Structure for Mounting Damper on Rotary Shaft

1. Field of the Invention

This invention relates to a structure for mounting a damper on a rotary shaft such as a drive shaft, propeller shaft and the like for a vehicle.

2. Description of the Prior Art

For the purpose of reducing vibration and noise of a drive line, there is a case where a mass damper is mounted on a rotary shaft such as a drive shaft and a propeller shaft (FORD FIESTA WORKSHOP MANUAL, '83.7, for example). This mass damper, as shown in FIG. 9 or 10, consists of two damper pieces 2. Each damper piece 2 is disposed around a rotary shaft 1, bolts 3 are inserted into the respective opposite ends and nuts 4 are screwed onto the bolts 3. Thus, the damper pieces 2 are mounted on the rotary shaft 1. Under such a mounting condition, an inner peripheral surface 5 of each damper piece 2 is brought into contact with the rotary shaft 1, so that the mass damper is held by the rotary shaft 1 with frictional force of contact portions. The inner peripheral surface 5 of each damper 2 is formed to have a V-shaped section. As shown in FIG. 10, the inner peripheral surface 5 of the damper piece 2 may be formed into a cylindrical surface to conform to a surface of the rotary shaft 1.

When the rotary shaft is twisted at the time of transmission of torque, relative displacement or relative slip occurs between the inner peripheral surface of each damper piece and the rotary shaft in the damper as noted above. Since the relative displacement or slip occurs repeatedly, fretting is generated.

Accordingly, an object of the present invention is to provide a damper mounting structure for preventing the generation of fretting by restraining the relative displacement between an inner peripheral surface of a damper and a rotary shaft to be as small as possible when the rotary shaft is twisted at the time of transmission of torque.

A damper mounting structure according to the present invention comprises a damper consisting of a plurality of damper pieces capable of being disposed around a rotary shaft and a plurality of connecting means. Each damper piece has a mass portion which is out of contact with the rotary shaft and a mounting portion having rigidity lower than that of the mass portion and mounted on the rotary shaft. The respective mounting portions of the adjacent damper pieces are connected with each other by the connecting means.

In a preferred embodiment, an inner peripheral surface of the mass portion of each damper piece is formed as an inclined surface diverging toward an opening end. A portion of the rotary shaft, on which the damper pieces are mounted, opposite to the mass portion is formed to have a diameter smaller than that of a portion of the rotary shaft opposite to the mounting portion.

When the rotary shaft is twisted at the time of transmission of torque, the mounting portion which is formed to be low in rigidity follows torsional deformation generated on the rotary shaft in a contact portion between the mounting portion of each damper piece and the rotary shaft subjected to deformation, so that no substantial relative slip between the mounting portion and the rotary shaft is generated, or is restrained to be small if generated. On the other hand, since the mass portion is out of contact with the rotary shaft, the relative slip is not generated. Thus, the generation of fretting can be prevented to improve the durability of the damper and rotary shaft.

The foregoing and other objects and features of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which:

FIGS. 1 through 6 show a first embodiment of the present invention, respectively, in which FIG. 1 is a perspective view showing an assembled damper, FIG. 2 is a sectional view showing the assembled damper, FIG. 3 is a side view showing a damper piece, FIG. 4 is a front view showing the damper piece, FIG. 5 is a bottom view showing the damper piece, and FIG. 6 is an enlarged-scale view showing a mounting portion of a rotary shaft mounting the damper pieces;

FIG. 7 is a general view of a front section of a vehicle showing a drive line of FF car;

FIG. 8 shows a second embodiment of the damper piece of the present invention, in which FIG. 8(a) is a sectional view showing an assembled damper piece and FIG. 8(b) is a front view showing the same; and

FIGS. 9 and 10 show prior art dampers respectively, in which FIG. 9(a) is a perspective view showing an assembled damper, FIG. 9(b) is a perspective view showing a damper piece, FIG. 10(a) is a perspective view showing another assembled damper and FIG. 10(b) is a perspective view showing a damper piece of the damper of FIG. 10(a).

A damper mounting structure, as shown in FIG. 1, comprises a damper 10 and a plurality of connecting means 12. The damper 10 includes two damper pieces 16 formed to be disposed around a rotary shaft 14 and identical in shape with each other. As will be later described, these damper pieces 16 are disposed around the rotary shaft to be connected with each other by the connecting means 12. Thus, the damper 10 is mounted on the rotary shaft 14.

Two damper pieces 16 of the damper 10 are formed in mirror image relationship to one another about a plane including an axis of the rotary shaft 14. Each of the damper pieces 16 has, as one body, a mass portion 17a and a mounting portion 17b extending from the mass portion in an axial direction of the rotary shaft. The mass portion 17a and mounting portion 17b are generally semi-cylindrical in shape. However, the mounting portion 17b has a pair of flanges 17c extending from both sides of the mounting portion. As is apparent from FIG. 4, each of the flanges 17c extends to an outer diameter of the mass portion 17a. Each flange 17c is provided with a hole 18 for a bolt. The damper piece 16 is manufactured by means of casting.

The mounting portion 17b of each damper piece 16 is formed to have a thickness smaller than that of the mass portion 17a and rigidity lower than that of the mass portion 17a. That has, the mass portion 17a is enough thickness and axial length to ensure necessary mass for a mass damper, whereas the mounting portion 17b will only have strength enough to connect firmly the mass portion 17a with the rotary shaft 14, and its thickness and axial length are determined from this point of view. As a result, the rigidity of the mounting portion 17b is smaller than that of the mass portion 17a. Further, by establishing the torsional rigidity of the mounting portion 17b to be lower than that of the rotary shaft 14, the elastic deformation of the mounting portion 17b can more easily follow the deformation of the rotary shaft. When the thickness of the mounting portion is lessened and carbon steel for machine structural use and spheroidal cast iron are used respectively for the rotary shaft 14 and the damper piece 16, it is possible to attain torsional rigidity of the mounting portion 17b which is lower than that of the rotary shaft 14.

As is apparent from FIGS. 2, 3 and 5, an inner peripheral surface 20 of the mass portion 17a of each damper piece 16 is formed into a semi-conical surface diverging with an inclined angle .theta. from the mounting portion 17b toward an opening end. On the other hand, an inner peripheral surface 21 of the mounting portion 17b is a semi-cylindrical surface conforming to the profile of the rotary shaft as shown in FIG. 4.

An example which satisfies the requirements for the damper piece 16 is numerically expressed as in the following; d.sub.1 =25 mm, d.sub.2 =35 mm, d.sub.3 =58 mm, d.sub.4 =29 mm, L.sub.1 =20 mm, L.sub.2 =28 mm and .theta.=5.degree. where the dimensions are defined as shown in FIGS. 3 and 4.

The damper piece 16 formed as mentioned above is preferably mounted on the rotary shaft 14 shown in FIG. 6. The rotary shaft 14 in the embodiment shown has a first portion 15a and at least two second portions 15b , each having a diameter smaller than that of the first portion 15a. The mounting portions 17b of two damper pieces 16 are brought into close contact with the first portion 15a provided between two second portions 15b and both damper pieces 16 are firmly fastened with the connecting means 12. In the embodiment shown in FIG. 1, each of the connecting means 12 includes a bolt 13a extending through the bolt hole 18 in the flange and a nut 13b screwed onto the bolt 13a. Use is made of a stud bolt as the bolt 13a while use is made of a rivet as the connecting means.

Since, as shown in FIG. 2, a clearance S is produced between the mass portion 17a and the rotary shaft 14 when damper piece 16 is mounted on the rotary shaft 14, the mass portion 17a is out of contact with the rotary shaft 14.

When the mounting portion 17b of each damper piece is connected with the first portion 15a of the rotary shaft 14, the torsional deformation of the rotary shaft 14 at the time of transmitting of torque appears largely on the second portion 15b, which is low in torsional rigidity, to thereby reduce the torsional deformation of the first portion 15a. Thus, the mounting portion 17b of each damper piece will be exposed to only a small degree of deformation, so that the mounting portion 17b easily follows the rotary shaft 14 to improve the effect upon prevention of fretting.

When the mounting portion 17b of each damper piece 16 is mounted on the rotary shaft 14 shown in FIG. 6, the length L of the mounting portion 17b is preferably set to be larger than the axial length l of the first portion 15a of the rotary shaft 14 as shown in FIG. 2. Thus, an edge of the mounting portion 17b on its free end is never in contact with the rotary shaft 14 to further improve the effect upon prevention of fretting. Also, the mounting portion 17b is adapted to follow the rotary shaft 14 to facilitate the elastic deformation.

As shown in FIGS. 2 and 3, when the inner peripheral surface 20 of the mass portion 17a of each damper piece 16 is provided with a conical surface diverging toward the opening end, even if foreign matters such as muddy water, dust and others intrude into the clearance S between the mass portion 17a and the rotary shaft 14, these foreign matters are easily purged to the outside by the action of centrifugal force. Thus, wear and corrosion due to the foreign matters can be restrained to improve the durability of the damper 10 and rotary shaft 14.

As shown in FIG. 7 for example, the damper 10 is mounted on a rotary shaft in a drive line of a vehicle to function as a mass damper. The drive line well known per se is constituted from an engine 30, a transmission 32, a differential gear 34 and drive shafts which will be later described. In the embodiment shown, the differential gear 34 is located to be offset toward one side from the lateral center of the vehicle. The differential gear 34 is connected to left and right wheels 36,38 through the rotary shafts, i.e., drive shafts 14,15 so as to be capable of transmitting power. The right and left drive shafts 14,15 are different in length from each other, and the right drive shaft 14 is longer than the drive shaft 15. The mass damper 10 is mounted on the longer right drive shaft 14 having problems in vibration. The mounting position of the mass damper 10 is set to be approximately in the center of the drive shaft 14.

While a damper piece 46 shown in FIG. 8 is constituted by a mass portion 47a, a mounting portion 47b and a connecting portion 47c for interconnecting both portions, the mass portion 47a of the damper piece surrounds the radial outside of the mounting portion 47b. Bolt holes 48 are provided in flanges 47d of the mounting portion 47b. A part of the mass portion 47a opposed to the flange 47d is formed into a recess 49. A notch 50 is provided in a position of the mass portion 47a opposed to each bolt hole 48. This notch 50 can be formed similarly to the notch provided in order to attach bolt and nut thereto in the damper shown in FIG. 9 or 10.

Instead of the embodiment as noted above, the damper 10 may be constituted by connecting three damper pieces 16 circumferentially with each other. In this case, while an angle of center defined by a pair of flanges 17c is 120.degree., other constitution of the damper piece may be the same as that of the previously-described embodiment.

The inner peripheral surface 20 of the mass portion 17a of each damper piece 16 may be formed to be straight as shown by a dot-dash imaginary line in FIG. 2. Then, the portion of the rotary shaft 14 opposed to the mass portion is formed to have the diameter smaller than that of the portion of the rotary shaft opposed to the mounting portion. On the other hand, the rotary shaft 14 may have a uniform diameter equal to that of the first portion 15a. In this case, the inner peripheral surface of the mass portion of each damper piece 16 is formed into an inclined surface diverging toward the opening end as shown in FIGS. 2 and 3.

While the damper 10 is used as a mass damper in the embodiments as noted above, the present invention can be exploited even if the damper is used for a dynamic damper instead of a mass damper.