Torque variation absorbing device

Abstract: A torque variation absorbing device comprises a driving plate (11), a flywheel (12) which is rotatable relative to the driving plate (11) through a bearing means (13) in common axis, an elastic member (14) which is disposed in a space (17) defined between the driving plate (11) and the flywheel (12), an inner peripheral portion (11c) of the elastic member (14) secured to either the driving plate (11) or the flywheel (12), and an outer peripheral surface corresponded to an inner peripheral surface (11c) of the other, a plate (15) secured to an outer peripheral surface of the elastic member (14) so as to correspond to the inner peripheral surface (11c), a plurality of rotational members (16) which are rotatabaly disposed between the plate (15) and the inner peripheral surface (11c) in the circumferential direction in such manner that each rotational member (16) is depressed by the elastic force of the elastic member (14), and a clearance which is defined between the plate (15) and the inner peripheral surface (11c), and narrows toward both ends of the plate (15) from a center of the plate (15) so as to obtain a large relative angle of torsion and to improve a performance during the high speed rotation.

Description: BACKGROUND OF THE INVENTION Field of the invention This invention relates to a torque variation absorbing device for use in an automotive vehicle or other vehicles, and more particularly relates to a torque variation absorbing device which is applied to an engine. Description of the Related Art Japanese Patent Publication No. 43176/1981 (Japanese Patent Laid-Open No. 20930/1980) discloses a conventional typed device. The device includes, as shown in Figures 4 and 5, a plurality of coil spring 3 which are disposed between a driving plate 1 and a flywheel 2 in the circumferential direction. The device transmits a torque from the driving plate 1 to the flywheel 2 through the coil springs 3. Moreover, the device absorbs a torque variation by operation of the coil springs 3 for accumlating or releasing a rotational energy according to a relative rotation between the driving plate 1 and the flywheel 2. As a result, vibrations of a vehicle caused by the torque variation can be reduced. It is generally well-known that the torque variation absorbing ability is more effective as torsional rigidity is less small. In this case, torsional rigidity is a coefficient which is represented by the relation between a transmitting torque and an relative angle of torsion between the driving plate 1 and the flywheel 2. Thus, the torque variation absorbing ability depends on the relative angle of torsion between the driving plate 1 and the flywheel 2. However, in the foregoing device, the relative angle of torsion between the driving plate 1 and the flywheel 2 is determined by allowable stress or deflection of the coil spring 3 and position of the coil springs 3 in the device. Therefore, it is difficult to obtain the relative angle of torsion greatly or largely due to the abovementioned design restrictions. In order to solve the abovementioned restrictions, Japanese Patent Laid-Open No. 62724/1984 discloses another conventional typed device. The device includes, as shown in Figure 6, a plurality of elastic members 7 which are rotatably disposed between the outer surface of a driven hub 5 and the inner surface of a driving plate 6. The outer surface of the driven hub 5 has polygonal shape, whereas, the inner surface of the driving plate 6 has circular shape. Therefore, the elastic member 7 is elastically and rotatably compressed between the outer surface and the inner surface by a relative rotation therebetween. As a result, the device transmits a torque from the driving plate 6 to the driven hub 5 by a reaction force of the elastic member 7. However, in this foregoing device, the elastic member 7 cannot tranform largely when a large torque is applied, because the position of the reaction force acting on the elastic member 7 is changed by the rotation of itself. As a result, the device cannot transmit the large torque. Also, the elastic member 7 easily wears due to the rotation of itself. Therefore, the reaction force becomes small in a short period of time. As a result, the device cannot transmit enough torque for a long period of time. Further, during the high speed rotation, the reaction force is decreased by a centrifugal force acting on the elastic member 7. Therefore, the transmitting torque decreases. Thus, the torque transfer efficiency results in decrease. SUMMARY OF THE PRESENT INVENTION It is an object of the invention to provide a torque variation absorbing device which is simple and low in cost and which prevents the generation of noise. This object is achieved by a torque variation aborbing device having the technical features according to claim 1. The gist of the invention consists in that the elastic member is secured to either the driving plate or the flywheel and, in this connection, forms bearing surfaces for a number of rotational members on the side opposite to the side where it is secured. In this connection, the respective ends of the bearing surfaces are directed to the driving plate or the flywheel respectively. Upon a rotation of the driving plate relative to the flywheel the rotational members roll on the bearing surfaces, wherein the contact pressure of the rotational members on the elastic member increases the further the rotational members travel in the direction of the end portions of the bearing surfaces. This design according to the invention is particularly simple and can be produced at low costs too, and it also has a longer service life than the known devices. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view but is partly shown in section, of the device of the invention. Fig. 2 is a sectional view taken substantially along the line A-A in Fig. 1. Fig. 3 is a functional view of a rotational member of the invention. Fig. 4 is a front view but is partly shown in section, of the Related Art of the invention. Fig. 5 is an enlarged operational view of a coil spring of Fig. 4. Fig. 6 is an elevational view but is partly shown in section, of the another Related Art of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION Referring to Fig. 1 and Fig. 2, a driving plate 11 is connected to an engine (not shown). A flywheel 12 is connected to a transmission (not shown) through a clutch (not shown). A hub 12a of the flywheel 12 is located at the outer side of a hub 11a of the driving plate 11 through a ball bearing 13 in common axle. Thereby, the flywheel 12 rotates relative to the driving plate 11. Also, a circular concave portion 11b is formed on the side face of the driving plate 11 at the opposite side of the side face of the flywheel 12. The hub 12a of the flywheel 12 extends into the circular concave portion 11b in the axial direction. Thereby, a space 17 is defined between the outer peripheral surface of the hub 12a and an inner peripheral surface 11c of the driving plate 11. An elastic member 14 made of rubber is disposed in the space 17, the inner peripheral portion of the elastic member 14 is secured to the outer peripheral surface of the hub 12a, the outer peripheral surface of the elastic member 14 is located at the opposite side of the inner peripheral surface 11c of the driving plate 11. The outer peripheral portion of the elastic member 14 is divided by plural cutting portions 14a which have equal pitch in the circumferential direction. In the case of this embodiment, the outer peripheral portion of the elastic member 14 is divided into 6 parts, wherein the outer surface of each devided portion 14b is a plain surface where meets at right angle to the radial direction of this device. Each cutting portion 14a prevents each divided portion 14b of the elastic member 14 from shearing at the both ends of the outer surface of the divided portion 14b. A plate 15 is secured to the outer surface of the divide portion 14a so as to correspond to the inner peripheral surface 11c of the driving plate 11. Thereby, a clearance which is defined between the plate 15 and the inner peripheral surface 11c is the broadest at the center of the plate 15, and becomes narrower as the clearance crosses to each end of the plate 15. Also, the plate 15 is made of steel plate. A first groove 15a is formed on the outer surface of the plate 15. A second groove 11d is formed on the inner peripheral surface 11c of the driving plate 11. A plurality of rotational members 16 are rotatably held by the first groove 15a and the second groove 11d in the circumferential direction in such manner that each rotational member 16 is depressed by the elastic force of each elastic member 14. Therefore, the rotational member 16 is rotated on the first groove 15a according to the relative rotation between the driving plate 11 and the flywheel 12. Also, the rotational member 16 is of ball-shaped or roller-shaped. The shape of the first groove 15a can be modified according to the design concept. Thereby, a torsion-torque characteristic is freely changeable according to the design. Further, both ends of the first groove 15a cross toward the inner peripheral surface 11c in comparison with the center thereof. As a result, the rotational member 16 is prevented from comming off the first groove 15a. The operation according to the abovementioned embodiment of the invention is described bellow. When a torque or a driving force is transmitted from the engine to the driving plate 11, the transmitting torque is applied to the flywheel 12 through the rotational member 16 and the elastic member 14. Also, it is well-known that a torque variation is included in the transmitting torque due to the nature of the engine. When the transmitting torque produced by an explosive stroke of the engine is transmitted to the driving plate 11, the driving plate 11 is accelerated. Thereby the driving plate 11 rotates relative to the flywheel 12 that tries to keep on a constant speed by inertia of the flywheel 12. In Fig. 1, for instance, when the driving plate 11 begins to rotate relative to the flywheel 12 in the counter-clockwise direction (the arrow X), the rotational member 14 also moves on the plate 15 in the leftward direction with its rotation due to the relative rotation. Namely, the rotational member 16 moves toward the direction along which the clearance between the plate 15 and the inner peripheral surface 11c of the driving plate 11 narrows. Therefore, the rotational member 16 radially compresses the elastic member 14 and transmitts the transmitting torque to the flywheel 12. Thus, the transmitting torque is transmitted from the driving plate 11 to the flywheel 12 with a time lag due to the relative rotation. As a result, after the transmitting torque which is transmitted to the driving plate 11 is over or exceeds a maximum torque or a peak torque in the explosive stroke of the engine and the rotational speed of the driving plate 11 begines to decrease, the rotational speed of the flywheel 12 catches up with that of the driving plate 11. Thus, the transmitting torque is transmitted to the flywheel 12 in such manner that the maximum torque or the peak torque is cut. Also, when the transmitting torque in the opposite direction of that in the explosive stroke of the engine is transmitted to the driving plate 11 in a compressive stroke of the engine, in the same way as the abovementioned, (the rotational direction of each parts is opposite.) the transmitting torque is transmitted to the flywheel 12 in such manner that the maximum torque or the peak torque is cut. Consequently, the torque variation can be reduced. The torque variation absorbing device of the invention includes a conventional torque limitting mechanism which cuts excessive torque. Namely, when the excessive torque is applied to the driving plate 11, the rotational member 16 slips on the plate 15. Therefore, the excessive torque is prevented from transmitting to the flywheel 12. Thereby, the device is prevented from being damaged. This is explained by the following equations, as shown in Fig. 3, wherein a force P is depression force of the elastic member 14, a force F is depression force acting on the rotaional member 16 by the force P, a force P' is reaction force of the force F acting on the rotational member 16, and a force F1 is resultant from the force p' and the force F. Thereby, when the relation between F1 and p' is defined as a formula of F1 < µ P' ( µ is a coefficient of friction), the torque is transmitted from the driving plate 11 to the flywheel 12. On the contrary, when the relation between F1 and p' is F1 ≧ µ P', the torque is not transmitted from the driving plate 11 to the flywheel 12 due to the slip of the rotational member 16. Consequently, the torque limitting mechanism of the invention is extremely simple construction. As described in the abovementioned embodiment according to the invention, since the rotational member 16 radially compresses the elastic member 14 and transmitts the transmitting torque to the flywheel 12, the direction of the depression force acting on the elastic member 14 is always the same direction. Therefore, the elastic member 14 can transform largely. Thus, the elastic member 14 can transform in response to the amount of the torque even though during the high speed rotation, the elastic member 14 is also excellent in durability. Moreover, the reaction force of the elastic member 14 is increased by the centrifugal force during the high speed rotation. Therefore, the transmitting torque is increased, the torque tranfer efficiency becomes high in the high speed rotation. As a result, the high speed performance is improved. Also, the shape of the first groove 15a is changeable according to the design. Therefore, a torsion-torque characteristic is freely changeable according to the design. There is not any restrictions in the design in comparison with the conventional elastic member accroding to the coil spring, and the compression force of the elastic member 14 is transformed to the rotational force. Therefore, a large relative angle of torsion is obtained. The rotational member is constantly attached to the plate 15 and the inner peripheral surface 11c of the driving plate 11 even if the direction indicated by the arrow X of the transmitting torque was changed into the opposite direction. Thereby, the device is prevented from making a noise. Moreover, the simple and low cost device is obtained. Still, the elastic member may be secured to the driving plate, and the elastic member may be disposed between an inner peripheral surface of the flywheel and the plate which is fixed to the driving plate. It should be understood that, although the preferred embodiment of the present invention has been described herein in considerable detail, certain modifications, changes, and adaptations may be made by those skilled in the art and that it is hereby intended to cover all modifications, cahnges and adaptations thereof falling within the scope of the appended claims. A torque variation absorbing device comprises a driving plate, a flywheel which is rotatable relative to the driving plate through a bearing means in common axis, an elastic member which is disposed in a space defined between the driving plate and the flywheel, an inner peripheral portion of the elastic member secured to either the driving plate or the flywheel, and an outer peripheral surface corresponded to an inner peripheral surface of the other, a plate secured to an outer peripheral surface of the elastic member so as to correspond to the inner peripheral surface, a plurality of rotational members which are rotatabaly disposed between the plate and the inner peripheral surface in the circumferential direction in such manner that each rotational member is depressed by the elastic force of the elastic member, and a clearance which is defined between the plate and the inner peripheral surface, and narrows toward both ends of the plate from a center of the plate so as to obtain a large relative angle of torsion and to improve a performance during the high speed rotation.

Claims: A torque variation absorbing device, comprising: a driving plate (11); a flywheel (12) which is rotatable relative to said driving plate (11) through a bearing means (13) in a common axis; an elastic member (14) which is disposed in a space (17) defined between said driving plate (11) and said flywheel (12), and a plurality of rotational members (16) which are rotatably disposed between said driving plate (15) and said fly wheel (12), characterized in that an inner peripheral portion of said elastic member (14) is secured to either said driving plate (11) or said flywheel (12), and an outer peripheral surface corresponds to an inner peripheral surface (11c) of the other; that a plate (15) is secured to an outer peripheral surface of said elastic member (14) so as to correspond to said inner peripheral surface (11c);that said rotational members (16) are rotatably disposed between said plate (15) and said inner peripheral surface (11c) in the circumferential direction in such a manner that each of said rotational members (16) is depressed by the elastic force of said elastic member (14); and that a clearance is defined between said plate (15) and said inner peripheral surface (11c), and narrows toward both ends of said plate (15) from a center of said plate (15). A torque variation absorbing device according to claim 1, wherein: said plate (15) and said rotational member (16) are made of steel plate. A torque variation absorbing device according to claim 1, wherein: an outer peripheral portion of said elastic member (14) is divided by a plurality of cutting portions (14a) equally pitched in the circumferential direction, and the outer surface of each divided portion (14b) is of a plain surface which is at right angle to the radial direction of this device. A torque variation absorbing device according to claim 1, wherein: said plate (15) includes a first groove (15a) which is formed on the outer surface of said plate (15). A torque variation absorbing device according to claim 4, wherein: said driving plate (11) includes a second groove (11d) which is formed on said inner peripheral surface (11c) thereof, said rotational member (16) is rotatably held by said first groove (15a) and said second groove (11d) in the circumferential direction in such a manner that each of said rotational members (16) is depressed by the elastic force of each of said elastic members (14). A torque variation absorbing device according to claim 4, wherein: both ends of said first groove (15a) are bent toward said inner peripheral surface (11c) in comparison with the center thereof.

Inventors: KOBAYASHI KIYONORI, NAKANE MOTOTAKA, KOBAYASHI, KIYONORI, NAKANE, MOTOTAKA
Applicants: AISIN SEIKI, AISIN SEIKI KABUSHIKI KAISHA
Application year: 1991
Main classification: F16F15
IPC codes: F16F15, F16D13