JP2007069674A - Torsion beam type suspension and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a torsion beam type suspension and its manufacturing method which has a sufficient durability, can be easily manufactured, can ensure high productivity, and is excellent in the dimensional precision. <P>SOLUTION: The torsion beam 4 forms a blank 21 from a hot-rolled steel for thermal hardening according to the torsion beam 4, molds the blank 21 in a pipe shape by press molding after both the ends of the blank 21 is molded at the terminal, and an abutting place of the blank 21 is welded to form in a pipe 23. Afterwards, a middle part in the axial direction of the pipe 32 is crushed to the inner side in the radial direction of the pipe 23 by press molding to form a recess 12, a bead 22 by welding is disposed outside of the recess 12, and annealed after press molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a torsion beam suspension including a torsion beam that connects left and right trailing arms that are supported at one end so as to be able to swing on a vehicle body and rotatably support wheels at the other end, and a method for manufacturing the same.

Conventionally, a torsion beam used for a torsion beam type suspension has been required to be further improved in durability with an increase in vehicle weight and an improvement in exercise performance. As such, as disclosed in Patent Document 1, it is formed from a pipe made of high-strength trace alloy steel or multiphase steel, and the pipe is cold formed, and the center of the pipe is U-shaped with a double wall. Form in cross section. The pipe is then annealed at a temperature between 850 ° C. and 960 ° C., then quenched in water at a temperature above Ac ₃ and then tempered at a temperature of about 280 ° C. for a period of 20 minutes. . Furthermore, after the surface of this pipe is shot peened, a pipe having both ends formed in a necessary shape has been proposed.
JP 2001-123227 A

  In such a conventional apparatus, when the left and right trailing arms are connected to the torsion beam, both ends of the torsion beam may have to be formed according to the outer shape of the left and right trailing arms. For example, when the left and right trailing arms are formed from pipes, the outer shape of the left and right trailing arms is a curved surface, and both ends of the torsion beam must be processed into an arc shape according to the curved surface shape.

  However, when a torsion beam is formed from a pipe having a circular cross section, there is a problem in that forming both ends of the torsion beam is complicated when forming both ends of the torsion beam according to the outer shape of the left and right trailing arms.

  In addition, a plurality of heat treatment steps of annealing, quenching, and tempering must be performed. In addition, since the oxide scale adheres to the surface in order to perform the quenching process, many processes such as a process of removing the scale by the shot peening process are required, resulting in high cost and low productivity. Further, in the quenching process and the shot peening process, distortion is unavoidable, and it is difficult to produce a product with excellent dimensional accuracy.

  An object of the present invention is to provide a torsion beam suspension having sufficient durability, easy to manufacture, ensuring high productivity, and excellent in dimensional accuracy, and a manufacturing method thereof.

In order to achieve this problem, the present invention has taken the following measures in order to solve the problem. That is,
In a torsion beam suspension comprising a left and right trailing arm that is supported at one end of a vehicle body so as to be swingable and a wheel is rotatably supported at the other end, and a torsion beam that connects the left and right trailing arms.
The torsion beam is formed into a pipe by welding a butt portion from a steel plate blank having both ends formed at the ends, and a recess is formed by crushing the middle in the axial direction of the pipe to the inside in the radial direction of the pipe. Is a torsion beam suspension characterized in that it is disposed outside the recess and subjected to a heat treatment for removing residual stress.

In addition, in a torsion beam type suspension comprising a left and right trailing arm that is pivotally supported by the vehicle body and rotatably supports a wheel at the other end, and a torsion beam that connects the left and right trailing arms,
The torsion beam forms a blank corresponding to the torsion beam from a steel plate, and after both ends of the blank are end-formed, the blank is formed into a pipe shape by press forming, and the butt portion of the steel plate is welded to form the pipe After that, the intermediate part in the axial direction of the pipe is crushed to the inside in the radial direction of the pipe by press molding to form a recess, and the weld bead is disposed outside the recess, and annealed after the press molding. This is a method for manufacturing a torsion beam type suspension.

  Furthermore, the said steel plate is a hot-rolled steel plate for heat-hardening, and this hot-rolled steel plate for heat-hardening is weight%, C: 0.05-0.20%, Si: 0.01-0.8%, Mn : 0.5-2.5%, P: 0.005-0.1%, S: 0.01% or less, Al: 0.01-0.08%, Ti: 0.08-0.20% It may have a structure made of Fe and unavoidable impurities, ferrite, and bainite having a volume ratio of 30 to 90%. The annealing is preferably in the temperature range of 550 ° C. to 700 ° C. In particular, the annealing is preferably in the temperature range of 600 ° C. to 650 ° C.

  In the torsion beam suspension of the present invention, the torsion beam is formed into a pipe by welding the butt portion from a steel plate blank having both ends formed, and the pipe is crushed radially inward to form a recess, and the bead is placed outside the recess. Since it is disposed and formed by heat treatment for removing residual stress, the connection between the trailing arm and the torsion beam is simplified, and the manufacturing is easy and the durability is improved. In addition, it is not necessary to perform quenching or shot peening after molding, and the dimensional accuracy can be improved.

  In addition, according to the torsion beam suspension manufacturing method, the torsion beam forms a blank corresponding to the torsion beam from the steel plate, ends the end of the blank, and then forms the blank into a pipe shape by press forming, and the butt portion of the steel plate Are welded to form a pipe, and then the pipe is crushed radially inward by press molding to form a recess, and the bead is placed outside the recess and annealed after press molding. As a result, it is easy to manufacture, and the residual stress can be removed by the annealing treatment, and the durability is improved. Further, when a hot-rolled steel sheet for heat curing is used for the steel sheet, the workability is excellent, and the strength is improved by the annealing treatment. Therefore, there is an effect that the forming is easy and the durability is improved.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
As shown in FIG. 2, reference numeral 1 denotes a left trailing arm. In this embodiment, the trailing arm 1 is formed by bending a hollow pipe having a circular cross section. A left trailing arm 1 and a symmetrical right trailing arm 2 are connected by a torsion beam 4. Since both the trailing arms 1 and 2 are bilaterally symmetric, in the present embodiment, the following description will be focused on the left trailing arm 1.

  A collar 6 is fixed to one end of the left trailing arm 1 by welding. The left trailing arm 1 is swingably supported by a vehicle body (not shown) via a collar 6. A carrier 8 is fixed to the outer periphery on the other end side of the trailing arm 1 by welding. The carrier 8 is bent in a U-shaped cross section, and a fitting hole 10 for attaching a spindle (not shown) that rotatably supports the wheel is formed in the carrier 8.

  As shown in FIG. 3, the torsion beam 4 is formed from a pipe-like material, and notches 4 a and 4 b corresponding to the outer peripheral shapes of the left and right trailing arms 1 and 2 are formed at both ends of the torsion beam 4. The notches 4a and 4b are brought into contact with the outer periphery in the middle of the left and right trailing arms 1 and 2, and the periphery thereof is welded.

  In the middle of the torsion beam 4 in the axial direction, the outer periphery thereof is recessed inward to form a recess 12. The recess 12 is recessed so that the inner wall surfaces are in contact with each other, and the double wall is formed in a substantially U-shaped cross section. In this embodiment, the recess 12 is recessed toward the upper side of the vehicle body, and the recess 12 is opened downward. However, the present invention is not limited to this, and the recess 12 is recessed toward the rear of the vehicle body, and the recesses are recessed forward. You may form so that 12 may open.

  The torsion beam 4 is a hot-rolled hot-rolled steel plate as a steel plate. In the present embodiment, the hot-rolled hot-rolled steel plate is C: 0.05-0.20%, Si: 0.0. 01-0.8%, Mn: 0.5-2.5%, P: 0.005-0.1%, S: 0.01% or less, Al: 0.01-0.08%, Ti: It contains 0.08 to 0.20%, consists of the balance Fe and inevitable impurities, and has a structure consisting of ferrite and bainite of 30 to 90% by volume.

The steel component may further contain Nb: 0.01 to 0.1% and / or one or more components selected from at least one of the following first to third groups.
First group: V: 0.01 to 0.5%
Second group: Cr: 0.05-0.8%, Mo: 0.05-1.0%, B: 0.0005-0.01%
Group 3: Ca: 0.005% or less, rare earth element: 0.05% or less First, the reasons for limiting the components will be described. All units are weight percent.
C: 0.05-0.20%
C has an effect on strengthening of steel. It is necessary to increase the strength by bonding with Ti or the like during heat treatment after cold working, and is also an element necessary for forming a bainite preferable for stretch flangeability. For this purpose, 0.05% or more It is necessary to add. However, if excessively added, the ductility is remarkably deteriorated and the weldability is also lowered, so the upper limit is made 0.20%. A desirable range is 0.07 to 0.15%.
Si: 0.01 to 0.8%
Si is very effective as a solid solution strengthening element for improving the tensile strength, but excessive addition deteriorates the surface properties and chemical conversion treatment, so 0.8% is made the upper limit.
Mn: 0.5 to 2.5%
Mn is also a solid solution strengthening element, which is effective for improving the tensile strength, and is an element necessary for suppressing the generation of coarse pearlite and generating bainite. In order to exhibit this effect effectively, it is necessary to add 0.5% or more. However, if excessively added, not only the ductility is lowered but also weldability is impaired, so the upper limit is made 2.5%.
P: 0.005-0.1%
P functions to improve the strength of the steel, but excessive addition degrades workability and toughness, so the lower limit is made 0.005% and the upper limit is made 0.1%.
S: 0.01% or less S is preferably as small as possible to degrade ductility. In the present invention, it is 0.01% or less for improving stretch flangeability.
Al: 0.01 to 0.08%
Al is added for deoxidation. If the content is less than 0.01%, the content is too small. On the other hand, if the content exceeds 0.08%, alumina inclusions increase and the workability deteriorates, so the upper limit is made 0.08%.
Ti: 0.08 to 0.20%
Ti is an important element in the hot-rolled steel sheet for heat hardening. That is, not only is it effective for obtaining the target ferrite + bainite structure together with Mn and Cr added as necessary, but also Ti dissolved in the hot rolling stage is treated with a fine TiC by heat treatment. It precipitates and has the effect of significantly increasing the strength. In order to ensure a tensile strength of 890 N / mm ² or more after heat treatment, 0.08% or more of addition is necessary, but if added excessively, workability deteriorates, so the upper limit is made 0.20%.

The hot-rolled steel sheet for heat hardening contains the above components as essential components, and the balance is substantially made of Fe. Further, Nb: 0.01 to 0.1%, and / or the following first to third groups One or more kinds of components selected from at least one of them can be contained.
Nb: 0.01 to 0.1%
Nb coexists with Mn, affects the transformed structure after hot rolling, and has the function of making it easy to obtain a bainite structure like Ti. Moreover, since it is also a precipitation strengthening element, heat treatment curability is demonstrated by suppressing precipitation at the time of hot rolling winding similarly to Ti. In order to exert these effects, addition of 0.01% or more is necessary. However, excessive addition causes an increase in yield ratio and a decrease in ductility, so 0.1% was made the upper limit.
First group: V: 0.01 to 0.5%
V is a precipitation strengthening element, and exhibits heat treatment curability by suppressing precipitation during hot rolling as in the case of Ti.
Second group: Cr: 0.05-0.8%, Mo: 0.05-1.0%, B: 0.0005-0.01%
Cr, Mo, and B are elements that improve the hardenability and advantageously give a desired structure. In order to exhibit this effect effectively, the lower limit of each element was set, and the amount of saturation of the effect was set as the upper limit from an economic standpoint.
Group 3: Ca: 0.005% or less, rare earth elements: 0.05% or less Ca and rare earth elements have an effect of improving ductility, particularly stretch flangeability, through the form control of sulfides. In order to exhibit this effect effectively, the lower limit of each element was set, and the amount of saturation of the effect was set as the upper limit from an economic standpoint.

  Next, the microstructure of the hot-rolled steel sheet for heat curing will be described. The microstructure is composed of ferrite and bainite having a volume ratio of 30 to 90%. Ferrite is necessary to ensure elongation. On the other hand, pearlite is inferior in stretch flangeability compared to bainite, and the increase in strength due to subsequent hardening heat treatment is small because the hard phase is composed of bainite. Further, martensite is greatly deteriorated in the stretch flangeability of the hot-rolled steel sheet for heat-hardening, and the heat-hardening property is lowered because the martensite is softened during the heat treatment. Further, the reason why the volume fraction of bainite is set to 30 to 90% is that when the amount is less than 30%, the strength is lowered and the stretch flangeability is not sufficient, while when it exceeds 90%, the elongation is greatly reduced.

Next, a method for manufacturing the above-described torsion beam 4 from the above-described hot-rolled hot-rolled steel sheet will be described in the order of steps.
First, as shown in FIG. 1 (1), a rectangular steel plate blank 21 is cut out from a hot-rolled hot-rolled steel plate wound in a roll shape by a plate material preparation step. The shape of the steel plate blank 21 corresponds to the shape of the torsion beam 4 developed in a flat plate shape.

  Next, as shown in FIG. 1 (2), both ends in the longitudinal direction of the steel plate blank 21 are cut out by the terminal forming step to form the cutouts 21a and 21b. The shapes of the notches 21a and 21b correspond to the notches 4a and 4b at both ends of the torsion beam 4. The notches 21a and 21b are formed in the same shape as the flat shape of the torsion beam 4 and are formed into a pipe shape by the next pipe forming process. The notches 21a and 21b become the notches 4a and 4b of the torsion beam 4.

  Subsequently, as shown in FIG. 1 (3), the steel plate blank 21 is formed into a pipe shape by press forming in the pipe forming step. In press forming, first, the steel plate blank 21 is formed into a U shape by press forming, and then both ends along the axial direction of the steel plate blank 21 are butted in an O shape. Then, as shown in FIG. 1 (4), a pipe 23 having a linear bead 22 along the axial direction is formed by welding, such as laser welding or plasma welding, at the butting position in the welding process.

  Then, as shown in FIG. 1 (5), in the crushing and forming step, the intermediate portion in the axial direction of the pipe 23 is crushed to the inside in the radial direction of the pipe 23 by press working to form the recess 12. Both ends of the pipe 23 are maintained in the shape of a circular cross section without being crushed. As described above, the recess 12 is recessed such that the inner wall surface contacts the opposite inner wall surface, and the double wall is formed in a substantially U-shaped cross section.

  At that time, the welded bead 22 is disposed so as to be outside the recess 12 and pressed. When the recess 12 is pressed, there are places where the steel plate blank 21 expands and contracts, but the beads 22 are preferably arranged at places where the influence of expansion and contraction due to the press processing is small. Since the concave portion 12 has a substantially U-shaped cross section, the bead 22 is preferably disposed outside the concave portion 12 and in a substantially straight portion where the influence of expansion and contraction due to press working is small.

  Further, the steel plate blank 21 exhibits excellent workability during cold working, has good workability of press forming for forming the recess 12 in the press forming or crushing forming process in the pipe forming process, and can be easily formed. . That is, since the steel plate blank 21 has a structure composed of ferrite and bainite having a volume ratio of 30 to 90%, it is excellent in workability and can be easily pressed.

  Next, as shown in FIG. 1 (6), the torsion beam 4 is heat-treated. The heat treatment is an annealing treatment in which the torsion beam 4 is heated to 600 ° C. to 650 ° C. for 15 minutes and gradually cooled. The annealing process is performed in a non-oxidation continuous furnace. As shown in FIG. 4, the torsion beam 4 formed from the above-described steel plate blank 21 is heated to 550 ° C. or higher, so that the residual stress generated during press forming becomes almost 0, and the tensile strength decreases when heated to 700 ° C. or higher. Resulting in. By heating to 600 ° C. to 650 ° C. for 15 minutes and gradually cooling, the tensile strength is maximized due to the heat curability of the steel plate blank 21. Therefore, the annealing treatment is in the temperature range of 550 ° C. to 700 ° C., more preferably in the temperature range of 600 ° C. to 650 ° C.

  By this annealing treatment, solute Ti is deposited to form TiC, the residual stress can be made substantially zero, and the tensile strength can be improved, so that the durability of the torsion beam 4 can be improved. When the residual stress of the portion subjected to press forming is 100 MPa or less, the fatigue strength improvement effect is remarkable. That is, the heat treatment for removing the residual stress is performed to reduce the residual stress to 100 MPa or less, and the durability of the torsion beam 4 is improved. In addition, it is not necessary to perform quenching or shot peening after molding, and the dimensional accuracy can be improved.

  Further, by this annealing treatment, solid solution Ti can be finely and uniformly deposited as TiC. In such a state where the processing is performed and when the deposition is performed while raising the temperature from room temperature, the deposition is very fine, so that the effect of increasing the strength is very large. In addition, by finely depositing a large amount in this manner, it is possible to prevent dislocations from being reduced and to prevent a reduction in strength due to a reduction in dislocation density. As a result, the strength is greatly improved and the durability of the torsion beam 4 is significantly increased. . This greatly improves the durability of the torsion beam 4.

  After the heat treatment, the torsion beam 4 is welded to the left and right trailing arms 1 and 2. At that time, notches 4a and 4b are formed at both ends of the torsion beam 4. By contacting these notches 4a and 4b with the outer circumferences of the left and right trailing arms 1 and 2, the contact length becomes longer. The coupling strength with the left and right trailing arms 1 and 2 is improved, and the lateral rigidity can be improved.

  Further, the bead 22 is disposed outside the concave portion 12 and at a substantially straight portion having a substantially U-shaped cross section. When an external force is applied to the torsion beam 4 when used as a suspension, the torsion beam is low. The durability of 4 is stabilized.

  Furthermore, since both ends in the longitudinal direction of the steel plate blank 21 are notched to form the notches 21a and 21b, it is not necessary to rework both ends after forming the pipe 23, and the outer shapes of the left and right trailing arms 1 and 2 are formed. Accordingly, the notches 4a and 4b of the torsion beam 4 can be easily formed. In addition, the shape of the notches 21a and 21b in the steel plate blank 21 can be freely set according to the outer shape of the left and right trailing arms 1 and 2, and the degree of design freedom increases.

  The present invention is not limited to such embodiments as described above, and can be implemented in various modes without departing from the gist of the present invention.

It is explanatory drawing which shows the manufacturing process of the torsion beam as one Embodiment of this invention. It is a perspective view of the torsion beam type suspension of this embodiment. It is an axial direction expanded sectional view of the torsion beam of this embodiment. It is a graph which shows the relationship between the temperature of the annealing process of this embodiment, tensile strength, and residual stress.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Left trailing arm 2 ... Right trailing arm 4 ... Torsion beam 4a, 4b ... Notch 6 ... Collar 8 ... Carrier 10 ... Fitting hole 12 ... Recess 21 ... Steel plate blank 21a, 21b ... Notch 22 ... Bead 23 ... Pipe

Claims (5)

In a torsion beam suspension comprising a left and right trailing arm that is supported at one end of a vehicle body so as to be swingable and a wheel is rotatably supported at the other end, and a torsion beam that connects the left and right trailing arms.
The torsion beam is formed into a pipe by welding a butt portion from a steel plate blank having both ends formed at the ends, and a recess is formed by crushing the middle in the axial direction of the pipe to the inside in the radial direction of the pipe. Is a torsion beam suspension, which is disposed outside the recess and subjected to heat treatment for removing residual stress. In a torsion beam suspension comprising a left and right trailing arm that is supported at one end of a vehicle body so as to be swingable and a wheel is rotatably supported at the other end, and a torsion beam that connects the left and right trailing arms.
The torsion beam forms a blank corresponding to the torsion beam from a steel plate, and after both ends of the blank are end-formed, the blank is formed into a pipe shape by press forming, and the butt portion of the steel plate is welded to form the pipe After that, the intermediate part in the axial direction of the pipe is crushed to the inside in the radial direction of the pipe by press molding to form a recess, and the weld bead is disposed outside the recess, and annealed after the press molding. A method of manufacturing a torsion beam suspension. The steel sheet is a hot-rolled steel sheet for heat-hardening, and the hot-rolled steel sheet for heat-hardened is in weight%: C: 0.05 to 0.20%, Si: 0.01 to 0.8%, Mn: 0 0.5 to 2.5%, P: 0.005 to 0.1%, S: 0.01% or less, Al: 0.01 to 0.08%, Ti: 0.08 to 0.20% included 3. The method for producing a torsion beam suspension according to claim 2, wherein the torsion beam suspension has a structure composed of Fe and inevitable impurities, ferrite, and bainite having a volume ratio of 30 to 90%. The method of manufacturing a torsion beam suspension according to claim 3, wherein the annealing is performed in a temperature range of 550 ° C to 700 ° C. The method of manufacturing a torsion beam suspension according to claim 3, wherein the annealing is performed in a temperature range of 600 ° C to 650 ° C.

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