TECHNICAL FIELD OF THE INVENTION

The present invention relates to a torsion beam manufacturing method and a torsion beam manufacturing apparatus for manufacturing a torsion beam which is applied to a torsion beam-type suspension apparatus for automobiles and in which metal fatigue is prevented.

Priority is claimed on Japanese Patent Application No. 2017-194394 filed on Oct. 4, 2017, and Japanese Patent Application No. 2018-056868 filed on Mar. 23, 2018, the contents of which are incorporated herein by reference.

RELATED ART

As is generally known, as a form of an automobile suspension system, torsion beam-type suspension apparatuses have come into wide use.

A torsion beam-type suspension apparatus includes: a torsion beam assembly in which a pair of right and left trailing arms freely rotatably supporting right and left wheels is coupled to a torsion beam and a pair of right and left spring receiving portions is joined to the vicinities of right and left ends of the torsion beam; and a spring and an absorber through which the torsion beam and a vehicle body arc coupled to each other. The torsion beam is oscillatably connected to the vehicle body via pivot axes extending from the right and left toward a center of the vehicle body.

For example, a torsion beam is formed by performing deformation processing of a metal pipe through press forming or hydro-form forming, and a cross-section of the torsion beam orthogonal to a longitudinal direction thereof is formed into a closed cross-section having a substantial V-shape or a substantial U-shape (for example, refer to Patent Document 1).

The torsion beam includes the uniformly shaped closed cross-sectional portion which has a substantially constant closed cross-section having a substantial V-shape or a substantial U-shape, the attachment portions which are connected to the right and left trailing arms, and shape changing portions (gradual change portions) which are positioned between the uniformly shaped closed cross-sectional portion and the attachment portions. In a case where a vehicle body receives an external force from a road surface, rolling rigidity of the vehicle body is ensured mainly by torsional rigidity of the torsion beam.

On the other hand, even when the torsion beam has sufficient rolling rigidity, since the torsion beam receives various external forces from a road surface via the wheels or the trailing arms, a complicated stress distribution is generated due to such external forces and metal fatigue is likely to progress. For example, this metal fatigue is significantly likely to occur in the vicinity of a connection portion between the shape changing portion and the uniformly shaped closed cross-sectional portion.

Therefore, even in a case where various external forces are received from a road surface, metal fatigue needs to be prevented from progressing, and various technologies have been developed to prevent such metal fatigue (for example, refer to Patent Documents 2 to 6).

According to a technology disclosed in Patent Document 2, a press-formed torsion beam is subjected to quenching, tempering, and shot-peening, and an outer surface of the torsion beam is hardened, so that fatigue durability of the torsion beam is improved.

According to a technology disclosed in Patent Document 3, surface hardness of a torsion beam is improved by using a steel pipe of which surface hardness increases after heat treatment, so that fatigue durability of the torsion beam is improved.

According to a technology disclosed in Patent Document 4, tensile stress is applied by applying a pressure outward from the inside of a steel pipe through hydro-forming. As a result, residual stress of a torsion beam is reduced, so that fatigue durability is improved.

According to a technology disclosed in Patent Document 5, by deforming a portion having a high residual stress out of a plane, the tensile residual stress is reduced and the fatigue durability is improved. As an out-of-plane deformation unit, hydro-forming working is used.

According to a technology disclosed in Patent Document 6, a tensile force along the longitudinal direction is applied to a torsion beam material, and thus the residual stress of the torsion beam is reduced to improve the fatigue durability.

PRIOR ART DOCUMENT

Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2011-635

[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2001-123227

[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2008-063656

[Patent Document 4] Japanese Unexamined Patent Application, First Publication No. 2013-091433

[Patent Document 5] PCT International Publication No. WO 2017/155056

[Patent Document 6] PCT International Publication No. WO 2017/169733

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, it is not always easy to improve the fatigue durability of the torsion beam by applying the technologies described in Patent Documents 2 to 5, and there is a problem that initial costs such as capital investment and manufacturing running costs increase. In particular, this problem is remarkable in the hydro-forming working disclosed in Patent Document 5.

According to a technology disclosed in Patent Document 6, these problems can be solved. However, in order to reduce the residual stress as calculated by applying a tensile force, the process to firmly secure the holding of both ends of the product is necessary.

Therefore, further improvement in productivity is required without this process. Thus, a torsion beam manufacturing technology capable of more efficiently manufacturing a torsion beam having excellent fatigue durability is desired.

The present invention has been made in consideration of the foregoing circumstances. An object thereof is to provide a torsion beam manufacturing method and a torsion beam manufacturing apparatus capable of more efficiently manufacturing a torsion beam having excellent fatigue durability.

Means for Solving the Problem

In order to solve the problem above, this invention proposes a method and an apparatus as follows.

(1) One aspect of the present invention is a torsion beam manufacturing method for manufacturing a torsion beam including a central portion of which a cross-section orthogonal to a longitudinal direction is a closed cross-section having a substantial V-shape or a substantial U-shape at any position in the longitudinal direction, and a shape changing portion which has a connection region leading to the central portion and including a closed cross-section having a shape different from the shape of the closed cross-section of the central portion, the method comprising: a compression step of thickening at least the connection region through application of a compression force in the longitudinal direction to at least the connection region of a torsion beam material to obtain the torsion beam, the torsion beam material being formed with the central portion and the shape changing portion.

According to the torsion beam manufacturing method of the above aspect, since a compression force is applied to at least the connection region in the compression step, the remaining residual stress can be reduced or removed and the torsion beam material can be reinforced by thickening at the same time.

As a result, a torsion beam having excellent fatigue durability can be manufactured. In addition, post-treatment such as heat treatment is not required, and the apparatus configuration and the manufacturing step are simpler in a case where axial direction compression is applied than in a case where axial direction tension is applied. Thereby, the torsion beam can be manufactured efficiently.

(2) In the torsion beam manufacturing method according to the above (1), in the compression step, in a state where an inner side of an outer portion in the longitudinal direction from the connection region is supported by an inner side support member and an outer side of the outer portion is pinched by an outer pinching member, the compression force may be applied by moving the inner side support member and the outer pinching member in a direction approaching the central portion.

In this case, in the compression step, since a compression force is applied in a state where the inner side of the outer portion of the torsion beam material is supported by the inner side support member and the outer side of the outer portion is pinched by the outer pinching member, the compression force can be easily applied while suppressing the out-of-plane deformation of the outer portion.

(3) In the torsion beam manufacturing method according to the above (2), in the compression step, the outer side of the connection region may be supported by an outer support member, and the outer support member may be moved synchronously with movement of the inner side support member and the outer pinching member in the same direction.

In this case, since the outer support member moves in synchronization with the movement of the inner side support member and the outer pinching member, the deformation of the torsion beam material along the longitudinal direction accompanying compression is not hindered. Therefore, since a compression force can be reliably applied to the torsion beam material, the residual stress can be reliably reduced or removed.

(4) In the torsion beam manufacturing method according to the above (1), in the compression step, the compression force may be applied over an entire length of the torsion beam material by causing both ends of the torsion beam material to approach each other along the longitudinal direction.

In this case, since the torsion beam material is compressed inward in the longitudinal direction over the entire length thereof, residual stress can be reduced or removed without omission.

(5) In the torsion beam manufacturing method according to any one of the above (1) to (4), in the compression step, a strain amount equal to or greater than 0.5% and equal to or smaller than 2.0% may be applied to at least the connection region of the torsion beam material in the longitudinal direction.

In this case, it is possible to apply a compression force sufficient to remove or reduce the residual stress of the torsion beam material without causing buckling.

(6) The torsion beam manufacturing method according to any one of the above (1) to (5) may further include a pressing step of obtaining the torsion beam material by pressing a raw pipe, before the compression step.

In this case, although residual stress is remaining in the torsion beam material at the point of time after the pressing step, the residual stress can be reduced or removed in the successive compression step.

(7) The torsion beam manufacturing method according to the above (1) may further include, a preparation step of preparing the torsion beam material having a warpage along the longitudinal direction in at least a part thereof in the longitudinal direction before the compression step, and in the compression step, in a state where an elongation between both end edges of the torsion beam material is regulated, a pressing force for reducing the warpage may be applied to the torsion beam material.

In this case, it is possible to apply a compression force to the torsion beam material with a simpler apparatus configuration.

(8) In the torsion beam manufacturing method according to the above (7), in the preparation step, the torsion beam material having both end edges inclined with respect to the longitudinal direction may be prepared.

In this case, depending on the inclination direction and the inclination angle of both end edges, a compression ratio of each part in the cross-section intersecting the longitudinal direction of the torsion beam material can be changed.

(9) In the torsion beam manufacturing method according to the above (7) or (8), in the compression step, a strain amount equal to or greater than 0.5% and equal to or smaller than 2.0% may be applied to at least the connection region of the torsion beam material in the longitudinal direction.

In this case, it is possible to apply a compression force sufficient to remove or reduce the residual stress of the torsion beam material without causing buckling.

(10) In the torsion beam manufacturing method according to any one of the above (1) to (9), when the compression force is applied in the compression step, at least the outer surface of the connection region may be supported.

In this case, in the compression step, since a compression force is applied while supporting at least the outer surface of the connection region, even when an object to be processed is a thin torsion beam material, buckling can be prevented.

(11) One aspect of the present invention is a torsion beam manufacturing apparatus for manufacturing a torsion beam including a central portion of which a cross-section orthogonal to a longitudinal direction is a closed cross-section having a substantial V-shape or a substantial U-shape at any position in the longitudinal direction, and a shape changing portion which has a connection region leading to the central portion and including a closed cross-section having a shape different from the shape of the closed cross-section of the central portion, the apparatus including: a pair of holding mechanisms that holds, in a view where a torsion beam material in which the central portion and the shape changing portion are formed is seen along the longitudinal direction, a part of the torsion beam material on one side of the connection region and a part of the torsion beam material on the other side of the connection region; and a first driving mechanism that causes the holding mechanisms to approach each other.

According to the torsion beam manufacturing apparatus of the above aspect, by applying a compression force in the longitudinal direction to at least connection region in the torsion beam material by the pair of holding mechanisms and the first driving mechanism, the residual stress remaining in the torsion beam material can be reduced or removed and the torsion beam material can be reinforced at the same time.

As a result, a torsion beam having excellent fatigue durability can be manufactured. In addition, since post-treatment such as heat treatment is not required, it is possible to manufacture a torsion beam efficiently.

(12) In the torsion beam manufacturing apparatus according to the above (11), the holding mechanisms may hold both ends of the torsion beam material respectively.

In this case, since both ends of the torsion beam material are held and compressed by the pair of holding mechanisms, a compression force can be applied over the entire length of the torsion beam material. Accordingly, the residual stress can be reduced or removed without leakage over the entire length of the torsion beam material.

(13) The torsion beam manufacturing apparatus according to the above (12) may further include: a movable die that has a shape corresponding to the central portion and the shape changing portion; and a second driving mechanism that pressurizes the movable die with respect to a raw pipe before the central portion and the shape changing portion are applied in the torsion beam material.

In this case, since the second driving mechanism presses the movable die against the raw pipe, a torsion beam material having the central portion and the shape changing portion can be obtained.

(14) In the torsion beam manufacturing apparatus according to the above (11), at least one of the holding mechanisms may include an inner side support member which is inserted into an inner side of the shape changing portion, and an outer pinching member which pinches an outer side of the shape changing portion.

In this case, since the inner side of the shape changing portion of the torsion beam material is supported by the inner side support member and then while the outer side of the shape changing portion is pinched by the outer pinching member, a compression force can be applied, it is possible to easily apply a compression force while suppressing the out-of-plane deformation of the shape changing portion.

(15) The torsion beam manufacturing apparatus according to the above (14) may further include: a movable die that has a shape corresponding to the central portion and the shape changing portion; and a second driving mechanism that presses the movable die against a raw pipe before the central portion and the shape changing portion are formed in the torsion beam material.

In this case, since the second driving mechanism pressurizes the movable die against the raw pipe, a torsion beam material having the central portion and the shape changing portion can be obtained.

(16) The torsion beam manufacturing apparatus according to the above (15) may employ the following configuration in which the movable die includes a movable die main body portion which has a shape corresponding to at least the central portion, a movable die end portion which has a shape corresponding to at least the shape changing portion and is provided to be movable with respect to the movable die main body portion, and a third driving mechanism which moves the movable die end portion with respect to the movable die main body portion, in which the movable die end portion also serves as the outer pinching member.

In this case, the shape corresponding to at least the central portion is given to the raw pipe pressed by the movable die main body portion and the shape corresponding to at least the shape changing portion is given by the movable die end portion. A compression force is applied to the torsion beam material in a state where the inner side support member is inserted into the shape changing portion of the torsion beam material and the outer side of the shape changing portion is pinched by the movable die end portion. According to this configuration, since the movable die end portion also serves as the outer pinching member, without transferring the torsion beam material obtained by performing press working on the raw pipe to another apparatus, a compression force can be continuously applied along the longitudinal direction as it is.

(17) The torsion beam manufacturing apparatus according to any one of the above (11) to (16) may employ the following configuration in which: the apparatus further includes a support die that supports the torsion beam material, wherein the support die includes a support die main body portion which supports the torsion beam material in a part including the central portion, and a support die end portion which is provided to be movable with respect to the support die main body portion and supports at least the shape changing portion.

In this case, since the support die end portion is freely movable with respect to the support die main body portion when a compression force is applied to the torsion beam material, deformation of the torsion beam material due to compression along the longitudinal direction is not inhibited. Therefore, since a compression force can be reliably applied to the torsion beam material, the residual stress can be reliably reduced or removed.

(18) The torsion beam manufacturing apparatus according to any one of the above (11) to (17) may employ the following configuration in which: the apparatus further includes a control unit that controls the first driving mechanism, wherein the control unit operates the first driving mechanism to apply a strain amount equal to or greater than 0.5% and equal to or smaller than 2.0% to at least the connection region of the torsion beam material in the longitudinal direction.

In this case, it is possible to apply a compression force sufficient to remove or reduce the residual stress of the torsion beam material without causing buckling.

(19) The torsion beam manufacturing apparatus according to any one of the above (11) to (18) may further include: a support portion which supports at least an outer surface of the connection region in the torsion beam material held by the pair of holding mechanisms.

In this case, when a compression force in the longitudinal direction is applied to at least connection region in the torsion beam material, a compression force is applied while supporting at least the outer surface of the connection region by the support portion. Thus, even when an object to be worked is a thin torsion beam material, buckling can be prevented.

(20) Another aspect of the present invention is a torsion beam manufacturing apparatus for manufacturing a torsion beam including a central portion of which a cross-section orthogonal to a longitudinal direction is a closed cross-section having a substantial V-shape or a substantial U-shape at any position in the longitudinal direction, and a shape changing portion which has a connection region leading to the central portion and including a closed cross-section having a shape different from the shape of the closed cross-section of the central portion, the apparatus including: a first die which has a recess to receive a torsion beam material having the central portion and the shape changing portion and has a warpage along the longitudinal direction in at least a part thereof in the longitudinal direction; a second die which approaches the torsion beam material disposed in the recess along a direction in which the warpage is reduced; and a fourth driving mechanism which causes the first die and the second die to approach each other, in which the recess has a pair of elongation regulating surfaces facing both end edges of the torsion beam material, and a distance between the pair of elongation regulating surfaces is shorter than an entire length along the warpage of the torsion beam material.

According to the torsion beam manufacturing apparatus of the above aspect, the torsion beam material is disposed in the recess of the first die, and then the second die approaches the second die by a driving force of the fourth driving mechanism. The torsion beam material is pressed from the second die to reduce warpage. At that time, since the elongation between both end edges is regulated by the pair of elongation regulating surfaces, a compression force in the longitudinal direction is applied to at least the shape changing portion of the torsion beam material. By the compression force, the residual stress remaining in the torsion beam material can be reduced or removed and the torsion beam material can be reinforced by thickening at the same time. As a result, a torsion beam having excellent fatigue durability can be manufactured. In addition, post-treatment such as heat treatment is not required, and it is possible to manufacture a torsion beam efficiently with a simple apparatus configuration.

In addition to the aspects described above, the present invention may employ the following aspects.

(a) As an alternative aspect of the present invention, there is provided a torsion beam manufacturing method for manufacturing a torsion beam being used in a torsion beam-type suspension apparatus, having a pair of right and left arms coupled to both end portions in a longitudinal direction, and including a central portion and an attachment closed cross-sectional portion of which a cross-section orthogonal to the longitudinal direction has a substantially constant closed cross-sectional shape of a substantial V-shape or a substantial U-shape in which a part between a front end and a rear end in a forward/rearward direction of a vehicle body protrudes upward or downward, and a shape changing portion which is positioned between the central portion and the attachment closed cross-sectional portion, the torsion beam manufacturing method including: a press working step of forming a torsion beam material which is obtained by pressing a metal material pipe and has the central portion and the shape changing portion, and a compression treatment step of compressing at least a connection portion connecting the central portion and the shape changing portion to each other in the torsion beam material in the longitudinal direction.

In the torsion beam manufacturing method of the above aspect, since the torsion beam manufacturing method includes the press working step of forming a torsion beam material which is obtained by pressing a metal material pipe and has the central portion and the shape changing portion, and the compression treatment step of compressing at least the connection portion connecting the central portion and the shape changing portion to each other in the torsion beam material in the longitudinal direction, tensile residual stress can be reduced or removed from the connection portion.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

In this specification, the central portion refers to a part in which a substantially constant closed cross-sectional shape of a substantial V-shape or a substantial U-shape (for example, a valley portion (bottom portion) of a wall portion constituting a recessed side of a substantial V-shape or a substantial U-shape) is formed continuously along the longitudinal direction. In addition, until the valley portion (bottom portion) of the wall portion constituting the recessed side of the substantial V-shape or the substantial U-shape reaches the shape changing portion that gradually becomes shallower, even when unevenness is partially formed, the valley portion is included in the central portion.

Further, the central portion may be configured such that from the left and right ends to the center along the longitudinal direction of the torsion beam, while the substantial V-shape or the substantial U-shape is maintained, the area of the closed cross-section is gradually changed. The torsion beam or the torsion beam material having such a shape can be obtained by pressing a metal material pipe whose diameter gradually changes from the left and right ends to the center along the longitudinal direction.

Further, in this specification, the shape changing portion is a part in which a shape in which the valley portion (bottom portion) of the wall portion constituting the recessed side of the substantial V-shape or the substantial U-shape becomes gradually shallower is continuously formed. In addition, a part in which the valley part (bottom portion) becomes partially shallower may be formed in the middle of the shape changing portion.

In addition, in this specification, the attachment closed cross-sectional portion denotes a part which is positioned outward in the longitudinal direction of the shape changing portion (outward in a vehicle width direction) and in which a recessed part having a substantial V-shape or a substantial U-shape is not formed.

Further, in this specification, the connection portion that connects the central portion and the shape changing portion refers to a portion including the boundary between the central portion and the shape changing portion, and the valley portion (bottom portion) of the wall portion constituting the recessed side of the substantial V-shape or the substantial U-shape formed in the central portion along the longitudinal direction is a part including a portion that is transferred to a shape which gradually becomes shallower in the shape changing portion and is inclined with respect to the longitudinal direction. In addition, the range of the connection portion can be randomly set based on distribution of tensile residual stress or the like.

(b) In the torsion beam manufacturing method according to the above (a), in the compression treatment step, an inner side support member is inserted into the shape changing portion of the torsion beam material and the shape changing portion is pinched by a shape changing portion support member to compress the connection portion in the longitudinal direction.

According to the torsion beam manufacturing method, in the compression treatment step, since the inner side support member is inserted into the shape changing portion of the torsion beam material and the shape changing portion is pinched by the shape changing portion support member to compress the connection portion in the longitudinal direction, the deformation of the shape changing portion can be reliably suppressed while easily compressing the connection portion of the torsion beam material inward in the longitudinal direction.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

(c) In the torsion beam manufacturing method according to the above (a), in the compression treatment step, the connection portion is compressed in the longitudinal direction by holding the attachment closed cross-sectional portion of the torsion beam material.

According to the torsion beam manufacturing method, in the compression treatment step, since the connection portion is compressed in the longitudinal direction by holding the attachment closed cross-sectional portion of the torsion beam material, the torsion beam material can be compressed inward in the longitudinal direction over the entire length.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

(d) As another alternative aspect of the present invention, there is provided a torsion beam manufacturing apparatus for manufacturing a torsion beam being used in a torsion beam-type suspension apparatus, having a pair of right and left arms coupled to both end portions in a longitudinal direction, and including a central portion and an attachment closed cross-sectional portion of which a cross-section orthogonal to the longitudinal direction has a substantial V-shape or a substantial U-shape in which a part between a front end and a rear end in a forward/rearward direction of a vehicle body protrudes upward or downward, and a shape changing portion which is positioned between the central portion and the attachment closed cross-sectional portion, the torsion beam manufacturing apparatus including: a shape changing portion outside holding member that has an exterior shape holding shape portion formed complementarily to the shape changing portion; a shape changing portion support member that is provided in the forming die, pinches the shape changing portion from an inner side in the longitudinal direction, and supports the shape changing portion; a driving unit that moves an attachment closed cross-sectional portion holding member forward and rearward in the longitudinal direction of a torsion beam material; and a control unit, in which the control unit is configured to move the shape changing portion support member inward in the longitudinal direction of the torsion beam material in a state where the shape changing portion is held by the shape changing portion outside holding member and the shape changing portion support member after the torsion beam material is formed.

According to the torsion beam apparatus, the connection portion is compressed in the longitudinal direction by moving the shape changing portion support member inward in the longitudinal direction of the torsion beam material in a state where the shape changing portion is held by the shape changing portion outside holding member which has the exterior shape holding shape portion formed complementarily to the shape changing portion, and the shape changing portion support member which is provided in the forming die, pinches the shape changing portion from the inner side in the longitudinal direction, and supports the shape changing portion. Therefore, stable compression treatment can be performed by preventing the shape changing portion from being deformed.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

(e) As further another alternative aspect of the present invention, there is provided a torsion beam manufacturing apparatus for manufacturing a torsion beam being used in a torsion beam-type suspension apparatus, having a pair of right and left arms coupled to both end portions in a longitudinal direction, and including a central portion and an attachment closed cross-sectional portion of which a cross-section orthogonal to the longitudinal direction has a substantial V-shape or a substantial U-shape in which a part between a front end and a rear end in a forward/rearward direction of a vehicle body protrudes upward or downward, and a shape changing portion which is positioned between the central portion and the attachment closed cross-sectional portion, the torsion beam manufacturing apparatus including: an attachment closed cross-sectional portion holding member that holds the attachment closed cross-sectional portion; a driving unit that moves the attachment closed cross-sectional portion holding member forward and rearward in the longitudinal direction of a torsion beam material, and a control unit, in which the control unit is configured to compress the torsion beam material in the longitudinal direction in a state where the attachment closed cross-sectional portion holding member holds the attachment closed cross-sectional portion.

According to the torsion beam apparatus, since the connection portion is compressed in the longitudinal direction by holding the attachment closed cross-sectional portion of the torsion beam material, the torsion beam material can be compressed inward in the longitudinal direction over the entire length.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

(f) As still another alternative aspect of the present invention, there is provided a torsion beam manufacturing apparatus for manufacturing a torsion beam being used in a torsion beam-type suspension apparatus, having a pair of right and left arms coupled to both end portions in a longitudinal direction, and including a central portion and an attachment closed cross-sectional portion of which a cross-section orthogonal to the longitudinal direction has a substantial V-shape or a substantial U-shape in which a part between a front end and a rear end in a forward/rearward direction of a vehicle body protrudes upward or downward, and a shape changing portion which is positioned between the central portion and the attachment closed cross-sectional portion, the torsion beam manufacturing apparatus including: a forming die that presses a metal material pipe and forms a torsion beam material having the central portion and the shape changing portion; a shape changing portion support member that is provided in the forming die, pinches the shape changing portion from an inner side in the longitudinal direction, and supports the shape changing portion; a shape changing portion support member driving unit that is provided in the forming die and moves the shape changing portion support member forward and rearward in the longitudinal direction; an inner side support member that is able to be inserted into the shape changing portion and holds the shape changing portion in cooperation with the shape changing portion support member; and a control unit, in which the control unit is configured to move the shape changing portion support member inward in the longitudinal direction of the torsion beam material in a state where the shape changing portion is held by the shape changing portion support member and the inner side support member after the torsion beam material is formed.

According to the torsion beam manufacturing apparatus, the control unit causes the driving unit to compress the torsion beam material inward in the longitudinal direction in a state where the shape changing portion support member and the inner side support member hold the shape changing portion in cooperation with each other after the metal material pipe is pressed and the torsion beam material is formed. Therefore, tensile residual stress can be reduced or removed from a connection portion.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

(g) There is provided a torsion beam manufacturing apparatus for manufacturing a torsion beam being used in a torsion beam-type suspension apparatus, having a pair of right and left arms coupled to both end portions in a longitudinal direction, and including a central portion and an attachment closed cross-sectional portion of which a cross-section orthogonal to the longitudinal direction has a substantial V-shape or a substantial U-shape in which a part between a front end and a rear end in a forward/rearward direction of a vehicle body protrudes upward or downward, and a shape changing portion which is positioned between the central portion and the attachment closed cross-sectional portion, the torsion beam manufacturing apparatus including: a forming die that presses a metal material pipe and forms a torsion beam material having the central portion and the shape changing portion; a shape changing portion support member that is provided in the forming die, pinches the shape changing portion from an inner side in the longitudinal direction, and supports the shape changing portion; a shape changing portion support member driving unit that is provided in the forming die and moves the shape changing portion support member forward and rearward in the longitudinal direction; and an inner side support member that is able to be inserted into the shape changing portion and holds the shape changing portion in cooperation with the shape changing portion support member, in which the driving unit is constituted of a cam mechanism which operates in accordance with strokes when the forming die forms the torsion beam material.

According to the torsion beam manufacturing apparatus, the driving unit compresses the torsion beam material inward in the longitudinal direction in a state where the shape changing portion support member and the inner side support member hold the shape changing portion in cooperation with each other as the cam mechanism operates in accordance with strokes when the torsion beam material is formed after the metal material pipe is pressed and the torsion beam material is formed. Therefore, tensile residual stress can be reduced or removed from a connection portion.

As a result, a torsion beam having excellent fatigue durability can be efficiently manufactured.

(h) The torsion beam manufacturing apparatus according to any one of the above (d) to (g) further includes a shape change absorption unit that is changed in shape in the longitudinal direction and is displaced when the torsion beam material is compressed in the longitudinal direction.

According to the torsion beam manufacturing apparatus, since the torsion beam manufacturing apparatus includes the shape change absorption unit that is changed in shape in the longitudinal direction and is displaced when the torsion beam material is compressed in the longitudinal direction, even in a case where a torsion beam has a shape with a significant central side in the longitudinal direction, compression treatment can be easily performed.

In addition, it is possible to prevent damage to the torsion beam material when performing the compression treatment and to efficiently reduce residual stress.

Effects of the Invention

According to the torsion beam manufacturing method and the torsion beam manufacturing apparatus in the aspects described above, a torsion beam having excellent fatigue durability can be more efficiently manufactured.

