Clutch disc

Abstract: Provided is a clutch disc having a superior performance of increasing an allowable torque or an angle of torsion of the damper plate. According to a first aspect , in a portion proximate to an end of a slit 31 at the peripheral or the inner peripheral side of the damper plate 21, the slit 31 is centrifugally curved or curved toward a clutch axis such that both ends thereof are close to a radius of a concentric circle, respectively. According to a second aspect , a damper plate 22 has a plurality of first rivets and a plurality of first rivet holes 254 through 257 formed thereon. The radii (r) of the first rivet holes 254 through 257 gradually decrease as the distance between the clutch axis (C) and each thereof decreases, whereas the radii (r) thereof increase gradually as the distance between the clutch axis (C) and each thereof increases. According to third and fourth aspect , there is a dislocation between the inner periphery of each of annular damper plate 23 and 24 and the periphery thereof in the direction parallel with the clutch axis (C) so that the annular damper plates 23 and 24 have a certain thickness in the direction parallel with the clutch axis (C), respectively.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutch disc according to the preamble of the patent claim 1. 2. Description of the Related Arts (Conventional Art) Heretofore, a dry clutch for a manual transmission is adopted as a friction clutch for use in a vehicle. The dry clutch has two types, one is a dry single clutch comprising a clutch disc combined with a pressure plate and the other is a dry multiple clutch comprising a plurality of dry single clutches. The Fig. 20 to 22 show in principle the design of a clutch disc of this kind. As shown in Fig. 20, a clutch disc 90 comprises a clutch hub 91 connected with an output shaft (input shaft of a transmission), a disc spring 93 (sub-plate 931) on which a clutch facing 92 has been mounted, and a damper member 94 interposed between the clutch hub 91 and the disc spring 93. Reference numeral 99 in Fig. 20 denotes a rivet pin which connects the disc spring 93 and the damper member 94 with each other. The damper member 94 transmits a torque between the clutch hub 91 and the disc spring 93 (sub-plate 931), thus applying a torsional characteristic to the clutch disc. The torsional characteristic changes torsional rigidity to be generated by the relative torsion of the damper member 94 in a single stage or multiple stages. It is known that hysteresis characteristic is applied to the torsional characteristic by means of a friction member mounted on the face of contact between the clutch hub 91 and the disc spring 93 (sub-plate 931), as will be described later with reference to Fig. 15. A damper member comprising a coil spring or a torsion rubber is known. As shown in Fig. 21, a damper member comprising a damper plate 95 having a spiral slit 96 formed thereon is also known. Reference numeral 991 in Fig. 21 denotes a rivet hole through which the rivet pin 99 (see Fig. 20) is inserted. A damper member as shown in Fig. 22 is also known. The damper member comprises damper plates 951 and 952 provided symmetrically between the clutch hub 910 and the disc spring 930 by inverting one damper plate with respect to the other damper plate by 180 degrees. Reference numeral 990 in Fig. 22 denotes a rivet connecting the clutch hub 910 and the damper plates 951 and 952 with each other. A damper member comprising two pairs of the damper plates 951 and 952 to provide a two-stage torsional characteristic is also known as shown in Fig. 23. The conventional damper members comprising the damper plate have, however, the following problems. One of the problems is that in order to increase the angle of torsion of the damper plate (damper member) and the allowable torque thereof, the size or weight of the damper plate should be increased. For example, in order to increase a maximum angle of torsion  m, the width ws of the slit of the damper plate shown in Fig. 21 is required to be increased. The increase in the width, however, reduces the total area of the spiral plate 950, thus resulting in decreasing a maximum allowable torque Tm. The maximum allowable torque Tm is determined by the width wp of the spiral plate 950 defined by the slit 96 formed therein and the thickness thereof. The allowable angle of torsion  m is determined by the width wp of the spiral plate 950 and the length (L) thereof. Thus, in order to increase the allowable angle of torsion  m as well as retaining the allowable torque Tm, it is necessary to increase the diameter of the damper plate as a whole. If the width wp and the length (L) of the belt-like elastic plate 950 are increased in order to increase the maximum allowable torque Tm and the allowable angle of torsion  m keeping the thickness and size of the damper plate unchanged, the width ws of the slit 96 is required to be reduced. If the width ws of the slit 96 is reduced, adjacent portions of the spiral plate 950 interfere with each other owing to the radial movement of the adjacent portions having the width wp caused by a torsion applied to the spiral plate 950. Consequently, the damper plate has a reduced maximum allowable angle of torsion  m (first problem.) A stress generated by a force applied to the damper plate 95 is maximum at the inner peripheral end of the slit 96 and the peripheral end thereof, as shown by reference numeral 961 in Figs. 21 and 22. That is, as shown in Fig. 3, a stress (S) concentrates on a portion, shown by an arrow (Y), of the inner peripheral end 961 of the slit 96. In order to prevent the stress from concentrating on the end 961 of the slit 96, it is necessary to allow the peripheral line of the end 961 to have a small curvature along the direction in which the stress (S) is applied. That is, it is necessary to allow the end 961 to have a great size. In order to do so, it is necessary to allow the slit 96 to have a great width, which means that the spiral plate 950 has a reduced width wp. Accordingly, the damper member has a reduced maximum allowable torque Tm (second problem.) In order to increase the product of the width wp and the length (L) of the long spiral elastic member comprising the damper plates 951 and 952 having insertion holes 959, through which the rivets are inserted, formed at the inner periphery of the spiral elastic member, with the outer diameter thereof fixed to a certain value, it is necessary to reduce the diameter of a circle C1 positioned at the inner periphery of the spiral elastic member and having the rivets 990 arranged thereon. On the other hand, because it is necessary to secure the strength of the rivet 990 and portions, of the damper plates 951 and 952, proximate to the rivet hole 959, it is difficult to make the diameter of the rivet 990 too small. Therefore, there is a limitation in the degree in reduction of the diameter of the circle C1 on which the rivets 990 are arranged and the diameter of the inner circle of the damper plates 951 and 952. This is a principal factor for which the maximum angle of torsion  m and the allowable torque Tm cannot be increased (third problem.) In order to apply a hysteresis characteristic to the torsional characteristic, it is necessary to provide a friction member for generating a frictional force between the damper plate and the clutch hub or between the damper plate and the disc spring. As a result, the weight of the clutch disc increases as well as the manufacturing cost.(fourth problem) If the clutch disc has a multi-stage torsional characteristic, it is unnecessary to apply the hysteresis characteristic to the torsional characteristic in a low torque region, but rather, preferably, no hysteresis characteristic is applied thereto. But if the friction member is provided between the damper plate and the clutch hub or between the damper plate and the disc spring, hysteresis is necessarily generated in the low torque region. (additional problem resulted from the fourth problem) In the document EP-A-0 341 133 a clutch disc of that kind is discloses, constituting a friction clutch which comprises a clutch hub connected with an output shaft a disc spring having a clutch facing mounted on a peripheral side thereof, and damper members each interposed between the clutch hub and the disc spring. By this construction a torsional characteristic is applied to the clutch disc. SUMMARY OF THE INVENTION The present invention has been developed to solve the above-described problems, and it is accordingly an object of the present invention to provide a clutch disc having a superior performance of increasing an allowable torque or an angle of torsion of the damper plate, supposing that the volume and weight thereof are fixed. This object is solved by a clutch disc comprising the technical features according to the patent claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front sectional view showing a clutch disc according to a first example (sectional view taken along the line X-X of Fig. 2) which is not part of the invention; Fig. 2 is a left side sectional view showing the clutch disc according to the first example; Fig. 3 is a view showing the configuration of a slit according to the first example in comparison with that of a conventional slit; Fig. 4 is a front view showing a damper plate according to a second example which is not part of the invention; Fig. 5 (a) is a front view showing a damper plate according to a third example, and Fig. 5 (b) is a left side sectional view showing the clutch disc according to the third example which is not part of the invention; Fig. 6 is a sectional view showing main portions in an enlarged side elevational view showing how the state of the damper plate has been changed from the state shown in Fig. 5 (b) when torsion is applied thereto); Fig. 7 (a) is a front view showing a damper plate according to a fourth example, and Fig. 7 (b) is a left side sectional view showing the clutch disc according to the fourth example, both are not part of the invention; Fig. 8 is a side sectional view showing a clutch disc according to a fifth example; Fig. 9 is a view in which a right front portion of the clutch disc of a fifth example is cut away; Fig. 10 is a view showing the interval between engaging holes of a stopper plate according to the fifth example and a corresponding first rivet; Fig. 11 is a side sectional view showing a clutch disc according to a sixth example Fig. 12 is a view in which a right front portion of the clutch disc of the sixth example is cut away; Fig. 13 is a view showing the interval between engaging holes of a stopper plate according to the sixth example and a corresponding second rivet ; Fig. 14 is a.view showing the interval between engaging holes of a stopper plate according to the sixth example and a corresponding second rivet ; Fig. 15 is a view showing the torsional characteristic of a damper member of the sixth example; Fig. 16 is a side sectional view showing a clutch disc according to a seventh example; Fig. 17 is a perspective view showing a second rivet according to the seventh example; Fig. 18 is a side sectional view showing a clutch disc according to an eighth example; Fig. 19 is a view in which a right front portion of the clutch disc of the eighth example is cut away; Fig. 20 is a side sectional view showing a conventional clutch disc; Fig. 21 is a front view showing a conventional damper plate; Fig. 22 is a front view showing another damper plate of a conventional clutch disc; and Fig. 23 is a side sectional view showing another conventional clutch disc. DETAILED DESCRIPTION OF THE INVENTION A clutch disc, according to a first aspect constituting a friction clutch comprises a clutch hub connected with an output shaft, a disc spring having a clutch facing mounted on a peripheral side thereof, and a damper member interposed between the clutch hub and the disc spring, thus applying a torsional characteristic to the clutch disc. The damper member has a single or a plurality of elastically deformable damper plates. The damper plate is formed of an annular elastic material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like slits formed thereon centrifugally spirally in a range from an inner peripheral side of the annulus toward a peripheral side thereof. The arc-like slit has a curved portion formed by centrifugally curving a portion of the slit proximate to an end thereof at the peripheral side of the annular damper plate such that the end of the slit is close to a radius of a concentric circle and/or a curved portion formed by curving a portion of the slit proximate to an end thereof toward the center of a concentric circle at the inner peripheral side of the annular damper plate such that the end of the slit is close to a radius of the concentric circle. The first aspect is characterized in that in the arc-like slit formed on the annular damper plate, in a region proximate to the end of the slit at the peripheral side of the annular damper plate, the slit is centrifugally curved such that the end thereof is close to a radius of a concentric circle, whereas in a region proximate to the end of the slit at the inner peripheral side of the annular damper plate, the slit is curved toward the center of a concentric circle such that the end thereof is close to a radius of the concentric circle. Supposing that the damper plate is connected with the clutch hub and the disc spring by means of the rivet pin, preferably, the damper plate has a plurality of first rivet holes through which rivets for fixing the damper plate to the clutch hub are inserted and which are formed in proximity to the inner peripheral side of the annulus and a plurality of second rivet holes through which rivets for fixing the damper plate to the disc spring are inserted and which are formed in proximity to the peripheral side thereof. The first and second rivet holes are formed at regular intervals concentrically, respectively. In this construction, an inner end of the arc-like slit is curved to be close to the radius, of the concentric circle, positioned approximately intermediate between the adjacent first rivet holes, and an outer end of the arc-like slit is curved to be close to the radius, of the concentric circle, positioned approximately intermediate between the adjacent second rivet holes. The strengths of portions of the damper plate proximate to the rivet holes can be allowed to be uniform against the stress of the damper plate by arranging the rivet holes as described above. A clutch disc, according to the second aspect , constituting a friction clutch comprises a clutch hub connected with an output shaft, a disc spring having a clutch facing mounted on a peripheral side thereof, and a damper member interposed between the clutch hub and the disc spring, thus applying a torsional characteristic to the clutch disc. The damper member has at least one elastically deformable damper plate. The damper plate is formed of an annular elastic material, a surface of which is perpendicular to a clutch axis and has an arc-like slit formed thereon centrifugally spirally in a range from an inner peripheral side of the annulus toward a peripheral side thereof and has a plurality of first rivet holes through which rivets for fixing the damper plate to the clutch hub are inserted and which are formed in proximity to the inner peripheral side of the annulus. The first rivet holes and the rivets are centrifugally spirally arranged along portions of the arc-like slit positioned in proximity to the inner peripheral side of the annulus by gradually increasing the distance between the clutch axis and each of the first rivet holes such that the radii (r) of the first rivet holes decrease as the distance between the clutch axis and each thereof decreases and the radii (r) thereof increase as the distance between the clutch axis and each thereof increases. The second aspect is characterized in that the first rivet holes and the rivets positioned at the inner peripheral side of the annular damper plate are centrifugally spirally arranged along portions of the arc-like slit positioned in proximity to the inner peripheral side of the annulus in such a manner that the radii (r) of the first rivet holes decrease as the distance between the clutch axis and each thereof decreases and the radii (r) thereof increase as the distance between the clutch axis and each thereof increases. The construction of the second aspect is applicable to the friction clutch of the first invention, and the advantage of the first invention and that of the second invention can be obtained in combination. A clutch disc, according to the third aspect constituting a friction clutch comprises a clutch hub connected with an output shaft, a disc spring having a clutch facing mounted on a peripheral side thereof, and a damper member interposed between the clutch hub and the disc spring, thus applying a torsional characteristic to the clutch disc. The damper member has at least one elastically deformable damper plate. The damper plate is formed of an annular deformable material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like cut lines or a plurality of arc-like slits formed thereon in a range from an inner peripheral side of the annulus toward a peripheral side thereof such that there is a dislocation between the inner periphery of the annulus and the periphery thereof in a direction parallel with the clutch axis to cause adjacent structures centrifugally spirally formed by the presence of the arc-like cut lines or the arc-like slits to be dislocated from each other in the axial direction of the clutch axis, so that when the adjacent structures are dislocated radially from each other as a result of circumferential twists applied thereto, the arc-like cut lines or the arc-like slits do not interfere with each other. The structures are formed of an elastically deformable material, respectively. The third aspect is characterized in that each damper plate is formed of an annular deformable material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like cut lines or a plurality of arc-like slits formed thereon in a range from an inner peripheral side of the annulus toward a peripheral side thereof such that there is a dislocation between the inner periphery of the annulus and the periphery thereof in a direction parallel with the clutch axis to form a thickness in the axial direction of the damper member. The structure thus formed increases the width of the arc-like cut lines or the arc-like slits. The structures are formed of an elastically deformable material. In the third aspect , preferably, an elastic return force is applied between the inner periphery of the annulus and the periphery thereof in the axial direction thereof so as to apply a thrust load between the damper plate and the clutch hub. Hysteresis characteristic can be applied to the torsional characteristic by applying an elastic return force between the inner periphery of the annulus and the periphery thereof, which eliminates the need for the provision of a friction and allows the clutch disc to be light and manufacturing cost to be reduced. The construction of the third aspect is applicable to the friction clutch of the first invention or the second invention, and thus the advantage of the first, second, and third inventions can be obtained in combination. A clutch disc, according the fourth aspect constituting a friction clutch comprises a clutch hub connected with an output shaft, a disc spring having a clutch facing mounted on a peripheral side thereof, and a damper member interposed between the clutch hub and the disc spring, thus applying a torsional characteristic to the clutch disc. The damper member has at least one elastically deformable damper plate. The damper plate is formed of an annular elastic material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like slits formed thereon centrifugally spirally in a range from an inner peripheral side of the annulus toward a peripheral side thereof such that the damper plate has long and narrow plates formed between the adjacent arc-like cut lines or between the adjacent arc-like slits by inclining the long and narrow plates with respect to a horizontal plane perpendicular to the clutch axis so as to axially space from each other faces of the long and narrow plates formed by the presence of the arc-like cut lines or the arc-like slits by more than the thicknesses of the long and narrow plates. The structures comprising the long and narrow plates are formed of an elastically deformable material. The fourth aspect is characterized in that the damper member has at least one elastically deformable damper plate and that the damper plate is formed of an annular elastic material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like slits formed thereon centrifugally spirally in a range from an inner peripheral side of the annulus toward a peripheral side thereof such that the damper plate has long and narrow plates formed between the adjacent arc-like cut lines or between the adjacent arc-like slits by inclining the long and narrow plates with respect to a horizontal plane perpendicular to the clutch axis so as to axially space from each other faces of the long and narrow plates formed by the presence of the arc-like cut lines or the arc-like slits by more than the thicknesses of the long and narrow plates. In this configuration, when the adjacent long and narrow plates are dislocated radially from each other as a result of circumferential twists applied thereto, they do not interfere with each other. The structure comprising the long and narrow plates are formed of an elastically deformable material. The construction of the fourth aspect is applicable to the friction clutch of the first invention or the second invention, and thus the advantage of the first, second, and third inventions can be obtained in combination. The arc-like slit of the first through fourth inventions may be single or plural. A clutch disc, according the fifth aspect , constituting a friction clutch comprises a clutch hub connected with an output shaft, disc springs each having a clutch facing mounted on a peripheral side thereof, and damper members each interposed between the clutch hub and the disc spring, thus applying a torsional characteristic to the clutch disc, stopper plates each fixed to the disc spring or the clutch hub, and stopper members each fixed to the stopper plate at an unfixed side thereof or to the clutch hub. The damper member has at least one elastically deformable damper plate. The stopper plate has at the unfixed side thereof a plurality of play interval-provided cut-out portions or a plurality of play interval-provided engaging holes, each of which has an interval greater than a predetermined interval between each of the stopper members and an edge of each thereof when the angle of torsion of the damper member is zero, and the edge of each of which is brought into contact with each of the stopper members when the angle of torsion of the damper member has reached a predetermined one. The fifth aspect is characterized in that the clutch disc has the stopper plates each fixed to the disc spring or the clutch hub, and the stopper members each fixed to the stopper plate at an unfixed side thereof or to the clutch hub; the damper member has a single or a plurality of elastically deformable damper plates; and the stopper plate has at the unfixed side thereof a plurality of play interval-provided cut-out portions or a plurality of play interval-provided engaging holes, each of which has an interval greater than a predetermined interval between each of the stopper members and an edge of each thereof when the angle of torsion of the damper member is zero, and the edge of each of which is brought into contact with each of the stopper members when the angle of torsion of the damper member has reached a predetermined one. The construction of the fifth aspect is applicable to the friction clutch of the first through fourth aspects and thus the advantage of the first through fourth aspects can be obtained in combination. According to the sixth aspect , a clutch disc constituting a friction clutch comprises a clutch hub connected with an output shaft, disc springs each having a clutch facing mounted on a peripheral side thereof, and damper members each interposed between the clutch hub and the disc springs, thus applying a torsional characteristic to the clutch disc, first rivets for fixing the clutch hub and the damper member to each other, and second rivets for fixing the disc spring and the damper member to each other. The damper member has a plurality of damper plates arranged side by side and including a damper plate to which a lower torque is assigned and another damper plate to which a higher torque is assigned; damper plates to which an intermediate torque and the higher torque are assigned are not fixed to the clutch hub or the disc spring, excluding a damper plate to which the lowest torque is assigned; a stopper pin is installed on an unfixed side of one of the adjacent damper plates to which the intermediate and higher torques are assigned; and a play interval-provided cut-out portion or a play interval-provided engaging hole which engage the stopper pin is formed on the other of the adjacent damper plates. Only when the angle of torsion of the damper plate at the lower torque-applied side has reached a predetermined one, the stopper pin is brought into contact with an edge of the play interval-provided cut-out portion or that of the play interval-provided engaging hole. The sixth aspect is characterized in that the damper member has a plurality of damper plates, arranged side by side, including a damper plate to which a lower torque is assigned and a damper plate to which a higher torque is assigned. Damper plates to which an intermediate torque and the higher torque are assigned are not fixed to the clutch hub or the disc spring, excluding a damper plate to which the lowest torque is assigned. A stopper pin is installed on an unfixed side of one of adjacent damper plates, and a play interval-provided cut-out portion or a play interval-provided engaging hole which engage the stopper pin is formed on the other of the adjacent damper plates. Only when the angle of torsion of the damper plate at the lower torque-applied side has reached a predetermined one, the stopper pin is brought into contact with an edge of the play interval-provided cut-out portion or that of the play interval-provided engaging hole. A clutch disc, according to the seventh aspect constituting a friction clutch comprises a clutch hub connected with an output shaft, a disc spring having a clutch facing mounted on a peripheral side thereof, and a damper member interposed between the clutch hub and the disc spring, thus applying a torsional characteristic to the clutch disc. The damper member has a plurality of damper plates including a damper plate to which a lower torque is assigned and a damper plate to which a higher torque is assigned; and the damper for applying a torsional characteristic to the clutch disc in a lower torque is integral with the disc spring. The seventh aspect is characterized in that the damper member has a plurality of elastically deformable damper plates and that the damper for applying a torsional characteristic to the clutch disc in a lower torque is integral with the disc spring. The construction of the seventh aspect is applicable to the friction clutch of the first through sixth aspects and thus the advantage of the first through sixth aspects can be combined. , In the clutch disc of the first aspect in the region proximate to the end of the arc-like slit positioned on the damper plate at the peripheral side thereof, the slit is centrifugally curved such that the end of the slit is close to the radius (R) of the concentric circle as shown by a reference numeral 31 of Fig. 3 (b), whereas in the region proximate to the end of the slit positioned at the inner peripheral side of the damper plate, the slit is curved toward the center of the concentric circle such that the end of the slit is close to the radius (R) of the concentric circle as shown by the reference numeral 31 of Fig. 3 (a). Consequently, a stress (S) generated by a force applied to the damper plate can be prevented from concentrating on the ends of the slit. That is, as can be understood from the fact that the curvatures of the slit at portions (A) and (B) thereof are smaller than that at a portion (Y) thereof, the curvature of the slit at the inner and outer ends thereof along the stress-applied direction is allowed to be small. Therefore, the stress (S) can be prevented from concentrating on the ends of the slit. Consequently, the allowable torque Tm of the damper plate or the maximum angle of torsion  m can be increased, with the size (width) of the slit fixed. As described above, the first aspect provides the clutch disc having a superior performance of increasing the allowable torque and the angle of torsion of the damper plate, supposing that the volume and weight thereof is fixed. The first rivet holes positioned at the inner peripheral side of the damper plate are centrifugally spirally arranged along portions of the slit 31 positioned in proximity to the inner periphery thereof by gradually increasing the distance between the clutch axis (C) and each of the first rivet holes. The radii (r) of the first rivet holes decrease as the distance between the clutch axis (C) and each thereof decreases, whereas the radii (r) thereof increase as the distance between the clutch axis (C) and each thereof increases. Consequently, the slit 31 of the second aspect is allowed to be longer than the slit of the conventional damper plate by a distance Δ L and an angle Δ  , supposing that the radius r0 of the inner circumference of the damper plate is equal to that of the inner circumference of the conventional damper plate. Thus, the plates interposed between adjacent slits are allowed to be longer than the conventional ones and hence the damper plate of the second invention has a greater maximum angle of torsion  m than the conventional one. That is, if the radii of the rivet holes are equal to each other as in the case of the conventional damper plate and if the rivet holes are arranged on a concentric circle and symmetrically with respect to the center of the concentric circle, the rivet holes are as shown by two-dot chain lines and by reference numerals 991 of Fig. 4. This construction prevents plates positioned between adjacent slits from having an area necessary for securing the strength of the damper plate, thus causing the width of the slit 96 to be long and length thereof to be short. Δ L and Δ  shown in Fig. 4 indicate a decreased length of the slit 96 and a reduced angle of torsion of the conventional damper plate. As described above, the second example provides the clutch disc applicable to an allowable torque higher than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. The damper member of the clutch disc according to the third aspect has at least one elastically deformable damper plate. The damper plate is formed of an annular deformable material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like cut lines or a plurality of arc-like slits formed thereon in a range from an inner peripheral side of the annulus toward a peripheral side thereof such that there is a dislocation between the inner periphery of the annulus and the periphery thereof in a direction parallel with the clutch axis to cause adjacent structures centrifugally spirally formed by the presence of the arc-like cut lines or the arc-like slits to be dislocated from each other in the axial direction of the clutch axis, so that when the adjacent structures are dislocated radially from each other as a result of circumferential twists applied thereto, the arc-like cut lines or the arc-like slits do not interfere with each other. The structures are formed of an elastically deformable material, respectively. Because there is a dislocation between the inner periphery of the damper plate and the periphery thereof in a direction parallel with the clutch axis to form a thickness in the axial direction of the damper member, adjacent damper plates can be prevented from interfering with each other in the movements thereof in the radial direction thereof as shown in Fig. 6 when the damper plates are twisted, even though a slit having a small width is formed. Thus, the damper plates are allowed to have an increased width and length as the slit width is reduced, and hence, the allowable torque and/or the angle of torsion can be increased. Consequently, the allowable torque Tm of the damper plate can be increased in correspondence to the reduction in the slit width, by increasing the width of the damper plate, with the size (radius) of the damper plate fixed to a certain one, and the length of the damper plate can be increased in correspondence to the reduction in the slit width, with the width of the damper plate fixed to a certain one. Consequently, the angle of torsion  m of the damper plate can be increased, with the allowable torque Tm fixed to a certain one. As described above, the third example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. In the clutch disc of the fourth aspect , the damper member has at least one elastically deformable damper plate, and the damper plate is formed of an annular elastic material, a surface of which is perpendicular to a clutch axis and has a plurality of arc-like slits formed thereon centrifugally spirally in a range from an inner peripheral side of the annulus toward a peripheral side thereof such that the damper plate has long and narrow plates formed between the adjacent arc-like cut lines or between the adjacent arc-like slits by inclining the long and narrow plates with respect to a horizontal plane perpendicular to the clutch axis so as to axially space from each other faces of the long and narrow plates formed by the presence of the arc-like cut lines or the arc-like slits by more than the thicknesses of the long and narrow plates. The structures comprising the long and narrow plates are formed of an elastically deformable material. According to the above construction, similarly to the third aspect , as shown in Fig. 7 (b), the long and narrow plates are inclined with a plane perpendicular to the clutch axis to generate an interval (g) between the adjacent long and narrow plates. In this manner, even though the width (b) of the slit is reduced, the movable region of the long and narrow plates in the radial direction can be increased to the interval (g). Consequently, the maximum angle of torsion  m of the damper plate can be increased, with the size (diameter) thereof and the allowable torque Tm f ixed to a certain one. As described above, the fourth example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. In the clutch disc of the fifth aspect , the stopper plate has a plurality of play interval-provided cut-out portions or a plurality of play interval-provided engaging holes. When the angle of torsion of the damper plate is zero, there is an interval, greater than a predetermined one, between each of the first rivets and an edge of each of the play interval-provided cut-out portions or the play interval-provided engaging holes. When the angle of torsion of the damper plate has reached a predetermined value  m, the edge of each of the play interval-provided cut-out portions or the play interval-provided engaging holes is brought into contact with each of the first rivets. Consequently, when the angle of torsion of the damper plate has reached the maximum value  m, each first rivet is brought into contact with the edge of the corresponding engaging hole of the stopper plate. Thus, a torque higher than the allowable maximum torque Tm corresponding to the maximum angle of torsion  m is applied to the stopper plate. That is, the highest torque to be applied to the damper plate is the allowable maximum torque Tm. Accordingly, the damper plate is not required to have a strength to cope with excessive force to be applied thereto. Thus, the damper plate can be allowed to be compact and light. As described above, the fifth example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. In the clutch disc of the sixth aspect the damper member has a plurality of damper plates arranged side by side and including a damper plate for a lower torque and another damper plate for a higher torque is assigned. The damper plates to which an intermediate torque and the higher torque are assigned are not fixed to the clutch hub or the disc spring, excluding a damper plate for the lowest torque. The stopper pin is installed on an unfixed side of one of adjacent damper plates, and a play interval-provided cut-out portion or a play interval-provided engaging hole which engage the stopper pin is formed on the other of the adjacent damper plates. That is, when a low torque (when the angle of torsion of one damper plate is zero) is applied to the clutch disc, there is a gapδ " between the edge of the play interval-provided engaging hole 271 (or play interval-provided cut-out portion) of the other damper plate and the stopper pin, as shown in Fig. 13, and a torsional torque is not applied to the other damper plate through the stopper pin. At this time, a torque is increasingly applied to one damper plate. As a result, when one damper plate is twisted by the gap δ " as shown in Fig. 14, a torsional force is applied to the other damper plate. Only when a torsion higher than a predetermined value is generated on one damper plate (previous stage) which operates in a low torque, the other damper plate (subsequent stage) which operates in a high torque is twisted. In this manner, the torsional characteristics of the damper plates are sequentially added to each other and consequently, the clutch disc is allowed to have a high allowable torque and a great angle of torsion m and have a multi-stage torsional characteristic as shown in Fig. 15. In this manner, the present invention provides a clutch disc having a three-stage torsional characteristic of a high allowable torque and a great angle of torsion, as shown by the lines of 0-A, A-B, and B-C shown in Fig. 15. In the clutch disc according to the seventh aspect , the damper member has a plurality of elastically deformable damper plates and that the damper for applying a torsional characteristic to the clutch disc in a lower torque is integral with the disc spring. That is, if the damper plate generating a torsional characteristic in a low torque region and the disc spring are integral with each other and if the clutch disc requires a hysteresis characteristic and thus the friction member is provided, no friction is generated between the damper plate which operates in a low torque and the disc spring. Accordingly, the clutch disc of the seventh invention eliminates an unnecessary hysteresis in a low torque region. As described above, the constructions of the respective aspects may be appropriately combined with each other. EXAMPLES (First Example) The first example relates to a clutch disc according to the first aspect which is not part of the invention. As shown in Fig. 2, a clutch disc 10 constituting a friction clutch comprises a clutch hub 11 connected with an output shaft, a disc spring 15 having a clutch facing 16 mounted on the periphery thereof, and a damper member 20 interposed between the clutch hub 11 and the disc spring 15, thus applying a torsional characteristic to the clutch disc 10. The damper member 20 has at least one damper plate 21 elastically deformable. As shown in Fig. 1, the damper plate 21 is formed of an annular elastic material, the surface of which is perpendicular to a clutch axis (C) and has a plurality of arc-like slits 31 formed thereon centrifugally spirally in a range from the vicinity of the inner periphery thereof toward the vicinity of the periphery thereof. As shown in Fig. 3 (b), in a portion proximate to the end of each slit 31 at the peripheral side of the damper plate 21, the slit 31 is centrifugally curved such that the end thereof is close to a radius of a concentric circle, whereas as shown in Fig. 3 (a), in a portion proximate to the end of the slit 31 at the inner peripheral side of the damper plate 21, the slit 31 is curved toward the center of a concentric circle such that the end thereof is close to a radius of the concentric circle. The damper plate 21 has a plurality of first rivet holes 251 formed in proximity to the inner periphery thereof and a plurality of second rivet holes 252 formed in proximity to the periphery thereof . Rivets 13 for fixing the damper plate 21 to the clutch hub 11 are inserted through the first rivet holes 251. Rivets 12 (see Fig. 2) for fixing the damper plate 21 to the disc spring 15 are inserted through the second rivet holes 252. The first and second rivet holes 251 and 252 are formed at regular intervals concentrically, respectively. As shown in Fig. 3, a portion of the slit 31 proximate to the inner end 311 thereof is curved to be close to the radius, of the concentric circle, positioned approximately intermediate between the adjacent first rivet holes 251 and 251, whereas a portion of the slit 31 proximate to the outer end 312 thereof is curved to be close to the radius, of the concentric circle, positioned approximately intermediate between the adjacent second rivet holes 252 and 252. Reference numerals 418 and 419 shown in Fig. 1 denote rivet facings for fixing the disc spring 15 and the clutch facing 16, repectively. As described above, in the clutch disc 10 of the first embodiment, in the portion proximate to the end 312 of the arc-like slit 31 at the peripheral side of the damper plate 21, the slit 31 is centrifugally curved such that the end 312 of the slit 31 is close to the radius of the concentric circle, as shown in Fig. 3 (b), whereas in the portion proximate to the end 311 of the slit 31 at the inner peripheral side of the damper plate 21, the slit 31 is curved toward the center of the concentric circle such that the end 311 of the slit 31 is close to the radius of the concentric circle as shown in Fig. 3 (a). Consequently, a stress (S) generated by a force applied to the damper plate 21 can be prevented from concentrating on a portion (A) of the slit 31. That is, because the ends 311 and 312 of the slit 31 are curved, the portions (A) and (B) are located at positions to which the stress (S) is applied to a small extent. Thus, the extent of the concentration of the stress (S) to be generated on each of the portions (A) and (B) is much lower than that of the stress (S) to be generated to the maximum on the end 961 of the conventional slit 96. Consequently, the allowable torque Tm of the damper plate 21 can be increased, with the size (width) (angle of torsion) of the slit 31 fixed or the maximum angle of torsion  m of the damper plate 21 can be increased, with the allowable torque Tm fixed (the second problem previously described can be solved by the second example.) As described above, the first example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. (Second Example) The second example relates to a clutch disc according to the second aspect which is not part of the invention. That is, as shown in Fig. 4, a damper plate 22 of the second example has a plurality of first rivets (not shown) and a plurality of first rivet holes 254 through 257 centrifugally spirally arranged along portions of an arc-like slit 31 positioned in proximity to the inner periphery thereof by gradually increasing the distance between the clutch axis (C) and each of the first rivet holes 254 through 257. The radii (r) of the first rivet holes 254 through 257 gradually decrease as the distance between the clutch axis (C) and each thereof decreases, whereas the radii (r) thereof increase gradually as the distance between the clutch axis (C) and each thereof increases. That is, as shown by two-dot chain lines in Fig. 4, the radii of the rivet holes 991 of the conventional damper plate 95 are equal to each other, and the rivet holes 991 are formed at regular intervals, whereas the radii (r) of the first rivet holes 254 through 257 of the second example gradually increase in the order from the first rivet hole 254 to the first rivet hole 257, and the distance between the clutch axis (C) and each of the first rivet hole 254 through the first rivet hole 257 gradually increases as the radii (r) thereof increase. Consequently, the slit 31 of the damper plate 22 according to the second example is longer than the slit 96 of the conventional damper plate 95. Thus, the distance between the inner end of the slit 31 and the clutch axis (C) is longer than that between the inner end of the slit 96 of the conventional damper plate 95 and the clutch axis (C). Δ L and Δ  shown in Fig. 4 indicate an increased length of the slit 31 of the second example and an increased angle of torsion of the damper plate 22 relative to the length of the slit 96 and the angle of torsion of the conventional damper plate 95, respectively. Therefore, the damper plate 22 has a greater angle of torsion  m than the conventional damper plate 95 (the third problem can be solved by the third example.) Other constructions and operations of the second example are similar to those of the first example. As described above, the second example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. (Third Example) The third example relates to a clutch disc according to the third aspect which is not part of the invention. That is, as shown in Figs. 5 (a) and 5 (b), the damper plate 23 is formed of an annular deformable material, the surface of which is perpendicular to the clutch axis (C) and has a plurality of arc-like cut lines 32 and a plurality of arc-like slits 31 formed thereon centrifugally spirally in the range from a position proximate to the inner periphery thereof toward a position proximate to the periphery thereof. There is a dislocation (d) between the inner periphery of the damper plate 23 and the periphery thereof in the direction parallel with the clutch axis (C) so that the damper plate 23 has a certain thickness in the axial direction thereof. Consequently, the cut line 32 and the slit 31 are allowed to have an increased width in the vertical direction thereof. The damper plate 23 is made of a material such as a spring steel plate elastically deformable. As shown in Fig. 5 (b), there is the dislocation (d) between an inner plate 231 positioned at the inner peripheral side of the damper plate 23 and an outer plate 232 positioned at the peripheral side thereof, as described above. The inner plate 231 and the outer plate 232 both fixed to the clutch hub by the rivets have surfaces perpendicular to the clutch axis (C). The dislocation (d) causes a plate 233 positioned intermediate between the inner plate 231 and the outer plate 232 to be inclined by a slight angle a and vertically spiral along the clutch axis (C). Because there is the dislocation (d) between the upper surface and the lower surface in the damper plate 23, the width of the slit 31 and that of the cut line 32 can be increased vertically, with the sum of the area of the plates 231 through 233 of the damper plate 23 fixed to a certain one. That is, there is little gap (for example, arrow f) in the slit 31 and the cut line 32 as shown in Fig. 5 (a) which is a plan view showing the damper plate 23, whereas they have a gap (g) in the axial direction of the clutch disc 23 when taking a side-view of the damper plate 23, as shown in Fig. 5 (b) which is a side sectional view showing the damper plate 23. Upon applying a torsional torque to the damper plate 23, as shown in Fig. 6, the plate 233 positioned intermediate between the inner plate 231 and the outer plate 232 is deformed from a position shown by one-dot chain to a position shown by a solid line, namely, toward the clutch axis (C). Consequently, the maximum angle of torsion  m of the damper plate 23 can be increased, with the size (diameter) thereof and the allowable torque Tm thereof fixed (the first problem can be solved by the second example.) Other constructions and operations of the third example are similar to those of the second example. As described above, the third example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. (Fourth Example) The fourth example relates to a clutch disc according to the fourth aspect which is not part of the invention. That is, as shown in Figs. 7 (a) and 7 (b), a damper plate 24 of the fourth example is formed of an annular deformable plate, the surface of which is perpendicular to the clutch axis (C) and has a plurality of arc-like cut lines 32 or arc-like slits 31 formed thereon centrifugally spirally from a position proximate to the inner periphery thereof toward a position proximate to the periphery thereof. Further, the damper plate 24 has long and narrow plates 243 formed between the adjacent cut lines 32 and 32 or between the adjacent slits 31 and 31 by forming a certain angle between the plates 243 and a horizontal plane perpendicular to the clutch axis (C). Thus, the cut line 32 and the slit 31 are allowed to have a large vertical width (gap). The damper plate 24 is made of a material such as a spring steel plate elastically deformable. The inclined plate 243 inclined by an angle β with a horizontal plane perpendicular to the clutch axis (C) is provided between an inner plate 241 positioned at the inner peripheral side of the damper plate 24 and an outer plate 142 positioned at the peripheral side thereof, as shown in Fig. 7 (b). That is, each of the inner plate 241 fixed at the inner peripheral side of the damper plate 24 by the rivet and the outer plate 142 fixed at the peripheral side thereof by the rivet has a surface perpendicular to the clutch axis (C), whereas the inclined plate 243 interposed therebetween has an inclination β . The damper plate 24 having a certain thickness allows the width (g) of the slit 31 and that of the cut line 32 to be increased vertically, with the sum of the area of the plates 241 through 243 of the damper plate 24 fixed to a certain one. That is, there is little gap (for example, arrow f) in the slit 31 and the cut line 32 as shown in Fig. 7 (a) which is a plan view showing the damper plate 24, whereas they have the gap (g) in the axial direction of the clutch disc 24 when taking a side-view of the damper plate 24, as shown in Fig. 7 (b) which is a side sectional view showing the damper plate 24. Upon applying a torsional torque to the damper plate 24, the plate 243 is radially moved by the gap (g). Consequently, the maximum angle of torsion  m of the damper plate 24 can be increased, with the size (diameter) thereof and the allowable torque Tm thereof fixed (the first problem can be solved by the second example.) Other constructions and operations of the third example are similar to those of the second example. As described above, the fourth example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. (Fifth Example) The fifth example relates to a clutch disc according to the fifth aspect. As shown in Figs. 8 and 9, a clutch disc 10 constituting a friction clutch comprises a clutch hub 11 connected with an output shaft, disc springs 150 each having a clutch facing 16 mounted on the periphery thereof, and damper members 20 each interposed between the clutch hub 11 and the each spring 150, thus applying a torsional characteristic to the clutch disc 10, stopper plates 41 fixed to each disc spring 150 and each damper member 20, first rivets 131 through 134 for fixing the clutch hub 11 and the damper member 20 to each other, and second rivets 14 for fixing the disc spring 150 and the damper member 20 to each other. Reference numeral 429 shown in Fig. 8 denotes a thrust lining interposed between the stopper plate 41 and a damper plate 25. The damper member 20 comprises the damper plate 25 and a damper plate 26 arranged symmetrically by inverting one by 180 ° with respect to the other and having elastically deformable materials 25' and 26', respectively. The elastically deformable material 25' (shown by broken line in Fig. 9) of the damper plate 25 is set to be wider and shorter than the elastically deformable material 26' (shown by solid line in Fig. 9) of the damper plate 26, thus operating in response to a high torque applied to the clutch disc. Because of the width and the length of the damper plates 25 and 26 set as described above, the damper plate 25 is capable of withstanding a high torque applied thereto, but has a smaller allowable angle of torsion than the damper plate 26. In consideration of this construction, as shown in Fig. 9, a play interval δ ' is formed on an engaging hole 253, through which the second rivet 14 is inserted, formed on the damper plate 25 so as to make the angle of torsion of the damper plate 25 smaller than that of the damper plate 26 by the play interval d'. That is, when a low torque is applied to the clutch disc, only the damper plate 26 is twisted and as a result, the second rivet 14 fixed to the periphery of the damper plate 26 moves by the play interval d', thus twisting the damper plate 25 together with the damper plate 26. a torsional characteristic of the clutch disc obtained in the fifth example is as shown by a line in the interval between 0 and B in Fig. 15. The clutch disc 10 of the fifth example has the stopper plate 41, the periphery of which is fixed to the damper plate 26. The stopper plate 41 has in the inner periphery thereof engaging holes 411 through 414 each provided with a play interval as shown in Fig. 10. When the angle of torsion of the damper plate 25 and that of the damper plate 26 are 0, there is an interval δ , greater than a predetermined one, between each of the first rivets 131 through 134 and an edge of each of the engaging holes 411 through 414. When the angle of torsion of the damper plate 25 and that of the clutch disc 26 have reached a predetermined one  m, the edge of each of the engaging holes 411 through 414 is brought into contact with each of the first rivets 131 through 134. Consequently, when the angle of torsion of the damper plate 25 and that of the damper plate 26 have reached the maximum one  m and  m', respectively, the first rivets 131 through 134 are brought into contact with the edge of the engaging holes 411 through 414 of the stopper plate 41, respectively. A torque higher than the allowable maximum torque Tm corresponding to the maximum angle of torsion  m and  m' is not applied to the damper plates 25 and 26 but to the stopper plate 41 through the first rivets 131 through 134. That is, the highest torque to be applied to the damper plates 25 and 26 is the allowable maximum torque Tm. Accordingly, the damper plates 25 and 26 are not required to cope with a possible excessive force generated by the clutch disc 10. Thus, the damper plates 25 and 26 can be allowed to be compact and light. As described above, the fifth example provides the clutch disc applicable to an allowable torque greater than that of the conventional clutch disc and having an angle of torsion greater than that of the conventional one, supposing that the volume and weight thereof is equal to those of the conventional clutch disc. (Sixth Example) In the sixth example, the clutch disc has a three-stage torsional characteristic, as shown in Fig. 15. As shown in Figs. 11 and 12, the damper member 20 comprises a damper plate 25 operating for a low torque, a 26 operating for an intermediate torque, and a 27 operating for a high torque. These damper plates 25, 26, and 27 are arranged side by side. The damper plate 25 operating for the low torque is connected (not shown) with the disc spring 150 having the facing 16 mounted on its periphery. The inner periphery of the damper plate 25 is fixed to the clutch hub 11 by means of a first rivet 13. The damper plate 25 has an engaging hole 253 provided with a play interval δ '. When the angle of torsion of the damper plate 25 is 0, there is an interval δ ', greater than a predetermined one, between a second rivet 14 and an edge of the engaging hole 253 as shown in Fig. 13, whereas when the angle of torsion of the damper plate 25 operating for a low torque has reached a predetermined one, the edge of the engaging hole 253 is brought into contact with the second rivet 14, as shown in Fig. 14. The inner periphery of the damper plate 26 operating for the intermediate torque is fixed to the clutch hub 11 by means of the first rivet 13, while the periphery thereof is connected with the stopper plate 41 by means of the second rivet 14. The damper plate 27 operating for the high torque has an engaging hole 271 provided with a play interval δ ". When the angle of torsion of the damper plate 26 operating for the intermediate torque is 0, there is an interval δ " greater than a predetermined interval between the second rivet 14 and an edge of the engaging hole 271, whereas when the angle of torsion of the damper plates 25 operating for the low torque and that of damper plate 26 operating for the intermediate torque have reached a predetermined one, respectively, the edge of the engaging hole 271 is brought into contact with the second rivet 14, as shown in Fig. 14. Consequently, the second rivet 14 does not contact the engaging hole 253 of the damper plate 25 in the interval 0-A shown in Fig. 15. Thus, the damper plates 26 and 27 are not concerned with the torsional characteristic of the clutch disc 10, but the damper plate 25 contributes to the generation of the torsional characteristic thereof. When the angle of torsion is in the interval A-B shown in Fig. 15 beyond the angle (A), the second rivet 14 contacts the engaging hole 253 of the damper plate 25 but not the engaging hole 271 of the damper plate 27. Thus, the damper plate 27 is not concerned with the generation of the torsional characteristic of the clutch disc 10, while the damper plate 26 is twisted together with the damper plate 25 through the second rivet 14. Thus, in the interval A-B, damper plates 25 and 26 contribute to the generation of the torsional characteristic of the clutch disc 10. When the angle of torsion is in the interval B-C shown in Fig. 15 beyond the angle (B), the second rivet 14 contacts the engaging holes 253 and 271. As a result, the damper plates 26 and 27 are twisted together with the damper plate 25 through the second rivet 14. Therefore, the damper plates 25, 26, and 27 contribute to the generation of the torsional characteristic of the clutch disc 10. Reference symbol δ ' shown in Fig. 13 denotes the angle of torsion (A) of Fig. 15. At the angle δ ' of Fig. 13, the degree of hysteresis is small in the interval 0-A of Fig. 15 because slide does not occur between the stopper plate 41 and the thrust lining 429, whereas the degree of hysteresis is great in the interval A-C of Fig. 15 because sliding friction occurs between the stopper plate 41 and the thrust lining 429. Thus, a performance conforming to a characteristic demanded by a vehicle can be obtained. In the characteristic demanded by the vehicle, a small degree of hysteresis is favorable in a low torque region, while in intermediate and high torque regions, hysteresis for damping action is required. In the sixth example, a pipe-shaped collar 40 is mounted on the second rivet 14, as shown in Fig. 11 to prevent the contact between the damper plates 25 and 27 in the axial direction thereof when the second rivet 14 is caulked. Other constructions and operations of the sixth example are similar to those of the fifth example. In the sixth example, preferably, the damper plate 25 operating for a low torque may be integrated with the disc spring 150 to eliminate the use of a member for clamping the disc spring 150 and the damper plate 25 to each other and produce a compact clutch disc. (Seventh Example) In the seventh example, as shown in Figs. 16 and 17 (a), the configuration of the second rivet 14 of the sixth example is modified to form a second rivet 18 having a large-diameter barrel portion 181 formed in the center of the shaft thereof and the engaging hole 253 (see Fig. 9) of the damper plate 25 operating for the low torque is increased in correspondence to the large-diameter barrel portion 181. The second rivet 18 is formed by caulking both ends 191 and 192 of a member 19 shown in Fig. 17 (b). Other constructions and operations of the seventh example are similar to those of the sixth example. (Eighth Example) In the eighth example which is a modification of the third example shown in Fig. 3, damper plates 28 and 29 are provided at both sides of the clutch hub to increase the thickness of the clutch disc in the axial direction thereof, as shown in Fig. 18. A hysteresis characteristic is applied between the damper plates 28 and 29, between the stopper plate 41 and a flange 111 of the clutch hub 11, and between the damper plate 28 and the flange 111 of the clutch hub 11. In addition, thrust linings 421, 422, and 423 are mounted between the damper plates 28 and 29 to prevent the contact therebetween. A first rivet hole of the damper plate 28 operating for the high torque is provided with a play gap between the second rivet and the edge thereof, similarly to the sixth example. Thus, the clutch disc of the eighth example has a two-stage torsional characteristic. As described in the example 3, because the damper plates 28 and 29 are provided at both sides of the clutch hub to increase the thickness of the clutch disc in the axial direction thereof, the maximum angle of torsion  m of the damper plate 23 can be increased, with the size (diameter) and the allowable torque Tm fixed. Fig. 19 shows the mode of change of the slit 31, the first rivets 131 through 133, and the engaging holes 414 and 413 of the stopper plate 41 by broken lines and chain lines. Other constructions and operations of the eighth example are similar to those of the sixth example. (Ninth Example) In the ninth example which is a modification of the eighth example, an elastic return force is applied between the inner periphery of the damper plates 28 and 29 and the periphery thereof in the axial direction thereof so as to apply a thrust load between the stopper plate 41 and the clutch hub 11 by the damper plates 28 and 29. That is, the damper plates 28 and 29 of the eighth example is in a balanced state in the configuration shown in Fig. 18. An elastic return force acts only when the configuration shown in Fig. 18 changes, whereas the damper plates 28 and 29 of the ninth example have an elastic return force which acts in the direction in which the thickness (d) (see Fig. 5) is reduced in the axial direction of the clutch disc when the damper plates 28 and 29 are in the state shown in Fig. 18. Thus, a frictional force is generated between the clutch hub 11 and the stopper plate 41. This construction eliminates the need for the provision of a friction member for applying a hysteresis characteristic to the torsional characteristic of the clutch disc, thus allowing the clutch disc to be light and manufacturing cost to be reduced. Other constructions and operations of the ninth example are similar to those of the eighth example. Provided is a clutch disc having a superior performance of increasing an allowable torque or an angle of torsion of the damper plate. , According to a first aspect , in a portion proximate to an end of a slit 31 at the peripheral or the inner peripheral side of the damper plate 21, the slit 31 is centrifugally curved or curved toward a clutch axis such that both ends thereof are close to a radius of a concentric circle, respectively. According to a second aspect a damper plate 22 has a plurality of first rivets and a plurality of first rivet holes 254 through 257 formed thereon. The radii (r) of the first rivet holes 254 through 257 gradually decrease as the distance between the clutch axis (C) and each thereof decreases, whereas the radii (r) thereof increase gradually as the distance between the clutch axis (C) and each thereof increases. According to third and fourth aspect , there is a dislocation between the inner periphery of each of annular damper plate 23 and 24 and the periphery thereof in the direction parallel with the clutch axis (C) so that the annular damper plates 23 and 24 have a certain thickness in the direction parallel with the clutch axis (C), respectively.

Claims: A clutch disc (10), constituting a friction clutch, comprising a clutch hub (11) connected with an output shaft, disc springs (150) each having a clutch facing (16) mounted on a peripheral side thereof, and damper members (20) each interposed between the clutch hub (11) and the disc springs (150), thus applying a torsional characteristic to the clutch disc (10), wherein the damper member (20) has a single or a plurality of elastically deformable damper plates (25, 26); characterized by stopper plates (41) fixed to each disc spring (150) and stopper members (131, 132, 133, 134) each fixed to the clutch hub (11), wherein each stopper plate (41) has at the unfixed side thereof at least one play interval-provided cut-out portion or at least one play interval-provided engaging hole (411, 412, 413, 414), each of which has an interval (δ) greater than a predetermined interval between each of the stopper members (131, 132, 133, 134) and an edge of each thereof when the angle of torsion of the damper member (20) is zero, and the edge of each of which is brought into contact with each of the stopper members (131, 132, 133, 134) when the angle of torsion of the damper member (20) has reached a predetermined one (). The clutch disc (10) according to claim 1, comprising first rivets (13) for fixing the clutch hub (11) and the damper member (20) to each other and second rivets (14) for fixing the disc spring (150) and the damper member (20) to each other, wherein each damper member (20) has a plurality of damper plates (25, 26, 27) including a damper plate (25) to which a lower torque is assigned and a damper plate (27) to which a higher torque is assigned; damper plates to which an intermediate torque (26) and the higher torque (27) are assigned are not fixed to the clutch hub (11) or the disc spring (150), excluding the damper plate (25) to which the lowest torque is assigned; a stopper pin (14) is installed on an unfixed side of one of the adjacent damper plates (26, 27) to which the intermediate and higher torques are assigned; and a play interval-provided cut-out portion or a play interval-provided engaging hole (271) which engage the stopper pin (14) is formed on the other of the adjacent damper plates (26, 27), and wherein only when the angle of torsion of the damper plate (25) at the lower torque-applied side has reached a predetermined one (δ), the stopper pin (14) is brought into contact with an edge of the play interval-provided cut-out portion or that of the play interval-provided engaging hole (271) . The clutch disc according to any of claims 1 and 2, wherein the damper member (20) has a plurality of damper plates including a damper plate (25) to which a lower torque is assigned and a damper plate to which a higher torque (27) is assigned; and the damper (25) for applying a torsional characteristic to the clutch disc (10) in a lower torque is integral with the disc spring (150).

Inventors: KOBAYASHI KIYONORI, NAKANE MOTOTAKA, KOBAYASHI, KIYONORI, NAKANE, MOTOTAKA
Applicants: AISIN SEIKI, AISIN SEIKI KABUSHIKI KAISHA
Application year: 1996
Main classification: F16D13
IPC codes: F16F1, F16D13, F16F15