Abstract:
A mechanism for de-lashing a gear assembly includes a first gear rotatable about a first axis and a first center rotatably fixed to the first axis and a first conical teeth portion. The gear assembly includes a second gear rotatable about a second axis and a second center rotatably fixed to said second axis and a second conical teeth portion configured to meshingly engage first conical teeth portion when the first and second gears are aligned substantially coplanarly. A biasing means operably biases the second conical teeth portion of the second gear against the first conical teeth portion of the first gear to reduce any lash therebetween. The biasing means is configured to bias the second gear in an axial direction while maintaining a fixed center distance between the first and second axes. The first gear is rotatably fixed about the fixed first axis such that the first gear is prevented from translation along the fixed first axis.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates generally to a gear configuration having a fixed center distance between parallel gears to eliminate backlash, and more particularly, to elimination of the lack of movement in a driven gear in the event of a change in rotational direction of the driver gear.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the prior art, gear set assemblies involved in transmitting angular movement from one shaft to another generally accommodate a relatively large tolerance to lash intrinsic with fabrication, and assembly of such gear set assemblies. In any gear set, backlash, or clearance between a tooth of one of the gears as it fills the space between two teeth of another gear, is necessary in the meshed engagement of the teeth of a gear in order to permit relative motion between two gears. In a gear system with no backlash, the meshing of the teeth between gears will be so tight that, absence any deflection of the teeth, the gears will bind and cause the system to jam.  
         [0003]     Various attempts to de-lash a gear system are well known in the prior art. The de-lashing of non-fixed parallel gear sets by adjusting the center distance between the gears is well understood and is usually accomplished using a spring or screw-type adjustment. These methods are generally effective through a very narrow range of manufacturing variability. More specifically, some attempts at so-called “active de-lashing” exist using the same shaped parallel gears and a spring to make the apparent tooth width bigger that accomplishes both lash control and fixed center distance. However, the de-lash is not suitable when using a spring having a low spring rate and rotation of the final gear assembly is difficult when using a spring having a high spring rate. A hand-wheel position sensor is one implementation requiring a pair of gears having a fixed center distance while zero backlash is recommended.  
         [0004]     Thus, there remains a need to control backlash for rotating gears having a fixed center distance from each other while meshingly engaged in substantially the same plane.  
       SUMMARY OF THE INVENTION  
       [0005]     A mechanism for de-lashing a gear assembly includes a first gear rotatable about a first axis having a first center rotatably fixed to the first axis and a first conical teeth portion. The gear assembly includes a second gear rotatable about a second axis having a second center rotatably fixed to said second axis and a second conical teeth portion configured to meshingly engage first conical teeth portion when the first and second gears are aligned substantially coplanarly. A biasing means operably biases the second conical teeth portion of the second gear against the first conical teeth portion of the first gear to reduce any lash therebetween. The biasing means is configured to bias the second gear in an axial direction while maintaining a fixed center distance between the first and second axes. The first gear is rotatably fixed about the fixed first axis such that the first gear is prevented from translation along the fixed first axis.  
         [0006]     In one embodiment, the de-lashing gear assembly is employed with a hand-wheel position sensor configured to sense the rotational position of a motor vehicle hand-wheel. The hand-wheel position sensor includes a housing; a PCB disposed within said housing; a sensor operably connected to circuitry on said PCB; and a gear assembly operably connected to the sensor having a mechanism for de-lashing the gear assembly. The gear assembly includes a first gear rotatable about a first axis having a first center rotatably fixed to the first axis and a first conical teeth portion. The gear assembly includes a second gear rotatable about a second axis having a second center rotatably fixed to said second axis and a second conical teeth portion configured to meshingly engage first conical teeth portion when the first and second gears are aligned substantially coplanarly. A biasing means operably biases the second conical teeth portion of the second gear against the first conical teeth portion of the first gear to reduce any lash therebetween. The biasing means is configured to bias the second gear in an axial direction while maintaining a fixed center distance between the first and second axes. The first gear is rotatably fixed about the fixed first axis such that the first gear is prevented from translation along the fixed first axis.  
         [0007]     The above-described 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, drawings, and appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Referring now to the Figures wherein like elements are numbered alike:  
         [0009]      FIG. 1  is a schematic diagram of an electric power steering system having a hand-wheel position sensor in communication with a controller;  
         [0010]      FIG. 2  is a partial cross section side elevated view of an exemplary embodiment of a taper based de-lashing mechanism used in the hand-wheel position sensor of  FIG. 1 ;  
         [0011]      FIG. 3  is a top plan view of an exemplary spring washer for use with the taper based de-lashing mechanism of  FIG. 2 ;  
         [0012]      FIG. 4  is an enlarged perspective view of the spring washer of  FIG. 3  illustrating biasing prongs extending therefrom;  
         [0013]      FIG. 5  is a cross section side elevated view of another exemplary embodiment of a taper based de-lashing mechanism;  
         [0014]      FIG. 6  is an enlarged perspective view illustrating an alternative embodiment of the spring washer of  FIG. 4 ; and  
         [0015]      FIG. 7  is a cross section side elevated view of an alternative embodiment of the taper based de-lashing mechanism of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Referring to  FIG. 1 , reference numeral  70  generally designates an Electric Power Steering (“EPS”) system for a motor vehicle. In an EPS system, it may be desirable to provide the absolute hand-wheel position using a handwheel position sensor. This position may be used, for example, to cause the hand-wheel to return to center following a steering input.  
         [0017]     Still referring to  FIG. 1 , a steering mechanism  72  is a rack-and-pinion type mechanism that includes a toothed rack (not shown) and a pinion gear (also not shown) located under a gear housing  74 . A steering wheel  76  is coupled to an upper steering shaft  78 . As the steering wheel  76  is turned, the upper steering shaft  78 , which is connected to a lower steering shaft  80  through a universal joint  82 , turns the pinion gear. Rotation of the pinion gear moves the toothed rack, which moves tie rods  84  (only one shown) that, in turn, move steering knuckles  86  (only one shown), which turn wheels  88  (only one shown). EPS assist torque is provided through an assist unit generally designated by reference numeral  90 , which includes a controller  92  and an electric motor  94 . A motor position commutation sensor  95  measures the relative position of the motor  94 . The controller  92  is powered by a vehicle power supply  96  through a supply line  98 . The controller  92  receives a signal indicative of the vehicle velocity on signal line  100 . Initial hand-wheel position is measured by hand-wheel position sensor  102  and fed to the controller  92  through line  104 . Position sensor  102  may be an optical-encoding type of sensor, a variable resistance type of sensor, or any other suitable type of position sensor for performing the functions of the hand-wheel position sensor  102 . In an exemplary embodiment, hand-wheel position sensor  102  includes a pairs of gears (not shown) rotating with a fixed center distance with respect to one another where zero lash is desirable. Hand-wheel  76  rotates shaft  78  which moves a large driving gear having a large magnet attached thereto. The large driving gear, in turn, operably engages a small driven gear having a small magnet attached to it. The large driving gear and the small driven gear are depicted as  118  and  120  in  FIG. 2 .  
         [0018]     The large magnet creates a magnetic field that is detected and converted into a signal. The small magnet also creates its own magnetic field, and it is also converted into a signal. The two fields are isolated from each other. A micro-controller  92  combines the two signals (the large magnetic field direction and the small magnetic field direction) into one and calculates the shaft rotational position in a 5-turn range. It will be noted that although hand-wheel position sensor  102  is disclosed in conjunction with EPS system  70 , other steering systems using operator steering input from a hand-wheel is contemplated to use hand-wheel position sensor  102 .  
         [0019]     Referring now to  FIG. 2 , an exemplary embodiment of a hand-wheel position sensor subassembly  112  is shown. Subassembly  112  includes a pair of conical gears substantially coplanar and meshingly engaged illustrated generally at  114 . Conical gears  114  extend axially from a printed circuit board (“PCB”) on which conical gears  114  are operably connected. PCB  116  is operably disposed with hand-wheel position sensor  102 .  
         [0020]     In an exemplary embodiment, conical gears  114  include a vertically fixed gear  118  and a biased gear  120  that is smaller than gear  118  as illustrated. It will be recognized that gear  120  may, in alternative embodiments, be the same size or larger than gear  118 , however. Gear  118  is vertically fixed in relation to PCB  116  and axially rotatable about axis  122 . Gear  118  includes conical teeth  124  that taper inwardly toward axis  122  extending form PCB  116 . Conical teeth  122  meshingly engage with complementary configured conical teeth  126  defining gear  120 . Conical teeth  126  of gear  120  taper outwardly from a top portion  128  of gear  120 .  
         [0021]     Gear  120  includes a hub portion  130  defining a bore  132  for disposing a bearing  134  therein. Bearing  134  allows gear  120  to rotate about an axis  136 . Axis  136  optionally includes a shaft (not shown) extending through a bore defined by bearing  134 . Gear  120  is biased in a direction indicated by arrow  138  that effectively reduces the lash caused by meshing engagement between conical teeth  124 ,  126  of gears  118 ,  120 , respectively. Gear  120  is biased in direction  138  via a spring washer  140  that has a base portion  142  disposed on PCB  116  and a biasing means  144  extending from base portion  142  urging bearing  134  in direction  138 . It will be recognized by one skilled in the pertinent art that outwardly tapered conical teeth  126  engage inwardly tapered conical teeth  124  of gear  118 , relative to viewing from the top down as illustrated, prevent further vertical translation of gear  120  while providing de-lashing between the two gears  118 ,  120 .  
         [0022]     Referring to  FIG. 3 , an exemplary embodiment of spring washer  140  is illustrated. Spring washer  140  includes base portion  142  configured as a flat disk washer having an aperture  146  configured to allow passage of a shaft (not shown) therethrough. Gear  120  or bearing  134  or both may include a shaft extending therethrough for transmitting or receiving angular movement of gear  120 . In one exemplary embodiment shown, biasing means  144  include three equidistant prongs  148  extending radially inwardly from base portion  142 . Prongs  148  are configured as not being coplanar with base surface  142  for providing a biasing force when prongs  148  are urged to be coplanar with base surface  142 . More specifically, an end portion  150  of each prong  148  extends from a top surface  152  defining base portion  142  and contacts a bottom surface of bearing  134 . In this manner, end portion  150  provides a bias in direction  138  against bearing  134 , and thus, against gear  120 .  
         [0023]     In an exemplary embodiment, aperture  146  is defined substantially by a circular shape having prongs  148  extending into the defined circular shape. It will be recognized by one skilled in the pertinent art that aperture  146  is further defined on either side of each prong  148  with a cutout  154  in base portion  142  to facilitate bending of each prong while reducing stress at a junction where a bottom portion  156  of each prong joins with base portion  142 . Washer  140  is preferably made of a non-magnetic material for use with an Absolute Hand-wheel Position Sensor (AHPS) described with reference to  FIG. 1 .  
         [0024]     It is also contemplated that non-magnetic stainless steel, as well as bronze and plastics can be used. For other applications where the magnetic properties are not a constraint, any material with enough elastic properties for reducing the distance between the gears is contemplated. It will be recognized that washer  140  or any other suitable device should exert enough force to reduce the distance between the “conical” surfaces of the small gear teeth and the large gear teeth and not so large that it would be impossible to rotate the gears or generate a permanent deformation on them.  
         [0025]      FIG. 4  illustrates an enlarged perspective view of spring washer  140  shown in  FIG. 3 . Each prong  148  is a resilient biasing member configured to be partially compressed toward top surface  152  when spring washer  140  is disposed between bearing  134  and PCB  116 . In this manner, prongs  148  bias conical teeth  126  of gear  120  toward conical teeth  124  of gear  118  to eliminate lash without adjustment of a center distance between the two gears. The center distance between the two gears  118 ,  120  is defined by a fixed distance between axis  122  and axis  136 , as gears  118 ,  120  are rotatably fixed with respect to each axis  122  and  136 , respectively (See  FIG. 2  and  5 ).  
         [0026]     Referring now to  FIG. 5 , an alternative embodiment of conical gears  114  is illustrated. More specifically, gear  118  is fixed vertically with respect to PCB  116  via bearing surfaces at an upper portion  158  and lower portion  160  of gear  118 . A first bearing surface  162  is disposed around a hub portion  164  defining lower portion  160 . A second bearing surface  166  resides in a cutout in upper portion  158  configured to receive second bearing surface  166 .  
         [0027]     Conical teeth  124  of gear  118  engage conical teeth  126  of gear  120  biased in a direction indicated by arrow  138 . Gear  120  is rotatable and translatable about axis  136  while also being fixed relative thereto. A pin shaft  168  extends axially from top surface  128  of gear  120  to transmit angular movement thereto. Spring washer  140  is disposed between hub  130  of gear  120  and a bearing surface  170  operably connected to PCB  116 . Spring washer  140  biases conical teeth  126  of gear  120  in direction  138  to optimize contact with complementary conical teeth  124  of gear  118 . In this manner, lash is reduced between gears  118  and  120  having complementary tapered conical teeth that in effect alter the effective fixed center distance between them by vertical translation of one gear relative to the other without altering the actual fixed center distance defined by each respective rotational axis.  
         [0028]     It will be noted that although spring washer has been described and illustrated having biasing means as three prongs  148 , any number of prongs is contemplated. Alternatively and referring to  FIG. 6 , biasing means  144  optionally includes a single biasing member  172  extending from an edge  174  defining aperture  146 . Biasing member  172  includes a hollow first frustocone  176  having a base  178  extending from edge  174 . A hollow second frustocone  180  having a second base  182  extends toward base portion  142  from a first top edge  184  defining an opening  186  of first frustocone  176 . Second hollow frustocone is an inverted hollow frustocone with respect to first frustocone  176 . A hollow third frustocone  188  having a third base  190  extends in the same direction of first frustocone  176  and from a second top edge  192  defining a second opening  194  of second frustocone  180 . A third top edge  196  defines an aperture  246  for passage of a shaft (not shown) therethrough. Top edge  196  operatively provides biasing contact against a gear  120  for reducing the lash between meshing engagement of conical teeth  126  and  124  of gears  120  and  118 , respectively. Biasing member  172  is configured to provide a biasing force in direction  138  when third frustocone  188  is compressed toward first frustocone  180 . More specifically, top edge  196  of third frustocone  188  exerts a bias in direction  138  when third frustocone  188  is further disposed by compression thereof within first frustocone  176  via first opening  186  of first frustocone  176 . It will be recognized that first, second and third frustocones  176 ,  180 , and  188  are concentric with respect to one another.  
         [0029]     It will be further noted that an alternative embodiment to that shown in  FIG. 6  optionally includes spring washer  140  having at least two hollow frustocones, wherein each frustocone is defined by a frustoconical wall defined by a top wall edge and a bottom wall edge. The bottom wall edge defines a bottom perimeter about second axis  136  larger than a top perimeter defining the top wall edge. Biasing means  144  urges second conical teeth portion  126  in a direction  138  urging the bottom wall edge of second conical teeth portion  126  toward facing first conical teeth portion  124  of first gear  118 .  
         [0030]     An alternative embodiment for a resilient biasing member includes at least a hollow first frustocone concentrically connected to a hollow second frustocone by connection of at least one of a top wall edge and a bottom wall edge defining each of the first and second frustcones. The first and second frustocones are contiguous and inverted with respect to each other. The contiguous frustocones are operably connected via a top wall edge of one of the first and second frustocones to a bottom wall edge of the other contiguous frustocone.  
         [0031]     Referring now to  FIG. 7 , an alternative embodiment of conical gears  114  is illustrated. More specifically, gear  118  is again fixed vertically with respect to PCB  116  via bearing surfaces at upper portion  158  and lower portion  160  of gear  118 . First bearing surface  162  is disposed around hub portion  164  defining lower portion  160 . Second bearing surface  166  resides in a cutout in upper portion  158  configured to receive second bearing surface  166 .  
         [0032]     Conical teeth  124  of gear  118  engage conical teeth  126  of gear  120  biased in a direction indicated by arrow  138 . Gear  120  is rotatable and translatable about axis  136  while also being fixed relative thereto. Pin shaft  168  extends axially from top surface  128  of gear  120  to transmit angular movement thereto. Pin shaft  168  is mounted to a housing  200  at one end  202 . A spring washer  240  is disposed between a bottom surface  204  of gear  120  and a bearing support  206  extending from pin shaft  168  opposite end  202 . Spring washer  240  is configured to bias conical teeth  126  of gear  120  in direction  138  to optimize contact with complementary conical teeth  124  of gear  118 . In this manner, lash is reduced between gears  118  and  120  having complementary tapered conical teeth that in effect alter the effective fixed center distance between them by vertical translation of one gear relative to the other without altering the actual fixed center distance defined by each respective rotational axis. Spring washer  240  thus provides a mechanism to bias gear  120  when gear  120  is operably suspended from a top portion thereof.  
         [0033]     Although conical gears  114  have been described with reference to a hand-wheel position sensor, the above described embodiments are optionally employed in any environment where a reduction of lash is desirable between a pair of fixed center gears. Backlash still exists within the conical gears  114  described above, but the characteristics of resilient biasing means  144  force conical teeth  126  to maintain contact with conical teeth  124 . This type of continuous engagement yields a only about half as much surface-to-surface contact as square edged contact between coplanar gears, thereby resulting in a significant reduction in backlash.  
         [0034]     While the invention 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 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.