Abstract:
A drive-by wire steering system is provided. The steering system comprises a steering shaft and a stop mechanism. The steering shaft is configured for a first angular displacement about a first axis. The steering shaft comprises a first geared portion and a first end. The first end is connectable to a vehicle&#39;s steering wheel. The stop mechanism comprises a stop portion and a second geared portion. The stop portion defines a first position and a second position. The first geared portion and the second geared portion are operatively engaged such that angular displacement of the steering shaft imparts a second angular displacement about a second axis to the stop mechanism. The first angular displacement is limited when the second angular displacement is such that the steering shaft abuts the stop portion at either the first position or the second position.

Description:
TECHNICAL FIELD  
         [0001]    This disclosure relates generally to drive-by-wire steering systems. More specifically, this disclosure relates to drive-by-wire steering systems having a stop mechanism.  
         BACKGROUND  
         [0002]    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.  
           [0003]    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 actuator.  
           [0004]    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.  
           [0005]    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.  
           [0006]    Unfortunately, mechanically isolating the steering wheel from the road wheel also eliminates desired feed back. For example, during the use of mechanical steering systems, the rotation of the steering wheel is mechanically limited by the travel of the road wheels of the vehicle. Unfortunately, the mechanical isolation provided by drive-by-wire steering systems eliminates this desired feedback.  
         SUMMARY  
         [0007]    A drive-by wire steering system is provided. The steering system comprises a steering shaft and a stop mechanism. The steering shaft is configured for a first angular displacement about a first axis. The steering shaft comprises a first geared portion and a first end. The first end is connectable to a vehicle&#39;s steering wheel. The stop mechanism comprises a stop portion and a second geared portion. The stop portion defines a first position and a second position. The first geared portion and the second geared portion are operatively engaged such that angular displacement of the steering shaft imparts a second angular displacement about a second axis to the stop mechanism. The first angular displacement is limited when the second angular displacement is such that the steering shaft abuts the stop portion at either the first position or the second position.  
           [0008]    A method is provided for protecting a sensor in a drive-by wire steering system where the sensor has a predetermined displacement range. The method includes connecting the sensor to a steering shaft, engaging a stop mechanism to the steering shaft, and abutting the stop mechanism and the steering shaft at a first position and a second position to limit the angular displacement of the steering shaft such that the sensor is maintained within the predetermined displacement range. The steering shaft is configured for a first angular displacement about a first axis. The stop mechanism is engaged to the steering shaft such that the first angular displacement imparts a second angular displacement about a second axis to the stop mechanism. The first angular displacement is greater than the second angular displacement.  
           [0009]    A method is provided for improving the driveability of a drive-by wire steering system. The method includes engaging a stop mechanism and a steering shaft such that a first angular displacement of the steering shaft about a first axis imparts a second angular displacement about a second axis to the stop mechanism. The first angular displacement is greater than the second angular displacement. The method also includes limiting the first angular displacement by an interference of the stop mechanism with the steering shaft at a first position and a second position such that a range of motion is provided to the drive-by wire steering system that mimics a mechanically linked steering system range of motion.  
           [0010]    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  
       [0011]    [0011]FIG. 1 is a schematic view of a steer-by wire system for a vehicle;  
         [0012]    [0012]FIG. 2 is a sectional view of an exemplary embodiment of steer-by wire system;  
         [0013]    [0013]FIG. 3 is an exemplary embodiment of a stop mechanism of the steer-by wire system of FIG. 2, taken along circle  3 - 3 ;  
         [0014]    [0014]FIG. 4 is a sectional view of the stop mechanism of FIG. 3, taken along lines  4 - 4 ;  
         [0015]    [0015]FIG. 5 is a view of the stop mechanism of FIG. 4 in a first position;  
         [0016]    [0016]FIG. 6 is a view of the stop mechanism of FIG. 4 in a second position; and  
         [0017]    [0017]FIG. 7 is a view of the stop mechanism of FIG. 4 in a third position.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    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.  
         [0019]    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.  
         [0020]    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  26  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 .  
         [0021]    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 signals  34  to the controller  36  indicative of the relative amount of angular displacement of the column. The controller  36  sends signals  40  to the motor  26  indicative of the relative amount of the angular displacement  30 . In response, the motor  26  moves the steering rod  28  laterally so that the road wheels  12  are turned. 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 . Movement of the steering rod  28  manipulates the tie rods  22  and knuckles  20  to reposition the road wheels  12  of vehicle  11 . Accordingly, when the steering wheel  14  is turned, the road wheels  12  are turned.  
         [0022]    In mechanical steering systems, rotation of the steering wheel  14  is limited by the travel of the road wheels  12 . The steering wheel  14  in such mechanical systems is usually configured to rotate 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, the rotation of the steering wheel  14  is not limited in the drive-by-wire steering system  10 .  
         [0023]    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. It has also been determines that limiting the movement of the steering wheel  14  to about ±540° protects the sensors  32  from over rotation.  
         [0024]    Referring now to FIG. 2, an exemplary aspect of a drive-by-wire system  10  is shown. Here, the steering column  16  is rotatably mounted in the main housing  18  and a stop housing  42  by way of bearings  44 . The stop housing  42  has an upper portion  46  that is connected to a lower portion  48  of the main housing  18 . For example, a bolt  50  secures the stop housing  42  and the main housing  18 . Of course, other means for connection the stop housing  42  and the main housing  18  are contemplated.  
         [0025]    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 stop mechanism  56 . The stop mechanism  56 , as well as the geared portion  52  of the steering column  16  are housed within the stop housing  42 .  
         [0026]    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 controller  36 .  
         [0027]    For example, the sensor  60  detects characteristics of the movement of and/or the 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°.  
         [0028]    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 the 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 road wheels  12  without the manipulation of steering wheel  14  by the operator.  
         [0029]    For example in an exemplary embodiment, the road wheels  12  include a sensor (not shown) configured to detect forces on the road wheels. The sensors  60  and/or  64  provide 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 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.  
         [0030]    The stop mechanism  56  is illustrated in FIGS.  3 - 7 . The stop 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 stop mechanism  56  is configured to provide the steering column  16  with about 1080° of angular displacement  30 . Accordingly, the stop mechanism  56  is configured to improve the feel of the steering system  10  by more closely mimicking mechanical steering systems, and is configured to prevent over rotation of the sensors  60  and  64 .  
         [0031]    The stop mechanism  56  includes a geared portion  68 , a cam face  70 , and a stop portion  72 . The stop 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 stop mechanism  56  defines the positive position  76  and the negative position  78  on either side of the stop portion  72 , respectively.  
         [0032]    The stop 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 the stop mechanism  56  by the geared portions  52  and  68 . Thus, 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 stop mechanism  56  rotates about a stop mechanism axis or centerline  84 . In sum, the rotation of the column  16  about the centerline  82  causes the geared portion  52  to impart rotation to drive the geared portion  68  such that the stop mechanism  56  rotates about its centerline  84 . The rotation of the stop mechanism  56  is limited when the stop mechanism has rotated to the point where the column  16  abuts or interferes with the stop portion  72  at either positive position  76  (FIG. 7) or negative position  78  (FIG. 6).  
         [0033]    Moreover, the geared portions  52  and  68  are configured such that rotation of the column  16  about ±540° rotates the stop 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 stop mechanism  56  +140° from the center position  74  to the positive position  76 . Conversely, the angular displacement  30  of the steering wheel  14  of −540° rotates the stop 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 stop mechanism  56  has a total range of motion of about 280°.  
         [0034]    When the stop mechanism  56  is in the center 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 stop 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 stop 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 are pointed to the left (e.g., line  90  in FIG. 1).  
         [0035]    Of course, it should be recognized that the stop mechanism  56  is described above by way of example as being configured for angular displacement  30  of column  16  of about ±540° translating into rotation of the stop portion  72  of about ±140°. The stop mechanism  56  being configured to provide alternate amounts of angular displacement for the steering wheel  14  and/or stop mechanism  56  are contemplated.  
         [0036]    The steering system  10  having the stop mechanism  56  provides the drive-by wire steering system with the “feel” of a mechanical steering system. Namely, the stop mechanism  56  provides a mechanical stop in the steering system  10  to provide the “feel” of a mechanical steering system. Thus, steering system  10  improves the “driveablity” or “feel” of vehicles  11  having such drive-by-wire steering systems. Additionally, the steering system  10  having the stop mechanism  56  protects the sensors  60  and  64  from over rotation beyond a predetermined limit.  
         [0037]    As illustrated, the drive-by-wire steering system  10  controls the direction of both the front and rear sets of road wheels  12  of 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.  
         [0038]    Referring again to FIG. 4, an alternate aspect of the stop 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 stop 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) do not protrude through the stop portion  72 .  
         [0039]    Thus, with adjustment screws  92  and  94  protruding past geared portion  68  the rotation of the stop mechanism  56  is limited when the stop mechanism has rotated to the point where column  16  abuts adjustment screw  92  at the positive position  76  or the adjustment screw  94  at 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 stop mechanism  56  is limited when the stop 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 the stop mechanism  56  has a total range of motion of about 280°, the adjustment screws  92  and  94  are configured to make fine tune or calibration type adjustments to the range of motion of the stop mechanism  56  by about ±5°.  
         [0040]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.