearing  18 .  
      The steering pinion  28  can interact with a second shaft or steering rack  32  at an intersection  35 , and the steering rack  32  can be supported by a bearing member or rack bearing  34 . The bearing  34  is moveable along a bearing axis  37  and rotatable about the axis  37 . The second shaft  32  defines a second longitudinal axis  33 . The axis  29 , 33  are transverse and offset with respect to one another. The rack  32  translates along the axis  33  in response to rotation of the first shaft  28  about the axis  29 . The steering rack  32  and rack bearing  34  are moveable in a direction transverse to the steering pinion  28  and rotatable. The steering rack  32  and rack bearing  34  are biased towards the steering pinion  28  by an adjustment member or adjuster plug  36  and a a biasing member or spring  38 . A post  40  is disposed between the rack bearing  34  and the adjuster plug  36 . The post  40  dictates where the first point of contact will occur. Additionally, it is the post  40 , which ensures a gap or clearance is defined between the rack bearing  34  and the adjustment plug  36 . In particular, the post  40  is sized to ensure that a space is defined between a first surface or face surface  42  of the rack bearing  34  and a second surfaces or second face surface  44  of the adjustment plug  36 . The post  40  can be integrally formed with respect to either the rack bearing  34  or the adjustment plug  36 . Alternatively, the post  40  can be assembled to either the rack bearing  34  or the adjustment plug  36 . The post  40  can be incorporated in any manual rack and pinion steering gear assembly, any power rack and pinion gear assembly (both center take-off and end take-off designs), quadrasteer assemblies, electric power steering gear assemblies, steering gears with Y-shaped steering racks, steering gears with rounded steering racks, steering gears with hollow steering racks, and steering gears with solid steering racks.  
      During assembly of the rack and pinion gear assembly  10 , the steering rack  32  is inserted in an aperture  46  defined by the housing assembly  12 . The rack bearing  34  is inserted in the aperture  46  and a receiving surface  48  engages the steering rack  32 . In the exemplary embodiment of the invention, the post  40  is integrally formed with the rack bearing  34  and is defined on an opposite side of the rack bearing  34  relative to the receiving surface  48 . The spring  38  is positioned over the post  40  and encircles the post  40 . Threads  50  of the adjustment plug  36  are engaged with threads  52  defined by the aperture  46  and the adjustment plug  36  is rotated in a first angular direction to move the plug  36  into the aperture  46 , in the direction of the steering pinion  28 .  
      The plug  36  is rotated in the first angular direction a first predetermined angular distance or a first predetermined level of torque. The first predetermined angular distance can correspond to a position wherein a tip  54  of the post  40  engages a surface  56  of the adjustment plug  36 . When the tip  54  engages the surface  56 , a clearance or gap will be defined between the surfaces  42 ,  44 . After the adjustment plug  36  has been rotated the first predetermined angular distance, the plug  36  can be rotated in a second angular direction a second predetermined angular distance. The second predetermined angular distance can correspond to the desired amount of travel of the steering rack  32  and rack bearing  34  in the aperture  46  relative to the adjustment plug  36 . In other words, it is not desirable for the tip  54  to engage and disengage the surface  56  during operation of the assembly  10 .  
      It is believed that the positioning of the post  40  between the adjustment plug  36  and the rack bearing  34  reduces several different types of noise observed in rack and pinion steering gear assemblies. In particular, it has been observed that noise can be generated when the rack bearing  34  and the adjustment plug  36  contacts along surfaces  44  and  42  and then move relative to one another. The post  40  prevents the surfaces  42 ,  44  from directly engaging one another. Furthermore, the tip  54  of the post  40  defines a smaller contact area between the rotatable rack bearing  34  and the adjustment plug  36  than the surfaces  42 ,  44 .  
      As a result of manufacturing tolerances, the surfaces  42 ,  44  are not perfectly flat or square. Sliding contact between the surfaces  42 ,  44  can induce moments with respect to the rack bearing  34 , urging the rack bearing  34  to wobble about its longitudinal axis during rotation. It has been observed that noise can be generated when a portion outer surface  58  of the rack bearing  34  engages in sliding contact with the aperture  46  as a result of a moment generated from sliding contact between the surfaces  42 ,  44 . In other words, particular portions of the outer surface  58  exert greater forces against the aperture  46  than other portions of the outer surface  58 . It is believed that the post  40  substantially reduces the likelihood that a moment will be generated that tends to urge the rack bearing  34  to wobble and substantially eliminates the noise associated with rack bearing  34  wobble.  
      It is also been observed that the noise associated with relative movement between the rack bearing  34  and the steering rack  32  is reduced when the post  40  is positioned between the rack bearing  34  and the adjustment plug  36 . It is believed that the post  40  decreases the sensitivity of the steering assembly  14  to the steering rack  34  rotating about its longitudinal axis. Similarly, it is believed that the post  40  reduces the likelihood that the rack bearing  34  will induce noise-generating intermittent contact between the steering rack  32  and the steering pinion  28 .  
      It has also been observed that the torque required for turning the pinion  28  and housing assembly  12  is more consistent when the post  40  is disposed between the rack bearing  34  and the adjustment plug  36 . It is believed that the enhanced torque consistency results from the reduced surface area over which the rack bearing  34  and the adjustment plug  36  contacts one another.  
      Referring now to  FIG. 2 , a manual rack and pinion gear assembly  10   a  according to a second exemplary embodiment of the invention includes a housing assembly  12   a  and a pinion assembly  14   a  received in the housing  12   a . The pinion assembly  14   a  can be supported for rotation in the housing assembly  12   a  by first bearing  16   a  and the second bearing  18   a . The pinion assembly  14   a  can include a steering pinion  28   a  disposed in the housing assembly  12   a . The first shaft  28   a  defines a first longitudinal axis  29   a.    
      The steering pinion  28   a  can interact with a steering rack  32   a  at an axis  35   a , and the steering rack  32   a  can be supported by a rack bearing  34   a . The second shaft  32   a  defines a second longitudinal axis  33   a . The axis  29   a , 33   a  are transverse and offset with respect to one another. The steering rack  32   a  and rack bearing  34   a  are moveable in a direction transverse to the steering pinion  28   a  and rotatable. The steering rack  32   a  and rack bearing  34   a  are biased towards the steering pinion  28   a  by an adjustment plug  36   a  and a spring  38   a . The bearing  34   a  is moveable along a bearing axis  37   a  and rotatable about the axis  37   a.    
      A post  40   a  is disposed between the rack bearing  34   a  and the adjustment plug  36   a . The post  40  dictates where the first point of contact will occur. Additionally, it is post  40   a , which ensures a gap or clearance is defined between the rack bearing  34   a  and the adjustment plug  36   a . In particular, the post  40   a  is sized to ensure that a space is defined between a face surface  42   a  of the rack bearing  34   a  and a face surface  44   a  of the adjustment plug  36   a . The post  40   a  can be integrally formed with respect to either of the rack bearing  34   a  or the adjustment plug  36   a . Alternatively, the post  40   a  can be assembled to either of the rack bearing  34   a  or the adjustment plug  36   a.    
      Referring now to  FIG. 3 , a rack bearing  34   b  according to a third exemplary embodiment of the invention includes a post  40   b . The post  40   b  is integrally formed with respect to the rack bearing  34   b . The post  40   b  extends past a surface  42   b  to a tip  54   a . The tip  54   a  may be rounded to minimize a contact area between the post  40   b  and an adjustment plug (not shown).  
      Referring now to  FIG. 4 , a rack bearing  34   c  according to a fourth exemplary embodiment of the invention is assembled to a post  40   c . The rack bearing  34   c  defines an aperture  60  for receiving a portion  62  of the post  40   c . When assembled to the rack bearing  34   c , the post  40   c  extends past a surface  42   c  to a tip  54   b . The tip  54   b  may be rounded to minimize a contact area between the post  40   c  and a surface  56   a  of an adjustment plug  36   b.    
      While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.