Abstract:
A differential steering actuator including an input shaft, an output shaft, a motor in operable communication with a vehicle sensor and a differential gear element, wherein the differential gear element is communicated with the input shaft, and the motor so as to translate motion of the input shaft into motion of the output shaft.

Description:
BACKGROUND  
         [0001]    Conventional vehicular steering systems have an articulated mechanical linkage connecting an input device (e.g., steering wheel or hand-wheel) to a steering actuator (e.g., steerable road wheel). Even with power assisted steering in an automobile, for example, a typical hand-wheel motion directly corresponds to a resulting motion of the steerable road wheels, substantially unaffected by any assist torque.  
           [0002]    This can be seen by referring to FIG. 1. As shown in FIG. 1, a conventional steering system with hydraulic assist, such as that disclosed in U.S. Pat. No. 4,454,801, issued Jun. 19, 1984 to Spann, assigned to the present assignee and wholly incorporated by reference herein, and U.S. Pat. No. 4,828,068, issued May 9, 1989 to Wendler et al., also assigned to the present assignee and wholly incorporated by reference herein, is indicated generally by the reference numeral  10 . An intermediate shaft  13  is mechanically linked at an upper end to a hand-wheel. The shaft  13  is fixed at its lower end to a hydraulic valve  12  and a pinion gear element  20 , wherein intermediate shaft  13  and pinion gear element  20  include a torsion bar. As the shaft  13  is rotated by the hand-wheel, it causes the torsion bar to twist, thereby actuating a hydraulic system  16  to generate complimentary pressure in a cylinder  18  that urges a piston  22 , which is fixed to a rack  30 , in the desired direction, thus reducing torque on the pinion  20  and reducing the effort required by the driver. The piston  22  and the rack  30  are formed integrally with a steering rod  25 , which includes two ball-joints  24  at either end thereof. The ball-joints  24  provide a connection to a pair of tie-rods  26 , which are connected to steerable wheel assemblies in the known manner for turning the steerable wheels of a vehicle.  
           [0003]    However, for a vehicular steering system with active steering, such as that used in an automotive front-controlled steering system, a given motion of the hand-wheel may be supplemented by an additional motion, such as that from a differential steering actuator, which translates into a motion of the steerable road wheels that does not necessarily correspond to the given motion of the hand-wheel. Consequently, when the differential steering actuator is inactive, the motion of the steerable road wheels directly corresponds to the hand-wheel motion due to the articulated mechanical linkage, just as in conventional systems.  
           [0004]    The term “active steering” relates to a vehicular control system which generates an output that is added to or subtracted from the front steering angle, wherein the output is typically responsive to the yaw and/or lateral acceleration of the vehicle. It is known that, in some situations, an active steering control system may react more quickly and accurately than an average driver to correct transient handling instabilities. In addition, active steering can also provide for variable steering ratios in order to reduce driver fatigue while improving the feel and responsiveness of the vehicle. For example, at very low speeds, such as that which might be experienced in a parking situation, a relatively small rotation of the hand-wheel may be supplemented using an active steering system in order to provide an increased steering angle to the steerable road wheels.  
           [0005]    Conventional hydraulic and electric power-assisted steering systems generally lack an active element for providing control over the steering angle independent of a driver&#39;s input. This is because prior attempts at adding such an active element have not integrated well with existing systems and/or create too much torque feedback to the driver during active steering control.  
         SUMMARY  
         [0006]    A differential steering actuator comprising: an input shaft; an output shaft; a motor in operable communication with a vehicle sensor; and a differential gear element, wherein the differential gear element is communicated with the input shaft, the output shaft and the motor so as to translate motion of the input shaft into motion of the output shaft.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Referring now to the drawings wherein like elements are numbered alike in the several figures:  
         [0008]    [0008]FIG. 1 shows a conventional steering system having a hydraulic assist;  
         [0009]    [0009]FIG. 2 shows a differential steering actuator in accordance with a first embodiment;  
         [0010]    [0010]FIG. 3 shows a top down cross sectional view of a differential steering actuator in accordance with a first embodiment;  
         [0011]    [0011]FIG. 4 shows a differential steering actuator in accordance with a second embodiment;  
         [0012]    [0012]FIG. 5 shows a differential steering actuator for use in an active steering system with electric assist in accordance with a third embodiment;  
         [0013]    [0013]FIG. 6 shows a differential steering actuator in accordance with a fourth embodiment;  
         [0014]    [0014]FIG. 7 shows a differential steering actuator in accordance with a fifth embodiment;  
         [0015]    [0015]FIG. 8 shows a differential steering actuator in accordance with a sixth embodiment;  
         [0016]    [0016]FIG. 9 shows a differential steering actuator in accordance with a seventh embodiment;  
         [0017]    [0017]FIG. 10 shows a differential steering actuator in accordance with an eighth embodiment; and  
         [0018]    [0018]FIG. 11 shows an alternate arrangement of a differential steering actuator in accordance with an ninth embodiment.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    Referring to the figures, an exemplary embodiment is discussed. Referring to FIG. 2, an active steering system  100  having a differential steering actuator  110  in accordance with a first embodiment is shown and discussed. Active steering system  100  preferably includes a gearbox  111 , a gear housing  112 , an upper shaft  125 , a gear element  114 , support bearings  115  and a hydraulic power assisted steering mechanism  160  integrated with differential steering actuator  110 . In accordance with a first embodiment, gear element  114  and support bearings  115  are preferably disposed within gear housing  112 . Support bearings  115  are preferably rotatingly associated with gear element  114  so as to allow gear element  114  to rotate relative to gear housing  112 . Upper shaft  125  is preferably communicated with gear element  114  so as to protrude from gear housing  112 , wherein upper shaft  125  is non-movably associated with gear element  114  and rotatably associated with gear housing  112 . In addition, upper shaft  125  is preferably non-movably associated with a steering shaft that is further non-movably associated with a hand-wheel.  
         [0020]    In accordance with a first embodiment, gear element  114  preferably includes an internal gear element  116  having a first pitch circle diameter for rotation on a primary axis  105 . Active steering system  100  preferably further includes a bearing support  124  disposed so as to be rotatingly supported within gear housing  112 . Furthermore, bearing support  124  preferably includes an external gear element  123  about its periphery, which is in engagement with a pinion  142  fixed to an output shaft  144  of a motor  140 . In accordance with a first embodiment, pinion  142  is preferably disposed so as to be parallel with output shaft  144  of motor  140 .  
         [0021]    In addition, active steering system  100  preferably further includes an eccentric gear element  120  having a secondary axis  107 . Eccentric gear element  120  preferably includes a first external gear element  122  having a second pitch circle diameter smaller than the first pitch circle diameter of internal gear element  116 , wherein eccentric gear element  120  is preferably disposed such that first external gear element  122  is engagingly associated with internal gear element  116 . Moreover, eccentric gear element  120  is preferably disposed within gear housing  112  so as to be rotatingly and eccentrically supported by bearing support  124 . As a result, when a stopper  145  holds the output shaft  144  stationary, the bearing support  124  remains stationary, thus preventing the secondary axis  107  from moving about the primary axis  105 . Therefore, in response to a rotation of the upper shaft  125 , the eccentric gear element  120  is forced to rotate on the secondary axis  107 .  
         [0022]    The eccentric gear element  120  also preferably has an internal gear element  126  in engagement with a shaft  113 , which has a shaft gear element  128  and which is again centered for rotation on the primary axis  105 .  
         [0023]    It should be noted, that internal gear element  126  may also be disposed so as to be external to eccentric gear element  120  and shaft gear element  128  maybe disposed so as to be internal to shaft  113 . In accordance with an exemplary embodiment, shaft gear element  128  is preferably disposed so as to be engagingly associated with internal gear element  126 . Rotation of the shaft  113  causes a torsion bar  117  to twist and thus open a passage for hydraulic fluid as hereinbefore described with respect to FIG. 1. Although not required, a one-to-one turning ratio of the upper shaft  125  and the shaft  113  may be achieved if the internal gear element  126  has a pitch circle of the first diameter being the same as the internal gear element  116 , and the shaft  113  has an external gear element having a pitch circle of the second diameter being the same as the eccentric gear element  120 . In accordance with an exemplary embodiment, different turning ratios of the upper shaft  125  and the shaft  113  may be achieved by varying the pitch circle of the first diameter and/or the pitch circle of the internal gear element  126  and/or the pitch circle of the shaft  113  and/or the pitch circle of the eccentric gear element  120 .  
         [0024]    A stopper-damper  147  is optionally located on the steering shaft. Stopper-damper  147  preferably functions to hold upper shaft  125  without rotation in case of active steering intervention such that a driver does not feel the additional steering input. The stopper-damper  147  may also function to damp vibrations at relatively high vehicle speeds.  
         [0025]    An electronic control unit  150  preferably receives inputs from various vehicle sensors (yaw, lateral acceleration, speed, etc.), and generates output signals to control electric motor  140 , stopper  145  and stopper-damper  147 . For example, electronic control unit  150  may receive such inputs as yaw, lateral acceleration, speed, steerable wheel angle, and tire slip angle from various sensors. Alternatively, yaw may be approximated rather than sensed as taught by U.S. Pat. No. 6,205,391, issued Mar. 20, 2001, to Ghoneim et al., which is assigned to the present assignee and wholly incorporated by reference herein. Upon detecting that corrective stabilizing action is required based on inputs from the various sensors, electronic control unit  150  preferably communicates this action to electric motor  140  so as to cause electric motor  140  to respond.  
         [0026]    Referring to FIG. 3, a cross section taken along section A-A of FIG. 2 is shown, in accordance with an exemplary embodiment. As can be seen, eccentric gear element  120  is supported by a first bearing set for rotation on a secondary axis  107  within the bearing support  124 , which is in turn supported by support bearings  115  disposed so as to allow for rotation on the primary axis  105 . The position of bearing support  124  defines the position of secondary axis  107  on which eccentric gear element  120  rotates. Thus, eccentric gear element  120  rotates on its own axis extending down the center of its body, which is secondary axis  107 , and can also rotate on primary axis  105 , which is parallel to secondary axis  107 .  
         [0027]    Referring to FIG. 2 and FIG. 3, under normal operating conditions, when a driver rotates the hand-wheel, this rotational motion is translated to upper shaft  125  via the steering shaft. The rotation of upper shaft  125  is, in turn, translated to gear element  114 , so as to cause gear element  114  to rotate about primary axis  105  relative to gear housing  112 . If electric motor  140  causes output shaft  144  to rotate in response to a signal from electronic control unit  150 , pinion  142  will also rotate. This in turn will interact with external gear element  123  and cause bearing support  124  to rotate about secondary axis  107 . Thus, eccentric gear element  120  is simultaneously rotating about secondary axis  107  and primary axis  105 . If electric motor  140  causes stopper  145  to hold output shaft  144  stationary, pinion  142  will also be stationary. This in turn will interact with external gear element  123  so as to cause bearing support  124  to remain stationary. Thus, eccentric gear element  120  will only rotate about secondary axis  107 .  
         [0028]    In either of the two situations described hereinabove, when eccentric gear element  120  rotates, internal gear element  126  and shaft gear element  128  will engage each other and cause shaft  113  to rotate. This action will then be translated to the road-wheels as described hereinabove.  
         [0029]    Referring to FIG. 4, a second embodiment of active steering system  100  having a differential steering actuator  210  is shown and discussed. In accordance with a second embodiment, elements in FIG. 4 that are the same or similar as elements in FIG. 2 are identified via a  200  series number. For example, a gear housing  112  in FIG. 2 is identified as a gear housing  212  in FIG. 4. In accordance with a second embodiment, active steering system  100  incorporates the elements of the first embodiment, with the exception of pinion  142 . Differential steering actuator  210  operates similarly to differential steering actuator  110  with the exception that the input from electronic control unit  150  is effected via a worm gear  242  communicated with electric motor  240 , as opposed to the first embodiment which uses pinion  142 . In accordance with a second embodiment, worm gear  242  is preferably movingly associated with external gear element  223 .  
         [0030]    Referring to FIG. 5, a third embodiment is of active steering system  100  having a differential steering actuator  310  is shown and discussed. In accordance with a third embodiment, differential steering actuator  310  primarily differs from the second embodiment of differential steering actuator  210  shown in FIG. 4 by the addition of planetary gear elements  356 . As described with respect to FIG. 2, under normal conditions a driver rotates a hand-wheel that rotates a steering shaft, which is communicated with an upper shaft  325 . Upper shaft  325  is communicated with a gear element  314 , which is rotatably supported by bearings  315  within a gear housing  312  of a gearbox  311 .  
         [0031]    In accordance with a third embodiment, gear element  314  preferably includes an external gear element  316  having a pitch circle diameter for rotation on an axis  305 . In engagement with external gear element  316  are planetary gear elements  356 . Planetary gear elements  356  are preferably each rotatably supported on spindle supports  358 , which are, in turn, rotatably supported in gear housing  312 . In addition, planetary gear elements  356  preferably include individual axes  360  and have a pitch circle diameter sized so as to allow engagement with external gear element  316  of gear element  314 . Spindle supports  358  are also preferably disposed so as to allow planetary gear elements  356  to interact with an external worm gear element  323  about their periphery, which is in engagement with a worm  342  communicated with an output shaft of a motor  340  having a stopper  345 . In accordance with a third embodiment, motor  340  is preferably communicated with an electronic control unit so as to receive control signals from the electronic control unit responsive to various vehicle sensors (yaw, lateral acceleration, speed, etc.).  
         [0032]    When upper shaft  325  rotates, this causes gear element  314  and thus external gear element  316  to rotate. As a result, external gear element  316  interacts with planetary gear elements  356  causing planetary gear elements  356  to rotate. If the electronic control unit causes stopper  345  to hold the output shaft stationary, worm  342  will remain stationary and thus spindle supports  358  remain stationary preventing spindle supports  358  from moving about axis  305 . In this case, in response to a rotation of upper shaft  325 , planetary gear elements  356  are forced to rotate only about their individual axes  360 .  
         [0033]    However, if the electronic control unit causes motor  340  to rotate the output shaft, worm  342  will rotate causing external worm gear element  323  to rotate. This, in turn, will cause spindle supports  358  to rotate about axis  305 . preventing spindle supports  358  from moving about axis  305 . In this case, in response to a rotation of upper shaft  325 , planetary gear elements  356  will simultaneously rotate about axis  305  and their individual axes  360 .  
         [0034]    In accordance with a third embodiment, spindle supports  358  of planetary gear elements  356  are preferably communicated with an output shaft  313 , which is centered for rotation on axis  305 . Rotation of output shaft  313  causes a torsion bar  317  to openingly engage a passage for hydraulic fluid as described hereinabove. Although not required, a one-to-one turning ratio of upper shaft  325  and output shaft  313  may be achieved if external gear element  316  has a pitch circle of the first diameter being the same as planetary gear elements  356 . In accordance with an exemplary embodiment, different turning ratios of upper shaft  325  and the output shaft  313  may be achieved by varying the pitch circle of external gear element  316  and/or the pitch circle of planetary gear elements  356 .  
         [0035]    Referring to FIG. 6, a fourth embodiment of active steering system  100  having a differential steering actuator  410  is shown and discussed. In accordance with a fourth embodiment, active steering system  100  incorporates all of the elements of the third embodiment, with the exceptions that the components of differential steering actuator  410  have a different orientation than that of the third embodiment and that a position sensor  462  is included and is preferably disposed so as to be adjacently associated with output shaft  413 , wherein position sensor  462  preferably produces a signal responsive to the position of output shaft  413 . In accordance with a fourth embodiment, position sensor  462  is preferably further communicated with an electronic control unit, so as to inform the electronic control unit of the position of output shaft  413 , wherein the electronic control unit may communicate a signal responsive to position sensor  462  to a motor  440 , so as to cause motor  440  to respond.  
         [0036]    Referring to FIG. 7, a fifth embodiment of an active steering system  100  having a differential steering actuator  510  is shown and discussed. Under normal conditions, a driver rotates a hand-wheel that rotates a steering shaft, which is communicated with an upper shaft  525 . Upper shaft  525  is further communicated with a gear element  514 , which is rotatably supported by bearings  515  within a gear housing  512  of a gearbox  511 . In accordance with a fifth embodiment, differential steering actuator  510  preferably includes a torsion bar  517 , a torque sensor  562  and a yaw sensor. Torque sensor  562  is preferably disposed so as to be communicated with upper shaft  525  and an electronic control unit, wherein torque sensor  562  senses the torque on upper shaft  525  and communicates a signal, responsive to the torque on upper shaft  525 , to the electronic control unit. In addition, yaw sensor is also preferably communicated with the electronic control unit and disposed so as to sense the yaw of the vehicle. Yaw sensor then communicates a signal, responsive to the yaw of the vehicle, to the electronic control unit.  
         [0037]    In accordance with a fifth embodiment, gear element  514  includes an internal gear element  516  having a first pitch circle diameter for rotation on a primary axis  505 . In engagement with internal gear element  516  is an eccentric gear element  520 . Eccentric gear element  520  is preferably rotatably and eccentrically supported in a bearing support  524 , which is, in turn, rotatably supported in gear housing  512 . Differential steering actuator  510  preferably includes a torque worm gear element  570  which is in engagement with gear element  514  and a torque worm  572 , wherein torque worm  572  is fixed to an output shaft of torque motor  574 . When a torque stopper holds the output shaft of torque motor  574  stationary, gear element  514  remains stationary, thus preventing gear element  514  from rotating about primary axis  505 .  
         [0038]    In addition, eccentric gear element  520  preferably includes a secondary axis  507  and a first external gear element  522  having a second pitch circle diameter smaller than the first pitch circle diameter in engagement with internal gear element  516  of gear element  514 . Bearing support  524  preferably includes an external yaw worm gear element  523  about its periphery, which is in engagement with a yaw worm  542  fixed to an output shaft of a motor  540 . When a yaw stopper holds the output shaft of motor  540  stationary, bearing support  524  remains stationary, thus preventing eccentric gear element  520  from rotating about secondary axis  507 . Thus, in response to a rotation of upper shaft  525 , eccentric gear element  520  is forced to rotate only on primary axis  505 .  
         [0039]    Moreover, eccentric gear element  520  also preferably includes an internal gear element  526  disposed so as to be engagedly associated with an output shaft element  519  of an output shaft  513 , wherein output shaft  513  is centered for rotation on primary axis  505 . Rotation of output shaft  513  causes a torsion bar  517  to engage a rack  580 , wherein rack  580  is communicated with the road-wheels. Torsion bar  517  causes rack  580  to move left or right, thus translating the action of output shaft  513  to the road-wheels.  
         [0040]    Referring to FIG. 8, a sixth embodiment of active steering system  100  having a differential steering actuator  610  is shown and discussed. In accordance with a sixth embodiment, active steering system  100  incorporates all of the elements of the fifth embodiment, with the exception that different gear ratios may be achieved by varying the sizes of gear element  614  and output shaft  613 . In accordance with an exemplary embodiment, different turning ratios of the upper shaft  625  and the output shaft  613  may be achieved by varying the size of the first pitch circle diameter of internal gear element  616  and/or the second pitch circle diameter of first external gear element  622 . In addition, different turning ratios of upper shaft  625  and output shaft  613  may also be achieved by varying the size of internal gear element  616  and/or external gear element  622 . In accordance with a sixth embodiment, the ratio between gear element  614  and output shaft  613  may be any ratio suitable to the desired end purpose.  
         [0041]    Referring to FIG. 9, a seventh embodiment of active steering system  100  having a differential steering actuator  710  is shown and discussed. In accordance with a seventh embodiment, active steering system  100  incorporates all of the elements of the fifth embodiment, with the exception that a position sensor  718  has been added. In accordance with a seventh embodiment, position sensor  718  is preferably disposed so as to be communicated with output shaft  713 , wherein position sensor  718  measures tire position and communicates that measurement to an electronic control unit. The electronic control unit then communicates with motor  740  and/or torque motor  774  so as to cause motor  740  and/or torque motor  774  to respond in a manner responsive position sensor  718 .  
         [0042]    Referring to FIG. 10, an eighth embodiment of active steering system  100  having a differential steering actuator  810  is shown and discussed. Under normal conditions, a driver rotates a hand-wheel that rotates a steering shaft, which is communicated with an upper shaft  825 . Upper shaft  825  is further communicated with a gear element  814 , which is rotatably supported by bearings  815  within a gear housing  812  of a gearbox  811 .  
         [0043]    In accordance with an eighth embodiment, active steering system  100  differential steering actuator  810  preferably includes a torsion bar  817 , a torque sensor  862  and a yaw sensor. Torque sensor  862  is preferably disposed so as to be communicated with upper shaft  825  and an electronic control unit, wherein torque sensor  862  senses the torque on upper shaft  825  and communicates a signal, responsive to the torque on upper shaft  825 , to the electronic control unit. In addition, yaw sensor is also preferably communicated with the electronic control unit and disposed so as to sense the yaw of the vehicle. Yaw sensor then communicates a signal, responsive to the yaw of the vehicle, to the electronic control unit.  
         [0044]    In accordance with an eighth embodiment, gear element  814  preferably includes an external gear element  816 . Differential steering actuator  810  preferably includes a torque worm gear element  870  which is in engagement with gear element  814  and a torque worm  872 , wherein torque worm  872  is fixed to an output shaft of torque motor  874 . In addition, differential steering actuator  810  also includes a yaw worm gear  819  having a yaw worm gear element  823  about its periphery, which is in engagement with a yaw worm  842  fixed to an output shaft of a yaw motor  840 . Moreover, Differential steering actuator  810  also preferably includes a planetary gear  880  having planetary gear elements  882  in engagement with external gear element  816 .  
         [0045]    In accordance with an eighth embodiment, differential steering actuator  810  also includes an output shaft  813  and an output shaft support  884  having shaft gear elements  886 , wherein shaft gear elements  886  are in engagement with planetary gear elements  882 .  
         [0046]    When a driver rotates the hand-wheel, the hand-wheel rotates a steering shaft, which in turn rotates upper shaft  825 . Torsion bar  817  twists in response to the rotation of upper shaft  825 . Torque sensor  862  sends a signal to the electronic control unit  150  which informs torque motor  874  to rotate torque worm  872  causing worm gear element  870  to rotate. This causes gear element  814  to rotate, which causes planetary gears  880  to rotate, which in turn causes an output shaft support  813  to rotate causing a rack  890  to move left or right. When a driver does not rotate the hand-wheel and the vehicle is traveling in a straight path, the yaw sensor senses the yaw rate of the vehicle and communicates a signal to the electronic control unit which informs yaw motor  840  to rotate yaw worm  842  causing yaw worm gear  819  to rotate. This causes planetary gears  880  to rotate around gear element  814  thus causing output shaft support  813  to rotate causing rack  890  to move left or right. In accordance with an eighth embodiment, yaw motor  840  and torque motor  874  may operate in a manner responsive to a position sensor  888 .  
         [0047]    In accordance with a ninth embodiment, the elements of active steering system  100  having a differential steering actuator  910  maybe arranged in any manner suitable to the desired end purpose as shown in FIG. 11.  
         [0048]    While the description has been made with reference to exemplary embodiments, it will be understood by those of ordinary skill in the pertinent art that various changes may be made and equivalents may be substituted for the elements thereof without departing from the scope of the disclosure. In addition, numerous modifications may be made to adapt the teachings of the disclosure to a particular object or situation without departing from the essential scope thereof.  
         [0049]    For example, the present teachings may be applied to general control algorithms wherein the actuation is preferably smoothed to optimize the man-machine interface. Such control algorithms may include, but are not limited to, input devices such as pedals and actuators such as linear motors, and more generally, any controlled device in contact with human skin. It is understood that such control algorithms have application to lane-keeping in addition to hand-wheel actuation. Therefore, it is intended that the Claims not be limited to the particular embodiments disclosed as the currently preferred best modes contemplated for carrying out the teachings herein, but that the Claims shall cover all embodiments falling within the true scope and spirit of the disclosure.