A chassis of an all-aluminum carriage

Abstract

The present invention provides an underframe of an all-aluminum car body, comprising a bottom frame, a bottom cross beam and a secondary longitudinal beam, the bottom cross beam and the secondary longitudinal beam are cross-connected, the secondary longitudinal beam is connected to a vehicle body beam, the secondary longitudinal beam is constructed as a groove structure with a horizontal opening, a double cross beam support is adopted to connect the bottom cross beam and the secondary longitudinal beam, a single support is adopted to connect the bottom frame and the secondary longitudinal beam at the front and rear of the vehicle, and a support block is adopted to support the secondary longitudinal beam connection node; the secondary longitudinal beam structure and the bottom cross beam of the present invention are simplified, small in size, and reduce the weight of the car body, simple bolt connection is adopted, the installation process is simplified, and the bearing capacity is strong, and the difficult problems of low welding strength and easy failure of aluminum alloy at the connection node are solved, and outstanding contributions are made to the overall force dispersion of the car body, the reduction of stress at the connection node, and the improvement of the firmness and reliability of the connection point.

Description

Technical Field

[0001] The invention belongs to the field of aluminum carriages, and in particular relates to an underframe of an all-aluminum carriage. Background Art

[0002] In the automotive industry, the lightweighting of automobiles has become a global development trend. In the field of trucks, the weight reduction of truck compartments can achieve lightweighting, which plays an important role in reducing vehicle energy consumption and increasing rated cargo capacity. Especially for new energy trucks, due to the large mass of the battery itself, the demand for weight reduction of the compartment is even stronger. Aluminum alloy materials have excellent characteristics such as light weight, high strength, extremely high corrosion resistance, not easy to fade, long life, and recyclability. At present, they have gradually replaced steel materials in the weight reduction design of truck compartments.

[0003] For example, Chinese patent CN 106080806B discloses an underframe of an all-aluminum carriage, comprising: a bottom frame, which comprises four frame beams connected to form a rectangular shape; two of the frame beams parallel to each other are transverse frame beams, and the other two are longitudinal frame beams; a secondary longitudinal beam, at least one secondary longitudinal beam is arranged in the bottom frame; both ends of the secondary longitudinal beam are respectively inserted and connected in a transverse frame beam; and a cross beam, at least one cross beam is arranged in the bottom frame, and both ends of the cross beam are respectively inserted and connected in a longitudinal frame beam; each cross beam is structurally connected with each secondary longitudinal beam by means of insertion at the intersection; the frame beams, the secondary longitudinal beams and the cross beams are all made of aluminum alloy.

[0004] The above structure uses a plug-in structure and a welding connection method to achieve the connection between the crossbeam and the secondary longitudinal beam. The crossbeam adopts a multi-cavity structure, and the insertion and welding production process requirements are relatively high, and the production cost is high.

[0005] In addition, in the prior art, U-bolts are used to connect the all-aluminum car body and the body frame. For example, Chinese patent CN209534855U discloses an all-aluminum structure sub-assembly type lightweight logistics car body, in which the straight beam is a closed cavity extruded aluminum profile, and a row of bolt holes connected to the cross beam are opened on the upper surface. The two straight beams are connected to the body frame through U-bolts to achieve the combination of the car body and the body.

[0006] The longitudinal beam structure of the vehicle chassis connected to the vehicle body beam by U-bolts can be set as a hollow square tube structure, such as the underframe of an all-aluminum vehicle body disclosed in Chinese patent CN 106080806 B, in which the secondary longitudinal beam includes a hollow square-shaped connecting portion and a hollow square-shaped supporting portion, the width of the supporting portion is smaller than the width of the connecting portion, and the upper end of the supporting portion is centrally connected to the lower end of the connecting portion. It can be seen that the secondary longitudinal beam of this structure is provided with multiple cavities, the structure is relatively complex, and the processing cost is high. Since the secondary longitudinal beam is connected to the chassis frame beam by U-bolts, the torsion reaches 90 to 100 N.m, and the local stress generated is relatively large. If the secondary longitudinal beam is constructed as a single cavity or an open structure, the structural strength is difficult to ensure, and the secondary longitudinal beam is easily deformed under the connection stress of the U-bolts, and the stability is poor. Summary of the invention

[0007] The present invention provides an underframe of an all-aluminum carriage, which has simplified auxiliary longitudinal beam structure and bottom cross beam, small volume, reduced carriage weight, simple bolt connection, simplified installation process, strong bearing capacity, and a support block structure to ensure the strength of the connection between the auxiliary longitudinal beam and the body beam. The problem of low welding strength and easy failure at the aluminum alloy connection node is solved, and outstanding contributions are made to the overall force dispersion of the carriage, reducing the stress of the connection node, and improving the firmness and reliability of the connection point.

[0008] The technical solution of the present invention is as follows:

[0009] A chassis of an all-aluminum car body, comprising a bottom frame, a bottom cross beam and a secondary longitudinal beam, wherein the bottom cross beam and the secondary longitudinal beam are cross-connected, the secondary longitudinal beam is connected to a vehicle body beam, the secondary longitudinal beam is constructed as a groove structure with a horizontal opening, the connection structure of the bottom cross beam and the secondary longitudinal beam comprises a double cross beam support, a sleeve and a bolt, the double cross beam support comprises a base arranged in pairs and a slot arranged above the middle of the base, the bottom cross beam is fixedly arranged in the slot, the bolt passes through the base, the secondary longitudinal beam in sequence The upper side and the sleeve gasket, the bolt and the sleeve gasket are threadedly fastened; the connection structure between the secondary longitudinal beam and the vehicle body beam includes a support block, a U-bolt, a pressure plate and a nut, the support block is arranged in the groove structure of the secondary longitudinal beam, the upper and lower ends of the support block are respectively abutted against the upper and lower ends of the inner side of the secondary longitudinal beam, the pressure plate, the secondary longitudinal beam and the vehicle body beam are connected in sequence from top to bottom, the bottom of the vehicle body beam is connected to the bottom of the U-bolt, and the upper end of the U-bolt is connected to the nut and then presses the pressure plate down.

[0010] The present invention adopts a double crossbeam support and a bolt fixing method to realize the connection between the bottom crossbeam and the secondary longitudinal beam. The bottom crossbeam and the secondary longitudinal beam are generally a lapped structure. According to the structure of the bottom crossbeam, a double support is designed. The double support can be inserted into the bottom crossbeam to form a structural connection, and the structure is subjected to force. A slider is designed at the connection between the secondary longitudinal beam and the bottom crossbeam, and the slider is bolted to the double support. The slider bears the complex stress of the connection between the secondary longitudinal beam and the bottom crossbeam, and the slider design can reduce the stress of this connection. The present invention avoids the installation and welding connection processing of the plug-in structure, simplifies the installation process, has a stable connection, strong bearing capacity, and is also convenient for later disassembly and maintenance; the opening section of the bottom crossbeam adopts a single-cavity structure, and the secondary longitudinal beam adopts a groove structure, the component structure is simple, the processing cost is low, and the lightweight effect is better.

[0011] In the present invention, after the secondary longitudinal beam is designed as a groove structure, since the secondary longitudinal beam is connected to the chassis frame beam with U-bolts, the torsion reaches 90 to 100 N.m, and the local stress generated is relatively large. In addition, the groove structure is weaker than the square structure, and it is difficult to meet the installation and use requirements. The present invention also takes into account the high lightweight requirements of the car body, and designs the secondary longitudinal beam as an open variable cross-section to reduce the dead weight.

[0012] The present invention is designed with a multi-cavity support block at the U-bolt connection to transmit and support the pressure and torsion of the U-bolt, disperse the stress, and ensure a reliable and firm connection. The present invention reinforces the upper and lower sides of the secondary longitudinal beam by filling a support block only in the groove structure of the secondary longitudinal beam at the connection node, thereby avoiding deformation of the secondary longitudinal beam under stress and ensuring the strength of the connection between the secondary longitudinal beam and the vehicle body beam.

[0013] The cross section of the secondary longitudinal beam of the chassis of the all-aluminum carriage of the present invention is an open variable cross section design, and the card slot is assembled with the secondary longitudinal beam slider. The chassis cross beam is designed as 9 long cross beams + 1 short cross beam, the bottom cross beam penetrates the left and right frames, and the triangular piece is welded and fixed. The frames are connected by a three-way part. The secondary longitudinal beam and the chassis can be shipped independently and assembled in different places, reducing transportation costs.

[0014] Preferably, the bottom cross beam is constructed as a cavity, and recessed parts are provided inwardly on both sides of the middle of the cross section of the bottom cross beam, and the double cross beam support is constructed as a groove structure with an opening upward, and bosses are provided inwardly on both sides of the double cross beam support, and the bosses and the recessed parts are engaged with each other. This structure realizes the connection between the double cross beam support and the bottom cross beam, eliminates the welding connection, has a simple structure, and is low in cost.

[0015] Preferably, a sleeve gasket groove is provided on the inner upper wall of the secondary longitudinal beam facing downward, and the sleeve gasket is installed in the sleeve gasket groove, so as to realize the positioning and fixing of the sleeve gasket and make the bolt connection more stable.

[0016] Preferably, the support block is constructed as a rectangular tube structure, and the support block is provided with crisscross reinforcing ribs. The support block can well fill the interior of the secondary longitudinal beam at the connection node. The support block is arranged as a tubular structure, which is conducive to weight reduction, and the reinforcing ribs increase the rigidity of the support block.

[0017] Preferably, the length of the support block along the longitudinal direction of the secondary longitudinal beam is 80-110 mm. The support block is a long rectangular tube structure, which can avoid the weight increase caused by the support block being too long and the stress concentration problem at the connection node.

[0018] Preferably, a cushion block is provided between the secondary longitudinal beam and the vehicle body beam. The cushion block is a rubber cushion that can buffer the impact generated when the vehicle is running and avoid impact damage at the connection node.

[0019] Preferably, the pad is fixedly connected to the lower part of the secondary longitudinal beam by nails, and a nail groove for accommodating the nail is provided in the lower part of the pad, so that the pad can be installed under the secondary longitudinal beam, the structure is simple, and the installation is convenient.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention simplifies the secondary longitudinal beam structure and designs it into a groove-type structure, which has a simple structure and achieves lightweight.

[0022] 2. To address the problem of poor strength of the secondary longitudinal beam, the present invention only fills a support block in the groove structure of the secondary longitudinal beam at the connection node, and designs a support block with a multi-cavity structure at the U-bolt connection to transmit and support the pressure and torsional force of the U-bolt, disperse the stress, and ensure a reliable and firm connection.

[0023] 3. The bottom cross beam and the secondary longitudinal beam are connected by double cross beam supports and bolt fixing, which avoids the installation and welding connection processing of the plug-in structure, simplifies the installation process, and has a stable connection, strong bearing capacity, and is also convenient for later disassembly and maintenance. It solves the problem of low welding strength and easy failure of aluminum alloy at the connection node, and makes outstanding contributions to the overall force dispersion of the car body, reducing the stress of the connection node, and improving the firmness and reliability of the connection point.

[0024] 4. The opening section of the bottom cross beam adopts a single-cavity structure, and the secondary longitudinal beam adopts a groove structure. The component structure is simple, the processing cost is low, and the lightweight effect is better.

[0025] 5. The cross section of the secondary longitudinal beam is designed as an open variable cross section, and the card slot is assembled with the secondary longitudinal beam slider. The chassis cross beam is designed as 9 long cross beams + 1 short cross beam. The bottom cross beam passes through the left and right frames, the triangular pieces are welded and fixed, and the frames are connected by three-way parts. The secondary longitudinal beam and the chassis can be shipped independently and assembled in different places to reduce transportation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of an underframe of an all-aluminum carriage according to the present invention.

[0027] Figure 2 It is a connection structure diagram of the bottom cross beam and the secondary longitudinal beam described in the present invention.

[0028] Figure 3 It is a structural diagram of the connection between the secondary longitudinal beam and the vehicle body beam of the present invention.

[0029] Figure 4 It is a stereoscopic diagram of the connection structure of the bottom cross beam and the secondary longitudinal beam according to the present invention.

[0030] Figure 5 and Figure 6 It is a structural schematic diagram of the double supports of the crossbeam described in the present invention.

[0031] Figure 7 and Figure 8 It is a structural schematic diagram of the sleeve cushion described in the present invention.

[0032] Fig. 9 It is a structural schematic diagram of the support block described in the present invention.

[0033] In the figure: 1-bottom frame, 2-bottom cross beam, 201-recessed portion, 3-secondary longitudinal beam, 301-shim groove, 4-cross beam double support, 401-base, 402-slot, 403-boss, 5-shim, 6-bolt, 7-body beam, 8-support block, 801-reinforcement rib, 9-U-bolt, 10-pressure plate, 11-nut, 12-nail, 13-shim block, 1301-nail groove. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] In the description of the present invention, it is necessary to understand that the terms "left", "right", "up", "down", "front", "back", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or structure referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0036] Embodiment 1:

[0037] like Figures 1 to 3As shown, as shown, a chassis of an all-aluminum car body includes a bottom frame 1, a bottom cross beam 2 and a secondary longitudinal beam 3, the bottom cross beam 2 and the secondary longitudinal beam 3 are cross-connected, the secondary longitudinal beam 3 is connected to the vehicle body beam 7, the secondary longitudinal beam 3 is constructed as a groove structure with a horizontal opening, the connection structure of the bottom cross beam 2 and the secondary longitudinal beam 3 includes a cross beam double support 4, a sleeve 5 and a bolt 6, the cross beam double support 4 includes a base 401 arranged in pairs and a slot 402 arranged above the middle of the base 401, the bottom cross beam 2 is fixedly arranged in the slot 402, and the bolt 6 passes through the base 401, The upper side of the secondary longitudinal beam 3 and the bushing 5, the bolt 6 and the bushing 5 are threadedly fastened; the connection structure between the secondary longitudinal beam 3 and the vehicle body beam 7 includes a support block 8, a U-bolt 9, a pressure plate 10 and a nut 11, the support block 8 is arranged in the groove structure of the secondary longitudinal beam 3, the upper and lower ends of the support block 8 are respectively abutted against the upper and lower ends of the inner side of the secondary longitudinal beam 3, the pressure plate 10, the secondary longitudinal beam 3 and the vehicle body beam 7 are connected in sequence from top to bottom, the bottom of the vehicle body beam 7 is connected to the bottom of the U-bolt 9, and the upper end of the U-bolt 9 is connected to the nut 11 to press the pressure plate 10 downward.

[0038] like Figure 3 As shown, the assembly method of the connection structure between the secondary longitudinal beam 3 and the vehicle body frame 7 in this embodiment is as follows: the support block 8 is installed into the groove body of the secondary longitudinal beam 3 and slid to the pre-connection node position, the U-bolt 9 passes through the vehicle body frame 7 of the chassis, the secondary longitudinal beam 3 and the pressure plate 10, and the thread on the upper end of the U-bolt 9 is connected with the nut 11 to press the pressure plate 10, thereby firmly fixing the vehicle body secondary longitudinal beam 3 and the chassis frame.

[0039] like Figure 2 As shown, this embodiment adopts the crossbeam double support 4 and bolt 6 fixing method to realize the connection between the bottom crossbeam 2 and the secondary longitudinal beam 3, avoiding the installation and welding connection processing of the plug-in structure, simplifying the installation process, and the connection is stable. The bearing capacity is strong and it is also convenient for later disassembly and maintenance; the opening cross section of the bottom crossbeam 2 adopts a single-cavity structure, and the secondary longitudinal beam 3 adopts a groove structure. The component structure is simple, the processing cost is low, and the lightweight effect is better.

[0040] Embodiment 2:

[0041] like Figures 1 to 3 As shown, a chassis of an all-aluminum car body includes a bottom frame 1, a bottom cross beam 2 and a secondary longitudinal beam 3. The bottom frame 1 includes four bottom frame beams 1 connected to form a rectangular shape. Both sides of each of the bottom cross beam 2 and the secondary longitudinal beam 3 are connected to the beam of the bottom frame 1 to form a car body chassis.

[0042] like Figure 2As shown, the bottom cross beam 2 and the secondary longitudinal beam 3 are cross-connected, the secondary longitudinal beam 3 is connected to the vehicle body beam 7, the secondary longitudinal beam 3 is constructed as a groove structure with a horizontal opening, the connection structure of the bottom cross beam 2 and the secondary longitudinal beam 3 includes a cross beam double support 4, a sleeve 5 and a bolt 6, the cross beam double support 4 includes a base 401 arranged in pairs and a slot 402 arranged above the middle of the base 401, the bottom cross beam 2 is fixedly arranged in the slot 402, the bolt 6 passes through the base 401, the upper side of the secondary longitudinal beam 3 and the sleeve 5 in sequence, and the bolt 6 and the sleeve 5 are threadedly fastened;

[0043] like Figure 3 As shown, the connection structure between the secondary longitudinal beam 3 and the vehicle body beam 7 includes a support block 8, a U-shaped bolt 9, a pressure plate 10 and a nut 11. The support block 8 is arranged in the groove structure of the secondary longitudinal beam 3. The upper and lower ends of the support block 8 are respectively abutted against the upper and lower ends of the inner side of the secondary longitudinal beam 3. The pressure plate 10, the secondary longitudinal beam 3 and the vehicle body beam 7 are connected in sequence from top to bottom. The bottom of the vehicle body beam 7 is connected to the bottom of the U-shaped bolt 9. The upper end of the U-shaped bolt 9 is connected to the nut 11 to press the pressure plate 10 downward.

[0044] This embodiment adopts the double crossbeam support 4 and bolt 6 fixing method to realize the connection between the bottom crossbeam 2 and the secondary longitudinal beam 3, avoiding the installation and welding connection processing of the plug-in structure, simplifying the installation process, and ensuring the connection is stable. The bearing capacity is strong and it is also convenient for later disassembly and maintenance. The opening cross section of the bottom crossbeam 2 adopts a single-cavity structure, and the secondary longitudinal beam 3 adopts a groove structure. The component structure is simple, the processing cost is low, and the lightweight effect is better.

[0045] In the present embodiment, after the middle secondary longitudinal beam 3 is designed as a groove-type structure, since the groove-type structure is weaker than the square structure and is difficult to meet the installation and use requirements, the present embodiment strengthens the upper and lower sides of the secondary longitudinal beam 3 by filling a support block 8 only in the groove-type structure of the secondary longitudinal beam 3 at the connection node, thereby avoiding deformation of the secondary longitudinal beam 3 due to stress and ensuring the strength of the connection between the secondary longitudinal beam 3 and the vehicle body beam 7.

[0046] like Figure 2 As shown, in this embodiment, the bottom cross beam 2 is constructed as a cavity, and recessed portions 201 are provided inwardly on both sides of the middle of the cross section of the bottom cross beam 2. Figure 5 and Figure 6 As shown, the double crossbeam support 4 is constructed as a groove structure with an opening upward, and bosses 403 are provided inwardly on both sides of the double crossbeam support 4, and the bosses 403 are engaged with the recessed portion 201. This structure realizes the connection between the double crossbeam support 4 and the bottom crossbeam 2, eliminates the welding connection, has a simple structure, and is low in cost.

[0047] like Figure 4 , Figure 7 and Figure 8 As shown, in this embodiment, the inner upper wall of the secondary longitudinal beam 3 is provided with a sleeve gasket groove 301 facing downward, and the sleeve gasket 5 is installed in the sleeve gasket groove 301. The sleeve gasket 5 is positioned and fixed, and the bolt 6 connection is more stable.

[0048] like Fig. 9 As shown, in this embodiment, the support block 8 is constructed as a rectangular tube structure, and the support block 8 is provided with longitudinal and transverse reinforcing ribs 801 inside, and the support block 8 is installed and filled inside the secondary longitudinal beam 3. The support block 8 can well fill the inside of the secondary longitudinal beam 3 at the connection node. The support block 8 is set as a tubular structure, which is conducive to weight reduction, and the reinforcing ribs 801 increase the rigidity of the support block 8.

[0049] In this embodiment, the length of the support block 8 along the longitudinal direction of the secondary longitudinal beam 3 is 80 mm. The support block 8 is a long rectangular tube structure, and this length mainly avoids the weight increase caused by the support block 8 being too long, while also avoiding the problem of stress concentration.

[0050] like Figure 3 As shown, in this embodiment, a cushion block 13 is provided between the secondary longitudinal beam 3 and the vehicle body beam 7. The cushion block 13 is a rubber cushion, which can buffer the impact generated when the vehicle is running and avoid the impact damage at the connection node.

[0051] like Figure 3 As shown, in this embodiment, the pad 13 is fixedly connected to the lower part of the secondary longitudinal beam 3 by means of a nail 12, a nail groove 1301 for accommodating the nail 12 is provided inwardly below the pad 13, and a nail hole for cooperating with the nail 12 is provided below the secondary longitudinal beam 3. It is convenient to install the pad 13 below the secondary longitudinal beam 3, with a simple structure and convenient installation.

[0052] Embodiment 3:

[0053] The difference between this embodiment and the above-mentioned embodiment 2 is that a single support is used to connect the bottom frame of the front and rear of the vehicle and the secondary longitudinal beam, and the length of the support block 8 along the longitudinal direction of the secondary longitudinal beam 3 is 110 mm, which can be mainly used to avoid stress concentration problems at the connection nodes and avoid weight increase caused by excessive length of the support block 8.

Claims

1. An underframe of an all-aluminum vehicle compartment, comprising a bottom frame (1), a bottom crossbeam (2) and a secondary longitudinal beam (3), wherein the bottom crossbeam (2) and the secondary longitudinal beam (3) are cross-connected, and the secondary longitudinal beam (3) is connected to a vehicle body beam (7), characterized in that: The secondary longitudinal beam (3) is constructed as a groove structure with a horizontal opening. The connection structure between the bottom cross beam (2) and the secondary longitudinal beam (3) comprises a double cross beam support (4), a bushing (5) and a bolt (6). The double cross beam support (4) comprises a base (401) arranged in pairs and a slot (402) arranged above the middle of the base (401). The bottom cross beam (2) is fixedly arranged in the slot (402). The bolt (6) passes through the base (401), the upper side of the secondary longitudinal beam (3) and the bushing (5) in sequence. The bolt (6) and the bushing (5) are threadedly fastened. The connection structure between the secondary longitudinal beam (3) and the vehicle body beam (7) comprises a support block (8), a U-bolt (9), a pressure plate (10) and a nut (11). The support block (8) is arranged in the groove structure of the secondary longitudinal beam (3). The support block (8) is arranged in the groove structure of the secondary longitudinal beam (3). ) upper and lower ends are respectively abutted against the upper and lower ends of the inner side of the secondary longitudinal beam (3); the pressure plate (10), the secondary longitudinal beam (3) and the vehicle body beam (7) are connected in sequence from top to bottom; the bottom of the vehicle body beam (7) is connected to the bottom of the U-shaped bolt (9); the upper end of the U-shaped bolt (9) is connected to the nut (11) and then presses the pressure plate (10) downward; the bottom cross beam (2) is constructed as a cavity; recessed portions (201) are provided inwardly on both sides of the middle of the cross section of the bottom cross beam (2); the double cross beam support (4) is constructed as a groove structure with an opening upward; bosses (403) are provided inwardly on both sides of the double cross beam support (4); the bosses (403) and the recessed portions (201) are snap-fitted; a sleeve gasket groove (301) is provided on the inner upper wall of the secondary longitudinal beam (3) facing downward, and the sleeve gasket (5) is installed in the sleeve gasket groove (301).

2. The chassis of an all-aluminum carriage according to claim 1, characterized in that: The support block (8) is constructed as a rectangular tube structure, and reinforcement ribs (801) are arranged vertically and horizontally inside the support block (8).

3. The underframe of an all-aluminum carriage according to claim 2, characterized in that: The length of the support block (8) along the longitudinal direction of the secondary longitudinal beam (3) is 80-110 mm.

4. The underframe of an all-aluminum carriage according to claim 1, characterized in that: A cushion block (13) is provided between the secondary longitudinal beam (3) and the vehicle body beam (7).

5. The underframe of an all-aluminum carriage according to claim 4, characterized in that: The pad (13) is fixedly connected to the bottom of the secondary longitudinal beam (3) via a nail (12); a nail groove (1301) for accommodating the nail (12) is provided inwardly below the pad (13).

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