Abstract:
A pedal assembly is disclosed that includes a gear having a first tooth with a root and terminal ends. The gear rotates due to an input force. The assembly also includes a rack having a second tooth with root and terminal ends. The second tooth meshes with the first tooth at a contact point such that rotation of the gear causes linear movement of the rack. The assembly further includes a biasing member that biases the rack. The assembly additionally includes a slide member on which the rack slides. The slide member is provided on a side of the rack opposite to that of the gear such that the rack pushes on the slide member due to meshing of the first tooth and the second tooth.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The following is based on and claims priority to Japanese Patent No. 2005-230557, filed Aug. 9, 2005, which is herein incorporated in its entirety by reference.  
       FIELD OF THE DISCLOSURE  
       [0002]     The follow generally relates to a pedal and, more specifically, relates to a pedal assembly for a vehicle.  
       BACKGROUND  
       [0003]     Pedal assemblies have been proposed that electrically detect the amount of rotational displacement of a pedal using a rotational angle sensor or the like. An accelerator pedal assembly, for instance, controls the throttle opening depending upon the detected amount of displacement of the accelerator pedal away from an at-rest position. U.S. Pat. No. 5,529,296 (Japanese Patent No. 3185498), U.S. Pat. No. 6,745,642 (Leaflet of International Patent Publication No. 01/019638), and European Patent No. 0748713 each describe such a pedal assembly.  
         [0004]     These pedal assemblies generate hysteresis characteristics between the rotational displacement of the pedal and the input force supplied by the driver. More specifically, a moving member is pushed on a slide member in an amount that depends upon the pedal displacement. The pushing force of the moving member on the slide member increases as the displacement of the accelerator pedal is increased. Therefore, frictional force between the moving member and the slide member increases with an increase in the displacement of the accelerator pedal.  
         [0005]     For the device of U.S. Pat. No. 5,529,296, however, the frictional force increases or decreases as the moving member moves in the direction of an axis of rotation of the accelerator pedal. Therefore, the size of the pedal assembly may need to be increased in the direction of axis of rotation.  
         [0006]     Further, the devices of U.S. Pat. No. 6,745,642, and European Patent No. 0748713 include tilted surfaces that slide relative to each other. As such, local wear may occur where the tilted surfaces slide against each other.  
       SUMMARY  
       [0007]     A pedal assembly is disclosed that includes a gear having at least one first tooth with a root end and a terminal end, wherein the gear rotates due to an input force. The assembly also includes a rack having at least one second tooth with a root end and a terminal end, wherein the second tooth meshes with the first tooth at a contact point such that rotation of the gear causes linear movement of the rack in a first linear direction. The assembly further includes a biasing member that biases the rack in a second direction, which is opposite to the first linear direction. Additionally, the assembly includes a slide member on which the rack slides in the first and second direction, wherein the slide member is provided on a side of the rack opposite to that of the gear such that the rack pushes on the slide member due to meshing of the first tooth and the second tooth. As the gear rotates, the contact point successively moves on one of the first tooth and the second tooth away from the root end toward the terminal end thereof. The contact point successively moves on the other of the first tooth and the second tooth away from the terminal end toward the root end thereof, depending upon the direction of rotation of the gear.  
         [0008]     A pedal assembly is also disclosed that includes a gear having at least one first tooth, wherein the gear rotates due to an input force. The assembly also includes a rack having at least one second tooth that meshes with the first tooth such that rotation of the gear causes linear movement of the rack in a first linear direction. The assembly further includes a biasing member that provides a biasing force to the rack in a second direction, which is opposite to the first linear direction. Additionally, the assembly includes a slide member on which the rack slides in the first and second direction. The slide member is provided on a side of the rack opposite to that of the gear such that the rack pushes on the slide member due to meshing of the first tooth and the second tooth. The biasing force increases with an increase in the amount of linear displacement of the rack in the first direction, and friction between the slide member and the rack increases with an increase in the amount of linear displacement of the rack in the first direction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic view of a pedal assembly according to one embodiment of the invention;  
         [0010]      FIG. 2  is a schematic view illustrating the forces transferred between a rack and a gear of the embodiment of  FIG. 1 ; and  
         [0011]      FIG. 3  is a diagram of characteristics illustrating a relationship between the rotational angle of the accelerator pedal and the input force on the pedal supplied by the driver. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     Referring initially to  FIG. 1 , one embodiment of a pedal assembly  10  is shown. In one embodiment, the pedal assembly  10  is an accelerator pedal assembly  10 .  
         [0013]     The accelerator pedal assembly  10  includes an accelerator pedal  12  and a gear  20  coupled via an arm  14 . The pedal assembly  10  also includes a rack  30 . The gear  20  and the rack  30  are enclosed within a housing  50 . In one embodiment, the gear  20 , rack  30 , and the housing  50  are made of a resin material having relatively high resistance to wear (e.g., POM (polyacetal), TEFLON™, or the like.  
         [0014]     The gear  20  includes a plurality of first teeth  24 . In the embodiment shown, there are a select number of first teeth  24  localized adjacent the rack  30 , and the first teeth  24  are spaced away from each other around a portion of the circumference of the gear  20 . In the embodiment shown, the first teeth  24  are shaped so as to be involute teeth. As such the width of the first tooth  24  at a root end  25   a  is larger than the width of the first tooth  24  at a terminal end  25   b , and the surfaces between the root end  25   a  and the terminal end  25   b  is curved outward.  
         [0015]     The rack  30  includes a plurality of second teeth  32 . The second teeth  32  are spaced linearly on the rack  30  in a direction perpendicular to an axis of rotation  22  of the gear  20 . In the embodiment shown, the second teeth  32  are shaped so as to be tapered teeth. In other words, the width at a root end  33   a  of the second tooth  32  is larger than the width at a terminal end  33   b  of the second tooth  32 , and the surfaces between the root end  33   a  and the terminal end  33   b  is flat.  
         [0016]     The first teeth  24  of the gear  20  are in mesh with the second teeth  32  of the rack  30  such that the gear  20  and rack  30  move together. More specifically, when an input force is supplied from a driver to the accelerator pedal  12 , the teeth  20  of the gear  20  rotate about the axis of rotation  22  in the directions of arrows A and B, and the rack  30  reciprocally moves in the linear directions indicated by arrows C and D. In the embodiment shown, the rack  30  moves linearly in a direction that is substantially perpendicular to the axis of rotation  22  of the gear  20 .  
         [0017]     Also, the pedal assembly  10  includes a slide surface  52  on which the rack  30  slides during movement in the C- and D-directions. Relative to the rack  30 , the slide surface  52  is positioned on a side opposite to the gear  20 . In the embodiment shown, the slide surface  52  is included on the housing  50 .  
         [0018]     Furthermore, the pedal assembly  10  includes a biasing member  40  that biases the rack  30  linearly in the D-direction. In other words, the biasing member  40  applies a load Fs (i.e., a return force) to the rack  30 . In the embodiment shown, the biasing member  40  is a coiled compression spring  40 .  
         [0019]     Thus, when an input force F 0  is applied to the accelerator pedal  12  by a driver, the gear  20  is rotated in the A-direction, and an acting force F is applied from the gear  20  to the rack  30  at an acting angle φ at a contact point E between the first tooth  24  of the gear  20  to the second tooth  32  of the rack  30 . As shown, in  FIG. 1 , the acting angle φ is an angle defined between the acting force F and a direction of linear movement of the rack  30  (i.e., the C-direction).  
         [0020]     The acting force F includes a vertical component F V  directed along the direction of linear movement of the rack  30  (i.e., the C-direction) relative to the coil spring  40 . The acting force F also includes a horizontal component F H  directed perpendicular to the slide surface  52 . When the coefficient of friction is μ between the rack  30  and the slide surface  52 , a frictional force μF H  acts between the rack  30  and the slide surface  52  in a direction opposite to the movement of the rack  30 .  
         [0021]     As mentioned previously, the first teeth  24  of the gear  20  are involute teeth, and the second teeth  32  of the rack  30  are tapered teeth. Thus as shown in  FIG. 2 , during operation of the pedal assembly  10 , the contact point E between the first tooth  24  of the gear  20  and the second tooth  32  of the rack  30  shifts on the same action line  100 , for example, from E 0  to E 1 . Therefore, the acting force F is applied to the rack  30  from the gear  20  at the same angle φ despite the rotational movement of the gear  20  and movement of the contact point E. Also, despite the movement of the contact point E, the vertical and horizontal force components F V , F H  remain at approximately the same ratio.  
         [0022]     Furthermore, as shown in  FIG. 2 , the position of the contact point E shifts from the root end  25   a ,  33   a  of either the first or the second tooth  24 ,  32  toward the terminal end  25   b ,  33   b  thereof and from the terminal end  25   b ,  33   b  of the other tooth  24 ,  32  to the root end  25   a ,  33   a  thereof depending on the rotational direction of the gear  20 . For instance, when the gear  20  rotates in the A-direction, the contact point E shifts away from the root end  25   a  of the first tooth  24  toward the terminal end  25   b  of the first tooth  24  and away from the terminal end  33   b  of the second tooth  32  toward the root end  33   a  of the second tooth  32 . Also, when the gear  20  rotates in the B-direction, the contact point E shifts away from the terminal end  25   b  of the first tooth  24  toward the root end  25   a  of the first tooth  24  and away from the root end  33   a  of the second tooth  32  toward the terminal end  33   b  of the second tooth  32 . As such, local wear on the first and second teeth  24 ,  32  is reduced. Furthermore, since a plurality of first teeth  24  is brought in mesh with a plurality of second teeth  32 , local wear is reduced on the teeth  24 ,  32 .  
         [0023]     Further, the load Fs which the rack  30  receives from the coil spring  40  increases as the gear  20  rotates in the A-direction and as the rack  30  moves toward the coil spring  40  in the C-direction. An increase in the load Fs is brought about by an increase in the input force F 0  from the driver (i.e., the force for depressing the accelerator pedal  12  and necessary for rotating the gear  20  in the A-direction against the load Fs or necessary for holding the gear  20  against the load Fs). In other words, the load Fs increases with an increase in the acting force F. When the acting force F increases as shown in  FIG. 2 , the horizontal component of force F H  for pushing the rack  30  perpendicularly toward the slide surface  52  increases from F H0  to F H1 . Accordingly, the frictional force μF H  increases.  
         [0024]     Furthermore, even when the gear  20  rotates and the position of contact point E shifts, the vertical and horizontal components of force F V , F H  remain at approximately the same ratio. Therefore, when the rotational angle of the accelerator pedal  12  changes and the acting force F varies, the frictional force μF H  varies as well at a constant rate. Accordingly, as shown in  FIG. 3 , there are generated regular hysteresis characteristics between the rotational angle of the accelerator pedal  12  and the input force F 0  of depressing the accelerator pedal  12 .  
         [0025]     Furthermore, for the gear  20 , further, the rack  30  and the slide surface  52  are arranged in a direction at right angles with the axis of rotation  22 , enabling the size of the pedal assembly  10  to be reduced in the direction of the axis of rotation  22 .  
       Other Embodiments  
       [0026]     In the embodiment shown, the first teeth  24  of the gear  20  are involute teeth, and the second teeth  32  of the rack  30  are tapered teeth. However, it will be appreciated that the shapes of teeth  24 ,  32  of the gear  20  and the rack  30  are not limited to those of the illustrated embodiment. Preferably, however, the contact point E successively moves from the root side  25   a ,  33   a  of one tooth  24 ,  32  toward the terminal side  25   b ,  33   b  thereof and from the terminal side  25   b ,  33   b  of the other tooth  24 ,  32  toward the root side  25   a ,  33   a  thereof in response to the rotation of the gear  20  so as to push the rack  30  onto the slide surface  52 .  
         [0027]     Furthermore, though the gear  20  and the rack  30  are each illustrated with pluralities of teeth  24 ,  32 , respectively, there may be provided only one tooth  24  and only one tooth  32  depending upon the range of rotational angles of the accelerator pedal  12 .  
         [0028]     In addition, though the rack  30  in the illustrated embodiment slides directly on the slide surface  52  of the housing  50 , the slide surface  52  can be included on something other than the housing  50  without departing from the scope of the present disclosure.  
         [0029]     Accordingly, while only the selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.