Induction heating apparatus and induction heating method of plate-like member

An induction heating apparatus of a plate-like member for arranging a plate-like member having a three-dimensional structure so that it is interposed between a pair of plate-like coils and inductively heating the plate-like member, the pair of plate-like coils having a three-dimensional structure that corresponds to the plate-like member and being arranged to be opposed to each other. The plate-like member arranged between the pair of plate-like coils includes a plurality of surfaces in a predetermined cross section perpendicular to a current that flows through the plate-like coil pair, and each of the coils of the plate-like coil pair is divided into a plurality of turns along the direction in which the current flows for at least each of the plurality of surfaces of the plate-like member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese patent application No. 2019-011057, filed on Jan. 25, 2019, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to an induction heating apparatus and an induction heating method of a plate-like member, and relates to, in particular, an induction heating apparatus and an induction heating method of a plate-like member for arranging a plate-like member having a three-dimensional structure in such a way that it is interposed between a pair of plate-like coils arranged to be opposed to each other and inductively heating the plate-like member.

In recent years, steel plate members (i.e., plate-like members) including a hard region resistant to an impact and a soft region for absorbing an impact have been developed, for example, as structural members for automobiles in order to improve impact resistance characteristics. Japanese Unexamined Patent Application Publication No. 2012-144773 discloses a technique of forming a hard region and a soft region in one plate-like member by locally heating only a region of the plate-like member to a temperature higher than an austenite transformation finish temperature A3 and quenching the heated region.

Alternatively, after forming a hard region in the entire plate-like member by quenching, only a region of the plate-like member may be heated and tempered, thereby forming the hard region and the soft region in one plate-like member.

SUMMARY

The present inventors have studied a method of arranging a plate-like member having a three-dimensional structure between a pair of plate-like coils arranged to be opposed to each other and inductively heating this plate-like member as a method of heating the plate-like member, and have found the following problem.

The problem will be explained with reference toFIGS. 10-12.FIG. 10is a perspective view showing one example of a plate-like member.FIG. 11is a perspective view of a plate-like coil pair which describes the problem solved by the present disclosure.FIG. 12is a perspective view of an induction heating apparatus which describes the problem solved by the present disclosure.

As shown inFIG. 10, a plate-like member10to be heated, which is, for example, a lower part of a center pillar reinforcement of an automobile, includes a body part11and a lower flange part13. The alternate long and short dash line shown inFIG. 10is a boundary line between the body part11and the lower flange part13that is defined to simplify the explanation. In a state in which the plate-like member10is attached to the automobile, the x-axis positive direction side is a lower side and the x-axis negative direction side is an upper side.

As shown inFIG. 10, the body part11is a part having a hat-shaped cross-section and includes a top plate111extending in the x-axis direction, a pair of side walls112, and flange parts113. The pair of side walls112are formed in the z-axis negative direction from the respective ends in the width direction (y direction) of the top plate111extending in the x-axis direction. Further, the flange parts113project outwardly from the ends of the respective side walls112.

The lower flange part13is a flat plate-shaped part projecting from the end in the x-axis positive direction side of the top plate111outwardly in the length direction and extending in the width direction (y-axis direction). The side walls112and the flange parts113of the body part11are extended in the y-axis direction along the lower flange part13from the ends of the top plate111. That is, the side walls112and the flange parts113of the body part11are L-shaped in an xy plan view.

Note that the shape of the plate-like member10shown inFIG. 10is merely one example, and the shape of the plate-like member having a three-dimensional structure to be inductively heated is not limited to this example. Further, the right-handed xyz Cartesian coordinate system shown inFIG. 10and other drawings is the one defined to simplify the explanation of the positional relationship among the constituting elements. In general, the z-axis positive direction corresponds to the vertically upward direction and the xy-plane forms a horizontal plane.

As shown inFIG. 11, the plate-like coil pair which describes the problem is formed of, for example, two plate-like coils (an upper plate-like coil200and a lower plate-like coil300) having a three-dimensional structure that corresponds to the plate-like member10.FIG. 11indicates the plate-like member10that is inductively heated by alternate long and two short dashes lines.

The upper plate-like coil200includes a hat-shaped part210that corresponds to the body part11of the plate-like member10, a connection wall220that connects the hat-shaped part210with the flat plate part230, and a flat plate part230that corresponds to the lower flange part13of the plate-like member10. The alternate long and short dash line shown in each ofFIGS. 11 and 12is a boundary line between the hat-shaped part210and the flat plate part230that is defined to simplify the explanation. The hat-shaped part210is a part having a hat-shaped cross-section and includes a top plate211that corresponds to the top plate111, side walls212that correspond to the side walls112, and bottom plates213that correspond to the flange parts113. The connection wall220connects the bottom plate213of the hat-shaped part210and the flat plate part230.

In a similar way, the lower plate-like coil300includes a hat-shaped part310that corresponds to the body part11of the plate-like member10, a connection wall320that connects the hat-shaped part310and the flat plate part330, and a flat plate part330that corresponds to the lower flange part13of the plate-like member10. The hat-shaped part310is a part having a hat-shaped cross-section and includes a top plate311that corresponds to the top plate111, side walls312that correspond to the side walls112, and bottom plates313that correspond to the flange parts113. The connection wall320connects the bottom plate313of the hat-shaped part310with the flat plate part330.

As shown inFIG. 12, in the induction heating apparatus which describes the problem, the tubular coil40is joined to the plate-like coil pair (the upper plate-like coil200and the lower plate-like coil300) shown inFIG. 11, and is provided to make one turn outside the plate-like coil pair. The respective ends of the tubular coil40are connected to a high frequency power supply PS, which forms an open circuit as a whole. The tubular coil40shown inFIG. 12is divided into two coils on the upper surface of the upper plate-like coil200and the lower surface of the lower plate-like coil300and is extended in the y-axis direction.

As shown inFIG. 12, in the upper plate-like coil200and the lower plate-like coil300, the cross-sectional length that is parallel to the current that flows in the y-axis direction varies depending on the position of the x-axis direction. For example, since the cross-sectional length of the hat-shaped parts210and310is longer than that of the flat plate parts230and330, resistance in the hat-shaped parts210and310becomes larger than that in the flat plate parts230and330. Therefore, there is a problem that, as shown inFIG. 12, currents concentrate in a region in which the resistance is small (e.g., the flat plate parts230and330) in each of the upper plate-like coil200and the lower plate-like coil300, whereby the plate-like member10cannot be heated uniformly.

The present disclosure has been made in view of the aforementioned circumstances and provides an induction heating apparatus and an induction heating method of a plate-like member capable of heating a plate-like member uniformly.

An induction heating apparatus of a plate-like member according to one aspect of the present disclosure is an induction heating apparatus of a plate-like member for arranging a plate-like member having a three-dimensional structure in such a way that it is interposed between a pair of plate-like coils and inductively heating the plate-like member, the pair of plate-like coils having a three-dimensional structure that corresponds to the plate-like member and being arranged to be opposed to each other, in which

the plate-like member arranged between the pair of plate-like coils includes a plurality of surfaces in a predetermined cross section that is perpendicular to a current that flows through the plate-like coil pair, and

each of the coils of the plate-like coil pair is divided into a plurality of turns along the direction in which the current flows for at least each of the plurality of surfaces of the plate-like member.

In the induction heating apparatus of the plate-like member according to one aspect of the present disclosure, the plate-like member arranged between the pair of plate-like coils includes the plurality of surfaces in the predetermined cross section that is perpendicular to the current that flows through the plate-like coil pair, and each of the coils of the plate-like coil pair is divided into a plurality of turns along the direction in which the current flows for at least each of the plurality of surfaces of the plate-like member. Therefore, the currents that flow through each of the coils of the divided plate-like coil pair can be made equal to each other, whereby it is possible to uniformly heat the plate-like member.

The plate-like coil pair may be formed in such a way that the outer form thereof overlaps that of the plate-like member in a plan view. The plate-like member is arranged in the whole part between the pair of plate-like coils, whereby the plate-like member can be heated uniformly.

The induction heating apparatus of the plate-like member may further include a tubular coil that is joined to respective outer surfaces of the divided plate-like coil pair and connects the divided plate-like coil pair in series. The tubular coil may be joined to at least one of the plate-like coils that form the divided plate-like coil pair in such a manner that the tubular coil is divided into first and second branch parts. The length of the part joined to the plate-like coil in the first branch part may be shorter than that in the second branch part, and the length of the part that is protruded from the plate-like coil in the first branch part may be longer than that in the second branch part. According to this configuration, the plate-like member can be heated more uniformly.

An induction heating method of a plate-like member according to one aspect of the present disclosure is an induction heating method of a plate-like member for arranging a plate-like member having a three-dimensional structure in such a way that it is interposed between a pair of plate-like coils and inductively heating the plate-like member, the pair of plate-like coils having a three-dimensional structure that corresponds to the plate-like member and being arranged to be opposed to each other, in which

the plate-like member arranged between the pair of plate-like coils includes a plurality of surfaces in a predetermined cross section that is perpendicular to a current that flows through the plate-like coil pair, and

each of the coils of the plate-like coil pair is divided into a plurality of turns along the direction in which the current flows for at least each of the plurality of surfaces of the plate-like member.

In the induction heating method of the plate-like member according to one aspect of the present disclosure, the plate-like member arranged between the pair of plate-like coils includes the plurality of surfaces in the predetermined cross section that is perpendicular to the current that flows through the plate-like coil pair, and each of the coils of the plate-like coil pair is divided into a plurality of turns along the direction in which the current flows for at least each of the plurality of surfaces of the plate-like member. Therefore, the currents that flow through each of the coils of the divided plate-like coil pair can be made equal to each other can be made equal to each other, whereby it is possible to uniformly heat the plate-like member.

According to the present disclosure, it is possible to provide an induction heating apparatus and an induction heating method of a plate-like member capable of uniformly heating the plate-like member.

DESCRIPTION OF EMBODIMENTS

Hereinafter, specific embodiments employing the present disclosure will be described in detail with reference to the drawings. It should be noted that the present disclosure is not limited to the embodiments described below. For clarity of explanation, the following description and the drawings are simplified as appropriate.

First Embodiment

Referring first toFIGS. 1-3, an induction heating apparatus and an induction heating method of a plate-like member according to a first embodiment will be explained.FIG. 1is a perspective view showing a plate-like coil pair in an induction heating apparatus of a plate-like member according to the first embodiment.FIG. 2is a plan view of the induction heating apparatus according to the first embodiment.FIG. 3is a cross-sectional view ofFIG. 2taken along the line III-III.

As a matter of course, the right-handed xyz Cartesian coordinate system shown inFIG. 1and other drawings is the one defined to simplify the explanation of the positional relationship among the constituting elements. In general, the z-axis positive direction corresponds to the vertically upward direction and the xy-plane forms a horizontal plane.

The induction heating apparatus of the plate-like member according to this embodiment is suitable as an induction heating apparatus of steel plate members for automobiles where it is required to achieve both high strength and excellent impact absorption characteristics. The induction heating apparatus of the plate-like member according to this embodiment can be used for both quenching and tempering. In the following description, a case in which the induction heating apparatus is used for tempering will be explained.

First, a plate-like member10shown by the alternate long and two short dashes lines inFIG. 1will be explained. The plate-like member10is, for example, a steel plate for hot stamping which is made of manganese-boron steel having a thickness of about 1-4 mm, although it is not particularly limited as long as it can be inductively heated. The plate-like member10before it is inductively heated is, for example, a hard material having a microstructure, the entire surface of which being made of martensite.

The plate-like member10is the one shown inFIG. 10. As shown inFIG. 10, the plate-like member10, which is, for example, a part (lower part) of a center pillar reinforcement of an automobile, includes a body part11and a lower flange part13. The alternate long and short dash line shown inFIG. 10is a boundary line between the body part11and the lower flange part13that is defined to simplify the explanation. In a state in which the plate-like member10is attached to an automobile, the x-axis positive direction side is a lower side and the x-axis negative direction side is an upper side.

As shown inFIG. 10, the body part11is a part having a hat-shaped yz cross-section and includes a top plate111extending in the x-axis direction, a pair of side walls112, and flange parts113. The pair of side walls112extend in the z-axis negative direction from the respective ends in the width direction (y direction) of the top plate111extending in the x-axis direction. Further, the flange parts113project outwardly from the ends of the respective side walls112.

The lower flange part13is a flat plate-shaped part projecting from the end in the x-axis positive direction side of the top plate111outwardly in the length direction (x-axis direction) and extending in the width direction (y-axis direction).

The side walls112and the flange parts113of the body part11are extended in the y-axis direction along the lower flange part13from the ends of the top plate111. That is, the side walls112and the flange parts113of the body part11are L-shaped in the xy plan view.

As shown inFIG. 1, the plate-like member10has a three-dimensional structure including a plurality of surfaces in a predetermined cross section perpendicular to a current that flows through the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) in the y-axis direction. Specifically, as shown inFIG. 3, in the predetermined xz cross section, the plate-like member10includes three surfaces formed of the lower flange part13, the side walls112, and the flange parts113, all of which having a flat plate shape.

Note that the intended use and the shape of the plate-like member10are not particularly limited.

Next, as shown inFIG. 1, the plate-like coil pair is formed of the upper plate-like coil20and the lower plate-like coil30having a three-dimensional structure that corresponds to the plate-like member10. As shown inFIG. 2, the induction heating apparatus according to this embodiment includes, besides the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) shown inFIG. 1, a tubular coil40, and a high frequency power supply PS.

As shown inFIGS. 1-3, each of the coils of the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) in the induction heating apparatus of the plate-like member according to this embodiment is divided into a plurality of turns along the direction in which the current flows (y-axis direction) for each of the plurality of surfaces of the plate-like member10.

In the example shown in the drawings, the upper plate-like coil20is divided into three parts, i.e., a hat-like coil21, a wall-like coil22, and a flat plate coil23for each of the three surfaces of the lower flange part13, the side walls112, and the flange parts113shown inFIG. 3. In a similar way, the lower plate-like coil30is divided into three parts, i.e., a hat-like coil31, a wall-like coil32, and a flat plate coil33for each of the three surfaces of the lower flange part13, the side walls112, and the flange parts113shown inFIG. 3.

As shown inFIG. 1, the hat-like coils21and31, which are plate-like coils having a hat-shaped yz cross-section that corresponds to the body part11of the plate-like member10, are arranged to be opposed to each other. The hat-like coil21includes a top plate211that corresponds to the top plate111, side walls212that corresponds to the side walls112, and bottom plates213that correspond to the flange parts113. In a similar way, the hat-like coil31includes a top plate311that corresponds to the top plate111, side walls312that corresponds to the side walls112, and bottom plates313that correspond to the flange parts113.

As shown inFIG. 1, the wall-like coils22and32, which are plate-like coils having wall parts that correspond to the side walls112extending in the y-axis direction along the lower flange part13of the plate-like member10, are arranged to be opposed to each other. The wall-like coil22has a structure in which a pair of wall parts extending in the y-axis direction between the bottom plate213of the hat-like coil21and the flat plate coil23are crosslinked by a rod-shaped part extending in the y-axis direction (this corresponds to the top plate211of the hat-like coil21). In a similar way, the wall-like coil32has a structure in which a pair of wall parts extending in the y-axis direction between the bottom plate313of the hat-like coil31and the flat plate coil33are crosslinked by a rod-shaped part extending in the y-axis direction (this corresponds to the top plate311of the hat-like coil31).

As shown inFIG. 1, the flat plate coils23and33, which are flat plate-shaped coils that correspond to the lower flange part13of the plate-like member10, are arranged to be opposed to each other.

As shown inFIG. 2, the tubular coil40connects the three pairs of plate-like coils that are arranged to be opposed to each other, i.e., the flat plate coils23and33, the wall-like coils22and32, and the hat-like coils21and31in series in this order. That is, the tubular coil40, which is joined to outer surfaces of the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30), each of the coils of the plate-like coil pair being divided into three parts along the direction in which the current flows (y-axis direction), is provided to make a total of three turns, one turn at a time. The respective ends of the tubular coil40are connected to the high frequency power supply PS, which forms an open circuit as a whole. Cooling water for cooling the tubular coil40, the upper plate-like coil20, and the lower plate-like coil30flows inside the tubular coil40.

The tubular coil40, which is divided into two coils on the upper surface of the hat-like coil21, the wall-like coil22, and the flat plate coil23and the lower surface of the hat-like coil31, the wall-like coil32, and the flat plate coil33, is extended in the y-axis direction.

While the tubular coil40is drawn by one coil without being divided in order to facilitate understanding inFIG. 2, the tubular coil40may not be actually divided.

Further, as shown inFIG. 3, in this embodiment, the tubular coil40is a square pipe. Then the tubular coil40divided into two coils is joined to the upper surface of the hat-like coil21, the wall-like coil22, and the flat plate coil23and the lower surface of the hat-like coil31, the wall-like coil32, and the flat plate coil33.

Note that the tubular coil40is not limited to a square pipe and may be, for example, a round pipe. Further, the tubular coil40may be divided into three or more coils, not into two coils.

In the induction heating apparatus shown inFIG. 12, in the upper plate-like coil200and the lower plate-like coil300, the cross-sectional length that is parallel to the current that flows in the y-axis direction varies depending on the position of the x-axis direction. For example, since the cross-sectional length of the hat-shaped parts210and310is longer than that of the flat plate parts230and330, the resistance in the hat-shaped parts210and310becomes larger than that in the flat plate parts230and330. Therefore, there is a problem that, as shown inFIG. 12, currents concentrate in a region whose resistance is small (e.g., the flat plate parts230and330) in each of the upper plate-like coil200and the lower plate-like coil300, whereby the plate-like member10cannot be heated uniformly.

On the other hand, in the induction heating apparatus of the plate-like member according to this embodiment, each of the coils of the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) is divided into a plurality of turns along the direction in which the current flows (y-axis direction) for each of the plurality of surfaces of the plate-like member10. As described above, the flat plate coils23and33, the wall-like coils22and32, and the hat-like coils21and31are connected in series by the tubular coil40. Therefore, the current that flows through the flat plate coils23and33, the current that flows through the wall-like coils22and32, and the current that flows through the hat-like coils21and31can be made equal to one another, whereby the entire plate-like member10can be heated uniformly.

Further, regarding the hat-like coils21and31, the cross-sectional length that is parallel to the current that flows in the y-axis direction does not change regardless of the position of the x-axis direction and is constant. Therefore, the resistance becomes constant regardless of the position of the x-axis direction in each of the hat-like coils21and31, whereby it is possible to uniformly heat the whole region of the plate-like member10interposed between the hat-like coils21and31.

Further, regarding the flat plate coils23and33as well, the cross-sectional length that is parallel to the current that flows in the y-axis direction does not change regardless of the position of the x-axis direction and is constant. Therefore, the resistance becomes constant regardless of the position of the x-axis direction in each of the flat plate coils23and33, whereby it is possible to uniformly heat the whole region of the plate-like member10interposed between the flat plate coils23and33.

Further, as described above, the current that flows through the flat plate coils23and33is equal to the current that flows through the hat-like coils21and31. Therefore, the heating temperature of the region of the plate-like member10interposed between the flat plate coils23and33can be made equal to the heating temperature of the region of the plate-like member10interposed between the hat-like coils21and31.

Regarding the wall-like coils22and32, the cross-sectional length that is parallel to the current that flows in the y-axis direction varies depending on the position of the width direction. However, since the widths of the wall-like coils22and32are narrow, the whole region of the plate-like member10interposed between the wall-like coils22and32can be heated substantially uniformly.

Further, as described above, the current that flows through the wall-like coils22and32is equal to the current that flows through the hat-like coils21and31and the flat plate coils23and33. Therefore, the heating temperature of the region of the plate-like member10interposed between the wall-like coils22and32can be made equal to the heating temperature of the region of the plate-like member10interposed between the hat-like coils21and31and the flat plate coils23and33.

Further, the wall-like coils22and32are located between the hat-like coils21and31and the flat plate coils23and33. As described above, the heating temperature of the region of the plate-like member10interposed between the flat plate coils23and33is equal to the heating temperature of the region of the plate-like member10interposed between the hat-like coils21and31. Therefore, the heating temperature of the region of the plate-like member10interposed between the wall-like coils22and32tends to be equal to the heating temperature of the region of the plate-like member10interposed between the hat-like coils21and31and the flat plate coils23and33.

Second Embodiment

Referring first toFIGS. 4 and 5, an induction heating apparatus of a plate-like member according to a second embodiment will be explained.FIG. 4is a plan view of the induction heating apparatus according to the second embodiment.FIG. 5is a cross-sectional view ofFIG. 4taken along the line V-V.

As shown inFIG. 4, in the induction heating apparatus according to the second embodiment, the upper plate-like coil20and the lower plate-like coil30are formed in such a way that the outer forms of the upper plate-like coil20and the lower plate-like coil30in the xy plan view overlap the outer form of the plate-like member10. Specifically, as shown inFIG. 4, a cut-out part213ais formed in the bottom plate213of the hat-like coil21in accordance with the outer form of the plate-like member10. A cut-out part (not shown) is formed also in the bottom plate313of the hat-like coil31.

In the induction heating apparatus of the plate-like member according to the first embodiment, as shown inFIG. 3, a non-arranging region, which is a region in which the plate-like member10is not arranged between the hat-like coils21and31, is formed. The resistance inside the hat-like coils21and31in the non-arranging region is different from that in the arranging region where the plate-like member10is arranged. Specifically, the resistance becomes high in the arranging region due to a demagnetizing field from the plate-like member10, whereas the influence of the demagnetizing field from the plate-like member10is small in the non-arranging region. Therefore, the resistance becomes smaller in the non-arranging region than that in the arranging region in the hat-like coils21and31, and currents tend to concentrate in the non-arranging region.

On the other hand, in the induction heating apparatus of the plate-like member according to the second embodiment, as shown inFIG. 5, the plate-like member10is arranged in the entire part between the hat-like coils21and31. That is, the non-arranging region, which is a region where the plate-like member10is not arranged between the hat-like coils21and31, is not formed. As a result, currents no longer concentrate in the non-arranging region, whereby the plate-like member10can be heated uniformly between the hat-like coils21and31.

Further, similar to the induction heating apparatus according to the first embodiment, the tubular coil40is divided into two coils on the upper surface of the hat-like coil21, the wall-like coil22, and the flat plate coil23and the lower surface of the hat-like coil31, the wall-like coil32, and the flat plate coil33, and is extended in the y-axis direction.

InFIG. 4, for the sake of facilitating understanding, the tubular coil40is drawn by one line without being divided.

Further, as shown inFIG. 5, in this embodiment, the tubular coil40is a square pipe. The tubular coil40divided into two coils is joined to the upper surface of the hat-like coil21, the wall-like coil22, and the flat plate coil23and the lower surface of the hat-like coil31, the wall-like coil32, and the flat plate coil33.

The tubular coil40is not limited to the square pipe and may be, for example, a round pipe. Further, the tubular coil40may be divided into three or more coils, not into two coils.

FIG. 6is a perspective view of the wall-like coil22in the induction heating apparatus of the plate-like member according to the second embodiment. As shown inFIG. 6, in the induction heating apparatus according to the second embodiment, the tubular coil40is joined to the wall-like coil22in such a manner that it is divided into a first branch part41and a second branch part42. The tubular coil40is divided into the first branch part41and the second branch part42between two branch points40a.

As shown inFIG. 6, the first branch part41is formed in a straight line, whereas the second branch part42is formed in such a way that it is bent to be a hat shape. Therefore, the length of the part joined to the wall-like coil22in the first branch part41is shorter than that in the second branch part42. If the length of the part protruded from the wall-like coil22in the first branch part41and that in the second branch part42are equal to each other, the total length of the first branch part41becomes shorter than the total length of the second branch part42. Therefore, the resistance of the first branch part41becomes smaller than that of the second branch part42, and currents are likely to flow through the first branch part41more than they flow through the second branch part42. Therefore, the part in the vicinity of the first branch part41is likely to be heated in the wall-like coil22.

As shown inFIG. 6, in this embodiment, the part that is protruded from the wall-like coil22in the first branch part41is longer than that in the second branch part42. That is, the length of the part that is protruded from the wall-like coil22in each of the first branch part41and the second branch part42is adjusted in such a way that the total length of the first branch part41becomes equal to the total length of the second branch part42. Therefore, the resistance of the first branch part41becomes substantially equal to that of the second branch part42, and the current that flows through the first branch part41becomes substantially equal to the current that flows through the second branch part42. It is therefore possible to heat the wall-like coil22more uniformly.

Since the other configurations are similar to those of the first embodiment, the descriptions thereof will be omitted.

Next, with reference toFIG. 7, a configuration of a specific example of the plate-like member to be heated using the induction heating apparatus of the plate-like member according to the embodiment will be explained.FIG. 7is a perspective view showing one example of the plate-like member. A plate-like member50shown inFIG. 7is a plate-like member for a pillar, which is a member for a vehicle, and more specifically, a center pillar reinforcement. The arrows shown inFIG. 7indicate the respective directions in a vehicle.

As shown inFIG. 7, the plate-like member50includes a body part51, an upper flange part52, and a lower flange part53.

The intended use and the shape of the plate-like member50shown inFIG. 7are only illustrative, and the intended use and the shape of the plate-like member that will be applied to the induction heating apparatus of the plate-like member according to this embodiment are not particularly limited.

As shown inFIG. 7, the body part51is a part having a hat-shaped cross-section and includes a top plate511, a side walls512, and flange parts513that are extended in the vertical direction. More specifically, the pair of side walls512are inwardly formed from the ends in the width direction of the top plate511extending in the vertical direction. Further, the flange parts513project outwardly from the ends of the respective side walls512.

Further, the body part51is slightly curved such that the body part51bulges outside as a whole. Additionally, the upper end part and the lower end part of the body part51are widened in the width direction (front-back direction) and are T-shaped in a plan view. The degree of widening in the width direction (front-back direction) is greater in the lower end part than that in the upper end part.

The upper flange part52includes a plate surface extending outwardly and perpendicularly from the upper end part of the body part51and a plate surface projecting from the end on the outer side of the above plate surface in the upper direction (outer side in the length direction of the body part51). That is, the upper flange part52is a part having an L-shaped cross section extending in the width direction (front-back direction).

The lower flange part53is a flat plate-shaped part projecting from the lower end part of the top plate511in the lower side (outer side in the length direction) and extending in the width direction (front-back direction). A cut-out part53ais provided in the lower side of the lower flange part53.

FIG. 7shows a plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) to be used for tempering the plate-like member50by the alternate long and two short dashes lines. In the plate-like member50, the lower flange part53and the lower part of the body part51positioned between the upper plate-like coil20and the lower plate-like coil30are a soft region. The other region is a hard region.

Next, with reference toFIGS. 8 and 9, results of a thermal analysis simulation obtained by inductively heating the plate-like member50shown inFIG. 7will be explained.FIG. 8is a diagram showing results of a simulation in an induction heating apparatus of a plate-like member according to a comparative example.FIG. 9is a diagram showing results of a simulation in an induction heating apparatus of a plate-like member according to an Example of the second embodiment. The upper stages inFIG. 8andFIG. 9show the configuration diagram according to the comparative example and that according to the Example, respectively. The lower stages inFIGS. 8 and 9show the results of the thermal analysis according to the comparative example and those according to the Example, respectively.

As shown in the upper stage ofFIG. 8, in the thermal analysis simulation according to the comparative example, an upper plate-like coil200is formed of three plate-like coils, i.e., a hat-like coil210a, an intermediate coil220a, and a flat plate coil230aextending in the y-axis direction. A lower plate-like coil300is also formed of three plate-like coils, i.e., a hat-like coil310a, an intermediate coil320a, and a flat plate coil330aextending in the y-axis direction.

The tubular coil40is a copper tube that connects the hat-like coil210a, the hat-like coil310a, the intermediate coil220a, the intermediate coil320a, the flat plate coil230a, and the flat plate coil330a, which are the three pairs of plate-like coils, in this order. That is, the tubular coil40is provided in such a way that it makes three turns outside the three pairs of plate-like coils. That is, the tubular coil40forms a three turn coil along with the plate-like coil pair (the upper plate-like coil200and the lower plate-like coil300), each of which being divided into three parts. The respective ends of the tubular coil40are connected to the high frequency power supply PS, which forms an open circuit as a whole.

As described above, each of the coils of the plate-like coil pair (the upper plate-like coil200and the lower plate-like coil300) according to the comparative example is divided into three turns along the direction in which the current flows (y-axis direction). However, each of the coils of the plate-like coil pair (the upper plate-like coil200and the lower plate-like coil300) according to the comparative example is not divided for each of the plurality of surfaces of the plate-like member50. Specifically, the intermediate coils220aand320aare formed across the three surfaces from the body part51to the lower flange part53. Therefore, as shown in the lower stage shown inFIG. 8, the plate-like member50cannot be heated uniformly.

On the other hand, as shown in the upper stage ofFIG. 9, in the thermal analysis simulation according to the Example, the upper plate-like coil20is divided into the hat-like coil21, the wall-like coil22, and the flat plate coil23extending in the y-axis direction for each of the plurality of surfaces of the plate-like member50. Further, the hat-like coil21is divided into two hat-like coils21aand21b. Further, the flat plate coil23is also divided into two flat plate coils23aand23b. That is, the upper plate-like coil20is divided into five parts along the direction in which the current flows (y-axis direction).

The lower plate-like coil30is also divided into the hat-like coil31, the wall-like coil32, and the flat plate coil33extending in the y-axis direction for each of the plurality of surfaces of the plate-like member50. Further, the hat-like coil31is divided into two hat-like coils31aand31b. Further, the flat plate coil33is also divided into two flat plate coils33aand33b. That is, the lower plate-like coil30is divided into five parts along the direction in which the current flows (y-axis direction).

The tubular coil40is a copper tube that connects in series the hat-like coils21aand31a, the hat-like coils21band31b, the wall-like coils22and32, the flat plate coils23aand33a, and the flat plate coils23band33b, which are five pairs of plate-like coils in this order. That is, the tubular coil40is provided to make five turns outside the five pairs of plate-like coils. That is, the tubular coil40forms a five turn coil along with the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30), each of which being divided into five parts. The respective ends of the tubular coil40are connected to the high frequency power supply PS, which forms an open circuit as a whole.

Further, the tubular coil40is divided into two coils on the upper surface of the hat-like coils21aand21b, the wall-like coil22, and the flat plate coils23aand23band the lower surface of the hat-like coils31aand31b, the wall-like coil32, and the flat plate coils33aand33b, and are extended in the y-axis direction. In the Example, the total lengths of the branch parts of the tubular coil40divided into two coils are adjusted to be equal to each other in each of the divided plate-like coils.

Further, in the Example, the upper plate-like coil20and the lower plate-like coil30are formed in such a way that the outer forms of the upper plate-like coil20and the lower plate-like coil30in the xy plan view overlap the outer form of the plate-like member50.

As described above, each of the coils of the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) according to the Example is divided along the direction in which the current flows (y-axis direction) for each of the plurality of surfaces of the plate-like member50. Therefore, as shown in the lower stage ofFIG. 9, the entire plate-like member50can be heated uniformly. Further, each of the coils of the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) shown inFIG. 1is divided into three turns. On the other hand, each of the coils of the plate-like coil pair (the upper plate-like coil20and the lower plate-like coil30) according to the Example shown inFIG. 9is divided into five turns. Therefore, the areas of the respective turns can be made more uniform, whereby the entire plate-like member50can be heated more uniformly.

As described above, the effects of the induction heating apparatus of the plate-like member according to this embodiment have been confirmed by the thermal analysis simulation.