Abstract:
The present invention enables a user to intuitively grasp the occurrence of prescribed phenomena during operation. Provided is a damper that restricts pivot pin ( 4 ) rotation associated with operation of an operating section, wherein the friction resistance that impedes the rotation of the pivot pin ( 4 ) is changed in a stepped fashion. When the pivot pin ( 4 ) rotates in direction α due to the depression of an accelerator pedal (operating section) ( 21 ), a slide cam ( 62 ) shifts an edge section ( 621 A) of an inclined cam surface ( 621 ) in a direction A away from a rotating cam ( 61 ) while staying in contact with a gradual first inclined region ( 611 A) of an inclined cam surface ( 611 ) of the rotating cam ( 61 ). Torque around the axis of the pivot pin ( 4 ) is produced, the entire region of the inclined cam surface ( 621 ) of the slide cam ( 62 ) comes into contact with a steep second inclined region ( 611 B) of the inclined cam surface ( 611 ) of the rotating cam ( 61 ) upon depression of the accelerator pedal ( 21 ) to a prescribed position (the pivot pin ( 4 ) has rotated by a prescribed angle θ1 in direction α), and the torque around the axis of the pivot pin ( 4 ) rapidly increases

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to structure of a damper that can notify a user of occurrence of a prescribed event by a tactile signal in an operation unit that receives a user&#39;s manual operation at an operating part. 
       BACKGROUND ART 
       [0002]    Patent Literature 1 describes an accelerator pedal unit that uses hysteresis characteristics of a damper having a pair of cams so that excessive pressing of the accelerator pedal is impeded by applying a suitable load against pressing of the accelerator pedal and a strain on a foot of a driver is reduced when the accelerator pedal is held at an almost-constant position. 
         [0003]    In this accelerator pedal unit, rotation of an accelerator pedal arm is transmitted to a rotating shaft of the damper through a transmission mechanism including a link member and the like so that rotations of the accelerator pedal arm in both directions are damped. In detail, one end of the link member is fixed to the rotating shaft of the damper so that rotation of the link member causes rotation of the rotating shaft of the damper. On the other hand, an engaging member is fixed to the accelerator pedal arm at its opposite end across a rotating shaft of the accelerator pedal arm from the accelerator pedal. This engaging member is slidably held by the link member. Accordingly, when the accelerator pedal arm rotates, the rotating shaft of the damper is rotated through the link member in the direction depending on the rotation direction of the accelerator pedal. Owing to the hysteresis characteristics of the damper, an appropriate load is given at the time of pressing the accelerator pedal while the load is reduced at the time of return of the accelerator pedal (Paragraphs 0071-0084 and FIGS. 13-19, for example). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Unexamined Patent Application Laid-Open No. 2002-12052 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    Excessive pressing of an accelerator pedal increases the energy expenditure rate of an automobile, and is undesirable from the viewpoint of traveling energy cost reduction or the like. Thus, in order to pursue so-called eco-driving, it is necessary for a driver to adjust the degree of pressing of an accelerator pedal while constantly grasping the traveling conditions of his automobile according to visual information obtained from, for example, an eco-meter in the instrument panel when the automobile is moving. 
         [0006]    However, the convenience of a driver is improved if the driver can grasp more intuitively a signal of prompting energy saving driving without confirming display on an instrument panel. This does not apply only to an automobile, and it is convenient if a user who manually operates an operating part can intuitively grasp a signal that notifies the user of occurrence of a prescribed event. 
         [0007]    The present invention has been made considering the above situation. An object of the invention is to provide an operation unit that receives user&#39;s manual operation at an operating part and can give an intuitively perceivable signal conveying notice of occurrence of a prescribed event, and a damper suitable for use in the operation unit. 
       Solution to Problem 
       [0008]    To solve the above problems, according to the present invention, a pivot pin, which rotates in conjunction with an operating part for receiving a user&#39;s manual operation, is connected with a damper for damping rotation of the pivot pin, and force of the damper to damp rotation of the pivot pin increases rapidly at a time when the pivot pin is rotated to a prescribed rotation angle. 
         [0009]    For example, the present invention provides a damper for damping rotation of a rotating shaft, comprising: 
         [0010]    a pair of cam members each having an inclined cam face inclined with respect to a rotation direction of the rotating shaft, upon a torque of the rotating shaft being transmitted to the cam members, the cam members rotating relative to each other about an axis of the rotating shaft and moving relative to each other in an axial direction of the rotating shaft; 
         [0011]    a housing part housing the pair of cam members and having an inner side surface on which the pair of the cam members moving and rotating relative to each other slide; and 
         [0012]    a friction resistance changing means changing a friction resistance impeding relative rotation of the pair of cam members stepwise by changing, in a stepwise manner, force of pressing the pair of cam members against an end portion of the housing part with increase of a relative rotation angle of the pair of cam members while pressing the pair of the cam members in the axial direction of the rotating shaft against the housing part at the end portion located in the axial direction of the rotating shaft so as to allow the pair of cam members to press against each other at the inclined cam faces. 
         [0013]    Here, the friction resistance changing means may comprise: 
         [0014]    an elastic body being placed within the housing part so as to be compressed in the axial direction of the rotating shaft by increase of an amount of a relative movement of the pair of cam members in the axial direction, biasing the pair of cam members in the axial direction of the rotating shaft; and 
         [0015]    at least two inclined areas being formed in the inclined cam face of at least one of the pair of cam members, being inclined at different angles from each other with respect to the direction of the relative rotation of the pair of cam members, and being arranged in the direction of the relative rotation of the pair of cam members. 
         [0016]    Or the friction resistance changing means may comprise an elastic means placed within the housing part so as to be compressed in the axial direction of the rotating shaft by increase of a relative moving amount of the pair of cam members in the axial direction, the elastic means biasing the pair of cam members in the axial direction of the rotating shaft by restoring force; and 
         [0017]    an elastic coefficient of the elastic means may increase stepwise with increase of a compression amount of the elastic means. 
         [0018]    Further, the present invention provides an operation unit for receiving a manual operation at an operating part from a user, wherein; 
         [0019]    the operation unit comprises; 
         [0020]    an arm having the operating part; 
         [0021]    a pivot pin, the arm being fixed to the pivot pin so that the operating part is located at a position away from an axis; 
         [0022]    a bracket holding the pivot pin rotatably about the axis of the pivot pin by force to be given to the operating part by the manual operation; and 
         [0023]    a damper damping rotation of the pivot pin; and 
         [0024]    the damper comprises; 
         [0025]    a pair of cam members each having an inclined cam face inclined with respect to a rotation direction of the pivot pin, upon a torque of the pivot pin being transmitted to the cam members, the cam members rotating relative to each other about the axis of the pivot pin and moving relative to each other in an axial direction of the pivot pin with the inclined cam faces in sliding contact with each other; 
         [0026]    a housing part being fixed to the bracket and housing the pair of cam members, housing part having an inner side surface, the pair of the cam members sliding on the inner side surface while moving and rotating relative to each other; 
         [0027]    a friction resistance changing means changing a friction resistance impeding relative rotation of the pair of cam members stepwise by changing, in a stepwise manner, force of pressing the pair of cam members against an end portion of the housing part with increase of an angle of relative rotation of the pair of cam members while pressing the pair of the cam members in the axial direction of the pivot pin against the housing part at the end portion located in the axial direction of the pivot pin so as to allow the pair of cam members to press against each other at the inclined cam faces. 
         [0028]    Here, the friction resistance changing means may comprise: 
         [0029]    an elastic body being placed within the housing part so as to be compressed in the axial direction of the pivot pin by increase of a relative moving amount of the pair of cam members in the axial direction, biasing the pair of cam members in the axial direction of the pivot pin; and 
         [0030]    at least two inclined areas being formed in the inclined cam faces of at least one of the pair of cam members, being inclined at different angles from each other with respect to a direction of the relative rotation of the pair of cam members, and being arranged in the direction of the relative rotation of the pair of cam members. 
         [0031]    Further, the friction resistance changing means may comprise an elastic means being placed within the housing part so as to be compressed in the axial direction of the pivot pin by increase of a relative moving amount of the pair of cam members in the axial direction and biasing the pair of cam members in the axial direction of the pivot pin by restoring force so as to allow the inclined cam faces of the pair of cam members to press against each other; and 
         [0032]    an elastic coefficient of the elastic means may increase stepwise with increase of a compression amount of the elastic means. 
       Advantageous Effects of Invention 
       [0033]    According to the present invention, a damper connected to a pivot pin rotating in conjunction with an operating part for receiving user&#39;s manual operation increases force of damping rotation of the pivot pin at a time when the pivot pin rotates to a prescribed rotation angle. Accordingly, the user can detect a change in feeling of operation of the operating part by tactile sensation. Thus, for example, in an application case where the operation unit is an accelerator pedal unit having an accelerator pedal as an operating part, it is possible to increase a load on a foot with which a driver presses the accelerator pedal at a time when the accelerator pedal is pressed to a position where the energy expenditure rate of an automobile increases to a prescribed level. By this, while driving the automobile, the driver can detect a change in operational feeling of the accelerator pedal as a signal for energy-saving driving of the automobile. Thus, while driving the automobile, the driver can intuitively perceive the signal for energy-saving driving of the automobile through pressing operation of the accelerator pedal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0034]      FIG. 1  is a view illustrating schematic configuration of a holding portion of an accelerator pedal arm  2  in an accelerator pedal unit  1  according to a first embodiment of the present invention; 
           [0035]      FIGS. 2(A) and 2(B)  are an external view and a right side view of a pedal pivot pin  4 , and  FIG. 2(C)  a view illustrating conceptually a state of the pedal pivot pin  4  fitted in a pedal bracket  5 ; 
           [0036]      FIG. 3  is an exploded view of a damper  6  according to the first embodiment of the present invention; 
           [0037]      FIGS. 4(A) and 4(B)  are left and right side views of the damper  6  in an initial state (with an accelerator pedal  21  being non-pressed), and  FIG. 4(C)  an A-A cross-section of  FIG. 4(A) ; 
           [0038]      FIGS. 5(A) and 5(B)  are left and right side views of a case  64 , and  FIG. 5(C)  a B-B cross-section of  FIG. 5(A) ; 
           [0039]      FIGS. 6(A) and 6(B)  are a front view and a back view of a cover  65 , and  FIG. 6(C)  a C-C cross-section of  FIG. 6(A) ; 
           [0040]      FIGS. 7(A) ,  7 (B) and  7 (C) are a front view and left and right side views of a rotating cam  61 ,  FIG. 7(D)  a D-D cross-section of  FIG. 7(C) , and  FIG. 7(E)  a view illustrating schematically a profile shape of a cam face  612  on a pitch circle  615  centering at an axis O; 
           [0041]      FIGS. 8(A) ,  8 (B) and  8 (C) are a front view, a back view and a side view of a slide cam  62 ,  FIG. 8(D)  an E-E cross-section of  FIG. 8(A) , and  FIG. 8(E)  a view illustrating schematically a profile shape of a cam face  622  on a pitch circle  625  centering at the axis O; 
           [0042]      FIGS. 9(A) ,  9 (B) and  9 (C) are views for explaining two-stage damping motion of the damper  6  associated with pressing the accelerator pedal  21 ; 
           [0043]      FIG. 10  is an exploded view of a damper  16  according to a second embodiment of the present invention; 
           [0044]      FIGS. 11(A) and 11(B)  are left and right side views of the damper  16  in an initial state (with an accelerator pedal  21  being non-pressed), and  FIG. 11(C)  an A-A cross-section of  FIG. 11(A) ; 
           [0045]      FIG. 12(A)  is a view for explaining structure of a combination spring  163 ,  FIG. 12(B)  a view illustrating a state of the combination spring  163  before increase of the spring constant, and  FIG. 12(C)  a view illustrating a state of the combination spring  163  having the increased spring constant; 
           [0046]      FIGS. 13(A) and 13(B)  are left and right side views of a case  164 , and  FIG. 13(C)  a B-B cross-section of  FIG. 13(A) ; 
           [0047]      FIGS. 14(A) ,  14 (B) and  14 (C) are a front view and left and right side views of a rotating cam  161 ,  FIG. 14(D)  a D-D cross-section of  FIG. 14(C) , and  FIG. 14(E)  a view illustrating schematically a profile shape of a cam face  1612  on a pitch circle  615  centering at an axis O; 
           [0048]      FIGS. 15(A) ,  15 (B) and  15 (C) are a front view, a back view and a side view of a slide cam  162 ,  FIG. 15(D)  an E-E cross-section of  FIG. 15(A) , and  FIG. 15(E)  a view illustrating schematically a profile shape of a cam face  622  on a pitch circle  625  centering at the axis O; 
           [0049]      FIG. 16  is a view for explaining two-stage damper motion of the damper  16  associated with pressing the accelerator pedal  21 ; 
           [0050]      FIG. 17  is a view for explaining two-stage damper motion of the damper  16  associated with pressing the accelerator pedal  21 ; and 
           [0051]      FIG. 18  is a view for explaining two-stage damper motion of the damper  16  associated with pressing the accelerator pedal  21 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0052]    In the following, embodiments of the present invention will be described referring to the drawings. 
       First Embodiment 
       [0053]    First, structure of an accelerator pedal unit  1  according to the present embodiment and structure of a damper  6  used in the accelerator pedal unit  1  will be described. 
         [0054]      FIG. 1  is a view illustrating schematic configuration of a holding portion of an accelerator pedal arm  2  in the accelerator pedal unit  1  according to the present embodiment. 
         [0055]    As illustrated, the accelerator pedal unit  1  of the present embodiment comprises: an accelerator pedal arm  2 , at one end portion of which an accelerator pedal  21  as an operating part for receiving driver&#39;s operation is fixed; a pedal pivot pin  4 , to which the accelerator pedal arm  2  is fixed so that the accelerator pedal  21  is located at a prescribed distance L3 from an axis O; a pedal bracket  5 , which holds the pedal pivot pin  4  rotatably in both directions α and β about the axis O so that the accelerator pedal arm  2  swings by operation (i.e. pressing and releasing) of the accelerator pedal  21 , and is fixed to a body (not shown) of an automobile; a retaining ring  7  for preventing dropping-off of the pedal pivot pin  4  from the pedal bracket  5 ; a spring  3 , whose both end portions are connected to the accelerator pedal arm  2  and the pedal bracket  5  so that the spring  3  is compressed with the press down of the accelerator pedal  21 , and which makes the accelerator pedal arm  2  (which has been rotated about the axis O of the pedal pivot pin  4  by pressing the accelerator pedal  21 ) return to an initial position by the elastic force of the spring  3  when the accelerator pedal  21  is released; and a detection part (not shown), which includes a potentiometer and the like for detecting an angle of rotation θ about the axis O of the pedal pivot pin  4  and outputting the detected angle to the outside. 
         [0056]    Further, the accelerator pedal unit  1  further comprises: a damper  6  in which resisting force for damping rotation of the pedal pivot pin  4  increases stepwise according to the angle θ of the rotation of the pedal pivot pin  4 , in order that a suitable load is applied on a foot with which driver presses down the accelerator pedal  21 , but the load on the driver&#39;s foot becomes rapidly heavier by at least tactually-detectable magnitude at the time when the accelerator pedal  21  is pressed to a position where the energy expenditure rate of the automobile deteriorates to a prescribed level (or at the time when the pedal pivot pin  4  rotates to a prescribed angle θ1 in the prescribed direction α about the axis O of the pedal pivot pin  4 ); and bolts  8  and nuts  9  for fixing the damper  6  to the pedal bracket  5 . 
         [0057]    In the following, these component parts  2 - 9  will be described. However, detailed description will be omitted with respect to parts similar to those in an ordinary accelerator pedal unit, such as the accelerator pedal arm  2 , the spring  3 , the retaining ring  7 , the detection part, and the like. In the following, the direction α in which the pedal pivot pin  4  rotates about its axis O at the time of pressing the accelerator pedal  21  is called the normal rotation direction α, and the direction β in which the pedal pivot pin  4  rotates about its axis O at the time of releasing the accelerator pedal  21  is called the reverse rotation direction β. 
         [0058]      FIGS. 2(A) and 2(B)  are an external view and a right side view of the pedal pivot pin  4 , and  FIG. 2(C)  a view illustrating conceptually a state of the pedal pivot pin  4  fitted in the pedal bracket  5 . 
         [0059]    As illustrated, the pedal pivot pin  4  is a stepped pin with integrally and concentrically formed three cylindrical shaft sections  41 - 43  having respective outer diameters different from one another. In detail, the pedal pivot pin  4  comprises a support section  41 , a damper connecting section  42  having a larger diameter than that of the support section  41 , and a pedal arm fixing section  43  having a larger diameter than that of the damper connecting section  42 , successively from the side of the other end face  412 . 
         [0060]    On the outer periphery  431  of the pedal arm fixing section  43 , is fixed the accelerator pedal arm  2  arranged in the direction crossing the axis O of the pedal pivot pin  4 . Accordingly, interlocking with swinging of the accelerator pedal arm  2 , the pedal pivot pin  4  rotates in both directions α and β about the axis O of the pedal pivot pin  4 . 
         [0061]    The damper connecting section  42  is formed integrally with an end face  432  of the pedal arm fixing section  43 , and the outer circumference  421  of the damper connecting section  42  is, along the direction of the axis O, cut off to have two flat surfaces at width-across-flat t1 which is nearly equal to as the outer diameter R2 of the support section  41 , extending from a step surface (an end face of the damper connecting section  42 )  422  produced by an outer diameter difference between that section  42  and the support section  41  to a position that does not reach a step surface (the end face of the pedal arm fixing section  43 )  432  produced by an outer diameter difference between that section  42  and the pedal arm fixing section  43 . That is to say, on the side of the pedal arm fixing section  43  of the outer circumference  421  of the damper connecting section  42 , is formed a support area  425  having cylindrical surface to be supported by one side plate  52  of the below-described two side plates  52  and  53  of the pedal bracket  5 ; and on the side of the support section  41  from this support area  425 , are formed the two flat surfaces  423  opposed to each other with width-across-flat t1 nearly same as the outer diameter R2 of the support section  41 . 
         [0062]    The support section  41  is formed integrally with the end face  422  of the damper connecting section  42 . In the outer circumference  411  of the support section  41 , is formed a groove  413  in the circumferential direction for fitting the retaining ring  7  at a least distance L2 (See  FIG. 1 ) between the two side plates  52  and  53  of the pedal bracket  5  from the step surface (the end face of the pedal arm fixing section  43 )  432  formed by the outer diameter difference between the pedal arm fixing section  43  and the damper connecting section  42 . 
         [0063]    The pedal pivot pin  4  having the above-described shape is inserted, first the side of the support section  41 , through a pin insertion hole  521  of the one side plate  52  of the pedal bracket  5 , through the damper  6  fixed to the other side plate  53  of the pedal bracket  5 , and through a pin insertion hole  531  of the other side plate  53  of the pedal bracket  5 , and rotatably supported by the two side plates  52  and  53  of the pedal bracket  5  at two positions, i.e. at the support area  425  of the damper connecting section  42  and at the support section  41 . In this state, the two flat surfaces  423  of the damper connecting section  42  are contained in the damper  6  fixed to the other side plate  53  of the pedal bracket  5 . Inside the damper  6 , the two flat surfaces  423  of the damper connecting section  42  face respective flat surfaces  618  of the inner wall of the below-described rotating cam  61 . Accordingly, when the pedal pivot pin  4  rotates about its axis O associated with swinging of the accelerator pedal arm  2 , the flat surfaces  423  of the damper connecting section  42  immediately make the rotating cam  61  rotate due to contact with the respective opposed flat surfaces  618  of the inner wall of the rotating cam  61 . Thus, as soon as the accelerator pedal  21  is pressed down, the damper  6  starts damping of rotation of the pedal pivot pin  4 , to apply a suitable load on the foot of the driver who presses the accelerator pedal  21 . 
         [0064]    As illustrated in  FIG. 1 , the pedal bracket  5  integrally comprises: a bottom plate  51 , which is fixed to an automobile body; and the two side plates  52  and  53 , which support the pedal pivot pin  4  rotatably in both directions α and β. Although not shown, the pedal bracket  5  further comprises a stopper, which comes in contact with the other end portion (the end portion opposite to the accelerator pedal  21  with respect to the pedal pivot pin  4 ) of the rotating accelerator pedal arm  2  in the normal rotation direction α of the pedal pivot pin  4  at a prescribed position. Contact between this stopper and the other end portion of the accelerator pedal arm  2  prevents the pedal pivot pin  4  from rotating more than a prescribed angle θ 2  (See  FIG. 9 ) in the normal rotation direction α. 
         [0065]    In the bottom plate  51 , are formed through-holes  511  at a plurality of positions corresponding to threaded holes in the automobile body. By screwing bolts inserted through these through-holes into the threaded holes in the automobile body, the pedal bracket  5  is fixed to the automobile body at a prescribed mounting position. 
         [0066]    A pin support hole  521 , whose diameter is smaller than that of the pedal arm fixing section  43  of the pedal pivot pin  4  and larger than that of the damper connecting section  42 , is formed in the one side plate  52  of the two side plates  52  and  53 . The other side plate  53  is placed across the one side plate  52  from the accelerator pedal arm  2  so as to face the one side plate  52  at a distance L2 greater than the case length (the distance L1 between both end faces  6410 A and  6410 B of a case body  641 ) of the damper  6 . Further, in the other side plate  53 , are formed the pin support hole  531  and bolt insertion holes (not shown) positioned on both sides of the pin support hole  531 . Here, the pin support hole  531  is concentric with the pin support hole  521  of the one side plate  52  and has a larger diameter than that of the support section  41  of the pedal pivot pin  4 . 
         [0067]    The damper  6  is placed between the two side plates  52  and  53 , and fixed to the other side plate  53  by tightening of nuts  9  and the bolts  8  inserted through bolt insertion holes  6421  in flange portions  642  of the case  64  and the bolt insertion holes in the other side plate  53 . In this state, the pedal pivot pin  4  is inserted, first the side of the support section  41 , through the pin support hole  521  of the one side plate  52  until the groove  413  of the support section  41  comes out of the pin support hole  531  of the other side plate  53 . As a result, as described above, the pedal pivot pin  4  is rotatably supported in the pin support holes  521  and  531  of the two side plates  52  and  53  at the two positions, i.e. at the support area  425  of the damper connecting section  42  and at the support section  41 , in a state that the two flat surfaces  423  of the damper connecting section  42  are contained in the damper  6  fixed to the other side plate  53 . Then, the retaining ring  7  having an outer diameter larger than the pin support hole  531  of the other side plate  53  is fitted in the groove  413  of the support section  41 , to prevent dropping-off of the pedal pivot pin  4  out of the pedal bracket  5 . 
         [0068]      FIG. 3  is an exploded view of the acceleration pedal unit  1  according to the present embodiment. Further,  FIGS. 4(A) and 4(B)  are left and right side views of the damper  6  in an initial state (a state in which the accelerator pedal  21  is not pressed), and  FIG. 4(C)  an A-A cross-section of  FIG. 4(A) . 
         [0069]    As illustrated in the figures, the damper  6  comprises: a pair of cams (the rotating cam  61  and a slide cam  62 ), whose rotation relative to each other about the axis O causes their inclined cam faces  611  and  621  to slide on and in contact with each other; a coil spring  63 , which biases the slide cam  62  in the direction of pressing the each inclined cam face  621  of the slide cam  62  against the corresponding inclined cam face  611  of the rotating cam  61 ; the case  64 , which houses these component parts  61 - 63  and is fixed to the other side plate  53  of the pedal bracket  5 ; and a disk-shaped cover  65 , which seals the case  64 . 
         [0070]    Inside the case  64  sealed by the cover  65 , the rotating cam  61  and the slide cam  62  are fitted in each other so that their inclined cam faces  611  and  621  engage with each other in accordance with the rotation relative between the rotating cam  61  and the slide cam  62  about the common axis O. The coil spring  63  is placed between a bottom face  62711  of a spring guide hole  6271  formed in the slide cam  62  and a bottom face  6415  of the case  64  so that the cam face  622  of the slide cam  62  are pressed against the cam face  612  of the rotating cam  61 . In the initial state of the damper  6 , the coil spring  63  has been preloaded, and owing to biasing by this coil spring  63 , each inclined cam faces  621  of the slide cam  62  is located at a prescribed position (initial position) relative to the corresponding inclined cam face  611  of the rotating cam  61 . Although details will be described later, each inclined cam face  611  of the rotating cam  61  includes two successive areas having different inclination angles with respect to a pitch circle  615  centering at the axis O (i.e. a first inclined area  611 A and a second inclined area  611 B having a larger inclination angle than that of the first inclined area  611 A, mentioned in order from the side of the initial position of the inclined cam face  621  of the slide cam  62 ) (See  FIG. 7(E) ). 
         [0071]    In the above-described structure, when the rotating cam  61  is rotated in the normal rotation direction α relative to the slide cam  62  while constraining rotational movement of the slide cam  62  relative to the case  64 , then the slide cam  62  moves in the direction of getting away from the rotating cam  61  along a cam guide portion  613  of the rotating cam  61  while the inclined cam faces  621  slide on the corresponding inclined cam faces  611  of the rotating cam  61 . 
         [0072]    Here, until the rotating cam  61  rotates to the prescribed angle θ1 in the normal rotation direction α relative to the slide cam  62 , each inclined cam face  621  of the slide cam  62  slides on the first inclined area  611 A while only an edge portion  621 A of the inclined cam face  621  is in contact with the first inclined area  611 A in the inclined cam face  611  of the rotating cam  61 . During this, the distance between the bottom face of the slide cam  62  and the bottom face  6415  of the case  64  becomes gradually smaller, and therefore the coil spring  63  is further compressed. As a result, the coil spring  63  presses more strongly the inclined cam faces  621  of the slide cam  62  against the first inclined areas  611 A in the inclined cam faces  611  of the rotating cam  61 , and presses more strongly the bottom face  617  of the rotating cam  61  against the cover  65  (the below-mentioned seating face  657 ; See  FIG. 6 ). Accordingly, with increase of the angle of rotation of the rotating cam  61  in the normal rotation direction α relative to the slide cam  62 , friction resistance, for example, between the inclined cam faces  621  of the slide cam  62  and the inclined cam faces  611  of the rotating cam  61  and between the bottom face  617  of the rotating cam  61  and the seating face  657  of the cover  65  increases gradually, and the torque of the rotating cam  61  in the rotation direction about the axis O increases gradually. 
         [0073]    When the rotating cam  61  is further rotated in the normal rotation direction α relative to the slide cam  62 , the whole area of each inclined cam face  621  of the slide cam  62  comes in contact with the second inclined area  611 B (which is steeper than the first inclined area  611 A with respect to the rotation direction of the pedal pivot pin  4  and the rotating cam  61 ) at the time when the rotating cam  61  rotates to the prescribed angle θ1 in the normal rotation direction α, and the inclined cam face  621  slides on the second inclined area  611 A. As a result, at the time when the rotating cam  61  rotates to the prescribed angle θ1 in the normal rotation direction α, the slide cam  62  exerts greater force in the direction of resisting rotation of the rotating cam  61  in comparison with the case where the inclined cam face  621  slides on the first inclined area  611 A of the gentle slope, and therefore the torque of the rotating cam  61  in the rotation direction about the axis O increases rapidly. The coil spring  63  is further compressed, and the inclined cam faces  621  of the slide cam  62  are pressed more strongly against the second inclined areas  611 B in the inclined cam faces  611  of the rotating cam  61 , and the bottom face  617  of the rotating cam  61  is pressed more strongly against the seating face  657  of the cover  65 . Accordingly, with increase of the angle of rotation of the rotating cam  61  in the direction α relative to the slide cam  62 , the friction resistance, for example, between the inclined cam faces  621  of the slide cam  62  and the inclined cam faces  611  of the rotating cam  61  and between the bottom face  617  of the rotating cam  61  and the seating face  657  of the cover  65  increases gradually, and the torque of the rotating cam  61  in the rotation direction about the axis O increases gradually. 
         [0074]    During this, when the rotation of the rotating cam  61  is once stopped at any point in time, the inclined cam faces  621  of the slide cam  62  come to rest on the inclined cam faces  611  of the rotating cam  61 . At that time, friction resistance is produced in the direction of resisting the tendency of the coil spring  63  toward elongation, and the torque of the rotating cam  61  in the rotation direction about the axis O decreases rapidly. 
         [0075]    Further, when the rotating cam  61  is rotated in the reverse rotation direction B, the slide cam  62  moves in the direction of getting close to the rotating cam  61  along the cam guide portion  613  of the rotating cam  61  while the inclined cam faces  621  slide on the inclined cam faces  611  of the rotating cam  61 . As a result, the distance between the bottom face of the slide cam  62  and the bottom face  6415  of the case  64  becomes gradually greater. And thus the coil spring  63  gradually returns (elongates) to the initial preload state, and the friction resistance, for example, between the inclined cam faces  621  of the slide cam  62  and the inclined cam faces  611  of the rotating cam  61  decreases gradually. Accordingly, with decrease of the rotation angle of the rotating cam  61  in the normal rotation direction α, the torque of the rotating cam  61  in the rotation direction about the axis O decreases gradually. 
         [0076]    The above-described damper  6  has hysteresis characteristics suitable to use as a hysteresis generation mechanism (hys-unit) that applies a suitable load at the time of pressing the accelerator pedal  21  and reduces load while the accelerator pedal  21  is held at a certain position. When the damper  6  is assembled in the accelerator pedal unit  1 , the damper  6  can not only realize natural accelerator pedal operation feeling while generating natural acceleration force, but also generate a rapid change in operational feeling of pressing the accelerator pedal  21 , which can be detected as a signal for energy-saving driving of an automobile, at the time when the accelerator pedal  21  is pressed excessively. Each of the component parts  61 - 65  of the damper  6  realizing such functions will be described. 
         [0077]      FIGS. 5(A) and 5(B)  are left and right side views of the case  64 , and  FIG. 5(C)  a B-B cross-section. 
         [0078]    As illustrated, the case  64  integrally comprises: a case body  641  of a bottomed cylindrical shape; and the two flange portions  642  projecting in radial directions from the outer periphery  6412  of the case body  641 . 
         [0079]    The cover  65  is fitted in an opening  6414  of the case body  641 . In the inner periphery of the opening  6414 , is formed a threaded portion  6416  into which a threaded portion  652  of the outer periphery  651  of the cover  65  is screwed. By tightening of this threaded portion  6416  and the threaded portion  652  in the outer periphery  651  of the cover  65 , the cover  65  is fitted in the opening  6414  of the case body  641  while preloading the coil spring  63  housed in the case body  641 . In an edge portion of the case body  641 , a plurality of recessed portions  6411  for welding, which are used for fixing the cover  65  fitted in the opening  6414 , are formed at almost regular angular intervals about the axis O of the case body  641 . 
         [0080]    In the central area of the bottom face  6415  of the case body  641 , are formed a through-hole  6413  through which the axis O of the case body  641  passes, and a ring-shaped spring guide portion  6417  surrounding the outer circumference of the through-hole  6413 . The spring guide portion  6417  is set into the coil spring  63  inserted in the case body  641 , and fixes the position of one end  631  of the coil spring  63 . 
         [0081]    Further, in the inner periphery  6418  of the case body  641 , are formed three grooves  6419  along the direction of the axis O of the case body  641  at almost regular angular intervals about the axis O of the case body  641 . One end of each groove  6419  passes through the end face  6410 A of the case body  641  on the opening side. When the slide cam  62  is inserted through the opening  6414  of the case body  641 , projecting portions  623  on the outer periphery  624  of the slide cam  62  are slidably inserted into these grooves  6419 . By this, rotational movement of the slide cam  62  relative to the case  64  is constrained. In other words, rotational movement of the slide cam  62  relative to the pedal bracket  5  is constrained. 
         [0082]    Although, in the present embodiment, the three grooves  6419  are formed in the inner periphery  6418  of the case body  641  at almost regular angular interval about the axis O, the number and layout of the grooves  6419  are determined in accordance with the number and layout of the projecting portions  623  of the slide cam  62  that is used. 
         [0083]    On the other hand, the two flange portions  642  are formed integrally with the outer periphery  6412  of the case body  641  so as to project outward from both sides of the opening-side end face  6410 A of the case body  641 . In these flange portions  642 , are formed the bolt insertion holes  6421  for inserting the bolts  8  at positions that correspond to the respective bolt insertion holes in the other side plate  53  of the pedal bracket  5  when a through-hole  653  formed in the central area of the cover  65  fitted in the opening  6414  of the case body  641  is aligned with the pin insertion hole  531  of the other side plate  53  of the pedal bracket  5 . 
         [0084]      FIGS. 6(A) and 6(B)  are a front view and a back view of the cover  65 , and  FIG. 6(C)  a C-C cross-section of  FIG. 6(A) . 
         [0085]    As illustrated, in the outer periphery  651  of the cover  65 , is formed the threaded portion  652  that is screwed into the threaded portion  6416  formed in the opening  6414  of the case body  641 . In one surface (the surface to be faced toward the outside of the case body  641 )  654  of the cover  65 , is formed a hexagon socket  656  for inserting a tool for rotating the cover  65  relative to the case body  641 . On the other surface (the rear surface to be faced toward the inside of the case body  641 )  655  of the cover  65 , is formed a seating face  657  on which the bottom face  617  of the rotating cam  61  moves frictionally in the course of rotation. By rotating the tool inserted in the hexagon socket  656  in the surface  654  of the cover  65 , the threaded portion  652  formed in the outer periphery  651  of the cover  65  is screwed in the threaded portion  6416  formed in the opening  6414  of the case body  641 , and thereby the bottom face  617  of the rotating cam  61  is pressed by the seating face  657  of the cover  65 . As a result, the rotating cam  61  and the slide cam  62  are pressed into initial positions within the case body  641 , and the coil spring  63  is preloaded between the bottom face  6415  of the case body  641  and the bottom face  62711  (See  FIG. 8(D) ) of the spring guide hole  6271 . 
         [0086]    Further, in the central area of the cover  65 , is formed the through-hole  653  having the inner diameter R2 larger than the outer diameter R1 of the damper connecting section  42  of the pedal pivot pin  4 . In an assembled state of the damper  6 , the axis O of the case body  641  passes through the through-hole  653 , the inside of the rotating cam  61 , and the through-hole  6413  of the bottom face  6415  of the case body  641  (See  FIG. 4(C) ). The pedal pivot pin  4  is inserted, first the side of the support section  41 , into the through-hole  653 , and passes through the inside of the rotating cam  61 , so as to protrude from the through-hole  6413  of the bottom face  6415  of the case body  641 . 
         [0087]      FIGS. 7(A) ,  7 (B) and  7 (C) are a front view and left and right side views of the rotating cam  61 ,  FIG. 7(D)  a D-D cross-section of  FIG. 7(C) , and  FIG. 7(E)  a view illustrating schematically a profile shape of the cam face  612  on the pitch circle  615  centering at the axis O. 
         [0088]    As illustrated, the rotating cam  61  has a stepped cylindrical shape including the cam guide portion  613  as a small-diameter portion and a cam portion  610  as a large-diameter portion that are integrally formed. The cam guide portion  613  is an inner-diameter guide for the slide cam  62  and inserted into the inside of the slide cam  62 . On the other hand, the cam portion  610  has the cam face  612  on which the inclined cam faces  621  of the slide cam  62  slide. 
         [0089]    Into the inside of the rotating cam  61 , the pedal pivot pin  4  is inserted from one end face  616  toward the other end face (bottom face  617 ) after passing through the through-hole  653  of the cover  65 . In an inner wall  614  of the rotating cam  61 , are formed two flat surfaces  618  facing each other at a width-across-flat T1 corresponding to the width-across-flat t1 of the damper connecting section  42  of the pedal pivot pin  4 . When the damper connecting section  42  of the pedal pivot pin  4  is inserted into the inside of the rotating cam  61 , these flat surfaces  618  come in contact with the corresponding flat surfaces  423  of the damper connecting section  42  of the pedal pivot pin  4 , so that the torque of the pedal pivot pin  4  is transmitted to the rotating cam  61 . As a result, associated with rotation of the pedal pivot pin  4  in both directions α and β caused by operation of the accelerator pedal  21 , the rotating cam  61  also rotates in both directions α and β about the axis O while generating friction resistance, for example, between the inclined cam faces  611  formed in the cam face  612  and the inclined cam faces  621  of the slide cam  62 . 
         [0090]    On the pitch circle  615  centering at the axis O, the cam face  612  (the face on the side of the cam guide portion  613 ) of the cam portion  610  periodically repeats concave forms and convex forms in the direction of the axis O. In detail, in the cam face  612  of the cam portion  610 , three inclined cam faces  611  inclined to the circumferential direction of the pitch circle  615  (the rotation direction of the pedal pivot pin  4  and the like) are formed at almost regular angular intervals about the axis O. Further, between each pair of adjacent inclined cam faces  611 , is formed a step face  619  for determining the initial position of an inclined cam face  621  of the slide cam  62 . 
         [0091]    In each inclined cam face  611 , the two inclined areas  611 A and  611 B, whose inclination angles with respect to the circumferential direction of the pitch circle  615  (i.e. inclination angles with respect to the rotation direction of the pedal pivot pin  4  and the like) are different from each other, are formed successively in the direction of the rotation of the pedal pivot pin  4  and the like. In detail, each inclined cam face  611  includes the first inclined area  611 A inclined at a prescribed angle A1 with respect to the circumferential direction of the pitch circle  615  and the second inclined area  611 B inclined at an angle A2 larger than the inclination angle A1 of the first inclined area  611 A with respect to the circumferential direction of the pitch circle  615 , being arranged in this order from the side of the corresponding step face  619  in the normal rotation direction α of the rotating cam  61 . Accordingly, when the rotating cam  61  rotates in the normal rotation direction α interlocking with the pedal pivot pin  4 , each inclined face  621  of the slide cam  62  starts rotational movement relative to the cam face  612  of the rotating cam  61 . First, the inclined cam face  621  goes sliding on the first inclined area  611 A of the gentle slope from the initial position determined by the corresponding step face  619  toward the second inclined area  611 B. Thereafter, at the time when the rotating cam  61  rotates to the prescribed angle θ1 in the normal rotation direction α, the inclined cam face  621  comes on the second inclined area  611 B that is steeper than the first inclined area  611 A, and slides on this second inclined area  611 B. 
         [0092]      FIGS. 8(A) ,  8 (B) and  8 (C) are a front view, a back view and a side view of the slide cam  62 ,  FIG. 8(D)  an E-E cross-section of  FIG. 8(A) , and  FIG. 8(E)  a view illustrating schematically a profile shape of the cam face  622  on the pitch circle  625  centering at the axis O. 
         [0093]    The slide cam  62  comprises: a cylindrical cam portion  620 , into which the cam guide portion  613  of the rotating cam  61  is slidably inserted; and projecting portions  623  formed on the outer periphery  624  of the cam portion  620  along the axis O of the cam portion  620 . 
         [0094]    In the inner periphery of the cam portion  620 , is formed a stepped hole  627  having a spring guide hole  6271  as a large-diameter portion on the side of a bottom face  626  of the cam guide portion  620 . This spring guide hole  6271  is used for receiving the one end  631  of the coil spring  63 . 
         [0095]    The cam face (the end face opposite to the bottom face  626 )  622  of the cam portion  620  periodically repeats concave forms and convex forms in the direction of the axis O on the pitch circle  625  centering at the axis O. In detail, in the cam face  622  of the cam portion  620 , three inclined cam faces  621  inclined at nearly the same angle A2 as that of the second inclined areas  611 B of the rotating cam  61  to the circumferential direction of the pitch circle  625  (the rotation direction of the pedal pivot pin  4  and the like) are formed at almost regular angular intervals about the axis O. Further, for each inclined cam face  621 , are formed a flat face  628 , which follows the inclined cam face  621 , and an inclined face  629  that comes in contact with a step face  619  in the cam face  612  of the rotating cam  61 . 
         [0096]    When the cam guide portion  613  of the rotating cam  61  is inserted into the inside of the cam portion  620  in a state that the cam face  622  of the cam portion  620  is faced toward the cam face  612  of the rotating cam  61 , the cam guide portion  613  of the rotating cam  61  protrudes from the side of the bottom face  626  of the cam portion  620 . The cam guide portion  613  protruding from the side of the bottom face  626  of the cam portion  620  is inserted into the coil spring  63 , and the spring guide hole  6271  of the cam portion  620  is made to enclose the one end  631  of the coil spring  63 . The coil spring  63 , the slide cam  62  and the rotating cam  61 , which are assembled in the above way, are housed, first the side of the other end  632  of the coil spring  63 , into the case body  641  through the opening  6414  of the case body  641 , after the projecting portions  623  of the slide cam  62  are aligned with the grooves  6419  of the case body  641 . 
         [0097]    The free length L0 of the coil spring  63  is greater than the distance between the bottom face  6415  of the case body  641  and the bottom face  62711  of the spring guide hole  6271  of the slide cam  62  in the initial state of the damper  6 . Accordingly, when the cover  65  is screwed in the opening  6414  of the case body  641 , the coil spring  63  is preloaded between the bottom face  6415  of the case body  641  and the bottom face  62711  of the spring guide hole  6271  of the slide cam  62 . As a result, the slide cam  62  is biased toward the direction of pressing the inclined cam faces  621  of the slide cam  62  against the inclined cam faces  611  of the rotating cam  61 . This causes rotation of the rotating cam  61 , and thereby the inclined faces  629  in the cam face  622  of the slide cam  62  come in contact with the respective step faces  619  in the cam face  612  of the rotating cam  61 . This position becomes the initial position of the inclined cam faces  621  of the slide cam  62  relative to the inclined cam faces  611  of the rotating cam  61 . 
         [0098]    Within the case body  641 , the one end  631  of the coil spring  63  is in contact with the bottom face  62711  of the spring guide hole  6271  of the slide cam  62 , and the other end  632  is in contact with the bottom face  6415  of the case body  641  (See  FIG. 4(C) ). Thus, it is favorable that both ends  631  and  632  of the coil spring  63  are polishing-processed closed ends so that both ends  631  and  632  of the coil spring  63  are stable in this state. 
         [0099]    Owing to the above-described construction, the accelerator pedal unit  1  of the present embodiment makes it possible that a suitable load is applied on a driver&#39;s foot during pressing of the accelerator pedal  21  down and the load applied on the driver&#39;s foot becomes rapidly larger by enough magnitude to be detected by tactile sensation at the time when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile deteriorates to the prescribed level (i.e. when the pedal pivot pin  4  rotates to the prescribed angle θ1 in the normal rotation direction α). This will be described in the following. 
         [0100]      FIGS. 9(A) ,  9 (B) and  9 (C) are views for explaining two-stage damping motion of the damper  6  associated with pressing the accelerator pedal  21 . 
         [0101]    As illustrated in  FIG. 9(A) , in the state where the accelerator pedal  21  is not pressed, each inclined cam face  621  of the slide cam  62  of the damper  6  is located in the initial position determined by the corresponding step face  619  of the cam face  612  of the rotating cam  61 . 
         [0102]    As illustrated in  FIG. 9(B) , when the accelerator pedal  21  is pressed, the pedal pivot pin  4  rotates in the normal rotation direction α interlocking with swinging of the accelerator pedal arm  2 . At that time, within the damper  6 , the flat surfaces  423  of the damper connecting section  42  of the pedal pivot pin  4  come in contact with the respective opposed flat surfaces  618  in the inner wall of the rotating cam  61 , so that the rotating cam  61  is rotated in the normal rotation direction α. As a result, the slide cam  62  moves in the direction A of getting away from the rotating cam  61  while only the edge portion  621 A of each inclined cam face  621  is in sliding contact with the first inclined area  611 A of the gentle slope in the corresponding inclined cam face  611  of the rotating cam  61  until the rotating cam  61  rotates to the prescribed angle θ1 in the normal rotation direction α. During this, the coil spring  63  is gradually compressed from the initial preloaded state, so that the coil spring  63  presses more and more strongly the edge portion  621 A of each inclined cam face  621  of the slide cam  62  against the first inclined area  611 A of the corresponding inclined cam face  611  of the rotating cam  61 . Accordingly, the friction resistance, for example, between the edge portion  621 A of the inclined cam face  621  of the slide cam  62  and the first inclined area  611 A in the inclined cam face  611  of the rotating cam  61  gradually increases, and the torque of the rotating cam  61  in the rotation direction about the axis O increases gradually with increase of the angle of rotation of the rotating cam  61  in the normal rotation direction α relative to the slide cam  62 . As a result, rotation of the pedal pivot pin  4  in the normal rotation direction α is damped, and the suitable load is applied on the driver&#39;s foot that presses the accelerator pedal  21 . 
         [0103]    As illustrated in  FIG. 9(C) , when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile deteriorates to the prescribed level (i.e. when the pedal pivot pin  4  rotates to the prescribed angle θ1 in the normal rotation direction α), then in each inclined cam face  611  of the rotating cam  61 , the whole area of the corresponding inclined cam face  621  of the slide cam  62  comes in contact with the second inclined area  611 B that is steeper than the first inclined area  611 A with respect to the circumferential direction of the pitch circle  615  (the rotation direction of the pedal pivot pin  4  and the like). Accordingly, the slide cam  62  exerts greater force in the direction of resisting rotation of the rotating cam  61  in comparison with the case where the inclined cam faces  621  slide on the first inclined areas  611 A of the gentle slope, and the torque of the rotating cam  61  in the rotation direction about the axis O increases rapidly. As a result, at the time when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile deteriorates to the prescribed level, the load applied on the driver&#39;s foot that presses the accelerator pedal  21  increases rapidly by at least magnitude such that a variation of load can be detected by tactile sensation. 
         [0104]    When the driver continues pressing down the accelerator pedal  21  furthermore (i.e. when the pedal pivot pin  4  rotates over the prescribed angle θ1 in the normal rotation direction α), then in each inclined cam face  611  of the rotating cam  61 , the corresponding inclined cam face  621  of the slide cam  62  goes on the second inclined area  611 B that is steeper than the first inclined area  611 A with respect to the circumferential direction of the pitch circle  615  (the rotation direction of the pedal pivot pin  4  and the like), and is in sliding contact with the second inclined area  611 B. During this, the coil spring  63  is further compressed, and presses further strongly the inclined cam faces  621  of the slide cam  62  against the second inclined areas  611 B of the inclined cam faces  611  of the rotating cam  61 . Accordingly, with increase of the angle of rotation of the rotating cam  61  in the normal rotation direction α, the friction resistance, for example, between the inclined cam face  621  of the slide cam  62  and the inclined cam face  611  of the rotating cam  61  increases gradually, and the torque of the rotating cam  61  in the rotation direction about the axis O increases gradually. As a result, also after the rapid increase of the load applied on the driver&#39;s foot that presses the accelerator pedal  21 , the load applied on the driver&#39;s foot that presses the accelerator pedal  21  further increases gradually as long as the driver continues pressing down the accelerator pedal  21 . Accordingly, the driver can intuitively grasp the continuous worsening of the energy expenditure rate of the automobile through operation of pressing the accelerator pedal  21  without constantly caring about a change of visual information obtained from the meters on the instrument panel. 
         [0105]    As describe hereinabove, according to the accelerator pedal unit  1  of the present embodiment, the pedal pivot pin  4 , which is rotated by operation (i.e. pressing and releasing) of the accelerator pedal  21 , is connected to the damper  6  that damps rotation of the pedal pivot pin  4 , and at the time when the pedal pivot pin  4  rotates to the angle θ1, at which the energy expenditure rate of the automobile deteriorates to the prescribed level, in the normal rotation direction α, the force of the damper  6  for damping the rotation of the pedal pivot pin  4  increases rapidly. Accordingly, it is possible that a suitable load is applied on the driver&#39;s foot pressing down the accelerator pedal  21  and the load applied on the driver&#39;s foot becomes rapidly heavier by at least magnitude that can be detected by tactile sensation when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile deteriorates to the prescribed level. Thus, the driver can detect a rapid change in operational feeling of pressing the accelerator pedal  21  as a signal for energy-saving driving of the automobile. 
         [0106]    Further, when the driver continues pressing down the accelerator pedal  21  thereafter (i.e. when the pedal pivot pin  4  rotates over the prescribed angle θ1 in the normal rotation direction α), the coil spring  63  is further compressed, and the inclined cam faces  621  of the slide cam  62  are further strongly pressed against the second inclined areas  611 B of the inclined cam faces  611  of the rotating cam  61 . Accordingly, with increase of the angle of rotation of the rotating cam  61  in the normal rotation direction α, the friction resistance, for example, between the inclined cam faces  621  of the slide cam  62  and the inclined cam faces  611  of the rotating cam  61  increases furthermore, and the torque of the rotating cam  61  in the rotation direction about the axis O increases furthermore. Accordingly, the load applied on the driver&#39;s foot that presses down the accelerator pedal  21  further increases gradually even after the rapid increase of the load. Therefore, the driver can intuitively catch the continuous worsening of the energy expenditure rate of the automobile through operation of pressing the accelerator pedal  21 . 
         [0107]    In the present embodiment, each inclined cam face  611  of the rotating cam  61  includes the two inclined areas  611 A and  611 B whose inclination angles with respect to the rotation direction of the pedal pivot pin  4  and the like are different from each other. However, it is possible to form three or more inclined areas, whose inclination angles with respect to the rotation direction of the pedal pivot pin  4  and the like are different from one another, in each inclined cam face  611  of the rotating cam  61 , so that the driver can detect change in the traveling state of the automobile in more-finely-divided stages. 
         [0108]    Although, in the present embodiment, each inclined cam face  611  of the rotating cam  61  includes the two inclined areas  611 A and  611 B whose inclination angles with respect to the rotation direction of the pedal pivot pin  4  and the like are different from each other, each inclined cam face  621  of the slide cam  62  may include a plurality of inclined areas whose inclination angles with respect to the rotation direction of the pedal pivot pin  4  and the like are different from one another. Or, for both inclined cam faces  621  of the slide cam  62  and inclined cam faces  611  of the rotating cam  61 , each inclined cam face may include two inclined areas (a first inclined area inclined at a prescribed angle A1 and a second inclined area inclined at an angle A2 larger than the inclination angle A1 of the first inclined area). Then, each inclined face  611  of the rotating cam  61  and the corresponding inclined face  621  of the slide cam  62  may be in sliding contact with each other at their first inclined areas of the gentle slope until the pedal pivot pin  4  rotates to the prescribed angle θ1, and then at their second inclined areas of the steeper slope when the pedal pivot pin  4  rotates over the prescribed angle θ1. 
         [0109]    Further, the present embodiment uses the coil spring  63  for biasing the slide cam  62 . However, another elastic body such as rubber, a spring other than the coil spring, or the like may be used. 
       Second Embodiment 
       [0110]    In the above-described embodiment (First Embodiment), each inclined cam face of at least one of the rotating cam  61  and the slide cam  62  in the damper  6  includes a plurality of inclined areas whose inclination angles with respect to the rotation direction of the pedal pivot pin  4  and the like are different from one another. However, a damper used in an accelerator pedal unit can have other structure in which friction resistance impeding relative rotation of a rotating cam and a slide cam changes stepwise as the angle of the relative rotation of the rotating cam and the slide cam increases. For example, in the damper  6 , it is possible to use an elastic member having non-linear characteristics, whose elastic coefficient increases stepwise as the rotation angle of the pivot pin  4  increases, so that the resistance force for damping the rotation of the pivot pin  4  increases rapidly at the time when the pivot pin  4  rotates to a prescribed rotation angle. In the following, this case (Second Embodiment) will be described. 
         [0111]    First, structure of an accelerator pedal unit  11  according to the present embodiment and structure of a damper  16  used in the accelerator pedal unit  11  will be described. However, in the present embodiment, component parts similar to those in the first embodiment will be given the same reference signs as those in the first embodiment, and their detailed description will be omitted. Similarly to the accelerator pedal unit  1  of the first embodiment, the accelerator pedal unit  11  of the present embodiment comprises: an accelerator pedal arm  2 ; a pedal pivot pin  4 ; a pedal bracket  5 ; retaining ring  7 ; a spring  3 ; and a detection part including a potentiometer and the like (See  FIG. 1 ). 
         [0112]    Further, this accelerator pedal unit  11  also further comprises: a damper  16  in which resisting force for damping rotation of the pedal pivot pin  4  increases stepwise according to angle θ of rotation of the pedal pivot pin  4  in a normal rotation direction α; and bolts  8  and nuts  9  for fixing the damper  16  to the pedal bracket  5 , in order that, while a suitable load is applied on a driver&#39;s foot that presses an accelerator pedal  21 , the load applied on the driver&#39;s foot becomes rapidly heavier by at least magnitude that can be detected by tactile sensation at the time when the accelerator pedal  21  is pressed to a position where the energy expenditure rate of the automobile deteriorates to a prescribed level (or when the pedal pivot pin  4  rotates to a prescribed angle θ1 in the prescribed direction α about the axis O of the pedal pivot pin  4 ). However, construction of the damper  16  is different from the damper  6  of the first embodiment. 
         [0113]    Similarly to the damper  6  of the first embodiment, the damper  16  is placed between two side plates  52  and  53 , and fixed to the other side plate  53  by tightening nuts  9  on bolts  8  inserted through bolt insertion holes  6421  in flange portions  642  of a case  164  and bolt insertion holes in the other side plate  53 . In this state, the pedal pivot pin  4  is inserted, first the side of a support section  41  of the pedal pivot pin  4 , through a pin support hole  521  of the one side plate  52  until a groove  413  of the support section  41  comes out of a pin support hole  531  of the other side plate  53 . As a result, the pedal pivot pin  4  is rotatably supported in the pin support holes  521  and  531  of the two side plates  52  and  53  at the two positions, i.e. at a support area  425  of a damper connecting section  42  and at the support section  41 , in a state that two flat surfaces  423  of the damper connecting section  42  are contained in the damper  16  fixed to the other side plate  53 . Then, a retaining ring  7  having an outer diameter larger than the pin support hole  531  of the other side plate  53  is fitted in the groove  413  of the support section  41 , to prevent dropping of the pedal pivot pin  4  out of the pedal bracket  5 . 
         [0114]      FIG. 10  is an exploded view of the damper  16  according to the present embodiment. Further,  FIGS. 11(A) and 11(B)  are left and right side views of the damper  16  in an initial state (a state in which the accelerator pedal  21  is not pressed), and  FIG. 11(C)  an A-A cross-section of  FIG. 11(A) . 
         [0115]    As illustrated, the damper  16  comprises: a pair of cams (a rotating cam  161  and a slide cam  162 ), whose rotation relative to each other about the axis O causes their inclined cam faces  611  and  621  to slide on and in contact with each other; a combination spring  163 , which biases the slide cam  162  in the direction of pressing the each inclined cam face  1621  of the slide cam  162  against the corresponding inclined cam face  1611  of the rotating cam  161 ; the case  164 , which houses these component parts  161 - 163  and is fixed to the other side plate  53  of the pedal bracket  5 ; and a disk-shaped cover  65 , which seals the case  164 . 
         [0116]    Inside the case  164  sealed by the cover  65 , the rotating cam  161  and the slide cam  162  are fitted in each other so that their inclined cam faces  1611  and  621  engage with each other in accordance with the rotation relative between the rotating cam  161  and the slide cam  162  about the common axis O. Although details will be described later, the combination spring  163  is constructed by combining in a nested state two type of coil springs (a first coil spring  163 A and a second coil spring  163 B) having different diameters and different natural lengths from each other, so as to have non-linear spring characteristics in that the spring constant increases at the time when the compression amount reaches a prescribed value. This combination spring  163  is placed between a bottom face  62711  of a spring guide hole  6271  formed in the slide cam  162  and a groove bottom  16417 C of a groove  16417  formed in the bottom portion  16415  of the case  164 , so that a cam face  1622  of the slide cam  162  is pressed against a cam face  1612  of the rotating cam  161  by the restoring force of the combination spring  163 . In the initial state of the damper  16 , each inclined cam face  1621  of the slide cam  162  is located at a prescribed position (initial position) relative to the corresponding inclined cam face  1611  of the rotating cam  161 , owing to biasing by the combination spring  163  preloaded (the first coil spring  163 A preloaded). 
         [0117]    In the above-described structure, when the rotating cam  161  is rotated in the normal rotation direction α relative to the slide cam  162  while constraining rotational movement of the slide cam  162  relative to the case  164 , then the slide cam  162  moves in the direction of getting away from the rotating cam  161  (in the direction toward the bottom portion  16415  of the case  164 ) along a cam guide portion  613  of the rotating cam  161  while each inclined cam face  1621  slides on and in contact with the corresponding inclined cam face  1611  of the rotating cam  61 . At this time, the distance between the bottom face  62711  of the spring guide hole  6271  of the slide cam  62  and the groove bottom  16417 C of the groove  16417  in the bottom portion  16415  of the case  164  becomes gradually smaller, and therefore the combination spring  163  is further compressed. As a result, the combination spring  163  presses more strongly the inclined cam faces  1621  of the slide cam  162  against the inclined cam faces  1611  of the rotating cam  161 , and presses more strongly a bottom face  617  of the rotating cam  161  against a seating face  657  (See  FIG. 6 ) of the cover  65 . Accordingly, with increase of the angle of rotation θ of the rotating cam  61  in the normal rotation direction a relative to the slide cam  162 , friction resistance, for example, between the inclined cam faces  1621  of the slide cam  162  and the inclined cam faces  1611  of the rotating cam  161  and between the bottom face  167  of the rotating cam  161  and the seating face  657  of the cover  65  increases gradually, and the torque of the rotating cam  161  in the rotation direction about the axis O increases gradually. 
         [0118]    When the rotating cam  161  is further rotated in the normal rotation direction α relative to the slide cam  162 , the slide cam  162  further moves toward the bottom portion  16415  of the case  164  along the cam guide portion  613  of the rotating cam  161  while rotating relative to the rotating cam  161 . As a result, the distance between the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  and the groove bottom  16417 C of the bottom portion  16415  of the case  164  becomes gradually smaller furthermore, and the combination spring  163  is further compressed. At the time when the rotating cam  161  rotates to the prescribed angle θ1 in the normal rotation direction α, the compression amount of the combination spring  163  reaches the prescribed value where the spring constant increases. Thus, at the time when the rotation cam  161  rotates to the prescribed angle θ1 in the normal direction α, the restoring force of the combination spring  163  increases rapidly by the magnitude corresponding to the increment of the spring constant. Accordingly, the friction resistance, for example, between the inclined cam faces  1621  of the slide cam  162  and the inclined cam faces  1611  of the rotating cam  161  and between the bottom face  617  of the rotating cam  161  and the bottom face  657  of the cover  65  increases rapidly. Thereby, the torque of the rotating cam  61  in the rotation direction about the axis O increases rapidly at the time when the rotating cam  161  rotates to the prescribed angle θ1 in the normal rotation direction α, and thereafter the torque increases gradually with increase of the rotation angle θ of the rotating cam  161  in the normal rotation direction α relative to the slide cam  162 . 
         [0119]    During this, when rotation of the rotating cam  161  is once stopped at any point in time, the inclined cam faces  1621  of the slide cam  162  come to rest on the inclined cam faces  1611  of the rotating cam  161 . At that time, friction resistance is produced in the direction of resisting the tendency of the combination spring  163  toward elongation, and the torque of the rotating cam  161  in the rotating direction about the axis O decreases rapidly. 
         [0120]    Further, when the rotating cam  161  is rotated in the reverse rotation direction β, the slide cam  162  moves in the direction of getting close to the rotating cam  161  along the cam guide portion  613  of the rotating cam  161  while the inclined cam faces  1621  slide on the inclined cam faces  1611  of the rotating cam  161 . As a result, the distance between the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  and the groove bottom  16417 C in the bottom portion  16415  of the case  164  becomes gradually greater. And thus the combination spring  163  returns (elongates) to the initial state, and the friction resistance, for example, between the inclined cam faces  1621  of the slide cam  162  and the inclined cam faces  1611  of the rotating cam  161  decreases gradually. Accordingly, with decrease of the rotation angle θ of the rotating cam  161  in the normal rotation direction α, the torque of the rotating cam  161  in the rotation direction about the axis O decreases gradually. 
         [0121]    The above-described damper  16  has hysteresis characteristics suitable to use as a hysteresis generation mechanism (hys-unit) that applies a suitable load at the time of pressing the accelerator pedal  21  and reduces load while the accelerator pedal  21  is held at a certain position. When the damper  16  is assembled in the accelerator pedal unit  11 , the damper  16  can not only realize natural accelerator pedal operation feeling while generating natural acceleration force, but also generate a rapid change in operational feeling of pressing the accelerator pedal  21 , which can be detected as a signal for energy-saving driving of an automobile, at the time when the accelerator pedal  21  is pressed excessively. Each of the component parts  161 - 164 ,  165  of the damper  16  realizing such functions will be described. 
         [0122]      FIG. 12(A)  is a view for explaining the structure of the combination spring  163 . Further,  FIG. 12(B)  is a view illustrating a state of the combination spring  163  before increase of the spring constant, and  FIG. 12(C)  is a view illustrating a state of the combination spring  163  with the spring constant increased. 
         [0123]    The combination spring  163  is constructed by combining in a nested state the two type of coil springs (the first coil spring  163 A and the second coil spring  163 B) having different diameters and different natural lengths from each other, so as to have the non-linear spring characteristics in that the spring constant increases at the time when the compression amount reaches the prescribed value. In detail, as illustrated in  FIG. 12(A) , the first spring  163 A and the second spring  163 B are prepared in advance such that the first spring  163 A has the natural length LA0 greater than the distance L4 (See  FIG. 11(C) ) between the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  and the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641  in the initial state of the damper  16  and the second spring  163 B has the natural length LB0 smaller than the distance L4 between the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  and the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641  in the initial state of the damper  16  and has the inner diameter r2 larger than the outer diameter r1 of the first coil spring  163 A. Then, as illustrated in  FIG. 12(B) , the combination spring  163  is constructed by inserting the first coil spring  163 A into the inside of the second coil spring  163 B so that the outer periphery of the first coil spring  163 A is surrounded by the second coil spring  163 B. 
         [0124]    When the combination spring  163  is compressed in the direction of axis O, only the first coil spring  163 A protruding from at least one end  1632 B of the second coil spring  163 B is compressed ( FIG. 12(B) ) up to the compression amount corresponding to the difference of the natural lengths (LA0-LB0) between the first and second coil springs  163 A and  163 B, and thus the combination spring  163  functions as a compression spring having the same spring constant as that of the first coil spring  163 A. When the compression amount becomes larger than that, both the first coil spring  163 A and the second coil spring  163 B are compressed (FIG.  12 (C)), and thus the combination spring  163  functions as a compression spring having a spring constant corresponding to the sum of the spring constants of the first and second coil springs  163 A and  163 B. 
         [0125]    The combination spring  163  having the non-linear spring characteristics described above is placed as follows in the inside of the below-described case body  1641  in the initial state of the damper  16 . The first coil spring  163 A is place in a preloaded state between the bottom face  62711  of the spring guide hole  6271  formed in the slide cam  162  and the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641  so that the cam face  1622  of the slide cam  162  is pressed against the cam face  1612  of the rotating cam  161 . In the initial state of the damper  16 , each inclined cam face  1621  of the slide cam  162  is pressed against the cam face  1612  of the rotating cam  161  being biased by the preloaded first coil spring  163 A, so as to be located in initial position determined by each step face  619  (See  FIG. 14(E) ) in the cam face  1612  of the rotating cam  161 . On the other hand, the second coil spring  163 B is placed in an unloaded state between the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  and the groove bottom  16417 C of the groove  14617  formed in the bottom portion  16415  of the case  164 . In other words, the combination spring  163  functions as a spring having the same spring constant as that of the first coil spring  163 A in the initial state of the damper  16 . When the combination spring  163  is compressed by more than the difference of the natural lengths (LA0-LB0) between the first and second coil springs  163 A and  163 B, the combination spring  163  functions as a spring having the spring constant larger than that in the initial state of the damper  16 . 
         [0126]    In the present embodiment, the first coil spring  163 A having the greater natural length than that of the second coil spring  163 B is placed in the inside of the second coil spring  163 B in the nested state. On the contrary, it is possible that the second coil spring  163 B is placed in the inside of the first coil spring  163 A having the greater natural length than that of the second coil spring  163 B in a nested state. 
         [0127]    Further, in the inside of the below-described case body  1641 , one end  1631 A of the first coil spring  163 A is in contact with the bottom face  62711  of the spring guide hole  6271  of the slide cam  162 , and the other end  1632 A is in contact with the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641  (See  FIG. 11(C) ). Thus, it is favorable that both ends  1631 A and  1632 A of the first coil spring  163 A are polishing-processed closed ends so that both ends  1631 A and  1632 A of the first coil spring  163 A are stable in the contact state. This is same for both ends  1631 B and  1632 B of the second coil spring  163 B. 
         [0128]      FIGS. 13(A) and 13(B)  are left and right side views of the case  164 , and  FIG. 13(C)  a B-B cross-section of  FIG. 13(A) . 
         [0129]    As illustrated, the case  164  integrally comprises: the case body  1641  of a bottomed cylindrical shape; and the two flange portions  642  projecting in radial directions from the outer periphery  6412  of the case body  1641 . 
         [0130]    The cover  65  is fitted in an opening  6414  of the case body  1641 . In the inner periphery of the opening  6414 , is formed a threaded portion  6416  into which a threaded portion  652  of the outer periphery  651  of the cover  65  is screwed. By tightening of this threaded portion  6416  and the threaded portion  652  in the outer periphery  651  of the cover, the cover  65  is fitted in the opening  6414  of the case body  641  while preloading the first coil spring  163 A housed in the case body  1641 . In an edge portion of the case body  1641 , a plurality of recessed portions  6411  for welding, which are used for fixing the cover  65  fitted in the opening  6414 , are formed at almost regular angular intervals about the axis O of the case body  1641 . 
         [0131]    In the central area of the bottom portion  16415  of the case body  1641 , are formed a through-hole  6413 , through which the axis O of the case body  1641  passes, and a ring-shaped groove  16417  surrounding the outer circumference of the through-hole  6413 . The one end  1631 A of the first coil spring  163 A is set on the inner wall surface  16417 A of the groove  16417  on the inner diameter side, so that the inner wall surface  16417 A functions as an inner-diameter spring guide for fixing the position of this end  1631 A. On the other hand, the one end  1631 B of the second coil spring  163 B is set on the inner wall surface  16417 B of the groove  14617  on the outer diameter side, so that the inner wall surface  16417 B functions as an outer-diameter spring guide for fixing the position of this end  1631 B. 
         [0132]    Further, in the inner periphery  6418  of the case body  1641 , are formed three grooves  6419  along the direction of the axis O of the case body  1641  at almost regular angular intervals about the axis O of the case body  1641 . One end of each groove  6419  passes through the opening-side end face  6410 A of the case body  1641 . When the slide cam  162  is inserted through the opening  6414  of the case body  1641 , projecting portions  623  on the outer periphery  624  of the slide cam  162  are slidably inserted into these grooves  6419 . By this, rotational movement of the slide cam  162  relative to the case  164  is constrained. In other words, rotational movement of the slide cam  162  relative to the pedal bracket  5  is constrained. 
         [0133]    Although, in the present embodiment, the three grooves  6419  are formed in the inner periphery  6418  of the case body  1641  at almost regular angular intervals about the axis O, the number and layout of the grooves  6419  are determined in accordance with the number and layout of the projecting portions  623  of the slide cam  162  that is used. 
         [0134]    On the other hand, the two flange portions  642  are formed integrally with the outer periphery  6412  of the case body  1641  so as to project outward from both sides of the end face  6410 A on the opening side of the case body  1641 . In these flange portions  642 , are formed the bolt insertion holes  6421  for inserting the bolts  8  at positions that correspond to the respective bolt insertion holes in the other side plate  53  of the pedal bracket  5  when a through-hole  653  formed in the central area of the cover  65  fitted in the opening  6414  of the case body  1641  is aligned with the pin insertion hole  531  of the other side plate  53  of the pedal bracket  5 . 
         [0135]    The cover  65  has similar construction to the cover  6  of the first embodiment (See  FIG. 6 ). That is to say, in the outer periphery  651  of the cover  65 , is formed the threaded portion  652  that is screwed into the threaded portion  6416  formed in the opening  6414  of the case body  1641 . In one surface (the surface to be faced toward the outside of the case body  1641 )  654  of the cover  65 , is formed a hexagon socket  656  for inserting a tool for rotating the cover  65  relative to the case body  1641 . On the other surface (the rear surface to be faced toward the inside of the case body  1641 )  655  of the cover  65 , is formed a seating face  657  with which the bottom face  617  of the rotating cam  161  is in sliding contact in the course of rotation. By rotating the tool inserted in the hexagon socket  656  in the surface  654  of the cover  65 , the threaded portion  652  formed in the outer periphery  651  of the cover  65  is tightened into the threaded portion  6416  formed in the opening  6414  of the case body  1641 , and thereby the bottom face  617  of the rotating cam  161  is pressed by the seating face  657  of the cover  65 . As a result, the rotating cam  161  and the slide cam  162  are pressed into initial positions within the case body  1641 . At that time, only the first coil spring  163 , whose natural length is greater than the distance between the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  and the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641 , is preloaded between the groove bottom  16417 C of the bottom portion  16415  of the case body  1641  and the bottom face  62711  (See  FIG. 15(D) ) of the spring guide hole  6271  of the slide cam  162 . 
         [0136]    Further, in the central area of the cover  65 , is formed the through-hole  653  having the inner diameter R2 larger than the outer diameter R1 of the damper connecting section  42  of the pedal pivot pin  4 . In an assembled state of the damper  16 , the axis O of the case body  1641  passes through the through-hole  653 , the inside of the rotating cam  161 , and the through-hole  6413  in the bottom portion  16415  of the case body  1641  (See  FIG. 11(C) ). The pedal pivot pin  4  is inserted, first the side of the support section  41 , into the through-hole  653 , and passes through the inside of the rotating cam  161 , so as to protrude from the through-hole  6413  of the bottom portion  16415  of the case body  1641 . 
         [0137]      FIGS. 14(A) ,  14 (B) and  14 (C) are a front view and left and right side views of the rotating cam  161 ,  FIG. 14(D)  a D-D cross-section of  FIG. 14(C) , and  FIG. 14(E)  a view illustrating schematically a profile shape of the cam face  1612  on the pitch circle  615  centering at the axis O. 
         [0138]    As illustrated, the rotating cam  161  has a stepped cylindrical shape including the cam guide portion  613  as a smaller-diameter portion and a cam portion  1610  as a large-diameter portion that are formed integrally. The cam guide portion  613  is an inner-diameter guide for the slide cam  162  and inserted into the inside of the slide cam  162 . On the other hand, the cam portion  1610  has the cam face  1612  on which the inclined cam faces  1621  of the slide cam  162  slide. 
         [0139]    Into the inside of the rotating cam  161 , the pedal pivot pin  4  is inserted from one end face  616  toward the other end face (bottom face), after passing through the through-hole  653  of the cover  65 . In an inner wall  614  of the rotating cam  161 , are formed two flat surfaces  618  facing each other at a width-across-flat T1 corresponding to the width-across-flat t1 of the damper connecting section  42  of the pedal pivot pin  4 . When the damper connecting section  42  of the pedal pivot pin  4  is inserted into the inside of the rotating cam  161 , these flat surfaces  618  come in contact with the corresponding flat surfaces  423  of the damper connecting section  42  of the pivot pin  4 , so that the torque of the pedal pivot pin  4  is transmitted to the rotating cam  161 . As a result, associated with rotation of the pedal pivot pin  4  in both directions α and β caused by operation of the accelerator pedal  21 , the rotating cam  161  also rotates in both directions α and β about the axis O while generating friction resistance, for example, between the inclined cam faces  1611  formed in the cam face  1612  and the inclined cam faces  1621  of the slide cam  162 . 
         [0140]    On the pitch circle  615  centering at the axis O, the cam face  1612  (the face on the side of the cam guide portion  613 ) of the cam portion  1610  periodically repeats concave forms and convex forms in the direction of the axis O. In detail, in the cam face  1612  of the cam portion  1610 , three inclined cam faces  1611  inclined at a prescribed angle W to the circumferential direction of the pitch circle  615  (the rotation direction of the pedal pivot pin  4  and the like) are formed at almost regular angular intervals about the axis O. Further, between each pair of adjacent inclined cam faces  1611 , is formed a step face  619  for determining the initial position of an inclined cam face  1621  of the slide cam  162 . When the rotating cam  161  rotates in the normal rotation direction α relative to the slide cam  162 , each inclined face  1621  of the slide cam  162  goes sliding on the corresponding inclined cam  1611  in the direction of getting away from the initial position determined by the corresponding step face  619 . When the rotating cam  161  rotates in the reverse rotation direction β relative to the slide cam  162 , each inclined cam face  1621  of the slide cam  162  goes sliding on the corresponding inclined cam face  1611  toward the initial position determined by the corresponding step face  619 . 
         [0141]      FIGS. 15(A) ,  15 (B) and  15 (C) are a front view, a back view and a side view of the slide cam  162 ,  FIG. 15(D)  an E-E cross-section of  FIG. 15(A) , and  FIG. 15(E)  a view illustrating schematically a profile shape of the cam face  1622  on the pitch circle  625  centering at the axis O. 
         [0142]    The slide cam  162  comprises: a cylindrical cam portion  1620 , into which the cam guide portion  613  of the rotating cam  161  is slidably inserted; and projecting portions  623  formed on the outer periphery  624  of the cam portion  1620  along the axis O of the cam portion  1620 . 
         [0143]    In the inner periphery of the cam portion  1620 , is formed a stepped hole  627  having a spring guide hole  6271  as a large-diameter portion on the side of a bottom face  626  of the cam portion  1620 . This spring guide hole  6271  encloses the one end  1631 A of the first coil spring  163 A, and the bottom face  62711  of the spring guide hole  6271  receives the one end  1631 A of the first coil spring  163 A from the initial state of the damper  16 . Further, the spring guide hole  6271  encloses the one end  1631 B of the second coil spring  163 B, and in the course of operation of the damper  16 , guides the one end  1631 B of the second coil spring  163 B toward the bottom face  62711 . 
         [0144]    On the pitch circle  625  centering at the axis O, the cam face (the face opposite to the bottom face  626 )  622  of the cam portion  1620  periodically repeats concave forms and convex forms in the direction of the axis O. In detail, in the cam face  1622  of the cam portion  1620 , three inclined cam faces  1621  inclined at nearly the same angle W as that of the inclined cam faces  1611  of the rotating cam  161  to the circumferential direction of the pitch circle  625  (the rotation direction of the pedal pivot pin  4  and the like) are formed at almost regular angular intervals about the axis O. Further, for each inclined cam face  1621 , are formed a flat face  628  which follows the inclined cam face  1621 , and an inclined face  629  that comes in contact with a step face  619  in the cam face  1612  of the rotating cam  161 . 
         [0145]    When the cam guide portion  613  of the rotating cam  161  is inserted into the inside of the cam portion  1620  in a state that the cam face  1622  of the cam portion  1620  is faced toward the cam face  1612  of the rotating cam  161 , the cam guide portion  613  of the rotating cam  161  protrudes from the side of the bottom face  626  of the cam portion  1620 . The cam guide portion  613  protruding from the side of the bottom face  626  of the cam portion  1620  is inserted into the inside of the combination spring  163  (the inside of the first coil spring  163 A placed within the second coil spring  163 B), and the spring guide hole  6271  of the cam portion  1620  is made to enclose the one end  1631 A of the first coil spring  163 A and the one end  1631 B of the second coil spring  163 B. 
         [0146]    The combination spring  163 , the slide cam  162  and the rotating cam  161 , which are assembled in the above way, are housed, first the side of the other end  1632 A of the first coil spring  163 A, into the case body  1641  through the opening  6414  of the case body  1641 , after the projecting portions  623  of the slide cam  162  are aligned with the grooves  6419  in the inner periphery  6418  of the case body  1641 . 
         [0147]    The free length LA0 of the first coil spring  163 A is greater than the distance L4 between the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641  and the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  in the initial state of the damper  16 . Accordingly, when the cover  65  is screwed in the opening  6414  of the case body  1641 , only the first coil spring  163 A is preloaded between the groove bottom  16417 C of the bottom portion  16415  of the case body  1641  and the bottom face  62711  of the spring guide hole  6271  of the slide cam  162 . On the other hand, the free length LB0 of the second coil spring  163 B is smaller than the distance L4 between the groove bottom  16417 C of the groove  16417  formed in the bottom portion  16415  of the case body  1641  and the bottom face  62711  of the spring guide hole  6271  of the slide cam  162  in the initial state of the damper  16 . Thus, the second coil spring  163 B is not compressed only by screwing the cover  65  in the opening  6414  of the case body  1641 . Thus, in the initial state of the damper  16 , only the first coil spring  163 A biases the slide cam  162  toward the direction of pressing the inclined cam faces  1621  of the slide cam  162  against the inclined cam faces  1611  of the rotating cam  161 . This causes rotation of the rotating cam  161 , and thereby the inclined cam faces  1621  in the cam face  1622  of the slide cam  162  come in contact with the respective step faces  619  in the cam face  1612  of the rotating cam  161 . This position becomes the initial position of the inclined cam faces  1621  of the slide cam  162  relative to the inclined cam faces  1611  of the rotating cam  161 . Thereafter, when, due to rotation of the rotating cam  161 , the slide cam  162  moves toward the bottom portion  16415  of the case  164  and reaches the prescribed position, the first coil spring  163 A and the second coil spring  163 B are both compressed between the groove bottom  16417 C of the bottom portion  16415  of the case body  1641  and the bottom face  62711  of the spring guide hole  6271  of the slide guide  162 . 
         [0148]    Owing to the above-described construction, the accelerator pedal unit  11  of the present embodiment makes it possible that a suitable load is applied on a driver&#39;s foot during pressing down of the accelerator pedal  21  and the load applied on the driver&#39;s foot becomes rapidly larger by magnitude that can be detected by tactile sensation at the time when the accelerator pedal  21  is pressed to the prescribed position where the energy expenditure rate of the automobile deteriorates to the prescribed level (i.e. when the pedal pivot pin  4  rotates to the prescribed angle θ1 in the normal rotation direction α), as described in the following. 
         [0149]      FIGS. 16-18  are views for explaining two-stage damping motion of the damper  16  associated with pressing the accelerator pedal  21 . 
         [0150]    As illustrated in  FIG. 16 , in the initial state of the damper  16  (the state where the accelerator pedal  21  is not pressed), each inclined cam face  1621  of the slide cam  162  of the damper  16  is located in the initial position determined by the corresponding step face  619  of the cam face  1612  of the rotating cam  161 . 
         [0151]    When the accelerator pedal  21  is pressed down, the pedal pivot pin  4  rotates in the normal direction α interlocking with swinging of the accelerator pedal arm  2 . At that time, within the damper  16 , the flat surfaces  423  of the damper connecting section  42  of the pedal pivot pin  4  come in contact with the respective opposed flat surfaces  618  in the inner wall of the rotating cam  161 , so that the rotating cam  161  is rotated in the normal rotation direction α. Until the rotating cam  61  rotates to the prescribed angle θ1 in the normal rotation direction α, the slide cam  162  moves in the direction A of getting away from the rotating cam  161  (the direction toward the bottom portion  16415  of the case  164 ) while each inclined cam face  1621  is in sliding contact with the corresponding inclined cam face  1611  of the rotating cam  161 . During this, only the first coil spring  163 A is gradually compressed from the initial preloaded state, so that each inclined cam face  1621  of the slide cam  162  is pressed more and more strongly against the corresponding inclined cam face  1611  of the rotating cam  161 . In other words, the combination spring  163  functions as a compression spring having the same spring contact as that of the first coil spring  163 A. Accordingly, the friction resistance, for example, between the inclined cam faces  1621  of the slide cam  162  and the inclined cam faces  1611  of the rotating cam  161  gradually increases, and the torque of the rotating cam  161  in the rotation direction about the axis O increases gradually with increase of the rotation angle θ of the rotating cam  161  in the normal rotation direction α relative to the slide cam  162 . As a result, rotation of the pedal pivot pin  4  in the normal rotation direction α is damped, and the suitable load is applied on the driver&#39;s foot that presses the accelerator pedal  21 . 
         [0152]    As illustrated in  FIG. 17 , when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile deteriorates to the prescribed level (i.e. when the pedal pivot pin  4  rotates to the prescribed angle θ1 in the normal rotation direction α), the slide cam  162  moves toward the bottom portion  16415  of the case  164  up to the position where the one end  1631 B of the second coil spring  163 B comes in contact with the bottom face  62711  of the spring guide hole  6271  of the slide cam  162 , with each inclined cam face  1621  in sliding contact with the corresponding inclined cam face  1611  of the rotating cam  161 . As a result, at the time when the rotating cam  161  rotates to the prescribed angle θ1 in the normal rotation direction α, also the second coil spring  163 B together with the first coil spring  163 A starts to bias the slide cam  162  so as to press each inclined cam face  1621  of the slide cam  162  against the corresponding inclined cam face  1611  of the rotating cam  161 . In other words, the combination spring  163  functions as a compression spring that has a spring constant corresponding to the sum of the spring constants of the first and second coil springs  163 A and  163 B. Accordingly, each cam face  1621  of the slide cam  162  is pressed against the corresponding cam face  1611  of the rotating cam  161  and the bottom face  617  of the rotating cam  161  against the seating face  657  of the cover  65  by force that is greater by additional biasing force of the second coil spring  163 B than the force at the time when only the first coil spring  163 A biases the slide cam  162 , and thus the torque of the rotating cam  161  in the rotation direction about the axis O increases rapidly. Thus, at the time when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile deteriorates to the prescribed level, the load applied on the driver&#39;s foot that presses the accelerator pedal  21  becomes rapidly larger by at least magnitude such that a variation of load can be detected by tactile sensation. 
         [0153]    As illustrated in  FIG. 18 , when the driver continues pressing down the accelerator pedal  21  furthermore (i.e. when the pedal pivot pin  4  rotates over the prescribed angle θ1 in the normal rotation direction α), then the slide cam  162  moves toward the bottom portion  16415  of the case  164  with each inclined cam face  1621  in sliding contact with the corresponding inclined cam face  1611  of the rotating cam  161 , so that the first coil spring  163 A and the second coil spring  163 B are compressed furthermore. Accordingly, the inclined cam faces  1621  of the slide cam  162  are pressed further strongly against the inclined cam faces  1611  of the rotating cam  161 , and the bottom face  617  of the rotating cam  161  is pressed further strongly against the seating face  657  of the cover  65 . Accordingly also after increase of the spring constant, the friction resistance, for example, between the inclined cam faces  1621  of the slide cam  162  and the inclined cam faces  1611  of the rotating cam  161  further increases gradually with increase of the rotation angle θ of the rotating cam  161  in the normal rotation direction α, and the torque of the rotating cam  161  in the rotation direction about the axis O increases gradually. As a result, also after the rapid increase of the load applied on the driver&#39;s foot that presses down the accelerator pedal  21 , the load applied on the driver&#39;s foot that presses the accelerator pedal  21  further increases gradually as long as the driver continues pressing down the accelerator pedal  21 . Accordingly, the driver can intuitively grasp the continuous worsening of the energy expenditure rate of the automobile through operation of pressing the accelerator pedal  21  without constantly caring about a change of visual information obtained from the meters on the instrument panel. 
         [0154]    As described hereinabove, according to the accelerator pedal unit  11  of the present embodiment, the pedal pivot pin  4 , which is rotated by operation (i.e. pressing and releasing) of the accelerator pedal  21 , is connected to the damper  16  whose resisting force for damping rotation of the pedal pivot pin  4  increases stepwise according to the rotation angle θ of the pedal pivot pin  4  in the normal rotation direction α. At the time when the pedal pivot pin  4  rotates in the normal rotation direction α to the prescribed rotation angle θ1 at which the energy expenditure rate of the automobile deteriorates to the prescribed level, the damper  16  rapidly increases the force of damping rotation of the pedal pivot pin  4 . Thus, it is possible that, while a suitable load is applied on the driver&#39;s foot pressing the accelerator pedal  21 , when the accelerator pedal  21  is pressed to the position where the energy expenditure rate of the automobile worsens to the prescribed level, the load applied on the driver&#39;s foot becomes rapidly heavier by at least magnitude that can be detected by tactile sensation. Thus, the driver can detect a rapid change in operational feeling of pressing the accelerator pedal  21  as a signal for energy-saving driving of the automobile while driving. 
         [0155]    Further, when the driver continues pressing down the accelerator pedal  21  (i.e. when the pedal pivot pin  4  rotates over the prescribed angle θ1 in the normal rotation direction α), the friction resistance, for example, between the inclined cam faces  1621  of the slide cam  162  and the inclined cam faces  1611  of the rotating cam  161  increases furthermore with increase of the rotation angle θ of the rotating cam  161  in the normal rotation direction α, and the torque of the rotating cam  161  in the rotation direction about the axis O increases furthermore. Accordingly, the load applied on the driver&#39;s foot that presses down the accelerator pedal  21  further increases gradually even after the rapid increase of the load. Therefore, the driver can intuitively grasp the continuous worsening of the energy expenditure rate of the automobile through operation of pressing the accelerator pedal  21 . 
         [0156]    In the present embodiment, the non-linear spring whose elastic constant increases at the time when the spring is compressed to the prescribed compression amount is constructed as the combination spring in which two coil springs  163 A and  163 B having different natural lengths from each other are arranged in the nested state, and this non-linear spring biases the slide cam  162 . At the time when the rotating cam  161  rotates to the prescribed angle θ1 in the normal rotation direction α, the torque of the pedal pivot pin  4  in the rotation direction about the axis O is increased by at least magnitude such that the driver can detect as a change in operational feeling of the accelerator pedal  21 . However, this is not indispensable. 
         [0157]    For example, the combination spring  163  can be constructed by arranging three or more coil springs having different natural lengths from each other in a nested state. In that case, the driver can detect change in the traveling state of the automobile in more-finely-divided stages. 
         [0158]    Further, instead of the combination spring  163  comprising the two spring coils  163 A and  163 B having the different natural lengths from each other, it is possible to use a non-linear spring such as an irregular pitch coil spring or a tapered coil spring, whose spring constant changes stepwise in the course of compression. When such a non-linear spring is used, the spring constant of the non-linear spring increases in a prescribed range of rotation angle including the time when the rotating cam  161  rotates to the prescribed angle θ1 in the normal rotation direction α. Therefore, the torque of the pedal pivot pin  4  in the rotation direction about the axis O can be increased by increment such that the driver can detect a change in operational feeling of the accelerator pedal  21  at the time when the rotating cam  161  rotates to the prescribed rotation angle θ1 in the normal rotation direction α. 
         [0159]    In the present embodiment, the coil springs  163 A and  163 B are used for biasing the slide cam  162 . However, another elastic body such as rubber, a spring other than the coil spring, or the like may be used. 
         [0160]    In the above-described first and second embodiments, the outer periphery  421  of the damper connecting section  42  of the pedal pivot pin  4  is formed to have the two flat surfaces and the opposed two flat surfaces  618  are formed in the inner wall  614  of the rotating cam  61 ,  161  of the damper  6 ,  16 , so that the rotating cam  61 ,  161  of the damper  6 ,  16  rotates interlocking with rotation of the pedal pivot pin  4 . However, this is not indispensable. It is sufficient that the outer periphery  421  of the damper connecting section  42  of the pedal pivot pin  4  and the inner wall  614  of the rotating cam  61 ,  161  of the damper  6 ,  16  include respective surfaces that interfere with each other, and rotation of the pedal pivot pin  4  is transmitted to the rotating cam  61 ,  161  of the damper  6 ,  16  by means of contact between these surfaces. For example, it is possible that the outer periphery  421  of the damper connecting section  42  of the pedal pivot pin  4  and the inner wall  614  of the rotating cam  61 ,  161  of the damper  6 ,  16  are each formed to have one flat surface or three or more flat surfaces so that the respective surfaces of the damper connecting section  42  and the inner wall  614  of the rotating cam  61 ,  161  come in contact with each other when the pedal pivot pin  4  rotates. Or, both a cross-section shape of the damper connecting section  42  of the pedal pivot pin  4  and a contour shape of the inner wall  614  of the rotating cam  61 ,  161  of the damper  6 ,  16  can be polygonal shapes. Or, one or more recessed portions may be formed in the outer periphery  421  of the pedal pivot pin  4  and one or more projecting portions to fit in these recessed portions may be formed in the inner wall  614  of the rotating cam  61 ,  161  of the damper  6 ,  16 . 
         [0161]    Further, the retaining ring  7  is used for preventing dropping-off of the pedal pivot pin  4  in the above-described first and second embodiments. However, another part for preventing dropping-off of the pedal pivot pin  4  can be used instead of the retaining ring  7 . For example, in the case of using a bush nut or the like, which can be fixed without a groove, it is not necessary to form the groove  413  in the support section  41  of the pedal pivot pin  4 . 
         [0162]    The above-described first and second embodiments take the examples of the accelerator pedal units  1  and  11  for an automobile. However, the present invention can be applied to operation units of various apparatuses such as musical instruments, game machines, various devices, and the like without limiting to an accelerator pedal unit  1 ,  11 , as far as it is useful to give, as a signal of occurrence of a predetermined event, a change in operational feeling of an operating part such as a pedal and a steering wheel to an operator at the time when the operator moves the operating part to a prescribed position by manual operation with hand, foot, or the like. In the damper  6  of the first embodiment, the number of the inclined cam faces, the inclination angles of the plurality of inclined areas included in the inclined cam faces, and sequential order of the inclined areas can be determined suitably depending on the intended use of the operation unit. Similarly, in the damper  16  of the second embodiment, the number of coil springs combined in the nested state as components of the combination spring  163  can be determined suitably depending on the intended use of the operation unit. 
         [0163]    Further, in the damper  6  of the first embodiment, it is possible to use the combination spring  163  of the damper  16  of the second embodiment instead of the coil spring  63 . By this, the stepwise change in the resisting force for damping rotation of the pedal pivot pin  4  according to the rotation angle θ of the pedal pivot pin  4  in the normal rotation direction α can be realized by a plurality of inclined areas of different inclination angles provided in the inclined cam faces  611  of the rotating cam  61  and a plurality of coil springs of different coil lengths as elements of the combination spring  163 , and thus the resisting force can be changed stepwise in more-finely-divided stages. Accordingly, the driver can detect a change in the traveling state of the automobile in more-finely-divided stages. 
       INDUSTRIAL APPLICABILITY 
       [0164]    The present invention can be widely applied to cases where it is beneficial for a user operating manually an operating part to grasp intuitively occurrence of a prescribed event. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1 ,  11 : accelerator pedal unit;  2 : accelerator pedal arm;  3 : spring;  4 : pedal pivot pin;  5 : pedal bracket;  6 ,  16 : damper;  7 : retaining ring;  8 : bolt;  9 : nut;  21 : accelerator pedal;  41 : support section;  42 : damper connecting section;  43 : pedal arm fixing section;  51 : bottom plate;  52 ,  53 : side plate;  61 ,  161 : rotating cam;  62 ,  162 : slide cam;  63 : coil spring;  64 ,  164 : case;  65 : cover;  411 : outer periphery of dropping-off preventing section;  412 : end face of pedal pivot pin;  413 : groove;  421 : outer periphery of damper connecting section;  423 : flat surface;  425 : support area;  431 : outer periphery of pedal arm fixing section;  422 ,  432 : step surface of pedal pivot pin;  521 ,  531 : pin support hole;  610 ,  1610 : cam portion;  611 ,  1611 : inclined cam face;  611 A: first inclined area;  611 B: second inclined area;  612 ,  1612 : cam face;  613 : cam guide portion;  614 : inner wall of rotating cam;  615 : pitch circle;  616 ,  617 : end face of rotating cam;  618 : flat surface of rotating cam&#39;s inner wall;  619 : step face;  620 ,  1620 : cam portion;  621 ,  1621 : inclined cam face;  622 ,  1622 : cam face;  623 : projecting portion;  624 : outer periphery of cam portion;  625 : pitch circle;  626 : bottom face of cam portion;  627 : stepped hole;  628 : flat surface;  629 : inclined face;  631 ,  632 : end of coil spring;  641 ,  1641 : case body;  642 : flange portion;  651 : outer periphery of cover;  652 : threaded portion;  653 : through-hole;  654 : surface of cover;  655 : rear surface of cover;  656 : hexagon socket;  657 : seating face for rotating cam;  6410 A,  6410 B: end face of case body;  6411 : recessed portion for welding;  6412 : outer periphery of case body;  6413 : through-hole;  6414 : opening of case body;  6415 : bottom face of case body;  6416 : threaded portion;  6417 : spring guide portion;  6418 : inner periphery of case body;  6419 : groove;  6421 : bolt insertion hole;  6271 : spring guide hole;  163 : combination spring:  163 A: first coil spring;  163 B: second coil spring;  16415 : bottom of case body;  16417 : groove;  16417 A,  16417 B: inner wall of groove; and  16417 C: groove bottom.