JP7754421B2 - Side wall structure of cargo compartment of freight vehicle - Google Patents

Description

The present invention relates to the luggage compartment (cargo compartment, container compartment) of a truck, and in particular to the side wall structure of the luggage compartment.

Many freight vehicles have a roughly rectangular cargo compartment with the direction of travel as its longitudinal axis. The cargo compartment is sometimes called a "cargo compartment" or "container compartment," but in this specification it will be collectively referred to as the "cargo compartment."

The cargo compartment of a freight vehicle consists of a floor, side walls, top wall, front wall, and rear wall. Among freight vehicles with cargo compartments, those whose side walls and top wall open and close vertically as a single unit are sometimes called "wing body vehicles." Furthermore, freight vehicles with double doors on the rear or side walls are sometimes called "van body vehicles."

In any type of freight vehicle, the left and right side walls of the luggage compartment are made up of a frame, exterior materials, interior materials, etc. The exterior materials are placed on the outside of the frame and form the outer surfaces of the side walls, while the interior materials are placed on the inside of the frame and form the inner surfaces of the side walls.

Traditionally, wooden boards such as waran plywood have been the primary material used for interior decoration. However, in recent years, synthetic resin boards have also come to be used as interior decoration. More specifically, multi-layered synthetic resin boards are sometimes used as interior decoration. Multi-layered synthetic resin boards have, for example, a pair of surface layers and an intermediate layer between the surface layers, with air sealed in the intermediate layer. Furthermore, each surface layer is formed from a resin sheet several millimeters thick.

In the following explanation, wooden boards used as interior materials will be referred to as "wooden boards" and synthetic resin boards will be referred to as "resin boards" to distinguish between the two. On the other hand, when no distinction is made between wooden boards and synthetic resin boards, they will be collectively referred to as "boards."

The wooden board is fixed to the frame with screws. If the screw head protrudes significantly from the surface of the wooden board (the inner surface of the side wall of the luggage compartment), not only will it look unsightly, but there is also a risk of damaging luggage placed in the luggage compartment. Therefore, the screw head is provided with protrusions to countersink the surface of the wooden board. More specifically, the underside of the head (the seating surface) has multiple protrusions along the circumferential direction. As the screw is screwed into the wooden board, the protrusions on the seating surface rotate and come into contact with the surface of the wooden board. The rotating protrusions then scrape and cave in the surface of the wooden board. As a result, all or part of the screw head is buried, and the top surface of the head becomes flush or nearly flush with the surface of the wooden board (the inner surface of the side wall of the luggage compartment).

Patent Document 1 describes a floor structure for the luggage compartment of a truck. The floor structure described in Patent Document 1 comprises multiple joists, wooden boards placed on top of the joists to form the floor of the luggage compartment, and countersunk tapping screws that secure the boards to the joists. The back surface (seat) of the head of the countersunk tapping screw has multiple notched projections.

Patent No. 4199690

Resin boards are softer than wooden boats. In other words, the surface of a resin board is more fragile than the surface of a wooden board. Therefore, when a resin board is fixed to a frame using conventional screws, the protrusions on the seat surface can scratch the surface of the resin board (the inner surface of the side wall of the cargo compartment). For example, the resin sheet that forms the surface layer of the multi-layered resin board can be torn or slashed. Furthermore, the tears and cuts can extend to the area around the screw head, exposing it. Furthermore, contact with the rotating screw head can pull the resin sheet, causing wrinkles on the surface of the resin sheet (the inner surface of the side wall of the cargo compartment).

On the other hand, if the screws are tightened less to avoid the above-mentioned problems, the heads will protrude significantly from the surface of the plastic board.

Overall, it was difficult to create a high-quality luggage compartment using resin boards for the interior side walls.

The objective of this invention is to improve the quality of luggage compartments in which resin boards are used for the interior materials of the side walls.

In one embodiment, the sidewall structure for a trunk of a truck includes a frame, an exterior material disposed on the outside of the frame and forming the outer surface of the trunk, an interior material disposed on the inside of the frame and forming the inner surface of the trunk, and a fixing screw threadedly coupled to the frame through the interior material, the fixing screw having a head and a shank extending from the back surface of the head. The back surface of the head is provided with an inner annular region having a first tapered portion, an intermediate annular region having multiple protrusions, and an outer annular region having a second tapered portion, arranged in this order from the radially inner side to the radially outer side. The surfaces of the first tapered portion and the second tapered portion are smooth surfaces that slope radially outward to gradually approach the surface of the head. The multiple protrusions are provided continuously around the entire circumference of the intermediate annular region.

This invention achieves a high-quality luggage compartment using resin boards for the interior sidewall materials.

FIG. FIG. 2 is a partially enlarged perspective view showing the side wall structure of the luggage compartment. 3 is a cross-sectional view taken along the line XX in FIG. 2. 1A is a plan view of the fixing screw, FIG. 1B is a front view of the fixing screw, FIG. 1C is a rear view of the fixing screw, FIG. 1D is a right side view of the fixing screw, and FIG. 1E is a left side view of the fixing screw. FIG. 4 is an enlarged view showing the back surface (bearing surface) of the head of the fixing screw. 5A is an end view taken along line A-A in FIG. 5, FIG. 5B is an end view taken along line B-B in FIG. 5, and FIG. 5C is an end view taken along line C-C in FIG. 10 is a cross-sectional view showing a process in which a fixing screw penetrates an interior material and is screwed into a post. FIG. FIG. 10 is a cross-sectional view showing another process in which the fixing screw penetrates the interior material and is screwed into the post. FIG. 10 is a cross-sectional view showing another process in which the fixing screw penetrates the interior material and is screwed into the post. FIG. 10 is a cross-sectional view showing another process in which the fixing screw penetrates the interior material and is screwed into the post. FIG. 10 is a cross-sectional view showing another process in which the fixing screw penetrates the interior material and is screwed into the post.

An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Note that in all drawings referred to in describing the embodiment, the same reference numerals will be used for identical or substantially identical components. Furthermore, as a general rule, once a component has been explained, it will not be explained again.

<Overview of luggage compartment>
FIG. 1 is a perspective view of a truck 1 according to this embodiment. The truck 1 shown in FIG. 1 is provided with a luggage compartment 10 that is configured with a floor 11, side walls 12, a top wall 13, a front wall 14, and a rear wall 15 and is capable of accommodating luggage A. The floor 11 and top wall 13 of the luggage compartment 10 are rectangular, with the longitudinal direction extending in the fore-and-aft direction of the truck 1. The side walls 12 include a right side wall 12R that is connected to one long side of the floor 11 and the top wall 13, and a left side wall 12L that is connected to the other long side of the floor 11 and the top wall 13. Although not shown, the rear wall 15 of the luggage compartment 10 is provided with double-door doors. In other words, the truck 1 is a van body vehicle.

<Outline of sidewall structure>
Figure 2 is a partially enlarged perspective view showing the sidewall structure of the luggage compartment 10. Figure 3 is a cross-sectional view taken along the line X-X in Figure 2. A frame structure is employed for the sidewall 12 of the luggage compartment 10 in order to achieve weight reduction while maintaining the necessary durability. More specifically, the sidewall 12 has a plurality of posts 20, an exterior material 30 disposed on the outside of the posts 20, and an interior material 40 disposed on the inside of the posts 20. From another perspective, the exterior material 30 and the interior material 40 face each other with the plurality of posts 20 in between.

<Post (frame)>
The posts 20 are lined up along the longitudinal direction of the truck 1. Adjacent posts 20 are parallel to each other. Each post 20 is a metal member extending in the vertical direction (vehicle height direction) of the truck 1, and is interposed between the floor 11 and the top wall 13 to support the load of the top wall 13. In other words, the posts 20 are both frames for the side walls 12 and pillars that support the top wall 13.

Each post 20 has a post body 21 with a U-shaped cross section and a post flange 22 extending forward and backward from the edge of the opening of the post body 21.

The exterior material 30 placed on the outside of the post 20 forms the outer surface of the side wall 12, and the interior material 40 placed on the inside of the post 20 forms the inner surface of the side wall 12. Note that a heat insulating material may be provided between the opposing exterior material 30 and interior material 40.

<Exterior materials>
The exterior material 30 is a metal (e.g., aluminum alloy) plate. A plurality of protrusions 31 extending in the front-to-rear direction are press-formed into the exterior material 30. These protrusions 31 are parallel to each other and lined up vertically. The exterior material 30 is fixed to the post 20 with fasteners 32 such as blind rivets. More specifically, the exterior material 30 is fixed to the bottom surface (rear surface) of the post body 21.

<Interior materials>
The interior material 40 is a plate material made of synthetic resin having a multi-layer structure. In other words, the interior material is a resin board. Note that in Figure 2, the cross-sectional structure of the interior material 40 is simplified for convenience of drawing.

As shown in Figure 3, the interior material 40 has a multi-layer structure including an intermediate layer 41 and a pair of surface layers 42, 43 that face each other across the intermediate layer 41. Furthermore, air is sealed in the intermediate layer 41, and the surface layers 42, 43 are formed from resin sheets.

More specifically, the intermediate layer 41 has numerous air chambers, each filled with air. Each air chamber is cylindrical, and the top and bottom of each air chamber are airtightly sealed by resin sheets that form the surface layers 42 and 43.

In the following description, the surface layer 42 may be referred to as the "inner surface layer 42" and the surface layer 43 as the "outer surface layer 43" to distinguish between them. However, this distinction is made merely for the sake of convenience. The surface layers 42 and 43 of the interior material 40 are essentially the same layer.

Multiple interior materials 40 are arranged side by side inside the frame, with the inner surface layer 42 facing the interior of the luggage compartment 10. Each interior material 40 is fixed to the post 20 that constitutes the frame with a fixing screw 50. More specifically, the fixing screw 50 penetrates each interior material 40 in order, through the inner surface layer 42, intermediate layer 41, and outer surface layer 43, and is threadedly connected to the post flange portion 22.

The interior material 40, which has the above-described multi-layer structure, is elastic. From another perspective, the interior material 40 functions as a cushioning material that protects luggage A loaded in the luggage compartment 10. For example, luggage A loaded in the luggage compartment 10 may collide with the side wall 12 (interior material 40) due to shaking or vibration while the truck 1 is traveling. When this happens, the impact of the collision is absorbed by the elastic deformation of the interior material 40, preventing damage to the luggage A.

The ends of the front and rear interior materials 40 are adjacent to each other on the post 20. More specifically, the side edge (connecting edge 44) of one interior material 40 is fixed to one post flange portion 22 of the post 20, and the side edge (connecting edge 44) of the other interior material 40 is fixed to the other post flange portion 22 of the same post 20.

<Joint material>
The two connecting edge portions 44 fixed to the same post 20 are fitted into the joint member 23. The joint member 23 is a metal plate that extends in the same direction as the post 20.

The joint member 23 comprises a central portion 24 that covers the opening of the post body 21, intervening pieces 25 integrally formed on both sides (front and back) of the central portion 24, and a decorative cover piece 26 that faces the central portion 24. Furthermore, the central portion 24 and the decorative cover piece 26 are connected via a connecting piece 27 that is perpendicular to them.

The central portion 24 of the joint member 23 and the decorative cover piece 26 face each other with a gap that is approximately the same as the thickness of the interior material 40. From another perspective, gaps are formed at the front and rear of the connecting piece 27 into which the connecting edge portion 44 of the interior material 40 can be inserted.

A portion of the connecting edge 44 of one interior material 40 is inserted into the gap between the central portion 24 and the decorative cover piece 26 in front of the connecting piece 27. Furthermore, a portion of the connecting edge 44 of the other interior material 40 is inserted into the gap between the central portion 24 and the decorative cover piece 26 behind the connecting piece 27. As a result, the end faces of the respective connecting edges 44 face each other with the connecting piece 27 in between. Furthermore, the gap between the end faces of the opposing connecting edges 44 is covered by the decorative cover piece 26.

Furthermore, the intermediate piece 25 of the joint member 23 is sandwiched between the connecting edge portion 44 of the interior material 40 and the post flange portion 22 of the post 20. The fixing screw 50 penetrates not only the connecting edge portion 44 of the interior material 40 but also the intermediate piece 25, and is screwed to the post flange portion 22. From another perspective, the connecting edge portion 44 of the interior material 40 and the intermediate piece 25 of the joint member 23 are fastened together to the post flange portion 22 by the fixing screw 50.

The central portion 24 of the joint member 23 is slightly bent toward the inside (bottom surface) of the post body 21. The surface of the decorative cover piece 26 is located slightly outside (toward the exterior material 30) the surface of the interior material 40 excluding the connecting edge portion 44.

<Fixing screw>
Next, the fixing screw 50 that fixes the interior material 40 to the post 20 will be described in more detail. Figures 4(a) to 4(e) are views showing different faces of the fixing screw 50. More specifically, Figure 4(a) is a plan view of the fixing screw 50, Figure 4(b) is a front view, Figure 4(c) is a rear view, Figure 4(d) is a right side view, and Figure 4(e) is a left side view.

Figure 5 is an enlarged view showing the back surface 61 of the head 60 of the fixing screw 50. Note that the shank 70 is not shown in Figure 5. Figure 6(a) is an end view taken along line A-A in Figure 5, Figure 6(b) is an end view taken along line B-B in Figure 5, and Figure 6(c) is an end view taken along line C-C in Figure 5.

The fixing screw 50 comprises a head 60 and a shank 70 extending from the back surface 61 of the head 60. In the following description, the back surface 61 of the head 60 may be referred to as the "bearing surface 61." The front surface 62 of the head 60 may be referred to as the "upper surface 62."

The shank 70 is located in the center of the head 60 (seat surface 61). The shank 70 has a threaded portion 71 with a screw thread formed on its outer surface, and a drill portion 72 with a cutting blade. In other words, the fixing screw 50 is a drill screw. Therefore, when fixing the interior material 40 to the post 20, there is no need to drill a pilot hole in advance.

The threaded portion 71 is located at the base end of the shank 70, and the drill portion 72 is located at the tip end of the shank 70. There are no restrictions on the dimensions of each part of the fixing screw 50, but in this embodiment, the threaded portion 71 has an outer diameter of 4.8 mm and a thread pitch of 1.06 mm. The diameter of the head 60 is 14.5 mm.

Multiple annular regions are concentrically arranged on the seating surface 61. More specifically, an inner annular region 63, an intermediate annular region 64, and an outer annular region 65 are arranged in this order from the radially inner side to the radially outer side.

<Inner annular region>
The inner annular region 63 is the innermost region of the three regions, and its inner edge is connected to the shaft portion 70 and its outer edge is connected to the intermediate annular region 64 .

The inner annular region 63 is provided with a first tapered portion 66. The surface 66a of the first tapered portion 66 is a sloped, smooth surface. More specifically, the surface 66a of the first tapered portion 66 slopes so as to gradually approach the upper surface 62 of the head portion 60 as it extends radially outward.

From another perspective, when the tip of the shaft portion 70 faces downward (as shown in Figures 4(b), (d), and (e)), the surface 66a of the first tapered portion 66 slopes upward. In other words, when the tip of the shaft portion 70 faces upward (as shown in Figure 4(c)), the surface 66a of the first tapered portion 66 slopes downward. In the following description, the surface 66a of the first tapered portion 66 may be referred to as the "inner tapered surface 66a."

<Intermediate annular region>
The intermediate annular region 64 is a region between the inner annular region 63 and the outer annular region 65 , and its inner edge is contiguous with the inner annular region 63 and its outer edge is contiguous with the outer annular region 65 .

While the inner annular region 63 and outer annular region 65 are smooth, the intermediate annular region 64 has undulations. More specifically, the intermediate annular region 64 has a plurality of protrusions 80 continuously provided around the entire circumference. These protrusions 80 are formed by serration processing applied to the intermediate annular region 64.

<Protrusion>
As shown most clearly in Figure 6(b), each protrusion 80 includes a vertical surface 81 and an inclined surface 82, and has a cross-sectional shape that is generally a right-angled triangle overall. The vertical surface 81 is a surface that faces the tip of the shank 70 and is parallel to the center line C of the shank 70. From another perspective, the vertical surface 81 rises vertically when the tip of the shank 70 faces upward (the state shown in Figure 4(c)). In other words, the vertical surface 81 falls vertically when the tip of the shank 70 faces downward (the states shown in Figures 4(b), (d), and (e)).

The inclined surface 82 is a surface extending from one end of the vertical surface 81 toward one end of the vertical surface 81 of the adjacent other protrusion 80. When the tip of the shaft 70 is facing downward (as shown in Figures 4(b), (d), and (e)), the inclined surface 82 is an upwardly sloping surface extending from the bottom end of the vertical surface 81 of the protrusion 80 toward the top end of the vertical surface 81 of the adjacent other protrusion 80. In other words, when the tip of the shaft 70 is facing upward (as shown in Figures 4(c) and 6(b)), the inclined surface 82 is a downwardly sloping surface extending from the top end of the vertical surface 81 of the protrusion 80 toward the bottom end of the vertical surface 81 of the adjacent other protrusion 80.

As shown most clearly in Figure 5, the intersection 83 between the vertical surface 81 and the inclined surface 82 of each protrusion 80 extends in the radial direction of the head 60. As a result, the intersections 83 of the multiple protrusions 80 extend radially on the seating surface 61. From another perspective, the apexes (tips) of each protrusion 80 are aligned radially on the seating surface 61.

<Outer annular region>
The outer annular region 65 is the outermost of the three regions, and its inner edge is connected to the intermediate annular region 64 and its outer edge is connected to the side surface of the head portion 60 .

A second tapered portion 67 is provided in the outer annular region 65. The surface 67a of the second tapered portion 67 is a sloped, smooth surface. More specifically, the surface 67a of the second tapered portion 67 slopes so that it gradually approaches the upper surface 62 of the head portion 60 as it extends radially outward.

From another perspective, when the tip of the shaft portion 70 faces downward (as shown in Figures 4(b), (d), and (e)), the surface 67a of the second tapered portion 67 slopes upward. In other words, when the tip of the shaft portion 70 faces upward (as shown in Figure 4(c)), the surface 67a of the second tapered portion 67 slopes downward. In the following description, the surface 67a of the second tapered portion 67 may be referred to as the "outer tapered surface 67a."

Here, the inclination of the outer tapered surface 67a relative to the center line C is gentler than the inclination of the inner tapered surface 66a relative to the center line C. Specifically, the angle θ1 shown in Figure 4(d) is approximately 41°, while the angle θ2 is approximately 75°.

<Procedure for fixing interior materials>
Next, the process by which the fixing screw 50 shown in FIG. 3 penetrates the interior material 40 and is screwed to the post 20 will be described. FIGS. 7 to 11 are cross-sectional views showing the above process in chronological order. However, for convenience of drawing, the joint member 23 is omitted from FIGS. 7 to 11. As described above, the fixing screw 50 shown in FIG. 3 penetrates the interior material 40 and the joint member 23 (interposition piece 25) and is screwed to the post 20. Note that in reality, the interior material 40 is fixed to the post 20 by a number of fixing screws 50, including the fixing screw 50 shown in FIG. 3. These multiple fixing screws 50 also include fixing screws 50 that fix portions of the interior material 40 other than the connecting edge portion 44 (portions that do not overlap with the joint member 23) to the post 20.

The fixing screw 50 shown in Figure 7 is screwed partway into the interior material 40 and post 20 (post flange portion 22), with the shank 70 passing through the interior material 40 and post 20. However, at the stage shown in Figure 7, the head 60 of the fixing screw 50 has not yet reached the interior material 40.

The fixing screw 50, which is a drill screw, drills its own holes in the interior material 40 and post 20 (post flange portion 22). Therefore, there is no need to drill pilot holes in the interior material 40 and post 20 before screwing the fixing screw 50 into them, and there is no need to form threads (female threads) on the inner surfaces of the pilot holes.

When the fixing screw 50 is screwed into the interior material 40 and post 20 to a certain extent and the head 60 reaches the interior material 40, the bearing surface 61 comes into contact with the inner surface layer 42 (resin sheet) of the interior material 40. More specifically, the inner annular region 63 (Figure 5) of the bearing surface 61 comes into contact with the inner surface layer 42 (resin sheet) of the interior material 40.

Then, as the fixing screw 50 continues to be screwed in, the first tapered portion 66 provided in the inner annular region 63 is pressed into the interior material 40. At this time, because the surface of the first tapered portion 66 (the inner tapered surface 66a) is inclined as described above, the first tapered portion 66 is smoothly pressed into the interior material 40.

See Figure 8. As the fixing screw 50 is further screwed in, the intermediate annular region 64 (Figure 5) of the bearing surface 61 comes into contact with the inner surface layer 42 (resin sheet) of the interior material 40. In other words, the tips of the multiple protrusions 80 come into contact with the inner surface layer 42 of the interior material 40. At this time, the tips of each protrusion 80 come into contact with the inner surface layer 42 while rotating.

As a result, the inner surface layer 42 of the interior material 40 is pulled in the rotational direction of the fixing screw 50 while being pushed in the direction of the fixing screw 50's advancement. However, at this stage, the contact state between the bearing surface 61 and the inner surface layer 42 of the interior material 40 is line contact. Therefore, the contact resistance between the bearing surface 61 and the inner surface layer 42 is small, and the load received by the inner surface layer 42 is also small. As a result, the inner surface layer 42 (resin sheet) is not cut or torn, and wrinkles do not occur in the inner surface layer 42 (resin sheet).

Referring now to Figure 9. As the fixing screw 50 is further screwed in, it is pushed by the bearing surface 61, causing the inner surface layer 42 and intermediate layer 41 of the interior material 40 to sink. During this time, the bearing surface 61 and the inner surface layer 42 of the interior material 40 remain in line contact. Therefore, the rotational resistance of the bearing surface 61 is small, allowing the inner surface layer 42 and intermediate layer 41 to sink smoothly.

See Figure 10. As the fixing screw 50 is further screwed in, the outer annular region 65 (Figure 5) of the bearing surface 61 comes into contact with the inner surface layer 42 (resin sheet) of the interior material 40. In other words, the second tapered portion 67 comes into contact (surface contact) with the inner surface layer 42 of the interior material 40. This increases the rotational resistance of the bearing surface 61. Furthermore, the surface of the second tapered portion 67 (outer tapered surface 67a) has a gentler slope than the surface of the first tapered portion 66 (inner tapered surface 66a). For this reason, the second tapered portion 67 is less likely to be pressed into the interior material 40 than the first tapered portion 66.

From another perspective, the operator can sense that the second tapered portion 67 has come into contact with the inner surface layer 42 of the interior material 40 due to the increased rotational resistance of the seat surface 61. Furthermore, the operator can stop the work before the second tapered portion 67 is pushed too far into the interior material 40.

Through the above steps, as shown in Figure 11, the head 60 of the fixing screw 50 is embedded exactly into the interior material 40. From another perspective, a substantially circular depression 45 is formed on the surface of the interior material 40, into which the head 60 of the fixing screw 50 is embedded exactly. Furthermore, during the above steps, the inner surface layer 42 (resin sheet) of the interior material 40 is not damaged, and no wrinkles are formed in the inner surface layer 42 (resin sheet) of the interior material 40.

Referring again to Figures 1 and 2, lashing rails 90 are provided on the inside of the side wall 12. However, the lashing rails 90 may be provided as needed and are not a required component for realizing the side wall structure described above.

The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the invention.

1...lorry, 10...luggage compartment, 11...floor, 12...side wall, 12L...left side wall, 12R...right side wall, 13...ceiling wall, 14...front wall, 15...rear wall, 20...post, 21...post main body, 22...post flange, 23...joint member, 24...central portion, 25...intervening piece, 26...decorative cover piece, 27...connecting piece, 30...exterior material, 31...protrusion, 32...fixing device, 40...interior material, 41...intermediate layer, 42...surface layer (inner surface layer), 43...surface layer (outer surface layer), 44...connecting edge, 60...head, 61...back surface (seat), 62...surface (top), 63...inner annular region, 64...intermediate annular region, 65...outer annular region, 66...first tapered portion, 66a...surface (inner tapered surface), 67...second tapered portion, 67a...surface (outer tapered surface), 70...shaft, 71...threaded portion, 72...drilled portion, 80...projection, 81...vertical surface, 82...inclined surface, 83...intersection line, 90...lashing rail, A...load, C...center line, θ1, θ2...angles

Claims (3)

A side wall structure of a luggage compartment of a freight vehicle,
The frame and
an exterior material disposed outside the frame and forming an outer surface of the luggage compartment;
an interior material disposed inside the frame and forming an inner surface of the luggage compartment;
a fixing screw that penetrates the interior material and is screwed to the frame,
The fixing screw includes a head and a shank extending from a rear surface of the head,
an inner annular region provided with a first tapered portion, an intermediate annular region provided with a plurality of protrusions, and an outer annular region provided with a second tapered portion are arranged in this order from the radially inner side to the radially outer side on the back surface of the head;
the surfaces of the first tapered portion and the second tapered portion are smooth surfaces that are inclined so as to gradually approach the surface of the head as they extend radially outward,
A side wall structure for a luggage compartment of a truck, wherein a plurality of the protrusions are provided without gaps around the entire circumference of the intermediate annular region. Each of the protrusions is
a vertical surface extending parallel to the center line of the shaft portion toward the tip side of the shaft portion, and an inclined surface extending from one end of the vertical surface toward one end of the vertical surface of another adjacent projection,
2. The sidewall structure of a luggage compartment of a truck according to claim 1, wherein an intersection line between the vertical surface and the inclined surface of each of the projections extends in a radial direction of the head portion. the interior material has a multilayer structure including an intermediate layer and a pair of surface layers facing each other with the intermediate layer interposed therebetween,
The intermediate layer contains air,
3. The side wall structure for a luggage compartment of a truck according to claim 1, wherein each of the surface layers is formed of a resin sheet.