Abstract:
A hand wheel actuator having a stationary hub is provided by a housing supporting a first shaft via bearings such that it is rotatable about its own axis. The first shaft has an upper end configured for attaching a hand wheel. The actuator also includes a position sensor for detecting an angular displacement of the first shaft from a selected origin and producing a signal indicative of said angular displacement and an electric motor in operative communication with the first shaft for providing feedback to a driver. A steering post is maintained in a fixed position with respect to the housing for maintaining the hub in a fixed position centrally of said hand wheel, so that the hub faces the driver when said hand wheel is operated. The steering post extends along an axis of rotation of the hand wheel and through the first shaft, which is fixed to the hand wheel and rotates therewith.

Description:
TECHNICAL FIELD  
         [0001]    This disclosure relates to a hand wheel actuator for a steer-by-wire system of an vehicle. More particularly, the disclosure relates to a hand wheel actuator having a stationary hub.  
         BACKGROUND  
         [0002]    Automobiles are conventionally equipped with a pair of front road wheels that are steered to enable the vehicle to turn left and right as it maneuvers on land. It is also known to provide actuators for steering rear wheels in automobiles. Vehicle steering systems commonly employ a mechanical connection between the driver-operated hand wheel and the front road wheels of an automotive vehicle. As the driver rotates the hand wheel, a mechanical linkage through the vehicle&#39;s tie-rods actuate the road wheels sometimes with the assistance of a power assist steering motor or hydraulic piston. The term, “hand wheel” as used herein refers to a driver-operated rotating steering input device, but it need not be round or wheel shaped, though that is the most common configuration.  
           [0003]    Recently, steer-by-wire steering systems have been introduced into automotive vehicles to provide road wheel steering function. Included in a typical steer-by-wire steering system is a hand wheel actuator for monitoring the angular position of the steering wheel, and road wheel motor actuators, which are controlled by controllers in response to tracking the sensed angular displacement of the hand wheel from a central or other position. In contrast to prior steering systems, the steer-by-wire steering system does not employ a mechanical linkage between the steering wheel and the individual road wheels. Exemplary of such known steer-by-wire systems is commonly-assigned U.S. Pat. No. 6,176,341, issued Jan. 23, 2001 to Ansari, which is incorporated herein by reference in its entirety.  
           [0004]    Along with the advent of steer-by-wire systems, automobile purchasers are always expecting an increased level of driver comfort and convenience. The desirability of placing some instruments, such as environmental and audio system controls on or near the steering wheel has long been recognized. Such controls are currently placed in various locations around the steering wheel, such as along a spoke or integrated in a multi-function stalk switch. As the sophistication of automobile electronics increases, and with the increased popularity of such systems as mobile communications, Global Positioning Satellite (GPS) systems and electronic maps, the locations available to place such controls and displays are not adequate, particularly since any control or display mounted on the hub or spoke of the steering wheel (over the airbag, for example) would turn with the steering wheel and therefore not be useful unless traveling in a relatively straight line.  
           [0005]    Accordingly, there is perceived a need for a steering wheel assembly having a stationary hub so that electronic controls and displays are viewable and conveniently provided.  
         SUMMARY  
         [0006]    The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by providing a hand wheel actuator having a stationary hub, including a housing supporting a first shaft via bearings such that it is rotatable about its own axis. The first shaft has an upper end configured for attaching a hand wheel. The actuator also includes a position sensor for detecting an angular displacement of the first shaft from a selected origin and producing a signal indicative of said angular displacement and an electric motor in operative communication with the first shaft for providing feedback to a driver. A steering post is maintained in a fixed position with respect to the housing for maintaining the hub in a fixed position centrally of said hand wheel, so that the hub faces the driver when said hand wheel is operated. The steering post extends along an axis of rotation of the hand wheel and through the first shaft, which is fixed to the hand wheel and rotates therewith.  
           [0007]    The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The present invention will now be described by way of example with reference to the accompanying drawings, in which:  
         [0009]    [0009]FIG. 1 shows a schematic overview of a steer-by-wire system;  
         [0010]    [0010]FIG. 2 shows a first embodiment of a hand wheel actuator having a stationary hub;  
         [0011]    [0011]FIG. 3 shows a second embodiment of a hand wheel actuator having a stationary hub;  
         [0012]    [0012]FIG. 4 shows a third embodiment of a hand wheel actuator having a stationary hub;  
         [0013]    [0013]FIG. 5 shows a fourth embodiment of a hand wheel actuator having a stationary hub;  
         [0014]    [0014]FIG. 6 shows a fifth embodiment of a hand wheel actuator having a stationary hub;  
         [0015]    [0015]FIG. 7 shows a sixth embodiment of a hand wheel actuator having a stationary hub; and  
         [0016]    [0016]FIG. 8 shows a schematic view of a return-to-center device of FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    [0017]FIG. 1 shows a schematic overview of an exemplary steer-by-wire system for a vehicle. Driver input is made to hand wheel  12 , which is connected by upper shaft  13  to hand wheel actuator  10 . Hand wheel actuator  10  includes a position sensor for detecting the angular displacement of hand wheel  12 . The position sensor output is directed to electronic control unit  20 , which includes a microprocessor and other assorted electronic components well known in the field of electronic control for providing memory, input/output, and processing functions. Electronic control unit  20  receives signals from hand wheel position sensors in hand wheel actuator  10  and determines what signals, if any, to send to road wheel actuator  17  so that the position of road wheels  19  (only one shown) properly correspond with the position of hand wheel  12 . Road wheel actuator  17  controls the steering position of road wheels  19  by means of a tie-rod  18 .  
         [0018]    Road wheel actuator  17  includes torque or strain sensors to measure force required by road wheel actuator  17  to rotate and maintain road wheels  19  in their desired position. Output from road wheel torque sensors (not shown) is transmitted to electronic control unit  20 , which then transmits driver feedback information to hand wheel actuator  10 . Hand wheel actuator  10  includes an electric motor or other actuator to provide force-feedback to steering wheel  12 , thus giving the driver feedback as to the road conditions. Hand wheel actuator  10  may also include a torque sensor for providing a signal to the electronic control unit to ensure that the driver is receiving the correct amount of driver feedback.  
         [0019]    [0019]FIG. 2 shows a first embodiment of a hand wheel actuator having a stationary hub. Hand wheel  12  is rigidly connected via one or more spokes  22  to arm  24  via first shaft  71  integrally formed therewith. While first shaft  71  and arm  24  are shown as being integrally formed, they may of course be constructed from separate components. First shaft  71  includes a central opening  26  through which post  25  extends, and serves to transmit force from hand wheel  12  to upper shaft  13  via arm  24 . Post  25  is fixed to actuator housing  30 , supports stationary hub  15  at one end thereof, the hub being fixed by nut  32 . Instrument cable  16  extends from hub  15  through channel  14  to additional electronics positioned behind the dashboard (not shown).  
         [0020]    As noted previously, arm  24  transmits force exerted on hand wheel  12  to upper shaft  13 . Upper shaft  13  contains a torsion bar  38 . Upper shaft  13  and torsion bar  38  are fixed with respect to each other at a first end  33  of upper shaft  13 . At a lower end, torsion bar  38  is fixed to lower shaft  36 . Upper shaft  13  and lower shaft  36  together make up steering shaft  55 . Torque/position sensor  39  detects the displacement between upper shaft  13  and lower shaft  36  caused by torquing of torsion bar  38  and translates this into toque information. Torque/position sensor  39  also determines a displacement angle of upper shaft  13  and/or lower shaft  36  to indicate position. The torque and angular displacement signals are transmitted to electronic control unit (ECU)  20 . ECU  20  receives the torque and angular displacement signals, as well as other signals such as, for example, vehicular speed and sensors at road wheels  19  (FIG. 1, only one shown) and outputs driving signals for road wheel steering actuator  17  (FIG. 1). ECU also uses feedback from one or more torque sensors in road wheel actuator  17  to calculate the necessary driver feedback torque. This calculation is translated into a motor input signal that is provided to motor  40 . Motor  40  imparts a torque against lower shaft  36  via worm  42  mounted or formed into the output shaft of motor  40 , and worm gear  44 , which is fixed to lower shaft  36 . Note that torque/position sensor provides torque feedback to ECU  20  for closed-loop control of driver feedback.  
         [0021]    Hand wheel actuator  10  includes a spring-biased mechanical return-to-center device  90 . With this device, rotational motion of lower shaft  36  is transmitted to ball screw  54  via pin  51 . As ball screw  54  rotates, ball nut  58  is permitted only to slide longitudinally. Spring adapter  92  is fixed to ball nut  58 , telescoping over ball screw extension  64 .  
         [0022]    Compression spring  95  is constrained between spring washers  93  and  94 . Spring washer  93  is limited from moving right as seen in FIG. 2 by either shoulder  91  of spring adapter  92  or shoulder  53  of housing  52 . Spring washer  94  is limited from moving left as seen in FIG. 2 by either nut  96  attached to end of spring adapter  92  or lip  99  of cover  98 . When ball nut  58  moves to the right from the center position shown in FIG. 2, nut  96  and spring washer  94  move with it, while spring washer  93  remains fixed against shoulder  53  of housing  52 . The spring compresses causing increased resistance the farther ball nut  58  is moved from center. On the other hand, when ball nut  58  moves left from the central position shown in FIG. 2, spring washer  93  is pushed to the left by shoulder  91  of spring adapter  92  while spring washer  94  remains fixed against lip  99  of cover  98 . The spring again compresses, causing increased resistance the farther ball nut  58  is moved from center. A mechanical return-to-center device  90  will bias the steering wheel towards the center position at all times. A ball plunger  55  may also be employed for improving driver feel at center. Ball plunger  55  cams against the outer surface of spring adapter  92 , which is shaped for a desirable center-feel.  
         [0023]    With the embodiment shown in FIG. 2, rotational motion of hand wheel  12  is limited to less than 180° from center in either direction by housing  30 , which supports post  25 . Although so limited, arm  24  provides a low cost, reliable, and effective connection between the hand wheel  12  and upper shaft  13 , while permitting hub  15  as well as electronics cables  16  to remain stationary. Furthermore, arm  24  provides a solid connection between hand wheel  12  and upper shaft  13 , which reduces turning resistance and improves overall driver feel.  
         [0024]    [0024]FIG. 3 shows a second embodiment. In this embodiment, as in the remaining embodiments to be described below, a hand wheel actuators including a fixed hub is configured such that the hand wheel is permitted to rotate in excess of 180° in either direction, e.g., they can provide a steering wheel rotation of ±540° rotation (i.e., one and one-half revolution in either direction) as in traditional mechanical steering systems. In this embodiment, hand wheel  12  is fixed to first shaft  71 , which includes conical gear  72 . Conical gear  72  is fixed to first shaft  71  or formed integrally therewith, as shown. Conical gear  72  engages second conical gear  73 , which is fixed to spindle  75  and supported by bearings  74 . While conical gear  72  and second conical gear  73  are arranged about 90 degrees with respect to each other, this is not a requirement, and other angles are possible. If a different angle is employed, the axis of upper shaft  13  may be angularly displaced, or some gear reduction may occur between first shaft  71  and upper shaft  13 .  
         [0025]    Second conical gear  73  engages third conical gear  76 , which is fixed to upper shaft  13 . The remaining apparatus is structurally and functionally similar to the first embodiment previously described. However, since housing  30  does not limit rotation of hand wheel  12 , stopper  50  is provided to limit rotation. Stopper  50  operates as a positive travel end stop and comprises ball screw  54  connected to lower shaft  36  by pin  51 . Ball nut  58  engages ball screw  54  and travels linearly along the axis of ball screw  54 . Rotation of ball nut  58  is prevented by bosses  61 , which slide in slots  56  formed in housing  52 . Bumpers  62  are optionally provided in slots  56  to provide rapidly increased resistance at the positive travel limits, thereby improving steering feel.  
         [0026]    In operation, hand wheel rotates first shaft  71  which rotates conical gear  72 . Conical gear  72 , second conical gear  73 , and third conical gear  76  are arranged series so that when conical gear  71  rotates in a first direction, conical gear  76  will rotate in an opposite direction around the common axis. Note that there is no requirement that the hand wheel axis and upper shaft axis be coincident. Using different sized gears or varying relative angles between them can customize the configuration of the actuator to any specific application.  
         [0027]    Upper shaft  13 , torsion bar  38 , lower shaft  36 , torsion/position sensor  39 , electronic control unit  20 , worm gear  44 , pin  51 , ball screw  54 , ball nut  58  and return-to-center device  90  all operate as described above with respect to the first embodiment shown in FIG. 2. As ball nut  58  slides to the left and right as seen in FIG. 3, it engages bumpers  62  positioned at either end of slots  56 , thereby limiting the linear movement of ball nut  58 . When ball nut  58  reaches one limit of movement, it prevents further rotation of ball screw  54 , which prevents further rotation of lower shaft  36 , upper shaft  13 , third conical gear  76 , second conical gear  73 , conical gear  72 , first shaft  71  and therefore hand wheel  12 . Preferably, slots  56  are sized to permit a maximum rotation of 540° (one and a half revolutions) from center in either direction.  
         [0028]    [0028]FIG. 4 shows a third embodiment. Differences between the second and third embodiments will be described. In this embodiment, spokes  22  of hand wheel  12  are integrally formed with shaft  81 , which is supported by bearings  83 . First gear  82  is fixed to shaft  81  and engages second gear  84 , which is fixed to upper shaft  13 . As can be seen, steering axis  86  and axis  87  of upper shaft  13  are parallel but not coincident. Motor  40  engages lower shaft  36  by means of a motor pulley  46 , belt  47 , and lower shaft pulley  48 . This pulley/belt configuration has the advantage of quieter operation and no possibility of backlash resulting from worm  42  and worm gear  44  of previous embodiments, and therefore has the potential for improved performance. In other respects the third and second embodiment are structurally and functionally similar.  
         [0029]    [0029]FIG. 5 shows a fourth embodiment which is similar to the third embodiment shown in FIG. 4, with the exception that first gear  82  is an inside gear formed inside first shaft  71 . First gear  82  engages second gear  84  which is fixed to upper shaft  13 .  
         [0030]    Because of second gear  84  is somewhat smaller than first gear  82 , steering axis  86  is just offset from axis  87  of upper shaft  13 . Post support  31 , which is fixed to housing  30 , extends through the gap between first gear  82  and second gear  84  to fixedly support post  25  and thereby maintain hub  15  in a stationary position. Post support  31  also supports bearings  21  which rotatably support first shaft  71 . Instrument cable  16  passes from hub  15  through post  25 , through post support  31 , and then to any associated electronic components (not shown). In all other respects the fourth embodiment is structurally and functionally similar to the previous embodiment.  
         [0031]    [0031]FIG. 6 shows a fifth embodiment of the invention. In this embodiment, hand wheel  12  is mounted to a first shaft  71 , which is supported by bearings  21  over post  25 , and a steering pulley  27  is formed into or attached to first shaft  71 . A steering belt  28  engages steering pulley  27  and upper shaft pulley  29  so that motion and force is transmitted from first shaft  71  to upper shaft  13 . This pulley/belt configuration has the advantage of quieter operation and no possibility of backlash resulting from gear interactions of previous embodiments, and therefore has the potential for improved performance. In other respects, the fifth embodiment is similar to the first and second embodiments.  
         [0032]    [0032]FIG. 7 shows a sixth embodiment of the invention. In this embodiment, rather than post  25  providing support for shaft  71  as in previous embodiments, shaft  71  is supported by bearings which are directly supported by housing  30 , and hub  15  is supported by shaft  71  via bearings  23 . Post  25  extends through shaft  71  and serves only as a conduit for instrument cable  16  and to maintain hub  15  in a fixed position, i.e., prevent hub  15  from rotating with shaft  71 .  
         [0033]    Shaft  71  includes a steering pulley  27  mounted thereon which, along with pulley  29  on upper shaft  13  and steering belt  28 , provide a means for placing first shaft  71  and upper shaft  13  into operable communication with each other. Other means, such as those described herein with respect to previous embodiments can easily be used in place of steering belt  28 . This embodiment includes torque/position sensor  39  and redundant position sensor  41  that directly measures the position of first shaft  71 .  
         [0034]    Return-to-center device  110 , shown in FIG. 7 and schematically in FIG. 8, includes a cam gear  120  mounted to an pin  122 , which is positioned parallel to lower shaft  36 . Lower shaft  36  includes a pinion  122  that interfaces with internal gear teeth  124 . Cam gear  120  includes a camming surface  126 .  
         [0035]    A cam follower  112  is fixed to housing  30  and positioned to engage camming surface  126 . Cam follower  112  comprises a housing  111  that is generally cylindrically shaped and containing spring  117 . Spring  117  is in compression and biases cam  116  towards camming surface  126 . Cam  116  includes a bearing surface  118  formed from a low friction material such as an acetal resin. An adjustable cam stop  114  is threaded to housing  111  on a side opposite said cam to adjust the compression force exerted by spring  117 .  
         [0036]    Cam surface  126  is represented in FIG. 8 as circular that has a center displaced from the center of rotation defined by pin  122 . However, the cam may have other shapes corresponding to an optimized return-to center feel for the driver.  
         [0037]    Cam gear  120  includes stop surfaces  128  to prevent cam gear  120  from rotating past a selected point, thereby also providing an absolute stop function as discussed above with respect to the second embodiment shown in FIG. 3.  
         [0038]    As used herein, the terms, “first”, “second”, “third”, etc., are used only to distinguish among various similar elements and not to designate an order in terms of position or importance.  
         [0039]    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 and not limitation.