Abstract:
A vehicle power steering assembly is provided. The vehicle power steering assembly includes an input shaft having first and second end portions that extend along an axis, and a first aperture that extends substantially axially into the first end portion. The vehicle power steering assembly further includes a torsion shaft having third and fourth end portions. The third end portion has a first plurality of splines and the fourth end portion has a second plurality of splines. The third end portion is disposed in the first aperture of the input shaft. The first plurality of splines on the third end portion fixedly couples the torsion shaft to the input shaft. The vehicle power steering assembly further includes an output shaft having fifth and sixth end portions, and a second aperture that extends substantially axially into the fifth end portion toward the sixth end portion. The fourth end portion of the torsion shaft is disposed in the second aperture of the output shaft. The second plurality of splines on the fourth end portion fixedly couples the torsion shaft to the output shaft. A rotational movement of the input shaft a predetermined distance in a first direction about the axis induces rotational movement of the output shaft in the first direction.

Description:
TECHNICAL FIELD  
       [0001]     This application relates to a vehicle power steering assembly and a method for assembling the vehicle power steering assembly.  
       BACKGROUND  
       [0002]     Vehicle steering systems have utilized torsion bars for actuating a gear or valve assembly for assisting a driver in steering a vehicle. The torsion bar is connected to an input shaft via a pin that extends through an aperture in both the torsion bar and input shaft.  
         [0003]     A problem associated with this configuration, is that both the torsion bar and the input shaft are constructed from a steel having a relatively low hardness, to allow drilling and reaming tools to drill the aperture through the torsion bar and the input shaft. As a result, an operational life-time of the torsion bar and the input shaft can be reduced.  
         [0004]     Accordingly, there is a need for an improved vehicle steering system that eliminates and/or reduces the foregoing problem.  
       SUMMARY OF THE INVENTION  
       [0005]     A vehicle power steering assembly in accordance with an exemplary embodiment is provided. The vehicle power steering assembly includes an input shaft having first and second end portions that extend along an axis, and a first aperture that extends substantially axially into the first end portion. The vehicle power steering assembly further includes a torsion shaft having third and fourth end portions. The third end portion has a first plurality of splines and the fourth end portion has a second plurality of splines. The third end portion is disposed in the first aperture of the input shaft. The first plurality of splines on the third end portion fixedly couples the torsion shaft to the input shaft. The vehicle power steering assembly further includes an output shaft having fifth and sixth end portions, and a second aperture that extends substantially axially into the fifth end portion toward the sixth end portion. The fourth end portion of the torsion shaft is disposed in the second aperture of the output shaft. The second plurality of splines on the fourth end portion fixedly couples the torsion shaft to the output shaft. A rotational movement of the input shaft a predetermined distance in a first direction about the axis induces rotational movement of the output shaft in the first direction.  
         [0006]     A method of assembling a vehicle power steering assembly in accordance with another exemplary embodiment is provided. The vehicle power steering assembly includes an input shaft, a torsion shaft, and an output shaft. The input shaft includes first and second end portions that extend along an axis, and a first aperture that extends substantially axially into the first end portion. The torsion shaft has third and fourth end portions. The third end portion has a first plurality of splines and the fourth end portion has a second plurality of splines. The output shaft has fifth and sixth end portions, and a second aperture that extends substantially axially into the fifth end portion toward the sixth end portion. The method includes disposing the third end portion of the torsion shaft into the first aperture of the input shaft. The method further includes applying a first axial force to either the input shaft or the torsion shaft to urge the first plurality of splines of the torsion shaft against an inner surface of the input shaft defined by the first aperture such that the third end portion of the torsion shaft is fixedly coupled to the input shaft. The method further includes disposing the fourth end portion of the torsion shaft into the second aperture of the output shaft. The method further includes applying a second axial force to an outer surface of the sixth end portion of the output shaft to urge the second plurality of splines on the torsion shaft against an inner surface of the output shaft defined by the second aperture such that the fourth end portion of the torsion shaft is fixedly coupled to the output shaft.  
         [0007]     A vehicle steering system in accordance with another exemplary embodiment is provided. The vehicle steering system includes a steering wheel. The vehicle steering system further includes an input shaft having first and second end portions that extend along an axis, and a first aperture that extends substantially axially into the first end portion. The second end portion is operably coupled to the steering wheel. The vehicle steering system further includes a torsion shaft having third and fourth end portions. The third end portion has a first plurality of splines and the fourth end portion has a second plurality of splines. The third end portion is disposed in the first aperture of the input shaft. The first plurality of splines on the third end portion fixedly couples the torsion shaft to the input shaft. The vehicle steering system further includes an output shaft having fifth and sixth end portions, and a second aperture that extends substantially axially into the fifth end portion toward the sixth end portion. The fourth end portion of the torsion shaft is disposed in the second aperture of the output shaft. The second plurality of splines on the fourth end portion of the torsion shaft fixedly couples the torsion shaft to the output shaft. The vehicle steering system further includes a gear assembly that is operably coupled to the output shaft such that rotation of the torsion shaft in a first direction induces operation of the gear assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective view of a vehicle steering system having a power steering assembly, an intermediate connecting assembly, a rack and pinion assembly, and a steering wheel in accordance with an exemplary embodiment of the present invention;  
         [0009]      FIG. 2  is a cross sectional view of the power steering assembly having an input shaft, a torsion shaft, and an output shaft utilized in the vehicle steering system of  FIG. 1 ;  
         [0010]      FIG. 3  is a side view of the torsion shaft of  FIG. 2 ;  
         [0011]      FIG. 4  is an enlarged view of a splined end of the torsion shaft of  FIG. 3 ;  
         [0012]      FIG. 5  is an enlarged end view of the torsion shaft of  FIG. 4 ;  
         [0013]      FIG. 6  is a cross sectional view of the input shaft, the torsion shaft, and an actuator for positioning the torsion shaft in the input shaft;  
         [0014]      FIG. 7  is a cross sectional view of the input shaft, the torsion shaft, a compression fixture, and actuators for coupling the torsion shaft to the input shaft;  
         [0015]      FIG. 8  is a cross sectional view of the input shaft, the torsion shaft, the output shaft, and an actuator for positioning the output shaft relative to the input shaft and the torsion shaft;  
         [0016]      FIG. 9  is cross sectional view of  FIG. 8  illustrating the output shaft in a first rotational position;  
         [0017]      FIG. 10  is a cross sectional view of  FIG. 8  illustrating the output shaft in a second rotational position;  
         [0018]      FIG. 11  is a cross sectional view of  FIG. 8  illustrating the output shaft in a third rotational position;  
         [0019]      FIG. 12  is a cross sectional view of the input shaft, the torsion shaft, the output shaft, and an actuator for affixing the output shaft to the torsion shaft;  
         [0020]      FIG. 13  is an enlarged cross sectional view of  FIG. 12  illustrating the input shaft, the torsion shaft, the output shaft, and portions of the actuator;  
         [0021]      FIG. 14  is an enlarged cross sectional view of  FIG. 12  illustrating the input shaft, the torsion shaft, the output shaft, and portions of the actuator applying a force to the output shaft; and  
         [0022]      FIG. 15  is a flow chart of a method of assembling a power steering assembly in accordance with an exemplary embodiment.  
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0023]     Referring to  FIG. 1 , a vehicle steering system  10  in accordance with an exemplary embodiment is illustrated. The vehicle steering system  10  includes a power steering assembly  12 , an intermediate connecting assembly  14 , a rack and pinion assembly  16 , and a steering wheel  18 . In the exemplary embodiment, the power steering assembly  12  is utilized in an electric column power steering system. In alternate embodiments, the power steering assembly  12  can be utilized in at least one of: (i) a hydraulic integral-gear power steering system, (ii) a hydraulic rack and pinion gear power steering system, (iii) an electric integral gear power steering system, (iv) an electric rack and pinion gear power steering system, (v) a steer-by-wire column power steering system.  
         [0024]     Referring to  FIGS. 2 and 7 , power steering assembly  12  includes an input shaft  32 , a torsion shaft  34 , and an output shaft  36 . The torsion shaft  34  is rigidly coupled to both the input shaft  32  and the output shaft  36 . The input shaft  32 , the torsion shaft  34 , and the output shaft  36  have substantially circular cross sections and are constructed from a rigid material, such as steel for example. The input shaft  32  includes end portions  38  and  40 , and an aperture  42  extending along an axis  35  substantially into the end portion  38  toward the end portion  40 . An inner surface  44  defined by the aperture  42  is configured for receiving a portion of the torsion shaft  34 . The input shaft  32  is configured to be operably coupled to the steering wheel  18  proximate the end portion  40 .  
         [0025]     Referring to  FIGS. 2 and 9 , the end portion  38  of the input shaft  32  includes stopping flanges  46 ,  47  spaced apart from each other and extending outwardly from an outer surface  49  of the input shaft  32 . The stopping flanges  46 ,  47  are provided for limiting the amount of rotational displacement of the torsion shaft  34  relative to the input and output shafts  32 ,  36 . The stopping flange  46  defines side surfaces  48 ,  50 . The stopping flange  47  defines side surfaces  52 ,  54 . Of course, the configuration and number of flanges disposed around the periphery of the inner shaft  32  can vary.  
         [0026]     Referring to  FIGS. 3-5 , the torsion shaft  34  is provided for indicating an amount of torque applied the input shaft  32 . The torsion shaft  34  comprises an intermediate portion  64  and end portions  56 ,  58 . The end portion  56  includes splines  60  disposed circumferentially about the end portion  56 . The end portion  58  includes splines  62  disposed circumferentially about the end portion  58 . The splines  60  fixedly engage the inner surface  44  of the input shaft  32 , therein fixedly coupling the torsion shaft  34  to the input shaft  32 . The splines  60 ,  62  each comprise a plurality of raised teeth  66  and valleys  68  disposed between teeth  66 , illustrated in  FIGS. 4 and 5 . The splines  60 ,  62  have a defined length “L.” In this embodiment, the splines  60 ,  62  have substantially similar configurations. In an alternative embodiment, the configuration of splines  60 ,  62  may be different from one another. Referring to  FIGS. 1, 2 , and  9  the output shaft  36  is provided to transmit torque from the input shaft  32  to the intermediate connecting assembly  14 . The output shaft  36  includes end portions  70 ,  72 , and an aperture  74  extending substantially axially into the end portion  70  toward the end portion  72 . The aperture  74  defines an inner surface  85 . Further, the aperture  74  is configured to receive at least a portion of the torsion shaft  34 .  
         [0027]     Referring to  FIGS. 2 and 9 - 11 , the output shaft  36  further includes slots  80 ,  81  spaced apart from one another and disposed proximate the end portion  70 . The slot  80  is configured to receive the stopping flange  46  of the input shaft  32  therein. The slot  81  is configured to receive the stopping flange  47  of the input shaft  32  therein. The slot  80  extends from the surface  85  defined by the aperture  74  into the output shaft  36 . Further, the slot  81  extends from the surface  85  defined by the aperture  74  into the output shaft  36 . The slot  80  defines surfaces  82 ,  84  of the output shaft  36  configured to contact surfaces  48 ,  50 , respectively of the input shaft  32  when the input shaft  32  rotates a predetermined distance counterclockwise or clockwise, respectively, relative to the output shaft  36 . Similarly, the slot  81  defines surfaces  86 ,  88  of the output shaft  36  configured to contact surfaces  54 ,  52 , respectively, of the input shaft  32  when the input shaft  32  rotates a predetermined distance counterclockwise or clockwise, respectively, relative to the output shaft  36 . In an alternative embodiment, the output shaft  36  may have a single slot configured to receive a single stopping flange, or a plurality of slots disposed around the periphery of aperture  74  where at least a portion of the slots are configured to receive stopping flanges. Further, the output shaft  36  is configured to be operably coupled to a gear assembly.  
         [0028]     Referring to  FIG. 8 , in one embodiment, a torque sensor (not shown) can be operably coupled to the surfaces  38 ,  70 . The torque sensor can generate an output signal indicative of an angular displacement of the output shaft  36  relative to the input shaft  32 . The output signal is utilized by the power steering system to assist an operator in turning vehicle wheels to a desired position. In another embodiment, a hydraulic valve (not shown) can be operably coupled to surfaces  38 ,  70  to generate a hydraulic fluid signal indicative of an angular displacement of the output shaft  36  relative to the input shaft  32 . The hydraulic fluid signal is utilized by the power steering system to assist the operator in turning vehicle wheels to the desired position.  
         [0029]     Referring to  FIG. 15 , a method of assembling the vehicle power steering assembly  12  in accordance with an exemplary embodiment is illustrated. At step  112 , a user provides (i) an input shaft  32  having end portions  38 ,  40 , an aperture  42  extending into the end portion  38  toward the end portion  40 , and stopping flanges  46 ,  47  extending outwardly from an outer surface  49  of the input shaft  32 ; (ii) a torsion shaft  34  having an end portion  56  having splines  60 , and an end portion  58  having splines  62 ; (iii) an output shaft  36  having end portions  70 ,  72 , an aperture  74  extending into the end portion  70  toward the end portion  72 , and slots  80 ,  81  extending from a surface  85  defined by the aperture  74  into the output shaft  36 .  
         [0030]     Referring to  FIGS. 6 and 15 , next at step  114 , an actuator  90  disposes the end portion  56  of the torsion shaft  34  into the aperture  42  of the input shaft  32 . Of course, in an alternative embodiment, the end portion  56  can be manually disposed into the aperture  42 .  
         [0031]     Referring to  FIGS. 7 and 15 , next at step  116 , an actuator  92  positions a compression fixture  94  about the end portion  58  of the torsion shaft  34  and the end portion  38  of input shaft  32 . The compression fixture  94  includes a buckling-stop or guide-member  96  positioned proximate the periphery of the torsion shaft  34  between the end portions  56 ,  58 . The compression fixture  94  is configured to support and guide the torsion shaft  34  into the aperture  42  of the torsion shaft  34  when the torsion shaft  34  is being coupled to the input shaft  32 . The buckling-stop  96  is configured to prevent the torsion shaft  34  from plastically deforming when the torsion shaft  34  is being coupled to the input shaft  32 .  
         [0032]     Next, at step  118 , the actuator  92  applies an axial force  104  to either the compression fixture  94  or the input shaft  32  urging the splines  60  into an inner surface  44  of the aperture  42  such that the end portion  56  of the torsion shaft  34  is fixedly coupled to the input shaft  32 .  
         [0033]     Referring to  FIGS. 8 and 15 , next at step  120 , an actuator  100  disposes the end portion  58  of the torsion shaft  34  into the aperture  74  of the output shaft  36 , where the end portion  70  of the output shaft  36  overlaps a portion of the end portion  38  of the input shaft  32 , and the stopping flanges  46 ,  47  of the input shaft  32  substantially align with the slots  80 ,  81  of the output shaft  36 .  
         [0034]     Referring to  FIGS. 9-11  and  15 , next at step  122 , while the input shaft  32  and the torsion shaft  34  are fixed from rotating, the actuator  100  rotates the output shaft  36  in a clockwise direction  106  until a surface  82  defined by the slot  80  of the output shaft  36  contacts a surface  48  defined by the stopping flange  46  of the input shaft  32 . Further, a surface  88  defined by the opposite slot  81  contacts a surface  52  defined by the opposite stopping flange  47  substantially at the same time as the surface  82  of the slot  80  contacts the surface  48  of the stopping flange  46 . The actuator  100  then rotates the output shaft  36  in a counterclockwise direction  108  until surfaces  84 ,  86  defined by the slots  80 ,  81  of the output shaft  36  contact respective surfaces  50 ,  54  defined by the stopping flanges  46 ,  47  of the input shaft  32 . The actuator  100  then rotates the output shaft  36  to a position such that the surfaces  82 ,  84 , and surfaces  86 ,  88  defined by the slots  80 ,  81 , respectively, of the output shaft  36  are positioned substantially equidistant from the surfaces  48 ,  50 , and surfaces  52 ,  54 , respectively, defined by the stopping flanges  46 ,  47  of the input shaft  32 . The actuator  100  is configured to measure, an amount of rotation between slot and flange contacting surfaces in order to position the output shaft  36  as described above.  
         [0035]     The sequence of rotational movements described in step  122  can be varied so long as the final position of the slots  80 ,  81  and the flanges  46 ,  47  allows for a substantially equal amount of rotation in a clockwise or counterclockwise direction  106 ,  108  before contact occurs between a slot and the respective flange surface. In the present embodiment, the maximum amount of rotation in either direction is approximately  10  degrees. In an alternative embodiment, the amount of rotation can be greater than 10 degrees.  
         [0036]     Referring to  FIGS. 12-15 , next at step  124 , an actuator  102  applies a force  110  to an outer surface  76  at the end portion  72  of the output shaft  36  to urge an inner surface  78  defined by the aperture  74  of the output shaft  36  against the splines  62  of the torsion shaft  34  such that the end portion  58  of the torsion shaft  34  is fixedly coupled to the output shaft  36 .  
         [0037]     In the exemplary embodiment illustrated in  FIGS. 13 and 14 , the actuator  102  may include separated members  103 ,  105  configured to contact a substantial circumferential portion of the outer surface  76  of the output shaft  36 . The actuator  102  applies the force  110  to the outer surface  76  of the input shaft  32  to urge the inner surface  78  of the output shaft  36  toward the splines  62  of the input shaft  32 . The force  110  urges inner surface  78  into the splines  62  such that a substantial plurality of portions of the inner surface  78  protrude into valleys  68  of the splines  62 . When the actuator  102  and members  103 ,  105  are removed from the output shaft  36 , the end portion  58  of the torsion shaft is fixedly coupled to the end portion  72  of the output shaft  36 , as illustrated in  FIG. 2 .  
         [0038]     During operation of the vehicle power steering assembly  12 , a torque applied to the input shaft  32  will urge the torsion shaft  34  to rotate in the same direction as the applied torque. The rotation of the torsion shaft  34  is limited by the amount of rotational movement of the input shaft  32  or output shaft  36  before surfaces defined by the stopping flanges  46 ,  47  contact the respective surfaces defined by the slots  80 ,  81  of the output shaft  36 . For instance, a torque applied to the input shaft  32  will rotate the torsion shaft  34  until contact occurs between a slot surface and a respective flange surface. Further rotation or torque applied to the input shaft  32  will not be transferred through the torsion shaft  34 , but only between the input shaft  32  and the output shaft  36 . Of course, the rotation of the torsion shaft  34  is limited in the same manner if torque is applied to the output shaft  36 , thereby transmitting the torque from the output shaft  36  through the torsion shaft  34  to the input shaft  32 .  
         [0039]     The exemplary embodiments of the vehicle power steering assembly  12  described herein, including the splines  60 ,  62 , permit the use of shafts having harder materials for rigidly coupling the torsion shaft  34  to the input and output shafts  32 ,  36 . The spline connections allow the use of a harder shaft material compared to vehicle steering column assemblies that use drill and pin connection methods. Further, the input shaft  32 , torsion shaft  34 , and the output shaft  36  can be made of a hard material such as but not limited to steel. In an exemplary embodiment discussed herein, the hardness of the torsion shaft  34  is greater than 30 Rockwell C. Of course, in another alternative embodiment, the hardness of the torsion shaft  34  is less than 30 Rockwell C. Alternative exemplary embodiments include configurations where the hardness values of the input, output and torsion shafts  32 ,  34 ,  36  may or may not be equal.  
         [0040]     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 present application.