Structure for improving strength of tabular portion and substantially rectangular parallelepiped member

A polygon in a tabular portion includes first and second axes of symmetry substantially orthogonal to each other. A top surface of the tabular portion has a swelling portion with an outline that is line-symmetric with respect to the first and second axes of symmetry. In a lateral half portion of the outline, a short-side side crest portion that is convex toward the polygonal outline in the direction of the first axis of symmetry, concave corner-side trough portions connected to each end of the short-side side crest portion and long-side side crest portions that are connected to each corner-side trough portion and convex toward the polygonal outline are formed. On one of a top surface and an undersurface of the swelling portion, a pair of lateral ribs or a pair of longitudinal ribs that spreads toward the polygonal outline and transversely crosses the swelling portion is formed.

TECHNICAL FIELD

The present invention relates to a structure for improving the strength of a substantially polygonal (four or more corners) tabular portion typified by a substantially rectangular tabular portion that has a short side extending in a longitudinal direction and a long side extending in a lateral direction.

BACKGROUND ART

Conventionally, a junction box of a photovoltaic power generation module is constructed of an upper case and a lower case, and an electronic circuit is accommodated therein. The upper case of this kind is generally made up of a substantially rectangular parallelepiped member whose lower part is opened or simply made up of a substantially rectangular tabular member (e.g., see Patent Documents 1 and 2).

Substantially rectangular parallelepiped members whose upper part or lower part is opened are used not only for a junction box but also for other industrial parts such as an oil pan of an engine and a waterproof pan for placing a washing machine.

Such substantially rectangular parallelepiped members are required to have a certain degree of strength depending on their target industrial parts. For example, since a junction box may be installed outdoors, its substantially rectangular tabular portion is required to have the strength resistant to a load from the outside (e.g., collision load of flying objects such as hail). Conventionally, various efforts have been made to secure the strength, including increasing the thickness of the tabular portion, modifying the material of the tabular portion, and the like.

RELATED ART REFERENCES

Patent Documents

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, in the method that improves the material of the tabular portion, the material cost may increase. On the other hand, the method that increases the thickness of the tabular portion not only cannot meet the need for space saving but also uses more material. For example, when an attempt is made to replace a conventional metal part by a resin part to place prime importance on a weight reduction, if the thickness of the resin part is increased to keep the same strength as that of the metal part, more resin material is used, which may prevent a sufficient weight reduction depending on the situation. From the standpoint of resource saving, it is desirable to provide the tabular portion with strength by using the smallest possible amount of resin material and still make the strength less susceptible to the difference in material.

The present invention has been implemented in view of the above-described background, and it is an object of the present invention to provide a structure and a substantially rectangular parallelepiped member capable of mechanically and effectively enhancing the strength of a resin-made substantially polygonal (four or more corners) tabular portion.

Means for Solving the Problem

As a result of an FEM analysis carried out by the present inventor, the present inventor discovered that the above-described problems could be solved by forming a swelling portion combining a certain outline and a certain rib configuration on a top surface of a resin-made tabular portion and came to complete the present invention.

That is, a first structure of the present invention is a structure for improving strength of a resin-made substantially polygonal (four or more corners) tabular portion, in which the polygon comprises a first axis of symmetry and a second axis of symmetry which are substantially orthogonal to each other, and a top surface of the tabular portion comprises a swelling portion formed so as to swell upward in a region inside the polygonal outline. The outline of the swelling portion is line-symmetric with respect to the first axis of symmetry and the second axis of symmetry. In a lateral half portion of the outline of the swelling portion, a short-side side crest portion that is convex toward the polygonal outline in a direction of the first axis of symmetry, a corner-side trough portion that is connected to each end of the short-side side crest portion and concave toward the polygonal outline in a region sandwiched between the first axis of symmetry and the second axis of symmetry, and a long-side side crest portion that is connected to an end opposite to the short-side side crest portion of the each corner-side trough portion and convex toward the polygonal outline are formed. At least a pair of lateral ribs that transversely crosses the swelling portion so as to spread toward the polygonal outline or a pair of longitudinal ribs that longitudinally crosses the swelling portion so as to spread toward the polygonal outline is formed on one of a top surface and an undersurface of the swelling portion.

According to the present invention, since a region whose shape is changed (swelling portion) is formed on the top surface of the tabular portion, the overall surface strength of the top surface of the tabular portion improves compared to a case without any such region. Regarding the outline of the swelling portion in particular, since the above-described crest portion and trough portion are combined and the crest portion and trough portion are arranged to be line-symmetric based on the outline of the tabular portion, it is possible to effectively improve impact strength against a pressure on the entire top surface (surface load).

Furthermore, regarding the top surface or undersurface of the swelling portion, impact strength can be improved by a rib configuration.

The above-described improvement of the design of the resin-made tabular portion, that is, a combination of the specific outline of the swelling portion and the specific rib configuration can mechanically and synergistically improve the strength of the tabular portion, and can thereby provide a tabular portion useful for securing impact strength resistant to a point load and surface load even when the smallest possible amount of resin material is used.

The structure preferably includes the lateral ribs and the longitudinal ribs, the lateral ribs are preferably arranged on at least one of the top surface and undersurface of the swelling portion, and the longitudinal ribs are preferably arranged on at least one of the top surface and undersurface of the swelling portion. In this case, the lateral ribs and the longitudinal ribs preferably cross each other. This can effectively improve the impact strength against a point load on the swelling portion.

According to a preferred aspect of the present invention, the polygon is preferably a rectangle whose short side extends parallel to the second axis of symmetry and whose long side extends parallel to the first axis of symmetry. In this case, the short-side side crest portion is preferably convex toward the center of the short side. The corner-side trough portion is preferably concave toward the corner portion at which the short side and the long side cross each other. Moreover, the long-side side crest portion is preferably convex toward the long side. Furthermore, the pair of lateral ribs are preferably arranged so as to be line-symmetric with respect to the first axis of symmetry, and further preferably transversely crosses the swelling portion so as to spread toward the short side. Similarly, the pair of longitudinal ribs are preferably arranged so as to be line-symmetric with respect to the second axis of symmetry, and preferably longitudinally crosses the swelling portion so as to spread toward the long side.

Furthermore, a second structure of the present invention is a structure for improving strength of a resin-made substantially rectangular tabular portion whose short side extends in a longitudinal direction and whose long side extends in a lateral direction, in which a top surface of the tabular portion includes a swelling portion formed so as to swell upward in a region inside the substantially rectangular outline, the outline of the swelling portion is line-symmetric with respect to a longitudinal center line and a lateral center line, and in a lateral half portion of the outline of the swelling portion, a short-side side crest portion that is convex toward the center of the short side, a corner-side trough portion that is connected to each end of the short-side side crest portion and concave toward the corner portion at which the short side and the long side cross each other, and a long-side side crest portion that is connected to the each corner-side trough portion and convex toward the long side, are formed. On one of a top surface and an undersurface of the swelling portion, at least a pair of lateral ribs that are arranged so as to be line-symmetric with respect to the lateral center line and transversely crosses the swelling portion so as to spread toward the short side and a pair of longitudinal ribs that are arranged so as to be line-symmetric with respect to the longitudinal center line and longitudinally crosses the swelling portion so as to spread toward the long side, are formed, and the lateral ribs and the longitudinal ribs cross each other.

According to the present invention, since a region whose shape is changed (swelling portion) is formed on the top surface of the tabular portion, the surface strength of the top surface of the tabular portion as a whole improves compared to a case without any such region. Regarding the outline of the swelling portion in particular, since the above-described crest portion and trough portion are combined and arranged so as to be line-symmetric based on the outline (short side, long side and corner portion) of the tabular portion, it is possible to effectively improve impact strength against a pressure on the entire top surface (surface load).

Furthermore, the strength of the top surface or undersurface of the swelling portion can be improved through a rib configuration. Particularly, since the lateral ribs and the longitudinal ribs are arranged so as to be line-symmetric in the above-described bent (spread) form and made to cross each other in the form of transversely and longitudinally crossing the swelling portion, it is possible to effectively improve the impact strength against a point load on the swelling portion.

The above-described improvement of the design of the resin-made tabular portion, that is, the combination of the specific outline and the specific rib configuration of the swelling portion can mechanically and synergistically improve the strength of the tabular portion, and can thereby provide a tabular portion useful for securing impact strength resistant to a point load and a surface load even when the smallest possible amount of resin material is used.

In the case of the second structure of the present invention and the first structure of the present invention, when the polygon is a substantial rectangle, the structure preferably assumes the following aspects.

That is, the long-side side crest portion is preferably most convex toward the long side at a position apart by a length of approximately ⅓ of the length of the long side from the short side. More preferably, in a longitudinal half portion of the outline of the swelling portion, the long-side side crest portion located in one lateral half portion of the outline and the long-side side crest portion located in the other lateral half portion of the outline are connected together with the long-side side inter-crest portion, and the long-side side inter-crest portion is preferably convex toward the center of the long side by an amount of protrusion smaller than that of these long-side side crest portions.

According to such a configuration, it is possible to more effectively improve the impact strength.

In a region outside the swelling portion, a first outside rib that extends so as to connect both ends of the lateral ribs to at least one of the short side and the long side and a second outside rib that extends so as to connect both ends of the longitudinal ribs to the long side are preferably formed.

According to this configuration, since the longitudinal ribs and lateral ribs located in the swelling portion are connected to the ribs outside the swelling portion, it is possible to enhance the reinforcement effect through the rib configuration. For example, when a load is applied to the swelling portion, it is possible to make the load propagate through the rib configuration to be released to outside the swelling portion, thus suppressing deformation of the swelling portion.

According to one more preferable aspect, the lateral ribs and the longitudinal ribs are preferably formed on the undersurface of the swelling portion, and the first outside rib and second outside rib are preferably formed on the top surface of the tabular portion.

According to this configuration, it is possible to widely secure a plane configuration on the top surface of the swelling portion. This is useful when the top surface of the swelling portion is desired to be used as a plane configuration, for example, when a predetermined display of manufacturer name, product name or the like is desired to be shown on the top surface. As a specific example, such a configuration is useful when the tabular portion is used for a cover of a junction box for a photovoltaic power generation module.

According to another more preferred aspect, the lateral ribs and the longitudinal ribs are preferably formed on the top surface of the swelling portion and the first outside rib and the second outside rib are preferably formed on the top surface of the tabular portion.

According to this configuration, it is possible to widely secure a plane configuration on the undersurface of the tabular portion. This configuration is useful when the undersurface of the tabular portion is desired to be used as a plane configuration, for example, when a liquid or the like is not desired to be continuously stored between the ribs of the undersurface. As a specific example, this configuration is useful when the tabular portion is used for a base of an oil pan.

In the region inside the swelling portion, a plurality of first intermediate ribs for connecting the lateral ribs, a plurality of second intermediate ribs for connecting the longitudinal ribs and a plurality of third intermediate ribs for connecting the lateral ribs and the longitudinal ribs are preferably formed.

According to this configuration, since the rib configuration is stretched around the region inside the swelling portion, it is possible to further enhance the reinforcement effect of the swelling portion by the lateral ribs and longitudinal ribs.

More preferably, a fourth intermediate rib may be formed in the region inside the swelling portion, which extends so as to connect the outline of the swelling portion at a position apart from the lateral ribs and the longitudinal ribs.

According to this configuration, it is possible to reinforce the region of the swelling portion to which the reinforcement effect by the lateral ribs and longitudinal ribs does not fully extend.

A corner rib is preferably formed in the region outside the swelling portion, which extends so as to connect the short side and the long side.

According to this configuration, it is possible to also reinforce the corner portion of the tabular portion. The corner rib may include at least part of the above-described first outside rib.

More preferably, a bridge rib that extends so as to connect the corner rib and the corner-side trough portion may be formed in a region outside the swelling portion.

According to this configuration, it is possible to enhance the reinforcement effect as in the case of the above-described relationship between the longitudinal ribs and the first outside rib. For example, when a load is applied to one of the swelling portion and corner portion, it is possible to make the load propagate through the rib configuration to be released to the other of the swelling portion and the corner portion, which suppresses these parts from deforming. The bridge rib may include at least part of the above-described first outside rib.

The substantially rectangular parallelepiped member of the present invention is provided with the above-described structure of the present invention (structure relating to the substantially rectangular tabular portion), is a substantially rectangular parallelepiped member whose lower part is opened and includes the tabular portion and a peripheral wall portion that extends downward from the perimeter of the tabular portion.

The present invention can provide a substantially rectangular parallelepiped member having a resin-made tabular portion whose impact strength is mechanically and effectively enhanced.

Here, the substantially rectangular parallelepiped member can be, for example, a junction box, oil pan of an engine, waterproof pan for placing a washing machine or various other industrial parts, and is not limited to these examples. Various types of material can be used as a resin material used to mold at least part of the substantially rectangular parallelepiped member and those adapted to the use of the substantially rectangular parallelepiped member are preferably used.

For example, when the substantially rectangular parallelepiped member constitutes at least part of an oil pan, the resin is preferably glass fiber reinforced polyamide 66 or polyamide 6. Adopting such resin can exert effects appropriate for the use of a part as an oil pan (impact resistance, heat resistance, creeping property, high rigidity and vibration fatigue property).

Furthermore, when the substantially rectangular parallelepiped member constitutes at least part of a junction box for a photovoltaic power generation module, the resin is preferably modified PPE. This can exert effects appropriate for the use of a part as a junction box (advantageous in aspects of hydrolysis resistance, flame retardancy, dimensional accuracy and electric characteristic).

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will be described with reference to the accompanying drawings. Position-related terms such as “upper” and “lower” used in the following description are relative to a case where a tabular portion is placed on an installation surface with a swelling portion facing up.

First Embodiment

First, with reference toFIGS. 1 to 3, a cover of a junction box for a photovoltaic power generation module will be described, to which a structure for improving strength of a substantially rectangular tabular portion is applied.

As shown inFIG. 1, a junction box1for a photovoltaic power generation module is provided with a junction box body2which is a lower case and a cover3which is an upper case. The junction box body2has a box shape whose top surface is opened and an electronic circuit is accommodated therein. The junction box body2is provided with a connection section between a cable for the photovoltaic power generation module and an outside connection cable so that electric power generated in the photovoltaic power generation module is distributed to an outside device or the like. The cover3is intended to cover the opening of the junction box body2and is provided with a substantially rectangular tabular portion4as a region that covers the opening. The cover3is provided with a peripheral wall portion5that extends downward from the perimeter of the tabular portion4. That is, the cover3is configured as a substantially rectangular parallelepiped member whose lower part is opened. Fixing portions6to fix the cover3to the junction box body2are provided at each of the front, back, left and right positions of the peripheral wall portion5.

Here, the structure of the cover3of the present embodiment is not particularly limited as long as it has the substantially rectangular tabular portion4. For example, the cover3may also be a substantially rectangular tabular member instead of the substantially rectangular parallelepiped member shown inFIG. 1. The “substantially rectangular” only requires that the four sides be composed of two short sides and two long sides, and neither means that the angle of the corner portion where one short side and one long side cross each other should be limited to 90 degrees nor means that part of one short side or one long side should be limited to straight line.

Resin is used as the material of the cover3. Of resin, modified PPE (polyphenylene ether) is preferably used from the standpoint of hydrolysis resistance, flame retardancy, dimensional accuracy and electric characteristics.

As shown inFIGS. 2 and 3, the tabular portion4has a substantially rectangular shape with short sides10A and10B extending in a longitudinal direction and long sides11A and11B extending in a lateral direction. On a top surface12of the tabular portion4, a swelling portion13is formed so as to swell upward in a region inside the substantially rectangular outline of the tabular portion4. When viewed from the undersurface14side of the tabular portion4(seeFIG. 2(B)), the swelling portion13appears as a concave form on the undersurface14. The swelling portion13is formed in the major portion of the tabular portion4centered on a central area of the tabular portion4, and the area occupied by the swelling portion13in the tabular portion4is approximately 50%.

The outline and rib configuration of the swelling portion13are line-symmetric with respect to a longitudinal center line (second axis of symmetry) and a lateral center line (first axis of symmetry). The longitudinal center line is a vertical bisector of the long sides11A and11B. The lateral center line is a vertical bisector of the short sides10A and10B.

First, the outline of the swelling portion13will be described.

In a left half portion (lateral half portion) of the outline of the swelling portion13, a short-side side crest portion21A which is convex toward the center of the short side10A, corner-side trough portions22A and22B which are concave toward corner portions15A and15B which are connected to each end of the short-side side crest portion21A and where the short side10A crosses the long sides11A and11B, and long-side side crest portions23A and23B which are connected to respective corner-side trough portions22A and22B and convex toward the long sides11A and11B are formed. The short-side side crest portion21A as a whole has a substantially semicircular outline whose crest is located on a lateral center line. The long-side side crest portions23A and23B are most convex toward the long sides11A and11B respectively at positions apart by a length of approximately ⅓ of the length of the long side11A and11B from the short side10A, and are located on the left side of the longitudinal center line. Note that the right half portion of the outline of the swelling portion13also has a similar configuration, and the corresponding portions are assigned reference characters C and D instead of A and B, and description thereof will be omitted here.

In the upper half portion (longitudinal half portion) of the outline of the swelling portion13, the long-side side crest portion23A and a long-side side crest portion23C are connected with a long-side side inter-crest portion24A. The long-side side inter-crest portion24A is convex toward the center of the long side11A by a smaller amount of protrusion than that of the long-side side crest portion23A and23C and a crest thereof is located on a longitudinal center line. In the lower half portion of the outline of the swelling portion13, the long-side side crest portion23B and a long-side side crest portion23D are likewise connected with a long-side side inter-crest portion24B.

Next, a rib configuration of the swelling portion13will be described.

The rib configuration of the swelling portion13can be roughly divided into a rib configuration (31A,31B,32A,32B, and41to45) in a region inside the outline of the swelling portion13and a rib configuration (51to57) in a region outside the outline of the swelling portion13. Hereinafter, these rib configurations will be described in order.

The inside rib configuration (31A,31B,32A,32B, and41to45) is formed on an undersurface13aof the swelling portion13which is one step lower than the undersurface14of the tabular portion4. Of the inside rib configuration (31A,31B,32A,32B, and41to45), a pair of lateral ribs31A and31B and a pair of longitudinal ribs32A and32B are designed to effectively improve impact strength against a point load on the swelling portion13. The lateral ribs31A and31B and the longitudinal ribs32A and32B cross each other in the central area of the swelling portion13.

In the following description, of the inside rib configuration (31A,31B,32A,32B, and41to45), the lateral ribs31A and31B and the longitudinal ribs32A and32B may be called “basic ribs” and the other ribs41to45may be called “supplementary ribs.” InFIG. 3(B), the lateral ribs31A and31B and longitudinal ribs32A and32B which are the basic ribs are colored in gray to secure viewability of the plurality of ribs.

The lateral ribs31A and31B are arranged so as to be line-symmetric with respect to the lateral center line and transversely cross the swelling portion13so as to spread toward the short sides10A and10B. In other words, the lateral ribs31A and31B as a whole extend so as to bend in a substantially drum-like shape in bottom view, both ends of the lateral rib31A reach the corner-side trough portions22A and22C and both ends of the lateral rib31B reach the corner-side trough portions22B and22D.

The longitudinal ribs32A and32B are arranged so as to be line-symmetric with respect to the longitudinal center line, and longitudinally cross the swelling portion13so as to spread toward the long sides11A and11B. In other words, the longitudinal ribs32A and32B as a whole extend so as to bend in a substantially drum-like shape in bottom view, both ends of the longitudinal ribs32A and32B reach the long-side side inter-crest portions24A and24B.

Two intermediate ribs41are formed at positions outside the longitudinal ribs32A and32B so as to connect the lateral ribs31A and31B together at two locations. Two intermediate ribs42are formed at positions outside the lateral ribs31A and31B so as to connect the longitudinal ribs32A and32B together at two locations. Intermediate ribs43are made up of a total of four ribs: two ribs connecting the lateral rib31A and the longitudinal ribs32A and32B, and two ribs connecting the lateral rib31B and the longitudinal ribs32A and32B. The intermediate ribs41,42and43are inter-connected to form an octagonal outline as a whole. The intermediate ribs44are made up of a total of two ribs: a rib that extends so as to connect bottom parts at both ends of the short-side side crest portion21A and a rib that extends so as to connect bottom parts at both ends of the short-side side crest portion21C, both ribs extending so as to connect the outline of the swelling portion13at positions apart from the lateral ribs31A and31B and the longitudinal ribs32A and32B. Intermediate portions of the two intermediate ribs44are connected via a straight line rib45positioned on a lateral center line, and this straight line rib45is also connected to the intermediate rib41and the longitudinal ribs32A and32B.

In this way, in the region inside the swelling portion13, the supplementary ribs41to45stretch around in addition to the basic ribs31A,31B,32A and32B. Of the supplementary ribs, the intermediate ribs41to43and straight line rib45in particular further enhance the reinforcement effect of the swelling portion13by the lateral ribs31A and31B and longitudinal ribs32A and32B, and enhance rigidity thereof. Furthermore, the intermediate ribs44reinforce the region of the swelling portion13to which the reinforcement effect by the lateral ribs31A and31B and the longitudinal ribs32A and32B does not fully extend and reinforce rigidity thereof.

Next, the rib configuration (51to57) in the region outside the swelling portion13will be described.

This outside rib configuration (51to57) is formed on the top surface12of the tabular portion4and is line-symmetric with respect to the longitudinal center line and the lateral center line. The height of each rib51to57is the same as the height of the swelling portion13.

A corner rib51is formed at a corner portion15A so as to connect the short side10A and the long side11A in the region outside the swelling portion13. The corner rib51is made up of a partial rib51athat extends rightward from the short side10A, a partial rib51bthat extends downward from the long side11A and an inclined partial rib51cthat connects the partial rib51aand the partial rib51b.

Bridge ribs52and53extend so as to connect the corner rib51and the corner-side trough portion22A. The bridge rib52extends from an inflection point of the corner rib51(intersection between the partial rib51aand the partial rib51c) toward the corner-side trough portion22A so as to be connected to the intermediate rib44on the undersurface13aof the swelling portion13at the corner-side trough portion22A. The bridge rib53extends from an inflection point of the corner rib51(intersection between the partial rib51band the partial rib51c) toward the corner-side trough portion22A so as to be connected to the lateral rib31B on the undersurface13aof the swelling portion13at the corner-side trough portion22A. Though not described in detail, the corner rib51, and the bridge ribs52and53are also formed around the corner portions15B,15C and15D likewise.

Here, focusing on the lateral rib31A, both ends of the lateral rib31A are connected to the short sides10A and10B, and the long side11A via the corner rib51and the bridge rib53. In this aspect, the same applies to the lateral rib31B. Therefore, it is understood that the “first outside rib” in Claims is formed of the corner rib51and the bridge rib53in the present embodiment.

Second outside ribs54and55extend so as to connect both ends of the longitudinal rib32A to the long sides11A and11B. Furthermore, the second outside ribs56and57extend so as to connect both ends of the longitudinal rib32B to the long sides11A and11B.

In this way, in the region outside the swelling portion13, the rib configuration (51to57) stretches around. Particularly the corner portions15A to15D of the tabular portion4where the swelling portion13, lateral ribs31A and31B and longitudinal ribs32A and32B are not located can be reinforced by the corner ribs51. The load on the swelling portion13can be released to outside the swelling portion13via the first outside ribs (corner rib51and bridge rib53) and the second outside ribs54to57, which enhances the reinforcement effect by the lateral ribs31A and31B and longitudinal ribs32A and32B and suppresses deformation of the swelling portion13. Similarly, even when a single load is imposed around the corner portions15A to15D, the load can be made to propagate through the bridge ribs52and53to be released to the swelling portion13, thus suppressing deformation around the corner portions15A to15D.

Next, an FEM analysis of the tabular portion4will be described with reference toFIGS. 4 to 8.

For a comparison with the present embodiment,FIGS. 4 and 5illustrate analysis models of a base shape60and a grid shape70respectively according to comparative examples. The base shape60is a substantially rectangular parallelepiped member whose underside is opened, and a tabular portion61and peripheral wall portions62all have a thickness of 2 mm. However, the thickness thereof is not limited to this size and their preferable thicknesses are 1 to 5 mm. Furthermore, the tabular portion61has a width of 100 mm and a depth of 66 mm, and the peripheral wall portion62has a height of 16 mm. The grid shape70corresponds to the tabular portion61of the base shape60with a plurality of ribs71formed in a grid shape on the top surface of the tabular portion61. All the ribs71have a thickness of 2 mm. The rib71has a height of 5 mm, the rib71has a pitch of 20 mm in the lateral direction and has a pitch of 13.2 mm in the longitudinal direction.

FIG. 6illustrates an analysis model of the cover3having the tabular portion4according to the present embodiment. This analysis model corresponds to the base shape60inFIG. 4with the aforementioned swelling portion13and the various rib configurations (31A,31B,32A,32B,41to45, and51to57) formed thereon. However, only the second outside ribs54to57have positions different from those inFIGS. 1 to 4. All the ribs have a thickness of 2 mm and each rib has a height of 5 mm. The thickness and height thereof are not limited to these sizes and a preferable thickness is 1 to 5 mm and each rib preferably has a height of 1 to 5 mm. The crest of the long-side side crest portion23A is located at a position apart by 34 mm from the short side10A and the long-side side inter-crest portion24A has a length of 19 mm.

As shown inFIG. 7, for a case with a point load inputted to the tabular portion (FIG. 7A) and a case with a plane load inputted thereto (FIG. 7B), FEM analyses were performed with the floor completely constrained. In the case of a point load, a load F=200 N was inputted within a range of φ10 in a central part of the tabular portion. In the case of a plane load, a pressure P=0.3 MPa was inputted over the entire top surface of the tabular portion. AlthoughFIG. 7illustrates the base shape60for convenience, an FEM analyses were performed on the grid shape70and the cover3of the present embodiment under similar conditions. In the FEM analyses, LEONA 14G33 (modulus of elasticity: 6300 MPa, Poisson's ratio: 0.34) manufactured and sold by Asahi Kasei Corporation was used as the material of the base shape60, the grid shape70and the cover3of the present embodiment.

FIG. 8is a graph illustrating FEM analysis results. As shown inFIG. 8, first of all, in the case of the point load input, maximum principal stress and maximum displacement of the cover3of the present embodiment are the smallest. This proves that the cover3of the present embodiment has improved impact strength (rigidity) against the point load input more than the base shape60and grid shape70. Next, also in the case of the plane load input, the maximum principal stress and maximum displacement of the cover3of the present embodiment are the smallest. This proves that the cover3of the present embodiment has improved impact strength (rigidity) against the plane load input more than the base shape60and grid shape70. In this way, the FEM analysis results show that the cover3of the present embodiment has exhibited excellent impact strength against the point load input and the plane load input.

Although not described in detail, the present inventor et al. have performed similar FEM analyses on and studied various analysis models in addition to the above-described three analysis models. As a result, it has been confirmed that forming the swelling portion13as the present embodiment, which combines at least the aforementioned outline and the basic ribs (lateral ribs31A and31B and longitudinal ribs32A and32B) on the top surface of the tabular portion4would be effective in mechanically and effectively enhancing impact strength of the resin-made tabular portion.

These confirmation results are analyzed as follows. First, since the swelling portion13which is a region with a changed shape is formed on the top surface12of the tabular portion4, it is analyzed that the surface strength of the top surface12of the tabular portion4as a whole has improved compared to the base shape60and grid shape70where such a region is absent. Furthermore, regarding the outline of the swelling portion13, the aforementioned crest portion and trough portion are combined and arranged so as to be line-symmetric based on the outline of the tabular portion4, and therefore it is analyzed that the impact strength against a pressure on the entire top surface12(plane load) has effectively improved. Moreover, the lateral ribs31A and31B and longitudinal ribs32A and32B of the swelling portion13are configured line-symmetrically in the aforementioned spread form and they are made to cross each other while transversely and longitudinally crossing the swelling portion13, and therefore it is analyzed that the impact strength against the point load on the swelling portion13has effectively improved.

Therefore, with the tabular portion4according to the present embodiment and the cover3that includes the tabular portion4, a combination of the specific outline and basic ribs of the swelling portion13can mechanically and synergistically improve the strength of the resin-made tabular portion4. Thus, even when the smallest possible amount of resin material is used for the tabular portion4and cover3, it is possible to provide the tabular portion4and cover3useful for securing the impact strength resistant to a point load and plane load.

The embodiment of the present invention has been described so far with reference to the specific examples. The above-described specific examples are illustrative for describing the present invention, and not intended to limit the present invention solely to the embodiment. That is, these specific examples whose design is further modified by those skilled in the art as appropriate also fall within the scope of the present invention as long as they include the features of the present invention. For example, the elements provided for the aforementioned respective specific examples and arrangement, material, shape, sizes and number thereof or the like are not limited to the illustrated ones but can be modified as appropriate.

For example, as shown inFIG. 9, even when the central part of the long side11A of the tabular portion4is bent inwardly, it is possible to apply various aspects including the aforementioned combination of the outline and basic ribs of the swelling portion13.

According to another embodiment, the rib configuration in the region inside the swelling portion13(31A,31B,32A,32B, and41to45) may be formed on the top surface of the swelling portion13. However, from the standpoint of widely securing the plane configuration on the top surface of the swelling portion13, it is desirable to form the respective ribs31A,31B,32A,32B, and41to45on the undersurface13aof the swelling portion13. When a wide plane configuration is secured on the top surface of the swelling portion13, a predetermined display such as the name of the manufacturer and the product name can be printed or formed on this top surface.

Similarly, according to a further embodiment, the rib configuration in the region outside the swelling portion13(ribs51to57) may be formed on the undersurface14of the tabular portion4.

At least one of the respective ribs (31A,31B,32A,32B,41to45, and51to57) of the tabular portion4may be provided on a plane different from that of the aforementioned embodiments. For example, it is also possible to form the lateral rib31B on the undersurface13aof the swelling portion13while forming the lateral rib31A on the top surface12of the swelling portion13. However, when balance or the like is taken into consideration, the ribs (e.g., lateral ribs31A and31B) arranged symmetrically are preferably formed on the same plane.

Second Embodiment

Next, with reference toFIGS. 10 and 11, a case will be described where the structure for enhancing the strength of the substantially rectangular tabular portion of the present invention is applied to an oil pan. A main difference from the first embodiment lies in that the rib configuration in the region inside the swelling portion13(31A,31B,32A,32B, and41to45) is formed on the top surface of the swelling portion13, and that the number of ribs in the tabular portion4is increased. Hereinafter, components of the second embodiment common to those of the first embodiment will be assigned the same reference numerals, description thereof will be omitted and description will be given focusing on the differences from the first embodiment.

An oil pan90is provided, for example, in a lower part of an automobile engine. The oil pan90includes the tabular portion4and peripheral wall portion5as in the case of the cover3of the first embodiment, and also includes a flange portion91protruding sideward from an end of the peripheral wall portion5opposite to the tabular portion4, and is configured as a whole as a substantially rectangular parallelepiped member whose lower part is opened. Resin is used as the material of the oil pan90. Of resin, glass fiber reinforced polyamide 66 or polyamide 6 is preferably used from the standpoint of impact resistance, heat resistance, creeping property, high rigidity and vibration fatigue property. The shape of the oil pan90may be constrained by members on the automobile side, but is not particularly limited as long as it has the substantially rectangular tabular portion4as in the case of the cover3of the first embodiment. For example, the oil pan90may also have a shape in which part of the short sides10A and10B and long sides11A and11B of the tabular portion4is dented and does not form a straight line.

The rib configuration inside the swelling portion13(31A,31B,32A,32B, and41to45) is formed on the top surface12of the swelling portion13, and all the ribs have the same height and connected to ribs located outside the swelling portion13. InFIG. 11(B), the lateral ribs31A and31B and longitudinal ribs32A and32B which are basic ribs are colored in gray to secure viewability of the plurality of ribs. Both ends of the lateral ribs31A and31B reach the short-side side crest portions21A and21C, and are then connected to the short sides10A and10B, and long side11A via the rib (first outside rib). On the other hand, both ends of the longitudinal ribs32A and32B reach the long-side side inter-crest portions24A and24B and are then connected to the long sides11A and11B via the ribs54to57. There are a total of 14 intermediate ribs41connecting the lateral ribs31A and31B, some of which extend beyond the lateral ribs31A and31B. There are a total of 8 intermediate ribs42connecting the longitudinal ribs32A and32B, some of which extend beyond the longitudinal ribs32A and32B. There are a total of 4 intermediate ribs43diagonally connecting the lateral rib31A or lateral rib31B and the longitudinal ribs32A and32B. Note that the above-described intermediate ribs44are not disposed here, but can also be certainly disposed.

Therefore, also in the present embodiment, since the resin-made tabular portion4has a combination of specific outline and basic ribs of the swelling portion13, it is possible to mechanically and synergistically improve the strength of the tabular portion4. Thus, even when a smallest possible amount of resin material is used for the tabular portion4and oil pan90, it is possible to provide the tabular portion4and oil pan90useful for securing impact strength resistant to a point load and plane load.

In particular, if a rib configuration is formed on the undersurface14of the oil pan90, oil will be retained between ribs, but the present embodiment is useful in that the rib configuration (31A,31B,32A,32B,41to45, and51to57) is not formed on the undersurface14of the tabular portion4, thus preventing such a phenomenon from occurring. On the other hand, since the rib configuration (31A,31B,32A,32B,41to45, and51to57) is formed on the top surface12of the tabular portion4, it is easier to reduce the pitch between ribs than assumed colliding stones.

The second embodiment as well as the first embodiment is also illustrative for describing the present invention, and not intended to limit the present invention solely to the embodiment and the design thereof can be further modified as appropriate without departing from the scope of the present invention.

OTHER EMBODIMENTS

Although not descried in detail, the present inventor et al. performed similar FEM analyses on and studied various analysis models in addition to the structures according to the first and second embodiments. As a result, it has been confirmed that strength of the tabular portion could be mechanically and effectively enhanced also in aspects described below. Therefore, the present invention can adopt the following aspects.

First, the tabular portion4may be substantially polygonal with four or more corners such as pentagonal and hexagonal, and may have an aspect having a substantially polygonal shape with two axes of symmetry substantially orthogonal to each other. That is, the tabular portion4may be substantially polygonal (four or more corners) having a first axis of symmetry and a second axis of symmetry substantially orthogonal to each other as in the case of the above-described substantial rectangle. Here, the first axis of symmetry is longer than the second axis of symmetry. The “substantially polygonal (four or more corners)” is a concept including “substantially rectangular”.

Regarding the case with the substantially rectangular tabular portion4, the crest portion and trough portion of the swelling portion13have been described based on the relationship between the long side and short side of the substantially rectangle. The case with the substantially polygonal tabular portion4will be described using a relationship with the long side or short side as follows. That is, the short-side side crest portions21A and21C (turtle head shaped and turtle bottom shaped crest portions) need only to be convex toward the substantially polygonal outline in the direction of the first axis of symmetry. Similarly, the long-side side crest portions23A to23D need only to be convex toward the substantially polygonal outline. Furthermore, the corner-side trough portions22A to22D need only to be concave toward the substantially polygonal outline in the region sandwiched between the first axis of symmetry and the second axis of symmetry.

Second, for the above-described substantially polygonal (four or more corners) tabular portion4, an aspect may be adopted in which among the basic ribs (lateral ribs31A and31B and longitudinal ribs32A and32B), one of the set of the lateral ribs31A and31B and the set of the longitudinal ribs32A and32B is omitted. In this case, the lateral ribs31A and31B may not be disposed line-symmetrically with respect to the first axis of symmetry, or similarly, the longitudinal ribs32A and32B may not be disposed line-symmetrically with respect to the second axis of symmetry. However, the lateral ribs31A and31B or longitudinal ribs32A and32B need to transversely or longitudinally cross the swelling portion so as to spread toward the substantially polygonal outline.

DESCRIPTION OF REFERENCE NUMERALS