Abstract:
A clutch having a friction spring for exerting a frictional torque for restraining resonance of the damper spring utilizing a small pressing force. The friction spring is disposed at a portion of the clutch member which is radially outward from the damper spring. This arrangement reduces the amount of spring force required of the friction spring. Also, the contact areas between the clutch member and the driven gear are located radially outwardly of the damper spring, which increases the annular contact area between the driven gear and the clutch member, and reduces wear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention relates to a clutch having a damper spring in a power transmission apparatus of a vehicle. Specifically, the present invention relates to a structure for restraining resonance of the damper spring. 
     2. Background Art 
     As conventional technology, a clutch for power transmission in a motorcycle having a damper spring with a structure for restraining resonance of the damper spring is known. Such a device is disclosed in, for example, FIG. 9 of Japanese Unexamined Utility Model Publication No. 4-30337 . 
     In the above document, the clutch having a damper spring is a multiple disk friction clutch used in a power transmission apparatus of a motorcycle having an internal combustion engine. The clutch is provided with a primary driven gear to which torque of a crankshaft of the internal combustion engine is transmitted. A clutch outer is capable of being connected to and disconnected from a main shaft of a transmission via a friction plate, and a clutch center and a plurality of damper springs are arranged between the primary driven gear and the clutch outer at intervals in a peripheral direction. 
     The clutch is provided with a friction spring comprising a coned disc spring for restraining resonance of the damper springs produced based on a variation in the torque of the crankshaft. The friction spring is disposed between a clutch side plate and the primary driven gear, and is positioned on an inner side of the damper springs arranged in the peripheral direction. The friction spring presses the primary driven gear in an axial direction to thereby bring the primary driven gear into contact with the clutch outer Further, slidable contact faces among the primary driven gear, the clutch outer and a cam ring are disposed on an inner side of the damper springs. 
     According to the above conventional multiple disk friction clutch, torque of the crankshaft transmitted to the primary driven gear is transmitted to the clutch outer via the damper springs, and is further transmitted from the friction plate to the main shaft via the clutch center in connecting the clutch. The damper spring can be elongated and contracted between the primary driven gear and the clutch outer and, accordingly, a damping function prevents an abrupt torque change produced in connecting the clutch or the like from being transmitted to the clutch outer. 
     The torque variation of the crankshaft results in elongation and contraction of the damper spring, and when a frequency of the torque variation coincides with natural frequency of the damper spring, the damper spring is resonated. However, frictional torque by frictional force produced on the slidable contact faces, based on press force of the friction spring, is operated to hinder the primary driven gear from rotating relative to the clutch outer. The resonance is therefore restrained. 
     In order to restrain the resonance of the damper spring in this way, a frictional torque is required which has a magnitude determined by frictional force produced on the slidable contact faces, and a distance from an axis line of the main shaft. The axis line of the main shaft is a rotational center line of the primary driven gear to an operational point of the frictional force. 
     When the slidable contact faces are disposed on an inner side of the damper spring as in conventional devices, the distance from the axis line of the main shaft to the slidable contact faces is comparatively short and, accordingly, in order to provide the required frictional torque magnitude, the frictional force produced on the slidable contact faces must increase by increasing the press force by the spring force of the friction spring. 
     Disadvantageously, when the press force is increased, the large press force operates on the slidable contact faces of the primary driven gear and the clutch outer and, accordingly, in order to minimize wear caused by the press force at the slidable contact faces of the both members, a wear resistant surface treatment is required on both of the members. This treatment adds to the difficulty and cost of manufacture. 
     SUMMARY OF THE INVENTION 
     The present invention is in part addressed to overcoming the disadvantages of the conventional art. The present invention includes a clutch having a damper spring in which frictional torque for restraining resonance of a damper spring can be provided by small press force by a frictional spring. The clutch member is capable of being connected to and disconnected from a driven gear and a driven shaft. 
     A driven gear and driven shaft are transmitted a torque of a drive shaft. The driven gear is arranged coaxially and rotatably to the drive shaft, and a plurality of damper springs are relatively rotatable between the driven gear and the clutch member by being elongated and contracted. 
     A friction spring is arranged between the driven gear and the clutch member, and transmits the torque of the driven gear to the clutch member The friction spring is arranged at intervals along a periphery, and presses the driven gear in an axial direction to thereby bring the driven gear into contact with the clutch member or a member integrated to the clutch member. 
     The contact restrains resonance of the damper springs by a frictional force produced on slidable contact faces of the members, the friction spring and the slidable contact faces are disposed on an outer side of the damper springs. 
     The friction spring is disposed on the outer side of the damper springs arranged along the peripheral direction, and presses the driven gear to the clutch member or the member integrated to the clutch member in the axial direction. This pressing brings both members into contact with each other. The slidable contact faces formed by the contact are disposed on the outer side of the damper springs and therefore, the slidable contact faces producing the frictional force are disposed on the outer side of the damper springs, and are disposed at positions at which distances from the axis line of the driven shaft are larger than those of the slidable contact faces according to the conventional technology, in which the contact faces are disposed on the inner side of the damper springs. 
     As a result of the above configuration, the frictional force for providing required frictional torque for restraining resonance of the damper spring may be smaller than that in the conventional technology. Therefore, the spring force by the friction spring may be small. 
     Further, the press force of the driven gear exerted on the clutch member or the member integrated to the clutch member at the slidable contact faces becomes small. Accordingly, wear at the slidable contact faces is minimized and durability increased. Further, since wear is minimized, there is no need for a wear resistant surface treatment on the slidable contact faces. This reduces difficulty and cost of manufacture. 
     Because the slidable contact faces are disposed on the outer side of the damper springs, an area of the slidable contact faces can be made larger than an area of conventional slidable contact faces. Therefore, without enlarging a diameter of the driven gear and a diameter of the clutch member or the member integrated to the clutch member, pressure based on the press force of the driven gear exerted on the clutch member can be reduced. This reduces wear at the slidable contact faces. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a sectional view of a multiple disk friction clutch having a damper spring according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a sectional view of a multiple disk friction clutch  1  to which a clutch having a damper spring according to the present invention is applied. The multiple disk friction clutch  1  is integrated to a power transmission apparatus of a motorcycle mounted with a V-type two cylinder overhead camshaft internal combustion engine. Torque of a crankshaft of the internal combustion engine is transmitted to a rear wheel via the multiple disk friction clutch  1 , a normally mesh type speed change gear and a drive chain. 
     The multiple disk friction clutch  1  includes elements common with conventional multiple disk friction clutches. A primary driven gear  3  having a driven gear in mesh with a primary drive gear  2  is fitted by a spline to a crankshaft of an internal combustion engine. The engine drive shaft is coaxially and rotatably supported by a main shaft  9  of the speed change gear having a driven shaft. 
     A clutch outer  5  is a bottomed cylinder having a clutch member connected to the primary driven gear  3  via damper springs  4  coaxially and rotatably to the main shaft  9 . A clutch center  8  is fitted by a spline to the main shaft  9  and is rotated integrally with the main shaft  9 . A plurality of clutch disks  6  are provided with, at their outer peripheries, claws inserted into a plurality of notches  5   c  extending in the axial direction. The notches are formed at intervals on the periphery of clutch outer  5 , at cylindrical portion  5   a.    
     A plurality of clutch plates  7  are fitted by a spline to an outer periphery of the clutch center  8  and are slidable in the axial direction. The clutch plates alternately overlap the clutch disks  6 . The clutch disks  6  and the clutch plates  7  respectively form friction plates. 
     A pressure plate  10  is arranged coaxially in a hollow portion formed in the main shaft  9  and is pivotably attached to a front end portion of a lifter rod  11 . The pressure plates are movably mounted in the axial direction under the influence of hydraulic pressure. The pressure plate  10  normally presses the clutch disks  6  and the clutch plates  7  by spring force of a clutch spring  12 , and the clutch  1  is brought into a connected state by friction among the clutch disks  6  and the clutch plates  7  in this state The clutch plates  7  are moved in the axial direction along with the lifter rod  11  by hydraulic pressure against the spring force of the clutch spring  12 , and the spring force of the clutch spring  12  exerted to the clutch disks  6  and the clutch plates  7  is released to thereby form clearances therebetween and to bring the clutch  1  into a disconnected state. 
     The mode of transmitting torque of the crankshaft according to such a multiple disk friction clutch  1  is as follows. 
     The torque of the crankshaft transmitted from the primary drive gear  2  to the primary driven gear  3  is transmitted to the clutch outer  5  via the damper springs  4 . When the clutch  1  is brought into the connected state, the torque of the clutch outer  5  is transmitted to the clutch center  8  via the clutch disks  6  and the clutch plates  7  having the friction plates and is further transmitted to the main shaft  9 . When the clutch  1  is brought into the disconnected state, there are clearances among the clutch disks  6  and the clutch plates  7  and accordingly, transmission of the torque is cut off at the portions, In this way, the clutch outer  5  can be connected to and disconnected from the main shaft  9 . The damper springs  4  can be elongated and contracted between the primary driven gear  3  and the clutch outer  5  and accordingly, abrupt torque change caused in connecting the clutch  1  in the disconnected state or the like is not transmitted to the clutch outer  5 . 
     Next, a detailed description will be given of the primary driven gear  3  and the clutch outer  5  of the multiple disk friction clutch  1 . 
     A cylindrical clutch outer guide  13  is fitted to the outer periphery of the main shaft  9 . The primary driven gear  3  is provided with a boss portion  3   a  fitted to the outer periphery of an outer race of a needle bearing  14 , which is mounted to the outer periphery of the clutch outer guide  13 . A gear portion  3   b  is formed with teeth in mesh with teeth of the primary drive gear  2 , and a flat plate portion  3   c  is formed between the boss portion  3   a  and the gear portion  3   b . An end face of the boss portion  3   a  on a side of the clutch outer  5  is brought into contact with a thrust washer  15 , which is in turn brought into contact with an end face of the clutch center  8 . An end face of the boss portion  3   a  on a side of the main shaft  9  for mounting the transmission is brought into contact with a drive sprocket  16  for driving an accessory. The accessory is rotated integrally with the primary driven gear  3  via an engaging portion engaging with the boss portion  3   a  to thereby prevent the primary driven gear  3  from moving in the axial direction. 
     In the flat plate portion  3   c , there are respectively formed six pieces of first through holes  3   d  substantially in a rectangular shape, and three pieces of second through holes  3   e  in an elliptical shape on a circumference having a center line by the axis line of the main shaft  9  at intervals in the peripheral direction. These first and second through holes  3   d  and  3   e  are arrayed in the peripheral direction to establish a relationship in which two pieces of the first through holes  3   d  are provided between two pieces of the second through holes  3   e .    
     The respective first through hole  3   d  is inserted with the damper spring  4  comprising a helical spring in a contracted state, such that both end portions of the damper spring  4  press both end portions of the first through hole  3   d  via spring receivers. The respective second through hole  3   e  is penetrated with a sleeve  17  in a cylindrical shape inserted with a rivet  21  The diameter of the second through hole  3   e  is larger than the outer diameter of the sleeve  17 , and a clearance in the peripheral direction is formed therebetween. Therefore, the primary driven gear  3  and the clutch outer  5  can be driven relative to each other within the range of the clearance. 
     The clutch outer  5  is provided with the cylindrical portion  5   a  and a side wall portion  5   b  on the side of the primary driven gear  3 . The outer periphery of the boss portion  3   a  of the primary driven gear  3  is fitted into a through hole formed at the central portion of the side wall portion  5   b , and accordingly, the clutch outer  5  is rotatably centered on the axis line of the main shaft  9 , along with the primary driven gear  3 . 
     Six recess portions  5   d  for containing the damper springs  4  are formed on a primary driven gear  3  side of the side wall portion  5   b  at intervals in a peripheral direction in correspondence with the first through holes  3   d  of the primary driven gear  3 . The side wall portion  5   b  is formed with three rivet holes  5   e  for the rivets  21  penetrating the second through holes  3   e  of the primary driven gear  3  at intervals in the peripheral direction in correspondence with the second through holes  3   e .    
     The primary driven gear  3  side of the clutch outer  5  has an annular clutch outer side plate  18  corresponding to a size of a side face of the flat plate portion  3   c  of the primary driven gear  3 , The clutch outer side plate  18  is formed with six recess portions  18   d  in correspondence with the recess portions  5   d  of the side wall portion  5   b  of the clutch outer  5  for containing the damper springs  4 , and is formed with three through holes  18   e . The through holes are sized to penetrate the sleeves  17  in correspondence with the rivet holes  5   e  of the side wall portions  5   b .    
     The recess portion  18   d  is fabricated by cutting a metal sheet in an H-shape and bending the cut portion in a shape substantially complying with the outer periphery of the damper spring  4 . The recess portion is cut in correspondence with the diameter and the length of the damper spring  4 . Element  18   f  indicates an opening produced by fabricating a side portion of the cut portion  12  to comply with the axial direction of the damper spring  4  into the bent shape. The clutch outer side plate  18  can have the relevant frictional coefficient and wear resistance which may differ from a material of the clutch outer  5 . 
     The clutch outer side plate  18  is mounted to the side wall portion  5   b  such that recess portions  18   d  are fitted to the recess portions  5   d  of the clutch outer  5 . The through holes  18   e  are disposed concentrically with the rivet holes  5   e  and the outer periphery of the boss portion  3   a  is fitted into the center hole. Accordingly, the clutch outer side plate  18  integrally rotates with the clutch outer  5 , and corresponds to a member integrated to the clutch outer  5 . 
     The boss portion  3   a  is formed with an oil hole  3   f  for supplying a lubricant not only to a portion of fitting together the boss portion  3   a  and the side wall portion  5   b , but also respective contact portions of the primary driven gear  3 , the clutch outer  5 , and the clutch outer side plate  18  to communicate with an oil hole provided to the outer race of the needle bearing  14 . Lubricant is supplied to portions of the clutch outer  5  and the clutch outer side plate  18  in contact with each other via the openings  18   f  formed at the bottom portions of the recess portions  18   d  of the clutch outer side plate  18 . 
     A side of the flat plate portion  3   c  of the primary driven gear  3  is opposed to a side thereof where the clutch outer  5  is disposed, and is arranged with an annular clutch side plate  19  in correspondence with the size of the side face of the flat plate portion  3   c  of the primary driven gear  3 . This holds the damper springs  4  with stability. 
     The boss portion  3   a  of the primary driven gear  3  is fitted into a central hole of the clutch side plate  19 . The clutch side plate  19  is respectively formed with six recess portions  19   d  for containing the damper springs  4  in correspondence with the first through holes  3   d  of the primary driven gear  3 , and three rivet holes  19   e  in correspondence with the rivet holes  5   e  of the side wall portion  5   b  of the clutch outer  5  at intervals in the peripheral direction. 
     A friction spring  20  includes a coned disc spring between the clutch side plate  19  and the flat plate portion  3   c  of the primary driven gear  3 . The friction spring  20  is disposed on an outer side of the damper springs  4  arranged in the peripheral direction. 
     When the clutch outer  5  and the clutch side plate  19  are fixedly attached by the rivets  21  and the sleeves  17  into which the rivets  21  are inserted, the friction spring  20  is pressed by a peripheral face near an outer peripheral edge of the clutch side plate  19 . In this case, a spring force of the friction spring  20  is exerted to press the primary driven gear  3  in the axial direction toward the side wall portion  5   b  of the clutch outer  5 . Because the clutch outer  5  and the clutch side plate  19  are integrated by rivets  21 , the clutch side plate  19  is integrally rotated with the clutch outer  5 , and corresponds to a member integrated with the clutch outer  5 . 
     By the spring force of the friction spring  20 , the flat plate portion  3   c  of the primary driven gear  3  is pressed to the clutch outer side plate  18  mounted on the clutch outer  5 . Both members are brought into contact with each other at a position on the outer side of the-damper springs  4 , and, at a position opposed to a position of the flat plate portion  3   c  attached with the friction spring  20  and an annular slidable contact face  22  is formed at the contact portion. Accordingly, when the primary driven gear  3  and the clutch outer  5  are rotated relative to each other within a range of the clearances in the peripheral direction formed between peripheral edges of the second through holes  3   e  and outer peripheries of the sleeves  17 , frictional force in correspondence with the press force based on the spring force of the friction spring  20  is produced on the slidable contact face  22  and frictional torque for hindering the relative rotation is produced. 
     The frictional force is set by experiment and is required to restrain resonance of the damper springs  4 . When the required frictional torque stays the same as that in the conventional technology, according to the embodiment, the slidable contact face  22  producing the frictional force is disposed on the outer side of the damper springs  4 , and is disposed at a position having a distance from the axis line of the main shaft  9  which is larger than that of the slidable contact face according to the conventional technology. 
     In the conventional technology, the slidable contact face is disposed on the inner side of the damper springs  4  (the frictional coefficient of the slidable contact face of the conventional technology is set to be equal to that of the embodiment). Accordingly, the frictional force for providing the required frictional torque may be smaller than that in the conventional technology. The spring force by the friction spring  20  may therefore be smaller. The pressing force of the primary driven gear  3  to the clutch outer side plate  18  at the slidable contact face  22  in turn becomes smaller. This reduces wear at the slidable contact face  22 . 
     The annular slidable contact face  22  is disposed on the outer side of the damper springs  4 , and accordingly, the area of the slidable contact face  22  can be made larger than the area of the slidable contact face according to the conventional technology. As a result, pressure based on the press force of the primary driven gear  3  exerted to the clutch outer side plate  18  can be reduced and wear at the slidable contact face  22  is further reduced. 
     The spring force can be adjusted by adjusting the spring force of the friction spring  20  or adjusting the frictional coefficient of the slidable contact face  22 . Alternatively, the spring force of the friction spring  20  can be adjusted by adjusting the spring constant of the spring or adjusting the length of the sleeve  17 . The frictional coefficient of the slidable contact face  22  can be adjusted by changing the material of the primary driven gear  3  or the clutch outer side plate  18 . The frictional coefficient may also be changed by changing the degree of lubrication, surface treatments, or the like. 
     In rotating the primary driven gear  3  and the clutch outer  5  relative to each other, the frictional spring  20  is rotated along with the primary driven gear  3  in view of the frictional coefficient between the primary driven gear  3  and the clutch side plate  19 . As a result, frictional force is produced at portions of the friction spring  20  and the clutch side plate  19  in contact with each other, and a frictional torque is produced by the frictional force. However, the frictional coefficient at the contact portion is made to be smaller than the frictional coefficient at the slidable contact face  22 . Therefore, the main portion of the frictional torque for restraining resonance of the damper springs  4  is shared by the frictional torque produced by the frictional force at the slidable contact face  22 . The resonance restraining operation depends on the frictional torque produced by the frictional force at the slidable contact face  22 . 
     An explanation follows of the operation of restraining resonance of the damper springs  4  by the frictional spring  20  in the multiple disk frictional clutch  1   
     When a frequency of a variation in torque caused in the crankshaft coincides with the natural frequency of the damper springs  4 , the damper springs  4  resonate. The primary driven gear  3  will then rotate significantly relative to the clutch outer  5  within the range of the clearances in the peripheral direction formed between the peripheral edges of the second through holes  3   e  and the outer peripheries of the sleeves  17 . At this time, the frictional force in accordance with the press force based on the spring force of the friction spring  20  is produced at the slidable contact face  22 . Further, the frictional torque produced by the frictional force hinders the primary driven gear  3  in rotating relative to the clutch outer  5 . Accordingly, the resonance of the damper spring  4  is restrained. 
     The above-described embodiment achieves the following effects. 
     The friction springs  20  disposed on the outer, side of the damper springs  4  arranged in The peripheral direction, presses the primary driven gear  3  to the outer side plate in the axial direction to thereby bring the both members into contact with each other. The annular slidable contact face  22  formed by the contact is disposed on the outer side of the damper springs  4  and accordingly, the slidable contact face  22  producing the frictional force is disposed on the outer side of the damper springs  4  and is disposed at a position at which the distance from the axis line of the main shaft  9  is larger than that of the slidable contact face according to the conventional technology. Therefore, the frictional force for providing the required frictional torque for restraining the resonance of the damper springs  4 , may be smaller than that of the conventional technology. The spring force by the frictional spring  20  may thus be smaller. The press force of the primary driven gear  3  exerted on the clutch outer side plate  18  at the slidable contact face  22  also becomes smaller. This reduces wear at the slidable contact face. Further, since wear is reduced, there is no need for wear resistant surface treatment on the slidable contact face. Difficulty and cost of manufacture are reduced. 
     By the spring force of the friction spring  20 , on the outer side of the damper springs  4 , the primary driven gear  3  and the clutch outer  5  are integrated in a state in which the both members press against each other via the clutch outer side plate  18  and accordingly, the damper springs  4  can stably be held and operation of the damper springs  4  is stabilized. 
     By installing the clutch outer side plate  18  mounted to the clutch outer  5 , wear of the clutch outer  5  caused by the contact with the damper springs  4  can be prevented, and wear of the clutch outer  5  at the slidable contact face  22  caused by being pressed by the primary driven gear  3  can be prevented. Further, in consideration of the fact that the clutch outer side late  18  forms the slidable contact face  22  along with the primary driven gear  3 , the material of the clutch outer side plate  18  can be different from the material forming the clutch outer  5 . 
     Although according to the above-described embodiment, the clutch outer side plate  18  is installed, the plate can also be dispensed with. 
     Although according to the embodiment, the friction spring  20  is provided between the clutch side plate  19  and the primary driven gear  3 , the friction spring  20  may be provided between the clutch outer side plate  18  and the primary driven gear  3  to thereby press the primary driven gear  3  toward the clutch side plate  19 . Also in this case, the clutch outer side plate  18  can be dispensed with and in that case, the friction spring  20  is provided between the clutch outer  5  and the primary driven gear  3 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.