torsion beam

Abstract

A torsion beam (10) comprises a central section (11) and end sections (12) connecting to the central section (11) on both sides thereof. The torsion beam (10) has a tubular shape and extends in the longitudinal direction. The ratio S1 / (L1×t1) is at least 1.4 but less than 10. S1 is the cross-sectional area of a transverse section of the central section (11) of the torsion beam (10) at the center in the longitudinal direction, the cross-sectional area including the internal space; L1 is the outer circumferential length of the transverse section; and t1 is the average wall thickness of the central section (11) of the torsion beam (10) at the center in the longitudinal direction.

Description

[Technical Field]

[0001] The present invention relates to a torsion beam. [Background technology]

[0002] A torsion beam described in Patent Document 1 below has been known. This torsion beam has a closed cross section, which is a cross section perpendicular to the longitudinal direction. In this torsion beam, the central portion in the longitudinal direction of the steel pipe used as the material is deformed into a substantially V-shaped cross section (a substantially inverted V-shaped cross section) in order to adjust the torsional rigidity within a predetermined range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-26012 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable for this type of torsion beam to maintain bending rigidity while suppressing an increase in weight.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a torsion beam that is prevented from becoming excessively heavy while ensuring bending rigidity. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention proposes the following means. (1) A torsion beam according to one aspect of the present invention is a tubular torsion beam that has a central portion and end portions that connect to both sides of the central portion and extends in the longitudinal direction, and in the central portion of the longitudinal direction of the torsion beam, the ratio S1 / (L1×t1) determined by the cross-sectional area S1 including the internal space in a transverse cross section that is a cross section perpendicular to the longitudinal direction, the outer periphery L1 in the transverse cross section, and the average wall thickness t1 of the central portion of the longitudinal direction of the torsion beam is 1.4 or more and less than 10. Note that the internal space in the transverse cross section is a closed cross section. In the cross section where the gap of the internal space is smallest, the minimum value between the inner surfaces of the central portion is 1.0 mm or more, and the outer peripheral length L1 is less than the outer peripheral length L2 in the cross section which is a cross section perpendicular to the longitudinal direction of the end portion. do.

[0007] The cross-sectional area S1 is related to the torsional rigidity of the torsion beam. The larger the cross-sectional area S1, the higher the torsional rigidity. Therefore, when the torsional rigidity of the torsion beam is to be kept within a predetermined range, the cross-sectional area S1 must be within a certain range depending on the torsional rigidity. The outer perimeter L1 and the average wall thickness t1 are related to the weight of the torsion beam. The longer the outer perimeter L1 and the thicker the average wall thickness t1, the heavier the torsion beam. Therefore, a low ratio S1 / (L1×t1) indicates that the weight of the torsion beam tends to be large relative to the torsional rigidity required of the torsion beam. The average thickness t1 is calculated by determining the maximum and minimum thickness values ​​in a cross section, which is a cross section perpendicular to the longitudinal direction, and then averaging these values.

[0008] Here, the cross-sectional area S1 is the sum of the wall cross-sectional area S1a and the space cross-sectional area S1b. The wall cross-sectional area S1a is the cross-sectional area of ​​the wall that constitutes the tubular torsion beam. The space cross-sectional area S1b is the cross-sectional area of ​​the internal space. The outer peripheral length L1 and the average wall thickness t1 are also related to the wall cross-sectional area S1a. The longer the outer peripheral length L1 and the thicker the average wall thickness t1, the larger the wall cross-sectional area S1a of the torsion beam. A high ratio of S1 / (L1×t1) indicates a low ratio of the outer perimeter L1 and the average value t1 of the wall thickness to the cross-sectional area S1. That is, a high ratio of S1 / (L1×t1) indicates a low ratio of the wall cross-sectional area (the cross-sectional area of the wall thickness portion) S1a to the cross-sectional area S1, and a high ratio of the space cross-sectional area S1b. And if the torsional rigidity is kept constant, when the ratio of the wall cross-sectional area S1a to the cross-sectional area S1 is low, the bending rigidity of the torsion beam becomes low. From the above, a high ratio of S1 / (L1×t1) indicates that the bending rigidity of the torsion beam tends to be low for a certain (appropriate) torsional rigidity.

[0009] In the torsion beam, the ratio of S1 / (L1×t1) is 1.4 or more and less than 10. By setting the ratio of S1 / (L1×t1) within an appropriate range, the bending rigidity of the torsion beam can be ensured without the torsion beam becoming overly heavy. That is, when the ratio of S1 / (L1×t1) is less than 1.4, the value of the ratio of S1 / (L1×t1) is too low and the torsion beam may become overly heavy. On the other hand, when the ratio of S1 / (L1×t1) is 10 or more, the value of the ratio of S1 / (L1×t1) is too high and the bending rigidity of the torsion beam may become overly low. By making the minimum distance between the central inner surfaces 1.0 mm or more in the cross section where the gap in the internal space is smallest, noise caused by the inner walls that make up the torsion beam rubbing against or colliding with each other when the torsion beam is in use can be suppressed. In this type of torsion beam, it may be necessary to make the cross-sectional area S1 of the central part of the torsion beam smaller than the cross-sectional area S2 of the ends of the torsion beam in order to appropriately reduce the torsional rigidity of the torsion beam while maintaining the connection strength between the torsion beam and the trailing arms connected to both ends of the torsion beam. <了 In such cases, with a torsion beam like the above-mentioned conventional technology, the central part of the tube that is the material for the torsion beam needs to be deformed so that the internal space is reduced (hereinafter referred to as volume reduction deformation) and processed into an approximately V-shaped cross section. However, if the central portion of the material is deformed to reduce its volume, stress may be concentrated when the torsion beam is in use, or noise may be generated due to the walls that make up the torsion beam rubbing against or colliding with each other. In contrast, in this torsion beam, the outer peripheral length L1 at the center of the torsion beam is less than the outer peripheral length L2 at the ends of the torsion beam. Therefore, for example, if the cross-sectional shape of the torsion beam at the center is similar to that of the ends of the torsion beam, the cross-sectional area S1 of the torsion beam at the center will necessarily be smaller than the cross-sectional area S2 at the ends of the torsion beam. Therefore, in this case, for example, by shortening the cross-sectional width (e.g., diameter) of the cross-sectional shape of the torsion beam at the center, the cross-sectional area S1 of the torsion beam at the center can be made smaller than the cross-sectional area S2 at the ends of the torsion beam, thereby reducing the torsional rigidity of the torsion beam. This makes it possible to design a lightweight torsion beam without the above-mentioned problems, while minimizing the amount of material used (by eliminating excess perimeter). If the tube used to make the torsion beam has a constant diameter along its entire length, it is possible to process the center of the torsion beam so that the diameter of the center is smaller than that of the ends, in order to make the cross-sectional area S1 less than the cross-sectional area S2. Possible processing methods include (a) a processing method that expands the diameter of the ends of the tube, and (b) a processing method that reduces the diameter of the center of the tube. Examples of the former (a) include so-called bulging (hydraulic bulging, rubber bulging), in which a pressure medium is supplied inside the tube to expand the diameter, so-called flaring using a press, and so-called stepped processing using a punch. Examples of the latter (b) include so-called necking, in which a roll is used to locally squeeze the tube.

[0010] (2) In the torsion beam according to (1) above, in the cross-section having the portion where the circumferential bending radius R of the central portion is the smallest, the relationship between the average value t1 and the bending radius R may be 1.5t1 < R. Note that the bending radius R is the bending radius on the bending inner side of the torsion beam.

[0011] In a cross-section having a portion where the circumferential bending radius R of the central portion is the smallest, 1.5t1 < R. Thereby, it is possible to suppress a decrease in the fatigue strength on the bending inner side of the torsion beam due to bending. Note that the bending radius R is the bending radius on the bending inner side of the torsion beam.

[0012] (3) In the torsion beam according to the above (1) or (2), the tensile strength of the material of the torsion beam may be 780 MPa or more.

[0013] By setting the tensile strength of the material of the torsion beam to 780 MPa or more, the fatigue characteristics of the torsion beam can be improved and a lightweight design can be achieved.

[0019] ( 4 ) In the torsion beam according to any one of the above (1) to ( 3 )), the average value t1 may be 2.5 mm or more.

[0020] The average value t1 of the wall thickness of the central portion of the torsion beam is 2.5 mm or more. Therefore, the bending rigidity of the torsion beam can be surely increased.

[0021] ( 5 ) In the torsion beam according to any one of the above (1) to ( 4 ), in a cross-section orthogonal to the longitudinal direction, the wall thickness of the torsion beam may be -20% or more and 0% or less of the maximum value of the wall thickness.

[0022] It is better for the thickness to be constant in a cross section perpendicular to the longitudinal direction. This is because any thin sections can cause stress to concentrate and become the starting point for fatigue fracture. However, in reality, variations in thickness can occur in the circumferential direction in industrial applications. Even if there are variations, as long as the circumferential thickness is within the tolerance (-20% to 0% of the maximum thickness, preferably -15% to 0%), the adverse effects of stress concentration in the thin sections can be ignored, and the thickness can be considered to be substantially constant in the circumferential direction.

[0023] ( 6 )From (1) above ( 5 In the torsion beam according to any one of the above items, the cross section at the central portion may not have a portion that is convex toward the internal space.

[0024] The cross section of the central part of the torsion beam does not have a convex portion toward the internal space. Therefore, for example, there is no need to reduce the volume of the tube that is the material for the torsion beam. In this case, for example, it is possible to suppress the generation of residual stress. In this case, specific shapes of the cross section of the central portion include, for example, a circle (e.g., a perfect circle or ellipse), a polygon (rectangular (square, rectangular), or a triangle). If the cross section is a perfect circle, the ratio of the cross-sectional area S1 to the outer perimeter L1 can be geometrically determined as S1 / L1 = 0.5·R1 (where R1 is the radius of the outer surface of the central portion). On the other hand, if the cross section is a square, S1 / L1 ≒ 0.39·R1' (where R1' is the equivalent radius of the outer surface of the central portion). If the cross section is an equilateral triangle, S1 / L1 ≒ 0.3·R1' (where R1' is the equivalent radius of the outer surface of the central portion). Therefore, if S1 / L1 and the ratio S1 / (L1×t1) calculated based on this are constant, the radii (equivalent radii) increase in the order of a perfect circle, a square, and an equilateral triangle. In other words, when the cross-sectional area S1 is constant, the outer perimeter L1 increases in the order of a perfect circle, a square, and an equilateral triangle. Here, the outer perimeter L1 is related to bending rigidity, as mentioned above. Therefore, when the cross-sectional area S1 is constant, the bending rigidity increases in the order of a perfect circle, a square, and an equilateral triangle. Therefore, for example, if the cross-sectional shape of the central part of the torsion beam is a perfect circle, and the value of the cross-sectional area S1 is reduced in the process of adjusting the torsional rigidity, resulting in an excessive decrease in bending rigidity, it may be possible to prevent an excessive decrease in bending rigidity by changing the cross-sectional shape from a circle to a square or equilateral triangle, etc.

[0025] In addition, even if the cross-sectional shape is made approximately V-shaped so that the material is in close contact with the inner surface, an excessive decrease in bending rigidity can also be prevented by making the cross-sectional shape such that there is a sufficient gap on the inner surface (1.0 mm or more, preferably 1.5 mm or more, and more preferably 2 mm or more).

[0026] ( 7 )From (1) above ( 6 In the torsion beam according to any one of the above items, the axis of the central portion in the longitudinal direction may be offset from the axis of the end portion in the longitudinal direction. Note that the axis refers to a line connecting the centers of gravity of the cross section.

[0027] The axis of the central portion of the torsion beam is offset from the axis of the end portion of the torsion beam. That is, the central portion and the end portion of the torsion beam are not limited to being coaxial. Therefore, for example, the degree of freedom in the shape of the torsion beam can be increased. As a result, for example, diversification of the layout can be achieved, such as designing to avoid other structures in the vehicle.

[0028] ( 8 ) In the torsion beam according to the above ( 7 ), the axis of the central portion may be a curve.

[0029] The axis of the central portion of the torsion beam is a curve. That is, the axis of the central portion of the torsion beam is not limited to a straight line. Therefore, for example, the degree of freedom in the shape of the torsion beam can be increased. As a result, diversification of the layout can be achieved, such as designing to avoid other structures in the vehicle. When the axis of the central portion is a curve, it is conceivable to manufacture the torsion beam by bending the tube that is the material of the torsion beam. This type of bending is often difficult when the cross section of the central portion of the torsion beam has a portion that protrudes toward the internal space. In other words, when the cross section of the central portion of the torsion beam does not have a portion that protrudes toward the internal space, this type of bending is easy.

[0030] ( 9 ) In the torsion beam according to any one of the above (1) to ( 8 ), the average value t1 and the average value t2 of the wall thickness at the end portion may be different.

[0031] The average value t1 of the wall thickness of the central portion of the torsion beam is different from the average value t2 of the wall thickness of the end portion. Therefore, an appropriate wall thickness can be adopted according to the longitudinal position. As a result, the quality of the torsion beam can be improved. For example, from the viewpoint of attaching the end portion of the torsion beam to the trailing arm, it is often considered preferable that t1 < t2. One way to make t1 and t2 different is to manufacture a pipe that will serve as the material for the torsion beam by UO forming a tailored blank made by joining multiple steel plates of different thicknesses. [Effects of the Invention]

[0032] According to the present invention, it is possible to provide a torsion beam that is prevented from becoming excessively heavy while ensuring bending rigidity. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a perspective view illustrating a schematic configuration of a torsion beam rear suspension device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view illustrating the schematic configuration of the torsion beam assembly according to the embodiment, as viewed from below. [Figure 3] FIG. 2 is a perspective view illustrating a schematic configuration of a torsion beam according to the embodiment. [Figure 4] FIG. 2 is a plan view illustrating a schematic configuration of a torsion beam according to the embodiment. [Figure 5] 5 is a diagram showing a schematic configuration of the torsion beam according to the embodiment, and is a closed cross-sectional view taken along the arrow VV in FIG. 4. [Figure 6] FIG. 6 is a diagram showing a schematic configuration of the torsion beam according to the embodiment, and is a closed cross-sectional view taken along the arrows VI-VI in FIG. 4. [Figure 7] FIG. 7 is a diagram showing a schematic configuration of the torsion beam according to the embodiment, and is a closed cross-sectional view taken along arrows VII-VII in FIG. 4. [Figure 8] FIG. 5 is a diagram showing a schematic configuration of a torsion beam according to a first modified example of the present invention, and is a closed cross-sectional view corresponding to the view taken along the arrow VV in FIG. 4. [Figure 9] 5 is a diagram showing a schematic configuration of a torsion beam according to a second modified example of the present invention, and is a closed cross-sectional view corresponding to the view taken along the arrow VV in FIG. 4. FIG. [Figure 10]5 is a diagram showing a schematic configuration of a torsion beam according to a third modified example of the present invention, and is a closed cross-sectional view corresponding to the view taken along the arrow VV in FIG. 4. FIG. [Figure 11] FIG. 10 is a perspective view showing a schematic configuration of a torsion beam according to a fourth modified example of the present invention. [Figure 12] FIG. 10 is a perspective view showing a schematic configuration of a torsion beam according to a fifth modified example of the present invention. [Figure 13] 5 is a diagram showing a schematic configuration of a torsion beam according to a comparative example of the present invention, and is a closed cross-sectional view corresponding to the view taken along the arrow VV in FIG. 4. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. Fig. 1 is a diagram showing the schematic configuration of a torsion beam rear suspension device (torsion beam suspension device) according to this embodiment. Fig. 1 shows a torsion beam rear suspension device 1, a torsion beam assembly 2, and a torsion beam 10. Fig. 1 also shows the front (FR) and rear (RE) of a vehicle (not shown) on which this torsion beam rear suspension device 1 is mounted.

[0035] (torsion beam rear suspension system) As shown in FIG. 1, the torsion beam rear suspension device 1 includes a torsion beam assembly 2, and a spring 3 and an absorber 4 that connect the torsion beam assembly 2 to a vehicle body (not shown).

[0036] The torsion beam assembly 2 supports the left and right wheels WL, WR with a pair of left and right trailing arms 5, and is connected to the vehicle body via pivot shafts JL, JR that extend slightly forward toward the center from the left and right sides of the vehicle body. The torsion beam assembly 2 is configured to be swingable relative to the vehicle body.

[0037] 2, the torsion beam assembly 2 includes, for example, a pair of left and right trailing arms (arms) 5, a torsion beam 10 connecting these trailing arms 5, and a pair of left and right spring receivers 3A that support the springs 3. In addition, one end of an absorber 4, which is a damping device, is connected to a buffer receiver (not shown).

[0038] The trailing arm 5 includes, for example, a trailing arm main body 5A, a pivot mounting member 5F connected to the front end of the trailing arm main body 5A and supported on the vehicle body via a pivot shaft J, and a wheel mounting member 5R connected to the rear end of the trailing arm main body 5A and supporting the wheels WL and WR.

[0039] The spring receiving portion 3A is disposed on the opposite side of the pivot mounting member 5F with the torsion beam 10 in between, and one end of the spring 3 is attached to the spring receiving portion 3A. The load received from the road surface is transmitted to the vehicle via the wheels WL, WR, trailing arm 5, and spring 3.

[0040] (torsion beam) Torsion beams are required to have rigidity against bending with the center of rotation being the vertical axis of the vehicle body in order to hold the tires. For example, this rigidity is what allows the torsion beam to brace and hold the tires when a lateral force is applied to the tires. At the same time, when there is a difference in the forces applied from the ground to the left and right tires when cornering, for example, a twist occurs around the beam axis, and the torsion beam must have the appropriate rigidity (neither too large nor too small) to brace and suppress vehicle roll.

[0041] The torsion beam 10 according to this embodiment will be described below with reference to FIGS. The torsion beam 10 has a closed cross section, which is a cross section perpendicular to the longitudinal direction. The torsion beam 10 is a hollow tube with an internal space. In this embodiment, the cross section of the torsion beam 10 has a perfect circular shape over the entire longitudinal length. The torsion beam 10 is a circular tube.

[0042] The tensile strength of the material of the torsion beam 10 is preferably 780 MPa or more, more preferably 980 MPa or more. The tensile strength of the material of the torsion beam 10 is preferably 1380 MPa or less, more preferably 1180 MPa or less. The length of the torsion beam 10 is not particularly limited, but is, for example, 500 mm or more and 1800 mm or less. The weight of the torsion beam 10 is not particularly limited, but is, for example, 2 kg or more and 20 kg or less.

[0043] As shown in FIGS. 3 and 4, the torsion beam 10 includes a central portion 11 and end portions 12 in the longitudinal direction, and shape-changing portions 13 connecting the central portion 11 and the end portions 12. The central portion 11 has the same diameter regardless of the position along the longitudinal direction. The end portions 12 have the same diameter regardless of the position along the longitudinal direction. The central portion 11 and the end portions 12 are cylindrical.

[0044] The central portion 11 has a smaller diameter than the end portions 12. The cross section of the central portion 11 is similar to the cross section of the end portions 12. Both longitudinal ends of the central portion 11 are connected to the shape-changing portions 13. The central portion 11 is longer in the longitudinal direction than the end portions 12. The length of the central portion 11 is between 2 and 20 times the length of the end portions 12. In this embodiment, as described above, the central portion 11 has a smaller diameter than the end portions 12, so that the outer peripheral length L1 of the central portion 11 in a cross section is less than the outer peripheral length L2 of the end portions 12 in a cross section. L1 is the outer peripheral length of the central portion 11 in a cross section that is perpendicular to the longitudinal direction. L2 is the outer peripheral length of the end portions 12 in a cross section that is perpendicular to the longitudinal direction.

[0045] Here, the outer perimeter L1 of the central portion 11 can be defined as the average of the outer perimeters at four boundaries of each of the five regions when the central portion 11 is equally divided in the longitudinal direction. The outer perimeter L2 of the end portion 12 can also be defined in the same way as the outer perimeter L1 of the central portion 11. The outer peripheral length L1 is not particularly limited, but is, for example, 90 mm or more and 300 mm or less. The outer peripheral length L2 is not particularly limited, but is, for example, 150 mm or more and 600 mm or less.

[0046] The shape-changing portion 13 continuously expands in diameter from the central portion 11 toward the end portions 12. The shape-changing portion 13 is frustoconical. In the shape-changing portion 13, the edge closer to the center in the longitudinal direction of the torsion beam 10 is connected to the central portion 11, and the edge on the outer side in the longitudinal direction is connected to the end portions 12.

[0047] The central portion 11, the end portions 12, and the shape-changing portion 13 are all formed in a straight tube shape. In other words, the axes of the central portion 11, the end portions 12, and the shape-changing portion 13 extend linearly. The axes are located on a common axis. That is, the central portion 11, the end portions 12, and the shape-changing portion 13 are arranged coaxially. The axis refers to the line connecting the centers of gravity of the cross section.

[0048] As described above, the cross section of the torsion beam 10 has a perfect circular shape over the entire longitudinal length. In other words, the cross section of the torsion beam 10 does not have any portion that is convex toward the internal space, regardless of the position in the longitudinal direction of the torsion beam 10. That is, none of the cross sections of the central portion 11, the end portions 12, and the shape-changing portions 13 have any portion that is convex toward the internal space.

[0049] The thickness (plate thickness) of the torsion beam 10 is substantially constant regardless of the longitudinal position or the circumferential position in the cross section. In other words, the average thickness t1 of the central portion 11, the average thickness t2 of the end portions 12, and the average thickness t3 of the shape-changing portions 13 are all the same (substantially constant). In this embodiment, the average wall thickness (plate thickness) of the torsion beam 10 is 2.5 mm or more.

[0050] The average thickness t1 of the central portion 11 can be, for example, the average thickness at each of the four boundaries of the central portion 11 when the central portion 11 is equally divided into five regions in the longitudinal direction. The thickness at each boundary is calculated by determining the maximum and minimum thickness values ​​in a cross section, which is a cross section perpendicular to the longitudinal direction, and then averaging these values. In this embodiment, the thickness of each region is the average value of the maximum and minimum thickness values ​​in the cross section of that region. The thickness t2 of the end portion 12 and the thickness t3 of the shape-changing portion 13 can also be defined in the same way as the average thickness t1 of the central portion 11.

[0051] Here, if the thickness of a torsion beam in a cross section is within -20% to 0% (preferably -15% to 0%) of the maximum thickness (i.e., if the circumferential variation in thickness is within the tolerance (-20% to 0% (preferably -15% to 0%) of the maximum thickness)), the thickness can be considered to be substantially constant in the circumferential direction. In other words, if the thickness of a torsion beam is within 80% to 100% (preferably -15% to 0%) of the maximum thickness, the thickness can be considered to be substantially constant in the circumferential direction. Note that it is better for the thickness to be constant in the cross section. If there are any thin portions, stress will concentrate and this could become the starting point for fatigue fracture. However, in industrial practice, variations in thickness in the circumferential direction can occur. Even if there is such a variation, as long as the thickness is within the range of -20% to 0% of the maximum value in the circumferential direction, and preferably within the range of -15% to 0%, the adverse effects of stress concentration in the thin wall portion can be ignored, and the wall thickness can be considered to be substantially constant in the circumferential direction.

[0052] Furthermore, t1 to t3 being equivalent (substantially almost constant) includes not only the case where t1 to t3 are completely the same, but also the case where they are slightly different but are substantially the same. A case where they are slightly different can be, for example, the case where the difference between the smallest and largest values ​​of t1 to t3 is less than 5% of the largest value.

[0053] In this embodiment, the ratio S1 / (L1×t1) determined by the cross-sectional area S1 including the internal space in the cross section of the central portion 11, the outer surface perimeter L1, and the average thickness t1 of the central portion 11 is 1.4 or more and less than 1.0. The cross-sectional area S1 is the sum of the wall cross-sectional area S1a and the space cross-sectional area S1b. The wall cross-sectional area S1a is the cross-sectional area of ​​the walls that constitute the torsion beam 10. The space cross-sectional area S1b is the cross-sectional area of ​​the internal space.

[0054] Here, the wall cross-sectional area S1a of the central portion 11 can be, for example, the average value of the wall cross-sectional areas at each of the four boundaries of the central portion 11 when the central portion 11 is equally divided into five regions in the longitudinal direction. The space cross-sectional area S1b can also be defined in the same way as the wall cross-sectional area S1a.

[0055] The cross-sectional area S1 is not particularly limited, but for example, 650 mm 2 Over 7000mm 2 The wall cross-sectional area S1a is not particularly limited, but may be, for example, 135 mm 2 Over 1200mm 2 The spatial cross-sectional area S1b is not particularly limited, but may be, for example, 100 mm 2 Over 6500mm 2 The following is the result. The central portion 11 has a smaller diameter than the end portion 12, and the cross-sectional area S1 is smaller than the cross-sectional area S2 of the end portion 12. The cross-sectional area S2 of the end portion 12 is not particularly limited, but may be, for example, 800 mm 2 More than 28000mm 2 The following is the result.

[0056] (Torsion beam manufacturing method) The torsion beam 10 can be manufactured from, for example, a steel pipe (not shown) that serves as the material for the torsion beam 10. The steel pipe may be any steel pipe, such as a forged steel pipe, an electric resistance welded steel pipe, a seamless steel pipe, or an arc-welded steel pipe (e.g., a UOE steel pipe). Here, if the steel pipe has a constant diameter along its entire length in the longitudinal direction, it is conceivable to process the central portion 11 of the torsion beam 10 so that the diameter of the central portion 11 is smaller than that of the end portions 12 in order to make the cross-sectional area S1 less than the cross-sectional area S2. Possible processing methods for this purpose include (a) a processing method for expanding the diameter of the end portions 12 of the steel pipe, and (b) a processing method for reducing the diameter of the central portion 11 of the steel pipe. Examples of the former (a) include so-called bulging (hydraulic bulging, rubber bulging), in which a pressure medium is supplied inside the steel pipe to expand the diameter, so-called flaring using a press, and so-called stepped processing using a punch. Examples of the latter (b) include so-called necking, in which a steel pipe is locally squeezed using a roll.

[0057] (Effects related to the ratio S1 / (L1×t1)) The cross-sectional area S1 is related to the torsional rigidity of the torsion beam 10. The larger the cross-sectional area S1, the higher the torsional rigidity. Therefore, when the torsional rigidity of the torsion beam 10 is to be kept within a predetermined range, the cross-sectional area S1 will be a value within a certain range according to the torsional rigidity. Furthermore, the outer peripheral length L1 and the average wall thickness t1 are related to the weight of the torsion beam 10. The longer the outer peripheral length L1 and the thicker the average wall thickness t1, the heavier the torsion beam 10 becomes. Therefore, a low ratio S1 / (L1×t1) indicates that the weight of the torsion beam 10 tends to be large relative to the torsional rigidity required of the torsion beam 10.

[0058] The outer peripheral length L1 and the average wall thickness t1 are also related to the wall cross-sectional area S1a. The longer the outer peripheral length L1 and the thicker the average wall thickness t1, the larger the wall cross-sectional area S1a of the torsion beam 10. A high ratio S1 / (L1×t1) indicates that the ratio of the outer surface perimeter L1 and the average thickness t1 to the cross-sectional area S1 is low. That is, a high ratio S1 / (L1×t1) indicates that the ratio of the wall cross-sectional area S1a to the cross-sectional area S1 is low and the ratio of the space cross-sectional area S1b is high. If the torsional rigidity is kept constant, a low ratio of the wall cross-sectional area S1a to the cross-sectional area S1 will result in a low bending rigidity of the torsion beam 10. From the above, a high ratio S1 / (L1×t1) indicates that the bending rigidity of the torsion beam 10 tends to be low for a given (appropriate) torsional rigidity.

[0059] In the torsion beam 10, the ratio S1 / (L1×t1) is equal to or greater than 1.4 and less than 10. By setting the ratio S1 / (L1×t1) within an appropriate range, the bending rigidity of the torsion beam 10 can be ensured without the torsion beam 10 becoming excessively heavy. In other words, if the ratio S1 / (L1×t1) is less than 1.4, the value of the ratio S1 / (L1×t1) is too low, which could result in the torsion beam 10 becoming excessively heavy. On the other hand, if the ratio S1 / (L1×t1) is 10 or greater, the value of the ratio S1 / (L1×t1) is too high, which could result in the bending rigidity of the torsion beam 10 becoming excessively low. The ratio S1 / (L1×t1) is preferably less than 5, more preferably less than 3.

[0060] (Effects of outer circumference L1 and L2) However, with this type of torsion beam 10, it may be necessary to make the cross-sectional area S1 of the central portion 11 of the torsion beam 10 smaller than the cross-sectional area S2 of the end portion 12 of the torsion beam 10 in order to appropriately reduce the torsional rigidity of the torsion beam 10 while maintaining the connection strength between the torsion beam 10 and the trailing arms 5 connected to both ends of the torsion beam 10. In such a case, in a torsion beam 100 such as that of the conventional technology (see Figure 13), the central portion 11 of the steel pipe that is the material for the torsion beam 100 must be deformed so as to reduce the internal space (hereinafter referred to as volume reduction deformation), and processed into an approximately V-shaped cross section so that the inner surfaces are tightly fitted together. However, if the central portion 11 of the aforementioned material is reduced in volume and deformed to form a shape that is close to a tight fit, stress may be concentrated when the torsion beam is in use, or noise may be generated due to the walls that make up the torsion beam rubbing or colliding with each other.

[0061] In contrast, in the torsion beam 10 according to this embodiment, the outer peripheral length L1 at the central portion 11 of the torsion beam 10 is less than the outer peripheral length L2 at the end portions 12 of the torsion beam 10. Therefore, for example, if the shape of the cross section at the central portion 11 of the torsion beam 10 is similar to the shape of the cross section at the end portions 12 of the torsion beam 10, the cross-sectional area S1 of the central portion 11 of the torsion beam 10 will inevitably be smaller than the cross-sectional area S2 of the end portions 12 of the torsion beam 10. Therefore, in this case, for example, by shortening the cross-sectional width (diameter) of the cross section while maintaining the cross-sectional shape of the central portion 11 of the torsion beam 10, the cross-sectional area S1 of the central portion 11 of the torsion beam 10 can be made smaller than the cross-sectional area S2 of the end portions 12 of the torsion beam 10, and as a result, the torsional rigidity of the torsion beam 10 can be reduced. This prevents the above-mentioned problems from occurring, and makes it possible to improve, for example, the fatigue characteristics of the torsion beam 10.

[0062] (Various variations) Next, various modifications of the present invention will be described with reference to FIGS. In each modification, the same components as those in the above embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0063] (First Modification) As shown in Fig. 8, in the torsion beam 10A according to the first modified example, the cross section of the central portion 11 and the cross section of the end portions 12 are not similar in shape. That is, the cross section of the end portions 12 is a perfect circle as in the above embodiment, while the cross section of the central portion 11 is triangular. However, in the torsion beam 10A according to this modified example, like the torsion beam 10 according to the above embodiment, none of the cross sections of the central portion 11, the end portions 12, and the shape-changing portions 13 have a portion that protrudes toward the internal space.

[0064] Such shapes that do not have a portion that is convex toward the internal space include a perfect circle, an equilateral triangle, an ellipse, a square, a regular pentagon, etc. That is, there are circular shapes including a perfect circle and an ellipse, regular polygonal shapes including an equilateral triangle, a square, a regular pentagon, etc., and polygonal shapes including these regular polygonal shapes. Alternatively, it may be a rectangular shape. Naturally, each corner or side of the polygonal shape may have a curvature that is concave toward the internal space.

[0065] Thus, specific shapes of the cross section of the central portion 11 include, for example, a circle (e.g., a perfect circle or an ellipse), a polygon (e.g., a rectangle (square or oblong), or a triangle). Here, when the shape of the cross section is a perfect circle, the ratio of the cross-sectional area S1 to the outer perimeter L1 can be geometrically determined as S1 / L1 = 0.5·R1 (where R1 is the radius of the outer surface of the central portion 11). On the other hand, when the shape of the cross section is a square, S1 / L1 ≒ 0.39·R1' (where R1' is the equivalent radius of the outer surface of the central portion 11). When the shape of the cross section is an equilateral triangle, S1 / L1 ≒ 0.3·R1' (where R1' is the equivalent radius of the outer surface of the central portion 11). Therefore, when S1 / L1 and the ratio S1 / (L1×t1) calculated based on S1 / L1 are constant, the radius (equivalent radius) increases in the order of a perfect circle, a square, and an equilateral triangle. In other words, when the cross-sectional area S1 is constant, the outer perimeter L1 increases in the order of a perfect circle, a square, and an equilateral triangle. Here, the outer perimeter L1 is related to bending rigidity, as mentioned above. Therefore, when the cross-sectional area S1 is constant, the bending rigidity increases in the order of a perfect circle, a square, and an equilateral triangle. Therefore, for example, when the cross-sectional shape of the central portion 11 of the torsion beam 10A is a perfect circle, and as a result of reducing the value of the cross-sectional area S1 in the process of adjusting the torsional rigidity, the bending rigidity becomes excessively low, in some cases, by changing the cross-sectional shape from a circular shape to a square shape, an equilateral triangular shape, etc., it may be possible to suppress an excessive decrease in the bending rigidity.

[0066] In the first modification, in a cross-section having a portion where the bending radius R in the circumferential direction of the central portion 11 is the smallest, the relationship between the average value t1 of the wall thickness of the central portion 11 and the bending radius R is 1.5t1 < R. As shown in FIG. 8, in the cross-section of the triangular corner portion 20A where the bending radius R is the smallest, 1.5t1 < R. Thereby, it is possible to suppress a decrease in the fatigue strength inside the torsion beam due to bending. More preferably, in a cross-section having a portion where the bending radius R is the smallest, 1.7t1 < R. Note that the bending radius R is the bending radius inside the triangular corner portion 20A.

[0067] As a torsion beam according to a further modification of the torsion beam 10A according to the first modification, similar to the torsion beam 10A according to the first modification, although the cross-section of the central portion 11 and the cross-section of the end portion 12 are not similar shapes, an example is a shape where the cross-section of the end portion 12 is not a perfect circular shape.

[0068] (Second modification) As shown in FIG. 9, in the torsion beam 10B according to the second modification, similar to the torsion beam 10A according to the first modification, the cross-section of the central portion 11 and the cross-section of the end portion 12 are not similar shapes. However, in the torsion beam l0B according to this modification, the cross-section of the central portion 11 is provided with a portion that protrudes toward the internal space. The cross-section of the central portion 11 is a heart shape.

[0069] In the second modification example, as shown in FIG. 9, the cross section having the portion with the smallest circumferential bending radius R of the central portion 11 is the heart-shaped corner portion 20B. The bending radius R is the inner bending radius of the heart-shaped corner portion 20B. In the cross section having the portion with the smallest circumferential bending radius R of the central portion 11, by setting the relationship between the average value t1 of the wall thickness of the central portion 11 and the bending radius R to 1.5t1 < R, it is possible to suppress a decrease in the fatigue strength inside the torsion beam due to bending. More preferably, in the cross section having the portion with the smallest bending radius R, 1.7t1 < R.

[0070] (Third modification example) As shown in FIG. 10, in the torsion beam 10C according to the third modification example, the cross section of the central portion 11 has a portion that protrudes toward the internal space. The cross section of the central portion 11 has a substantially V-shaped and a shape with a gap in the internal space.

[0071] The cross section where the gap in the internal space is the smallest is inside the corner portion 20C. By setting the gap to 1.0 mm or more in the cross section where the gap in the internal space is the smallest, the gap is maintained during torsional deformation, and the bending rigidity can be ensured. Also, when the torsion beam is in use, it is possible to suppress noise caused by the surfaces of the walls constituting the torsion beam rubbing against or colliding with each other. More preferably, the gap is 1.5 mm or more, and even more preferably 2 mm or more. The gap in the internal space is the shortest distance between two opposing inner surfaces and is defined as the "gap". In FIG. 10, the gap in the internal space is exaggerated for easier understanding.

[0072] (Fourth modification example) As shown in FIG. 11, in the torsion beam 10D according to the fourth modification example, the axis of the central portion 11 of the torsion beam and the axis of the end portion 12 are displaced. The two end portions 12 are arranged coaxially.

[0073] The axis of the central portion 11 of the torsion beam 10D is offset from the axis of the end portion 12 of the torsion beam 10. That is, the central portion 11 and the end portion 12 of the torsion beam 10D are not limited to being coaxial. Therefore, for example, the degree of freedom in the shape of the torsion beam 10D can be increased. As a result, for example, diversification of the layout can be achieved, such as designing to avoid other structures in the vehicle.

[0074] (Fifth modification example) As shown in FIG. 12, in the torsion beam 10E according to the fifth modification example, the axis of the central portion 11 is a curve. That is, the central portion 11 is curved. This torsion beam 10E is formed by bending the torsion beam 10D according to the fourth modification example.

[0075] The axis of the central portion 11 of the torsion beam 10E is a curve. That is, the axis of the central portion 11 of the torsion beam 10E is not limited to a straight line. Therefore, for example, the degree of freedom in the shape of the torsion beam 10E can be increased. As a result, diversification of the layout can be achieved, such as designing to avoid other structures in the vehicle. When the axis of the central portion 11 is a curve, it is conceivable to manufacture the torsion beam 10E by bending a steel pipe that is the material of the torsion beam 10E.

[0076] Note that the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0077] The average value t1 of the wall thickness in the central portion 11 and the average value t2 of the thickness in the end portion 12 may be different. In this case, an appropriate average value of the thickness can be adopted according to the position in the longitudinal direction. As a result, the quality of the torsion beam can be improved. For example, from the viewpoint of attaching the end portion 12 of the torsion beam to the trailing arm, it is considered that t1 < t2 is often preferable. One way to make t1 and t2 different is to manufacture a steel pipe that will be used as the material for the torsion beam by UO forming a tailored blank made by joining multiple steel plates of different thicknesses.

[0078] The torsion beam may not have an open cross section in part, but not in the entire longitudinal direction. For example, the torsion beam may have holes in one or more locations, as long as the performance of the torsion beam is not affected.

[0079] The torsion beam does not have to be made of a steel pipe. Steel, other metals (such as aluminum alloys, titanium alloys, and stainless steel), nonmetals (such as carbon fiber-reinforced resin and glass fiber-reinforced resin), and composites thereof (such as multi-layered materials) can also be used. The shape of the pipe material does not have to be uniform in cross-sectional dimensions or shape; it can be a tapered pipe or a pipe with an irregular cross section. Alternatively, a plate-shaped material can be formed into the shape of a torsion beam without first forming it into a tubular shape, and the seams of the plate can then be joined to form a closed cross section. The method for forming a plate-shaped material into the shape of a torsion beam is not particularly limited, but for example, the method disclosed in Japanese Patent No. 6477716 can be applied. The method for joining the seams of the plate after forming the plate-shaped material into the shape of a torsion beam is not particularly limited, but for example, welding (such as arc welding, laser welding, seam welding, resistance welding, and spot welding), pressure welding, brazing, or adhesive bonding can be applied.

[0080] In addition, within the scope of the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modifications may be combined as appropriate.

[0081] (Example) Next, a verification test for the above-mentioned effects will be described.

[0082] In this verification test, two types of torsion beams were prepared: Comparative Example 1 and Example 1. In both Comparative Example 1 and Example 1, a steel pipe was used for the torsion beam, with a tensile strength of 800 MPa, a wall thickness of 2.9 mm, and a diameter of 94 mm. The wall thickness of the torsion beam was measured after molding using an ultrasonic measuring device and by measuring the cross section of a cut sample with vernier calipers. The shape of the torsion beam in Example 1 is the shape of a torsion beam 10C according to a third modified example shown in Fig. 10. The shape of the torsion beam in Comparative Example 1 is the shape of a torsion beam 100 according to a comparative example shown in Fig. 13. In this verification experiment, the weight reduction rate was calculated from the weight (kg) of each torsion beam, and performance such as torsional rigidity and bending rigidity was verified. The results of the verification test are shown in Table 1.

[0083] [Table 1]

[0084] The "outer surface perimeter L2 (mm) of the tube end" in Table 1 is the outer surface perimeter L2 (mm) of the cross section, which is a cross section perpendicular to the longitudinal direction of the end 12 of the torsion beam. The "small diameter portion length (mm)" in Table 1 is the longitudinal length (mm) of the central portion 11 of the torsion beam. The "ratio (%) of the outer surface perimeter of the V-shaped cross section of the central portion to the outer surface perimeter of the tube end" in Table 1 is the ratio (%) of the outer surface perimeter L1 of the V-shaped cross section of the central portion 11 to the outer surface perimeter L2 of the end 12. The "minimum R (mm) of the inner surface of the central portion" in Table 1 is the R (mm) of the smallest circumferential bending radius of the central portion 11. The "minimum value (mm) between the inner surfaces of the central portions" in Table 1 is the smallest value (mm) of the gap in the internal space of the central portion 11. [Industrial Applicability]

[0085] According to the present invention, it is possible to provide a torsion beam that is prevented from becoming excessively heavy while ensuring bending rigidity. [Explanation of symbols]

[0086] 10, 10A, 10B, 10C, 10D, 10E Torsion beam 11 Central 12 ends

Claims

1. A longitudinally extending tubular torsion beam having a central portion and end portions connected to opposite sides of the central portion, a ratio S1 / (L1×t1) determined by a cross-sectional area S1 including an internal space in a transverse cross section that is a cross section perpendicular to the longitudinal direction at the central portion of the torsion beam, an outer surface perimeter L1 at the transverse cross section, and an average wall thickness t1 at the central portion of the torsion beam in the longitudinal direction is 1.4 or more and less than 1.4, In the cross section where the gap of the internal space is smallest, the minimum value between the inner surfaces of the central portions is 1.0 mm or more, A torsion beam in which the outer peripheral length L1 is less than the outer peripheral length L2 in a cross section that is a cross section perpendicular to the longitudinal direction of the end portion.

2. 2. The torsion beam according to claim 1, wherein in the cross section having the central portion where the circumferential bending radius R is smallest, the relationship between the average value t1 and the bending radius R satisfies 1.5t1<R.

3. 3. A torsion beam according to claim 1, wherein the material of the torsion beam has a tensile strength of 780 MPa or more.

4. 3. The torsion beam according to claim 1, wherein the average value t1 is 2.5 mm or more.

5. 3. The torsion beam according to claim 1, wherein the thickness of the torsion beam in a cross section perpendicular to the longitudinal direction is −20% or more and 0% or less of the maximum value of the thickness.

6. 3. The torsion beam according to claim 1, wherein the cross section at the central portion does not have a portion that is convex toward the internal space.

7. 3. The torsion beam according to claim 1, wherein an axis of the central portion in the longitudinal direction is offset from an axis of the end portion in the longitudinal direction.

8. 8. A torsion beam according to claim 7, wherein said axis of said central portion is curved.

9. 3. The torsion beam according to claim 1, wherein the average value t1 is different from the average value t2 of the wall thickness at the end portion.

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