Abstract:
A gear assembly comprising a linear differential disposed at the gear assembly wherein the linear differential has a predetermined ratio from an input shaft to an output shaft, the ratio being adjustable by axially rotating the linear differential. A method of adjusting steering output as compared to steering input, which comprises powering a motor in operable communication with a worm and worm gear mechanism and rotating the worm and the worm gear mechanism fixed to a differential carrier. The method also comprises rotating the differential carrier, which comprises an input sun gear meshed with input differential planet gear, an input differential planet gear meshed with an output differential planet gear, and an output sun gear meshed with the output differential planet gear. The method further comprises rotating the output sun gear fixed to a differential output shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is based upon, and claims the benefit of, U.S. Provisional Patent Application No. 60/193,113 filed Mar. 30, 2000, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     
       BACKGROUND  
         [0002]    Steering systems function to assist a vehicle operator in directing the road wheels in order to steer the vehicle. In conventional steering systems, the operator controls the direction of the vehicle with the aid of a hand wheel mechanically connected to the road wheels.  
         SUMMARY  
         [0003]    The gear assembly is comprised of a linear differential disposed at the gear assembly wherein the linear differential has a predetermined ratio from an input shaft to an output shaft, the ratio being adjustable by axially rotating the linear differential. The method for adjusting steering output as compared to steering input is comprised of powering a motor in operable communication with a worm and worm gear mechanism and rotating the worm and the worm gear mechanism, which is fixed to a differential carrier. The method also comprises rotating the differential carrier, which comprises an input sun gear meshed with input differential planet gears, input differential planet gears meshed with output differential planet gears, and an output sun gear meshed with the output differential planet gears. The method further comprises rotating the output sun gear fixed to a differential output shaft.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0004]    The present disclosure will now be described, by way of example, with reference to the accompanying drawings, wherein like elements are numbered alike in the several Figures:  
         [0005]    [0005]FIG. 1 is a schematic view of a steering system of a vehicle.  
         [0006]    FIGS.  2 - 5  are an exploded perspective view of a steering system of a vehicle. 
     
    
     DETAILED DESCRIPTION  
       [0007]    Introduction  
         [0008]    Referring to FIG. 1, a steering system  20  of a vehicle is shown generally. The steering system comprises a hand wheel  16  in operable communication with road wheels  18  (only one illustrated) of the vehicle through a steering column  15 . Steering column  15  receives input from either hand wheel  16 , which is in operable communication with a shaft  22 , or a motor  70 , which is in operable communication with a worm shaft  90  and a worm gear  60 . After receiving the input, a steering ratio adjuster  17  selects the appropriate ratio to adjust road wheels  18 . A steering ratio adjuster  17  may be a linear differential gear system  11  and may be incorporated into steering column  15 .  
         [0009]    For example, the driver turns hand wheel  16 , which turns shaft  22  at a 1:1 ratio to an output shaft  158 , ultimately steering the road wheels  18  of the vehicle. Alternatively, motor  70  activates pursuant to a command from a controller (not shown) receiving and processing sensory information about an angle of road wheels  18 , which occurs when road wheels  18  assume a position that is not desirable. When motor  70  activates, it rotates a linear differential gear system  11 , which is part of steering column  15 . Linear differential gear system  1   1  rotates an output shaft  158  at a different speed from shaft  22 . This rotation repositions road wheels  18  to achieve a more desirable handling and ride condition. A more detailed explanation of the operation is set forth herein under the “Operation” section.  
         [0010]    Structural Connection  
         [0011]    Referring to FIGS. 2 and 3, in an exemplary embodiment, a column head (shown on FIG. 1 as  21 ) is connected to a shaft  22 , which is in operable communication with an input shaft  38 , preferably by a coupling  24 . An input gear  48  is in operable communication with input shaft  38  and supported by bearings  42 ,  50 . Preferably, the operable communication is accomplished by a key  41  and key ways (not shown) disposed at input gear  48  and input shaft  38 . The key/key way system prevents relative rotation between input gear  48  and input shaft  38 . A retaining ring  52  secures both bearing  50  and input gear  48 .  
         [0012]    Input gear  48  is meshed with a differential input gear  54 . Differential input gear  54  is in operable communication with a differential input shaft  112 . Preferably, the operable communication is accomplished by a key  109  and key ways (one not shown),  55  disposed at differential input shaft  112  and differential input gear  54 . The key/key way system prevents relative rotation between differential input gear  54  and differential input shaft  112 . Differential input gear  54  is also axially supported along differential input shaft  112  by a retaining ring  56 . Differential input shaft  112  is supported by bearings  44 ,  110 .  
         [0013]    Adjacent to differential input gear  54 , a sensor  59  is plugged into a first end  57  of input shaft  112 . Sensor  59  monitors the position of linear differential gear system  11 . On the other side of differential input gear  54  is a worm gear  60 , which is disposed at differential input shaft  112 . Differential input shaft  112  passes through worm gear  60  and turns independently of worm gear  60 . Worm gear  60  is rigidly connected to a differential carrier  127  so that differential carrier  127  rotates when worm gear  60  rotates. Differential carrier  127  comprises an input carrier plate  114  and an output carrier plate  126 , which may be properly aligned by alignment pins  131 . A pin  62  is disposed at worm gear  60  to stop worm gear  60  from rotating once worm gear  60  has turned a set distance. Pin  62  is more fully described in the operation section of this detailed description.  
         [0014]    Referring to FIGS. 3 and 5, a worm  92  is in operable communication with a worm shaft  90 . Preferably, the operable communication is accomplished by a key  88  and key ways  91 ,  93  disposed at worm  92  and worm shaft  90 . The key/key way system prevents relative rotation between worm  92  and worm shaft  90 . Worm  92  meshes with worm gear  60 . Worm shaft  90  is supported by two bearings  66 ,  82 . Bearing  66  is pressed against worm bearing thrust washer  96  and is axially supported to worm shaft  90  by a nut  68 . Bearing  82  is pressed against worm bearing thrust washer  84  and is axially supported by a retaining ring  80 . Belleville spring washers  86 ,  98  are disposed between worm bearing thrust washers  84 ,  96  and worm thrust washers  85 ,  94 . Belleville spring washers  86 ,  98  prevent worm  92  from locking when worm gear  60  is prevented from rotating by pin  62 . A motor  70  is in operable communication with worm shaft  90  so that motor  70  drives worm shaft  90 . Preferably, the communication between motor  70  and worm shaft  90  is by a coupling  78 . Motor  70  is mounted to a housing  64  by an adapter  76 , which is secured by fasteners  72 .  
         [0015]    Referring to FIG. 3, adjacent to worm gear  60  is bearing  110 , which is axially supported by a retaining ring  108 . A retaining ring  107  supports bearing  110  and differential input shaft  112 . Fixed at the end of differential input shaft  112  is an input sun gear  111 . Differential input gear  54 , input sun gear  111 , and differential input shaft  112  rotate at the same speed.  
         [0016]    Input sun gear  111  meshes with preferably two input differential planet gears  115 ,  117 . Input differential planet gears  115 ,  117  mesh with two output differential planet gears  118 ,  119 . Input differential planet gears  115 ,  117  and output differential planet gears  118 ,  119  are connected to both input carrier plate  114  and output carrier plate  126  in a manner that allows rotation. Preferably, that connection is accomplished by mounting input differential planet gears  115 ,  117  and output differential planet gears  118 ,  119  on a pin  122 . Also mounted on pin  122  are bushings  120 ,  121 . Bushing  121  is pressed against input carrier plate  114 . Bushing  120  is pressed against output carrier plate  126 .  
         [0017]    Referring to FIGS. 3 and 4, output differential planet gears  118 ,  119  mesh with an output sun gear  123 , which is fixed at the end of a differential output shaft  124 . Differential output shaft  124  is supported by a bearing  134 . Bearing  162  is assembled into output cover  164  and supports shaft  146 . Bearing  134  is supported at differential output shaft  124  by retaining rings  132 ,  140 . Input carrier plate  114  and output carrier plate  126  are mounted together by a fastener  142  and are supported by bearings  106 ,  128 . Retaining rings  138 ,  144  also support differential carrier  127 .  
         [0018]    A differential output gear  136  is disposed outside of differential carrier  127  and is in operable communication with differential output shaft  124 . Preferably, the operable communication is accomplished by a key  130  and key ways  129 , (one not shown) disposed at differential output shaft  124  and differential output gear  136 . The key/key way system prevents relative rotation between differential output gear  136  and differential output shaft  124 . Differential output gear  136 , output sun gear  123 , and differential output shaft  124  rotate at the same speed.  
         [0019]    Differential output gear  136  meshes with an idler gear  152 . Idler gear  152  is disposed at an idler shoulder bolt  146 , secured by a retaining ring  150  and supported by a bearing  148 . Shoulder bolt  146  is threaded into output cover  164 . Idler gear  152  meshes with an output gear  154 . Output gear  154  is in operable communication with an output shaft  158 . Preferably, the operable communication is accomplished by a key  156  and key ways  161 ,  159  disposed at output shaft  158  and output gear  154 . The key/key way system prevents relative rotation between output gear  154  and output shaft  158 . A retaining ring  150  supports output gear  154  at output shaft  158 . A bearing  160  supports output shaft  158  and is assembled into output cover  164 .  
         [0020]    Referring to FIGS. 1 through 4, steering column  15  is contained in a housing  64 , which preferably includes an input cover  45 , an output cover  164 , and a worm cover  100 . Worm cover  100  is secured to housing  64  by fasteners  101 . Input cover  45  is secured to housing  64  by fasteners  31 . Output cover  164  is secured to housing  64  by fasteners  163 . Input shaft  38  and output shaft  158  extend from housing  64 . A bearing  166  supports output shaft  158  at output cover  164  and is secured by a retaining ring  168 . Housing  64  is mounted to a bracket/jacket assembly  30  and secured by fasteners  25 . Bracket/jacket assembly  30  mounts to column head (not shown).  
         [0021]    A position sensor  36  is mounted on input shaft  38  at the outside of housing  64  and adjacent to input housing cover  45 . Another position sensor  170  is mounted at output shaft  158 , outside of housing  64 , and adjacent to output cover  164 . Output shaft  158  is in operable communication with an intermediate shaft  182  by a universal joint  180 .  
         [0022]    Operation  
         [0023]    Referring to FIG. 1, steering column  15  comprises a linear differential gear system  11 , which operates with or without motor  70  being powered. When motor  70  is not powered, steering system  20  operates in the following manner. The driver turns hand wheel  16 , which is in operable communication with shaft  22  and input shaft  38 . While the driver may turn hand wheel  16  either clockwise or counterclockwise, for purposes of illustration, assume that the driver has turned hand wheel  16  clockwise. The rotational force of hand wheel  16  is transmitted to input shaft  38 , which rotates input gear  48  clockwise. Input gear  48 , which is meshed with differential input gear  54 , rotates differential input gear  54  counterclockwise. Moreover, the torque ratio steps up 1:3 from input gear  48  to differential input gear  54 .  
         [0024]    Differential input gear  54  rotates differential input shaft  112 , which in turn rotates input sun gear  111  counterclockwise. Worm gear  60  is disposed at differential input shaft  112  between differential input gear  54  and input sun gear  111 ; however, differential input shaft  112  rotates independently from worm gear  60 . Worm gear  60  is not directly rotated by hand wheel  16 . Input sun gear  111 , which meshes with two input differential planet gears  115 ,  117 , rotates input differential planet gears  115 ,  117  clockwise. Two input differential planet gears  115 ,  117  mesh with two output differential planet gears  118 ,  119  and rotate output differential planet gears  118 ,  119  counterclockwise. Output differential planet gears  118 ,  119  mesh with output sun gear  123  and rotate output sun gear  123  clockwise. Output sun gear  123  rotates differential output shaft  124 . All rotation from differential input gear  54  to output sun gear  123  occurs at a 1:1 ratio.  
         [0025]    Disposed at differential output shaft  124  at the opposite end from output sun gear  123  is differential output gear  136 . Differential output gear  136  rotates in the same direction as output sun gear  123 . Differential output gear  136  meshes with idler gear  152 , which rotates counterclockwise. Idler gear  152  meshes with output gear  154 , which rotates clockwise. Idler gear  152  is utilized to change the rotational direction of output shaft  158  without redesigning the linear differential. The torque is stepped back down by a 3:1 ratio from differential output gear  136  to output gear  154 . The 1:3 ratio is used to enable the employment of smaller diameter gears in the linear differential gear system. By doing so, the overall dimension of the linear differential gear system are minimized. Moreover, the 1:3 ratio allows employment of a motor having a lower torque output. When output gear  154  turns clockwise, it rotates intermediate shaft  182  clockwise, which ultimately steers road wheels  18  to the right (passenger side) of the vehicle.  
         [0026]    Linear differential gear system  11  operates when motor  70  is powered. In that situation, the driver has either oversteered or understeered the vehicle and a controller (not shown) senses an inconsistency in the velocity, yaw, and direction of the vehicle. At the point that the driver has either oversteered or understeered the vehicle, controller (not shown) sends a signal to electric motor  70  to turn on.  
         [0027]    Assuming for purposes of illustration that the driver turns hand wheel  16  too far clockwise and road wheels  18  assume a position that is not desirable, then the linear differential system  11  activates. While the driver holds hand wheel  16  in a manner that sufficiently restricts hand wheel  16  from moving counterclockwise, motor  70  activates and rotates worm  92 , which in turn rotates worm gear  60 . Worm gear  60 , which is rigidly connected to a differential carrier (not shown), rotates differential carrier (not shown), which in turn rotates output differential planet gears  118 ,  119  clockwise.  
         [0028]    Output differential planet gears  118 ,  119  mesh with output sun gear  123  rotating output sun gear  123  counterclockwise. Output sun gear  123 , rotates differential output shaft  124 . When differential output shaft  124  rotates, it turns differential output gear  136 , which rotates in the same direction as output sun gear  123 . The differential output gear  136  meshes with idler gear  152 , which rotates clockwise. Idler gear  152  meshes with output gear  154 , which rotates counterclockwise. Output gear  154  turns counterclockwise, it rotates intermediate shaft  182  counterclockwise, which ultimately steers road wheels  18  to the left (driver&#39;s side) of the vehicle.  
         [0029]    In addition, if the driver continues to turn hand wheel  16  clockwise, linear differential gear system  11  operates to slow down the steering output. Thus, the rotation of road wheels  18  can vary as to the input of the rotation of hand wheel  16  from ratios ranging from 1:1 up to 1:20. Motor  70  only operates long enough to adjust road wheels  18  enough to reposition road wheels  18  to a more desirable setting. In one embodiment, road wheels  18  can only adjust a maximum of plus or minus five degrees as compared to the angle commanded by the driver. In such embodiment, a pin  62  is located at worm gear  60  to stop worm gear  60  from rotating once it has steered road wheels  18  plus or minus five degrees. It will be appreciated that in an alternate embodiment, if worm gear  60  did not have pin  62  so located, then worm gear  60  could continue to turn, which would continue to turn road wheels  18  in a direction consistent with worm rotation direction.  
         [0030]    While the disclosure has been described with reference to a preferred 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 disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.