Patent Publication Number: US-8984986-B2

Title: Accelerator apparatus for vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2011-262075 filed on Nov. 30, 2011 and Japanese Patent Application No. 2012-79748 filed on Mar. 30, 2012. 
     TECHNICAL FIELD 
     The present disclosure relates to an accelerator apparatus for a vehicle. 
     BACKGROUND 
     In an accelerator apparatus of an electronic type, the amount of depression of an accelerator pedal is sensed with a sensor, and the sensor outputs an electrical signal, which indicates the sensed amount of depression of the accelerator pedal, to an electronic control device. The electronic control device drives a throttle valve based on the sensed amount of depression of the accelerator pedal and other information. 
     JP2010-158992A teaches an accelerator apparatus of an electronic type, which includes a pedal rotor and a return rotor that are rotatably supported by a shaft. An accelerator pedal, which is depressible by a foot of a driver of the vehicle, is connected to the pedal rotor to rotate integrally therewith. When the accelerator pedal is depressed by the foot of the driver to rotate the pedal rotor from an accelerator-full-closing position, which corresponding to an idling state of an engine, in an accelerator-opening direction, the pedal rotor and the return rotor are urged away from each other in an axial direction of the shaft. 
     In the state where the pedal rotor and the return rotor are urged away from each other in the axial direction of the shaft, the pedal rotor axially urges a first friction member, which is fixed to the pedal rotor, against the support member. Thereby, the pedal rotor receives a resistance torque through the first friction member. Furthermore, the return rotor urges a second friction member, which is axially placed between the return rotor and the support member, against the support member. Thereby, the return rotor receives a resistance torque through the second friction member. These resistance torques act to maintain the rotation of the accelerator pedal connected to the pedal rotor and generate the pedal force hysteresis characteristics such that the pedal force, which is applied to the accelerator pedal at the time of releasing the accelerator pedal, is smaller than the pedal force, which is applied to the accelerator pedal at the time of depressing the accelerator pedal. 
     In the accelerator apparatus of JP2010-158992A, when a foreign object is clamped between the first friction member and the support member or between the return rotor and the second friction member or when the frictional force of each friction member is increased due to an environmental change, the first friction member may be fastened (jammed) to the support member, and/or the second friction member may be fastened (jammed) to the return rotor. When at least one of the first friction member and the second friction member is fastened, the accelerator pedal may not be returned to the accelerator-full-closing position. Thereby, in such a state, when the depressed accelerator pedal is released by removing the foot of the driver from the accelerator pedal, the engine may not be returned to the idling state. 
     SUMMARY 
     The present disclosure is made in view of the above disadvantages. 
     According to the present disclosure, there is provided an accelerator apparatus for a vehicle. The accelerator apparatus includes a support member, a shaft, a pedal boss, an accelerator pedal, a first urging device, a rotational angle sensing device, a first rotor, a second rotor, a projection, a plurality of first-bevel-gear teeth, a plurality of second-bevel-gear teeth, a second urging device, a first friction member and a second friction member. The support member is installable to a body of the vehicle. The shaft is rotatably installed to the support member. The pedal boss is placed coaxial with the shaft and is rotatable integrally with the shaft. The accelerator pedal is fixed to the pedal boss and is rotatable integrally with the pedal boss in both of an accelerator-closing direction and an accelerator-opening direction, which are circumferentially opposite to each other, in response to an amount of depression of the accelerator pedal. The first urging device urges the pedal boss in the accelerator-closing direction. The rotational angle sensing device senses a rotational angle of the shaft relative to the support member. The first rotor is placed radially outward of the shaft and is rotatable relative to the pedal boss. The second rotor is placed radially outward of the shaft and is located on an axial side of the first rotor, which is opposite from the pedal boss. The second rotor is rotatable relative to the first rotor. The projection is formed integrally with the first rotor and axially projects from the first rotor on an axial side of the first rotor where the pedal boss is located. The projection is circumferentially engageable with an engaging portion provided in the pedal boss. The first-bevel-gear teeth are formed integrally with the first rotor and axially project from the first rotor on the axial side of the first rotor where the second rotor is located. An amount of axial projection of each of the plurality of first-bevel-gear teeth, which is measured in an axial direction of the shaft toward the second rotor, progressively increases in the accelerator-closing direction. The second-bevel-gear teeth are formed integrally with the second rotor and axially project from the second rotor on an axial side of the second rotor where the first rotor is located. An amount of axial projection of each of the plurality of second-bevel-gear teeth, which is measured in the axial direction of the shaft toward the first rotor, progressively increases in the accelerator-opening direction. When the first rotor is circumferentially positioned on a circumferential side of an accelerator-full-closing position of the first rotor where an accelerator-full-opening position of the first rotor is located, the plurality of second-bevel-gear teeth engages the plurality of first-bevel-gear teeth, respectively, to urge the first rotor and the second rotor away from each other in the axial direction of the shaft. The second urging device urges the second rotor in the accelerator-closing direction. The first friction member is placed between the projection and the support member in the axial direction of the shaft. When the first rotor is urged away from the second rotor in the axial direction of the shaft, the first friction member is frictionally engaged with the projection or the support member to apply a resistance torque to the projection. The second friction member is placed between the second rotor and the support member in the axial direction of the shaft. When the second rotor is urged away from the first rotor in the axial direction of the shaft, the second friction member is frictionally engaged with the second rotor or the support member to apply a resistance torque to the second rotor. The pedal boss has a projection-receiving space, which circumferentially extends on a circumferential side of the engaging portion in the accelerator-opening direction and receives the projection. When the pedal boss is rotated in the accelerator-closing direction, the pedal boss is rotatable to an accelerator-full-closing position of the pedal boss without being stopped by the projection through engagement with the projection regardless of a rotational position of the projection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic side view showing an entire structure of an accelerator apparatus according to a first embodiment of the present disclosure; 
         FIG. 2  is a cross sectional view taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a cross sectional view taken along line III-III in  FIG. 2 ; 
         FIG. 4  is a cross sectional view taken along line IV-IV in  FIG. 2 ; 
         FIG. 5  is an enlarged cross-sectional view taken along line V-V in  FIG. 2 , showing a first rotor, a second rotor and a pedal boss portion of the accelerator apparatus; 
         FIG. 6  is a diagram showing a relationship between a pedal force applied to an accelerator pedal and a rotational angle of the accelerator pedal at the accelerator apparatus of the first embodiment; 
         FIG. 7  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a second embodiment of the present disclosure; 
         FIG. 8  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a third embodiment of the present disclosure; 
         FIG. 9  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a fourth embodiment of the present disclosure; 
         FIG. 10  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a fifth embodiment of the present disclosure; 
         FIG. 11  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a sixth embodiment of the present disclosure; 
         FIG. 12  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a seventh embodiment of the present disclosure; 
         FIG. 13  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to an eighth embodiment of the present disclosure; 
         FIG. 14  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a ninth embodiment of the present disclosure; 
         FIG. 15  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to a tenth embodiment of the present disclosure; 
         FIG. 16  is an enlarged partial cross-sectional view showing a first rotor, a second rotor and a pedal boss portion of an accelerator apparatus according to an eleventh embodiment of the present disclosure; 
         FIG. 17  is a cross-sectional view of an accelerator apparatus of a twelfth embodiment of the present disclosure, showing a cross section of the accelerator apparatus similar to  FIG. 2  of the first embodiment; and 
         FIG. 18  is a cross-sectional view of an accelerator apparatus of a thirteenth embodiment of the present disclosure, showing a cross section of the accelerator apparatus similar to  FIG. 3  of the first embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present disclosure will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIGS. 1 to 4  show an accelerator apparatus according to a first embodiment of the present disclosure. The accelerator apparatus  10  is an input apparatus, which is manipulated by a driver of a vehicle (automobile) to determine a valve opening degree of a throttle valve of an internal combustion engine of the vehicle (not shown). The accelerator apparatus  10  is an accelerator apparatus of an electronic type and transmits an electric signal, which indicates an amount of depression of an accelerator pedal  87 , to an electronic control device. The electronic control device drives the throttle valve through a throttle actuator (not shown) based on the amount of depression of the accelerator pedal  87  and the other information. 
     The accelerator apparatus  10  of  FIGS. 1 to 4  are indicated in its installed position relative to a vehicle body (not shown). In the following description, for the descriptive purpose, the upper side of  FIGS. 1 to 4  will be described as an upper side, and the lower side of  FIGS. 1 to 4  will be described as a lower side. Furthermore, the right side of  FIG. 1  will be described as a rear side, and the left side of  FIG. 1  will be described as a front side. 
     The accelerator apparatus  10  includes a housing  20 , a cover  40 , a shaft  50 , a manipulation member  60 , a first spring  88 , a rotational position sensor  90  and a pedal force hysteresis mechanism  100 . The housing  20  and the cover  40  serve as a support member of the present disclosure. The first spring  88  serves as a first urging device (a first urging means). The rotational position sensor  90  serves as a rotational angle sensing device (a rotational angle sensing means) of the present disclosure. 
     The housing  20  includes two bearing portions (left and right bearing portions)  22 ,  24 , a connecting portion (a front side connecting portion)  26 , a connecting portion (a rear side connecting portion)  28 , two installation portions (left and right installation portions)  30 ,  32  and a full-opening-side stopper portion  34 . The two bearing portions  22 ,  24  are spaced from each by a predetermined distance and are opposed to each other in an axial direction of the shaft  50 . The connecting portion  26  connects between a front part of the bearing portion  22  and a front part of the bearing portion  24 . The connecting portion  28  connects between a rear part of the bearing portion  22  and a rear part of the bearing portion  24 . The installation portion  30  is formed integrally with a left side of the connecting portion  26 , and the installation portion  32  is formed integrally with a right side of the connecting portion  26 . The full-opening-side stopper portion  34  is formed integrally with a lower part of the connecting portion  26 . The installation portions  30 ,  32  are installable to the vehicle body (not shown) with, for example, bolts, respectively. When the full-opening-side stopper portion  34  contacts the manipulation member  60 , as indicated by a dot-dot-dash line in  FIG. 3 , the rotation of the manipulation member  60  and associated components rotated therewith is stopped at an accelerator-full-opening position. The accelerator-full-opening position is a position, at which the amount of depression of the manipulation member  60  by the driver is in the full amount, i.e., the accelerator opening degree is 100% (full opening position). 
     The cover  40  includes a covering portion  42  and a fixing portion  44 . The covering portion  42  closes an upper opening of the housing  20 . The fixing portion  44  extends downward from an end part of the covering portion  42 , which is located on a side where the bearing portion  22  is located. 
     One end portion of the shaft  50  is rotatably supported by the bearing portion  22  of the housing  20 , and the other end portion of the shaft  50  is rotatably supported by the bearing portion  24  of the housing  20 . A sensor receiving recess  52  is formed in a center part of the one end portion of the shaft  50 , and a sensing device of the rotational position sensor  90  is received in the sensor receiving recess  52 . 
     The shaft  50  (together with the pedal boss portion  64 ) is rotatable through a predetermined angular range from an accelerator-full-closing position of the shaft  50  (and of the manipulation member  60 ) to an accelerator-full-opening position of the shaft  50  (and of the manipulation member  60 ). The accelerator-full-closing position is a position, at which the amount of depression of the manipulation member  60  by the driver is zero, i.e., the accelerator opening degree is 0% (full closing position). In  FIG. 3 , the accelerator-full-closing position of the manipulation member  60  is indicated by a solid line, and the accelerator-full-opening position of the manipulation member  60  is indicated by the dot-dot-dash line. 
     Hereinafter, the rotational direction of the manipulation member  60  and the associated components thereof from the accelerator-full-closing position toward the accelerator-full-opening position will be referred to an accelerator-opening direction X. Furthermore, the rotational direction of the manipulation member  60  and the associated components thereof from the accelerator-full-opening position toward the accelerator-full-closing position will be referred to an accelerator-closing direction Y. The associated components, which are rotated integrally with the manipulation member  60 , include a first rotor  102  and a second rotor  104 , which will be described in detail later. 
     The manipulation member  60  includes a rotatable body  62 , a rod  84  and a pad  86 . The rotatable body  62  includes a pedal boss portion  64 , a rod-connecting portion  76 , two cover portions  78 ,  80  and a full-closing-side stopper portion  82 . The rod-connecting portion  76 , the rod  84  and the pad  86  form the accelerator pedal  87 . The pedal boss portion  64  serves as a pedal boss of the present disclosure. The full-closing-side stopper portion  82  serves as a full-closing side stopper of the present disclosure. 
     The pedal boss portion  64  is configured into an annular form (i.e., a cylindrical tubular form) and is fixed to an outer peripheral wall of the shaft  50  by, for example, press-fitting at a location between the bearing portion  22  and the bearing portion  24  of the housing  20 . The cover portion  78  is configured into an arcuate form, which projects from a peripheral edge of an end surface (a bearing portion  22  side end surface) of the pedal boss portion  64  toward the bearing portion  22 . The cover portion  80  is configured into an arcuate form, which projects from a peripheral edge of an end surface (a bearing portion  24  side end surface) of the pedal boss portion  64  toward the bearing portion  24 . One end part of the rod-connecting portion  76  is connected to the pedal boss portion  64 , and the other end portion of the rod-connecting portion  76  extends downward from a lower opening of the housing  20 . 
     The pedal boss portion  64  and the cover portions  78 ,  80  close the lower opening of the housing  20 , more specifically an accommodating portion  23 . The housing  20  and the cover  40  form the accommodating portion  23 , in which an accommodating chamber  36  is formed. The accommodating chamber  36  receives the full-closing-side stopper portion  82  of the manipulation member  60  and the pedal force hysteresis mechanism  100 . 
     The full-closing-side stopper portion  82  is formed integrally with the pedal boss portion  64  such that the full-closing-side stopper portion  82  extends upwardly in the accommodating chamber  36  of the pedal boss portion  64 . The full-closing-side stopper portion  82  is located in an upper side area of the accommodating chamber  36 . When the full-closing-side stopper portion  82  contacts the inner wall (a wall extending in a top-to-bottom-direction) of the connecting portion  26  of the housing  20 , the full-closing-side stopper portion  82  limits the rotation of the manipulation member  60  and the associated components thereof in the accelerator-closing direction Y at the accelerator-full-closing position. When the full-closing-side stopper portion  82  contacts the inner wall of the connecting portion  26  of the housing  20 , the full-closing-side stopper portion  82  contacts a vertical surface  38  of the inner wall of the connecting portion  26 , which extends in the top-to-bottom direction in  FIG. 3 . 
     One end portion of the rod  84  is fixed to the rod-connecting portion  76 , and the other end portion of the rod  84  extends downward. The rod  84  is insert molded integrally with the rotatable body  62  at the time of molding the rotatable body  62  with resin. The pad  86  is fixed to the other end portion of the rod  84 . 
     The driver of the vehicle depresses the pad  86  to manipulate the accelerator pedal  87 . The accelerator pedal  87  converts a pedal force of the driver applied to the accelerator pedal  87  into a torque and conducts the converted torque to the shaft  50 . 
     When the accelerator pedal  87  is rotated in the accelerator-opening direction X, a rotational angle of the shaft  50  in the accelerator-opening direction X relative to the accelerator-full-closing position, which serves as a reference point, is increased. Thereby, the accelerator opening degree, which corresponds to this rotational angle, is also increased. Furthermore, when the accelerator pedal  87  is rotated in the accelerator-closing direction Y, the rotational angle of the shaft  50  is reduced, and thereby the accelerator opening degree is reduced. 
     One end portion of the first spring  88 , which is formed as a coil spring, is engaged with the full-closing-side stopper portion  82  of the manipulation member  60 , and the other end portion of the first spring  88  is engaged with the connecting portion  28  of the housing  20 . The first spring  88  urges the manipulation member  60  in the accelerator-closing direction Y. The urging force, which is exerted from the first spring  88  against the manipulation member  60 , is increased, when the rotational angle of the manipulation member  60  is increased, i.e., when the rotational angle of the shaft  50  is increased. Furthermore, the urging force is set to enable returning of the manipulation member  60  and the associated components thereof, such as the shaft  50 , to the accelerator-full-closing position regardless of the rotational position of the manipulation member  60 . 
     The rotational position sensor  90  includes a yoke  92 , two permanent magnets  94 ,  96  and a Hall element  98 . The yoke  92  is made of a magnetic material and is configured into a tubular form. The yoke  92  is fixed to an inner wall of the sensor receiving recess  52  of the shaft  50 . The magnet  94  and the magnet  96  are located radially inward of the yoke  92  and are diametrically opposed to each other about the rotational axis of the shaft  50 . The magnets  94 ,  96  are fixed to the inner peripheral wall of the yoke  92 . The Hall element  98  is placed between the magnet  94  and the magnet  96  and is installed to a circuit board (not shown), which is fixed to the housing  20 . 
     When a magnetic field is applied to the Hall element  98 , through which an electric current flows, a voltage is generated in the Hall element  98 . This phenomenon is referred to as a Hall effect. A density of a magnetic flux, which penetrates through the Hall element  98 , changes when the shaft  50  and the magnets  94 ,  96  are rotated about the shaft  50 . A value of the voltage discussed above is proportional to the density of the magnetic flux, which penetrates through the Hall element  98 . The rotational position sensor  90  senses the relative rotational angle of the Hall element  98  and the magnets  94 ,  96 , i.e., the relative rotational angle of the shaft  50  relative to the housing  20  by sensing the voltage, which is generated in the Hall element  98 . The rotational position sensor  90  outputs an electrical signal, which indicates the sensed relative rotational angle, to the electronic control device. 
     With reference to  FIGS. 1 to 5 , the pedal force hysteresis mechanism  100  includes the first rotor  102 , the second rotor  104 , a plurality of projections  106 , a plurality of first-bevel-gear teeth  108 , a plurality of second-bevel-gear teeth  112 , a first friction member  116 , a second friction member  118  and a second spring  120 . The second spring  120  may serve as a second urging device (a second urging means) of the present disclosure. 
     The first rotor  102  is located radially outward of the shaft  50  and is rotatably supported by the shaft  50 . The first rotor  102  is placed between the pedal boss portion  64  of the manipulation member  60  and the bearing portion  22  of the housing  20  in the axial direction of the shaft  50 . The first rotor  102  is configured into an annular form (a cylindrical tubular form) and is rotatable relative to the shaft  50  and the pedal boss portion  64 . Furthermore, the first rotor  102  is movable toward and away from the pedal boss portion  64  in the axial direction of the shaft  50 . 
     The second rotor  104  is located radially outward of the shaft  50  and is rotatably supported by the shaft  50 . The second rotor  104  is placed between the first rotor  102  and the bearing portion  22  of the housing  20  in the axial direction of the shaft  50 . The second rotor  104  is configured into an annular form (a cylindrical tubular form) and is rotatable relative to the shaft  50  and the first rotor  102 . Furthermore, the second rotor  104  is movable toward and away from the bearing portion  22  of the housing  20  in the axial direction of the shaft  50 . 
     The projections  106  are formed integrally with an outer wall of the first rotor  102 , which is located on the pedal boss portion  64  side in the axial direction of the shaft  50 . The pedal boss portion  64  includes a plurality of through-holes  70  (each through-hole  70  defining a projection-receiving space  70   a , which receives the corresponding projection  106 ). The projections  106  are received through the through-holes  70 , respectively, and project toward the axial side, which is opposite from the first rotor  102 . In the present embodiment, the number of the projections  106  is four, and these four projections  106  are arranged one after another at generally equal intervals in the circumferential direction. Each projection  106  is circumferentially engageable (contactable) with a closing-side end wall  72  of the corresponding through-hole  70  in the accelerator-closing direction Y. The closing-side end wall  72  of the through-hole  70  serves as an engaging portion of the present disclosure. 
     The closing-side end wall  72  of each through-hole  70  and the corresponding projection  106  can engage with each other in the circumferential direction to transmit the rotation (rotational force) between the manipulation member  60  and the first rotor  102 . That is, the rotation of the manipulation member  60  in the accelerator-opening direction X can be conducted to the first rotor  102  through the closing-side end wall  72  of the through-hole  70  and the projection  106 . Furthermore, the rotation of the first rotor  102  in the accelerator-closing direction Y can be conducted to the manipulation member  60  through the projection  106  and the closing-side end wall  72  of the through-hole  70 . 
     The first-bevel-gear teeth  108  are formed integrally with an outer wall of the first rotor  102 , which is located on the second rotor  104  side in the axial direction of the shaft  50 . Each of the first-bevel-gear teeth  108  is configured such that an amount of projection of the first-bevel-gear tooth  108  toward the second rotor  104  in the axial direction of the shaft  50  is progressively increased in the accelerator-closing direction Y. As shown in  FIG. 5 , each first-bevel-gear tooth  108  has a sloped surface  110 , which progressively approaches the second rotor  104  in the accelerator-closing direction Y. 
     The second-bevel-gear teeth  112  are formed integrally with an outer wall of the second rotor  104 , which is located on the first rotor  102  side in the axial direction of the shaft  50 . Each of the second-bevel-gear tooth  112  is configured such that an amount of projection of the second-bevel-gear tooth  112  toward the first rotor  102  in the axial direction of the shaft  50  is progressively increased in the accelerator-opening direction X. As shown in  FIG. 5 , each second-bevel-gear tooth  112  has a sloped surface  114 , which progressively approaches the first rotor  102  in the accelerator-opening direction X. 
     When each of the first-bevel-gear teeth  108  contacts the corresponding one of the second-bevel-gear teeth  112  in the circumferential direction, the rotation can be transmitted between the first rotor  102  and the second rotor  104 . Specifically, the rotation of the first rotor  102  in the accelerator-opening direction X can be conducted to the second rotor  104  through the first-bevel-gear teeth  108  and the second-bevel-gear teeth  112 . Also, the rotation of the second rotor  104  in the accelerator-closing direction Y can be conducted to the first rotor  102  through the second-bevel-gear teeth  112  and the first-bevel-gear teeth  108 . 
     Furthermore, when the rotational position of the first rotor  102  is located on a circumferential side of an accelerator-full-closing position of the first rotor  102  where an accelerator-full opening position of the first rotor  102  is located, the sloped surface of each of the first-bevel-gear teeth  108  engages the sloped surface of the corresponding one of the second-bevel-gear teeth  112  to urge the first rotor  102  and the second rotor  104  away from each other in the axial direction of the shaft  50 . During the normal operation (i.e., the operation, during which each projection  106  and the first rotor  102  are not jammed and are thereby rotatable), when the manipulation member  60  is placed in the accelerator-full-closing position, which is indicated by the solid line in  FIG. 3 , the projections  106  and the first rotor  102 , which are formed integrally, are placed in the accelerator-full-closing position of the projections  106  and of the first rotor  102  shown in  FIG. 3 . Also, during the normal operation, when the manipulation member  60  is placed in the accelerator-full-opening position, which is indicated by the dot-dot-dash line in  FIG. 3 , the projections  106  and the first rotor  102 , which are formed integrally, are placed in the accelerator-full-opening position thereof. The accelerator-full-opening position of each of the projections  106  (and thereby of the first rotor  102 ) is circumferentially placed on the clockwise side of the position of the projection  106  shown in  FIG. 3  and is circumferentially displaced from the position of the projection  106  shown in  FIG. 3  by a corresponding angle, which correspond to an angular difference between the accelerator-full-closing position and the accelerator-full-opening position of the manipulation member  60  shown in  FIG. 3 . 
     When the rotational angle of the first rotor  102  from the accelerator-full-closing position of the first rotor  102  toward the accelerator-full-opening position of the first rotor  102  is increased, the urging force of the first-bevel-gear teeth  108 , which urges the first rotor  102  toward the pedal boss portion  64  in the axial direction of the shaft  50 , is increased. Furthermore, when the rotational angle of the first rotor  102  from the accelerator-full-closing position of the first rotor  102  toward the accelerator-full-opening position of the first rotor  102  is increased, the urging force of the second-bevel-gear teeth  112 , which urges the second rotor  104  toward the bearing portion  22  of the housing  20  in the axial direction of the shaft  50 , is increased. 
     The first friction member  116  is located radially outward of the shaft  50  and is placed between the projections  106  and the bearing portion  24  of the housing  20  in the axial direction of the shaft  50 . The first friction member  116  is configured into an annular form (a circular disk form) and is fixed to distal ends of the projections  106 . When the first rotor  102  is urged away from the second rotor  104  in the axial direction of the shaft  50 , the projections  106  urge the first friction member  116  against the bearing portion  24  of the housing  20 . At this time, the first friction member  116  frictionally engages the bearing portion  24 . A frictional force between the first friction member  116  and the bearing portion  24  acts as a rotational resistance of the projections  106 . When the urging force, which is applied to the first rotor  102  toward the pedal boss portion  64 , is increased, a resistance torque, which is applied to the projections  106  from the bearing portion  24  through the first friction member  116 , is increased. 
     The second friction member  118  is located radially outward of the shaft  50  and is placed between the second rotor  104  and the bearing portion  22  of the housing  20 . The second friction member  118  is configured into an annular form (a circular disk form) and is fixed to the second rotor  104 . When the second rotor  104  is urged away from the first rotor  102  in the axial direction of the shaft  50 , the second rotor  104  urges the second friction member  118  against the bearing portion  22  of the housing  20 . At this time, the second friction member  118  frictionally engages the bearing portion  22 . A frictional force between the second friction member  118  and the bearing portion  22  acts as a rotational resistance of the second rotor  104 . When the urging force, which is applied to the second rotor  104  toward the bearing portion  22 , is increased, a resistance torque, which is applied to the second rotor  104  from the bearing portion  22  through the second friction member  118 , is increased. The resistance torque, which is applied to the second rotor  104 , is conducted to the projections  106  through the second-bevel-gear teeth  112 , the first-bevel-gear teeth  108  and the first rotor  102 . 
     One end portion of the second spring  120 , which is formed as a coil spring, is engaged with a spring receiving member  122  that is engaged with a spring engaging portion  105  of the second rotor  104 . The other end portion of the second spring  120  is engaged with the connecting portion  28  of the housing  20 . The spring engaging portion  105  extends upwardly in the accommodating chamber  36 . The second spring  120  urges the second rotor  104  in the accelerator-closing direction Y. An urging force of the second spring  120  is increased, when the rotational angle of the second rotor  104  from the accelerator-full-closing position (i.e., the position of the second rotor  104  shown in  FIG. 4 ) in the accelerator-opening direction X is increased. A torque, which is applied to the second rotor  104  by the urging force of the second spring  120 , is conducted to the projections  106  through the second-bevel-gear teeth  112 , the first-bevel-gear teeth  108  and the first rotor  102 . 
     The manipulation member  60  includes a spring-supporting portion  35 , which extends from a distal end part of the full-closing-side stopper portion  82  toward the connecting portion  26 . The spring-supporting portion  35  is placed on one side of the spring engaging portion  105  of the second rotor  104  in the accelerator-closing direction Y. 
     An inner peripheral wall of each of the through-holes  70  defines the projection-receiving space  70   a , which is circumferentially elongated and receives the corresponding projection  106 . Each of the projections  106  is circumferentially urged against the closing-side end wall  72  of the corresponding through-hole  70  by the urging force of the second spring  120 . When the projection  106  contacts the closing-side end wall  72  of the through-hole  70 , a space is formed on a circumferential side of the projection  106  in the accelerator-opening direction X. When the accelerator pedal  87  is rotated in the accelerator-opening direction X, the closing-side end wall  72  of each through-hole  70  contacts the corresponding projection  106  and conducts the resistance torque, which is received by the projection  106 , to the pedal boss portion  64 . 
     When the accelerator pedal  87  is rotated in the accelerator-closing direction Y, the pedal boss portion  64  can rotate to the accelerator-full-closing position without engaging the projections  106  in the circumferential direction. That is, the pedal boss portion  64  is rotatable relative to the housing  20  within a predetermined angular range from the accelerator-full-closing position to the accelerator-full-opening position. In contrast, the through-hole  70  is configured such that the pedal boss portion  64  can rotate relative to the projection  106  through an angular range that is larger than the predetermined angular range of the pedal boss portion  64 , through which the pedal boss portion  64  can rotate relative to the housing  20 . 
     Specifically, a circumferential length of the through-hole  70 , which is measured circumferentially about the rotational axis of the shaft  50  from the closing-side end wall  72  of the through-hole  70  to the opening-side end wall  74  of the through-hole  70 , is denoted as X 1 . A circumferential moving distance of the projection  106 , which is measured circumferentially about the rotational axis of the shaft  50  from the accelerator-full-closing position to the accelerator-full-opening position, is denoted as X 2 . A circumferential length (specifically, an outer diameter in the case of the projection  106  having a circular cross section) of the projection  106 , which is measured circumferentially about the rotational axis of the shaft  50 , is denoted as X 3 . In such a case, the circumferential length X 1  is set to be larger than a sum of the circumferential moving distance X 2  and the circumferential length X 3  (i.e., X 1 &gt;X 2 +X 3 ). Thereby, even when the projection  106  is fixed, i.e., fastened at the accelerator-full-opening position, the pedal boss portion  64  can move back to the accelerator-full-closing position without generating interference between the projection  106  and the pedal boss portion  64 . 
     Next, the operation of the accelerator apparatus  10  will be described. 
     When the accelerator pedal  87  is depressed, the manipulation member  60  is rotated together with the shaft  50  about the rotational axis of the shaft  50  in the accelerator-opening direction X in response to the pedal force applied from the foot of the driver to the pad  86 . At this time, in order to rotate the manipulation member  60  and the shaft  50 , the pedal force needs to generate a torque that is larger than a sum of the torque, which is generated by the urging forces of the first and second springs  88 ,  120 , and the resistance torque, which is generated by the frictional forces of the first and second friction members  116 ,  118 . 
     When the accelerator pedal  87  is depressed, the resistance torque, which is generated by the frictional forces of the first and second friction members  116 ,  118 , limits the rotation of the accelerator pedal  87  in the accelerator-opening direction X. Therefore, with reference to  FIG. 6 , the pedal force F (N) at the time of depressing the accelerator pedal  87  (see a solid line L 1 , which indicates the relationship between the pedal force F (N) and the rotational angle θ (degrees) at the time of depressing the accelerator pedal  87 ), is larger than the pedal force F (N) at the time of returning the accelerator pedal  87  toward the accelerator-full-closing position (see a dot-dash line L 3 , which indicates the relationship between the pedal force F (N) and the rotational angle θ (degrees) at the time of returning the accelerator pedal  87  toward the accelerator-full-closing position) even for the same rotational angle θ. 
     In order to maintain the depressed state of the accelerator pedal  87 , it is only required to apply the pedal force that generates the torque, which is larger than a difference between the torque generated by the urging forces of the first and second springs  88 ,  120  and the resistance torque generated by the frictional forces of the first and second friction members  116 ,  118 . In other words, when the driver wants to maintain the depressed state of the accelerator pedal  87  after depressing the accelerator pedal  87 , the driver may reduce the applied pedal force by a certain amount. 
     For example, as indicated by a dot-dot-dash line L 2  in  FIG. 6 , in the case where the depressed state of the accelerator pedal  87 , which is depressed to the rotational angle θ 1 , needs to be maintained, the pedal force may be reduced from the pedal force F( 1 ) to the pedal force (F 2 ). In this way, the depressed state of the accelerator pedal  87  can be easily maintained. The resistance torque, which is generated by the frictional forces of the first and second friction members  116 ,  118 , is exerted to limit the rotation of the accelerator pedal  87  in the accelerator-closing direction Y at the time of maintaining the depressed state of the accelerator pedal  87 . 
     In order to return the accelerator pedal  87  to the accelerator-full-closing position, the pedal force applied to the accelerator pedal  87  should generate a torque that is smaller than the difference between the torque, which is generated by the urging forces of the first and second springs  88 ,  120 , and the resistance torque, which is generated by the frictional forces of the first and second friction members  116 ,  118 . Here, at the time of returning the accelerator pedal  87  to the accelerator-full-closing position, it is only required to stop the depressing of the accelerator pedal  87  (i.e., required to fully release the accelerator pedal  87 ). Therefore, there is no burden to the driver. In contrast, when the accelerator pedal  87  is gradually returned toward the accelerator-full-closing position, it is required to apply a predetermined pedal force on the accelerator pedal  87 . In the first embodiment, the pedal force, which is required to gradually return the accelerator pedal toward the accelerator-full-closing position, is relatively small. 
     For example, as indicated by the dot-dash line L 3  in  FIG. 6 , in the case where the accelerator pedal  87 , which is depressed to the rotational angle θ 1 , is gradually returned toward the accelerator-full-closing position, the pedal force may be adjusted between the pedal force F( 2 ) and 0 (zero). The pedal force F( 2 ) is smaller than the pedal force F( 1 ). Therefore, when the depressed accelerator pedal  87  is returned toward the accelerator-full closing position, the burden on the driver is reduced. The resistance torque, which is generated by the frictional forces of the first and second friction members  116 ,  118 , acts to limit the rotation of the accelerator pedal  87  in the accelerator-closing direction Y at the time of returning the accelerator pedal  87  toward the accelerator-full closing position. Therefore, as indicated in  FIG. 6 , the pedal force F at the time of returning the accelerator pedal  87  toward the accelerator-full-closing position (see the dot-dash line L 3 , which indicates the relationship between the pedal force F and the rotational angle θ at the time of returning the accelerator pedal  87  toward the accelerator-full-closing position) is smaller than the pedal force F at the time of depressing the accelerator pedal  87  (see the solid line L 1 , which indicates the relationship between the pedal force F and the rotational angle θ at the time of depressing the accelerator pedal  87 ) even for the same rotational angle θ. 
     Here, it is now assumed that the rotation of the first and second rotors  102 ,  104  is disabled (i.e., the first and second rotors  102 ,  104  become non-rotatable) due to, for example, clamping of a foreign object between the first friction member  116  and the bearing portion  24  of the housing  20  or between the second friction member  118  and the bearing portion  22  of the housing  20  or increasing of the frictional forces of the first and second friction members  116 ,  118  caused by an environmental change. In such a case, the urging force of the second spring  120  is not applied to the pedal boss portion  64 . However, the urging force of the first spring  88  is applied to the pedal boss portion  64 . The pedal boss portion  64  can be returned to the accelerator-full closing position by the urging force of the first spring  88  without causing an interference with the projections  106  even in the case where the first and second rotors  102 ,  104  become non-rotatable at the accelerator-full closing position due to, for example, the jamming. 
     As described above, in the accelerator apparatus  10  of the first embodiment, the pedal boss portion  64  of the manipulation member  60  includes the through-holes  70 , each of which receives the corresponding projection  106  and is elongated in the circumferential direction. At the time of rotating the pedal boss portion  64  to the accelerator-full closing position, the pedal boss portion  64  can be rotated to the accelerator-full closing position without engaging with the projections  106  in the circumferential direction. Therefore, when the first rotor  102  becomes non-rotatable due to fastening (jamming) of the first and second friction members  116 ,  118 , the pedal boss portion  64  can be rotated to the accelerator-full-closing position regardless of the rotational positions of the first rotor  102  and the projections  106 . At this time, the urging force of the first spring  88  is exerted against the pedal boss portion  64 . Therefore, when the depressed accelerator pedal  87  is fully released, the accelerator pedal  87  and the associated components rotated integrally therewith can be reliably returned to the accelerator-full-closing position. 
     Furthermore, in the first embodiment, the pedal boss portion  64  of the manipulation member  60  is rotatable relative to the housing  20  within the predetermined angular range from the accelerator-full-closing position to the accelerator-full-opening position. The through-holes  70  are formed such that the pedal boss portion  64  can be rotated relative to the projections  106  through the corresponding angular range, which is larger than the predetermined angular range discussed above. Therefore, when the first rotor  102  becomes non-rotatable due to the fastening (jamming) of at least one of the first and second friction members  116 ,  118 , the pedal boss portion  64  can be rotated to the accelerator-full-closing position without causing the interference with the projections  106 . 
     Furthermore, according to the first embodiment, the engaging portions of the pedal boss portion  64 , which are circumferentially engageable with the projections  106 , are formed by the inner peripheral walls of the through-holes  70 . Therefore, in comparison to a case where the engaging portions of the pedal boss portion  64  are formed by inner walls of notched grooves, which are recessed in the outer peripheral surface of the pedal boss portion  64 , the strength of the pedal boss portion  64  can be increased. 
     Furthermore, according to the first embodiment, the first spring  88  generates the urging force, which can return the shaft  50  and the manipulation member  60  to the accelerator-full-closing position. Thereby, in the case where the first rotor  102  becomes non-rotatable, and the urging force of the second spring  120  is not applied to the pedal boss portion  64 , the shaft  50  and the manipulation member  60  can be reliably returned to the accelerator-full-closing position by the urging force of the first spring  88 . 
     Furthermore, according to the first embodiment, the full-closing-side stopper portion  82  is received in the accommodating chamber  36 , which is defined by the housing  20 , the pedal boss portion  64  and the cover portions  78 ,  80 . Therefore, it is possible to limit the clamping of the foreign object between the full-closing-side stopper portion  82  and the surface  38  of the connecting portion  26  of the housing  20 . Therefore, at the time of releasing the depressed accelerator pedal  87  toward the accelerator-full-closing position, it is possible to avoid the occurrence of the non-returnable state of the accelerator pedal  87 , at which the accelerator pedal  87  cannot be returned to the accelerator-full-closing position, and which is caused by, for example, the clamping of the foreign object between the full-closing-side stopper portion  82  and the surface  38  of the connecting portion  26 . 
     Furthermore, according to the first embodiment, the full-closing-side stopper portion  82  is located at the upper side of the accommodating chamber  36 . At the time of limiting the rotation of the shaft  50  in the accelerator-closing direction Y, the full-closing-side stopper portion  82  contacts the vertical surface  38  that extends in the top-to-bottom direction in the inner wall of the connecting portion  26  of the housing  20 . Therefore, the foreign objects, such as abrasive particles, which are lifted into the upper area of the accommodating chamber  36 , fall onto the lower side of the accommodating chamber  36  without adhering to the surface  38  of the connecting portion  26  of the housing  20 . Thus, it is possible to limit the clamping of the foreign objects, which are located in the inside of the accommodating chamber  36 , between the full-closing-side stopper portion  82  and the surface  38  of the connecting portion  26 . 
     Furthermore, according to the first embodiment, in the case where the first spring  88  and the spring engaging portion  105  of the second rotor  104  are broken, the urging force of the second spring  120  is urged against the pedal boss portion  64  through the spring-supporting portion  35 , which is engaged with the broken spring engaging portion  105 . Therefore, in the case where the first spring  88  and the spring engaging portion  105  of the second rotor  104  are broken, the manipulation member  60  and the shaft  50  can be returned to the accelerator-full-closing position. 
     Second Embodiment 
     An accelerator apparatus according to a second embodiment of the present disclosure will be described with reference to  FIG. 7 . 
     In the second embodiment, a circumferential distance between the projection  130  and the closing-side end wall  136  of the through-hole  135  (each through-hole  135  defining a projection-receiving space  135   a , which receives the corresponding projection  130 ) is progressively reduced in the axial direction of the shaft  50  from the distal end  131  side of the projection  130  toward the base end  132  side of the projection  130 . Specifically, a first outer wall  133  of the projection  130 , which is placed on a circumferential side where the closing-side end wall  136  of the through-hole  135  is located, is tilted relative to the axial direction of the shaft  50  such that a base end  132   a  of the first outer wall  133  is circumferentially displaced from a distal end  131   a  of the first outer wall  133  in the accelerator-closing direction Y. Furthermore, the closing-side end wall  136  of the through-hole  135  is tilted relative to the axial direction of the shaft  50  such that one axial end  136   a  of the closing-side end wall  136 , which is located on the one axial side (base side) where the base end  132  of the projection  130  is located, is circumferentially displaced from the other axial end  136   b  of the closing-side end wall  136 , which is located on the other axial side (distal side) where the distal end  131  of the projection  130  is located, in the accelerator-closing direction Y. Furthermore, a degree of tilting of the closing-side end wall  136  of the through-hole  135  (relative to the axial direction of the shaft  50 ) is smaller than a degree of tilting of the first outer wall  133  of the projection  130  (relative to the axial direction of the shaft  50 ). The closing-side end wall  136  of the through-hole  135  serves as an engaging portion of the present disclosure. 
     Therefore, in the second embodiment, when the projection  130  contacts the closing-side end wall  136  of the through-hole  135 , the closing-side end wall  136  contacts an outer wall of a base end portion  134  of the projection  130 . Thereby, a bending stress, which is applied to the base end  132  of the projection  130 , is reduced, and thereby the durability of the projection  130  can be improved, and a size of the projection  130  can be reduced. 
     Furthermore, according to the second embodiment, when each of the projections  130  and the closing-side end wall  136  of the corresponding one of the through-holes  135  are circumferentially engaged with each other (i.e., are circumferentially contacted with each other), the pedal boss portion  64  is urged by the first outer wall  133  of each projection  130  toward the first friction member  116  side in the axial direction of the shaft  50 . At this time, the first friction member  116  receives the urging force of each projection  130  and the urging force of the pedal boss portion  64 . Thereby, the resistance torque, which is applied to the pedal boss portion  64 , is increased. Thus, it is possible to generate the pedal force hysteresis characteristics such that a relatively large pedal force difference exists between the time of depressing the accelerator pedal  87  and the time of returning the accelerator pedal  87  toward the accelerator-full-closing position. 
     Third Embodiment 
     An accelerator apparatus according to a third embodiment of the present disclosure will be described with reference to  FIG. 8 . 
     In the third embodiment, similar to the second embodiment, the circumferential distance between the projection  140  and the closing-side end wall  146  of the through-hole  145  (each through-hole  145  defining a projection-receiving space  145   a , which receives the corresponding projection  140 ) is progressively reduced from the distal end  141  side of the projection  140  toward the base end  142  side of the projection  140  in the axial direction of the shaft  50 . Specifically, a first outer wall  143  of the projection  140 , which is placed on a circumferential side where the closing-side end wall  146  of the through-hole  145  is located, is tilted relative to the axial direction of the shaft  50  such that the base end  142   a  of the first outer wall  143  is circumferentially displaced from the distal end  141   a  of the first outer wall  143  of the projection  140  in the accelerator-closing direction Y. Furthermore, the closing-side end wall  146  of the through-hole  145  is tilted relative to the axial direction of the shaft  50  such that one axial end  146   a  of the closing-side end wall  146 , which is located on the one axial side where the base end  142  of the projection  140  is located, is circumferentially displaced from the other axial end  146   b  of the closing-side end wall  146 , which is located on the other axial side where the distal end  141  of the projection  140  is located, in the accelerator-closing direction Y. Furthermore, a degree of tilting of the closing-side end wall  146  of the through-hole  145  (relative to the axial direction of the shaft  50 ) is smaller than a degree of tilting of the first outer wall  143  of the projection  140  (relative to the axial direction of the shaft  50 ). The closing-side end wall  146  of the through-hole  145  serves as an engaging portion of the present disclosure. 
     Furthermore, a second outer wall  144  of the projection  140 , which is circumferentially opposite from the first outer wall  143  of the projection  140 , is tilted relative to the axial direction of the shaft  50  such that the base end  142   b  of the second outer wall  144  is circumferentially displaced from the distal end  141   b  of the second outer wall  144  in the accelerator-opening direction X. Furthermore, the opening-side end wall  147  of the through-hole  145 , which is circumferentially opposite from the closing-side end wall  146  of the through-hole  145 , is tilted relative to the axial direction of the shaft  50  such that one axial end  147   a  of the opening-side end wall  147 , which is located on the one axial side where the base end  142  of the projection  140  is located, is circumferentially displaced from the other axial end  147   b  of the opening-side end wall  147 , which is located on the other axial side where the distal end  141  of the projection  140  is located, in the accelerator-opening direction X. Furthermore, a degree of tilting of the opening-side end wall  147  of through-hole  145  (relative to the axial direction of the shaft  50 ) is smaller than a degree of tilting of the second outer wall  144  of the projection  140  (relative to the axial direction of the shaft  50 ). 
     Therefore, according to the third embodiment, the advantages, which are similar to those of the second embodiment, can be achieved. Furthermore, the strength of the base end  142  of the projection  140  is increased. Therefore, the durability of the projection  140  can be further improved, and the size of the projection  140  can be reduced. 
     Fourth Embodiment 
     An accelerator apparatus according to a fourth embodiment of the present disclosure will be described with reference to  FIG. 9 . 
     In the fourth embodiment, the shape of the closing-side end wall  151  of the through-hole  150  (each through-hole  150  defining a projection-receiving space  150   a , which receives the corresponding projections  130 ) is different from the shape of the closing-side end wall  136  of the through-hole  135  of the second embodiment. Similar to the closing-side end wall  136  of the through-hole  135  of the second embodiment, the closing-side end wall  151  of the through-hole  150  is tilted relative to the axial direction of the shaft  50  such that one axial end  151   a  of the closing-side end wall  151  is circumferentially displaced from the other axial end  151   b  of the closing-side end wall  151  in the accelerator-closing direction Y. A degree of tilting of the closing-side end wall  151  (relative to the axial direction of the shaft  50 ) is smaller than the degree of tilting of the first outer wall  133  of the projection  130  (relative to the axial direction of the shaft  50 ). However, the shape of the axial end  151   a  side part of the closing-side end wall  151  differs from the shape of the axial end  136   a  side part of the closing-side end wall  136  of the second embodiment. Specifically, the closing-side end wall  151  has a contact surface  152 , which is substantially parallel to a surface of the outer wall of the base end portion  134  of the projection  130  (a circumferentially opposed surface of the first outer wall  133  of the projection  130 ), which is circumferentially opposed to the contact surface  152  of the closing-side end wall  151 . A tilt angle of the contact surface  152  relative to the axial direction of the shaft  50  is substantially the same as that of the outer wall of the base end portion  134  of the projection  130  (the circumferentially opposed surface of the first outer wall  133  of the projection  130 ), which is circumferentially opposed to the contact surface  152 . When the outer wall of the base end portion  134  of the projection  130  contacts the closing-side end wall  151  of the through-hole  150 , the circumferentially opposed outer wall of the base end portion  134  makes a surface-to-surface contact with the contact surface  152  of the closing-side end wall  151  of the through-hole  150 . The closing-side end wall  151  serves as an engaging portion of the present disclosure. 
     Therefore, in the fourth embodiment, the pressure applied to the projection  130  and the pressure applied to the closing-side end wall  151  of the through-hole  150  can be reduced in comparison to the second embodiment where the projection  130  and the closing-side end wall  151  of the through-hole  150  make a point-to-point contact (or a line-to-line contact) therebetween. Therefore, it is possible to limit an increase in the amount of deformation with time at the contact between the projection  130  and the closing-side end wall  151 , i.e., it is possible to limit the creep phenomenon. Thus, it is possible to limit a change in the pedal force hysteresis characteristics with time. 
     Fifth Embodiment 
     An accelerator apparatus according to a fifth embodiment of the present disclosure will be described with reference to  FIG. 10 . 
     In the fifth embodiment, each through-hole  70  is the same as that of the first embodiment, and each projection  130  is the same as that of the second embodiment. 
     Even in the fifth embodiment, in which the closing-side end wall  72  of the through-hole  70  and an opening-side end wall  74  of the through-hole  70  are parallel to the rotational axis of the pedal boss portion  64  (i.e., the rotational axis of the shaft  50 ), the advantages similar to those of the second embodiment can be achieved. 
     Sixth Embodiment 
     An accelerator apparatus according to a sixth embodiment of the present disclosure will be described with reference to  FIG. 11 . 
     In the sixth embodiment, each through-hole  70  is the same as that of the first embodiment, and each projection  140  is the same as that of the third embodiment. 
     Even in the sixth embodiment, in which the closing-side end wall  72  of the through-hole  70  and the opening-side end wall  74  of the through-hole  70  are parallel to the rotational axis of the pedal boss portion  64  (i.e., the rotational axis of the shaft  50 ), the advantages similar to those of the third embodiment can be achieved. 
     Seventh Embodiment 
     An accelerator apparatus according to a seventh embodiment of the present disclosure will be described with reference to  FIG. 12 . 
     In the seventh embodiment, each through-hole  150  is the same as that of the fourth embodiment, and each projection  140  is the same as that of the third embodiment. 
     In comparison to the third embodiment, in which the projection  140  and the closing-side end wall  146  make the point-to-point contact (or the line-to-line contact) therebetween, according to the seventh embodiment, the pressure applied to the projection  140  and the pressure applied to the closing-side end wall  151  can be reduced. Therefore, it is possible to limit the creep phenomenon. Thus, it is possible to limit the change in the pedal force hysteresis characteristics with time. 
     Eighth Embodiment 
     An accelerator apparatus according to an eighth embodiment of the present disclosure will be described with reference to  FIG. 13 . 
     In the eighth embodiment, each projection  140  is the same as that of the third embodiment. Furthermore, the closing-side end wall  161  of the through-hole  160  (each through-hole  160  defining a projection-receiving space  160   a , which receives the corresponding projection  140 ) is tilted relative to the axial direction of the shaft  50  such that one axial end  161   a  of the closing-side end wall  161 , which is located on the one axial side where the base end  142  of the projection  140  is located, is circumferentially displaced from the other axial end  161   b  of the closing-side end wall  161 , which is located on the other axial side where the distal end  141  of the projection  140  is located, in the accelerator-opening direction X. Furthermore, the opening-side end wall  162  of the through-hole  160  is tilted relative to the axial direction of the shaft  50  such that one axial end  162   a  of the opening-side end wall  162 , which is located on the one axial side where the base end  142  of the projection  140  is located, is circumferentially displaced from the other axial end  162   b  of the opening-side end wall  162 , which is located on the other axial side where the distal end  141  of the projection  140  is located, in the accelerator-closing direction Y. 
     Even in the eighth embodiment, in which the tilting direction of the closing-side end wall  161  and the tilting direction of the opening-side end wall are opposite from those of the third embodiment, the advantages, which are similar to those of the third embodiment, can be achieved. 
     Ninth Embodiment 
     An accelerator apparatus according to a ninth embodiment of the present disclosure will be described with reference to  FIG. 14 . 
     In the ninth embodiment, each projection  106  is the same as that of the first embodiment, and each through-hole  160  is the same as that of the eighth embodiment. 
     Even in the ninth embodiment, in which the closing-side end wall  161  and the opening-side end wall  162  are not parallel to the rotational axis of the pedal boss portion  64  (the rotational axis of the shaft  50 ), the advantages, which are similar to those of the first embodiment, can be achieved. 
     Tenth Embodiment 
     An accelerator apparatus according to a tenth embodiment of the present disclosure will be described with reference to  FIG. 15 . 
     In the tenth embodiment, the shape of the closing-side end wall  171  of the through-hole  170  (each through-hole  170  defining a projection-receiving space  170   a , which receives the corresponding projection  130 ) is different from the shape of the closing-side end wall  72  of the through-hole  70  of the fifth embodiment. Similar to the closing-side end wall  72  of the through-hole  70  of the fifth embodiment, the closing-side end wall  171  of the through-hole  170  of the present embodiment is generally parallel to the rotational axis of the pedal boss portion  64  (the rotational axis of the shaft  50 ). However, the shape of one axial end  171   a  side part of the closing-side end wall  171  differs from that of the closing-side end wall  72  of the fifth embodiment. Specifically, the closing-side end wall  171  has a contact surface  172 , which is substantially parallel to the outer wall of the base end portion  134  of the projection  130  (the circumferentially opposed surface of the first outer wall  133  of the projection  130 ), which is circumferentially opposed to the contact surface  172  of the closing-side end wall  171 . A tilt angle of the contact surface  172  relative to the axial direction of the shaft  50  is substantially the same as that of the outer wall of the base end portion  134  of the projection  130  (the circumferentially opposed surface of the first outer wall  133  of the projection  130 ), which is circumferentially opposed to the contact surface  172 . When the outer wall of the base end portion  134  of the projection  130  contacts the closing-side end wall  171  of the through-hole  170 , the circumferentially opposed outer wall of the base end portion  134  makes a surface-to-surface contact with the contact surface  172  of the closing-side end wall  171  of the through-hole  170 . The closing-side end wall  171  of the through-hole  170  serves as an engaging portion of the present disclosure. 
     Therefore, in the tenth embodiment, the pressure applied to the projection  130  and the pressure applied to the closing-side end wall  171  of the through-hole  170  can be reduced in comparison to the fifth embodiment where the projection  130  and the closing-side end wall  72  of the through-hole  70  make the point-to-point contact (or the line-to-line contact) therebetween. Therefore, it is possible to limit the creep phenomenon. Thus, it is possible to limit the change in the pedal force hysteresis characteristics with time. 
     Eleventh Embodiment 
     An accelerator apparatus according to an eleventh embodiment of the present disclosure will be described with reference to  FIG. 16 . 
     In the eleventh embodiment, each projection  140  is the same as that of the third embodiment, and each through-hole  170  is the same as that of the tenth embodiment. 
     According to the eleventh embodiment, the advantages, which are similar to those of the tenth embodiment can be achieved. 
     Twelfth Embodiment 
     An accelerator apparatus according to a twelfth embodiment of the present disclosure will be described with reference to  FIG. 17 . 
     According to the twelfth embodiment, the structures of the manipulation member  181 , the first rotor  182  and the second rotor  183  are different from those of the first embodiment. The manipulation member  181  is configured into a shape of  FIG. 17 , which is implemented by inverting the manipulation member  181  in the axial direction. Furthermore, the first rotor  182  is configured into a shape of  FIG. 17 , which is implemented by inverting the first rotor  102  in the axial direction. Furthermore, the second rotor  183  is configured into a shape of  FIG. 17 , which is implemented by inverting the second rotor  104  in the axial direction. 
     According to the twelfth embodiment, the advantages, which are similar to those of the first embodiment can be achieved. 
     Thirteenth Embodiment 
       FIG. 18  shows an accelerator apparatus according to a thirteenth embodiment of the present disclosure. The accelerator apparatus  200  of the thirteenth embodiment differs from the accelerator apparatus  10  of the first embodiment with respect to the structures of the projections  202 , the manipulation member  204  and the pedal boss portion  206 . 
     As shown in  FIG. 18 , according to the present embodiment, the number of projections  202  is two. Each projection  202  is configured to have an arcuate cross section that circumferentially extends in a plane, which is perpendicular to the rotational axis of the shaft  50 . The projections  202  are arranged one after another at generally equal intervals in the circumferential direction. Each of the projections  202  is received through a corresponding one of two notched grooves  208  (each notched groove  208  defining a projection-receiving space  208   a , which receives the corresponding projection  202 ) formed in the pedal boss portion  206  and axially projects on a side of the pedal boss portion  206 , which is opposite from the first rotor  102  in the axial direction of the shaft  50 . The projection  202  can circumferentially engage a closing-side end wall  210  of the notched groove  208  in the accelerator-closing direction Y. The closing-side end wall  210  serves as an engaging portion of the present disclosure. 
     The closing-side end wall  210  of the notched groove  208  and the projection  202  can engage with each other in the circumferential direction to transmit the rotation (rotational force) between the manipulation member  204  and the first rotor  102 . Specifically, the rotation of the manipulation member  204  in the accelerator-opening direction X can be conducted to the first rotor  102  through the closing-side end wall  210  of each notched groove  208  and the corresponding projection  202 . Furthermore, the rotation of the first rotor  102  in the accelerator-closing direction Y can be conducted to the manipulation member  204  through each projection  202  and the closing-side end wall  210  of the corresponding notched groove  208 . 
     The inner wall of each notched groove  208  defines the circumferential gap (the projection-receiving space  208   a ), which circumferentially extends and receives the corresponding projection  202 . Each of the projections  202  is circumferentially urged against the closing-side end wall  210  of the corresponding notched groove  208  by the urging force of the second spring  120 . When the projection  202  contacts the closing-side end wall  210  of the notched groove  208 , a space is formed on a circumferential side of the projection  202  in the accelerator-opening direction X. When the accelerator pedal  87  is rotated in the accelerator-opening direction X, the closing-side end wall  210  of the notched groove  208  contacts the projection  202  and conducts the resistance torque, which is received from each corresponding friction member  116 ,  118  through the projection  202 , to the pedal boss portion  206 . 
     Each notched groove  208  is configured such that the pedal boss portion  206  can rotate to the accelerator-full-closing position without causing the engagement of the pedal boss portion  206  with the projection  202  in the circumferential direction at the time of rotating the accelerator pedal  87  in the accelerator-closing direction Y. That is, the pedal boss portion  206  is rotatable relative to the housing  20  within a predetermined angular range from the accelerator-full-closing position to the accelerator-full-opening position. In contrast, the notched groove  208  is configured such that the pedal boss portion  206  can rotated relative to the projection  202  through an angular range that is larger than the predetermined angular range of the pedal boss portion  206 , through which the pedal boss portion  206  can rotate relative to the housing  20 . 
     Specifically, a circumferential length of the notched groove  208 , which is measured circumferentially about the rotational axis of the shaft  50  from the closing-side end wall  210  of the notched groove  208  to the opening-side end wall  212  of the notched groove  208 , is denoted as Y 1 . A circumferential moving distance of the projection  202 , which is measured circumferentially about the rotational axis of the shaft  50  from the accelerator-full-closing position to the accelerator-full-opening position, is denoted as Y 2 . A circumferential length of the projection  202 , which is measured circumferentially about the rotational axis of the shaft  50 , is denoted as Y 3 . In such a case, the circumferential length Y 1  is set to be larger than a sum of the circumferential moving distance Y 2  and the circumferential length Y 3  (i.e., Y 1 &gt;Y 2 +Y 3 ). In this way, even when the projection  202  is fastened (is stuck) at the accelerator full-opening position, the pedal boss portion  206  can rotate to the accelerator-full-closing position without causing interference between the pedal boss portion  206  and the projection  202 . 
     Next, the operation of the accelerator apparatus  200  will be described. 
     For instance, it is now assumed that the rotation of the first and second rotors  102 ,  104  is disabled (i.e., the first and second rotors  102 ,  104  become non-rotatable) due to, for example, clamping of a foreign object between the first friction member  116  and the bearing portion  24  of the housing  20  or between the second friction member  118  and the bearing portion  22  of the housing  20  or increasing of the frictional forces of the first and second friction members  116 ,  118  caused by an environmental change. In such a case, the urging force of the second spring  120  is not applied to the pedal boss portion  206 . However, the urging force of the first spring  88  is applied to the pedal boss portion  206 . The pedal boss portion  206  can be returned to the accelerator-full closing position by the urging force of the first spring  88  without causing interference with the projections  202  even in the case where the first and second rotors  102 ,  104  become non-rotatable at the accelerator-full closing position. 
     As described above, in the accelerator apparatus  200  of the thirteenth embodiment, the pedal boss portion  206  of the manipulation member  204  includes the notched grooves  208 , each of which receives the corresponding projection  202  and is elongated in the circumferential direction. At the time of rotating the pedal boss portion  64  to the accelerator-full closing position, the pedal boss portion  64  can be rotated to the accelerator-full closing position without engaging with the projections  202  in the circumferential direction. 
     Therefore, when the first rotor  102  becomes non-rotatable due to fastening (jamming) of the first and second friction members  116 ,  118 , the pedal boss portion  206  can be rotated to the accelerator-full-closing position regardless of the rotational positions of the first rotor  102  and the projections  202 . At this time, the urging force of the first spring  88  is exerted against the pedal boss portion  206 . Therefore, similar to the first embodiment, when the depressed accelerator pedal  87  is fully released, the accelerator pedal  87  and the associated components rotated integrally therewith can be reliably returned to the accelerator-full-closing position. 
     Now, modifications of the above embodiments will be described. 
     In a modification of the above embodiments, the projections  106 ,  130 ,  140 ,  202  do not need to be arranged at generally equal intervals in the circumferential direction. 
     Furthermore, the number of the projections  106 ,  130 ,  140  does not need to be four. It is only required to form two or more projections, which are arranged one after another in the circumferential direction. 
     Also, in another modification of the above embodiments, the projections  106 ,  130 ,  140 ,  202  may be formed separately from the first rotor  102 ,  182 . 
     Furthermore, in another modification of the above embodiments, the full-closing-side stopper portion  82  may not need to be received in the accommodating chamber  36  formed by the housing  20 . Furthermore, in the case where the full-closing-side stopper portion  82  is received in the accommodating chamber  36  of the housing  20 , it is not required to place the full-closing-side stopper portion  82  in the upper side area of the accommodating chamber  36 . 
     Furthermore, in another modification of the above embodiments, it is possible to provide an insensible area, in which the depression of the accelerator pedal is not sensed. The insensible area may be from the contact point, at which the full-closing-side stopper portion  82  contacts the housing  20 , to a predetermined angular point, which is displaced from the contact point by a predetermined angle in the accelerator-opening direction X. The accelerator-full-closing position may be set at this position, which is displaced from the contact point, at which the full-closing-side stopper portion  82  contacts the housing  20 , by the predetermined angle in the accelerator-opening direction X. 
     Furthermore, in another modification of the above embodiments, the first friction member  116  may be fixed to the housing  20 . Also, the second friction member  118  may be fixed to the housing  20 . 
     Also, in another modification of the above embodiments, the first spring  88  and the second spring  120  may not need to be the coil springs. For instance, the first spring and/or the second spring may be made of any other appropriate urging member, such as a leaf spring, a torsion spring. 
     Also, in another modification of the above embodiments, the first spring may be provided more than one (i.e., providing a plurality of first springs). Also, the second spring may be provided more than one (i.e., providing a plurality of second springs). 
     Furthermore, in another modification of the above embodiments, the first spring  88  may be engaged to, for example, the pedal boss portion  64 ,  206  or the accelerator pedal  87 . The first spring  88  is only required to urge the accelerator pedal or the member, which is rotated integrally with the accelerator pedal. 
     Furthermore, in another modification of the above embodiments, the rotational position sensor  90  does not need to use the magnet  96  and the Hall element. As long as the rotational position sensor can sense the rotational position of the shaft  50 , any other appropriate type of rotational sensor may be used. 
     The present disclosure is not limited the above embodiments and modifications thereof. That is, the above embodiments and modifications thereof may be modified in various ways without departing from the sprit and scope of the present disclosure.