Curved elongate member of closed sectional shape and method and apparatus for fabricating the same

Hollow closed-sectional elongate member is provided by bending a plastic strip widthwise. The closed-sectional elongate member has a crimped joint section provided on any one of its walls. The crimped joint section is formed by crimping together opposite longitudinal edge portions of the strip as the strip is bent widthwise. The crimped joint section extends along the length of the closed-sectional elongate member and thus functions as a rib reinforcing the rigidity of the elongate member. The closed-sectional elongate member is also curved along its longitudinal direction, to provide a closed-sectional curved elongate member.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to curved elongate members of a closed
 sectional shape which are particularly suitable for use as bumper beams
 reinforcing automotive vehicle bumpers, as well as methods and apparatus
 for fabricating such closedsectional curved elongate members.
 2. Related Prior Art
 As bumper-reinforcing beams (bumper beams) for automotive vehicles and the
 like, there have been used elongate tubular members which have a sectional
 shape of, for example, a closed rectangle and are curved along a
 longitudinal direction thereof. These elongate tubular members will
 hereinafter be referred to as "closed-sectional curved elongate members".
 Such closed-sectional curved elongate members are generally fabricated by
 pressing or rolling; in recent years, the rolling has been used more
 popularly than the pressing because it achieves higher productivity than
 the pressing. Examples of the known methods of fabricating the
 closedsectional curved elongate members using the rolling include a
 "method of fabricating a reinforcing member for a vehicle bumper"
 disclosed in Japanese Patent Laid-open Publication No. HEI-9-141329.
 According to the disclosure in the No. HEI-9-141329 publication,
 closed-sectional curved elongate members are formed of a continuous
 plastic sheet or strip (typically a metal strip) sequentially supplied
 from an uncoiler disposed at an upstream end of a fabricating apparatus.
 More specifically, the disclosed fabricating method comprises a first
 roll-bending step, a laser welding step, a second roll-bending step and a
 cutting step.
 In the first roll-bending step, the plastic strip supplied from the
 uncoiler is bent widthwise into a semifinished tubular structure having a
 substantially closed section by means of a roll-bending machine which
 includes a series of roller pairs, each made up of upper and lower
 rollers, disposed along a traveling direction of the strip (i.e., in an
 upstream-to-downstream direction). Also, as the strip sequentially passes
 through the roller pairs, it is progressively curved along the traveling
 direction, i.e., along its length.
 Then, in the laser welding step, opposite longitudinal edge portions of the
 plastic strip, which have been caused to substantially butt against each
 other through the bending in the first roll-bending step, are welded
 together by a laser welding machine disposed downstream of the
 roll-bending machine, to thereby provide a finished tubular structure with
 a welded joint section.
 Next, in the second roll-bending step, the finished tubular structure is
 further curved by means of a three-point roll-curving machine having three
 rollers disposed downstream of the laser welding machine. Finally, in the
 cutting step, the finished tubular structure with the welded joint
 section, transferred from the second roll-bending step, is cut into a
 predetermined length to provide the bumper-reinforcing member.
 Because the bumper-reinforcing member fabricated by the method disclosed in
 the No. HEI-9-141329 publication is in the form of a closed-sectional
 curved elongate member, it has great rigidity against bending and twisting
 forces and great robustness against impacts as compared to the traditional
 open-sectional curved elongate member having its opposite longitudinal
 edge portions left unjointed.
 However, because the method discussed in the No. HEI-9-141329 publication
 uses the expensive laser welding machine to butt-weld the opposite
 longitudinal edge portions of the semifinished tubular structure, it would
 require complicated manufacturing lines and increased costs. Further, if a
 high-tensile steel sheet is used as the strip, the butt-welded joint
 section would become more brittle (i.e., would have a reduced strength),
 so that there would arise a need for an extra step of locally annealing
 the butt-welded joint section.
 SUMMARY OF THE INVENTION
 It is accordingly an object of the present invention to provide a
 closed-sectional curved elongate member which can be fabricated in
 quantity at low costs in a greatly simplified manner.
 It is another object of the present invention to provide method and
 apparatus capable of fabricating a closed-sectional curved elongate member
 in quantity at low costs in a greatly simplified manner.
 According to an aspect of the present invention, there is provided a
 closed-sectional curved elongate member which includes a crimped joint
 section that is formed on any one of a plurality of wall surfaces of the
 elongate member defining a closed section of the elongate member, the
 crimped joint section extending along a length of the elongate member, and
 which is curved along a longitudinal direction thereof.
 The crimped joint section thus formed along the length of the elongate
 member can function as a rib reinforcing the elongate member, so that the
 closed-sectional curved elongate member of the present invention has
 rigidity equal to or greater than that of the conventional
 closed-sectional curved elongate member having the welded joint section.
 The crimped joint section may be provided on either the outside or the
 inside of the elongate member. However, it is more preferable that the
 crimped joint section be provided inside the closed section of the
 elongate member, because the crimped joint section thus provided will not
 interfere with other components already placed or to be placed near the
 elongate member.
 Further, it is preferable that the crimped joint section have gatherings
 that will achieve an increased strength of the joint.
 According another aspect of the present invention, there is provided a
 method of fabricating a closed-sectional curved elongate member, which
 comprises: a step of bending a plastic strip, such as a metal strip,
 widthwise into a closed sectional shape by means of a series of bending
 rollers disposed along a longitudinal direction of the strip; a step of
 crimping together opposite longitudinal edge portions of the strip that
 are caused to substantially butt against each other through the bending by
 the step of bending, by means of crimping rollers, to thereby provide a
 closed-sectional elongate member with a crimped joint section; and a step
 of curving the closed-sectional elongate member along a length of the
 closed-sectional elongate member, by means of a series of curving rollers,
 as the closed-sectional elongate member is transferred in a predetermined
 traveling direction.
 The step of curving may be initiated either after completion of the step of
 bending or during the step of crimping. However, performing the step of
 curving during the step of crimping is more preferable in that the curving
 step can be done concurrently with the crimping step and thus the overall
 necessary time for the fabrication can be significantly reduced.
 According still another aspect of the present invention, there is provided
 an apparatus for fabricating a closed-sectional curved elongate member,
 which comprises: a roll-bending unit including a series of bending rollers
 disposed along a traveling direction of a plastic strip for bending the
 strip widthwise into a semifinished closed sectional shape; a rolling unit
 for rolling a bottom portion of the strip bent via the roll-bending unit,
 to thereby curve the strip along the traveling direction; a crimping-roll
 unit for sequentially crimping together opposite longitudinal edge
 portions of the strip that are caused to substantially butt against each
 other through the rolling by the rolling unit, to thereby provide a
 closed-sectional elongate member with a crimped joint section; and a
 roll-curving unit including a series of curving rollers for further
 curving the closed-sectional elongate member along the traveling
 direction.
 The apparatus of the present invention can sequentially crimp together the
 substantially butting opposite longitudinal edge portions of the strip by
 means of the crimping-roll unit and can perform the crimping and curving
 of the elongate member in succession. Thus, the inventive apparatus can
 fabricate the closed-sectional curved elongate member in a greatly
 simplified manner.
 Further, it is preferable that the crimping-roll unit comprise a gathering
 unit that, by means of a pair of gathering rollers, crimps together the
 substantially butting opposite longitudinal edge portions of the strip
 bent via the roll-bending unit, to thereby impart a series of gatherings
 in the longitudinal edge portions. In this case, the gatherings can be
 formed at the same time the opposite longitudinal edge portions of the
 strip are being crimped together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The following description is merely exemplary in nature and is in no way
 intended to limit the invention, its application or uses.
 FIG. 1A is a perspective view showing a general configuration of a
 closed-sectional curved elongate member in accordance with a first
 embodiment of the present invention. As shown, the closed-sectional curved
 elongate member 1 has a sectional shape of a hollow rectangle and is
 curved along the full length thereof. The closed-sectional curved elongate
 member 1 is suitable for use as a structural member of an automotive
 vehicle and particularly as a bumper beam to reinforce the vehicle bumper.
 Essentially, the elongate member 1 is formed by first bending a plastic
 strip widthwise into a semifinished tubular structure of a hollow
 rectangular sectional shape such that its opposite longitudinal edge
 portions substantially butt against each other, and then crimping together
 the substantially butting longitudinal edge portions so as to provide a
 finished tubular structure of a closed sectional shape, as shown in FIG.
 1B. The elongate member 1, having been thus formed into the finished
 tubular structure of a hollow square or rectangular sectional shape,
 includes four flat walls: an upper wall 2; a lower wall 3; a left side
 wall 4; and right side wall 5, and a crimped joint section 10 formed
 centrally on any one of the four walls 2 to 5. In the illustrated example,
 the crimped joint section 10 is formed centrally on the right side wall 5.
 Specifically, the crimped joint section 10 of the elongate member 1 is
 formed by crimping together two extensions 13 and 14 of the opposite
 longitudinal edge portions 11 and 12, having been caused to substantially
 butt against each other through the bending, into the semifinished tubular
 configuration, of the strip. More specifically, the extensions 13 and 14
 protrude outwardly from the substantially butting longitudinal edge
 portions 11 and 12, respectively, in a superposed relation to each other.
 These extensions 13 and 14 are crimped together with one of the extensions
 13 enfolded by the other extension 14. The crimped joint section 10
 extends continuously along the full length of the elongate member 1, and
 thus it can function as a rib reinforcing the elongate member 1 in the
 longitudinal direction thereof to thereby increase rigidity of the entire
 elongate member 1.
 Further, in the preferred embodiment, the strip used to form the elongate
 member 1 is a steel sheet or plate of high tensile strength. Thus, using
 such a high tensile strength steel plate, the elongate member 1 can be
 significantly reduced in weight and also is capable of effectively
 absorbing impact energy in case of collision of the vehicle against
 something else. The high tensile strength steel plate for forming the
 elongate member 1 may be, for example, a hot or cold rolled high tensile
 strength steel sheet with improved formability for automobile structural
 uses (JIS G 3134 SPFH; JIS G 3135 SPFC).
 FIG. 2 is a view schematically showing an apparatus for fabricating the
 elongate member 1 of the above-mentioned construction. In FIG. 2,
 reference numeral 28 represents a frame of the elongate-member fabricating
 apparatus 20, on which are supported various components as will be
 described below. The elongate-member fabricating apparatus 20 includes an
 uncoiler 21 disposed at an upstream end of the apparatus, on which the
 continuous plastic strip PL is wound and from which the strip PL is
 supplied sequentially to downstream processing units. Of the processing
 units, a front-stage roll-bending unit 22 is disposed downstream of the
 uncoiler 21 and bends widthwise the plastic strip PL, uncoiled or supplied
 from the uncoiler 21, into a semifinished tubular structure, i.e., a
 semifinished closed-sectional elongate member. The front-stage
 roll-bending unit 22 comprises a series of bending roller sets 22A
 disposed along a traveling direction x of the strip, and each of the
 roller sets 22A includes a pair of upper and lower rollers 22a and 22b and
 a pair of left and right rollers (not shown). Further, downstream of the
 front-stage roll-bending unit 22, there is provided a rolling unit 23
 which curves the semifinished elongate member along the length of the
 elongate member by rolling the elongate member along the strip traveling
 direction X. Rear-stage roll-bending unit 24 is disposed downstream of the
 rolling unit 23 and further bends the semifinished elongate member
 widthwise into a substantially rectangular sectional configuration such
 that the opposite longitudinal edge portions of the elongate member
 substantially butt against each other or placed close enough to each other
 for subsequent crimping. Downstream of the rear-stage roll-bending unit
 24, there. is provided a crimping-roll unit 25 which crimps together the
 butting opposite longitudinal edge portions of the elongate member
 sequentially in the longitudinal direction of the elongate member, to
 thereby provide the crimped joint section 10 and hence the finished
 tubular structure (i.e., closed-sectional elongate member) as shown in
 FIG. 1B. Roll-curving unit 26 is disposed downstream of the crimping-roll
 unit 25 and further curves the closed-sectional elongate member, delivered
 from the crimping-roll unit 25, along the strip traveling direction x, to
 thereby provide the closed-sectional curved elongate member with the
 crimped joint section 10. Further, downstream of the roll-curving unit 26,
 there is provided a cutting unit 27 for cutting the closed-sectional
 curved elongate member into a predetermined length.
 The fabricating apparatus 20 as shown in FIG. 2 is characterized by the
 provision of the front- and rear-stage roll-bending units 22 and 24 with
 the rolling unit 23 interposed therebetween. Such a combination of the
 units 22, 23 and 24 allows the curving process to be initiated upon
 completion of the process of bending the strip PL into the finished
 tubular structure of the rectangular sectional shape.
 FIG. 3 is an enlarged fragmentary view of the fabricating apparatus shown
 in FIG. 2. In FIG. 3, the rolling unit 23 includes a pair of upper and
 lower rollers 23a and 23b. The plastic strip is curved along its
 longitudinal direction into a predetermined first radius of curvature R1,
 by adjusting a rolling force with which the strip is rolled by the rollers
 23a and 23b; specifically, the strip PL, having been bent via the
 front-stage roll-bending unit 22 into the semifinished tubular structure
 (semi-closed rectangular sectional configuration), is rolled at its bottom
 portion between the rollers 23a and 23b until it is bent to the
 predetermined first radius of curvature R1.
 The rear-stage roll-bending unit 24 comprises front and rear bending roller
 sets 24A each including a pair of upper and lower rollers 24a and 24b and
 a pair of left and right rollers (not shown).
 The roll-curving unit 26 comprises a plurality of curving roller sets
 disposed along the strip traveling direction x, with each of the roller
 sets including three small curving rollers 26a. In this embodiment, the
 leading one of the curving roller sets constitutes the above-mentioned
 crimping-roll unit 25.
 Fore half of the roll-curving unit 26 progressively curves the elongate
 member from the first radius of curvature R1 to a predetermined second
 radius of curvature R2, and then a rear half of the roll-curving unit 26
 progressively curves the elongate member from the second radius of
 curvature R2 to a predetermined third radius of curvature R3. Accordingly,
 the elongate member is curved via the roll-curving unit 26 successively
 from the first radius of curvature R1 to the third radius of curvature R3.
 Here, the second radius of curvature R2 is smaller than the first radius
 of curvature R1, and the third radius of curvature R3 is smaller than the
 second radius of curvature R2 (i.e., R1&gt;R2&gt;R3). In this way, the
 elongate member is progressively curved into the predetermined radius of
 curvature as it is transferred in the strip traveling direction x.
 FIG. 4 is a sectional view showing details of the crimping-roll unit 25.
 More particularly, FIG. 4 is explanatory of a manner in which the
 crimping-roll unit 25 crimps together the opposite longitudinal edge
 portions to form the crimped joint section 10 as the elongate member 44
 having the semifinished tubular configuration 44 is moved in a direction
 normal to the sheet of the drawing, i.e., from the obverse side to the
 reverse side of the sheet.
 The crimping-roll unit 25 includes a lower roller 31 for supporting the
 underside of the elongate member 44, an upper roller 32 for pressing and
 crimping the opposite longitudinal edge portions of the elongate member
 44, left and right rollers 33 and 34 for supporting the left and right
 side surfaces of the elongate member 44, and an auxiliary roller mechanism
 35 for preventing the elongate member 44 from collapsing vertically when
 the opposite longitudinal edge portions of the elongate member 44 are
 being crimped together by the upper or crimping roller 32.
 The upper or crimping roller 32 has a central crimping groove 32a that is
 formed around its outer peripheral surface for receiving and crimping
 together the extensions 13 and 14 protruding outwardly from the butting
 longitudinal edge portions 11 and 12 of the elongate member 44. Namely,
 opposed inner side surfaces of the crimping roller 32, defining the
 crimping groove 32a, firmly press the extensions 13 and 14 against each
 other to join them together into narrow folds.
 The auxiliary roller mechanism 35 includes a pair of upper and lower
 rollers 36 and a pair of links 37 for rotatably supporting the upper and
 lower rollers 36 in place. Bearings 38 in FIG. 4 rotatably support the
 respective shafts of the lower roller 31, upper or crimping roller 32 and
 left and right rollers 33 and 34.
 The following paragraphs describe a method, i.e., a sequence of steps, for
 fabricating the closed-sectional curved elongate member 1 of FIG. 1, with
 reference to FIGS. 2 and 5.
 First, the plastic strip PL is supplied from the uncoiler 21 of FIG. 2 in
 the traveling direction x, as shown in part (a) of FIG. 5 (strip supply
 step).
 Then, as shown in parts (b) and (c) of FIG. 5, the supplied strip PL is
 bent widthwise, via the front-stage roll-bending unit 22 of FIG. 2, into a
 semifinished tubular structure of a substantially rectangular sectional
 shape opening upwardly, to thereby provide a semifinished elongate member
 41 (first bending step).
 After completion of the first bending step, the semifinished elongate
 member 41 is curved along its length, i.e., along the strip traveling
 direction x, into the first radius of curvature R1 as shown in part (d) of
 FIG. 5 (first curving step). More specifically, the semifinished elongate
 member 41 is passed between the upper and lower rollers 23a and 23b of the
 rolling unit 23 of FIG. 2 so that the elongate member 41 is curved at its
 bottom 42 with the first radius of curvature. As a result of this first
 curving step, there is provided a semifinished curved elongate member 43
 having the upwardly-opening rectangular sectional shape.
 Then, as shown in part (e) of FIG. 5, the semifinished curved elongate
 member 43 is further bent, via the rear-stage roll-bending unit 24 of FIG.
 2, to such an extent that the opposite longitudinal edge portions of the
 elongate member 43 are caused to substantially butt against each other or
 placed close enough to each other for subsequent crimping (second bending
 step). As a result of this second bending step, there is provided a
 semifinished closed-sectional curved elongate member 44.
 Further, as shown in part (f) of FIG. 5, the semifinished closed-sectional
 curved elongate member 44 is delivered to the crimping-roll unit 25, where
 the extensions 13 and 14 protruding outwardly from the butting
 longitudinal edge portions 11 and 12 of the elongate member 44 are crimped
 together (crimping step). Also, the elongate member 44 is further curved
 from the first radius of curvature R1 to the second radius of curvature R2
 (second curving step). As a result of these steps, there is provided a
 finished closed-sectional curved elongate member 45 having the crimped
 joint section 10 along the full length thereof.
 Then, as shown in part (g) of FIG. 5, the finished closed-sectional curved
 elongate member 45 with the crimped joint section 10, provided by the
 steps of part (f) of FIG. 5, is further curved from the second radius of
 curvature R2 to the third radius of curvature R3 (third curving step). As
 a result, there is provided a completely-finished closed-sectional curved
 elongate member 46.
 Finally, the completely-finished closed-sectional curved longate member 46
 is cut via the cutting unit 27 into a predetermined length (cutting step),
 so that the predetermined length of the completely-finished
 closed-sectional curved elongate member 46 can be provided.
 As understood from the foregoing, the successive curving steps in the
 present invention are initiated after the bending of the strip into the
 semifinished tubular structure of the substantially rectangular section.
 FIGS. 6A and 6B are perspective views of a closed-sectional curved elongate
 member in accordance with a second embodiment of the present invention.
 The elongate member 1 according to the second embodiment is characterized
 in that the crimped joint section 10 is formed on an inner wall surface,
 i.e., inside the closed section, of the elongate member 1 so that the
 joint section 10 is invisible from outside the elongate member 1, which
 greatly enhances the appearance of the elongate member 1 as a product.
 Specifically, in the crimped joint section 10 of the closed-sectional
 curved elongate member 1 shown in FIGS. 6A and 6B, the extensions 13 and
 14 protrude inwardly from the butting longitudinal edge portions 11 and
 12, respectively, in a superposed relation to each other. These extensions
 13 and 14 are pressed and crimped together with one of the extensions 13
 enfolded by the other extension 14. More specifically, the crimped joint
 section 10 is formed centrally on the inner surface of any one of the four
 walls 2-5 that together constitute the closed-sectional configuration, and
 it protrudes inwardly from the one wall at right angles to the inner
 surface of that wall. The thus-formed crimped joint section 10 extends
 continuously along the full length of the elongate member 1 as in the
 above-described first embodiment.
 Other structural features of the second embodiment and material used in the
 second embodiment are the same as in the first embodiment and will not be
 described here to avoid unnecessary duplication.
 Now, with reference to FIGS. 7-12, a description will be given about
 results of various bending tests performed on the closed-sectional curved
 elongate member 1 with the crimped joint section 10 as shown in FIG. 6 and
 the conventionally-known closed-sectional curved elongate member with the
 welded joint section as discussed earlier in the introductory part of this
 specification.
 The bending tests were performed using a bending test device 90 as shown in
 FIG. 7A, which includes a fixed base 91, a pair of jigs 92 for clamping
 the to-be-tested closed-sectional curved elongate member 1, i.e., the test
 sample, at opposite ends thereof so that the elongate member 1 can be
 secured to the base 91, and a jig 93 for pressing a central portion of the
 to-be-tested closed-sectional curved elongate member 1 toward the fixed
 base 91. In the following description, a pressing force applied by the
 pressing jig 93 is represented by F and a stroke of the pressing jig 93 is
 represented by S. The stroke S of the pressing jig 93 corresponds to an
 amount of deformation or flection of the longate member 1.
 The elongate member 1 had a wall thickness of 1.6 mm and a square section
 of 85 mm.times.85 mm, as illustrated in FIG. 7B. The elongate member 1 was
 clamped by the pair of clamping jigs 92 disposed at a pitch of 1,000 mm.
 The pressing jig 93 had a 150 mm height and a 300 mm width, and the
 clamping jigs 92 each had a 85 mm height and a 60 mm width. Further, the
 elongate member 1 was formed of a high-tensile steel plate cold-rollable
 for automobile manufacturing based on the JIS G 3135 SPFC standard. The
 tests were performed in relation to various positions, on the elongate
 member, of the crimped joint section 10, as shown in FIGS. 8-11.
 The first bending test was performed on the elongate member 1 with the
 crimped joint section 10 provided on its upper wall as shown in FIG. 8A.
 Results of this first bending test are shown in the graph of FIG. 8B,
 where the vertical axis represents the pressing force that acted as a
 bending load on the elongate member 1 while the horizontal axis represents
 the amount of flection (deformation) of the test sample 1 as the stroke S
 of the pressing jig 93 shown in FIG. 7A. According to the graph of FIG.
 8B, the pressing force F reached a maximum value of about 30 kN when the
 stroke S was about 16 mm, after which the stroke S changed with
 substantially the same maximum pressing force F. Namely, the test sample 1
 deformed elastically while the amount of deformation was not greater than
 about 16 mm, but deformed plastically with a constant pressing force F
 after the maximum pressing force of 30 kN was reached.
 The second bending test was performed on the elongate member 1 with the
 crimped joint section 10 provided on the left side wall adjacent the
 pressing jig 93 (i.e., opposite to the clamping jigs 92) as shown in FIG.
 9A. Results of this second bending test are shown in the graph of FIG. 9B.
 According to the graph of FIG. 9B, the crimped joint section 10 was
 disjointed or forced out of the duly crimped state between arrowed points
 A and B. The A point is where the disjointed condition took place in a
 portion of the elongate member 1 located lower than the pressing jig 93 in
 FIG. 7A, while the B point is where the disjointed condition took place in
 a portion of the elongate member 1 located higher than the pressing jig
 93. Namely, the disjointed condition of the crimped joint section 10 first
 took place at the A point and then at the B point. Following the B point,
 the test sample 1 deformed with the pressing force F of about 30 kN.
 The third bending test was performed on the elongate member 1 with the
 crimped joint section 10 provided on the lower wall as shown in FIG. 10A.
 Results of this third bending test are shown in the graph of FIG. 10B.
 According to the graph of FIG. 10B, the pressing force F reached a maximum
 value of about 30 kN when the stroke S was about 16 mm, after which the
 stroke S changed with substantially the same maximum pressing force F.
 Namely, the third bending test showed the same results as the first
 bending test shown in FIG. 8B.
 The fourth bending test was performed on the elongate member 1 with the
 crimped joint section 10 provided on the right side wall adjacent the
 clamping jigs 92 (i.e., remote from the pressing jig 93) as shown in FIG.
 11A. Results of this fourth bending test are shown in the graph of FIG.
 11B. According to the graph of FIG. 11B, deformation occurred, at an
 arrowed point C, in clamping holes in the test sample 1 due to the
 rigidity of the crimped joint section 10. Then, the maximum pressing force
 F was 35 kN.
 The fifth bending test was performed on the conventional closed-sectional
 curved elongate member with the welded joint section, where the welded
 joint section was provided on the upper wall as shown in FIG. 12A
 similarly to the FIG. 8A case. Results of this fifth bending test are
 shown in the graph of FIG. 12B. According to the graph of FIG. 12B, the
 pressing force F reached a maximum value of about 30 kN when the stroke S
 was about 16 mm. At a point D circled by a dot-and-dash line, the pressing
 force temporarily dropped because the test sample had no such crimped
 joint section as shown in FIGS. 8A to 10A and did not present enough
 rigidity against the pressing force applied by the pressing jig 93.
 The above-described bending test results clearly showed that the crimped
 joint section 10 formed on the inventive elongate member 1 achieved
 generally the same bending strength as the conventional welded joint
 section, irrespective of which one of the upper, lower, left and right
 walls, constituting the closed rectangular sectional configuration, the
 crimped joint section 10 was provided. Particularly, when the bending test
 was performed on the elongate member 1 with the crimped joint section 10
 provided on the upper or lower wall as shown in FIG. 8A or FIG. 10A, the
 variation characteristic of the stroke S responsive to the generally
 constant pressing force F was better than in the conventional elongate
 member equipped with the welded joint section.
 From the test results, it should be evident that the inventive
 closed-sectional curved elongate member 1 with the crimped joint section
 10 can be quite suitable for use as a structural component, especially a
 bumper beam, of an automotive vehicle. In the case where the inventive
 closed-sectional curved elongate member 1 is used as a bumper beam subject
 to impact energy from forward, it is preferable that the crimped joint
 section 10 be provided on one of the surfaces intersecting the direction
 in which the impact energy acts on the bumper beam. Namely, in the case
 where the inventive closed-sectional curved elongate member 1 as shown in
 FIG. 6A or 6B is used as a bumper beam of an automotive vehicle, the
 crimped joint section 10 is preferably provided to protrude upward or
 downward from the lower or upper wall of the elongate member 1.
 Apparatus for fabricating the closed-sectional curved elongate member 1 in
 accordance with the second embodiment as shown in FIG. 6 can be readily
 constructed by only replacing the crimping-roll unit 25 of FIGS. 2 and 3
 with a modified crimping-roll unit 50 shown in FIG. 13. Further, the
 closed-sectional curved elongate member 1 according to the second
 embodiment of the present invention may be fabricated using the same step
 sequence as described earlier in relation to FIG. 5.
 The following paragraphs describe the crimping-roll unit 50 that is
 employed to form the crimped joint section 10 on the closed-sectional
 curved elongate member 1 of FIG. 6, with reference to FIG. 13. As shown in
 FIG. 13, the crimping-roll unit 50 includes a lower roller 51 for
 supporting the underside of the elongate member 44, an upper roller 52 for
 engaging the upside of the elongate member 44, left and right rollers 53
 and 54 for supporting the left and right side surfaces of the elongate
 member 44, and a crimping mechanism 55 for crimping the opposite
 longitudinal edge portions of the elongate member 44 within the closed
 section of the elongate member 44.
 Further, the crimping mechanism 55 is connected to a supporting rod (not
 shown) that was previously inserted in the elongate member 44 through an
 opening of the semifinished tubular elongate member 44. This crimping
 mechanism 55 includes a crimping roller 56, a base 57 for rotatably
 supporting the crimping roller 56, and a pair of left and right wheels 58
 rotatably mounted on opposed sides of the base 57. The crimping roller 56
 has a central crimping groove 56a that is formed around its outer
 peripheral surface for receiving and crimping together the extensions 13
 and 14 protruding inwardly from the substantially butting longitudinal
 edge portions of the elongate member 44. Namely, opposed inner side
 surfaces of the crimping roller 56, defining the crimping groove 56a,
 firmly press the extensions 13 and 14 against each other to join them
 together into narrow folds.
 FIGS. 14A and 14B are perspective views schematically showing a
 modification of the closed-sectional curved elongate member 1 of FIGS. 1A
 and 1B. This modified closed-sectional curved elongate member 1 is
 characterized in that the crimped joint section 10 has gatherings. In the
 crimped joint section 10, extensions 13 and 14 protrude outwardly from the
 butting longitudinal edge portions 11 and 12, respectively, in a
 superposed relation to each other with one of the extensions 13 enfolded
 by the other extension 14. These superpose extensions 13 and 14 each have
 a multiplicity of small gatherings that are made up of a multiplicity of
 land and valley portions 10a and 10b alternating in the longitudinal
 direction of the crimped joint section 10 and hence of the elongate member
 1. Other structural features of the modified closed-sectional curved
 elongate member 1 and material used in the modification are the same as in
 the first embodiment of FIG. 1 and are shown in the figures by the same
 reference numerals as in FIG. 1, but will not be described here to avoid
 unnecessary duplication.
 Apparatus for fabricating the modified closed-sectional curved elongate
 member 1 can be readily constructed by only replacing the crimping-roll
 unit 25 of FIGS. 2 and 3 with a gathering unit 60 as will be described
 below. Further, the modified closed-sectional curved elongate member 1 may
 be fabricated using the same step sequence as described earlier in
 relation to FIG. 5.
 The following paragraphs describe the gathering unit 60 for forming the
 gatherings in the crimped joint section 10 of the modified
 closed-sectional curved elongate member 1, with reference to FIGS. 15, 16A
 and 16B. As shown in FIG. 15, the gathering unit 60 is provided in between
 the rear-stage roll-bending unit 24 and the roll-curving unit 26.
 In FIG. 16A, the gathering unit 60 includes a lower roller 61 for
 supporting the underside of the elongate member 44, left and right rollers
 62 and 63 for supporting the left and right side surfaces of the elongate
 member 44, a pair of left and right gathering rollers 64 and 65 located
 above the elongate member 44 for crimping the extensions 13 and 14
 extending outwardly from the opposite longitudinal edge portions of the
 elongate member 44, and an auxiliary roller mechanism 66 for preventing
 the elongate member 44 from collapsing vertically when the extensions 13
 and 14 are being crimped together.
 As seen in a top plan of FIG. 16B, the gathering rollers 64 and 65 each
 have a multiplicity of teeth 64a or 65a formed in the outer peripheral
 surface thereof with a predetermined pitch. The auxiliary roller mechanism
 66 includes a pair of upper and lower auxiliary rollers 67 and a pair of
 links 68 for rotatably supporting the auxiliary rollers 67 in place.
 Further, the auxiliary roller mechanism 66 is connected to a supporting
 rod (not shown) that was previously inserted in the elongate member 44
 through an opening of the elongate member 44. Bearings 69 in FIG. 16A
 rotatably support the respective shafts of the lower roller 61, left and
 right rollers 62 and 65 and gathering rollers 64 and 65.
 FIGS. 17A and 17B are perspective views schematically showing a
 modification of the closed-sectional curved elongate member 1 according to
 the second embodiment of FIGS. 6A and 6B, where the crimped joint section
 10 is provided on an inner wall surface of the elongate member 1. This
 modified closed-sectional curved elongate member 1 is also characterized
 in that the crimped joint section 10 has gatherings. Namely, in the
 crimped joint section 10, the extensions 13 and 14 protrude inwardly from
 the butting longitudinal edge portions 11 and 12, respectively, in a
 superposed relation to each other with one of the extensions 13 enfolded
 by the other extension 14. These superpose extensions 13 and 14 are
 crimped together such that a multiplicity of small gatherings, made up of
 a multiplicity of land and valley portions 10a and 10b alternating in the
 longitudinal direction of the crimped joint section 10 and hence of the
 elongate member 1, are formed in each of the extensions 13 and 14. Other
 structural features of the modified closed-sectional curved elongate
 member 1 and material used in the modification are the same as in the
 first embodiment of FIG. 1 and are shown in the figures by the same
 reference numerals as in FIG. 1, but will not be described here to avoid
 unnecessary duplication.
 Apparatus for fabricating the modified closed-sectional curved elongate
 member 1 of FIGS. 17A and 17B can be readily constructed by only replacing
 the crimping-roll unit 25 of FIGS. 2 and 3 with a gathering unit 70 as
 will be described below. Further, the modified closed-sectional curved
 elongate member 1 of FIGS. 17A and 17B may be fabricated using the same
 step sequence as described earlier in relation to FIG. 5.
 The following paragraphs describe the gathering unit 70 for forming the
 gatherings in the crimped joint section 10 of the modified
 closed-sectional curved elongate member 1, with reference to FIG. 18. As
 shown in FIG. 18, the gathering unit 70 includes a lower roller 71 for
 supporting the underside of the elongate member 44, an upper roller 72 for
 engaging the upside of the elongate member 44, left and right rollers 73
 and 74 for supporting the left and right side surfaces of the elongate
 member 44, a crimping mechanism 75 for crimping together the extensions 13
 and 14 inside the hollow section of the elongate member 44 while forming
 the gatherings therein.
 This crimping mechanism 75 also includes a base 76, a pair of left and
 right gathering rollers 77 and 78 for crimping together the extensions 13
 and 14 while forming the gatherings therein, and a pair of left and right
 wheels 79 rotatably mounted on opposed sides of the base 76. The crimping
 mechanism 75 is connected to a supporting rod (not shown) that was
 previously inserted in the elongate member 44 through an opening of the
 elongate member 44.
 The left and right gathering rollers 77 and 78 employed in the gathering
 unit 70 are constructed similarly to the gathering rollers 64 and 65 shown
 in FIG. 16. Specifically, these gathering rollers 77 and 78 each have a
 multiplicity of teeth formed in the outer peripheral surface thereof with
 a predetermined pitch so that the extensions 13 and 14 are firmly pressed
 between the toothed gathering rollers 77 and 78 and joined together in a
 crimped fashion. Bearings 81 in FIG. 18 rotatably support the respective
 shafts of the lower roller 71, upper roller 72 and left and right rollers
 73 and 74.
 In summary, the closed-sectional curved elongate member 1, having been
 described above in connection with the various embodiments and
 modifications of the present invention, can afford various superior
 benefits in the case where it is applied as a bumper beam of an automotive
 vehicle, such as an enhanced impact-energy absorbing capability and a
 minimized transmission of the impact energy to the vehicle body,
 especially when the crimped joint section is positioned on the upper or
 lower wall surface of the bumper beam.
 Whereas the closed-sectional curved elongate member of the present
 invention has been described as having a rectangular sectional shape, the
 present invention is not so limited; for example, the closed-sectional
 curved elongate member may have a triangular sectional shape. Further,
 although the closed-sectional curved elongate member of the present
 invention has been described as being curved along its entire length, it
 may be curved only in part of the length.
 Furthermore, the steps of curving the elongate member may be initiated
 during or substantially concurrently with the crimping step.
 Obviously, various minor changes and modifications of the present invention
 are possible in the light of the above teaching. It is therefore to be
 understood that within the scope of the appended claims, the invention may
 be practiced otherwise than as specifically described.