JP4203063B2 - Vibration isolator - Google Patents

Description

  The present invention relates to a cylindrical anti-vibration comprising an inner cylinder, an outer cylinder surrounding the inner cylinder, and a vibration-proof base made of a rubber elastic body that is interposed between the inner cylinder and the outer cylinder and connects the two cylinders. The present invention relates to a vibration device.

  Conventionally, as this type of vibration isolator, there is a body mount interposed between an automobile body and an underbody member. In the body mount, the inner cylinder is attached to a body side member such as a frame with the axial direction set up and down, and the outer cylinder is fixed to the fitting hole formed on the vibration member side such as a suspension member member by press-fitting inner fitting. Various types of structures have been proposed (for example, see Patent Document 1 below).

  In such a vibration isolator, the inner cylinder is assembled in a state in which one end portion in the axial direction is in pressure contact with the body side member by a connecting member such as a bolt inserted through the hollow portion. For this reason, if the area of the end surface of the inner cylinder that is in pressure contact with the body side member is small, the inner cylinder tends to fall during driving of the vehicle, and there is a problem that steering stability is reduced.

  Such a problem is solved by enlarging the end surface on the inner cylinder side that contacts the body side member. As a technique for enlarging the end surface on the inner cylinder side, for example, in Patent Document 2 below, after vulcanization molding of the vibration-proof base, one end surface in the axial direction of the inner cylinder is pressed in the axial direction with a pressure welding jig, A technique for expanding the diameter of the end of the inner cylinder by plastic working has been proposed. However, with this technique, there is a certain limit to increasing the amount of diameter expansion, it is difficult to sufficiently suppress the collapse of the inner cylinder, and time is required for the diameter expansion process.

On the other hand, in Patent Document 3 below, in order to prevent the inner cylinder from collapsing, a stopper member is interposed between the end of the inner cylinder and the body side member, and then the end of the inner cylinder is placed on the stopper member. It has been proposed to provide an annular projection that fits around the outer periphery of the lens. Since such an annular protrusion generally impairs workability when the stopper member is press-fitted and fitted into the end portion of the inner cylinder, improvement is required.
Japanese Patent Laid-Open No. 4-327033 JP 2003-106359 A JP 2003-21194 A

  Accordingly, an object of the present invention is to provide an anti-vibration device that can sufficiently suppress the falling of the inner cylinder during driving of the vehicle, improve steering stability, and is excellent in manufacturability. .

An anti-vibration device according to the present invention includes an inner cylinder whose one end in the axial direction is attached to the body side member, an outer cylinder that surrounds the inner cylinder and is press-fitted into a fitting hole formed on the vibrating body side, A vibration isolator comprising a rubber elastic body interposed between the inner cylinder and the outer cylinder and coupling the two cylinders to the one end of the inner cylinder on the body side An abutting member that abuts against the body side member is attached in a state of being sandwiched between the members, and a surface of the abutting member that abuts against the body side member is more than an end surface of one end of the inner cylinder The outer peripheral shape is set to be large, and the contact member includes an annular wall that fits to the outer periphery of one end of the inner cylinder, and is externally fitted to one end of the inner cylinder by the annular wall, ribs extending in the axial direction on the inner peripheral surface of the annular wall provided with a plurality of circumferentially to the vibration isolating substrate, a phase across the inner cylinder A pair of cavities are formed penetrating in the axial direction, and the cavity is formed by a stopper rubber portion with a central portion in the circumferential direction as a stopper gap portion, and both circumferential ends are wider than the stopper gap portion. The inner wall surface of the cavity portion is inclined with respect to the axial direction so that the cavity portion expands from the central portion in the axial direction toward the opening end portion, and the wide space is formed. The inclination of the inclined surface portion in the portion is set larger than the inclination of the inclined surface portion in the stopper gap portion .

According to the above configuration, the abutment member attached to one end of the inner cylinder ensures a large abutment surface with respect to the body side member, so that the inner cylinder is not easily toppled during driving of the vehicle, and steering stability is improved. Can be made. In addition, since the plurality of ribs extending in the axial direction are provided on the inner peripheral surface of the annular wall that fits to the outer periphery of the inner cylinder end, the contact area between the annular wall and the inner cylinder end is reduced, and the shaft is The inner cylinder end can be guided in the axial direction by the rib extending in the direction, and the inner cylinder end can be easily press-fitted into the annular wall. Therefore, the attachment workability of the abutting member is excellent, and after the attachment, the outer peripheral surface of the inner cylinder end portion is supported by the plurality of ribs, thereby ensuring the function of preventing the inner cylinder from falling.
In addition, regarding the shape of the cavity provided in the vibration isolator base, the volume of the rubber elastic body around the opening of the wide space is reduced by increasing the inclination of the inclined surface in the wide space at both ends in the circumferential direction. Thus, generation of wrinkles around the opening at the time of drawing the outer cylinder after vulcanization can be suppressed. Also, strain concentration around the opening of the wide space can be prevented even when a load is input after being mounted on an automobile. On the other hand, with respect to the stopper gap portion in the central portion in the circumferential direction, it is easy to ensure the function as a stopper for limiting excessive relative displacement between the inner cylinder and the outer cylinder by setting the inclination of the inclined surface portion small. Therefore, durability can be improved by reducing wrinkles and strain concentration at both ends in the circumferential direction while ensuring a stopper function at the center in the circumferential direction of the cavity.

  In the vibration isolator of the present invention, a rubber film continuous from the vibration isolating base may be vulcanized and bonded to the outer peripheral surface of one end of the inner cylinder into which the annular wall is fitted. In this case, the plurality of ribs provided on the annular wall bite into the rubber film at the end of the inner cylinder, so that the relative displacement in the circumferential direction between the inner cylinder and the contact member is suppressed. Generation of sound can be prevented.

  In the vibration isolator of the present invention, the inner wall surface of the hollow portion includes a central surface portion formed of a surface parallel to the axial direction in the axial central portion, and the inclined surface portions are provided on both sides of the central surface portion. May be. In this case, the axial dimension of the central surface part is preferably set smaller than the axial dimension of the inclined surface parts provided on both sides of the central surface part in order to better exhibit the above-described effects. .

  Furthermore, in the vibration isolator of the present invention, the stopper gap portion of the hollow portion is formed between an inner stopper rubber portion protruding from the inner cylinder side and an outer stopper rubber portion protruding from the outer cylinder side. It is preferable that the contact surface of the outer stopper rubber portion with the inner stopper rubber portion is formed in a curved surface convex toward the inside in the radial direction in a cross section perpendicular to the axial direction. Thus, by forming the shape of the contact surface of the outer stopper rubber portion into an inwardly convex curved surface, the initial contact with the inner stopper rubber portion can be softened and noise can be reduced.

  The vibration isolator of the present invention is a member that is attached to a body side member of an automobile with the inner cylinder extending in the vertical direction, and the outer cylinder surrounds the inner cylinder coaxially, and is a member member of a suspension. It is a member that is press-fitted and fitted into the fitting hole formed in, and is particularly suitable for a body mount in which the hollow portion is provided at a position facing the front-rear direction of the automobile across the inner cylinder.

As described above, according to the present invention, there is provided a vibration isolator that can sufficiently suppress the falling of the inner cylinder during driving of the vehicle, improve steering stability, and is excellent in manufacturing workability. can do. In addition, it is possible to improve the durability by reducing wrinkles and strain concentration at both ends in the circumferential direction while securing a stopper function at the center in the circumferential direction of the cavity provided in the vibration isolating base.

  Hereinafter, the vibration isolator which concerns on one Embodiment of this invention is demonstrated based on FIGS.

  The vibration isolator of the present embodiment is a body mount for supporting an undercarriage member such as an automobile suspension in a vibration-proof manner with respect to a body such as a frame, and an inner cylinder 10 made of a rigid material such as metal, An outer cylinder 12 made of a rigid material such as a metal and concentrically surrounding the outer cylinder 12 and a rubber elastic body interposed between the inner cylinder 10 and the outer cylinder 12 by a vulcanization bonding means to couple them together. And an anti-vibration base 14.

  As shown in FIG. 8, the inner cylinder 10 is a member whose upper end portion 16 is attached to the body side member 2 with the axial direction Z set to the vertical direction L, and the bolt 1 as a connecting member is inserted into the hollow portion 18. The bolt 1 is fastened and fixed to the body side member 2 in a pressed state. The hollow portion 18 is formed such that the upper side 18a for receiving the shaft portion 2a of the body side member 2 has a larger diameter than the lower side 18b into which the bolt 1 is inserted. A tapered surface portion 18c (see FIG. 1) that is opened upward is provided to guide the tip of the lens and facilitate its insertion. As for the inner cylinder 10, the lower end part 20 is formed in the small diameter through the step part in the outer peripheral surface.

  The outer cylinder 12 is a member that is attached to the member member 3 of the suspension, which is a vibrating body, and is press-fitted and fitted from below into the fitting hole 4 a formed in the member member 3 by the cylindrical holder 4. A flange 22 extending radially outward is provided at the lower end of the outer cylinder 12, and a stopper rubber portion 24 is formed on the lower surface of the flange 22 by rubber continuous from the vibration isolation base 14. In addition, a plurality of annular rubber portions 26 (see FIG. 1) extending around the entire circumference in the circumferential direction are added to the outer peripheral surface of the outer cylinder 12 in order to improve the retaining and setting after press-fitting into the fitting hole 4a. It is formed in a convex shape by sulfur molding.

  The vibration-proof base 14 is provided with a pair of cavities 28, 28 that are referred to as straight holes penetrating in the axial direction Z at opposite positions in the diameter direction (specifically, the vehicle longitudinal direction X) with the inner cylinder 10 interposed therebetween. It has been. As a result, the spring constant in the longitudinal direction X of the vehicle is low, and the spring constant in the left-right direction Y of the vehicle is set high, so that the ride comfort is good and the steering stability is enhanced.

  As shown in FIGS. 2 and 3, the hollow portion 28 is formed in a shape in which both end portions in the circumferential direction P swell broadly with respect to the central portion, and an inner stopper rubber portion 30 protruding from the inner cylinder 10 side, A stopper gap 34 at the center in the circumferential direction formed between the outer stopper rubber part 32 protruding from the outer cylinder 12 side, and located at both ends of the stopper gap 34 in the radial direction from the stopper gap 34. It consists of a wide space 36 at both ends in the circumferential direction with an increased width. The stopper gap 34 is set to have such a width that durability is ensured by limiting excessive relative displacement in the front-rear direction X of the inner cylinder 10 with respect to the outer cylinder 12 during acceleration / deceleration of the automobile. Further, the wide space 36 has a substantially circular round shape in a cross-sectional shape perpendicular to the axial direction Z in order to suppress local distortion when the inner cylinder 10 is displaced (see FIG. 2 and 3).

  As shown in FIGS. 4 and 5, the hollow portion 28 extends from the central portion 28 b in the axial direction Z (that is, the vehicle vertical direction L) toward the upper and lower open end portions 28 c thereof. 28a includes an inclined surface portion 38 that is inclined with respect to the axial direction Z. That is, the inclined surface portion 38 is inclined so that the cross-sectional area of the cavity portion 28 gradually increases toward the outside in the axial direction Z. More specifically, the inner wall surface 28 a of the cavity portion 28 includes a central surface portion 40 formed of a surface parallel to the axial direction Z at the central portion in the axial direction, and inclined surface portions 38 are provided on both sides in the axial direction of the central surface portion 40. It has been. And the axial direction dimension A of this center surface part 40 is set smaller than the axial direction dimension B of each inclined surface part 38 provided in the both sides. In the present embodiment, the dimensional relationship between the two is set to be constant over the entire circumferential direction of the cavity 28. The inclined surface portion 38 is chamfered and rounded at the open end 38 a of the cavity portion 28.

  As apparent from the comparison between FIG. 4 and FIG. 5, in the inclined surface portion 38, the inclination α with respect to the axial direction Z in the wide space portion 36 is set larger than the inclination β with respect to the axial direction Z in the stopper gap portion 34. . Specifically, it is preferable that the inclination α of the inclined surface portion 38 in the wide space portion 36 is set to 15 ° to 40 °, while the inclination β of the inclined surface portion 38 in the stopper gap portion 34 is 5 ° or less. In the present embodiment, the inclination of the inclined surface portion 38 gradually changes from both circumferential ends of the wide space portion 36 toward the stopper gap portion 34 in the central portion in the circumferential direction.

  As shown in FIGS. 2 and 3, the inner stopper rubber portion 30 is formed to protrude outwardly in the radial direction R from the inner cylinder 10 by rubber continuous from the vibration-proof base 14, and its front end surface, that is, the outer side The contact surface 30a with respect to the stopper rubber portion 32 is formed flat in a cross section perpendicular to the axial direction Z. On the other hand, the outer stopper rubber portion 32 is formed so as to protrude from the outer cylinder 12 toward the inner side in the radial direction R from the rubber continuous from the vibration isolating base 14, and is in contact with the distal end surface, that is, the inner stopper rubber portion 30. The surface 32a is formed in a curved surface convex inward in a cross section perpendicular to the axial direction Z.

  As shown in FIGS. 1 and 8, a ring-shaped contact member 42 that contacts the body-side member 2 is attached to the upper end portion 16 of the inner cylinder 10. The contact member 42 is a member made of a rigid material such as a metal, and includes an end surface of the upper end portion 16 of the inner cylinder 10, that is, an upper end surface 16 a, and a lower surface of the flange portion 2 b around the shaft portion 2 a of the body side member 2. It is assembled in a state sandwiched between them. More specifically, as shown in FIGS. 6 and 7, the contact member 42 includes a circular ring plate-shaped pressure contact wall portion 44 that is pressed against the lower surface of the body side member 2, and a peripheral edge of the pressure contact wall portion 44. An annular wall 46 that extends downward from the portion and fits to the outer periphery of the upper end portion 16 of the inner cylinder 10. The contact member 42 is externally fitted and fixed to the upper end portion 16 of the inner cylinder 10 by press-fitting the upper end portion 16 of the inner cylinder 10 into the annular wall 46.

  The surface of the contact member 42 that contacts the body side member 2, that is, the upper surface 48 of the pressure contact wall portion 44 is set to have a larger outer peripheral shape than the upper end surface 16 a of the inner cylinder 10. In the example, the outer diameter of the upper surface 48 of the press contact wall 44 is set larger than the outer diameter of the upper end surface 16a of the inner cylinder 10, and the area of the upper surface 48 is larger than the area of the upper end surface 16a of the inner cylinder 10. Also set to great.

  On the inner peripheral surface 46a of the annular wall 46, eight ribs 50 extending in the axial direction Z are distributed and arranged at regular intervals in the circumferential direction P1. As shown in FIG. 6, the rib 50 is a protrusion that protrudes in an arc shape in cross section. The rib 50 may be chamfered at the tip end in the axial direction Z so that the upper end 16a of the inner cylinder 10 can be easily press-fitted. Moreover, as shown in FIG. 7, the outer peripheral surface 46b of the annular wall 46 is formed in a tapered surface shape with a smaller diameter at the tip (lower end).

  As shown in FIG. 1, a rubber film 52 having a constant thickness is formed by vulcanizing and bonding with rubber continuous from the vibration isolating base 14 on the outer peripheral surface 16 b of the inner cylinder upper end portion 16 to which the annular wall 46 is fitted. The plurality of ribs 50 bite into the rubber film 52. The rubber film 52 is formed one step lower than the other rubber film part 54 between the vibration isolating substrate 14 and the other rubber film part 54, that is, has a smaller diameter than the other rubber film part 54.

  The anti-vibration device of the present embodiment having the above-described configuration is obtained by vulcanizing and molding the anti-vibration base 14 between the inner cylinder 10 and the outer cylinder 12 to obtain the shape shown in FIGS. In order to remove residual strain due to shrinkage after vulcanization at 14, a so-called throttling is performed to compress the outer cylinder 12 inward in the radial direction R. Further, as shown in FIG. 16 is manufactured by covering the contact member 42 by press-fitting.

  As shown in FIG. 8, the vibration isolator thus manufactured fixes the outer cylinder 12 by press-fitting and fitting it into the fitting hole 4 a of the member member 3 from below, and the hollow portion of the inner cylinder 10. The inner cylinder 10 is pressed and fixed to the body side member 2 by inserting the shaft portion 2a of the body side member 2 into the shaft 18 from above and inserting the bolt 1 from below to fasten the shaft portion 2a. At that time, a disc-shaped stopper fitting 58 for receiving the stopper rubber portion 24 in the vertical direction L is clamped and fixed to the lower end of the inner cylinder 10 by the bolt 1. Further, a stopper member 60 that restricts the upward displacement on the outer cylinder 12 side is disposed between the cylindrical holder 4 of the member member 3 and the flange portion 2 b of the body side member 2. The stopper member 60 includes a ring-shaped plate 62 disposed in contact with the upper end portion of the cylindrical holder 4 and a stopper rubber portion 64 provided on the upper surface thereof and in contact with the flange portion 2b. An inward lip rubber portion 66 that contacts the outer peripheral surface 46b of the annular wall 46 of the contact member 42 is provided.

  In the vibration isolator of this embodiment, a large contact area with respect to the body side member 2 is secured by the contact member 42 attached to the upper end portion 16 of the inner cylinder 10, so that the twisting direction acts during the operation of the automobile. The inner cylinder 10 is unlikely to fall down with respect to the load, so that the steering stability is excellent. In particular, with such a configuration using the abutting member 42, it is not necessary to increase the outer diameter of the entire inner cylinder, so that an increase in the weight of the inner cylinder can be avoided. In addition, the free length of the end face of the anti-vibration base can be made sufficiently long compared with the case where the vibration-proof base is vulcanized after the end portion of the inner cylinder is expanded by turning, and the durability of the anti-vibration base is improved. Can be improved. Furthermore, compared to the case where the diameter of the end of the inner cylinder is increased by cold plastic working, processing defects are less likely to occur, and the end surface on the inner cylinder that contacts the body side member can be made sufficiently large.

  Further, by providing a plurality of ribs 50 extending in the axial direction Z on the inner peripheral surface 46a of the annular wall 46, the upper end portion 16 of the inner cylinder 10 is secured to the annular wall 46 while ensuring the function of preventing the inner cylinder 10 from falling. It is easy to press fit into the inside, and the mounting workability of the contact member 42 is excellent.

  Further, these ribs 50 bite into the rubber film 52 provided on the outer peripheral surface 16b of the upper end portion 16 of the inner cylinder 10, whereby the relative displacement in the circumferential direction between the inner cylinder 10 and the contact member 42 is suppressed. Therefore, it is possible to prevent the generation of abnormal noise due to such relative displacement.

  Further, in the vibration isolator of the present embodiment, in the cavity portion 28 provided in the vibration isolator base 14, the axial dimension B of the inclined surface portion 38 is set larger than the axial dimension A of the central surface portion 40, By increasing the inclination α of the inclined surface portion 38 in the wide space portion 36 at both ends in the circumferential direction, the volume of the rubber elastic body around the upper and lower openings of the wide space portion 36 is reduced. Therefore, generation | occurrence | production of the flaw around the said opening part at the time of the drawing | extracting of the outer cylinder 12 after a vulcanization molding is suppressed. In addition, even when a load in the front-rear direction X is mainly input after mounting in the automobile and the inner cylinder 10 is relatively displaced in the front-rear direction X, the rubber elastic body around the opening in the wide space portion 36 as described above. Since the volume is reduced, strain concentration around the opening of the wide space 36 can be prevented.

  On the other hand, in the stopper gap portion 34 in the central portion in the circumferential direction, the inclination β of the inclined surface portion 38 on the inner wall surface 28a of the cavity portion 28 is set small, and the volume of the stopper rubber portions 30 and 32 around the opening portion is increased. Therefore, it is easy to ensure a stopper function against relative displacement of the inner cylinder 10 in the front-rear direction X.

  As described above, according to the present embodiment, durability can be improved by reducing wrinkles and strain concentration at both ends in the circumferential direction while ensuring a stopper function at the center in the circumferential direction of the cavity 28. .

  Further, in the present embodiment, since the inclined surface portion 38 as described above is provided on the inner wall surface 28a of the cavity portion 28, the core mold for removing the cavity portion 28 can be smoothly removed during vulcanization molding. The moldability is also excellent.

  Further, in the present embodiment, the contact surface 32a of the outer stopper rubber portion 32 in the stopper gap portion 34 is formed in a curved surface convex inward, so that the initial contact with the inner stopper rubber portion 30 is soft. Thus, abnormal noise can be reduced.

  The vibration isolator of the present invention can be suitably used as a mount device in various vehicles such as automobiles including body mounts.

It is a longitudinal cross-sectional view of the vibration isolator which concerns on one Embodiment of this invention. It is a top view of the vibration isolator before attaching a contact member. It is a bottom view of the vibration isolator before attaching a contact member. It is sectional drawing of the IV-IV line of FIG. It is sectional drawing of the VV line of FIG. It is a bottom view of a contact member. It is a longitudinal cross-sectional view of a contact member. It is sectional drawing of the use condition which built the vibration isolator into the suspension.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inner cylinder, 12 ... Outer cylinder, 14 ... Anti-vibration base | substrate, 16 ... Upper end part (one end part) of an inner cylinder, 16a ... Upper end surface (one end surface) of the upper end part of an inner cylinder, 16b ... Upper end part of an inner cylinder 28 ... hollow portion, 28a ... inner wall surface of the hollow portion, 28b ... central portion in the axial direction of the hollow portion, 28c ... open end portion of the hollow portion, 30 ... inner stopper rubber portion, 32 ... outer stopper rubber portion , 32a: Contact surface of the outer stopper rubber portion with respect to the inner stopper rubber portion, 34: Stopper gap portion, 36: Wide space portion, 38 ... Inclined surface portion, 40 ... Center surface portion, 42 ... Contact member, 46 ... Annular wall , 46a ... inner peripheral surface of the annular wall, 48 ... upper surface of the pressure-contact wall portion (surface on the side of the contact member that contacts the body side member), 50 ... rib, 52 ... rubber film, 2 ... body side member, 3 ... Member member (vibrating body), 4a: fitting hole, A: axial dimension of central surface portion, B: inclined surface portion Axial dimension, L: vertical direction, P: circumferential direction of vibration isolator, P1: circumferential direction of contact member, R: radial direction, X: front-rear direction, Y: left-right direction, Z: axial direction, α: wide Inclination of the inclined surface portion in the space portion, β: inclination of the inclined surface portion in the stopper gap portion

Claims (5)

An inner cylinder whose one end in the axial direction is attached to the body side member, an outer cylinder that surrounds the inner cylinder and is press-fitted into a fitting hole formed on the vibrating body side; the inner cylinder and the outer cylinder; An anti-vibration device comprising an anti-vibration base made of a rubber elastic body interposed between the two cylinders,
A contact member that contacts the body side member is attached to one end portion of the inner cylinder between the body side member and a surface of the contact member that contacts the body side member is The outer peripheral shape is set to be larger than the end surface of one end of the inner cylinder, and the contact member includes an annular wall that fits to the outer periphery of the one end of the inner cylinder, and the annular wall causes the inner cylinder to A plurality of ribs extending in the axial direction are provided on the inner peripheral surface of the annular wall ;
A pair of cavities facing each other across the inner cylinder are provided in the vibration-proof base so as to penetrate in the axial direction, and the cavity is formed by a stopper rubber part as a stopper gap in the circumferential center. At the same time, both end portions in the circumferential direction are made wider than the stopper gap portion, and the inner wall surface of the cavity portion extends in the axial direction so that the cavity portion extends from the central portion in the axial direction toward the opening end portion. An anti-vibration device comprising an inclined surface portion that is inclined, and the inclination of the inclined surface portion in the wide space portion is set larger than the inclination of the inclined surface portion in the stopper gap portion . Comprising a central surface which inner wall surface of the cavity is made of a plane parallel to the axial direction in the axial center portion of claim 1, wherein said inclined surface portion on both sides of the central surface is provided Anti-vibration device. The vibration isolator according to claim 2 , wherein an axial dimension of the central surface portion is set to be smaller than an axial dimension of each of the inclined surface portions provided on both sides of the central surface portion. The stopper gap portion of the hollow portion is formed between an inner stopper rubber portion protruding from the inner cylinder side and an outer stopper rubber portion protruding from the outer cylinder side, and the inner stopper rubber of the outer stopper rubber portion. abutment surface vibration isolating apparatus according to claim 1, characterized in that formed radially inward on the convex curved surface shape in a cross section perpendicular to the axial direction with respect to part. The inner cylinder is a member that is attached to a body side member of an automobile with the axial direction set to the vertical direction, and the outer cylinder surrounds the inner cylinder coaxially and is a fitting formed on a member member of the suspension 2. The vibration isolator according to claim 1 , wherein the vibration isolator is a member press-fitted into a hole, and the hollow portion is provided at a position facing the front-rear direction of the automobile with the inner cylinder interposed therebetween.

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