Abstract:
The friction damper includes a hollow cylindrical member having an axially movable non-rotational member within the cylindrical member. A spring is disposed between the movable and cylindrical members. A rotating member lies within the cylindrical member in opposition to the movable member. A frictional resisting element resists relative rotation of the rotating member and the cylindrical member and causes the movable member to move axially away from the rotating member against the bias of the spring to increase the spring force of the spring and the frictional resisting force.

Description:
This is a divisional of application Ser. No. 09/270,794, filed Mar. 16, 1999, now U.S. Pat. No. 6,240,801, the entire content of which is incorporated by reference in this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a friction damper, and more particularly to a friction damper suitable for imparting an appropriate brake to an accelerator pedal, a brake pedal, a clutch pedal, or the like of a vehicle and a pedal device having the friction damper. 
     2. Description of the Related Art 
     Pedal devices, including an accelerator pedal, a brake pedal, a clutch pedal, and the like of a vehicle, are each comprised of a pedal disposed at an upper-limit position at which the pedal can be pressed down as well as an urging means consisting of a coil spring for urging the pedal in a direction in which the pedal returns to its upper-limit position when the pedal was pressed down. 
     In the case of the pedal device including an accelerator pedal, for example, as the accelerator pedal is pressed down, a throttle is opened or closed in the case of a gasoline engine, and a fuel injector is actuated in the case of a diesel engine. Conventionally, to open or close the throttle or actuate the fuel injector, the accelerator pedal and the throttle or the accelerator pedal and the fuel injector are linked together by an accelerator wire cable, and the accelerator pedal is adapted to pull the accelerator wire cable as it is pressed down. 
     Accordingly, when the accelerator pedal is pressed down, a reaction force (resisting force) of a value in which the resilient reaction force of the coil spring and the tensile reaction force of the accelerator wire cable are added together is applied to the accelerator pedal. 
     Meanwhile, fine control of fuel injection for the automotive engine is required for the purposes of low fuel consumption of vehicles and reduction of carbon dioxide, and electronic control of fuel injection such as the regulation of the throttle valve opening based on the pressing down of the accelerator pedal has been put to practical use. 
     In vehicles in which fuel injection of the engine is effected by electronic control, the accelerator wire cable arranged between the accelerator pedal and the throttle valve is normally omitted. With the vehicles without the accelerator wire cables, however, the reaction force with respect to the pedal pressing force differs in comparison with vehicles with the accelerator wire cables, and if a general driver who is accustomed to driving a vehicle with the accelerator wire cable drives the vehicle without the accelerator wire cable, there is a possibility of excessively pressing down on the accelerator, thereby consuming fuel more than before. 
     To obtain a large reaction force with respect to the pedal pressing force, if the spring force of a return spring for returning the pedal arm to the initial position of rotation is simply made large, there is a possibility of causing early fatigue to the pedal pressing foot due to the large reaction force from the return spring during constant traveling. 
     As a countermeasure for overcoming this problem, an arrangement has been proposed in which the pedal arm is linked to one end of a dummy cable passed through a fixed helical pipe, the other end of the dummy cable being terminated via a coil spring, to ensure that a reaction force exhibiting a hysteresis characteristic with respect to the pedal pressing force, which is similar to the conventional case in which the accelerator wire cable is provided, can be obtained by the dummy cable. However, since this countermeasure using the dummy cable requires a relatively large space for installing the dummy cable, this countermeasure can be adopted only in vehicles of large vehicle types, such as trucks and RVs, in which there is sufficient leeway in space. In addition, since various factors are involved, the adjustment of reaction force by using the dummy cable is relatively difficult, and there is a possibility of increasing the cost in order to set the reaction force to a desired value. Furthermore, although, in order to obtain the hysteresis characteristic, a metallic dummy cable is allowed to slide within the inner surface of a resin sheathing of the pipe so as to produce sliding resistance between the metallic dummy cable and the inner surface of the resin sheathing of the pipe, there is a possibility that a large change in the characteristic can occur due to the wear caused by this sliding over a long period of use. 
     The above-described problem occurs not only in the accelerator pedals, but can also occur in cases where appropriate rotational resistance is produced by using the above-described dummy cable or the like in brake pedals or clutch pedals, for example. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised in view of the above-described circumstances, and it is an object of the present invention to provide a pedal device which makes it possible to simply set the hysteresis characteristic concerning the reaction force acting on the pedal to a desired value without using the accelerator wire cable and the dummy cable, as well as a friction damper suitable for use in the pedal device. 
     Another object of the present invention is to provide a pedal device which is capable of obtaining an appropriate reaction force with respect to the pedal pressing force, is capable of being installed compactly in comparison with the dummy cable, makes it possible to effect very simply the adjustment of reaction force having a hysteresis characteristic, and exhibits a small change in the characteristic, as well as a friction damper suitable for use in the pedal device. 
     Still another object of the present invention is to provide a friction damper which is capable of varying the magnitude of reaction force, and a pedal device using the friction damper. 
     A further object of the present invention is to provide a friction damper which is capable of varying the value of a resisting torque in correspondence with relative rotational displacement, and a pedal device using the friction damper. 
     To attain the above objects, in accordance with a first aspect of the present invention, there is provided a damper comprising: a hollow cylindrical member with a bottom; a movable member disposed in the hollow cylindrical member in such a manner as to be movable in an axial direction of the hollow cylindrical member but immovable about an axis of the hollow cylindrical member; a spring means disposed between the movable member and the bottom of the hollow cylindrical member, one end of the spring means abutting against the bottom of the hollow cylindrical member and another end thereof abutting against the movable member; a rotating member disposed in the hollow cylindrical member in such a manner as to oppose the movable member and to be relatively rotatable about the axis of the hollow cylindrical member; and a frictionally-resisting-force generating means for generating a frictionally resisting force to the relative rotation of the rotating member with respect to the hollow cylindrical member, and for causing the movable member to move away from the rotating member in the axial direction against the resiliency of the spring means and to approach the bottom of the hollow cylindrical member so as to increase the spring force of the spring means, thereby increasing the frictionally resisting force. 
     Furthermore, to attain the above objects, in accordance with a second aspect of the present invention, there is provided a friction damper comprising: an inner member extending like a shaft; a tubular outer member disposed coaxially with the inner member and on an outer side of the inner member; a frictionally engaging means provided in an annular space on a radially outward side of the inner member and on a radially inward side of the outer member; a resilient means provided in the annular space; an urging-force varying means provided in the annular space, wherein the frictionally engaging means has a first portion which rotates integrally with the inner member and a second portion which rotates integrally with the outer member and is provided in such a manner as to be capable of coming into contact with the first portion in the axial direction, wherein the resilient means is arranged to urge the first portion and the second portion in a direction in which the first portion and the second portion are brought into contact with each other and are pressed against each other, and wherein the urging-force varying means is arranged to make variable an urging force of the resilient means in correspondence with a relative rotational displacement of the inner member and the outer member. 
     In accordance with the friction damper according to the second aspect of the invention, when a relative rotational displacement occurs between the inner member and the outer member, the urging force of the resilient means for pressing the first portion and the second portion against each other is varied by the urging-force varying means. 
     In the friction damper in accordance with a third aspect of the invention, in the friction damper according to the second aspect, a shaft inserting hole extending in the axial direction is penetratingly formed in a center of the inner member. 
     In the friction damper in accordance with a fourth aspect of the invention, in the friction damper according to the second or third aspect, a flange portion projecting radially outward is formed at an axial end of the inner member, and the first portion is formed by the flange portion. 
     In the friction damper in accordance with a fifth aspect of the invention, in the friction damper according to any one of the second to fourth aspects, a friction plate which rotates integrally with the inner member is provided in the annular space in such a manner as to be movable in the axial direction, and the first portion is formed by the friction plate. 
     In the friction damper in accordance with a sixth aspect of the invention, in the friction damper according to any one of the second to fifth aspects, the outer member has a hollow cylindrical portion, a longitudinal end of the hollow cylindrical portion is formed as an open end which is open, a flange portion projecting radially inward is formed at another longitudinal end of the hollow cylindrical portion, and the second portion is formed by the flange portion. 
     In the friction damper in accordance with a seventh aspect of the invention, in the friction damper according to any one of the second to sixth aspects, a friction plate which rotates integrally with the outer member is provided in the annular space in such a manner as to be movable in the axial direction, and the second portion is formed by the friction plate. 
     In the friction damper in accordance with an eighth aspect of the invention, in the friction damper according to any one of the second to seventh aspects, the resilient means is disposed between the frictionally engaging means and the urging-force varying means in the annular space, and the urging-force varying means is arranged to change an axially extending space for accommodating the resilient means, in correspondence with the relative rotational displacement of the inner member and the outer member. 
     In the friction damper in accordance with a ninth aspect of the invention, in the friction damper according to any one of the second to eighth aspects, the urging-force varying means is provided with a restricting means for restricting the movement of the urging-force varying means in a direction away from the frictionally engaging means. 
     In the friction damper in accordance with a 10th aspect of the invention, in the friction damper according to the ninth aspect, the urging-force varying means is provided with an annular inner variable member joined integrally to the inner member, an annular outer variable member disposed in such a manner as to oppose the inner variable member and joined integrally to the outer member, a cam portion formed on a surface of the inner variable member opposing the outer variable member, and a cam portion formed on a surface of the outer variable member opposing the inner variable member, the cam portions being arranged to change a distance between the inner variable member and the outer variable member in the axial direction in correspondence with the relative rotational displacement of the inner member and the outer member. 
     In the friction damper in accordance with an 11th aspect of the invention, in the friction damper according to any one of the second to eighth aspects, the urging-force varying means is formed by a variable member which is threadedly joined to one of the inner member and the outer member, and is joined to another one of the inner member and the outer member in such a manner as to be unrotatable but movable in the axial direction. 
     In the friction damper in accordance with a 12th aspect of the invention, in the friction damper according to any one of the second to 11th aspects, the inner member is joined to a rotating shaft in such a manner as to be rotatable integrally with the shaft, the outer member is unrotatably joined to a member which rotatably supports the shaft, and the second portion is unrotatable together with the outer member. 
     Furthermore, to attain the above objects, in accordance with a 13th aspect of the present invention, there is provided a pedal device for a vehicle, comprising: a pedal arm which is rotatably supported by a supporting frame; a first spring means for rotatively urging the pedal arm to an initial position of its rotation; and a damper for imparting a resisting force to the rotation of the pedal arm, wherein the damper includes: a hollow cylindrical member with a bottom; a movable member disposed in the hollow cylindrical member in such a manner as to be movable in an axial direction of the hollow cylindrical member but immovable about an axis of the hollow cylindrical member; a second spring means disposed between the movable member and the bottom of the hollow cylindrical member, one end of the spring means abutting against the bottom of the hollow cylindrical member and another end thereof abutting against the movable member; a rotating member disposed in the hollow cylindrical member in such a manner as to oppose the movable member and to be relatively rotatable about the axis of the hollow cylindrical member; and a frictionally-resisting-force generating means for generating a frictionally resisting force as the resisting force to the relative rotation of the rotating member with respect to the hollow cylindrical member, and for causing the movable member to move away from the rotating member in the axial direction against the resiliency of the second spring means and to approach the bottom of the hollow cylindrical member so as to increase the spring force of the second spring means, thereby increasing the frictionally resisting force, and wherein the rotation of the pedal arm is transmitted as the relative rotation of the hollow cylindrical member and the rotating member. 
     In accordance with the pedal device according to the  13 th aspect, when the rotating member is relatively rotated with respect to the hollow cylindrical member due to the rotation of the pedal arm based on the pressing down of the pedal, an increasing frictionally resisting force is generated by the frictionally-resisting-force generating means. On the other hand, when the pressing down of the pedal is canceled and the rotating member is relatively reversely rotated with respect to the hollow cylindrical member, the frictionally resisting force in the frictionally-resisting-force generating means becomes small. Consequently, by virtue of the frictionally resisting force having this hysteresis characteristic, a resisting force similarly having the hysteresis characteristic is imparted to the rotation of the pedal arm. This resistance force makes it possible, for instance, to prevent the accelerator pedal from being excessively pressed down, which can otherwise consume fuel more than before. 
     In the pedal device for a vehicle in accordance with a 14th aspect of the invention, in the pedal device according to the 13th aspect, the frictionally-resisting-force generating means has a projection formed integrally on one surface of the rotating member, opposing the movable member, in such a manner as to project in the axial direction toward one surface of the movable member and a projection formed integrally on the one surface of the movable member, opposing the rotating member, in such a manner as to project in the axial direction toward the one surface of the rotating member, the projections being arranged to come into planar contact with each other. 
     In the pedal device in accordance with the 14th aspect, since the frictionally-resisting-force generating means is formed by projections which are disposed between the movable member and the rotating member and are formed integrally to the movable member and the rotating member, respectively, the pedal device can be made very compact, and can be installed by making effective use of a small space. Moreover, since the projections are brought into planar contact with each other, the coefficients of friction at the contact surfaces can be set appropriately, thereby making it possible to determine a resisting force having a hysteresis characteristic which can be imparted to the rotation of the pedal arm, and making it possible to effect the adjustment of the reaction force very simply. 
     In the pedal device for a vehicle in accordance with a 15th aspect of the invention, in the pedal device according to the 13th or 14th aspect, the frictionally-resisting-force generating means has an inclined surface formed on the one surface of the rotating member opposing the movable member, and an inclined surface formed on the one surface of the movable member opposing the rotating member and arranged to come into planar contact with the inclined surface formed on the one surface of the rotating member. 
     In accordance with the pedal device in accordance with the 15th aspect, by appropriately setting the coefficients of friction a t the inclined surface formed on the one surface of the rotating member and at the inclined surface formed non the one surface of the movable member opposing the rotating member, it is possible to determine in the frictionally resisting-force generating means the resisting force with the hysteresis characteristic which can be substantially imparted to the rotation of the pedal arm, so that the adjustment of the reaction force can be effected very simply. 
     In the pedal device for a vehicle in accordance with a 16th aspect of the invention, in the pedal device according to any one of the 13th to 15th aspects, the frictionally-resisting-force generating means has a fixed surface which comes into planar contact with another surface of the rotating member. 
     In the pedal device in accordance with the 16th aspect, since it is possible to determine the resisting force with the hysteresis characteristic which can be substantially imparted to the rotation of the pedal arm by appropriately setting the coefficients of friction at the other surface of the rotating member and the fixed surface, the adjustment of the reaction force can be effected very simply in the same way as the pedal device in accordance with the 15th aspect. 
     It should be noted that, in the pedal device in accordance with the 16th aspect, the other surface of the rotating member and the fixed surface which are brought into planar contact with each other may be formed by inclined surfaces in the same way as the pedal device in accordance with the 15th aspect. 
     In the pedal device for a vehicle in accordance with a 17th aspect of the invention, in the pedal device according to the 16th aspect, the fixed surface is formed on the hollow cylindrical member. 
     In the pedal device in accordance with the 17th aspect, since the fixed surface is formed on the hollow cylindrical member, the pedal device can be formed more compactly. It goes without saying that the fixed surface may be formed on the supporting frame or the pedal arm, instead of being formed on the hollow cylindrical member. 
     In the pedal device for a vehicle in accordance with an 18th aspect of the invention, in the pedal device according to any one of the 13th to 17th aspects, the bottom of the hollow cylindrical member can be adjustably positioned in the axial direction. 
     In the pedal device in accordance with the 18th aspect, since the bottom of the hollow cylindrical member can be adjustably positioned in the axial direction, the initial resilient force generated by the second spring means, i.e., the initial resisting force, can be adjusted and set arbitrarily, so that an optimum initial resisting force can be obtained. 
     In the pedal device for a vehicle in accordance with a 19th aspect of the invention, in the pedal device according to any one of the 13th to 18th aspects, the second spring means has at least two coil springs arranged concentrically, and the at least two coil springs have mutually different moduli of elasticity. 
     As the second spring means, a spring means using such as rubber or a leaf spring may be used. Preferably, if the second spring means is formed by at least one coil spring, the pedal device can be made to excel in durability and simple in the structure. In addition, if the second spring means is formed by at least two coil springs having mutually different moduli of elasticity as in the case of the pedal device in accordance with the seventh aspect, one coil spring can be used for fine adjustment, and the design and adjustment of the resisting force can be effected simply. Hence, such an arrangement is very preferable from this standpoint. 
     In the pedal device for a vehicle in accordance with a 20th aspect of the invention, in the pedal device according to any one of the 13th to 19th aspects, the pedal arm is an accelerator pedal arm. 
     In the pedal device for a vehicle in accordance with the present invention, an arrangement may be provided such that the rotation of the pedal arm is transmitted to either the hollow cylindrical member or the rotating member. Preferably, however, the rotation of the pedal arm is arranged to be transmitted to the rotating member, in which case, the hollow cylindrical member is fixedly supported by the frame. In the case where the rotation of the pedal arm is arranged to be transmitted to the hollow cylindrical member, the rotating member is fixedly supported by the frame. 
     Furthermore, to attain the above objects, in accordance with a 21st aspect of the present invention, there is provided a pedal device comprising: a rotating shaft supported by a supporting frame; an accelerator pedal which is disposed at an upper-limit position where the accelerator pedal can be pressed down and which swings about the rotating shaft; a resisting means for generating resistance in a direction in which the pressing down of the accelerator pedal is hampered when the accelerator pedal is pressed down; and an urging means for urging the accelerator pedal in a direction in which the accelerator pedal returns to the upper-limit position when the accelerator pedal is pressed down at the upper-limit position; wherein the resisting means is formed by a friction damper in which a portion which rotates by following the swinging motion of the accelerator pedal comes into contact with a stationary portion so as to generate resistance. 
     In the pedal device in accordance with a 22nd aspect of the invention, in the pedal device according to the 21st aspect, the rotating shaft is supported by mutually opposing portions of the supporting frame, and the friction damper is disposed in a space between the mutually opposing portions of the supporting frame. 
     In the pedal device in accordance with a 23rd aspect of the invention, in the pedal device according to the 21st or 22nd aspect, the friction damper is disposed coaxially with the rotating shaft. 
     In the pedal device in accordance with a 24th aspect of the invention, in the pedal device according to any one of the 21st to 23rd aspects, the friction damper is arranged to generate torque of a fixed value irrespective of displacement in the swinging motion of the accelerator pedal. 
     In the pedal device in accordance with a 25th aspect of the invention, in the pedal device according to any one of the 21st to 23rd aspects, the friction damper is arranged such that the value of torque changes in correspondence with the displacement in the swinging motion of the accelerator pedal. 
     In the pedal device in accordance with a 26th aspect of the invention, in the pedal device according to the 21st aspect, the rotating shaft is rotatably supported by the supporting frame and is provided so as to rotate in interlocked relation to the swinging motion of the accelerator pedal, wherein the friction damper is disposed coaxially with the rotating shaft and includes an inner member into an interior of which the rotating shaft is inserted and which rotates integrally with the rotating shaft coaxially therewith, a tubular outer member disposed coaxially with the inner member on an outer side of the inner member in such a manner as to be unrotatable, a frictionally engaging means provided in an annular space on a radially outward side of the inner member and on a radially inward side of the outer member, and a resilient means provided in the annular space, wherein the frictionally engaging means has a first portion which rotates integrally with the inner member and a second portion which is unrotatable and is provided in such a manner as to be capable of coming into contact with the first portion, and wherein the resilient means is arranged to urge the first portion and the second portion in a direction in which the first portion and the second portion are brought into contact with each other and are pressed against each other. 
     In the pedal device in accordance with a 27th aspect of the invention, in the pedal device according to the 21st aspect, the rotating shaft is rotatably supported by the supporting frame and is provided so as to rotate in interlocked relation to the swinging motion of the accelerator pedal, wherein the friction damper is disposed coaxially with the rotating shaft and includes an inner member into an interior of which the rotating shaft is inserted and which rotates integrally with the rotating shaft coaxially therewith, a tubular outer member disposed coaxially with the inner member on an outer side of the inner member in such a manner as to be unrotatable, a frictionally engaging means provided in an annular space on a radially outward side of the inner member and on a radially inward side of the outer member, a resilient means provided in the annular space, and an urging-force varying means provided in the annular space, wherein the frictionally engaging means has a first portion which rotates integrally with the inner member and a second portion which is unrotatable and is provided in such a manner as to be capable of coming into contact with the first portion, wherein the resilient means is disposed between the frictionally engaging means and the urging-force varying means in the annular space and is arranged to urge the first portion and the second portion in a direction in which the first portion and the second portion are brought into contact with each other and are pressed against each other, and wherein the urging-force varying means is arranged to change an axially extending space for accommodating the resilient means, in correspondence with the relative rotational displacement of the inner member and the outer member. 
     In the pedal device in accordance with a 28th aspect of the invention, in the pedal device according to any one of the 21st to 27th aspects, the resisting means includes the urging means. 
     In the pedal devices in accordance with the 21st to 28th aspects of the invention, the resisting means is formed by a friction clutch, and the adjustment of increase or decrease of resistance occurring in the friction clutch can be made easily, so that the hysteresis characteristic in the pedal device can be easily set to a desired value. 
     It should be noted that the pedal arm in the device of the present invention is preferably the aforementioned accelerator pedal arm, but the pedal arm is also applicable to a brake pedal arm, a clutch pedal arm, or the like. 
     In accordance with the friction damper of the present invention, the value of torque can be varied in correspondence with the relative rotational displacement of the inner member and the outer member. Accordingly, the friction damper of the present invention can be used at a location where the value of torque is to be varied in correspondence with the relative rotational displacement of the inner member and the outer member. 
     In accordance with the pedal device of the present invention, it is possible to obtain an appropriate reaction force with respect to the pedal pressing force, the pedal device can be installed compactly in comparison with the dummy cable, and the adjustment of reaction force having a hysteresis characteristic can be made very simply. 
     In addition, in accordance with the pedal device of the present invention, the hysteresis characteristic can be simply set to a desired value without using a cable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Hereafter, a detailed description will be given of a friction damper and a pedal device having the friction damper in accordance with the present invention by citing embodiments in which the present invention is applied to an accelerator pedal device for a vehicle, particularly an automobile, illustrated in the drawings, wherein: 
     FIG. 1 is a front cross-sectional view of a preferred embodiment of a pedal device for an automobile in accordance with the present invention; 
     FIG. 2 is a left side view of the embodiment shown in FIG. 1; 
     FIG. 3 is a detailed cross-sectional view of a damper of the embodiment shown in FIG. 1; 
     FIG. 4 is a right side view of the damper shown in FIG. 3; 
     FIG. 5 is a left side view of a movable member of the damper shown in FIG. 3; 
     FIG. 6 is a cross-sectional view taken along line VI—VI of FIG. 5, in which projections, recesses, and stepped portions of a frictionally-resisting-force generating means are omitted; 
     FIG.  7 ( a ) is a right side view of the movable member of the damper shown in FIG. 3; 
     FIG.  7 ( b ) is an explanatory diagram in which the projections, the recesses, and the stepped portions of the frictionally-resisting-force generating means which is formed integrally with the movable member are illustrated in developed form; 
     FIG.  8 ( a ) is a left side view of a rotating member of the damper shown in FIG. 3; 
     FIG.  8 ( b ) is an explanatory diagram in which the projections, the recesses, and the stepped portions of the frictionally-resisting-force generating means which is formed integrally with the rotating member are illustrated in developed form; 
     FIG. 9 is a right side view of the rotating member of the damper shown in FIG. 3; 
     FIG. 10 is a cross-sectional view taken along line X—X of FIG. 9, in which projections, recesses, and stepped portions of the frictionally-resisting-force generating means are omitted; 
     FIG. 11 is a diagram explaining the operation of the damper of the example shown in FIGS. 1 and 3; 
     FIG. 12 is a cross-sectional view of another preferred example of the damper of the present invention; 
     FIG. 13 is a cross-sectional view of still another preferred example of the damper of the present invention; 
     FIG. 14 is a front cross-sectional view of another preferred embodiment of the pedal device in accordance with the present invention; 
     FIG. 15 is a right side view of the embodiment shown in FIG. 14; 
     FIG.  16 (A) is a left end face view of the friction damper shown in FIG. 14; 
     FIG.  16 (B) is a cross-sectional view, taken along line B—B of FIG.  16 (D), of the friction damper in a state in which a coil spring has been compressed after the pressing down of an accelerator pedal of the embodiment shown in FIG. 14; 
     FIG.  16 (C) is a cross-sectional view, taken along line C—C of FIG.  16 (D), of the friction damper in a state in which the coil spring is not compressed with the foot removed from the accelerator pedal of the embodiment shown in FIG. 14; 
     FIG.  16 (D) is a right end face view of the friction damper shown in FIG. 14; 
     FIG. 17 is an explanatory diagram of members composing the friction damper of the embodiment shown in FIG. 14, an upper row of the drawings being side views of the respective members and a lower row of the drawings being cross-sectional views or a front view; 
     FIG. 18 is a perspective view of a first variable plate and a second variable plate of the embodiment shown in FIG. 14; 
     FIG. 19 is a cross-sectional view of another example of attaching a retaining cap to an inner member in such a manner as to be incapable of coming off in the friction damper of the embodiment shown in FIG. 14; 
     FIG.  20 (A) is a left end face view of still another embodiment of the friction damper; 
     FIG.  20 (B) is a cross-sectional view, taken along line B—B of FIG.  20 (C), of the still other embodiment of the friction damper in a state in which the coil spring is not compressed with the foot removed from the accelerator pedal; 
     FIG.  20 (C) is a right end face view of the still other embodiment of the friction damper; 
     FIG. 21 is an explanatory diagram of members composing the friction damper of the embodiment shown in FIG. 20, an upper row of the drawings being side views of the respective members and a lower row of the drawings being cross-sectional views or a front view; 
     FIG. 22 is a cross-sectional view of a further embodiment of the friction damper; and 
     FIG. 23 is a cross-sectional view of a still further embodiment of the friction damper. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 to  10 , a pedal device  1  for an automobile in accordance with an embodiment of the present invention is comprised of a supporting frame  2 ; a pedal arm, in this embodiment, an accelerator pedal arm  3  which is supported by the supporting frame  2  in such a manner as to be rotatable about an axis A in directions R; a spring means  4  for rotatively urging the accelerator pedal arm  3  toward an initial position of its rotation; a damper  5  serving as a resisting means for imparting a resisting force to the rotation in the R directions of the accelerator pedal arm  3  of an accelerator pedal  10 , and a stopper (not shown) for stopping the rotation of the accelerator pedal arm  3  at the initial position of its rotation. 
     In the pedal device  1 , an accelerator wire cable for linking the accelerator pedal arm  3  and a throttle or linking the accelerator pedal arm  3  and a fuel injector is not used, and an actuator is connected at the location on the throttle or the fuel injector where the accelerator wire cable is conventionally connected. The arrangement provided is such that the displacement in the rotation of the accelerator pedal arm  3  is detected by an angle detector  9 , which consists of a light projector  6 , a light receiver  7 , a disk  8  with slits formed in its periphery and rotatable with a rotating shaft  14 , which will be described later, and the like, and the actuator connected at the location on the throttle or the fuel injector is driven via an electronic controller on the basis of a detection signal from the detector  9 , whereby the throttle and the fuel injector are operated on the basis of the displacement in the rotation of the accelerator pedal arm  3 . 
     The supporting frame  2  at its bottom plate portion  13  is fixed to a vehicle body  11  by means of rivets or bolts  12  or the like, and rotatably supports the rotating shaft  14  at its both side walls  15  and  16 . 
     In the accelerator pedal  10  having a pedal  20  and the accelerator pedal arm  3  with the pedal  20  secured to a distal end thereof, the accelerator pedal arm  3  is secured to the rotating shaft  14  by means of welding or the like, and is supported by the supporting frame  2  via the rotating shaft  14  in such a manner as to be rotatable in the R directions. 
     The spring means  4  in this embodiment is formed by a torsion coil spring  19  in which one end portion  17  thereof is engaged with the side wall  15  of the supporting frame  2 , another end portion  18  thereof is passed through a hole  30 , which is formed in the side wall  16 , and is engaged with the accelerator pedal arm  3 , and an intermediate coil portion thereof is wound around the rotating shaft  14  between both side walls  15  and  16  with gaps therebetween, thereby constantly resiliently urging the accelerator pedal arm  3  counterclockwise in FIG. 2 in the R direction. 
     The damper  5  is comprised of a hollow cylindrical member  22  with a bottom fixed to the side wall  15  of the supporting frame  2  by means of bolts  12  or the like; a movable member  23  formed in the shape of an annular plate and disposed in the hollow cylindrical member  22  in such a manner as to be movable with respect to the hollow cylindrical member  22  in the direction of its axis A but immovable in directions about the axis A, i.e., in the directions R; a coil spring  27  serving as a spring means disposed between the movable member  23  and a bottom portion of the hollow cylindrical member  22  and having one end  24  abutting against the bottom portion  25  of the hollow cylindrical member  22  and another end  26  abutting against the movable member  23 ; a rotating member  28  disposed in the hollow cylindrical member  22  in such a manner as to oppose the movable member  23  serving as a movable spring receiver and to be rotatable about the axis A in the R directions with respect to the hollow cylindrical member  22 ; and a frictionally-resisting-force generating means  29  which generates a frictionally resisting force as the aforementioned resisting force in the rotation in the R directions of the rotating member  28 , causes the movable member  23  to move away from the rotating member  28  in the axial direction against the resiliency of the coil spring  27  and approach the bottom portion  25  of the hollow cylindrical member  22  so as to increase the spring force of the coil spring  27 , thereby increasing the frictionally resisting force. 
     The hollow cylindrical member  22  with a bottom in this embodiment has a hollow cylindrical portion  31 , a collar portion  32  formed integrally with one end face of the hollow cylindrical portion  31 ; and a cover portion  36  serving as a fixed spring receiver which is threadedly engaged with an internally threaded portion  34  formed on an inner peripheral surface  33  of the hollow cylindrical portion  31  and is secured to the other end portion  35  of the hollow cylindrical portion  31 . 
     In addition to the threaded portion  34 , the hollow cylindrical portion  31  has on its inner peripheral surface  33  at least one, in this embodiment six, grooves  41  (only two are shown) formed in such a manner as to extend in the direction of the axis A. The grooves  41  are arranged at equal angular intervals in the R direction. 
     The collar portion  32  having a substantially elliptical outer shape has a through hole  42  in its center and through holes  43  and  44  at opposite end portions in its long-axis direction. The hollow cylidrical member  22  is fixedly supported at the collar portion  32  by the side wall  15  by means of bolts  21  or the like which are passed through the through holes  43  and  44 . 
     The collar portion  36  serving as the bottom portion  25  of the hollow cylindrical member  22  has an annular groove  46  at its end face  45 , a hexagonal recess  48  in the center of its other end face  47 , and an externally threaded portion  50  on its peripheral surface  49 . One end  24  of the coil spring  27  is seated in the groove  46  of the cover portion  36 , and the externally threaded portion  50  of the cover portion  36  is threadedly engaged with the internally threaded portion  34  by means of a rotating jig inserted in the recess  48 , so that the cover portion  36  is tightened and secured to the other end portion  35  of the hollow cylindrical portion  31 . 
     As shown in detail in FIGS. 5,  6 , and  7 , the movable member  23  includes a main body  56  formed in the shape of an annular plate and having a through hole  55  in its center; at least one, in this embodiment six, projections  58  formed integrally with an outer peripheral surface  57  of the main body  56 ; and an annular groove  60  formed in a face  59  facing one end face  45  of the cover portion  36 . The projections  58  are arranged at equal angular intervals in the R direction, and are disposed in the grooves  41  in such a manner as to be movable in the direction of the axis A. As a result, the movable member  23  is movable in the direction of the axis A but immovable in the directions R. The other end  26  of the coil spring  27  is seated in the groove  60  of the main body  56 . 
     The coil spring  27  is disposed in the hollow cylindrical portion  31  concentrically therewith in such a manner as to be resiliently compressed so as to cause the movable member  23  to move away from the cover portion  36  in the direction of the axis A. 
     As shown in detail particularly in FIGS. 8,  9 , and  10 , the rotating member  28  has a hollow cylindrical portion  65  and an annular plate portion  67  formed integrally at one end side of an outer peripheral surface  66  of the hollow cylindrical portion  65 . One end side of the hollow cylindrical portion  65  is disposed in the through hole  42 , and is supported by an inner peripheral surface  64  of the collar portion  32 , which defines the through hole  42 , in such a manner as to be rotatable in the directions R. The other end side of the hollow cylindrical portion  65  is passed through the through hole  55 , and extends in such a manner as to contact an inner peripheral surface  68  of the main body  56 , which defines the through hole  55 , and so as to be relatively slidable with respect to the inner peripheral surface  68  of the main body  56  in the direction of the axis A and in the R directions. A pair of mutually opposing flat surfaces  70  and  71  are formed in a central circular hole  69  of the hollow cylindrical portion  65 , and one end portion of the rotating shaft  14  is fitted in the central circular hole  69  defined by the flat surfaces  70  and  71 , whereby the rotation in the R directions of the pedal arm  3  is transmitted to the rotating member  28  via the rotating shaft  14 . 
     The frictionally-resisting-force generating means  29  is comprised of at least one, in this embodiment three, projections  84  formed integrally on an outer peripheral side of an annular surface  82  of the annular plate portion  67  of the rotating member  28 , which faces an annular surface  81  of the main body  56  of the movable member  23 , the projections  84  projecting toward the surface  81  of the movable member  23  in the direction of the axis A and each having an inclined surface  83 ; at least one, in this embodiment three, projections  86  formed integrally on an outer peripheral side of the surface  81  of the main body  56  of the movable member  23 , which faces the surface  82  of the annular plate portion  67  of the rotating member  28 , the projections  86  projecting toward the surface  82  of the rotating member  28  in the direction of the axis A and each having an inclined surface  85  in planar contact with the inclined surface  83 ; and a fixed surface  88  formed on the collar portion  32  of the hollow cylindrical member  22  in such a manner as to come into planar contact with an annular surface  87  of the annular plate portion  67  of the rotating member  28 . 
     The three projections  84  are arranged on the surface  82  at equal angular intervals in the R direction and are formed integrally on the annular plate portion  67 , while the projections  86  are similarly arranged on the surface  81  at equal angular intervals in the R direction and are formed integrally on the main body  56 . The inclined surfaces  83  and  85  are formed complementarily in such a manner as to come into planar contact with each other, preferably in such a manner as to be inclined about 45* with respect to the axis A. 
     On the surface  81 , recesses  91 , into which distal ends in the direction of the axis A of the respective projections  84  are fitted, as well as stepped portions  92  defining the recesses  91 , are formed continuously from the respective projections  86 . Meanwhile, on the surface  82  as well, recesses  93 , into which distal ends in the direction of the axis A of the respective projections  86  are fitted, as well as stepped portions  94  defining the recesses  93 , are formed continuously from the respective projections  84 . The position of initial planar contact between the inclined surface  83  and the inclined surface  85  is defined by the stepped portion  92  and the stepped portion  94 . The fixed surface  88 , in this embodiment, is formed by an annular surface of an annular portion  95  which projects radially inwardly of the collar portion  32 . 
     In the above-described pedal device  1 , if the accelerator pedal  10  is pressed down, which in turn causes the accelerator pedal arm  3  to be rotated clockwise in the R direction in FIG. 2 against the resiliency of the coil spring  16 , fuel injection for the engine is increased by the unillustrated electronic controller which received a detection signal from the detector  9  for detecting the rotational angle of the accelerator pedal arm  3 , thereby accelerating the automobile. On the other hand, if the pressing of the accelerator pedal  10  is canceled, which in turn causes the accelerator pedal arm  3  to be rotated counterclockwise in the R direction in FIG. 2 by the resiliency of the coil spring  16 , fuel injection for the engine is decreased by the unillustrated electronic controller, thereby decelerating the automobile. 
     With the pedal device  1 , if the rotating member  28  is rotated in the R direction through the rotating shaft  14  by the rotation of the accelerator pedal arm  3  due to the pressing of the pedal, the projections  84  are also rotated in the R direction, and the movable member  23 , which is integrally provided with the projections  86  with their inclined surfaces  85  brought into planar contact with the inclined surfaces  83 , is moved toward the bottom portion  25  against the resiliency of the coil spring  27  in the direction of the axis A owing to the rotation in the R direction of the projections  84 , as shown in FIG.  11 . On the other hand, if the pressing of the pedal is canceled, the accelerator pedal arm  3  is returned to its original position by the resiliency of the coil spring  16 , and the movable member  23  is similarly returned to its original position, as shown in FIG.  1 . 
     With the pedal device  1 , when the pedal is pressed down, an appropriate gradually increasing resisting force (reaction force) is imparted to the rotation of the accelerator pedal arm  3  based on the pressing of the pedal owing to the frictional resistance between the inclined surfaces  83  and the inclined surfaces  85  and the frictional resistance between the surface  87  and the fixed surface  88 , which are pressed against each other by the gradually increasing resiliency of the coil spring  27 . Thus, it is possible to avoid the excessive pressing of the accelerator pedal, which would consume fuel more than is necessary, and to avoid the risk of the occurrence of an accident due to out-of-control running. On the other hand, when the pressing of the pedal is canceled, the frictional resistance between the inclined surfaces  83  and the inclined surfaces  85 , as well as the frictional resistance between the surface  87  and the fixed surface  88 , become very small, and the accelerator pedal arm  3  is rotated and returned to its initial position at an early period with a small resisting force by the resiliency of the coil spring  16 . 
     According to the pedal device  1 , since the resisting force which can be imparted to the rotation of the accelerator pedal arm  3  can be substantially determined by the frictional resistance between the inclined surfaces  83  and the inclined surfaces  85  as well as the frictional resistance between the surface  87  and the fixed surface  88 , the adjustment of reaction force can be effected very simply. Further, by appropriately setting the respective values, the pedal device  1  can be made very compact, and can be installed by making effective use of a small space. 
     According to the pedal device  1 , since the bottom portion  25  of the hollow cylindrical member  22  is formed by the cover portion  36  which is threadedly engaged with the hollow cylindrical portion  31  in such a manner as to be capable of being adjustably positioned with respect to the direction of the axis A, the initial resiliency generated by the coil spring  27 , i.e., the initial resisting force, can be arbitrarily adjusted and set, thereby making it possible to obtain an optimum initial resisting force. 
     According to the pedal device  1 , since the coil spring  27  produces practically no returning force for returning the accelerator pedal arm  3  to the initial position, virtually no reaction force is produced in the accelerator pedal arm  3  during the constant-speed traveling. Therefore, there is a further advantage in that the foot which presses on the pedal does not experience early fatigue. 
     According to the pedal device  1 , since the coil spring  27  is interposed between the movable member  23  and the bottom portion  25  of the hollow cylindrical member  22 , which do not rotate relative to each other, the coil spring  27  is not twisted even when the rotating member  28  rotates, and such trouble as the faulty operation and the like due to the twisting of the coil spring  27  does not occur. 
     In the pedal device  1 , the hollow cylindrical member  22  may be fixed to the accelerator pedal arm  3 , and the rotating member  28  may be secured to the supporting frame  2 . 
     Although, in the above-described pedal device  1 , the bottom portion  25  of the hollow cylindrical member  22  is formed by the cover portion  36  which is separate from the hollow cylindrical portion  31 , but the hollow cylindrical portion  31  and the cover portion  36  may be formed integrally as shown in FIG. 12, or an arrangement may be provided such that, as shown in FIG. 13, a threaded portion  104  formed on an inner peripheral surface  103  of the cover portion  36  is threadedly engaged with a threaded portion  102  formed on an outer peripheral surface  101  of the hollow cylindrical portion  31 , and the cover portion  36  is secured to the hollow cylindrical portion.  31  in such a manner as to be capable of being adjustably positioned with respect to the direction of the axis A. 
     Although, in the above-described pedal device  1 , the spring means interposed between the movable member  23  and the bottom portion  25  of the hollow cylindrical member  22  is formed by the single coil spring  27 , the spring means may formed by at least two coil springs  111  and  112  which are arranged concentrically, as shown in FIG. 13, wherein, of these at least two coils springs  111  and  112 , the modulus of elasticity of one coil spring  111  is made relatively large, while the modulus of elasticity of the other coil spring  112  is made relatively small, thereby varying their moduli of elasticity. A multiplicity of coil springs  112  having small but variously different moduli of elasticity are prepared in advance, and an appropriate one may be selected from among them, as required, so as to be used for the adjustment of the reaction force. In this case, the through hole  55  of the main body  56  of the movable member  23  may be omitted, and the hollow cylindrical portion  65  of the rotating member  28  may be formed to be short in the direction of the axis A so as not to penetrate the main body  56 . 
     Next, a description will be given of another embodiment of the accelerator pedal device in accordance with the present invention. In FIGS. 14 and 15, an accelerator pedal device  121  in this embodiment is comprised of, among others, the supporting frame  2  secured to the vehicle body side; the accelerator pedal  10  provided swingably on the supporting frame  2 ; the torsion coil spring  19  for upwardly urging the accelerator pedal  10 ; and a friction damper  122  disposed between the both side walls  15  and  16 . 
     As shown in detail in FIGS. 16 and 17, the friction damper  122  includes an inner member  126  extending like a shaft; a tubular outer member  127  disposed on the outer side of the inner member  126  concentrically therewith; a friction means  129  disposed in an annular space  128  on the radially outward side of the inner member  126  and on the radially inward side of the outer member  127 ; a coil spring  130  serving as a resilient means for urging the friction means  129  in the axial direction; a frictionally engaging means  131  for producing a torque by a frictional force; an urging-force varying means  132  for making the urging force of the coil spring  130  variable; at least one, in this embodiment three, washers  133  for setting an initial torque; and a retaining cap  134  serving as a restricting means. 
     A shaft inserting hole  135  extending in the axial direction is formed penetratingly in a central portion of the inner member  126 , and the cross section of the hole  135  is identical to that of the rotating shaft  14 , and has a shape in which a segment of a circle is cut off. As the rotating shaft  14  is inserted in the hole  135 , the inner member  126  and the rotating shaft  14  are rotated as a unit. 
     A flange portion  136  protruding radially outward is formed at one axial end of the inner member  126 , while four projections  137  projecting radially outward are formed at the other axial end thereof at equal intervals in the circumferential direction. Four recesses  138  extending in the axial direction and arranged at equal intervals in the circumferential direction are formed on an outer peripheral portion of the inner member  126  in such a manner as to be open at the aforementioned other end. 
     The outer member  127  has a hollow cylindrical portion  140  and a flange portion  141  formed at an axial end of the hollow cylindrical portion  140  in such a manner as to protrude radially inward. 
     Four recesses  142  extending in the axial direction and arranged at equal intervals in the circumferential direction are formed on an inner peripheral portion of the hollow cylindrical portion  140  in such a manner as to be open at one end of the hollow cylindrical portion  140 . Two leg portions  143  projecting in the axial direction are formed on an outer end face of the flange portion  141 . As shown in FIG. 14, the leg portions  143  are inserted in holes formed in the side wall  15 , whereby the outer member  127  is attached to the side wall  15  in such a manner as to be unrotatable. 
     A through hole is formed in the center of the flange portion  141 . In a state in which the inner member  126  is inserted into this hole and the flange portions  136  and  141  abut against each other, the inner member  126  extends concentrically on the inner side of the hollow cylindrical portion  140  of the outer member  127 , and the annular space  128  is formed on the inner side of the hollow cylindrical portion  140  and on the outer side of the inner member  126 . 
     As the outer member  127  is attached to the side wall  15  in such a manner as to be unrotatable, the flange portion  136  of the inner member  126  is located between the flange portion  141  of the outer member  127  and the side wall  15 , as shown in FIG.  14 . As a result, the inner member  126  is disposed in such a manner as to be axially immovable, i.e., in such a manner as to be axially immovable relative to the outer member  127 . 
     The friction means  129  disposed in the annular space  128  in this embodiment has first to fifth, i.e., five kinds of, friction plates  151 ,  152 ,  153 ,  154 , and  155 . 
     These friction plates  151  to  155  are formed in the shape of annular plates, the inner member  126  is inserted in their central holes, the friction plates  151  to  155  are arranged in the annular space  128  in that order, and the friction plates  152  and  154  are formed by friction plates of the same configuration. 
     Four projections  156  are formed on inner peripheral portions at the central holes of the friction plates  151 ,  153 , and  155  at equal intervals in the circumferential direction, and four recesses  157  are respectively formed between adjacent ones of the projections  156 . In the state in which the inner member  126  is inserted in the central holes of the friction plates  151 ,  153 , and  155 , the projections  156  are engaged in the recesses  138  of the inner member  126 , with the result that the friction plates  151 ,  153 , and  155  are adapted to rotate integrally with the inner member  126 . The recesses  157  are formed to allow the projections  137  of the inner member  126  to pass therethrough when the friction plates  151 ,  153 , and  155  are fitted to the outer periphery of the inner member  126 . 
     Four projections  158  are formed on outer peripheries of the friction plates  152  and  154  at equal intervals in the circumferential direction. In the state in which the inner member  126  is inserted in the outer member  127 , the projections  158  are engaged in the recesses  142  of the outer member  127 , whereby the friction plates  152  and  154  are joined to the outer member  127  so as to rotate integrally therewith. In this embodiment, however, since the outer member  127  is attached to the side wall  15  in such a manner as to be unrotatable, the friction plates  152  and  154  do not rotate, and remain stationary integrally with the outer member  127 . 
     The friction plates  151  to  155  of the friction means  129  are set in the state of being pressed against the flange portion  141  by the coil spring  130 , as will be described later. As the inner member  126  rotates, the friction plates  151 ,  153 , and  155  rotate relative to the flange portion  141  and the friction plates  152  and  154 , the friction means  129  generates a frictional force by the rotation of the inner member  126 , thereby causing the frictionally resisting torque to be generated in the friction damper  122 . In this embodiment, the frictionally engaging means  131  is formed by the flange portions  136  and  141  and the friction means  129 . 
     The friction plates  151  to  155  are formed of, for example, a thermoplastic resin composition. The thermoplastic resin composition is composed of a base resin, as well as a first additive and a second additive which are added to the base resin. The base resin is a polyacetal resin or a polyphenylene sulfide resin. As the first additive, at least one kind is selected from an olefin-based polymer, a styrene-based polymer, and a fluorine-based polymer. As the second additive, at least one kind is selected from lubricating oil, wax, a fatty acid, graphite, molybdenum disulfide, and phosphate. 
     As the polyacetal resin, in addition to a polyacetal homopolyer, it is possible to use a polyacetal copolymer in which a major portion of its principal chain consists of an oxymethylene chain. Further, it is possible to use a resin which is modified by crosslinking or graft-copolymerizing a polyacetal in a known method. 
     Specifically, it is possible to cite a homopolymer “DELRIN (tradename)” made by E. I. Du Pont de nemours &amp; Co., and a copolymer “Duracon (tradename)” made by POLYPLASTICS CO., LTD. 
     As the polyphenylene sulfide resin, it is possible to use either a crosslinked type or a straight chain type. Specifically, it is possible to cite “RYTON (tradename)” made by Phillips Petroleum International Ltd., “TOHPREN PPS (tradename)” made by TOHPREN CO., LTD., and “FORTRON (tradename)” made by Kureha Chemical Industry Co., Ltd. 
     The first additive is used to improve the sliding characteristic of the base resin. As the first additive, at least one kind selected from an olefin-based polymer, a styrene-based polymer, and a fluorine-based polymer is added. As the olefin-based polymers, it is possible to cite a homopolymer such as polyethylene and polypropylene and a copolymer containing them as principal constituents. As the copolymers, it is possible to cite an ethylene-a-olefin copolymer, an ethylene-propylene-diene copolymer, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-glycidyl methacrylate copolymer, an ethylene-ethyl acrylate-maleic anhydride copolymer, and the like. Further, a copolymer in which polystyrene, polymethyl methacrylate, or an acrylonitrile-styrene copolymer is grafted to the homopolymer or the copolymer is also included. The olefin-based polymer is used singly or in the form of a mixture or a reaction product of two or more kinds. The styrene-based polymer is a triblock copolymer or a radial block copolymer having a polystyrene-rubbery intermediate block-polystyrene structure. As the rubbery intermediate blocks, it is possible to cite polybutadiene, polyisoprene, and hydrogenated compounds thereof. 
     As the block copolymers, it is possible to specifically cite a polystyrene-polybutadiene-polystyrene block copolymer, a polystyrene-polyisoprene-polystyrene block copolymer, a polystyrene-poly(ethylene/butylene)-polystyrene block copolymer, and a polystyrene-poly(ethylene/propylene)-polystyrene block copolymer. 
     Further, in the present invention, it is possible to use the aforementioned block copolymers into which functional groups are introduced. As the functional groups which are introduced, it is possible to cite maleic acid, endocis-dicyclo[2,2,1]hepto-5-en-2,3-dicarboxylic acid (nadic acid), maleic anhydride, citraconic anhydride, itaconic anhydride, tetrahydrophthalic anhydride, nadic anhydride, nadic methyl anhydride, monomethyl maleate, dimethyl maleate, dimethyl itaconate, dimethyl citraconate, maleimide, a graft monomer of malenyl chloride, and the like. In particular, maleic acid, nadic acid, or an acid anhydride thereof is preferable. 
     As the fluorine-based polymers, it is possible to cite polytetrafluoroethylene, a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-ethylene copolymer, polychlorotrifluoroethylene, a chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polyvinylfluoride, and the like. 
     The amount of compounding of the first additive is 0.3 to 10 wt. % in the case of the olefin-based polymer, preferably 0.5 to 7 wt. %; 0.1 to 10 wt. % in the case of the styrene-based polymer, preferably 0.3 to 6 wt. %; and 2 to 50 wt. % in the case of the fluorine-based polymer, preferably 2 to 40 wt. %. 
     The second additive is used by being added to the first additive so as to further improve the sliding characteristic. As the second additives, at least one kind selected from lubricating oil, wax, a fatty acid, graphite, molybdenum disulfide, and phosphate is added. As the lubricating oils, it is possible to cite mineral oils including engine oil, spindle oil, turbine oil, machine oil, cylinder oil, gear oil, and the like; a vegetable oil such as castor oil; an animal oil such as whale oil; and a synthetic oil such as silicone oil. As waxes, it is possible to cite, in addition to paraffin wax, a fatty acid ester, a fatty acid amide, and a fatty acid salt derived from a higher fatty acid, and the like. 
     As the phosphates, it is possible to cite a tribasic phosphate, a dibasic phosphate, a pyrophosphate, a phosphite, and a metaphosphate of an alkaline metal or an alkaline earth metal. Specifically, it is possible to cite tribasic lithium phosphate (Li3PO4), dibasic lithium phosphate (Li2HPO4), lithium pyrophosphate (Li4P2O7), tribasic calcium phosphate (Ca3(PO4)2), dibasic calcium phosphate (CaHPO4 or CaHPO4 Σ 2H2O), and calcium pyrophosphate (Ca2P2O7). 
     The amount of compounding of the second additive is 0.1 to 10 wt. %, preferably 0.3 to 6 wt. %. 
     In addition, a third additive may be additionally used for the purpose of reinforcing the thermoplastic resin composition. As the third additive, at least one kind selected from a glass powder, a carbon powder (excluding graphite), a glass fiber, a carbon fiber, an aramid fiber, potassium titanate whiskers, a metal fiber, a metal powder, and the like is compounded in a proportion of 10 wt. % or less. 
     After the friction plates  151  to  155  are disposed in the annular space  128  in that order, the coil spring  130  is disposed in such a manner as to oppose the friction plate  155 , the washers  133  and the urging-force varying means  132  are then disposed, and the retaining cap  134  is finally disposed. 
     As for the coil spring  130 , its material, wire diameter, coil diameter, and the number of turns are determined so that a desired hysteresis can be obtained. 
     The urging-force varying means  132  is formed of a pair of mutually opposing variable plates  161  and  162 , and are both formed in the shape of annular plates. 
     Four projections  163  projecting radially outward are formed on an outer periphery of the variable plate  161 , serving as an outer variable member, in such a manner as to be arranged at equal intervals in the circumferential direction, and the projections  163  are engaged in the recesses  142  of the outer member  127 , so that the variable plate  161  is joined to the outer member  127  so as to rotate integrally therewith. In this embodiment, however, since the outer member  127  is attached to the side wall  15  in such a manner as to be unrotatable, the variable plate  161  also does not rotate, and remains stationary integrally with the outer member  127 . 
     Four projections  164  projecting radially inward are formed on an inner periphery of the variable plate  162 , serving as an inner variable member, in such a manner as to be arranged at equal intervals in the circumferential direction, and the projections  164  are engaged in the recesses  138  of the inner member  126 , so that the variable plate  162  rotates integrally with the inner member  126 . 
     As shown in FIG. 18, cam portions  165  and  166  capable of engaging each other are respectively formed on outer peripheries of mutually opposing surfaces of the variable plates  161  and  162 . Each of the cam portions  165  and  166  has a proximal portion  167 , a projecting portion  168  projecting from the proximal portion  167 , and an inclined portion  169  connecting the proximal portion  167  and the projecting portion  168 . 
     Four recesses  171  which are recessed radially outward are formed on an inner periphery of the retaining cap  134 , which is formed in the shape of an annular plate, in such a manner as to be arranged at equal intervals in the circumferential direction, and the projections  137  of the inner member  126  are inserted in the recesses  171 . 
     Two projections  172  projecting in the axial direction are formed on an end face of the retaining cap  134  at diametrically opposing positions thereof, and four notches  173  are formed adjacent to the recesses  171 , respectively. The projections  172  are designed to facilitate the operation when the retaining cap  134  is attached or detached. 
     In assembly, after the friction plates  151  to  155 , the coil spring  130 , the washers  133 , and the variable plates  161  and  162  are disposed in the annular space  128  in that order, the retaining cap  134  is disposed. Subsequently, the retaining cap  134  is rotated by using the projections  172 , and the projections  137  of the inner member  126  are engaged in the notches  173  in a snap-fitting manner, thereby attaching the retaining cap  134  to the inner member  126  in such a manner as to be incapable of coming off. Thus, the retaining cap  134  is secured to the inner member  126  so as to rotate integrally with the inner member  126 . 
     It should be noted that, as for the structure for attaching the retaining cap  134  to the inner member  126  in such a manner as to be incapable of coming off, an arrangement may be provided as shown in FIG. 19, wherein an internal thread is formed on the inner periphery of the retaining cap  134 , while an external thread is formed at a distal end of the inner member  126 , so as to make use of threaded engagement  174  between the internal thread and the external thread. 
     With the accelerator pedal device  121  in this embodiment, in a state in which the foot is removed from the pedal  20 , the pedal  20  is at an upper-limit position, and the friction damper  122  is in the state shown in FIG.  16 (C). 
     Namely, the projecting portions  168  of the cam portions  165  of the variable plate  161  abut against the proximal portions  167  of the cam portions  166  of the variable plate  162 , while the projecting portions  168  of the cam portions  166  of the variable plate  162  abut against the proximal portions  167  of the cam portions  165  of the variable plate  161 . In this state, the axial dimension between the variable plate  161  and the flange portion  141  is maximum, and the axial dimension of the space in which the coil spring  130  is accommodated in the annular space  128  is maximum. 
     When the accelerator pedal  10  is pressed down, in this state the rotating shaft  14  starts to rotate, and the inner member  126  starts to rotate. The initial rotation-resisting torque occurring in the frictional means  129  at this time can be adjusted simply by changing the number of the washers  133  or by changing the washers  133  to those having different thicknesses. 
     Next, if the accelerator pedal  10  is pressed down, a resisting torque of a value in which the resiliently resisting torque generated by the resiliency of the torsion coil spring  19  and the frictionally resisting torque generated by the friction damper  122  are added together is applied to the foot as a load. 
     In this case, the resisting torque generated by the friction damper  122  is constant while the projecting portions  168  of the cam portions  165  of the variable plate  161  abut against the proximal portions  167  of the cam portions  166  of the variable plate  162 , and the projecting portions  168  of the cam portions  166  of the variable plate  162  abut against the proximal portions  167  of the cam portions  165  of the variable plate  161 . 
     When the accelerator pedal  10  is further pressed down, and when the projecting portions  168  of the cam. portions  165  of the variable plate  161  abut against the inclined portions  169  of the cam portions  166  of the variable plate  162 , and the projecting portions  168  of the cam portions  166  of the variable plate  162  abut against the inclined portions  169  of the cam portions  165  of the variable plate  161 , the axial dimension between the variable plate  161  and the flange portion  141  becomes smaller by following the amount of the accelerator pedal  10  pressed. This, in turn, causes the coil spring  130  to be compressed, and increases the force with which the friction means  129  is pressed, so that the rotation-resisting torque generated by the friction damper  122  becomes gradually larger. 
     Then, a resisting torque of a value in which the reaction torque generated by the resiliency of the torsion coil spring  19  and the gradually increasing frictional torque generated by the friction damper  122  are added together is applied to the foot as the load. 
     When the accelerator pedal  10  is further pressed down and reaches a lower-limit position, as shown in FIG.  16 (B), the projecting portions  168  of the cam portions  165  of the variable plate  161  abut against the projecting portions  168  of the cam portions  166  of the variable plate  162 , and the projecting portions  168  of the cam portions  166  of the variable plate  162  abut against the projecting portions  168  of the cam portions  165  of the variable plate  161 . Hence, the axial dimension between the variable plate  161  and the flange portion  141  becomes minimum, and the axial dimension of the space for accommodating the coil spring  130  in the annular space  128  becomes minimum. As a result, the amount of the coil spring  130  compressed becomes maximum, and the force for pressing the friction means  129  becomes maximum, so that the frictional torque generated by the friction damper  122  becomes maximum. 
     Thus, in this embodiment, if the accelerator pedal  10  is pressed down, a resisting torque of a value in which the rotational torque generated by the resiliency of the torsion coil spring  19  and the maximum torque generated by the friction damper  122  are added together is applied to the foot as the load at the lower-limit position of the pedal  20 . 
     In this embodiment, the initial frictionally-resisting torque of the friction damper  122  can be adjusted simply by changing the number of the washers  133  or by changing the washers  133  to those having different thicknesses. 
     The torque occurring in the friction damper  122  can be simply adjusted to a desired value by appropriately selecting the material, wire diameter, coil diameter, and the number of turns of the coil spring  130  and the material of the friction plates  151  to  155  of the friction means  129 . 
     Further, the timing at which the torque occurring in the friction damper  122  is increased or decreased, as well as the rate at which that torque is increased or decreased, can also be simply adjusted to desired values by changing the configurations of the cam portions  165  and  166 . 
     For these reasons, the load applied to the foot, i.e., the torque of a value in which the reaction torque generated by the resiliency of the torsion coil spring  19  and the frictionally resisting torque generated by the friction damper  122  are added together, and hence its hysteresis characteristic can be simply set to desired values. 
     Accordingly, in accordance with this embodiment, even if a conventional accelerator wire cable for linking the accelerator pedal  10  and the throttle or the accelerator pedal  10  and the fuel injector is omitted, the same load as in the case where that cable is used can be simply imparted to the foot, and the accelerator pedal device  121  can be arranged by using the angle detector, the electronic controller, and the actuator. 
     Then, as the accelerator wire cable is omitted, the arrangement around the accelerator pedal  10 , particularly around the supporting frame  2 , can be made compact. 
     Referring now to FIGS. 20 and 21, a description will be given of still another embodiment of the friction damper which can be applied to the accelerator pedal device for an automobile in the same way as the foregoing embodiments. 
     A friction damper  201  shown in FIGS. 20 and 21 is comprised of, among others, an inner member  202  extending like a shaft; a tubular outer member  203  disposed on the outer side of the inner member  202  concentrically therewith; a frictionally engaging means  205  disposed in an annular space  204  on the radially outward side of the inner member  202  and on the radially inward side of the outer member  203 ; a coil spring  206  serving as a resilient means for pressing the frictionally engaging means  205 ; an urging-force varying means  207  for making the pressing force of the coil spring  206  variable; three washers  208  for setting an initial torque; and a retaining cap  209 . 
     A shaft inserting hole  211  extending in the axial direction is formed penetratingly in a central portion of the inner member  202 . In the same way as in the above-described embodiment, the cross section of the hole  211  is identical to that of the rotating shaft  14 , and as the rotating shaft  14  is inserted in the hole  211 , the inner member  202  and the rotating shaft  14  are rotated as a unit. 
     A flange portion  212  protruding radially outward is formed integrally at one axial end of the inner member  202 , while four recesses  223  extending in the axial direction and arranged at equal intervals in the circumferential direction are formed at the other axial end of the inner member  202  in such a manner as to be open at that end. 
     The outer member  203  has a hollow cylindrical portion  221  and a flange portion  222  formed at an axial end of the hollow cylindrical portion  221  in such a manner as to protrude radially inward. In this embodiment, the frictionally engaging means  205  is formed by the flange portion  222  and the flange portion  212  of the inner member  202 . 
     An internal thread  231  is formed on an inner peripheral surface of the hollow cylindrical portion  221 . Two leg portions  224  which are inserted and fixed in holes formed in the side wall  15  are formed at the outer end face of the flange portion  222  in the same way as in the above-described embodiment. 
     A through hole is formed in the center of the flange portion  222 . In a state in which the inner member  202  is inserted into this hole and the flange portions  212  and  222  abut against each other, the inner member  202  extends concentrically on the inner side of the hollow cylindrical portion  221  of the outer member  203 , and the annular space  204  is formed on the inner side of the hollow cylindrical portion  221  and on the outer side of the inner member  202 . 
     A retaining ring  225  is attached to a tip of the inner member  202  projecting from hole in the center of the flange portion  222 . As the flange portion  222  of the outer member  203  is clamped by the retaining ring  225  and the flange portion  212 , the inner member  202  is disposed in such a manner as to be slightly movable in the axial direction, i.e., in such a manner as to be slightly axially movable relative to the outer member  203 . 
     The friction damper  201  does not employ friction plates formed separately from the inner member  202  and the outer member  203  used in the above-described embodiment, and the flange portions  212  and  222  correspond to the friction plates in the above-described embodiment. These flange portions  212  and  222  are set in a state of being pressed against each other by the coil spring  206 , as is described later, and as the inner member  202  rotates, the flange portion  212  rotates relative to the flange portion  222 . As a result, a frictional force is produced between the flange portions  212  and  222 , thereby causing a frictional torque to be generated in the friction damper  201 . As the material of the flange portions  212  and  222 , it is possible to use the same material as that for the friction plates in the foregoing embodiment. 
     As for the coil spring  206 , its material, wire diameter, coil diameter, and the number of turns are determined so that a desired hysteresis characteristic can be obtained concerning the frictional torque. 
     An external thread  213  is formed on the outer periphery of the retaining cap  209  which is formed in a tubular shape, while four projections  232  projecting radially inward are formed on an inner peripheral portion of the retaining cap  209  at equal intervals in the circumferential direction. The projections  232  are engaged in the recesses  223  of the inner member  202 , and the retaining cap  209  is joined to the inner member  202  so as to rotate integrally therewith. 
     Two projections  233  projecting in the axial direction are formed at an end face of the retaining cap  209  at equal intervals in the circumferential direction. The projections  233  are designed to facilitate the operation when the retaining cap  209  is attached or detached. 
     In assembly, the coil spring  206 , the washers  208 , and the retaining cap  209  are fitted around the inner member  202 . Then, this subassembly is inserted into the outer member  203  such that the external thread  213  is threadedly engaged in the internal thread  231 , and after the insertion, the retaining ring  225  is fitted to the tip of the inner member  202  projecting from the hole in the center of the flange portion  222 . 
     With the friction damper  201 , in the state in which the foot is removed from the accelerator pedal  10 , the pedal  20  is at the upper-limit position, and the friction damper  201  is in the state shown in FIG.  20 (B). In this state, the axial dimension between the flange portion  222  of the outer member  203  and the retaining cap  209  becomes maximum, and the flange portion  222  of the outer member  203  and the flange portion  212  of the inner member  202  are pressed and abutted against each other by the coil spring  206 . 
     When the accelerator pedal  10  is pressed down, the rotating shaft  14  starts to rotate, and the inner member  202  starts to rotate. The initial frictional torque occurring between the flanges  212  and  222  at this time can be adjusted simply by changing the number of the washers  208  or by changing the washers  208  to those having different thicknesses. 
     Next, when the accelerator pedal  10  is pressed down, a torque of a value in which the resilient reaction torque generated by the resiliency of the torsion coil spring  19  and the frictionally resisting torque generated in the friction damper  201  are added together is applied to the foot as the load. 
     In this case, since the retaining cap  209  is threadedly engaged with the outer member  203  by means of the internal thread  231  and the external thread  213 , and is joined to the inner member  202  through the engagement between the projections  232  and the recesses  223  in such a manner as to be unrotatable, the retaining cap  209  moves in the direction of approaching the flange portion  222  of the outer member  203 , by following the rotation of the rotating shaft  14  and the inner member  202  based on the pressing down of the accelerator pedal  10 . As a result, the axial dimension between the flange portion  222  of the outer member  203  and the retaining cap  209  becomes smaller, so that the coil spring  206  is compressed, and the force with which the flange portions  212  and  222  are pressed against each other increases. Consequently, the frictional torque generated by the friction damper  201  becomes gradually larger. In the friction damper  201 , the urging-force varying means  207  is formed by the retaining cap  209 , the internal thread  231 , the external thread  213 , the projections  232 , and the recesses  223 . 
     Thus, also with the accelerator pedal device having the friction damper  201 , when the accelerator pedal  10  is pressed down, the torque of a value in which the reaction torque generated by the resiliency of the torsion coil spring  19  and the gradually increasing frictional torque generated in the friction damper  201  are added together is applied to the foot as the load. 
     The frictional torque occurring in the friction damper  201  can be simply adjusted to a desired value by appropriately selecting the material, wire diameter, coil diameter, and the number of turns of the coil spring  206  and the material of the flange portions  212  and  222 . Further, the rate at which the torque occurring in the friction damper  201  increases in correspondence with the rotational displacement of the inner member  202  can also be simply adjusted to a desired rate by changing the pitches of the internal thread  231  and the external thread  213 . 
     From these reasons, also with the accelerator pedal device having the friction damper  201 , the load applied to the foot, i.e., the torque of a value in which the torque generated by the resiliency of the torsion coil spring  19  and the torque generated by the friction damper  201  are added together, and hence the hysteresis characteristic concerning the torque can be simply set to desired values. 
     Accordingly, in accordance with this embodiment as well, even if the conventional accelerator wire cable for linking the accelerator pedal and the throttle or the accelerator pedal and the fuel injector is omitted, the same load as in the case where that cable is used can be simply imparted to the foot, and the accelerator pedal device can be arranged by using the angle detector, the electronic controller, and the actuator. Then, as the accelerator wire cable is omitted, the arrangement around the accelerator pedal  10 , particularly around the supporting frame  2 , can be made compact. 
     Referring next to FIG. 22, a description will be given of a further embodiment of the friction damper which can be applied to the accelerator pedal device. 
     In a friction damper  251  in the embodiment shown in FIG. 22, the urging-force varying means  132  is omitted from the friction damper  122 , and the other arrangement is similar to that of the friction damper  122 , the operation being effected in the same way as in the friction damper  122  by excluding the operation of the urging-force varying means  132 . The friction damper  251  which does not have the urging-force varying means  132  differs from the friction damper  122  in which the frictionally resisting torque occurring due to the amount of the accelerator pedal  10  pressed changes, in that a fixed frictionally resisting torque is produced irrespective of the amount of the accelerator pedal  10  pressed. 
     FIG. 23 shows a still further embodiment of the friction damper in which the produced torque is fixed irrespective of the amount of the accelerator pedal  10  pressed, in the same way as the friction damper  251 . 
     A friction damper  252  shown in FIG. 23 is arranged such that, in the friction damper  201  shown in FIG. 20, an external thread  253  is formed on an outer peripheral portion of the retaining cap  209 , an internal thread  254  is formed on an inner peripheral portion of the hollow cylindrical portion  221  of the outer member  203  in the friction damper  201  shown in FIG. 20, and the retaining cap  209  is secured to the hollow cylindrical portion  221  of the outer member  203  through the threaded engagement between the external thread  253  and the internal thread  254 . 
     It should be noted that, in the friction damper  252 , it is unnecessary to form the recesses  223  on the inner peripheral portion of the hollow cylindrical portion  221  of the outer member  203 , the internal thread  231  on the outer peripheral portion of the inner member  202 , and the external thread  213  on the inner peripheral portion of the retaining cap  209 , respectively. 
     With the friction damper  252  shown in FIG. 23, when the accelerator pedal  10  is pressed down, the retaining cap  209  does not move in the axial direction, so that a fixed frictionally resisting torque is generated irrespective of the amount of the accelerator pedal  10  pressed. 
     Although, in the foregoing embodiments, a description has been given of cases where the friction damper is applied to the accelerator pedal device, the friction damper in accordance with the present invention is not limited to the accelerator pedal device, and is also applicable to a device for which the value of torque is to be changed in correspondence with a relative rotational displacement.