Abstract:
This invention provides a manufacturing method of a dynamic damper comprising steps of: forming an annular elastic body; fitting a weight on the inner periphery of the annular elastic body and an outer pipe on the outer periphery; and bonding the weight and the outer pipe on the inner periphery and the outer periphery of the annular elastic body.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a manufacturing method for a dynamic damper.  
           [0003]    2. Description of the Related Art  
           [0004]    There are dynamic dampers, which reduce vibration of an automobile driving power-transmitting member, such as a propeller shaft, in order to reduce vehicle vibration and mechanical noise. Such dynamic dampers include an outer pipe, a weight disposed inside the outer pipe and an elastic body disposed between the outer pipe and the weight. This dynamic damper is pressed into a hollow shaft constituting the propeller shaft and is fixed thereto.  
           [0005]    In the dynamic damper disclosed in Japanese Utility Model Application Publication No. H7-29324, an elastic body is disposed in an annular space between an outer pipe and a weight, and a rod-like elastic interposed portion is provided so as to extend in the radius direction at each of a plurality of positions (five positions) in the circumferential direction of the annular space.  
           [0006]    In conventional art, when a dynamic damper is manufactured, rubber is injected into an annular space defined between an outer pipe and a weight such that the outer pipe and the weight have been disposed in a mold to form an elastic body by vulcanization. The elastic body is thereby formed integrally with the outer pipe and the weight.  
           [0007]    However, in the rubber injection in the mold, it is difficult to vulcanization-form an elastic body having uniformly even properties along the circumferential direction of the annular space between the outer pipe and the weight. If the spring constants of respective rod-like elastic interposed portions are fluctuated, the resonant characteristic of the dynamic damper is changed, so that a stable damping characteristic cannot be obtained. A mold design and injection are required so that stable vulcanization and cooling of rubber can be obtained. Therefore, the shape of a manufactured product is determined necessarily.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to secure a stable spring constant in an elastic body of a dynamic damper so as to acquire a stable damping characteristic.  
           [0009]    According to the present invention, there is disclosed a manufacturing method of a dynamic damper comprising an outer pipe, a weight disposed inside the outer pipe and an elastic body interposed between the outer pipe and the weight. The steps include forming an annular elastic body, fitting a weight in an inner periphery of the annular elastic body and fitting an outer pipe on an outer periphery thereof, and bonding the weight and the outer pipe to the inner periphery and the outer periphery of the annular elastic body respectively. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The present invention will be more fully understood from the detailed description given below and from the accompanying drawings, which should not be taken to be a limitation on the invention, but are for explanation and understanding only.  
         [0011]    The drawings:  
         [0012]    [0012]FIGS. 1A and 1B show a dynamic damper of the first embodiment, where FIG. 1A is a front view thereof and FIG. 1B is a sectional view taken along the line B-B;  
         [0013]    [0013]FIG. 2 is a perspective view showing a dynamic damper;  
         [0014]    [0014]FIGS. 3A to  3 E are schematic views showing a manufacturing method for a dynamic damper according to the first embodiment;  
         [0015]    [0015]FIGS. 4A and 4B show a dynamic damper of the second embodiment, where FIG. 4A is a front view thereof and FIG. 4B is a sectional view taken along the line B-B; and  
         [0016]    [0016]FIGS. 5A to  5 E are schematic views showing a manufacturing method for a dynamic damper according to the second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    (First Embodiment)(FIGS. 1A and 1B, FIG. 2, FIGS. 3A to  3 E)  
         [0018]    Reference numeral  10  in FIGS. 1A, 1B and FIG. 2 denotes a dynamic damper  10 , which is pressed into a hollow shaft  2  of an automobile propeller shaft  1  and disposed at a predetermined position thereof in the axial direction. The dynamic damper  10  reduces vibration of the propeller shaft  1  so as to reduce vehicle body vibration and mechanical noise.  
         [0019]    The dynamic damper  10  comprises an outer pipe,  20 , a weight  30  and an elastic body  40 .  
         [0020]    The outer pipe  20  is formed by bending a metallic pipe such as thin steel pipe, in the form of an irregularly shaped cylinder. This outer pipe  20  contains convex portions  21  protruded in the direction of its inside diameter at a plurality of positions (5 positions in this specification) along the circumferential direction. More specifically, in the outer pipe  20 , the convex portions  21  are formed by bending the plural portions along the circumferential direction of a round pipe in the direction of the inside direction with a press while remaining portions are kept as circular portions  22  (circular portion  22  having substantially the same curvature of a hollow shaft  2 ). An end face of the convex portion  21  of the outer pipe  20  acts as a round face pressure-contact face  21 A to the outer circumferential portion of an elastic body  40 . The outside diameter of the outer pipe  20  under the free state formed by the circular portions  22  is set larger than the inside diameter of the hollow shaft  2 . The outside diameter can be contracted elastically from the free state due to the elastic distortion characteristic possessed by the bent portion of the convex portion  21 .  
         [0021]    The weight  30  is formed of a metallic rod such as steel rod in the form of a short cylinder, such as a circular cylinder. The weight  30  has annular grooves  31  provided in the entire circumference for loading the elastic body  40 . The weight  30  is disposed inside the outer pipe  20  coaxially with the outer pipe  20 . The weight  30  is wider than the outer pipe  20  (FIG. 1B).  
         [0022]    The elastic body  40  is an annular body fitted to an annular groove  31  in the weight  30  over the entire periphery between the outer pipe  20  and the weight  30 . The outer periphery of the elastic body  40  has a larger diameter than an outer diameter of the weight  30  and is formed with arc faces continuous along the entire periphery. The elastic body  40  is formed of synthetic rubber or the like and is bonded to the outer pipe  20  and the weight  30  by vulcanization.  
         [0023]    In the dynamic damper  10 , the elastic body  40  on the weight  30  is nipped and held by a front end pressure-contact face  21 A of each convex portion  21  of the outer pipe  20  from radial directions. An outer peripheral portion  41  of the elastic body  40  is nipped and held in the circumferential direction between the front end pressure-contact faces  21 A of the convex portions  21  adjacent in the circumferential direction of the outer pipe  20 . The front end pressure-contact face  21 A of each convex portion  21  engages the outer peripheral portion  41  of the elastic body  40  in a specified depth so that the outer peripheral portion  41 A is nipped between the front end pressure-contact faces  21 A of the adjacent convex portions  21 .  
         [0024]    The manufacturing procedure of the dynamic damper  10  is as follows (FIGS. 3A to  3 F).  
         [0025]    (1) A tube-like elastic body  40 A, which is raw material for the annular elastic body  40 , is formed separately (FIG. 3A). The tube-like elastic body  40 A is cut out to a necessary length to form the annular elastic body  40  (FIG. 3B).  
         [0026]    (2) The weight  30  is fitted into the elastic body  40  (FIGS. 3C, 3D). The inner periphery of the elastic body  40  is fitted in the annular groove  31  in the weight  30 .  
         [0027]    (3) The outer pipe  20  is fitted on an outer periphery of the elastic body  40  (FIG. 3E). The front end pressure-contact face  21 A of each convex portion  21  of the outer pipe  20  is fitted to the outer periphery of the elastic body  40 .  
         [0028]    (4) An assembly obtained by assembling the outer pipe  20  and the weight  30  to the inner and outer peripheries of the elastic body  40  is heated so as to bond the weight  30  and the outer pipe  20  to the inner and outer peripheries of the elastic body  40  by vulcanization respectively.  
         [0029]    (5) After cooling of the above-described assembly ( 4 ), the convex portions  21  of the outer pipe  20  are pressed into the outer periphery of the elastic body  40  with a press so as to complete the dynamic damper  10  (FIG. 3F).  
         [0030]    This embodiment exhibits the following characteristics.  
         [0031]    (1) By forming the annular elastic body  40  preliminarily, a uniformly even spring constant in the circumferential direction of the elastic body  40  can be secured easily so as to allow the dynamic damper  10  to acquire a stable damping performance.  
         [0032]    (2) By engaging the convex portions  21  provided at plural positions of the outer pipe  20  in the circumferential direction thereof with the elastic body  40  with a press, the elastic body  40  is provided with a preliminary load, thereby improving the durability of the dynamic damper  10 . At the same time, the outer peripheral portion  41 A of the elastic body  40  can be nipped and held firmly between the convex portions  21  of the outer pipe  20  adjacent to each other. Consequently, repeated load due to compression in the radial direction from the weight  30  and shearing stress in the rotation direction based on rotary vibration of the propeller shaft  1  is distributed widely to respective portions of the elastic body  40 . Therefore, concentration of stress on the elastic body  40  is suppressed so as to prevent damage from cracks, thereby improving the durability of the dynamic damper  10 .  
         [0033]    (3) The diameter A of an inscribed circle coming in contact with the respective convex portions  21  of the outer pipe  20  can be made smaller than the diameter B at both end portions of the weight  30 . Accordingly, even when slippage of the weight  30  in a lateral direction is caused by deterioration of the elastic body  40  or the like, the outer flanges of the weight  30  at both ends thereof abut the convex portion  21  of the outer pipe  20 , so that a large slippage of the weight  30  and therefore falling-off of the weight  30  from the outer pipe  20  is prevented.  
         [0034]    (4) Because the convex portions  21  of the outer pipe  20  nip and hold the elastic body  40  through the round face pressure-contact face  21 A, the distribution property of the load (1) that is described above, to the elastic body  40  based on vibration of the propeller shaft  1 , can be improved.  
         [0035]    (5) Because the convex portions  21  are formed by bending respective portions of the outer pipe  20  in the circumferential direction inward, elastic flexibility in the radial direction can be obtained in the bent portion of the convex portion  21 . Therefore, when the dynamic damper  10  is press-fit into a hollow shaft  2 , any dimensional error between the inner diameter of the hollow shaft  2  and the outer diameter of the outer pipe  20  can be absorbed by elastically flexing deformation of the outer pipe  20  and elastically flexing deformation of the elastic body  40  so as to facilitate the pressing-in. Additionally, after the press-fitting, the dynamic damper can be fixed firmly to the inside face of the hollow shaft due to an elastic restoration force of the outer pipe  20  and the elastic body  40 .  
         [0036]    (6) Only the plural arc circular portions  22 , except the bent portions in which the convex portions  21  are formed on the entire periphery of the outer pipe  20 , are press-fitted into the hollow shaft  2  in a rubbing manner. Thus, the contact area of the outer pipe  20  to the inside face of the hollow shaft  2  is decreased, thereby reducing the press-fitting operation force which leads to a reduction of cost in manufacturing equipment.  
         [0037]    (7) Because the convex portions  21  can be formed easily on the outer pipe  20  by a bending operation using a press or the like, the round face pressure-contact faces  21 A of the convex portions  21  described in (4) can be formed easily.  
         [0038]    (8) The items (1) to (7) described above are achieved in the propeller shaft  1 , thereby improving the durability of the dynamic damper  10 . Additionally, the dynamic damper  10  can be press-fit into the hollow shaft  2  easily and fixed thereto stably.  
         [0039]    (Second Embodiment) (FIGS. 4A and 4B, FIGS. 5A to  5 E)  
         [0040]    A dynamic damper  100  of a second embodiment is different from the dynamic damper  10  of the first embodiment in that the front end pressure-contact face  21 A of each convex portion  21  of the outer pipe  20  engages a concave engaging portion  42  with a predetermined depth which is provided on the outer periphery  41  of the elastic body  40  so as to nip and hold the outer peripheral portion  41 A between the front end pressure-contact faces  21 A of the adjacent convex portions  21 .  
         [0041]    The manufacturing procedure for the dynamic damper  100  is as follows (FIGS. 5A to  5 E).  
         [0042]    (1) The tube-like elastic body  40 A, which is raw material of the annular elastic body  40 , is formed separately (FIG. 5A). The tube-like elastic body  40 A contains the concave grooves  42 A which constitute the concave engaging portions  42 , at plural positions (five positions in this embodiment) along the circumferential direction. Then, the tube-like elastic body  40 A is cut to necessary lengths so as to form the annular elastic bodies  40  (FIG. 5B).  
         [0043]    (2) The weight  30  is fitted into the inner periphery of the elastic body  40  (FIGS. 5C, 5D). The inner peripheral portion of the elastic body  40  is fitted in the annular groove  31  in the weight  30 .  
         [0044]    (3) The outer pipe  20  is fitted on the outer periphery of the elastic body  40  (FIG. 5E). The front end pressure-contact face  21 A of the convex portion  21  of the outer pipe  20  is fitted in the concave engaging portion  42  in the elastic body  40 .  
         [0045]    (4) An assembly obtained by assembling the outer pipe  20  and weight  30  onto the inner and outer peripheries of the elastic body  40  is heated, and the weight  30  and the outer pipe  20  are bonded to the inner and outer peripheries of the elastic body  40  by heating so as to form the dynamic damper  100 .  
         [0046]    In the meantime, after the assembly described in the above description (4) is cooled, it is possible to further engage the convex portion  21  of the outer pipe  20  into the concave engaging portion  42  in the elastic body  40  in a pressing manner. Additionally, it is also possible to provide the engaging portions between the weight  30  and the elastic body  40 .  
         [0047]    According to this embodiment, the following operations and characteristics are exhibited as well as the operations described already in the first embodiment.  
         [0048]    By fitting the convex portions  21  provided at plural positions of the outer pipe  20  in the circumferential direction thereof to the concave engaging portions  42  provided in the outer periphery of the elastic body  40 , the outer peripheral portion  41 A of the elastic body  40  can be nipped and held firmly between the convex portions  21  of the outer pipe  20  adjacent to each other. Repeated load due to compression in the radial direction from the weight  30  and shearing stress in the rotation direction based on rotary vibration of the propeller shaft  1  is distributed widely to respective portions of the elastic body  40 . Therefore, concentration of stress upon the elastic body  40  can be suppressed so as to prevent damage by cracks, thereby improving the durability of the dynamic damper  10 .  
         [0049]    As heretofore explained, embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configurations of the present invention are not limited to the embodiments, but those having a modification of the design within the range of the present invention are also included in the present invention. For example, the dynamic damper of the present invention can be applied to a power transmitting member other than the propeller shaft.  
         [0050]    As described above, the present invention enables a stable spring constant to be secured in the elastic body of the dynamic damper so as to acquire a stable vibration resistant characteristic.  
         [0051]    Although the invention has been illustrated and described with respect to several exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made to the present invention without departing from the spirit and scope thereof. Therefore, the present invention should not be understood as limited to the specific embodiment set out above, but should be understood to include all possible embodiments which can be embodied within a scope encompassed and equivalents thereof with respect to the features set out in the appended claims.