Abstract:
An angular-position and torque sensor assembly includes a low-hysteresis coupling for an assembly including a plurality of shafts. The coupling comprises an inner member, an outer member, and a base member disposed outside the outer member. The inner member and base member are coupled to the shafts. First rails connect the inner member to the outer member, and the first rails allow the inner member to be readily displaced relative to the outer member only in a direction substantially perpendicular to a longitudinal axis of the first rails. Second rails connect the outer member to the base member, and the second rails are aligned perpendicular to the first rails. The second rails allow the outer member to be readily displaced relative to the base member only in a direction substantially perpendicular to a longitudinal axis of the second rails. Due to the connection means of the first and second rails, the inner member is free to move in an x-y direction relative to the base member in an x-y plane parallel to the surface of the base while being rotatively fixed in a z axis relative to the base member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/295,921, filed Apr. 21, 1999, now U.S. Pat. No. 6,190,264, which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a low-hysteresis coupling for a shaft 
     BACKGROUND OF THE INVENTION 
     There are many applications which require a coupling to couple a device to a shaft. Often, such couplings allow rotational movement of a shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device. In certain application, the coupling must substantially eliminate hysteresis (which is the lagging of a physical effect on a body behind its cause) in rotational movement of the shaft with respect to the device. 
     One application of the coupling is a torque sensor device which determines a torque input on a shaft which comprises a torsion bar longitudinally connected to a primary bar. The primary bar is relatively inflexible to a torque input, while the torsion bar torsionally flexes to a torque input. The magnitude of the torque input may be determined by measuring the rotation of the torsion bar relative to the primary bar. One of the difficulties in coupling the torsion bar to the primary bar is that the torsion and primary bar may not be coaxial due to manufacturing tolerances or design requirements. External forces acting perpendicularly to the longitudinal axis of the torsion bar may also cause translation of the torsion bar in an x-y direction of an x-y plane (which is perpendicular to the longitudinal axis of the torsion and primary bar) such that the torsion bar may become temporarily non-coaxial with the primary bar. In addition to connecting with non-coaxial bars, the coupling should transmit the relative rotation of the torsion bar to the torque sensor device without backlash. In other words, the coupling allows rotational movement of the shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device. Thus, the coupling substantially eliminates hysteresis in rotational movement of the primary bar with respect to the torque sensor device. 
     The torque sensor device may be used to accurately measure the input torque acting on a steering column shaft in an electronic power steering system of an automobile or truck. In this application, an input torque acts on the steering column shaft when an operator turns the steering wheel. The steering column shaft includes the primary bar and the torsion bar. The rotation of the torsion bar relative to the primary bar may be measured with a potentiometer. The torque sensor device may include a coupling which couples the torsion bar to the primary bar so that a sensor brush may slidingly contact a variable resistor as the torsion bar rotates relative to the primary bar. In order to accurately determine the relative rotation of the torsion bar, the coupling should accurately transfer the relative rotation of the torsion bar to the sensor brush with substantially no hysteresis and still allow the translation of the torsion bar in the x-y plane. 
     Several devices are currently available which couple non-coaxial shafts. However, none of the devices thus far appear to be without problems. One attempt to satisfy the needs discussed above is disclosed in U.S. Pat. No. 3,834,182 (Trask et al.). Referring to FIGS. 1 and 2, this patent describes a flexible coupler  20  for connecting nominally coaxial shafts drivingly connected to one another. The coupler  20  permits a limited amount of axial misalignment between the shafts. The coupler  20  comprises three basic elements: an enlarged cylindrical hub  22  fixed to a first shaft, a second smaller cylindrical flange  26  fixed to another shaft  28  in juxtaposition to the hub  22 , and a “floating” annular ring  30  also juxtaposed with the hub  22  about the flange  26 . Loose fitting complementary axial lugs  32  and notches  34  interconnect the hub  22  and ring  30 , and loose fitting complementary radial lugs  36  and notches  38  are interfitted between the ring  30  and flange  26 . The flange  26  and ring  30  are located relative to the hub  22  for axial clearance, permitting limited angular misalignment between the two shafts  24 ,  28 . The flange  26  and circumjacent ring  30  form a planar surface juxtaposed with the inner planar surface  40  of the hub  22 . However, due to the loose fitting complementary axial lugs  32  and notches  38  and the loose fitting complementary radial lugs  36  and notches  38 , gaps  42  between the lugs  32  and notches  34  may lead to rotational play between the first and second shaft  24 ,  28 . 
     U.S. Pat. No. 2,956,187 (Wood), U.S. Pat. No. 3,859,821 (Wallace), U.S. Pat. No. 4,357,137 (Brown), and U.S. Pat. No. 4,464,141 (Brown) appear to provide a coupling with less rotational play between a first and second shaft than the Trask patent. These patents describe a flexible coupling for transmitting power from a drive shaft to a driven shaft. The coupling includes a primary coupling member having a hub section for receiving and rotating with a first shaft, a flange section having a resilient insert therein, and a secondary coupling member located centrally within the resilient insert for receiving and rotating with a second shaft. The resilient insert is interference fitted into the primary coupling member, and the secondary coupling is interference fitted into the central region of the resilient insert The resilient insert is adequately flexible to allow for axial misalignments between the shafts. However, a slight rotational play appears to exist between the first and second shafts because the resilient insert flexes to an input torque acting on the shafts. 
     Another coupling with reduced rotational play is disclosed in U.S. Pat. No. 3,728,871 (Clijsen) which describes a coupling for connecting two approximately registering shafts. Referring to FIGS. 3 and 4, the coupling  50  comprises two connecting pieces  52 ,  54  respectively connected to a first  56  and second shaft  58 . A loose coupling disc  60  is fitted between the two connecting pieces  52 ,  54  and couples the rotary movements of both connecting pieces  52 ,  54  to each other and has a limited play in two mutually perpendicular radial directions with respect to the individual connecting pieces  52 ,  54 . Play in the direction of rotation is reduced by a resilient C-shaped spring member  62 . One drawback of this coupling  50  appears to be that it is relatively complicated. This may result in an increase in manufacturing time and cost due to the numerous precision shaped components required. It also may result in a less reliable device because the inclusion of more components may translate into a statistically less reliable device. 
     Another coupling with reduced rotational play is a conventional Oldham coupling. 
     Referring to FIG. 5, the Oldham coupling  100  comprises three basic elements: a first member  102  connected to a first shaft at one end and having an axially extending tongue  104  at the other end, a second member  106  connected to a second shaft at one end and an axially extending tongue  108  at the other end, and a third member  110  positioned between the first member  102  and the second member  106 . The third member  110  has a groove  112  at each end which slidingly mates with the respective tongues  104 ,  108 . One drawback of the Oldham coupling  100  is that it appears to be relatively complicated. For the same reasons discussed above in regards to the Clijsen patent, the Oldham coupling may not satisfy certain needs for the torque sensor device. 
     Thus, there remains a need for a coupling that allows rotational movement of a shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device in an inexpensive, reliable, and rugged manner. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a coupling is coupled to a device in a manner that allows rotational movement of a shaft to be transferred to a device while not allowing translational movement of the shaft to be transferred to the device. The coupling is particularly suited for any device which requires substantially no hysteresis in rotational movement of the shaft with respect to the device. The present invention achieves the objective of coupling a shaft to a device in an inexpensive, reliable, and rugged manner. 
     The coupling of the present invention is particularly useful in an angular-position and torque sensor assembly for an electronic power assisted rack and pinion steering system of an automobile or truck. The steering system includes a steering wheel, column shaft, sensor assembly, steering gear, servo motor, pinion, and rack. The steering wheel is coupled to one end of the column shaft, and the opposite end of the column shaft is coupled to the steering gear. The other end of the steering gear is connected to a pinion which is rotatively coupled to the rack such that an operator turning the steering wheel causes the pinion to rotate along the rack. The rack moves longitudinally and turns the tires of the automobile. The servo motor is connected to the steering gear to provide power assist. The sensor assembly is coupled to the column shaft and accurately determines the angular position of the column shaft and input torque acting on the column shaft by the operator turning the steering wheel. Based on the data received from the sensor assembly, the controller processes the data and directs the rotational direction and power output of the servo motor such that a larger input torque results in providing more power to the servo motor. Thus, the steering system provides an appropriate level of power assistance to aid in steering. 
     Generally, in accordance with an exemplary illustrative embodiment of the present invention, the sensor assembly may comprise (1) a position substrate having a slip ring and a variable resistor ring, (2) a first rotating member rotating about the position substrate and having an electrical contact on the bottom side and a second variable resistor on the top side, and (3) a second rotating member rotating about the first rotating member and having a coupling on the top side and an electrical contact on the bottom side such that the electrical contact of the second rotating member slidingly contacts the second variable resistor. 
     The coupling comprises an inner member, an outer member, and a base member disposed outside the outer member. First rails connect the inner member to the outer member, and the first rails are aligned substantially perpendicular to a reference axis (the reference axis is on an x-y plane substantially parallel to the top surfaces of the inner member, outer member, and base member) to allow the inner member to be readily displaced relative to the outer member only in a direction substantially parallel to the reference axis. Second rails connect the outer member to the base member, and the second rails are aligned substantially parallel to the reference axis to allow the outer member to be readily displaced relative to the base member only in a direction substantially perpendicular to the axis. Due to the configuration of the first and second rails, the inner member is free to move relative to the base member in an x-y direction of the x-y-plane while being rotatively fixed in a z axis which is perpendicular to the x-y plane. 
     Other objects, features, and advantages of the present invention will become apparent from a consideration of the following detailed description 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a top view of a prior art flexible coupling; 
     FIG. 2 is an exploded perspective view of the prior art flexible coupling of FIG. 1; 
     FIG. 3 is a cross-sectional view of another prior art coupling; 
     FIG. 4 is a cross-sectional view of the prior art coupling of FIG. 3 along line  4 — 4 ; 
     FIG. 5 is an exploded perspective view of a prior art Oldham coupling; 
     FIG. 6 is a block diagram musing the main components of a steering assembly for a motor vehicle utilizing a coupling in accordance with the present invention; 
     FIG. 7 is a perspective view of an exemplary embodiment of a sensor assembly coupled to a column shaft by a coupling in accordance with the present invention; 
     FIG. 8 is a schematic cross-sectional view taken through the column shaft along line  7 — 7  of FIG. 7; 
     FIG. 9 is a cross-sectional view of the sensor assembly of FIG. 7; 
     FIG. 10 is a-perspective view of a housing and rear lid for the sensor assembly shown in FIG. 7; 
     FIG. 11A is a top view of an element assembly for the sensor assembly shown in FIG. 7; 
     FIG. 11B is a bottom view of the element assembly for the sensor assembly shown in FIG. 7; 
     FIG. 12 is a top view of the element assembly shown in FIGS. 11A and 11B attached to the housing shown in FIG. 10; 
     FIG. 13A is a cross-sectional view of a position rotor for the sensor assembly shown in FIG. 7; 
     FIG. 13B is a bottom view of the position rotor shown in FIG. 13A; 
     FIG. 13C is a top view of the position rotor shown in FIG. 13A; 
     FIGS. 14A and 14B are exploded perspective views of a rotor assembly for the sensor assembly shown in FIG. 7; 
     FIG. 14C is a top view of the rotor assembly shown in FIGS. 14A and 14B; 
     FIG. 15A is a top view of a torque element for the position rotor shown in FIGS. 14A and 14B; 
     FIG. 15B is a bottom view of the torque element shown in FIG. 15A; 
     FIG. 16 is a bottom view of a coupling ring assembly for the rotor assembly shown in FIGS. 14A and 14B; 
     FIG. 17 is a top view of a CV ring for the rotor assembly shown in FIGS. 14A-14C; 
     FIG. 18A is a schematic circuit of a circular potentiometer for an angular-position sensing unit; and 
     FIG. 18B is a schematic circuit of a potentiometer for a torque sensing unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to a low-hysteresis coupling for a shaft. The coupling of the invention may be thought of (in Cartesian coordinates) as allowing rotational movement of a shaft about a z axis to be transferred to a device while not allowing translational movement of the shaft in an x-y plane to be transferred to the device. In certain applications, the coupling substantially eliminates hysteresis in rotational movement of the shaft with respect to the device. In the particular embodiment shown in the drawings and herein described, the shaft is coupled to an angular-position and torque sensor assembly for a motor vehicle such as an automobile or truck. However, it should be understood that the principles of the invention are equally applicable to virtually any form of shaft For example, the low hysteresis coupling may be used for a steering system in aircraft, boats, or other vehicles. In addition, the low hysteresis coupling may be used in test equipment, robotics, manufacturing equipment, or any other device requiring the coupling of non-coaxial shafts. Therefore, the present invention should not be limited to the specific embodiment shown and such principles should be broadly construed. 
     Referring to FIG. 6, a block diagram of an electronic power assisted rack and pinion steering system  150  for an automobile or truck utilizing a low hysteresis coupling of the present invention is illustrated. The steering system  150  includes a steering wheel  152 , column shaft  154 , sensor assembly  156 , steering gear  158 , servo motor  160 , controller  159 , pinion  162 , and rack  164 , and tires  166 . The steering wheel  152  is coupled to one end of the column shaft  154 , and the opposite end of the column shaft  154  is coupled to the steering gear  158 . The other end of the steering gear  158  is connected to the pinion  162  which is rotatively coupled to the rack  164  such that an operator turning the steering wheel  152  causes the pinion  162  to rotate along the rack  164 . The rack  164  moves longitudinally and turns the tires  166  of the automobile. The servo motor  160  is connected to the steering gear  158  to provide power assist. The sensor assembly  156  is coupled to the column shaft  154  and accurately determines the angular position of the column shaft  154  and the input torque acting on the shaft  154  when the operator turns the steering wheel  152 . The sensor assembly  156  is electrically coupled to the controller  159 . Based on the data from the sensor assembly  156 , the controller  159  processes the data and directs the rotational direction and power output of the servo motor  160  such that a larger torque input results in providing more power to the servo motor  160 . Thus, the steering system  150  provides an appropriate level of power assistance to aid in steering. 
     Many other types of power steering systems exist such as a recirculating ball system comprising a steering gear in the form of a recirculating ball unit. The recirculating ball unit is connected to the column shaft at one end and to an idler arm at the other end. The idler arm is connected to a center link, and the center link is connected to the wheels of the automobile or truck. The present invention is intended to work equally well with either type of power steering system. 
     Referring to FIGS. 7-9, the sensor assembly  156  is shown coupled to the column shaft  154 . The column shaft  154  may include a primary bar  166  and a torsion bar  168 . A portion of the primary bar  166  is hollow so that it may accept a portion of the torsion bar  168 . The primary bar  166  has a length of about 9 inches, an outer diameter of about 1 inch, and a bore diameter slightly larger than 0.6 inch. The torsion bar  168  has a length of about 11 inches and includes a thick portion  170  and a thin portion  172 . The thick portion  170  has a length of about 6½ inches and a diameter of about 0.6 inch, and the thin portion  172  has a length of about 4½ inches. In the embodiment shown in the drawings, the thick  170  and thin portions  172  of the torsion bar  168  are integrally formed. A first end  174  of the torsion bar  168  is connected to the steering wheel  152 , while the second end  176  is connected to an inner end portion  178  of the primary bar  166 . The second end  180  of the primary bar  166  is connected to the steering gear  158 . The first end  182  of the primary bar  166  includes a first adapter  184  for coupling with the sensor assembly  156 . In a similar fashion, the thick portion  170  of the torsion bar  168  (near the connection of the thick  170  and thin portion  172 ) includes a second adapter  186  for coupling with the sensor assembly  156 . The first  184  and second adapter  186  are positioned adjacent to each other. 
     In the embodiment shown in the drawings, the column shaft  154  is formed of a substantially solid and continuous construction. Preferably, the column shaft  154  is made from a high strength metal such as carbon steel. It should be noted that other materials exhibiting similar qualities may also be used to form the column shaft such as aluminum, titanium, magnesium, polymers, and the like. The column shaft may be sized and shaped in other forms to accommodate different purposes. For typical automobiles, a relatively short and thin column shaft would be preferable such as the embodiment shown in FIGS. 2-4. Larger and thicker column shafts would be more appropriate for larger vehicles such as trucks and off-road vehicles requiring heavy duty column shafts. The column shaft may also be configured with a non-circular cross-section such as a square, oval, octagon, or any other shape. 
     The sensor assembly  156  includes an angular-position sensing unit and a torque sensing apparatus enclosed in a housing  188  and a rear lid  189 . Referring to FIG. 10, the housing  188  is disc shaped with a centrally located circular opening  190  which accepts and engages with the first  184  and second adapter  186  of the column shaft  154 . The housing  188  has an outer diameter of about 3 inches and a thickness of 0.7 inch The opening has a diameter of about 1 inch. 
     The housing  188  includes a rectangularly shaped interface portion  191  protruding outwardly from the disc shaped housing. The interface portion  191  accepts a wiring harness (not shown) which includes a plurality of wires which interconnect the sensor assembly to the controller. 
     Referring to FIG. 9, the angular-position sensing unit includes a circular potentiometer which determines the angular position of the column shaft  154 . The potentiometer comprises an element assembly  192 , a position rotor  194 , and a plurality of position sensor brushes  196 . The element assembly  192  includes a position substrate  198  formed from alumina and has a diameter of about 3 inches and a thickness of about 40 mils. Referring to FIG. 11A, the top side  200  of the position substrate  198  includes a first  202  and second slip ring  204  and further includes a first  206 , second  208 , third  210 , fourth  212 , and fifth resistive ring  214 . The slip rings  202 ,  204  and resistive rings  206 ,  208 ,  210 ,  212 ,  214  are formed using conventional thick film processes, wherein the slip  202 ,  204  and resistive rings  206 ,  208 ,  210 ,  212 ,  214  are screen patterned onto the top surface of the position substrate, dried, and then fired. The slip rings are burnished to form a smooth surface to reduce wearing of the position sensor brushes  196  as they slidingly contact the slip rings  202 ,  204 . The resistive rings  206 ,  208 ,  210 ,  212 ,  214  are formed from a resistor ink blend to achieve a nominal film resistivity of  197  ohms/square. Each resistive ring  206 ,  208 ,  210 ,  212 ,  214  is electrically interconnected with the two slip rings  202 ,  204 . In the embodiment shown in the drawings, the following respective resistance values are achieved for the resistive rings  206 ,  208 ,  210 ,  212 ,  214 : 2640 ohms, 2790 ohms, 3000 ohms, 3180 ohms and 3390 ohms. 
     Referring to FIG. 11B, a plurality of termination patterns  216  are formed on the bottom side  218  of the position substrate  198 . The plurality of termination patterns  216  interconnect the various components of the angular-position sensing unit such as the plurality of position sensor brushes  196 , slip rings  202 ,  204 , and resistive rings  206 ,  208 ,  210 ,  212 ,  214  with the controller  159 . The plurality of termination patterns  216  are formed using conventional thick film processes. Each of the termination patterns  216  are electrically connected to their respective slip rings  202 ,  204  and resistive rings  206 ,  208 ,  210 ,  212 ,  214  by trough holes  220  formed through the position substrate  198 . The termination patterns  216  comprise silver ink screen printed onto the bottom side  218  of the position substrate  198 , dried, and fired. Each end  222  of the termination patterns  216  is connected to a terminal clip  224  using solder paste. 
     Referring to FIG. 12, the element assembly  192  is attached to the inner surface  226  of the housing  188 . In the embodiment shown in the drawings, the housing  188  includes a plurality of tabs  228  extending outwardly from the inner surface  226  of the housing  188 . The plurality of tabs  228  are positioned adjacent to the peripheral edges of the position substrate  198 , and the plurality of tabs  228  extend beyond the top surface of the position substrate  198 . The element assembly  192  is heat staked onto the housing  188  by melting the top portion of the each of the tabs  228  onto the top surface of the position substrate  198 . 
     Referring to FIGS. 13A,  13 B and  13 C, the position rotor  194  is substantially a disc shaped member with a hub  230  extending outwardly from the bottom side  232 . The position rotor  194  is rotatably mounted to the housing  188  such that the circular opening  190  of the housing  188  accepts the hub  230  of the position rotor  194 . The position rotor  194  is electrically interconnected to the position substrate  198  by the plurality of position sensor brushes  196  which include a first  196   a,  second  196   b,  third  196   c,  and fourth sensor brush  196   d  attached to the bottom side  232  of the position rotor  194 . The first  196   a  and second sensor brush  196   b  slidingly contact the third  210  and fourth resistive ring  212  respectively, while the third  196   c  and fourth sensor  196   d  brush slidingly contact the fifth resistive ring  214 . 
     Referring to FIGS. 14A,  14 B and  14 C, the torque sensing unit includes a potentiometer which determines the angular position of torsion bar  168  relative to the angular position of the primary bar  166 . The potentiometer for the torque sensing unit comprises a torque element  234 , the position rotor  194 , a rotor ring  236 , a plurality of torque sensor brushes  238 , a coupling  240 , and a torque rotor  290 . 
     Referring to FIGS. 15A and 15B, the torque element  234  includes a torque substrate  242  which is crescent shaped and formed from alumina. The torque substrate  242  has a width of about 0.3 inch and a thickness of about 25 mils. The torque substrate  242  is attached to the bottom side  232  of the position rotor  194 , and a portion of the top side  244  of the torque substrate  242  is exposed through a first  246  and second opening  248  formed in the position rotor  194 . 
     A first  250 , second  252 , third  254 , and fourth resistive pattern  256  is formed on the top side  244  of the torque substrate  242 . These resistive patterns  250 ,  252 ,  254 ,  256  are formed using conventional thick film processes. The bottom side  258  of the torque substrate  242  includes a first  260 , second  262 , third  264  and fourth termination pattern  266  which interconnect the plurality of resistive patterns  250 ,  252 ,  254 ,  256  to the various components of the torque sensing unit such as the plurality of torque sensor brushes  238 , slip rings  202 ,  204 , and resistive rings  206 ,  208 ,  210 ,  212 ,  214  with the controller  159 . The termination patterns  260 ,  262 ,  264 ,  266  comprise thick film silver and are formed using conventional thick film processes. Each of the termination patterns  260 ,  262 ,  264 ,  266  are interconnected to their respective resistive patterns  250 ,  252 ,  254 ,  256  by trough holes  268  formed through the torque substrate  242 . Each end  270  of the plurality of termination patterns  260 ,  262 ,  264 ,  266  is connected to a torque sensor brush  272  at one end and by another torque sensor brush  274  at the other end so that the first  260 , second  262 , third  264 , and fourth termination pattern  266  are respectively interconnected with the first slip ring  202 , second slip ring  204 , first resistive ring  206 , and second resistive ring  208  (see FIG.  13 B). 
     Referring to FIGS. 14A and 16, the rotor ring  236  has an outer diameter of about three inches and is rotatively mounted to the top side  278  of the position rotor  194  so that the rotor ring  236  is able to rotate relative to the position rotor  194 . A first  238   a,  second  238   b,  third  238   c,  and fourth torque sensor brush  238   d  are attached to the bottom side  272  of the rotor ring  236  and slidingly contact the first  250 , second  252 , third  254 , and fourth resistive pattern  256 , respectively. The rotor ring  236  is held in place by a retaining ring  274 , and the retaining ring  274  is covered by an adapter ring  276 . Both the retainer ring  274  and adapter ring  276  are formed from 7075-T6 aluminum. 
     Referring to FIGS. 14B and 17, the coupling  240  has an inner ring member  278 , outer ring member  280 , and a base ring member  282 . The inner ring member  278  is connected to the outer ring member  280  which, in turn, is connected to the base ring member  282 . The base ring member  282  is fixedly secured to the top side  284  of the adapter ring  276  such that the base ring member  282  is fixedly connected to the rotor ring  236 . At the connections of the inner  278  and outer ring member  280  are formed perpendicularly projecting lateral rails  286 . Similarly, at the connections of the outer  280  and base ring members  282  are formed perpendicularly projecting longitudinal rails  288 . A torque rotor  290  is fixedly connected to the inner ring member  278 , and the torque rotor  290  engages and is fixedly secured to the second adapter  186  of the torsion bar  168  such that a rotation of the torsion bar  168  about the z axis results in an equal rotation of the torque rotor  290 , coupling  240 , and rotor ring  236 . 
     The base ring member  282  may be secured to the adapter ring  276  with an adhesive (not shown). To further aid in the securement, the base ring member  282  may provided with a plurality of slots  291  which allow any excess adhesive to escape the interface of the base ring member  282  and adapter ring  276 . In a similar fashion, the inner ring member  278  may include a plurality of slots  291  to further aid in the securement of the inner ring member  278  to the torque rotor  290 . In addition, the inner ring member  278  includes a plurality of fingers  292  extending outwardly which fasten onto an inner wall  294  of the torque rotor  290 . 
     The coupling  240  is preferably made from a single piece of flexible metal such as a sheet of stainless steel, and the pattern is formed by photo etching the sheet. The pattern may also be formed by a stamping process. The rails  286 ,  288  are formed by folding lengths of metal  286 ′,  288 ′ upwardly. The lateral rails  286  are rigid along the x axis but flexible along the y axis, and the longitudinal rails  288  are rigid along the y axis but flexible along the x axis. Accordingly, when the torsion bar  168  is secured to the inner ring member  278  and when the base ring member  282  is secured to the rotor ring  236 , the torsion bar  168  may move with respect to the base ring member  282  in the x-y direction of the x-y plane. More specifically, the torsion bar  168  may move with respect to the base ring member  282  along the x axis through the flexing of the longitudinal rails  288  (with both the inner  278  and outer ring member  280  moving with the torsion bar  168 ), and the torsion bar  168  may move with respect to the base ring member  282  along the y axis through the flexing of the lateral rails  286  (with the inner ring member  278  moving with the torsion bar  168 ). In the embodiment illustrated in the drawings, it is contemplated that a force of about three ounces directed in the x-y direction should deflect the inner ring member about fifteen mils in the x-y direction. Of course, the coupling may be designed with differing spring characteristics which are more appropriate for a specific application. 
     The torsion bar  168 , however, is not able to rotate with respect to the secured base ring member  282  about the z axis because of the collective rigidity of the rails  286 ,  288  in the x-y plane. In other words, in order for the torsion bar  168  to rotate about the z axis, the base ring member  282  also needs to rotate. Because of the rigidity in the x-y plane, any rotation of the torsion bar  168  will be translated into rotation of the base ring member  282 . Accordingly, hysteresis is minimized or substantially eliminated between the torsion bar  168  and the base ring member  282  in terms of rotation about the z axis. Thus, the coupling  240  allows the torque sensing unit to accurately measure the rotation of the torsion bar  168  relative to the primary bar  166 . 
     In the particular embodiment shown in the drawings and herein described, the housing  188 , rear lid  190 , position rotor  194 , rotor ring  236 , and torque rotor  290  are each formed of a substantially solid and continuous construction. Preferably, each of these elements are molded from a high impact and high temperature stable material such as LFL-4036 or RTP 4005TFE15 (30% glass, 15% PTFE, PPA). It should be noted that other materials exhibiting similar qualities may also be used. In addition, the position and torque substrate may be formed from non-ceramic materials such as a printed circuit boards (PCB), printed wiring board (PWB), polyglass substrate, or any other type known in the art. The slip rings, resistive rings, resistive patterns, and termination patterns may be formed by non-thick film processes such as thin film processes utilizing photolithographic techniques or the like. 
     FIGS. 18A illustrates a schematic circuit of the circular potentiometer for the angular-position sensing unit of the sensor assembly  156 . The circular potentiometer comprises variable resistors R 1  and R 2 , resistors R 3  and R 4 , and terminals B, C, D, and F. The circular potentiometer may measure over an angular range −90≦T&lt;270, where T is the rotation angle in degrees. Let Vout(T) represent the output voltage which varies as a function of the rotation angle T, and Vin represent the input voltage. By measuring output voltages Vout(M) at terminals C and F, the controller can determine the angular position of the primary bar. The output voltage Vout(T) at terminal C is given by:                Vout        (   T   )       =     Vin   ·     (     0.5   +     T   /   180       )                 where              -   90     ≤   T   ≤   90                 Vout        (   T   )       =     Vin   ·     (       (     270   -   T     )     /   180     )                 where                 90     &lt;   T   &lt;   270                                
     The output voltage Vout(T) at terminal F is given by: 
       Vout ( T )= Vin ·( T/ 180) where 0 ≦T≦ 180 
     
       
           Vout ( T )= Vin ·(360 −T )/180 where 180 &lt;T&lt; 360 
       
     
     FIG. 18B illustrates a schematic of the potentiometer for the torque sensing unit of the sensor assembly. The potentiometer comprises variable resistors R 5  and R 6 , resistors R 7 -R 10 , and terminals A, B, D and E. The potentiometer may measure the rotation of the torsion bar  168  relative to the primary bar  166  over an angular range of −8≦S≦8, where S is the relative rotation angle in degrees. Let Vout(S) be the output voltage as a function of the relative rotation angle S, and Vin represent the input voltage. By measuring output voltages Vout(S) at terminals E and A, the controller can determine the relative rotation angle S. The voltage output Vout(S) at terminal E is given by:                Vout        (   S   )       =     Vin   ·     (     0.90   -     0.8          (     S   +   8     )     /   16         )                 where                 S     -   8                 Vout        (   S   )       =     0.90      Vin               where                 S     &lt;     -   8                   Vout        (   S   )       =     0.10      Vin               where                 S     &lt;     -   8                                  
     The voltage output Vout(S) at terminal A is given by:                Vout        (   S   )       =     Vin   ·     (     0.90   -     0.8          (     S   +   8     )     /   16         )                 where   -   8     ≤   S   ≤   8                 Vout        (   S   )       =     0.90      Vin               where                 S     &lt;     -   8                   Vout        (   S   )       =     0.10      Vin               where                 S     &gt;   8                                
     In operation, when the operator turns the steering wheel  152 , the resulting torque input torsionally flexes the torsion bar  168 . The rotor ring  236  rotates relative to the position rotor  194  such that the first  238   a,  second  238   b,  third  238   c,  and fourth torque sensor brush  238   d  respectively slide along the first  250 , second  252 , third  254 , and fourth resistive pattern  256  of the torque element. The resistance from each resistive pattern  250 ,  252 ,  254 ,  256  depends on the location each torque sensor brush  238   a,    238   b,    238   c,    238   d  contacts their respective resistive pattern  250 ,  252 ,  254 ,  256 . The operating range of the torque sensing unit is from −8 to +8 degrees, and the output voltage Vout(S) resulting from the potentiometer is a function of the resistances obtained from the first  250 , second  252 , third  254 , and fourth resistive pattern  256 . For example, if the controller  159  measures output voltage Vout(S)=0.7Vin at terminal E and output voltage Vout(S)=0.3Vin at terminal A, the controller  159  will determine that the angular position of torsion bar  168  relative to the angular position of the primary bar  166  is +4 degrees. With this information, the controller  159  can determine the magnitude of the torque input and send the appropriate bias and power to the servo motor  160  so that the electronic power steering system  150  provides the appropriate rotational direction and level of power assistance to aid in steering. If the output voltage Vout(S) at terminal E does not correlate with the output voltage Vout(S) at terminal A, the controller  159  should terminate power assistance to the steering system for safety purposes. 
     As the operator turns the steering wheel  152 , the primary bar  166  also rotates due to the torque input on the primary bar  166 . The position rotor rotates  194  relative to the element assembly  192  such that the first  196   a  and second position sensor brush  196   b  respectively slide along the third  210  and fourth resistive ring  212  of the element assembly  192 , and the third  196   c  and fourth position sensor brush  196   d  slide along the fifth resistive ring  214  of the element assembly  192 . The resistance from each variable resistor ring  206 ,  208 ,  210 ,  212 ,  214  depends on the location each position rotor brush contacts their respective resistive ring  206 ,  208 ,  210 ,  214 . The angular-position sensing unit can determine the angular position over an angular range −90≦T 360, and the output voltage resulting from the circular potentiometer is a function of the resistances from the third  210 , fourth  212 , and fifth resistive ring  214 . For example, if the controller measures output voltage Vout(T)=0.94Vin at terminal C and output voltage Vout(T)=0.44Vin at terminal F, the controller  159  will determine that the angular position of the primary bar  166  is +80 degrees. With this information, the controller  159  can send the appropriate bias and power to the servo motor  160  so that the electronic power steering system  150  provides the appropriate rotational direction and level of power assistance to aid in steering. In a similar fashion, the controller  159  should terminate power assistance if the output voltage Vout(T) at terminal C does not correlate with the output voltage Vout(T) at terminal F. 
     The circuits described hereinabove for the potentiometers are one operative preferred circuits, but other known potentiometer circuits could be used instead of the particular circuits described hereinabove. 
     Although the present invention has been described in detail with regarding the exemplary embodiments and drawings thereof, it should be apparent to those skilled in the art that various adaptations may be accomplished without departing from the spirit and scope of the invention. Accordingly, the invention is not limited to the precise embodiment shown in the drawings and described in detail hereinabove.