JP2003120738A - Suspension cross member installing bush and suspension cross member installing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aimed bush characteristic when fixing a bush to a car body by preventing deformation of the bush when pressing the bush in a suspension cross member. SOLUTION: This bush 2 is composed of an outer member 21 composed of an outer body 211 and an outer flange 212, an inner member composed of an inner body and an inner flange inserted inside the outer member 21, and having a through hole, and an elastic body between the outer member 21 and the inner member, and is pressed in an upper surface in a bush installing hole 11 of the cross member 1 by pressing the outer flange 212 by a press-in tool. The bush 2 is similarly pressed in an under surface of the cross member. A reinforcing part 213 is formed between the outer flange 212 and the outer body 211 of the outer member 21 to prevent deformation of the outer flange 212 when pressing the bush 2 in the bush installing hole 11 by pressing the outer flange 212.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suspension cross member mounting bush and a suspension cross member mounting structure.

[0002]

2. Description of the Related Art As a bush used for attaching parts such as suspension arms to a vehicle body, for example, Japanese Patent Laid-Open No.
As described in 000-145854, a cylindrical outer member, a cylindrical inner member that is inserted into the inner member and that can be penetrated by a bolt, and an elastic body provided between them. There is a structure in which the bush is divided into two parts, and the two bushes are press-fitted into the press-fitting part provided on the suspension arm from both sides until the inner members come into contact with each other, and the bolt is penetrated into the inner member and fixed together with the vehicle body. Are known. The bush is press-fitted by applying the bush to the press-fitting portion and pressing the outer flange portion extending radially outward from the outer member in the press-fitting direction by a press-fitting jig.

[0003]

However, in the above structure, when the outer diameter of the outer member becomes relatively larger than the inner diameter of the press-fitting portion due to the variation in the dimensional accuracy of parts, the press-fitting resistance is increased. It may become large and may deform the outer flange during press fitting. For example, when the above bush is used for the mounting part of the suspension cross member (hereinafter referred to as the cross member) that is mounted on the bottom surface of the vehicle body at multiple points, the bush is pressed into the cross member until the outer flange abuts the entire surface. However, if the outer flange is deformed in the pressing direction at the time of press-fitting, the press-fitting of the bush will be completed in a state where the predetermined press-fitting length in the bush body is not obtained.

The incomplete press-fitting of the bush as described above is such that when the bush is fixed to the vehicle body, the elastic body of the bush is interposed between the vehicle body and the cross member in a state of being unnecessarily deformed in the axial direction. Also, it causes variation in the deformation of the elastic body between the bushes that are press-fitted into the above-mentioned mounting parts, and the preset characteristics of the bushes cannot be obtained, which adversely affects the vehicle's controllability and riding comfort. give.

In particular, a bush used for a suspension cross member is in a state where the elastic body of the bush is compressed by a predetermined amount in the axial direction (a predetermined amount in the axial direction) in order to satisfy the needs of maneuverability and riding comfort. In the state with pre-compression) may be interposed between the vehicle body and the suspension cross member. In this case, the pre-compression is applied
This is done by fixing the cross member to the vehicle body in a state where the elastic member of the bush is compressed by tightening the fastening member.However, the incomplete press-fitting of the bush as described above requires tightening the fastening member to tighten the bush. When the vehicle is fixed to the vehicle body, there is a problem that the pre-compression amount cannot be obtained as set, or the pre-compression amount varies greatly among the bushes. The characteristics cannot be obtained.

The present invention has been made in view of the above points, and prevents a bush used for fixing a suspension cross member to a vehicle body at a plurality of places from being deformed when being pressed into the suspension cross member. As a result, it is possible to mount the suspension cross member on the vehicle body while reliably preventing the incomplete press-fitting due to the deformation of the bush and exerting the desired characteristics on the bush. The purpose is to ensure comfort.

[0007]

The first structure of the present invention is as follows.
It can be press-fitted into the mounting hole that penetrates the suspension cross member that is mounted on the underside of the vehicle body from both sides in the vertical direction, and has an axial length that is less than half the penetrating length of the mounting hole of the suspension cross member. A cylindrical outer body, a jig abutting portion that extends outward in the circumferential direction from the outer body at one axial end of the outer body, and a press-fitting jig abuts, and a bead shape along the circumferential direction. An outer member having an outer flange having a plurality of reinforcing portions formed so as to be continuous with the outer body, and an axial length longer than half the penetrating length of the mounting hole of the suspension cross member and the outer length. A substantially cylindrical inner body having an outer diameter smaller than the inner diameter of the outer body, and at one axial end of the inner body. An inner flange extending outward from the inner body in the circumferential direction and having an outer diameter larger than the inner diameter of the outer body, and a fastening member for fastening and fixing the suspension cross member to the vehicle body are pierceable in the axial direction. An inner member that has a through hole and is inserted substantially concentrically inside the outer member such that the inner flange and the outer flange are located on the same side in the axial direction; and the inner member and the outer member. The inner main body, the inner flange, the outer main body, and the outer flange are provided between the outer member and the member, and the outer member and the inner member together with the outer member from above and below the mounting hole of the suspension cross member. Wait until the flange contacts the suspension cross member above. In a state where there is substantially no elastic deformation before being fastened by the fastening members in the respective press-fitted states, a predetermined separation distance is generated between the other axial end portions of the pair of inner members, and the fastening is performed. Elasticity is provided between the inner member and the outer member such that the pair of inner members are displaced in the axial direction toward each other by the tightening of the members until the other ends contact each other. A suspension cross member mounting bush having a deformable elastic body.

With this structure, when the bush is press-fitted into the mounting hole of the cross member from above and below, the outer flange is prevented from being deformed by the reinforcing portion. Therefore, the bushes are press-fitted into the respective mounting holes from above and below in a proper state, and after the press-fitting, a predetermined separation distance is generated between the end portions of the inner member with very high accuracy. By tightening the fastening members until they come into contact with each other, the bush members are accurately pre-compressed in the axial direction, which corresponds to the separation distance between the inner members. Can be fixed to the car body.

According to a second aspect of the present invention, the jig abutting portion is provided between the reinforcing portions in the circumferential direction of the outer flange, and the jig is in contact with the outer body in a sectional view including the central axis of the bush. It is a plane portion that is continuous with the outer body at an angle of approximately 90 degrees.

With such a structure, when the press-fitting jig is brought into contact with the above-mentioned plane portion upon press-fitting, the press-fitting jig presses the portion of the outer flange near the outer body. Therefore, in combination with the effect of the reinforcing portion, it is possible to reliably prevent the deformation of the outer flange during press fitting.

According to a third aspect of the present invention, the reinforcing portion has an outer flange inclined surface which is continuous with the outer main body at an angle greater than 90 degrees with the outer main body in a sectional view including the central axis of the bush. And the inner flange has an inner flange inclined surface that faces the outer flange inclined surface and is substantially parallel to the outer flange inclined surface.

With such a structure, the shape of the reinforcing portion can be used for improving the accuracy of the characteristics of the bush. That is, in the state where the bush is fixed to the vehicle body, the elastic bodies cause pre-compression in the vertical direction while the inclined surfaces face each other substantially in parallel, so that the variation in deformation of the elastic body between the mounting portions, that is, the pre-compression occurs. The variation in the amount of compression is less likely to occur.

A fourth structure of the present invention has a bush mounting hole into which a bush is press fitted from an upper surface and a lower surface, and the first to third embodiments of the present invention are press fitted into the upper surface and the lower surface of the bush mounting hole. A structure for mounting a suspension cross member, which is mounted on the lower surface of the vehicle body through the bush by fastening and fixing the bush according to the configuration to the vehicle body together with a corresponding fastening member, and is press-fitted on the upper surface in the bush mounting hole. A suspension cross member mounting structure, characterized in that the bush and the inner member of the bush press-fitted to the lower surface are fixed to the vehicle body by the fastening member in a state where the other axial end portions are in contact with each other. is there.

With such a structure, it is possible to provide a suspension cross member mounting structure having the effects of the first to third structures.

A fifth structure of the present invention can be press-fitted into a mounting hole provided in a suspension cross member mounted on a vehicle body, and is provided with a substantially cylindrical outer main body, and extends from the outer main body in the circumferential direction to the outside. An outer member having a plurality of reinforcing portions formed in a bead shape along the circumferential direction so as to be continuous with the outer body while being pressed in a press-fitting direction by a press-fitting jig; The outer body includes a substantially cylindrical inner body having an outer diameter smaller than an inner diameter of the outer body, and a through hole through which a fastening member for fastening and fixing the suspension cross member together with the vehicle body can penetrate in the axial direction. An inner member inserted substantially concentrically inside the member; and an elastic body provided between the inner member and the outer member. The suspension is a cross-member mounting bush.

With such a structure, the bush is prevented from being deformed when it is press-fitted into the bush mounting hole of the suspension cross member, and the bush is pressed into the bush mounting hole in an appropriate state. Therefore, the bush is fixed to the vehicle body. In that case, the desired characteristics can be exhibited.

[0017]

According to the present invention, in a bush used to fix a suspension cross member to a vehicle body at a plurality of locations, deformation of the bush is prevented by preventing deformation when the suspension cross member is press-fitted into the suspension cross member. It is possible to mount the suspension cross member on the vehicle body while reliably preventing the incomplete press-fitting due to the bushing and exhibiting the desired characteristics in the bush, and it is possible to secure the steering stability and ride comfort of the vehicle as set. I can.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a top view of a front suspension cross member 1 (hereinafter referred to as a cross member) mounted on a vehicle body using a bush 2 according to the present invention. The cross member 1 is formed of a frame having a closed cross-section structure into a frame shape as shown in the drawing, and the bushes 2 are press-fitted into the bush mounting holes 11 to 14 at four positions. Figure 1
Although only the bush on the upper surface side is shown in the figure, the bush is press-fitted correspondingly to the lower surface. On the other hand, on the vehicle body (not shown), bolts are projectingly provided at four positions corresponding to the above-mentioned four bush positions.
Is fixed to the vehicle body by fastening the bushes 2 press-fitted into the bush mounting holes 11 to 14 together with the bolts and nuts.

Bush mounting hole 11 of the cross member 1
The bush 2 press-fitted into the shafts 14 to 14 is of a so-called two-split type in which it is split at the center in the axial direction before the press-fitting. That is, the two bushes 2 are press-fitted into the upper and lower surfaces of the bush mounting holes 11 to 14 of the cross member 1, respectively.

With reference to FIGS. 2 to 4, the bush 2
The configuration of will be described.

As shown in FIG. 2, the bush 2 has a substantially annular shape in a top view. Further, as shown in FIG. 3 which is a sectional view taken along the line AA of FIG. 2 and FIG. 4 which is a sectional view taken along the line BB of FIG. And a metal inner member having a substantially cylindrical portion having an outer diameter portion smaller than the outer shape of the outer member 21 and having a through hole 224 through which a bolt for mounting a cross member can penetrate. 22 and an elastic body 23 arranged between the outer member 21 and the inner member 22 and bonded to each.

As shown in FIGS. 3 and 4, the outer member 21 has a cylindrical outer body 211 having a diameter larger than the outer diameter of the inner member 22, and an outer end of the outer body 211 in the axial direction. Outer flange 212 extended toward
The axial length of the outer member 21 is set to be shorter than half the thickness of the cross member of the bush mounting hole portions 11 to 14 into which the bush 2 is press fitted. The outer flange 212 is further formed with a bead-shaped reinforcing portion 213 partially in the circumferential direction of the flange.

Specifically, the reinforcing portions 213 are provided at four locations at equal intervals along the circumferential direction of the outer flange as shown by the ridge lines in FIG. 2 in broken lines, and as shown in FIG. It has an inner inclined surface 214 and an outer inclined surface 215, respectively, which are formed by deforming the flange so as to project toward the one end in the axial direction of the flange 212. As shown in FIG. 3, the inner inclined surface 214 makes an angle larger than 90 degrees with the outer body 211 in a cross-sectional view including the central axis of the bush 2. Further, as shown in FIG. 4, a flat surface portion substantially perpendicular to the outer body 21 between four reinforcing portions 213 along the circumferential direction serves as a jig contact portion 216 which will be described in detail later. As shown in FIG. 4, the jig contact portion 216 makes an angle of approximately 90 degrees with the outer main body 211 in a sectional view including the central axis of the bush 2.

As shown in FIGS. 3 and 4, the inner member 22 has a through hole 224 having a substantially constant cross section in the axial direction, through which the bolt 42 for mounting the cross member can penetrate, and has a cylindrical shape. Inner body 221 and inner body 221
Of the inner flange 222, which is provided at one axial end and extends outward in the circumferential direction, and which has an outer diameter larger than the inner diameter of the outer body 21, inside the outer member 21.
The inner flange 222 and the outer flange 212 are concentrically inserted so as to be located on the same side in the axial direction. On the surface of the inner flange 222 on the other end side in the axial direction with respect to the inner body, an inclined surface 223 having a predetermined angle with respect to the inner body 221 and continuous with the inner body 221 is continuously formed in the circumferential direction. The inclined surface 223 of the inner flange is set to be substantially parallel to the inner inclined surface 214 provided on the outer flange 212. Also,
The axial length of the inner member 22 is set to be longer than half the thickness of the cross member in the bush mounting hole portion into which the bush is press fitted.

An elastic body 23 is arranged between the inner member 22 and the outer member 21. The elastic body 23 is made of rubber, and as shown in FIGS. 3 and 4, a substantially cylindrical elastic body main body 231 and an extending portion 232 formed at one axial end of the elastic body.
Consists of. Further, the elastic body 23 is adhered to the inner member 22 and the outer member 21 over the entire contact surface with an adhesive, respectively, and also in the extending portion 232, the radial inner surface thereof is different from the outer surface of the inner body 221. The inner flange inclined surface 223 is closely contacted, and the radially outer surface is closely contacted from the inner surface of the outer body 211 to the reinforcing portion 213 formed on the outer flange 212. In addition, as shown in FIG. 2, the extending portion 232 is provided with a portion of the outer flange other than the reinforcing portion 213, that is, a portion that covers the reinforcing portion 213 except for the jig contact portion 216. Even in the elastic body
23 is bonded to the outer flange 212. Therefore, the peeling resistance of the elastic body 23 to the outer member 21 is maintained.

Press-fitting the bush 2 into the cross member 1,
The mounting of the cross member 1 to the vehicle body will now be described with reference to FIGS. 5 to 7, using the bush mounting hole 11 as an example.

The bush 2 is press-fitted into the bush mounting holes 11 to 14 provided in the cross member 1 from the upper surface and the lower surface thereof. Explaining the mounting hole 11 as an example, the mounting hole 11 provided in the cross member 1 as shown in FIG. 5 which is a cross-sectional view corresponding to a cross section taken along the line BB of FIG.
Then, the upper surface and the lower surface (only the upper surface side is shown in FIG. 5) are press-fitted by the press-fitting jig 5. Then, as shown in FIG. 6, which is a cross-sectional view corresponding to the cross section taken along the line AA of FIG. 2, the bolt 42 fixed to the vehicle body 3 is attached to the cross member 1 in which the press-fitting of the bush 2 is completed. 7 is a cross-sectional view corresponding to the cross section taken along the line AA of FIG. 2 by fastening the nuts 41 to the bolts 42 of each support portion and fixing them together, after locating through 224. The cross member 1 is fixed to the vehicle body 3 in the state shown. Also, before being fixed to the vehicle body 3,
A suspension arm (not shown), a wheel hub supported by them, a coil damper, a stabilizer, and the like are previously assembled to the cross member.

Insert each bush 2 into each bush mounting hole 11 to 14
5, the jig 5 is brought into contact with the jig contact portion 216 formed on the outer flange 212, so that the outer flange 212 is brought into contact with the upper surface or the lower surface of the cross member 1 by the jig 5. This is done by pressing the bush 2 in the press-fitting direction until it comes into contact with.

Therefore, since the jig 5 presses the outer flange portion relatively close to the central axis of the bush 2 between the reinforcing portions 213, the jig 5 presses in cooperation with the action of the reinforcing portion 213. Deformation of the outer member 21 due to press-fitting resistance, specifically, the outer body 211 and the outer flange 2.
The deformation near the connection with 12 is prevented.

Here, in the state before the bush 2 is press-fitted into the cross member 1 and before being fixed to the vehicle body, as shown in FIG. 6, there is a space L between both inner members.
Since the outer flange 212 is prevented from being deformed at the time of press-fitting by the reinforcing portion 213 and the jig contact portion 216, the gap L has a very small deviation from a preset amount.

Similarly to the bush mounting hole 11, the bushes 2 are press-fitted into the other bush mounting holes 12 to 14, and a predetermined gap is formed between the inner members after the bushes 2 are press-fitted. Each bush mounting hole 11
The bushes 2 which are press-fitted into the upper and lower surfaces of the through holes 14 have a through-hole 224 whose cross-sectional shape substantially matches the cross-sectional shape of the fastening member in order to absorb variations in positioning and dimensional accuracy of the cross member 1, one direction. Only those with elongated holes,
It is also possible to prepare three types, that is, one having a uniform diameter, and to assign the bush mounting holes 11 to 14 to the upper surface and the lower surface.

As described above, in the cross member 1 in which the bush 2 and the above-mentioned components are assembled, the bolts 42 are inserted into the through holes 224 of the press-fitted bush 2, and then the nuts 41 are attached to the bolts 42. The bush 2 is fixed to the vehicle body 3 through the bush 2 by fastening the bush 2 and the bush 2 together. As shown in FIG. 7 again, the nut 41 is tightened until the inner members 22 of the upper and lower bushes 2 are displaced relative to the outer member 21 and come into contact with each other. In the state after being tightened, the elastic members 23 above and below the inner member 22 and the outer member by the above-mentioned interval L.
The compression is performed in the vertical direction between 21 and the pre-compression in the axial direction corresponding to the compression, that is, the vertical direction of the vehicle body occurs.

Therefore, as long as the distance between the upper surface and the lower surface of the cross member 1 at the portion where the outer flange 212 abuts is proper, the inner members of the upper and lower bushes 2 are each.
By a simple operation of tightening the nut 41 until the two members come into contact with each other, the bush 2 can be subjected to a certain vertical precompression corresponding to the compression of the interval L.

Similarly to the bush mounting holes 11, the other bush mounting holes 12 to 14 are bolted through the press-fitted bush 2 through holes 224 and tightened by the nut 41 until the inner members come into contact with each other.

Therefore, by setting the interval L so that an appropriate pre-compression is generated, such an appropriate pre-compression is generated in a state where the variation between the bushes 2 press-fitted into each mounting hole is extremely small. It becomes possible. Moreover, since the gap L deviates very little from the set amount as described above, the pre-compression amount obtained in the state where the nut 41 is tightened can be surely made exactly as intended. Furthermore, since the inclined surface 223 of the inner flange 222 and the inner inclined surface of the outer flange reinforcing portion 213 are set to be substantially parallel to each other as described above, the elastic body 23 pre-compresses between the inclined surfaces. However, it becomes more uniform. Further, since the surfaces are made to face each other substantially in parallel, variation in deformation of the elastic body, that is, variation in the amount of pre-compression, is unlikely to occur between the mounting portions, which contributes to improvement in accuracy.

The above-described present embodiment is an example in which the bush according to the present invention is applied to the front cross member, but it is also possible to apply the bush to the rear cross member,
And, needless to say, in that case, the same operational effect is obtained.

Further, the present invention is not limited to the bush having the two-divided structure as in the above-mentioned embodiment and fixed to the vehicle body with a predetermined amount of pre-compression in the axial direction. Instead, it can be applied to a bush that is pressed into the cross member from only one direction, or a bush that is fixed to the vehicle body without precompression.

[Brief description of drawings]

FIG. 1 is a top view of a suspension cross member attached to a vehicle body using a bush according to the present invention.

FIG. 2 is a top view of a bush according to the present invention.

3 is a cross-sectional view taken along the line AA in FIG.

FIG. 4 is a sectional view taken along the line BB in FIG.

5 is a cross-sectional view of the bush during press fitting, which corresponds to a cross section taken along the line BB in FIG.

FIG. 6 is a view of the bush, which has been press-fitted, in FIG.
It is sectional drawing equivalent to the A arrow cross section.

[Fig. 7] Fig. 7 shows a bush of a state in which joint tightening to a vehicle body is completed.
It is sectional drawing equivalent to the AA arrow cross section in FIG.

[Explanation of symbols]

1 Suspension cross member 5 Press-fitting jig 11, 12, 13, 14 Bush mounting hole 21 Outer member 22 Inner member 23 Elastic body 211 Outer body 212 outer flange 213 Reinforcement part 214 Inside slope (outer flange slope) 216 Jig contact part 221 Inner body 222 Inner flange 223 Inner flange inclined surface 224 through hole

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3J059 AA03 AA04 AD02 BA42 BA54                       BB01 BC06 BD01 BD05 CB09                       CB16 DA12 GA02

Claims (5)

[Claims] 1. An axial direction which can be press-fitted into a mounting hole penetrating a suspension cross member mounted on the lower surface of a vehicle body from both sides in the vertical direction, and which is less than half the penetrating length of the mounting hole of the suspension cross member. A substantially cylindrical outer body having a length, a jig contact portion that extends outward in the circumferential direction from the outer body at one axial end portion of the outer body, and a jig contact portion with which a press-fitting jig contacts, along the circumferential direction. And an outer flange having a plurality of reinforcing portions formed in a bead shape so as to be continuous with the outer body, and an outer member having a longer length than half the length of the suspension cross member in the penetrating direction of the mounting hole. A substantially cylindrical inner body having an axial length and an outer diameter smaller than the inner diameter of the outer body; In the portion, an inner flange extending outward from the inner body in the circumferential direction and having an outer diameter larger than the inner diameter of the outer body, and a fastening member for fastening and fixing the suspension cross member to the vehicle body penetrates in the axial direction. A possible through hole, and an inner member that is inserted substantially concentrically inside the outer member such that the inner flange and the outer flange are located on the same side in the axial direction, and the inner member. Between the outer member and the inner body, the inner flange, the outer body, and the outer flange, the outer member and the inner member together with the upper and lower sides of the mounting hole of the suspension cross member. The outer flange is the suspension cross member. In a state where they are press-fitted until they come into contact with each other, a predetermined separation distance is generated between the other axial end portions of the pair of inner members when there is substantially no elastic deformation before fastening by the fastening member, The inner member and the outer member are arranged so that the pair of inner members are displaced by the fastening member in the axial direction toward the outer member until the other ends come into contact with each other by tightening with the fastening member. A suspension cross member mounting bush having an elastic body that can be elastically deformed between. 2. The jig contact portion is provided between the reinforcing portions in the circumferential direction of the outer flange, and makes an angle of about 90 degrees with the outer body in a cross-sectional view including the central axis of the bush. The bush for mounting the suspension cross member according to claim 1, wherein the bush is a plane portion that is continuous with the outer body. 3. The inner flange, wherein the reinforcing portion has an outer flange inclined surface that is continuous with the outer main body at an angle of more than 90 degrees with the outer main body in a cross-sectional view including the central axis of the bush. The bush for mounting the suspension cross member according to claim 1, further comprising an inner flange inclined surface that faces the outer flange inclined surface and is substantially parallel to the outer flange inclined surface. 4. A bushing mounting hole into which a bush is press-fitted from an upper surface and a lower surface, and a corresponding fastening of the bush according to any one of claims 1 to 3, which is press-fitted into the upper surface and the lower surface of the bush mounting hole. A suspension cross member mounting structure, which is mounted on the lower surface of the vehicle body through the bush by fastening together with a member by a member, wherein the bush and the lower surface are press-fitted in the bush mounting hole. A mounting structure for a suspension cross member, characterized in that the inner member of the bush is fixed to the vehicle body by the fastening member in a state where the other axial end portions are in contact with each other. 5. A substantially cylindrical outer body that can be press-fitted into a mounting hole provided in a suspension cross member mounted on a vehicle body, and extends outward in the circumferential direction from the outer body, and the bead extends in the circumferential direction. An outer flange having a jig contact portion with which a plurality of reinforcing portions and the press-fitting jig are formed so as to be continuous with the outer body,
An outer member having, an inner body having a substantially cylindrical shape having an outer diameter smaller than the inner diameter of the outer body, and a through hole through which a fastening member for fastening and fixing the suspension cross member to the vehicle body is pierceable in the axial direction. And a bushing for mounting a suspension cross member, comprising: an inner member inserted substantially concentrically inside the outer member; and an elastic body provided between the inner member and the outer member.