Patent Publication Number: US-6705419-B2

Title: Drive-by-wire steering systems having a center feel mechanism and methods of providing

Description:
TECHNICAL FIELD 
     This disclosure relates generally to drive-by-wire steering systems. More specifically, this disclosure relates to drive-by-wire steering systems having a center feel mechanism, and methods of providing such steering systems with a center feel. 
     BACKGROUND 
     Vehicles require a steering system to control the direction of travel. Previously, mechanical steering systems have been used. Mechanical steering systems typically include a mechanical linkage or a mechanical connection between the steering wheel and the vehicle&#39;s road wheels. Thus, movement of the steering wheel causes a corresponding movement of the road wheels. Movement of such mechanical systems is often power assisted through the use of hydraulic assists or electric motors. 
     Mechanical steering systems are being replaced and/or supplemented by electrically driven steering systems, commonly known as “steer-by-wire” systems. Such steer-by-wire systems to varying extents replace, for example, the mechanical linkage between the steering wheel and the vehicle wheels with an electrically assisted system. 
     This migration to steer-by-wire systems is being made to improve fuel economy, increase vehicle modularity, reduce load on the engine of the vehicle, reduce vehicle weight, and provide four-wheel-steering. For example, the use of steer-by-wire systems eliminates the need for hydraulic fluids, provides a tighter turning radius, and reduces the weight of the vehicle. 
     Additionally, steer-by-wire systems eliminate various undesirable problems present in mechanical systems. For example in steer-by-wire systems, the steering wheel is mechanically isolated from the road wheels. Thus, excessive deleterious feed back to the steering wheel in the form of shudders, and steering wheel kickback from the road wheels is eliminated. 
     Unfortunately, mechanically isolating the steering wheel from the road wheel also eliminates desired feed back. For example, during the use of mechanical steering systems, an operator applies a force to the steering wheel to turn the road wheels of the vehicle. After releasing the turning force on the steering wheel, the gyroscopic and other forces on the road wheels tend to act on the mechanical steering system to return the steering wheel to its normal or center position. Unfortunately, the mechanical isolation provided by drive-by-wire steering systems eliminates this desired feedback. Namely, during the use of drive-by-wire steering systems, the steering wheel maintains its turned position after being released instead or returning to its center position. 
     In vehicles having mechanical steering systems, the force applied by the operator to the steering wheel to turn the road wheels of the vehicle is typically proportion to the amount or degree of vehicle turn desired. Namely, in order to turn the vehicle slightly, only a slight force must be applied to the steering wheel. Conversely, in order to turn the vehicle sharply, a large force must be applied. It is known to provide mechanical steering systems with power assistance through the use of hydraulic assists or electric motors to reduce the amount of force applied to the steering wheel necessary to turn the road wheels. Thus, it has been seen that “over assisting” by removing all of the force associated with turning the vehicle, or even making the force required to turn the vehicle constant regardless of the degree of turn changes the “feel” of the steering system. 
     In mechanical systems, the amount of assistance applied by the hydraulic assists or electric motors has been regulated so as to avoid these “over assist” problems. However, during the use of drive-by-wire steering systems the force applied to the steering wheel necessary to turn the wheels is both minimal and constant due to the mechanical isolation of the steering wheel from the road wheels. Thus, prior drive-by-wire steering systems often suffer from the same problems experienced in overly assisted mechanical steering systems. 
     SUMMARY 
     A drive-by wire steering system is provided. The system comprises a steering shaft and a center feel mechanism. The steering shaft is configured for a first angular displacement about a first axis. The steering shaft has a first geared portion and a first end connectable to a vehicle&#39;s steering wheel. The center feel mechanism comprises a cam face, an urging member and a second geared portion. The first geared portion and the second geared portion are operatively engaged such that the first angular displacement of the steering shaft imparts a second angular displacement about a second axis to the center feel mechanism. The cam face and the urging member are configured to generate a retuning torque to the center feel mechanism. The retuning torque has a direction opposite the second angular displacement. 
     A method of providing a center feel in a drive-by wire steering system is provided. The method comprises engaging a center feel mechanism to a steering shaft such that an angular displacement of the steering shaft about a first axis imparts a second angular displacement about a second axis to the center feel mechanism. The center feel mechanism comprises a cam face that defines a center position. The method further comprises urging a cam follower into the cam face such that the second angular displacement generates a retuning torque on the center feel mechanism. The retuning torque acts on the center feel mechanism to return and maintain the cam follower at the center position. 
     A method of improving the driveability of a drive-by wire steering system is provided. The method comprises engaging a center feel mechanism to a steering shaft such that an angular displacement of the steering shaft about a first axis imparts a second angular displacement about a second axis to the center feel mechanism. The center feel mechanism comprises a cam face having a cam profile. The method further comprises biasing a cam follower into the cam face such that the angular displacement of the steering shaft generates a retuning torque on the center feel mechanism. The retuning torque has a direction opposite the angular displacement, and is proportional to the angular displacement. 
     The above-described and other features are appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a steer-by wire system for a vehicle; 
     FIG. 2 is a sectional view of an exemplary embodiment of steer-by wire system; 
     FIG. 3 is an exemplary embodiment of a return to center mechanism of the steer-by wire system of FIG. 2, taken along circle  3 — 3 ; 
     FIG. 4 is a sectional view of the center feel mechanism of FIG. 3, taken along lines  4 — 4 ; 
     FIG. 5 is a view of the center feel mechanism of FIG. 4 in a first position; 
     FIG. 6 is a view of the center feel mechanism of FIG. 4 in a second position; 
     FIG. 7 is a view of the center feel mechanism of FIG. 4 in a third position; 
     FIG. 8 is a sectional view of an alternated exemplary embodiment of steer-by wire system; 
     FIG. 9 is an alternate exemplary embodiment of a return to center mechanism of the steer-by wire system of FIG. 8, taken along circle  8 — 8 ; and 
     FIG. 10 is a sectional view of the center feel mechanism of FIG. 9, taken along lines  10 — 10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a drive-by-wire steering system  10  for use in a vehicle  11  is illustrated. The steering system  10  allows the operator of the vehicle  11  to control the direction of the road wheels  12  of the vehicle through the manipulation of a steering wheel  14 . The steering wheel  14  is operatively coupled to a steering column or shaft  16 . The steering column  16  is installed in a main housing  18  such that the column is rotatable within the housing. 
     The road wheels  12  are connected to knuckles  20 , which are in turn connected to tie rods  22 . The tie rods  22  are connected to a steering assembly  24 . The steering assembly  24  includes an electric motor  26  and a steering rod  28 . The steering rod  28  is operatively coupled to the electric motor  26  such that the motor is adapted to move the steering rod. The movement of the steering rod  28  controls the direction of the road wheels  12  through the knuckles  20  and tie rods  22  in a known manner. 
     One or more sensors  32  detect angular displacement or travel  30  of the steering column  16 , as well as detecting the torque of the angular displacement. The sensors  32  provide electric signals  34  to a controller  36  indicative of the angular displacement  30  and torque. The controller  36  sends and receives signals  40  to/from the electric motor  26  to actuate the electric motor in response to the angular displacement  30  of the steering wheel  14 . 
     In use, the steering wheel  14  is angularly displaced  30  such that the steering column  16  is also angularly displaced. The sensors  32  detect the angular displacement  30  of the column  16 , and the sensors send the signals  34  to the controller  36  indicative of the relative amount of the angular displacement of the column. The controller  36  sends the signals  40  to the motor  26  indicative of the relative amount of angular displacement  30 , which in turn laterally moves the steering rod  28 . Thus, the controller  36  controls the distance that the steering rod  28  is moved based on the amount of the angular displacement  30  of the column  16 . The movement of the steering rod  28  manipulates the tie rods  22  and knuckles  20  to reposition the road wheels  12  of the vehicle  11 . Accordingly, when the steering wheel  14  is turned, the road wheels  12  are turned. 
     In mechanical steering systems, the rotation of the steering wheel  14  is limited by the travel of the road wheels  12 . The travel of the road wheels is usually equal to a rotation of the steering wheel  14  of about 1.5 times in either direction. However, in the drive-by-wire steering system  10  the steering wheel  14  is mechanically isolated from road wheels  12 . Thus, in the drive-by-wire steering system  10  the rotation of the steering wheel  14  is not limited. 
     Now, it has been determined that limiting the rotation of the steering wheel  14  to about 1.5 times in either direction (e.g. about ±540°) is desirable. Also, limiting movement of the steering wheel  14  to about ±540° protects the sensors  32  from over rotation. 
     Referring now to FIG. 2, an exemplary embodiment of a drive-by-wire system  10  is shown. Here, the steering column  16  is rotatably mounted in the main housing  18  and a lower housing  42  by way of bearings  44 . The lower housing  42  has an upper portion  46  that is connected to a lower portion  48  of main housing  18 . For example, a bolt  50  secures the lower housing  42  and the main housing  18 . Of course other means of connection are contemplated. 
     The steering column  16  includes a geared portion  52  defined at its lower end  54 , namely at the end opposite the steering wheel  14 . The geared portion  54  is in operative contact with a center feel mechanism  56 . The center feel mechanism  56 , as well as the geared portion  52  of the steering column  16 , is housed within the lower housing  42 . 
     The lower end  54  of the steering column  16  is operatively coupled to a secondary shaft  58  by way of a torque sensor  60  having a torsion bar  62 . Additionally, position sensors  64  are operatively positioned proximate the steering column  16  and/or the secondary shaft  58  to detect the angular displacement  30  of the steering column and/or the secondary shaft, respectively. The sensors  60  and  64  provide the signals  34  to the controller  36 . 
     For example, the sensor  60  detects characteristics of the movement or angular rotation  30  of the steering column  16  by detecting the torque and speed of the angular displacement of the steering column. However, the sensor  60  operates within a predetermined range of motion. Namely, the sensor  60  typically has a range of motion of about ±540°. 
     The secondary shaft  58  is connected to an electric servomotor  66  through a planetary gear reducer  68 . The motor  66  is operatively connected to the controller  36 . The motor  66 , as controlled by controller  36 , is configured to angularly displace  30  the secondary shaft  58 , which in turn angularly displaces the steering column  16 . Accordingly, the steer-by-wire system  10  is configured to control the direction of the road wheels  12  without the manipulation of steering wheel  14  by the operator, and is configured to communicate road feel to the steering wheel  14 . 
     For example in an exemplary embodiment, the road wheels  12  include a sensor (not shown) configured to detect forces on the road wheels. The sensor provides signals to the controller  36  indicative of such forces on the road wheels  12 . The controller  36  actuates the motor  66  in response to such road forces to simulate road feeling on the steering wheel  14 . 
     Also, the motor  66  is used to return or help return the steering wheel  14  to its center position. For example, after turning the vehicle  11 , the operator typically releases the steering wheel  14 , expecting the steering wheel to return to its center position as in mechanical steering systems. Once the controller  36  detects via the sensors  60  and  64  that the operator has released the steering wheel  14 , the controller activates the servomotor  66  to return the steering wheel to its center position as expected. 
     However, the activation of the motor  66  consumes energy from the battery (not shown) of the vehicle  11 , and thus reduces the overall efficiency of the vehicle. Additionally, the motor  66  and the planetary gear reducer  68  add weight and expense to the vehicle  11 , and take up valuable space within the vehicle. 
     Now, it has been determined that the planetary gear reducer  68  can be eliminated and/or reduced in size by incorporating a center feel mechanism  56  into the drive-by-wire system  10 . Thus, the drive-by-wire steering system  10  have the center feel mechanism  56  eliminates the cost and weight of the planetary gear reducer  68 , and reduces the size of the steering system  10 , while eliminating many of the deleterious effects of mechanically isolating the steering wheel  14  from the road wheels  12 . Further, it has been determined that the motor  66  can be reduced in size and/or usage by incorporating the center feel mechanism  56  into the drive-by-wire system  10 . 
     A first exemplary embodiment of the center feel mechanism  56  is illustrated in FIGS. 2-7. The center feel mechanism  56  is configured to limit rotation of the steering wheel  14  and the steering column  16  to about 1.5 rotations (e.g., ±540°). The center feel mechanism  56  is configured to provide the steering column  16  with about 1080° of angular displacement  30 . Accordingly, the center feel mechanism  56  improves the feel of the steering system  10  by more closely mimicking the feel of mechanical steering systems, and prevents over rotation of the sensors  60  and  64 . 
     The center feel mechanism  56  includes a geared portion  68 , a cam face  70 , and a stop portion  72 . The center feel mechanism  56  defines a home or center position  74  (FIG.  5 ), a positive or rightmost position  76  (FIG. 7) and a negative or leftmost position  78  (FIG.  6 ). The stop portion  72  is defined within the geared portion  68 , and is located diametrically opposed from the center position  74 . Thus, the center feel mechanism  56  defines the positive position  76  and the negative position  78  on either side of the stop portion  72 , respectively. 
     The center feel mechanism  56  is rotatably mounted on a stop shaft  80  such that the geared portion  68  is engaged with the geared portion  52  of the column  16 . Accordingly, the angular displacement  30  of the steering wheel  14  is translated to center feel mechanism  56  by the geared portions  52  and  68 . The rotation of the column  16  about an axis or centerline  82  causes the geared portion  52  to drive the geared portion  68  such that the center feel mechanism  56  rotates about its center feel mechanism axis or centerline  84 . In sum, the rotation of the column  16  about its centerline  82  causes the geared portion  52  to impart rotation to the drive geared portion  68  such that the center feel mechanism  56  rotates about its centerline  84 . The rotation of the center feel mechanism  56  is limited when the center feel mechanism has rotated to the point where the column  16  abuts or interferes with the stop portion  72  at either the positive position  76  (FIG. 7) or the negative position  78  (FIG.  6 ). 
     Moreover, the geared portions  52  and  68  are configured such that rotation of the column  16  of about ±540° rotates the center feel mechanism  56  an angle  57  prior to the steering column abutting or interfering with stop portion  72 . In an exemplary embodiment, angle  57  is about ±140°. Thus, the angular displacement  30  of the steering wheel  14  of +540° rotates the center feel mechanism  56  +140° from the center position  74  to the positive position  76 . Conversely, the angular displacement  30  of the steering wheel  14  −540° rotates the center feel mechanism  56  −140° from the center position  74  to the negative position  78 . In sum, the steering column  16  has a total range of motion of about 1080° and the center feel mechanism  56  has a total range of motion of about 280°. 
     When the center feel mechanism  56  is in the position  74 , the steering wheel  14  is in its center or normal position. In this position, the road wheels  12  are pointed parallel to the vehicle  11  (e.g., line  86  in FIG.  1 ). However, the angular displacement  30  of the steering wheel  14  to its rightmost or positive position causes the center feel mechanism  56  to rotate to the positive position  76 . Here, the motor  26  moves the road wheels  12  via the steering assembly  24  such that the road wheels are pointed to the right (e.g., line  88  in FIG.  1 ). Similarly, the angular displacement  30  of the steering wheel  14  to its negative or leftmost position causes the center feel mechanism  56  to rotate to the negative position  78 . Again, at this point the motor  26  moves the road wheels  12  via the steering assembly  24  such that the road wheels  12  are pointed to the left (e.g., line  90  in FIG.  1 ). 
     Of course, it should be recognized that the center feel mechanism  56  is described above by way of example as being configured for the angular displacement  30  of the column  16  of about ±540° translating into rotation of the stop portion  72  of about ±140°. The center feel mechanism  56  being configured to provide alternate amounts of angular displacement for the steering wheel  14  and/or center feel mechanism  56  are contemplated. 
     The steering system  10  having the center feel mechanism  56  provides the drive-by wire steering system with the “feel” of a mechanical steering system. Thus, the steering system  10  improves the “drivability” or “feel” of the vehicles  11  having such drive-by-wire steering systems. Additionally, the steering system  10  having center feel mechanism  56  prevents over rotation of the sensors  60  and  64  beyond a predetermined limit. 
     As illustrated, the drive-by-wire steering system  10  controls the direction of both the front and rear sets of road wheels  12  of the vehicle  11 . However, control of only the front or rear set of road wheels  12  is contemplated. Additionally, the steering system  10  is illustrated controlling the front and rear set of road wheels in a similar direction. Of course, the steering system  10  controlling the front and rear set of road wheels  12  in a different direction, and/or controlling the front and rear set of road wheels in a similar different at some speeds, and a different direction at other speeds are contemplated. 
     Referring again to FIG. 5, an alternate embodiment of the center feel mechanism  56  is illustrated. Here, the stop portion  72  further includes adjustment screws  92  and  94  shown in phantom. The adjustment screws  92  and  94  are configured to provide the center feel mechanism  56  with the ability to adjust or calibrate the positive position  76  and the negative position  78 , respectively. The adjustment screws  92  and  94  are tightenable to the point where the screw(s) protrudes from the stop portion  72  (e.g., past geared portion  68 ). Conversely, the adjustment screws  92  and  94  are retractable to the point where the screw(s) does not protrude through the stop portion  72 . 
     Thus, with the adjustment screws  92  and  94  protruding past the geared portion  68  the rotation of the center feel mechanism  56  is limited when the center feel mechanism has rotated to the point where the column  16  abuts the adjustment screw  92  at the positive position  76  or the adjustment screw  94  at the negative position  78 . Alternately, with the adjustment screws  92  and  94  retracted to the point where the screw(s) do not protrude past the geared portion  68 , the rotation of the center feel mechanism  56  is limited when the center feel mechanism has rotated to the point where the column  16  abuts the stop portion  72  at the positive position  76  or the negative position  78 . In this manner, the adjustment screws  92  and  94  are configured to make fine tune or calibration type adjustments to angle  57 . Thus, in the example where the steering column  16  has a total range of motion of about 1080° and angle  57  of the center feel mechanism  56  of about 280°, the adjustment screws  92  and  94  are configured to make fine tune or calibration type adjustments to the angle  57  of about ±5°. 
     In sum, one aspect of the center feel mechanism  56  is that it provides the steering system  10  with the stop portion  72  to prevent over rotation of the sensors  60  and  64 , and more closely mimics a mechanical steering system by preventing infinite rotation of the steering wheel  14 . 
     Referring again to FIGS. 2-3, the center feel mechanism  56  also provides the steering system  10  with the ability to mimic or simulate a mechanical steering system by providing desired feedback to the steering wheel  14 . For example, the center feel mechanism  56  is configured to apply a returning torque (Tr) to the steering wheel  14 . The returning torque (Tr) has a direction opposite that of the angular displacement  30 . During a turn of the vehicle  11 , the returning torque (Tr) provides a resistance to the angular displacement  30  to mimic mechanical steering systems. The center feel mechanism  56  is configured such that the returning torque (Tr) applied to the steering wheel  14  by the center feel mechanism  56  is proportional to the degree of turn of the steering wheel to more closely mimic or simulate the “feel” of a mechanical steering system. Additionally, after the completion of a turn of vehicle  11 , returning torque (Tr) acts to return the center feel mechanism  56  to center position  74   
     The center feel mechanism  56  includes cam face  70  and an urging member  96 . The urging member  96  comprises a cam follower  98  biased into operative engagement with cam face  70 . Housing  42  includes an extension portion  100  extending radially outward therefrom. The cam follower  98  is rotatably mounted on a riser  102  by way of a bolt  104 . Thus, the cam follower  98  is rotatable about an axis  106  that is parallel to the centerline  84  of rotation of the center feel mechanism  56 . 
     A compression member  108  is retained in the extension portion  100  by way of a cap  110 . The riser  102  is slidably retained in the extension portion  100  such that the cam follower  98  is moves radially toward and away from the cam face  70 . The compression member  108  is exerts a spring force (Fo) on the riser  102  to bias the riser toward the cam face  70  such that the cam follower  98  is in operative engagement with the cam face. 
     The cam face  70  has a detent  112  defined at the center position  74  and a cam profile  114 . The cam profile  114  is defined on both sides of the detent  112 , and each side is preferably symmetrical to the other. The cam profile  114  is configured to translate the spring force (Fo) of the compression member  108  into the returning torque (Tr). 
     In use, the angular displacement  30  of the steering wheel  14  rotates the column  16  about its centerline  82  to cause the geared portion  52  to the drive geared portion  68 , which rotates the center feel mechanism  56  about its centerline  84 . The rotation of the center feel mechanism  56  about its centerline  84  causes the cam face  70  to act upon the cam follower  98 . The cam follower  98  rides along the cam profile  114  of the cam face  70  by overcoming the spring force (Fo) exerted by the compression member  108 . By overcoming the spring force (Fo) exerted by the compression member  108 , the riser  102  is slid radially away from the cam face, which further compresses the compression member and further increases the spring force (Fo). Thus, the spring force (Fo) of the compression member  108  is translated into the retuning torque (Tr) by the contact of the cam follower  98  and the cam profile  114 . 
     The action of the cam profile  114 , the detent  112 , and the compression member  108  create the returning torque (Tr) on the center feel mechanism  56 . Thus, the center feel mechanism  56  transmits the returning torque (Tr) to the column  16 . The returning torque (Tr) has the tendency to return and maintain the steering wheel  14  in position  74  providing the steering system  10  with a center feeling. 
     The cam profile  114  is configured to provide the returning torque (Tr) with a variable resistance as a function of the amount of the angular displacement  30  of the steering wheel  14 . Thus, the center feel mechanism  56  prevents and/or mitigates the feeling that drive-by-wire system  10  “over assists” by removing all of the force associated with turning the vehicle  11 , or even making the force required to turn the vehicle constant regardless of the degree of turn. Incorporating the center feel mechanism  56  into the drive-by-wire system  10  enables the elimination of and/or reduction in size of the planetary gear reducer  68 . Further, incorporating the center feel mechanism  56  into the drive-by-wire system  10  enables the reduction in size and/or usage of the motor  66 . 
     In an alternate embodiment, the cap  110  is secured to extension portion  100  by way of a thread  116 . The thread  116  is configured such that the cap  110  is adjustable to increase and/or decrease the force (Fo) with which the spring  102  biases the follower  98  into the cam face  70 . 
     A second exemplary embodiment of the center feel mechanism  56  is illustrated in FIGS. 8-10. 
     Again, the center feel mechanism  56  includes the cam face  70  and the urging member  96 . In this embodiment, the urging member  96  comprises two cam followers  98  biased toward the cam face  70 . The housing  42  includes an extension portion  100  extending radially outward therefrom. The cam followers  98  are rotatably mounted on the riser  102  by way of bolts  104 . Thus, the cam followers  98  are rotatable about axes  106  that are parallel to the centerline  84  of rotation of the center feel mechanism  56 . 
     The compression member  108  is retained in the extension portion  100  by way of the cap  110 . The riser  102  is slidably retained in the extension portion  100  such that the cam followers  98  move radially toward and away from the cam face  70 . The compression member  108  acts on the riser  102  to slide the riser toward the cam face  70 . Here, only one of the cam followers  98  is in operative engagement with the cam face  70 . 
     The cam profile  114  comprises three cam zones, namely a first zone  118 , a second zone  120 , and a third zone  122 . The first zone  118  runs along the cam face  70  between points  124 . The second zone  120  runs along the cam face  70  between point  124  and point  126 . The third zone  122  runs along the cam face  70  between point  126  and point  128 . 
     The first zone  118  has a constant radius from the centerline  84  of the center feel mechanism  56 . The center feel mechanism  56  is at starting position  74  when the cam followers  98  are positioned at points  124 , namely when the center feel mechanism is in the first zone  118 . The second zones  120  have a radius from the centerline  84  of the center feel mechanism  56  that increases sharply from point  124  to point  126 . However, the third zones  122  have a radius from the centerline  84  of the center feel mechanism  56  that increases mildly from point  126  to point  128 . 
     The zones  118 ,  120 , and  122  result in the cam profile  114  providing a variable return torque (Tr) to the steering wheel  14  depending upon the degree of the angular displacement  30 . The angular displacement  30  of the steering wheel  14  rotates the column  16  about its centerline  82  such that the center feel mechanism  56  rotates about its centerline  84 . The rotation of the center feel mechanism  56  causes the cam face  70  to act upon the cam followers  98 . The leading cam follower  98  (i.e., the cam follower in the direction of rotation) rides along the cam profile  114  of the cam face  70  by overcoming the spring force (Fo) exerted by the compression member  108 . This slides the riser  102  radially away from the cam face  70 . At this point, the trailing cam follower  98  (i.e., the cam follower opposite to the direction of rotation) is no longer in contact with the cam face  70 . Thus, the spring forces (Fo) of the compression member  108  are transferred only at the cam follower  98  in contact with the cam face  70 . 
     The returning torque (Tr) is equal to the spring force (Fo) of the compression member  108  multiplied by the distance (X) the spring force is applied from centerline  84  (e.g., Tr=Fo*X). As provided above, the zones  118 ,  120 , and  122  of the cam profile  114  have differing radii, which increase from point  124  to point  128 . In use, the angular displacement  30  of the center feel mechanism  56  causes the compression member  108  to be compressed an amount corresponding to the increase in the radii of the cam profile  114 . Thus, the spring force (Fo) of the compression member  108  increases as the cam followers  98  are rotated along the cam profile  114 . This causes a corresponding increase in the retuning torque (Tr) as the cam followers  98  are rotated along the cam profile  114  away from the center position. 
     Accordingly, the action of the cam profile  114  and the compression member  108  create the returning torque (Tr) on the center feel mechanism  56 . The returning torque (Tr) on the center feel mechanism  56  provides the steering system  10  with the tendency to return and maintain the steering wheel  14  in the center position  74 . Additionally, the returning torque (Tr) on the center feel mechanism  56 , which increases as the mechanism is angularly rotated  30  from position  74  towards positive or rightmost position  76  and negative or leftmost position  78 , provides the steering system  10  with a feel that more closely mimics that of a mechanical steering system. 
     For example, a return torque (Tr) of about 1 Newton-meter (nm) is required to move center feel mechanism  56  from first zone  118 . The angular rotation  30  of the steering wheel  14  from the first zone  118  to the end of second zone  120  (e.g. about ±300° of steering wheel  14  rotation) causes a subsequent increase in the torque from 1 nm to about 3 nm. Finally, the retuning torque (Tr) increases from about 3 nm to about 4.5 nm from the end of second zone  120  to the end of third zone  122  (e.g., about ±300° to about ±540° of steering wheel  14  rotation). It should be recognized that the returning torques (Tr) provided above for the zones  118 ,  120 , and  122  are provided by way of example only. Of course larger or smaller returning torques, more or less cam zones, and the like are contemplated. 
     It is seen that the center feel mechanism  56  is configured to provide the returning torque (Tr) with a variable resistance as a function of the amount of angular displacement  30  of the steering wheel  14 . Thus, the center feel mechanism  56  prevents and/or mitigates the feeling that the drive-by-wire system  10  “over assists” the driver by removing all of the force associated with turning the vehicle  11 . Further, the center feel mechanism  56  prevents and/or mitigates the feeling that the drive-by-wire system  10  “over assists” the driver by making the force required to turn the vehicle constant regardless of the degree of turn. Accordingly, incorporating the center feel mechanism  56  into the drive-by-wire system  10  enables the elimination of and/or reduction in size of the planetary gear reducer  68 . Further, incorporating the center feel mechanism  56  into the drive-by-wire system  10  enables the reduction in size and/or usage of the motor  66 . 
     In an alternate embodiment, the cap  110  is secured to the extension portion  100  by way of the thread  116 . The thread  116  is adjustable to increase and/or decrease the spring force (Fo) with which the compression member  108  biases the follower  98  into the cam face  70 . More specifically, the compression member  108  is preloaded to a higher spring force (Fo) by tightening the cap  110  (e.g., towards the center feel mechanism  56 ), and the compression member is relaxed to a lower spring force (Fo) by loosening the cap (e.g., away from the center feel mechanism  56 ). 
     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.