Abstract:
A torque sensor apparatus and method for use with an automotive steering system is disclosed. The torque sensor apparatus includes a shaft having a primary shaft coaxially connected to a secondary shaft and a first substrate operably connected to the primary shaft oriented substantially perpendicular to an axis defining the shaft. A second substrate is operably connected to the secondary shaft oriented substantially perpendicular to the axis. First and second substrates each have an aperture therethrough configured to receive an alignment pin therethrough. First and second substrates are substantially parallel to each other defining an electrical interface therebetween that is configured to generate a signal indicative of an amount of torque applied to the shaft. A housing is configured to enclose the first and second substrates having the electrical interface therebetween, wherein one side of the housing includes an alignment aperture therethrough positioned to align with the apertures of the first and second substrates having the alignment pin therethrough and extending from an exterior of the housing. The alignment aperture is configured to limit contact with the alignment pin disposed between edges defining the alignment aperture in the housing while allowing the alignment pin to align the apertures of the first and second substrates with the alignment aperture.

Description:
TECHNICAL FIELD 
     This invention relates to an automotive steering system with a torque sensor. 
     BACKGROUND OF THE INVENTION 
     Current methods of measuring the torque applied to an automotive column shaft are of the compliant kind and are typically accomplished by use of a torsion bar as part of the shaft, joining an upper and lower section thereof. The torsion bar is made of material with known mechanical properties and hence has known compliance. Thus, the applied torque can be calculated from a measured angular displacement, Δθ, of the torsion bar (usually in the range of plus or minus a few degrees). The calculated torque is applied to a controller which then directs an electric steering torque assist motor to provide assist torque to the column shaft. 
     The torque sensor device may be used to accurately measure the input torque acting on a steering column shaft in an electronic power steering (EPS) system or steer-by-wire system of a vehicle. In this application, an input torque acts on the steering column shaft when an operator turns the steering wheel. The steering column shaft includes a primary shaft and a secondary shaft. The primary and secondary shafts are connected by a torsion bar. The rotation of the primary shaft relative to the secondary shaft may be measured with a potentiometer. 
     Typically in the assembly of such a torque sensor device the primary shaft is operably connected to a first substrate and the secondary shaft is connected to a second substrate. The primary and secondary shafts are operably coupled by a torsion bar. Each of the first and second substrates are aligned with each other using a pin extending through an aperture in a housing containing the sensor substrates to maintain alignment while assembly with the respective primary and secondary shaft assembly. The alignment pin prevents rotation of the substrates with respect to each other and with respect to the housing during assembly. During assembly of the torque sensor, the aperture in the housing is aligned with the openings in each of the substrates to receive the alignment pin. After assembly and installation of the torque sensor to the steering column shaft, the alignment pin is slidably removed from the respective parts in an attempt to have a sensor offset after such assembly of 50 percent plus or minus 4.5 percent of the source voltage, for example Vcc (2.50 V+/−0.225V) assuming Vcc=5V. 
     However, due to dimensional stack up tolerances during assembly of the first and second PCB&#39;s within the housing having the alignment pin extending through each, when the pin is removed from each corresponding aperture, the required offset voltage requirement between the PCB&#39;s may be defeated by removal of the pin to allow rotation of both first and second PCB&#39;s with respect to the housing in which they are contained. The required offset is defeated because the alignment pin preventing rotation of the components also stores mechanical energy therein caused by the misalignment as a result of the stack up condition. When the pin is removed, the stored mechanical energy in the pin is reflected in rotation of the now unrestricted components, thus defeating the offset. It has been found that any deviation from the preferred offset of zero degrees greater than 0.9 degrees of the system components will cause a failure of the offset voltage requirement based on a sensor having a sensor resolution of 0.25 Volts/degree, for example. 
     Thus, it is desired to provide a torque sensor that will be more forgiving of assembly tolerance stack conditions, such that a required offset voltage is not affected when the alignment pin is removed after assembly. It is advantageous to provide a simplified torque sensor assembly for direct sensing of the torque applied to a shaft to which the sensor is connected. In particular it is desirable to provide a torque sensor that will accommodate larger stack tolerances when the first and second torque sensing substrates are assembled within the housing and the alignment pin is installed to prevent rotation and set the required voltage offset, such that when the pin is removed, the offset isn&#39;t affected by the mechanical energy stored in the pin as a result of the tolerance stack between the sensor and housing. 
     SUMMARY OF THE INVENTION 
     A torque sensor apparatus and method for use with an automotive steering system is disclosed. The torque sensor apparatus includes a shaft having a primary shaft coaxially connected to a secondary shaft and a first substrate operably connected to the primary shaft oriented substantially perpendicular to an axis defining the shaft. A second substrate is operably connected to the secondary shaft oriented substantially perpendicular to the axis. First and second substrates each have an aperture therethrough configured to receive an alignment pin therethrough. First and second substrates are substantially parallel to each other defining an electrical interface therebetween that is configured to generate a signal indicative of an amount of torque applied to the shaft. A housing is configured to enclose the first and second substrates having the electrical interface therebetween, wherein one side of the housing includes an alignment aperture therethrough positioned to align with the apertures of the first and second substrates having the alignment pin therethrough and extending outside the housing. The alignment aperture is configured to limit contact with the alignment pin disposed between edges defining the alignment aperture in the housing while allowing the alignment pin to align the apertures of the first and second substrates with the alignment aperture. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is made to the drawings wherein like elements and features are numbered alike and wherein 
         FIG. 1  is a block diagram illustrating the main components of a steering assembly for a motor vehicle utilizing a sensor assembly in accordance with the present invention; 
         FIG. 2  is a perspective view of an exemplary embodiment of a sensor assembly coupled to a column shaft in accordance with the present invention; 
         FIG. 3  is a schematic cross-sectional view taken through the column shaft along line  2 — 2  of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the sensor assembly of  FIG. 2 ; 
         FIG. 5  is a-perspective view of a housing and rear lid for the sensor assembly shown in  FIG. 2 ; 
         FIG. 6  is a cross-sectional view of a position rotor for the sensor assembly shown in  FIG. 2 ; 
         FIGS. 7A and 7B  are exploded perspective views of a rotor assembly for the sensor assembly shown in  FIG. 2 ; 
         FIG. 8  is a perspective view of a prior art sensor assembly illustrating a prior art alignment aperture in the lid thereof; 
         FIG. 9  is a perspective view of an exemplary embodiment of the sensor assembly of  FIG. 2  illustrating an elongated and oversized aperture for an alignment pin to be received therethrough; and 
         FIG. 10  is a cross-sectional view of another alternative embodiment of the sensor assembly of FIG.  9 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention discloses a general type of torque sensor. In particular, the sensor may be useful to measure torque for electric power steering and/or steer-by-wire applications. The sensor is operably coupled with a rotating shaft to which torque is applied. In one embodiment described more fully below, the application of torque to a primary shaft of a column shaft is translated to a torsion bar to which the torsion bar is connected. The rotation of the torsion bar relative to the primary shaft changes the resistance of a potentiometer which generates a signal indicative of the torque transmitted from the primary shaft to the sensing device. The sensing device responds to changes in resistance from an offset resistance between a rotor and stator operably connected to the torsion bar and primary shaft, respectively, in the form of a measurable change in resistance. An electronic circuit converts the change in resistance into a voltage output signal that is linearly related to torque. 
     The invention features easy manufacturability and low cost. In addition, is suitable to fit different applications; namely the sensor can operate with steering systems that are non-compliant, highly compliant, or that may possess a compliance therebetween, depending on the requirements of the application. 
     Referring to  FIG. 1 , a block diagram of an electronic power assisted rack and pinion steering system  150  for a vehicle using a torque sensor device 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  165 . 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. Furthermore, although an EPS steering system has been described, it is also contemplated that sensor assembly  156  may be employed in a steer-by-wire system, where the mechanical connection of shaft  154  is absent from steering sensor  156  to steering gear  158 . 
     Referring to  FIGS. 2-4 , the sensor assembly  156  is shown coupled to the column shaft  154 . The column shaft  154  may include a primary shaft or 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 . 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. 5 , 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 about 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. 4 , 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  FIGS. 6 , 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 are attached to the bottom side  232  of the position rotor  194 . 
     Referring to  FIGS. 7A and 7B , 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 (not shown), a coupling  240 , and a torque rotor  290 . 
     Referring to  FIG. 7A , the rotor ring  236  has an outer diameter of about three inches and is rotatively mounted to the top side  238  of the position rotor  194  so that the rotor ring  236  is able to rotate relative to the position rotor  194 . A plurality of torque sensor brushes (not shown) are attached to the bottom side  272  of the rotor ring  236  and slidingly contact corresponding resistive patterns on position rotor  194 , 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  FIG. 7B , the coupling  240  has an inner ring member  278 , an 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 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 (not shown). The 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 . 
     In the particular embodiment shown in the drawings and herein described, the housing  188 , rear lid  189 , position rotor  194 , rotor ring  236 , and torque rotor  290  are each formed of a substantially solid and continuous construction. In addition, the position and torque substrates 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. 
     Referring again to  FIG. 7A , rotor ring  236  includes an opening  300  aligned with an opening  302  configured in position rotor  194  upon assembly therebetween in housing  188  and lid  189 . More particularly with specific reference to  FIG. 8 , a prior art sensor assembly  156  is illustrated. Rotor ring  236  and position rotor  194  are aligned with each other via respective openings  300 ,  302  configured in each after disposing the same within housing  188 . Lid  189  is defined with an alignment aperture  304  configured to receive an alignment pin  306  therethrough and be received in openings  300  and  302 . In this manner, upon further assembly of sensor assembly  156  with column shaft  154  or further installation with the vehicle, a required offset voltage can be maintained, such that after assembly and installation of the torque sensor device, the required offset voltage is not disturbed and results in about 50 percent of the Vcc voltage available. However, because of tolerance stack between housing  188  and lid  189 , alignment of opening  300  and  302  may not align with alignment aperture  304  in lid  189  when lid is assembled to housing  188 . In the event, that dimensional stack up creates misalignment between openings  300 ,  302  and aperture  304 , alignment pin  306  in effect stores mechanical energy that is caused by a periphery defining pin  306  abutting edges defining each of the openings  300 ,  302  and aperture  304  forcibly aligned with each other upon insertion of pin  306 . When pin  306  is removed, the stored mechanical energy in pin  306  is reflected in misalignment of openings  300 ,  302  and aperture  304 , thus upsetting the offset voltage reference to detect torque when column shaft  154  is rotated in either direction. Any offset deviation greater than 0.9 degrees between the system components causes a failure of the offset voltage requirement (i.e., based on a sensor resolution of 0.25 Volts/degree). 
     In an exemplary embodiment of a sensor assembly  256  illustrated in  FIG. 9 , a floating pin design with respect to a lid  389  is depicted such that this configuration will accommodate larger stack tolerances between the housing assembly and torsion bar or primary bar position with respect to the sensor assembly (e.g., rotor ring  236  and position rotor  194 ) having the sensor anti-rotation device or pin  306  disposed therewith. More specifically, lid  389  includes an elongated aperture  404  being dimensioned to allow a periphery defining pin  306  substantially no contact with edges defining aperture  389 . Furthermore, elongated aperture  389  is preferably crescent shape to follow an arc  390  created in lid  389  if pin  306  were allowed to rotate about center  392  coinciding with an axis  394  about which shaft  154  rotates. The above configuration allows the sensor to find a “home assembly position” while maintaining the offset voltage requirement (e.g., 2.5V+/−0.225 V when Vcc+5.0 V) when alignment pin  306  is removed. 
     Referring now to  FIG. 10 , another exemplary embodiment of a sensor assembly  356  is illustrated. In this embodiment, a torque rotor  490  is operably coupled with a rotor ring or torque substrate  436  while a position substrate  494  is operably connected to column shaft  154  via a collar  496  therebetween. Torque substrate  436  and position substrate  494  are substantially parallel and coaxially aligned with respect to axis  394  defining an axis of shaft  154 . Torque substrate  436  and position substrate  494  are further aligned with each other via respective openings  500  and  502  having alignment pin  306  therethrough. It will be recognized by one skilled in the pertinent art that when alignment pin is removed from opening  500  and  502 , substrates  436  and  494  rotate about axis  394  and with respect to each other to sense torque applied via a steering wheel connected to a torsion bar operably connected to torque rotor  490 . 
     Substrates  436  and  494  are further housed in a housing  488  having interface  591  extending therefrom for electrical connection therewith. Housing  488  is C-shaped having an elongated aperture  504  configured in a top surface defining a top surface of three surfaces defining housing  488 . It will be recognized that housing  488  may be any number of shapes and is not limited to a C-shaped housing as described above. Aperture  504  allows free floating movement of substrates  436  and  494  having pin  306  installed limited only by the dimensions defining aperture  504 . In this manner, dimensional stack tolerances in housing  488  will not affect the required offset voltage when pin  306  is removed, because aperture  504  is configured as to not allow any stored mechanical energy therein by misalignment caused between openings  500 ,  502  and aperture  504 . 
     In operation with respect to  FIGS. 1-7 , 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 torque sensor brushes (not shown) slide along respective resistive patterns of the torque element. The operating range of the torque sensing unit is from about −8 to about +8 degrees, and the output voltage varies from about 0 to about 5 Volts having a required offset of about 50 percent +/−4.5 percent of Vcc. When Vcc is 5 Volts, for example, the required offset voltage is about 2.50 Volts+/−0.225 Volts. The potentiometer is a function of the resistances obtained from the resistive pattern obtained when rotor ring  236  rotates relative to the position rotor  194 . 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. 
     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. 
     It is therefore apparent from the foregoing description of the present invention that one advantage of this invention is that the sensing device is well adapted to large scale manufacturing, offers low cost, high durability, and high stability. In addition, the sensor allows for greater dimensional stack up tolerances that will not affect the required offset voltage after assembly and installation thereof in a vehicle steering system. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration only, and such illustrations and embodiments as have been disclosed are not to be construed as limiting to the claims.