Dynamic damper

Abstract: Disclosed are dynamic dampers for suppressing harmful vibrations excited in a rotary shaft which enable to complete the installation thereof around the rotary shaft by only fixing one end thereof on the rotary shaft without imparing the performances thereof. One of the dynanic dampers are provided with elastic members (11, 12) disposed at both ends thereof, only one of the elastic members (11) has an engaging grove (15a) going round the outer surface thereof, and the inner diameter of one of the elastic members is made larger than that of the other elastic member (⊘A, ⊘B). The other dynamic damper is provided with elastic members disposed at both ends thereof, the elastic members have a supporting portion and an elastic portion, and only one of the supporting portion has a fixing portion having an engaging groove (15a) going round the outer surface thereof and an intermediate portion, the length of the intermediate portion is larger than the length of the supporting portion of the other elastic member in the axial direction of the rotary shaft. With these arrangenments, the dynamic dampers are free from the influence of the deformations resulting from the fixing at one end thereof only. Thus, the dynamic dampers enable to reduce the number of component parts, improve the assembly operability and reduce the manufacturing cost as well.

Description: BACKGROUND OF THE INVENTION [Field of the Invention] The present invention relates to a dynamic damper installed around a rotary shaft, such as a drive shaft of an automobile. The dynamic damper is for suppressing harmful vibrations occurred in the rotary shaft. More particularly, the present invention relates to a dynamic damper which enables to complete the installation thereof around the rotary shaft by fixing one end thereof only to the rotary shaft while maintaining the performances thereof, thereby reducing the manufacturing cost and improving the assembly operability. [Related Art Statement] When a rotary shaft, such as a drive shaft and a propeller shaft of an automobile and the like, rotates, unbalanced rotations occur. As a result of the unbalanced rotations, there occurs harmful vibrations like bending vibrations and torsional vibrations. It is naturally preferred that the harmful vibrations should not occur at all. However, various dynamic dampers have been widely used to suppress the harmful vibrations. The dynamic dampers work in the following manner: The dynamic dampers adjust their intrinsic frequencies to the dominant frequencies of the harmful vibrations excited in the rotary shaft, convert the vibration energy of the rotary shaft to the vibration energy of the dynamic dampers by resonance, and absorbs the vibration energy of the rotary shaft. Such a dynamic damper according to the preambles of the independent claims 1 and 4 of the present invention is shown in US 1,934,597. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a dynamic damper which enables to complete the installation thereof around the rotary shaft by fixing one end thereof only, thereby reducing the manufacturing cost and improving the assembly operability. In one aspect of the present invention, a dynamic damper according to the present invention is defined by claim 1. In the dynamic damper according to the one aspect of the present invention, the inner diameter of the first fixing portion of the first elastic member is larger than the inner diameter of the second fixing portion of the second elastic member, and only the first fixing portion of the first elastic member has an engaging groove formed in a ring shape in a manner going round the outer surface of the first fixing portion. When a dynamic damper employs such arrangements, a tightening allowance for fixing the first fixing portion of the first elastic portion on the rotary shaft can be set smaller than a tightening allowance for fixing the second fixing portion of the second elastic member thereon. As a result, the first fixing portion of the first elastic portion of the dynamic damper can be engaged with the rotary shaft in a degree equal to a degree of the engagement between the second fixing portion of the second elastic portion and the rotary shaft, thereby eliminating unbalance between the degree of engagements at both ends of the dynamic damper. Therefore, even when only the first fixing portion of the first elastic portion is fixed on the rotary shaft with a fixing band, the shear spring constants exhibited by the first elastic portion of the first elastic member agree with the shear spring constants exhibited by the second elastic portion of the second elastic member. Hence, no resonance occurs except at the intrinsic frequency of the dynamic damper adjusted to the dominant frequencies of the harmful vibrations excited in the rotary shaft. In this way, the dynamic damper according to the one aspect of the present invention enables to complete the installation thereof around the rotary shaft by fixing one end thereof only. Accordingly, the number of the component parts and the man-hour requirements for the assembly have been reduced. Therefore, it is possible to improve the assembly operability and reduce the manufacturing cost. In another aspect of the present invention, a dynamic damper according to the present invention is defined by claim 4. When a dynamic damper employs such arrangements and when the dynamic damper is installed around the rotary shaft by installing a fixing band only around the supporting portion of the elastic member in which the fixing portion is provided and the engaging groove is formed on the outer surface of the fixing portion in a manner going round the outer surface thereof, the intermediate portion blocks, relieves and absorbs the influences resulting from the deformations of the fixing portion thus fixed. Accordingly, the influences do not reach the elastic portion of the elastic member in which the fixing portion and the intermediate portion are provided. Therefore, when the rotary shaft rotates, the shear spring constants exhibited by the elastic portion of one of the elastic members, in which the supporting portion is provided with the fixing portion, the fixing portion is provided with the engaging groove going round the outer surface thereof, the intermediate portion is disposed between the fixing portion and the elastic portion, and the length of the intermediate portion in the axial direction of the rotary shaft is made at least equal to or larger than that of the supporting portion of the other elastic member, agree with the shear spring constants exhibited by the elastic portion of the other elastic member which is free from such arrangements. Hence, no resonance occurs except at the intrinsic frequency of the dynamic damper adjusted to the dominant frequencies of the harmful vibrations excited in the rotary shaft. Likewise, the dynamic damper according to another aspect of the present invention also enables to complete the installation thereof around the rotary shaft by fixing one end thereof only. Accordingly, the number of the component parts and the man-hour requirements for the assembly have been also reduced. Therefore, it is also possible to improve the assembly operability and reduce the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure 1 is a cross sectional view of a dynamic damper of a first preferred embodiment according to the present invention, in which the dynamic damper is cut along the central axis thereof; Figure 2 is a cross sectional view of the dynamic damper thereof installed around a rotary shaft; Figure 3 is a cross sectional view of a dynamic damper of a second preferred embodiment according to the present invention, in which the dynamic damper is cut along the central axis thereof; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Having generally described the present invention, a further understanding can be obtained by reference to certain specific preferred embodiments which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. [First Preferred Embodiment] A dynamic damper 1 of a first preferred embodiment according to the present invention will be hereinafter described with reference to Figures 1 and 2. Figure 1 is a cross sectional view of the dynamic damper 1 of the first preferred embodiment, in which the dynamic damper is cut along the central axis thereof. Figure 2 is a cross sectional view of the dynamic damper thereof installed around a rotary shaft. The dynamic damper 1 of the first preferred embodiment comprises: a mass member 10 formed in a cylindrical shape; a first elastic member 11 formed integrally with the mass member 10 and a second elastic member 12 formed integrally with the mass member 10. This dynamic damper 1 is formed integrally, and has a cylindrical shape as a whole in which the outer diameter at the middle portion is larger than the outer diameters at both ends. The mass member 10 has an inner surface larger than the outer surface of a rotary shaft "S", and is inserted into the rotary shaft "S". The mass member 10 has a mass body made of metal such as a thick-wall cylinder-shaped steel pipe. When the dynamic damper 1 is molded integrally by vulcanization molding with a mold, the outer and inner surfaces of the mass member 10 are coated with a rubber material such as natural rubber and the like constituting the first and second elastic members 11 and 12 by the thickness of approximately 1 mm. The cylindrical mass body made of metal thus coated with the rubber material is disposed around the outer circumference of the rotary shaft "S", and integrally works as the mass member 10. Here, there is formed a clearance of approximately 1.5 mm between the inner surface of the mass member 10 and the outer surface of the rotary shaft "S". The first elastic member 11 has a first fixing portion 15 formed in a ring shape and a first elastic portion 13 formed in a hollow truncated cone, and is formed of a rubber material such as natural rubber and the like. The first fixing portion 15 is inserted into and supported by the rotary shaft "S". The inner diameter (⊘A) of the ring shaped first fixing portion 15 is formed so that it is larger than the inner diameter (⊘B) of the second fixing portion 16 of the second elastic member 12 (described later) in the following manner. Namely, when the outer diaseter of the rotary shaft "S" is ⊘C, the inner diameter (⊘A) of the first fixing portion 15 of the first elastic portion 11 is set according to the following formula: ⊘A = ⊘C - (0.5 to 1.0) (mm) , and the inner diameter (⊘B) of the second fixing portion 16 of the second elastic member 12 is set according to the following formula: ⊘B = ⊘C - (1.2 to 2.5) (mm) . Thus, ⊘A is set larger than ⊘B, i.e., ⊘A > ⊘B. Here, it is preferable to set the inner diameter (⊘A) of the first fixing portion 15 of the first elastic portion 11 so as to fall in the range of 94 to 99 % of the dimension of the outer diameter (⊘C) of the rotary shaft "S", and to set the inner diameter (⊘B) of the second fixing portion 16 of the second elastic portion 12 so as to fall in the range of 87 to 96 % of the dimension of the outer diameter (⊘C) of the rotary shaft "S", and to set ⊘A larger than ⊘C (⊘A > ⊘B). Thus, the tightening allowance for fixing the first fixing portion 15 of the first elastic member 11 around the rotary shaft "S" is set smaller than the tightening allowance for fixing the second fixing portion 16 of the second elastic member 12 around the rotary shaft "S". Further, a ring-shaped engaging groove 15a is formed on the outer surface of the first fixing portion 15 in a manner going round the outer surface thereof. The first elastic portion 13, formed in a hollow truncated cone shape, connects the first fixing portion 15 of the first elastic member 11 and one end of the mass member 10 integrally in the following manner. Namely, the inner surface 13a of the first elastic portion 13 is formed in a tapered shape, i.e., the inner surface 13a of the first elastic portion 13 starts at the inner surface end of the first fixing portion 15 to be brought into close contact with the outer surface of the rotary shaft "S", and reaches the inner surface end of the mass member 10 while gradually increasing the inner diameter thereof. Further, the outer surface 13b of the first elastic portion 13 is formed also in a tapered shape, i.e., the outer surface 13b of the first elastic portion 13 starts at the outer surface end of the first fixing portion 15, and reaches the outer surface end of the mass member 10 while gradually increasing the outer diameter thereof. The second elastic member 12 has a second fixing portion 16 formed in a ring shape and a second elastic portion 14 formed in a hollow truncated cone, and is formed of a rubber material such as natural rubber and the like. The second fixing portion 16 is inserted into and supported by the rotary shaft "S". The inner diameter (⊘B) of the ring-shaped second fixing portion 16 is formed so that it is smaller than the inner diameter (⊘A) of the first fixing portion 15 of the first elastic member 11 in the above-mentioned manner. Namely, the tightening allowance for fixing the second fixing portion 16 of the second elastic member 12 around the rotary shaft "S" is set larger than the tightening allowance for fixing the first fixing portion 15 of the first elastic member 11 around the rotary shaft "S". The second elastic portion 14, formed in a hollow truncated cone shape, connects the second fixing portion 16 of the second elastic member 12 and one end of the mass member 10 integrally in the following manner. Namely, the inner surface 14a of the second elastic portion 14 is formed in a tapered shape, i.e., the inner surface 14a of the second elastic portion 14 starts at the inner surface end of the second fixing portion 16 to be brought into close contact with the outer surface of the rotary shaft "S", and reaches the inner surface end of the mass member 10 while gradually increasing the inner diameter thereof. Further, the outer surface 14b of the second elastic portion 14 is forned also in a tapered shape, i.e., the outer surface 14b of the second elastic portion 14 starts at the outer surface end of the second fixing portion 16, and reaches the outer surface end of the mass member 10 while gradually increasing the outer diameter thereof. The dynamic damper 1 arranged as described above is installed around the rotary shaft "S" and used in the following manner. When installing the dynamic damper 1 around the rotary shaft "S", the inner surface of the first fixing portion 15 of the first elastic member 11 of the dynamic damper 1 is placed on the shaft end of the rotary shaft "S" before mounting the rotary shaft "S" on an automobile body. Because the inner diameter of the first fixing portion 15 of the first elastic member 11 is made smaller than the outer diameter of the rotary shaft "S" by 0.5 to 1.0 mm, the rotary shaft "S" is press-fitted into the first fixing portion 15 while pressing and expanding the inner surface of the first fixing portion 15. Similarly, because the inner diameter of the second fixing portion 16 of the second elastic member 12 is made smaller than the outer diameter of the rotary shaft "S" by 1.2 to 2.5 mm, the rotary shaft "S" is press-fitted into the second fixing portion 16 while further pressing and expanding the inner surface of the second fixing portion 16, when the rotary shaft "S" is further inserted into the dynamic damper 1. After disposing the dynamic damper 1 at a predetermined position of the rotary shaft "S" in this manner, the engaging groove 15a formed in the first fixing portion 15 is fixed by installing the fixing band 15b therearound, whereby the dynamic damper 1 is fixed around the rotary shaft "S". Figure 2 illustrates the cross sectional view of the dynamic damper 1 installed around the rotary shaft "S" in the above-mentioned manner. In the state illustrated in Figure 2, the first fixing portion 15 of the first elastic member 11 of the dynamic damper 1 is firmly pressed by the fixing band 15b in the central axis direction thereof. Accordingly, the degree of the force fixing the first fixing portion 15 of the first elastic member 11 around the rotary shaft "S" is made substantially equal to the degree of the force fixing the second fixing portion 16 of the second elastic member 12 around the rotary shaft "S" by installing the fixing band 15b around the engaging groove 15a of the first fixing portion 15 of the first elastic member 11. In this way, the first fixing portion 15 of the first elastic member 11 and the second fixing portion 16 of the second elastic member 12 are brought into close contact with the rotary shaft "S". Here, the degrees of the forces fixing the first fixing portion 15 and the second fixing portion 16 around the rotary shaft "S" are made substantially equal to each other, and accordingly the first fixing portion 15 and the second fixing portion 16 can be brought into close contact with the rotary shaft "S". These effects result from the arrangement that the inner diameter of the first fixing portion 15 is made larger than the inner diameter of the second fixing portion 16. When the rotary shaft "S" rotates and harmful vibrations are excited, the mass member 10 of the dynamic damper 1 resonates because the intrinsic frequency of the mass menber 10 is adjusted to the frequencies of the harmful vibrations. The adjustment of the intrinsic frequency is performed by varying the configurations of the first elastic portion 13 of the first elastic member 11 and the second elastic portion 14 of the second elastic member 12. Here, only the first fixing portion 15 of the first fixing member 11 are fixed by the fixing band 15b, but the deformation of the first elastic portion 13 of the first elastic member 11 does not differ from the deformation of the second elastic portion 14 of the second elastic member 12 during the rotation of the rotary shaft "S" because the degree of the engagement between the first fixing portion 15 and the rotary shaft "S" and the degree of the engagement between the second fixing portion 16 and the rotary shaft "S" are equal to each other as aforementioned. Therefore, the shear spring constants exhibited in the first elastic portion 13 of the first elastic member 11 do not differ from the shear spring constants exhibited in the second elastic portion 14 of the second elastic member 12, and accordingly no resonance occurs except at the intrinsic frequency of the dynamic damper 1 adjusted to the dominant frequencies of the harmful vibrations excited in the rotary shaft "S". In this way, the dynamic damper 1 of the first preferred embodiment can be fixed around the rotary shaft "S" by installing the fixing band 15b only around the fixing portion 15 of the first elastic member 11 without imparing its inherent performances. As a result, the number of the component parts and the man-hour requirements for the assembly have been reduced. Therefore, the assembly operability can be improved and the manufacturing cost can be reduced by employing the dynamic damper 1 of the first preferred embodiment arranged in the above-mentioned manner. [Second Preferred Embodiment] A dynamic damper of a second preferred embodiment according to the present invention will be hereinafter described with reference to Figure 3. Figure 3 is a cross sectional view of the dynamic damper of the second preferred embodiment, in which the dynamic damper is cut along the central axis thereof. The dynamic damper 2 of the second preferred embodiment comprises: a mass member 20 formed in a cylindrical shape; and a pair of elastic members 21 and 22 disposed at both ends of the mass member 20 and formed integrally with the mass member 20. This dynamic damper 2 is formed integrally, and has a cylindrical shape as a whole in which the outer diameter at the middle portion is larger than the outer diameters at both ends. Further, only the elastic member 21 of the pairs of the elastic members 21 and 22 is provided with a supporting portion 25 which has a fixing portion 27 having an engaging groove 27a going round the outer surface thereof and an intermediate portion 29 disposed between the fixing portion 27 and an elastic portion 23. Furthermore, the length (A) of the intermediate portion 29 in the axial direction of the rotary shaft "S" is made larger than the length (B) of a supporting portion 26 of the other elastic member 22 in the axial direction of the rotary shaft "S" by 3 mm. Here, when the length (B) of the supporting portion 26 of the other elastic member 22 in the axial direction of the rotary shaft "S" can be set at 5 mm or more, the length (A) of the intermediate portion 29 in the axial direction of the rotary shaft "S" may be made equal to the length (B) of the supporting portion 26 in the axial direction of the rotary shaft "S". The mass member 20 has an inner surface larger than the outer surface of a rotary shaft "S", and is inserted into the rotary shaft "S". The mass member 20 has a mass body made of metal such as a thick-wall cylinder-shaped steel pipe. When the dynamic damper 2 is molded integrally by vulcanization molding with a mold, the outer and inner surfaces of the mass member 20 are coated with a rubber material such as natural rubber and the like constituting the elastic members 21 and 22 by the thickness of approximately 1 mm. The cylindrical mass body made of metal thus coated with the rubber material is disposed around the outer circumference of the rotary shaft "S", and integrally works as the mass member 20. Here, there is formed a clearance of approximately 1.5 mm between the inner surface of the mass member 20 and the outer surface of the rotary shaft "S". The elastic member 21 has the supporting portion 25 formed in a ring shape and the elastic portion 23 formed in a hollow truncated cone, and is formed of a rubber material such as natural rubber and the like. The ring-shaped supporting portion 25 is inserted into and supported by the rotary shaft "S". Here, the inner diameter of the ring-shaped supporting portion 25 is made smaller than the outer diameter of the rotary shaft "S" by 1 mm. The ring-shaped supporting portion 25 further has the fixing portion 27 having tle engaging groove 27a going round the outer surface thereof and the intermediate portion 29 disposed between the fixing portion 27 and the elastic portion 23 and connecting them integrally. As aforementioned, the length (A) of the intermediate portion 29 in the axial direction of the rotary shaft "S" is made larger than the length (B) of the supporting portion 26 of the other elastic member 22 by approximately 3 mm, i.e., "A" > "B". The elastic portion 23, formed in a hollow truncated cone shape, connects the intermediate portion 29 of the supporting portion 25 of the elastic member 21 and one end of the mass member 20 integrally in the following manner. Namely, the inner surface 23a of the elastic portion 23 is formed in a tapered shape, i.e., the inner surface 23a of the elastic portion 23 starts at the inner surface end of the intermediate portion 29 to be brought into close contact with the outer surface of the rotary shaft "S", and reaches the inner surface end of the mass member 20 while gradually increasing the inner diameter thereof. Further, the outer surface 23b of the elastic portion 23 is formed also in a tapered shape, i.e., the outer surface 23b of the elastic portion 23 starts at the outer surface end of the intermediate portion 29, and reaches the outer surface end of the mass member 20 while gradually increasing the outer diameter thereof. The other elastic member 22 has the supporting portion 26 formed in a ring shape and an elastic portion 24 formed in a hollow truncated cone, and is formed of a rubber material such as natural rubber and the like. The ring-shaped supporting portion 26 is inserted into and supported by the rotary shaft "S". Here, the inner diameter of the ring-shaped supporting portion 26 is made smaller than the outer diameter of the rotary shaft "S" by 1 mm. The other elastic member 22 differs from the elastic member 21 in that the ring-shaped supporting portion 26 does not have a fixing portion having an engaging groove going round the outer surface thereof and an intermediate portion, and that the supporting portion 26 and the elastic portion 24 are directly connected without an intermediate portion. As aforementioned, the length (B) of the supporting portion 26 of the elastic member 22 in the axial direction of the rotary shaft "S" is made smaller than the length (A) of the intermediate portion 29 of the elastic member 21 by approximately 3 mm. The elastic portion 24, formed in a hollow truncated cone shape, connects the supporting portion 26 of the elastic member 22 and one end of the mass member 20 integrally in the following manner. Namely, the inner surface 24a of the elastic portion 24 is formed in a tapered shape, i.e., the inner surface 24a of the elastic portion 24 starts at the inner surface end of the supporting portion 26 to be brought into close contact with the outer surface of the rotary shaft "S", and reaches the inner surface end of the mass member 20 while gradually increasing the inner diameter thereof. Further, the outer surface 24b of the elastic portion 24 is formed also in a tapered shape, i.e., the outer surface 24b of the elastic portion 24 starts at the outer surface end of the supporting portion 26, and reaches the outer surface end of the mass member 20 while gradually increasing the outer diameter thereof. The dynamic damper 2 arranged as described above is installed around the rotary shaft "S" and used in the following manner. When installing the dynamic damper 2 around the rotary shaft "S", the central axis bore of the supporting portion 25 of the elastic member 21 of the dynamic damper 2 is placed on the shaft end of the rotary shaft "S" before mounting the rotary shaft "S" on an automobile body. Because the inner diameter of the supporting portion 25 of the elastic member 21 is made smaller than the outer diameter of the rotary shaft "S" by 1.0 mm, the rotary shaft "S" is press-fitted into the supporting portion 15 while pressing and expanding the inner surface of the supporting portion 25. Similarly, because the inner diameter of the supporting portion 26 of the elastic member 22 is also made smaller than the outer diameter of the rotary shaft "S" by 1.0 mm, the rotary shaft "S" is press-fitted into the supporting portion 26 while similarly pressing and expanding the inner surface of the supporting portion 26, when the rotary shaft "S" is further inserted into the dynamic damper 2. After disposing the dynamic damper 2 at a predetermined position of the rotary shaft "S" in this manner, the engaging groove 27a formed in the supporting portion 25 of the elastic member 21 is fixed by installing the fixing bands 27b therearound, whereby the dynamic damper 2 is fixed around the rotary shaft "S". Figure 3 illustrates the cross sectional view of the dynamic damper 2 installed around the rotary shaft "S" in the above-mentioned manner. In the state illustrated in Figure 3, the inner surface of the supporting portion 25 of the elastic member 21 of the dynamic damper 2 and the inner surface of the supporting portion 26 of the elastic member 22 thereof are brought into close contact with the outer surface of the rotary shaft "S". Further, the fixing portion 27 of the supporting portion 25 of the elastic member 21 is pressed firmly and deformed in the central axis direction thereof by the fixing band 17b which is installed around the engaging groove 27a going round the outer surface of the fixing portion 27. However, the deformation of the fixing portion 27 thus fixed is blocked, relieved and absorbed, because the intermediate portion 29 is disposed between the fixing portion 27 and the elastic portion 23 and because the length (A) of the intermediate portion 29 in the axial direction of the rotary shaft "S" is made larger than the length (B) of the supporting portion 26 of the elastic member 22 by approximately 3 mm. Accordingly, the deformation of the fixing portion 27 fixed with the fixing band 27b does not influence on the elastic portion 23 of the elastic member 21 at all. When the rotary shaft "S" rotates and harmful vibrations are excited, the mass member 20 of the dynamic damper 2 resonates because intrinsic frequency of the mass member 20 is adjusted to the frequencies of the harmful vibrations. The adjustment of the intrinsic frequency is performed by varying the configurations of the elastic portion 23 of the elastic member 21 and the elastic portion 24 of the elastic member 22. Here, only the fixing portion 27 of the supporting portion 25 are pressed and fixed firmly with the fixing band 17b in the central direction, but the deformation of the fixing portion 27 thus pressed and fixed firmly does not interfere with the configuration deformations of the elastic portion 23 of the elastic member 21 during the adjustment of the intrinsic frequency of the dynamic damper 2. Hence, no difference occurs between the configuration deformations of the elastic portion 23 of the elastic member 21 and the configuration deformations of the elastic portion 24 of the elastic member 22 during the adjustment of the intrinsic frequency of the dynamic damper 2. Therefore, the shear spring constants exhibited in the elastic portion 23 agree with the shear spring constants exhibited in the elastic portion 24, and accordingly no resonance occurs except at the intrinsic frequency of the dynamic damper 2 adjusted to the dominant frequencies of the harmful vibrations excited in the rotary shaft "S". In this way, the dynamic damper 2 of the second preferred embodiment can be also fixed around the rotary shaft "S" by installing the fixing band 27b only around the fixing portion 27 of the supporting portion 25 of the elastic member 21 without imparing its inherent performances. As a result, the number of the component parts and the man-hour requirements for the assembly have been also reduced. Therefore, the assembly operability can be also improved and the manufacturing cost can be also reduced by employing the dynamic damper 2 of the second preferred embodiment arranged in the above-mentioned manner. Disclosed are dynamic dampers for suppressing harmful vibrations excited in a rotary shaft which enable to complete the installation thereof around the rotary shaft by only fixing one end thereof on the rotary shaft without imparing the performances thereof. One of the dynamic dampers are provided with elastic members disposed at both ends thereof, only one of the elastic members has an engaging grove going round the outer surface thereof, and the inner diameter of one of the elastic members is made larger than that of the other elastic member. The other dynamic damper is provided with elastic members disposed at both ends thereof, the elastic members have a supporting portion and an elastic portion, and only one of the supporting portion has a fixing portion having an engaging groove going round the outer surface thereof and an intermediate portion, the length of the intermediate portion is larger than the length of the supporting portion of the other elastic member in the axial direction of the rotary shaft. With these arrangements, the dynamic dampers are free from the influence of the deformations resulting from the fixing at one end thereof only. Thus, the dynamic dampers enable to reduce the number of component parts, improve the assembly operability and reduce the manufacturing cost as well.

Claims: A dynamic damper (1) and a rotatable shaft (S) comprising: a rotatable shaft (S) ; a cylindrically shaped mass member (10) surrounding the shaft (S) and having an inner diameter larger than the outer diameter of the rotatable shaft (S) ; a first elastic member (11) having a ring-shaped first fixing portion (15) and a first elastic portion (13) integrally connecting said first fixing portion (15) and one end of said mass member (10) , the first elastic member (11) being mounted on the shaft (S) by said first fixing portion (15) ; a second elastic member (12) having a ring-shaped second fixing portion (16) and a second elastic portion (14) integrally connecting said second fixing portion (16) and the other end of said mass member (10) , the second elastic member (12) being mounted on the shaft (S) by said second fixing portion (16) ; characterized in that said first fixing portion (15) of said first elastic member (11) has an annular groove (15a) formed in the outer surface thereof, and the inner diameter (⊘A) of said first fixing portion (15) is larger than the inner diameter (⊘B) of said second fixing portion (16) of said second elastic member (12) . The dynamic damper according to claim 1, wherein said inner diameter (⊘A) of said first fixing portion (15) is smaller than the outer diameter of said rotary shaft (S) by 0.5 to 1.0 mm, and said inner diameter (⊘B) of said second fixing portion (16) is smaller than the outer diameter (⊘C) of said rotary shaft (S) by 1.2 to 2.5 mm. The dynamic damper according to claim 1, wherein the following conditions are to be fulfilled: said inner diameter (⊘A) of said first fixing portion (15) is larger than said inner diameter (⊘B) of said second fixing portion (16) of said second elastic member (12) , said inner diameter (⊘A) of said first fixing portion (15) falls in the range of 94 to 99 % of said outer diameter (⊘C) of said rotary shaft (S) , wherein said inner diameter (⊘B) of said second fixing portion (16) falls in the range of 87 to 96 % of said outer diameter (⊘C) of said rotary shaft (S) . A dynamic damper (2) and a rotatable shaft (S) comprising: a rotatable shaft (S) ; a cylindrically shaped mass member (20) surrounding said shaft (S) and having an inner diameter larger than the outer diameter of said rotatable shaft (S) ; a first elastic member (21) having a ring-shaped first supporting portion (25) and a first elastic portion (23) integrally connecting said first supporting portion (25) and one end of said mass member (20) , wherein said first elastic member (21) is mounted on said shaft (S) by said first supporting portion (25) ; a second elastic member (22) having a ring-shaped second supporting portion (26) and a second elastic portion (24) integrally connecting said second supporting portion (26) and the other end of said mass member (10) , wherein said second elastic member (22) is mounted on the shaft (S) by said second supporting portion (26) and the inner surface of each of said supporting portions (25, 26) is in contact with the outer surface of said rotatable shaft (S) and the outer portion of each of said supporting portions (25, 26) extends parallel to the axis of said shaft (S) , characterized in that, said first supporting portion (25) has a fixing portion (27) having an engaging groove (27a) formed in a ring shape in a manner going round the outer surface thereof and an intermediate portion (29) having a length (A) in the axial direction and beeing disposed between said fixing portion (27) and said first elastic portion (23) , wherein the end of said fixing portion (27) adjacent to said intermediate portion (29) is delimited by said groove (27a) and in that said second supporting portion (26) has a length (B) in the axial direction, wherein said length (A) is equal or larger than said length (B) . The dynamic damper according to claim 4, wherein the length (A) of said intermediate portion (29) of said first supporting portion (25) is larger than the length (B) of said supporting portion (26) by at least 3 mm. The dynamic damper according to claim 1 or claim 4, wherein a fixing band (15b, 27b) is installed only around said engaging groove (15a, 27a) of said fixing portion (15, 27) of said first elastic member (11, 21) , and said fixing portion (15, 27) is fixed around said rotary shaft by the tightening force of said fixing band (15b, 27b) . The dynamic damper according to claim 1 or claim 4, wherein said mass member (10, 20) and said pair of said elastic members (11, 12; 21, 22) are integrally formed of a rubber material.

Inventors: HAMADA MASAAKI TOKAI RUBBER IN, HAMADA, MASAAKI, TOKAI RUBBER INDUSTRIES, LTD.
Applicants: TOKAI RUBBER IND LTD, TOKAI RUBBER INDUSTRIES, LTD.
Application year: 1990
Main classification: F16F15
IPC codes: F16F15