Abstract:
A strut mount capable of reducing the weight and of intensifying the strength and having a good durability is provided. It comprises an inner cylinder, a vibration isolating base body and a pair of upper and lower brackets. The lower bracket is fabricated from aluminum alloy and includes a peripheral wall portion, a bottom wall portion and a first attachment flange while the upper bracket includes a second attachment flange and a lid wall portion. The first attachment flange has plural first through-holes for inserting plural attachment members, the second attachment flange has plural second through-holes for inserting the plural attachment members, and flange portions around the first through-holes of the first attachment flange bulge at their undersides to form respective thick-walled portions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a strut mount comprising an inner cylinder to be fixed to a top end of a piston rod of a shock absorber, a vibration isolating base body made of rubber-like elastomer provided on the inner cylinder, and a pair of upper and lower brackets to be fixed to a vehicle body side by means of a plurality of attachment members and forming a housing part in which the vibration isolating base body is accommodated. 
     2. Description of the Related Art 
     A strut suspension is generally equipped with a shock absorber for the purpose of damping vertical vibrations. The extremity of the shock absorber is located on a vehicle body side, to which the top end of a piston rod is supported through a vibration isolating base body of a strut mount. 
     JP Patent Application Publication 2001-171323 A discloses a strut mount comprising a core material (inner cylinder) to be fixed to the top end of the shock absorber, a rubber elastomer (vibration isolating base body) bonded by vulcanization to the core material, and a pair of upper and lower brackets forming a box part (housing room) in which the rubber elastomer is accommodated. 
     According to this strut mount, the pair of upper and lower brackets are formed respectively in a flat plate shape and a cup shape, and both components are superposed one upon the other and assembled, thereby forming internally the cylindrical housing room. The vibration isolating base body is accommodated in the housing room under compression between the pair of brackets. A cup member assuming S-like form in cross-section is attached to a bottom surface side of the bracket (the surface on an axle side), and in the cup member there is housed and held a base extremity of a bound bumper that is fabricated in a columnar shape from urethane or the like. In the conventional strut mounts like the aforesaid strut mount, the brackets were constructed of an iron press formed product. 
     In recent years, a demand to low fuel consumption has been stronger and accordingly, a demand to weight reduction of automotive components has been stronger. According to the conventional configuration, however, inasmuch as the brackets were constructed of an iron press formed product, the demand to weight reduction could not be met. It is conceivable to construct the brackets of aluminum alloy, instead, but if the structure of the iron-made brackets is adopted for brackets made of aluminum alloy, the brackets will be wanting in strength. 
     Therefore an object of the invention is to provide a strut mount that is capable of intensifying the strength thereof while reducing the weight and is superior in durability. 
     SUMMARY OF THE INVENTION 
     The present invention is generically directed to a strut mount comprising an inner cylinder to be fixed to a piston rod of a shock absorber, a vibration isolating base body made of rubber-like elastomer provided on the inner cylinder, and a pair of an upper and a lower brackets to be attached to a car body side by means of a plurality of attachment members and forming a housing part, in which the vibration isolating base body is accommodated. And the strut mount is characterized in that the lower bracket is fabricated from aluminum alloy, and includes a peripheral wall portion forming a peripheral wall of the housing part, a bottom wall portion forming a bottom wall of the housing part, and a first attachment flange overhanging radially outwardly from an upper end of the peripheral wall portion, and the upper bracket includes a second attachment flange superposed on an upside of the first attachment flange and a lid wall portion covering the vibration isolating base body; and in that the first attachment flange has a plurality of first through-holes for inserting the plurality of the attachment members, the second attachment flange has a plurality of second through-holes for inserting the plurality of the attachment members, and the first attachment flange has such flange portions around the first through-holes that bulge outwardly of undersides of the flange portions to be configured each as a thick-walled portion. 
     By the configuration as described above, the plurality of attachment members are respectively inserted through the plurality of first through-holes on the first attachment flange and inserted through the plurality of second through-holes on the second attachment flange, and the first attachment flange and the second attachment flange are superposed one upon the other to be fixed to the car body side. Because the lower bracket is fabricated of aluminum alloy, a weight reduction is feasible. If the first attachment flange is weak in strength, the first attachment flange will repeat downward swaying and parting around the attachment members (e.g., attachment bolts) relative to the second attachment flange and returning to the original superposing position, which leads to the trouble that a strange noise is liable to be generated due to impingement of the first attachment flange to the second attachment flange. In contrast, according to the configuration of this invention, because the undersides of the flange portions around the first through-holes of the first attachment flange are bulged outwardly of the undersides and the flange portions are configured as a thick-walled portion, it is possible to intensify the strength to avoid the aforesaid trouble. Moreover it is possible to achieve a weight reduction of the first attachment flange as compared with a structure that the entirety of the first attachment flange is rendered thick-walled. 
     In the invention, when the upper bracket is fabricated from aluminum alloy, and when a curved portion is interposed between the first attachment flange and the peripheral wall portion, the curved portion assuming an arc-like shape in axial cross-section inclusive of the axis center of the peripheral wall portion in a manner that the curved portion joins with the first attachment flange and the peripheral wall portion, an upwardly splaying, taper slanting wall portion is interposed between the lid wall portion and the second attachment flange in a manner that the taper slanting wall portion joins with the lid wall portion and the second attachment flange, and the vibration isolating base body is bonded by vulcanization to the inner cylinder, it is possible to achieve a further weight reduction and to construct the upper and lower brackets as a strong structural body. 
     In the invention, when the attachment members are each an attachment bolt, the first through-holes are each a first bolt through-hole, and the second through-holes are each a second bolt through-hole; the curved portion and the taper slanting wall portion are configured so that a gap between an underside of the taper slanting wall portion and a curved inner peripheral surface portion of the curved portion opposed to the underside is defined to be gradually larger toward a radially inward side and an obliquely downward side of the peripheral wall portion in the state that the first attachment flange and the second attachment flange are fixed to the car body side by means of the plurality of attachment bolts, it is possible to stabilize the fixing state of the first attachment flange and the second attachment flange to the car body, without the taper slanting wall portion riding over the curved portion even if the second attachment flange is bolted to the car body side under its misalignment condition to the first attachment flange. 
     When each of the thick-walled portions extends, in a radial direction of the first attachment flange, up to a downward side of the curved inner peripheral surface portion thereby joining at its underside with an outer peripheral surface of the peripheral wall portion, it is possible to intensify further the strength of the flange portion. 
     In the present invention, when the taper slanting wall portion is configured in a manner such that a center of a taper angle of its upside and a center of a taper angle of its downside are located in the same position and the taper angle of the upside is set to be smaller than the taper angle of the downside and that a thickness of the taper slanting wall portion is gradually increased from the lid wall portion toward the second attachment flange, the following operations can be achieved: 
     Due to the feature that in the taper slanting wall portion, the taper angle of the upside is set smaller than the taper angle of the downside and the thickness is increased gradually from the lid wall portion toward the second attachment flange, it is possible to achieve a weight reduction and to assure the strength of the lid wall portion (and the taper slanting wall portion) against a load input through the vibration isolating base body. Further because the area of the upside of the second attachment flange is enlarged, it is possible to make its contact area with the car body large, thereby to stabilize the installation condition of the strut mount. 
     According to this invention, it is thus possible to afford such a strut mount that is capable of intensifying the strength while achieving a weight reduction and is superior in durability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Now the best mode for carrying the invention into effect will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a front elevation of a strut mount of the invention; 
         FIG. 2  is a sectional view of the strut mount taken along II-II line in  FIG. 1 ; 
         FIG. 3  is a partial enlarged cross-sectional view of a lower bracket; 
         FIG. 4  is a partial enlarged cross-sectional view of an upper bracket; 
       and  FIG. 5  is a sectional view showing a thick-walled portion of a first attachment flange and its surrounding portion. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a strut mount  100  of a front suspension for a FR (front engine/rear drive) type automobile, and  FIG. 2  shows a piston rod  20  of a shock absorber, a bound bumper  30 , and a nut  40  threaded on a top end  20 A of the piston rod  20  illustrated in two-dot-dash lines. 
     The strut mount  100  as shown in  FIGS. 1 and 2  is made up of an inner cylinder  1  to be fixed to the top end  20 A of the piston rod  20  of the shock absorber SB, a ring-like vibration isolating base body  2  made of rubber-like elastomer bonded by vulcanization to a flange portion  1   a  of the inner cylinder  1 , and a pair of an upper and a lower brackets  4 ,  3  forming a housing part  1  in which the vibration isolating base body  2  is accommodated and to be fixed to a side of a vehicle body F (cf.  FIG. 5 ) by means of a plurality attachment bolts  5  having respective heads  115  (corresponding to attachment members). 
     The inner cylinder  1  is an iron-made cylinder, on an inner periphery side of which the piston rod  20  of the shock absorber SB is inserted, as shown in  FIG. 2 . The piston rod  20  is locked and fixed to the inner cylinder  1  by means of the nut  40  threaded on the top end  20 A. 
     The vibration isolating base  2  is accommodated in a housing part  111  formed by the pair of the upper and lower brackets  4 ,  3  under a compressive condition, and thus imparted with a predetermined prestress. 
     Of the paired brackets  4 ,  3 , the lower bracket  3  is a cold forging product of aluminum alloy. The lower bracket  3  is configured in a deep dish-like shape assuming a triangular form when viewed from a top plane (cf.  FIG. 1 ) and is a one-piece member made up of a peripheral wall portion  3   a  forming the peripheral wall of the housing part  111 , a bottom wall portion  3   b  forming the bottom wall of the housing part, a first attachment flange  3   d  overhanging radially outwardly (toward G 1 ) from an upper end portion  112  of the peripheral wall portion  3   a , a first curved portion  3   e  interposed between the first attachment flange  3   d  and the peripheral wall portion  3   a  and curved in an arc form in cross-section in the axial direction inclusive of a center axis O of the peripheral wall portion  3   a , a second curved portion  3   c  interposed between the bottom wall portion  3   b  and the peripheral wall portion  3   a  and curved in an arc form in cross-section in the axial direction inclusive of the center axis O of the peripheral wall portion  3   a , and a bound bumper holding portion  3   f  located beneath the second curved portion  3   c . Being interposed between the first attachment flange  3   d  and the peripheral wall portion  3   a  in this manner, the first curved portion  3   e  joins smoothly with the first attachment flange  3   d  and the peripheral wall portion  3   a.    
     As shown in  FIG. 3 , the bottom wall portion  3   b  is formed, at its central part, with an opening  3   b   1  through which to insert the inner cylinder  1 . A plate thickness t 1  of the first attachment flange  3   d  (cf.  FIG. 2 , plate thickness of the other portion than a thick-walled portion  73  which will be hereinafter described) is formed to be thinner than a plate thickness t 2  of the peripheral wall portion  3   a , while a wall thickness t 3  of the bottom wall portion  3   b  is formed to be thicker than the plate thickness t 2  of the peripheral wall portion  3   a . For example, t 1 =3 mm, t 2 =4 mm, t 3 =6.5 mm are set. In the axial cross-section, a radius of curvature Ri 1  of the second curved portion  3   c  on its inner peripheral curved surface  77  is set in a range of 2 to 3 times the plate thickness t 2  of the peripheral wall portion  3   a . Ro 2  is a radius of curvature of the second curved portion  3   c  on its outer peripheral curved surface  78 . For example, Ri 1 =10 mm and Ri 2 =20 mm. 
     As shown in  FIG. 2 , Ri 3  is a radius of curvature of the first curved portion  3   e  (radius of curvature of other portion than the thick-walled portion  37  as described below) on its outer peripheral curved surface  62  (concave surface) while Ro 4  is a radius of curvature of it on an inner peripheral curved surface  61  (convex surface), and for instance, Ri 3 =7 mm and Ro 4 =11 mm are set. In the axial cross-section, an inner peripheral surface  72  of the bound bumper holding portion  3   f  is contoured in the form of an S-like concave-and-convex surface. Thus the bound bumper holding portion  3   f  has an upper holding concave portion  54  recessed in an arc form in cross-section and a solid lower holding convex portion  55  bulging in an arc form in cross-section. The reference numeral  51  designates an outer peripheral surface of the bound bumper holding portion  3   f.    
     Of the pair of the upper and lower brackets, the upper bracket  4  is a cold forging product of aluminum alloy. As shown in  FIG. 4 , the upper bracket  3  is made up of a second attachment flange  4   a  superposed on an upside  75  of the first attachment flange  3   d , a lid wall portion  4   b  covering the vibration isolating base body  2  and compressing the vibration isolating base body  2  between the lower bracket  3  and itself, and an upwardly splaying taper slanting wall portion  4   c  interposed between the lid wall portion  4   b  and the second attachment flange  4   a , and has, at its central part, an opening  4   b   1  pierced through. The upper bracket  4  is formed in a smaller triangular shape than the lower bracket  3  when viewed from a top plane and superposed on the lower bracket  3 , with its peripheral positions (apexes of the triangle) registered with those of the latter (cf.  FIG. 1 ). Thus the taper slanting wall portion  4   c  interposed between the lid wall portion  4   b  and the second attachment flange  4   a  joins smoothly with the lid wall portion  4   b  and the second attachment flange  4   a  so that the lid wall portion  4   b  and the lower bracket  3  may compress the vibration isolating base body  2 . 
     As illustrated in  FIG. 4 , the taper slanting wall portion  4   c  is configured so that a taper angle center O 1  of an upside  63  thereof and a taper angle center O 2  of an underside  64  thereof (outer peripheral surface of the taper slanting wall portion  4   c ) in axial cross-section are located in the same or substantially same position, and given that the taper angle of the upside  63  and the taper angle of the underside  64  are respectively θ 1  and θ 2 , the relationship of: θ 1 &lt;θ 2  holds true. For example, θ 1 =106 degrees and θ 2 =116 degrees. A plate thickness t 5  of the lid wall portion  4   b  and a plate thickness t 6  of the taper slanting wall portion  4   c  are formed to be thicker than a plate thickness t 4  of the second attachment flange  4   a . By setting the plate thicknesses t 4  to t 6  of the respective members  4   a  to  4   c  in this way, it is possible to achieve both a weight reduction and assuring of strength. Because the taper angle θ 1  of the upside  63  of the taper slanting wall portion  4   c  is set smaller than the taper angle θ 2  of the underside  64 , the thickness t 6  of the taper slanting wall portion  4   c  is gradually increased from the lid wall portion  4   b  toward the second attachment flange  4   a  (t 6   a &lt;t 6   b ). Thereby it is possible to achieve a weight reduction and ensure the strength of the lid wall portion  4   b  (and the taper slanting wall portion  4   c ) to a load input through the vibration isolating base body  2 . Further because the area of the upside of the second attachment flange  4   a  is widened, it is possible to render a contact area of it with the car body large, thereby to stabilize the installation state of the strut mount  100 . For example, t 4 =3 mm, t 5 =3.5 mm are set. The magnitude of t 6  is determined by the taper angles θ 1 , θ 2 . 
     Between the second attachment flange  4   a  and the taper slanting wall portion  4   c , a third curved portion  4   c   1  curved in an arc form in axial cross-section is provided and between the slanting wall portion  4   c  and the lid wall portion  4   b , a fourth curved portion  4   c   2  curved in an arc form in cross-section is provided. Given that radii of curvature of an outer peripheral curved surface  65  (concave surface) and an inner peripheral surface  66  (convex surface) of the third curved portion  4   c   1  are Ri 5  and Ro 6 , and radii of curvature of an outer peripheral curved surface  67  (concave surface) and an inner peripheral surface  68  (convex surface) of the fourth curved portion  4   c   2  are Ri 7  and Ro 8 , respectively, of these radii of curvature Ri 5  to Ro 8 , the radius of curvature Ri 5  of the outer peripheral curved surface  65  of the third curved portion  4   c   1  is set at a largest value. For example, Ri 5 =10 mm, Ro 6 =Ri 7 =Ro 8 =5 mm. 
     On the first attachment flange  3   d , three pieces of the first bolt through-holes  69  for inserting three pieces of the respective attachment bolts  5  are formed, while on the second attachment flange  4   a , second bolt through-holes  70  for inserting the three pieces of respective attachment bolts  5  are formed. In this way, the three first bolt through-holes  69  and the three second bolt through-holes  70  overlap with each other. And in the state that the first attachment flange  3   d  and the second attachment flange  4   a  are fixed to the car body side by means of the three attachment bolts  5  inserted through the three first bolt through-holes  69  and three second bolt through-holes  70  respectively, the first curved portion  3   e  and the taper slanting wall portion  4   c  are formed so that a clearance gap S between the underside  64  which is the outer peripheral surface of the taper slanting wall portion  4   c  and the inner peripheral curved surface  61  of the first curved portion  3   e  opposed to the underside  64  may be gradually enlarged toward an obliquely downward side J on a radially inward side N of the peripheral wall portion  3   a.    
     As also illustrated in  FIG. 5 , an underside  72  of each flange portion around each of the first bolt through-holes  69  of the first attachment flange  3   d  bulges outwardly U (the downward side) of the underside  72  whereby the flange portion is configured as the thick-walled portion  73  having a uniform wall thickness. The thick-walled portion  73  is configured in a rectangular shape lengthy in the radial direction of the first attachment flange  3   d  when viewed from a top plane and extends from the outer peripheral edge side of the first attachment flange  3   d  to a side of the outer peripheral surface  50  of the peripheral wall portion  3   a . More specifically, the thick-walled portion  73  is extended up to an underside  130  of the inner peripheral curved surface  61  in the radial direction of the first attachment flange  3   d  whereby the underside of the thick-walled portion  73  (namely the underside  72  of the flange portion) joins smoothly with the outer peripheral surface  50  of the peripheral wall portion  3   a . A plate thickness t 7  of the thick-walled portion  73  is set to be 5 mm. 
     The present embodiment has been described with the strut mount  100  for use in a front suspension of a FR type automobile, but this invention is also applicable to different strut mounts. The numerical values mentioned above are exemplary only, and another values may be adopted.