KR100902837B1 - Tube type torsion beam for rear wheel suspension of automobile using different steel materials - Google Patents

Abstract

A tube type torsion beam for a rear wheel suspension of an vehicle using different steel materials is provided to obtain optimum endurance design by differently controlling the partial thickness of the different steel materials according to the distribution of the stress. A tube type torsion beam for a rear wheel suspension of an vehicle using different steel materials comprises: both end parts which is coupled on the trailing arm for a rear suspension system with forming an enclosed section; a central part having an opened section of a V shape; and a transition part which connects the both end parts and the central part with changing the section. The tube type steel material is made of different steel materials formed by welding different steel sheets according to each section. The tube type steel material is formed in order to have the different thicknesses according to each section. Each section is classified by section 1(S1), section 2(S2) and section 3(S3). The thickness of the section 1 and the section 3 is 3-4mm. The thickness of the section 2 is 2-3mm.

Description

Tube type torsion beam for rear wheel suspension of automobile using different steel materials}

The present invention relates to a tubular torsion beam for a rear wheel suspension of a vehicle using a dissimilar steel pipe, and when manufacturing a tubular torsion beam using a dissimilar steel pipe made by bonding different steel sheets, the sections are divided according to the longitudinal direction of the torsion beam. The present invention relates to a tubular torsion beam for a rear wheel suspension of an automobile having different thicknesses and optimizing roll strength and roll rigidity.

Suspension of the vehicle is a structural device that prevents the impact of the road surface generated during driving from being transmitted to the vehicle body or the occupant, and improves ride comfort by relieving the impact of the road surface while adjusting the stability of the road's traction while driving. It should be designed to increase the In addition, it must be designed to maintain a constant stiffness and endurance performance in the event of continuous road impact. Suspension deformation or cracking has a fatal adverse effect on the running stability of the vehicle, so durability design plays an important part in the functional design of the suspension system.

In particular, the torsion beam suspension, which is mainly used as the rear wheel suspension of a small vehicle, requires a stable durability design of the torsion beam because the torsional beam is continuously applied to the torsion beam. The durability design of such a torsion beam suspension device needs to be closely determined in terms of roll stiffness and roll strength of the vehicle. In other words, the torsion beam connects the left wheel and the right wheel, which is an important component for maintaining the overall rigidity of the rear suspension and determining the dynamic characteristics when driving the vehicle. Therefore, the torsion beam should not only be designed to have proper roll stiffness according to the weight of the vehicle against the torsional deformation or bending deformation generated when the left wheel and the right wheel are reversed, and the vertical and shear stresses are concentrated. It must be designed to have roll strength and to maintain the fatigue life from running.

The torsion beam is divided into a plate-shaped torsion beam and a tubular torsion beam according to its shape, and FIG. 1 shows a mounting state of a tubular torsion beam which is mainly used as a rear wheel suspension of a small vehicle. The tubular torsion beam suspension device has a left and right pair of trailing arms 2 interconnected by tubular torsion beams 10, and a front end of the trailing arm 2 is provided with a bushing bush with a rubber bush mounted thereon. 1) is pivotally coupled to the body. In addition, the rear end of the trailing arm 2 is provided with a spring seat 3 on which the suspension spring is mounted and a damper bracket 4 on which the shock absorber is mounted, and outside the rear end of the trailing arm 2. At the side, a wheel carrier 5 and a spindle plate 6 are installed to couple the rear wheels of the vehicle. The bush sleeve (1), trailing arm (2), spring seat (3), damper bracket (4), wheel carrier (5) and spindle plate (6) are the basic components of the torsion beam suspension. .

The tubular torsion beam 10 is formed by processing a tubular steel having a circular cross section to have a different shape over its entire length, thereby forming a closed cross section having a predetermined cross-sectional area and being coupled to the trailing arm 2 for the rear suspension. Both end portions 11 and the central portion 13 formed in a “V” shape and one side semicircle surface 13a is in close contact with the other side semicircle surface 13b to form an open cross section with one side opened, and the size of the cross section is changed. It consists of a transition portion 12 that naturally connects both ends 11 and the central portion (13). In FIG. 2, the both ends 11 are illustrated as rectangles having rounded corners, but are not limited thereto. Various shapes having a closed cross section, such as a triangle or a circle, may be used depending on the vehicle type.

The tubular torsion beam 10 configured as described above has excellent rigidity and durability against torsion and bending deformation when compared to a plate-shaped torsion beam having only an open cross section, and thus may be used without additional reinforcement. However, the conventional tubular torsion beam has a tubular steel made by folding one steel plate in the form of a pipe and then joining it by welding or the like, and manufactured using a general press method or a hydroforming method.

As described above, since the torsion or bending stress having various directions and sizes is applied to the tubular torsion beam while the vehicle is running, the stress distribution for each part is different. Therefore, in order to have optimal roll strength and roll rigidity, it is necessary to vary the size or thickness in consideration of the stress applied to each part of the tubular torsion beam.

However, when a tubular torsion beam is manufactured using only one tubular steel as in the prior art, it is difficult to control precise size or thickness for each part of the torsion beam, thereby providing an optimal durability design.

The present invention was developed to overcome the above limitations, and in the manufacture of a tubular torsion beam by the hydroforming method, instead of using a tubular steel of one steel plate, different steel plates are joined along the longitudinal direction thereof. The purpose of the present invention is to provide an optimal durability design by using tubular steel (hereinafter referred to as "heterogeneous steel pipe") and controlling the thickness of each portion of the dissimilar steel pipe differently according to the distribution of stress.

In order to achieve the above object, the present invention, the tubular steel is press-molded in different shapes over the entire length, thereby forming a closed cross-section having a predetermined cross-sectional area and is coupled to the trailing arm for the rear suspension and "V" "In the torsion beam consisting of a central portion constituting the open cross section of the cross-section and the transition portion connecting the two ends and the central portion as the cross-section, the tubular steel is made of a different type made by joining different steel sheets for each section divided in the longitudinal direction It is composed of a steel pipe, each section is formed to have a different thickness.

In addition, the respective sections are divided into sections 1, 2, and 3 according to the following formula (1), and the thickness of the sections 1 and 3 is preferably larger than that of the section 2.

0 ≤ length of section 1 ≤ {(length of tubular steel / 3) ± outer diameter of tubular steel}

{(Length of tubular steel / 3) ± outer diameter of tubular steel} ≤ length of section 2 ≤ {(length of tubular steel / 3) × 2 ± outer diameter of tubular steel}

{(Length of tubular steel / 3) × 2 ± outer diameter of tubular steel} ≤ length of section 3 ≤ length of tubular steel (1)

In addition, the thickness of the section 1, section 3 is 3 ~ 4mm, the thickness of the section 2 is preferably set to 2 ~ 3mm.

According to the present invention configured as described above, by manufacturing a tubular torsion beam using a dissimilar steel pipe and adjusting the thickness for each section, it is possible to reduce the roll strength, which is the maximum stress applied to the torsion beam, and to maintain the roll rigidity at an optimum value. The high performance of the suspension system can be satisfied.

At present, more than 70% of the parts that make up automobiles are made of steel, and in recent years, a variety of automotive design requirements have been diversified. Taylor weld methods are widely used. Particularly, the parts that require local rigidity for automobile fillers and bumpers are manufactured with the Taylor weld method of thin and high strength steel to be lightweight while improving collision, torsion and bending stiffness.

Manufacturing all parts from high-strength steel reduces costs and productivity because of increased costs, but the Taylor Weld method can be used to change only those parts where local performance is required.

According to the present invention, in producing a tubular torsion beam by hydroforming, the tubular torsion beam is manufactured using a dissimilar steel pipe according to the Taylor Weld method, and the thickness of each part is controlled according to the stress distribution to provide an optimal durability design. It is a basic feature.

Hereinafter, with reference to the accompanying drawings will be described in more detail the technical configuration of the present invention.

2 shows a suspension equipped with a tubular torsion beam using heterogeneous steel tubes according to the present invention. In the suspension of the tubular torsion beam, the bush sleeve (1), the trailing arm (2), the spring seat (3), the damper bracket (4), the wheel carrier (5) and the spindle plate (6) constitute the basic components. As described above with reference to FIG. 1.

In addition, the tubular torsion beam 20 according to the present invention is formed by pressurizing the tubular steel into different shapes over the entire length by hydroforming, thereby forming a closed cross section having a predetermined cross-sectional area and on the trailing arm for the rear suspension. It is the same as a general tubular torsion beam in that both ends are joined, a central part forming an open cross section of the “V” shape, and a transition part connecting the both ends and the center part when the cross section is changed.

As described above, the biggest feature of the tubular torsion beam 20 according to the present invention is a method in which different steel sheets are welded for each section S1, S2, S3 in which the tubular steel, which is a raw material, is divided in its longitudinal direction. It is composed of a heterogeneous steel pipe made by joining, and is formed to have a different thickness for each section.

Each section (S1, S2, S3) may be divided into various lengths according to the material and thickness of the steel sheet to be bonded, but according to the present invention, each section is one side of the tubular torsion beam according to the following equation (1) It is preferred to be divided into section 1 (S1), section 2 (S2) and section 3 (S3) based on the stage.

0 ≤ length of section 1 ≤ {(length of tubular steel / 3) ± outer diameter of tubular steel}

{(Length of tubular steel / 3) ± outer diameter of tubular steel} ≤ length of section 2 ≤ {(length of tubular steel / 3) × 2 ± outer diameter of tubular steel}

{(Length of tubular steel / 3) × 2 ± outer diameter of tubular steel} ≤ length of section 3 ≤ length of tubular steel (1)

In more detail, the division of each section is made according to the stress distribution applied to the torsion beam during driving. Looking at the stress distribution applied to the tubular torsion beam during driving, it can be seen that the greater stress is applied from the center to both ends, especially in the transition portion where the size of the cross-sectional area is changed.

In the present invention, in consideration of such a stress distribution, the central portion with small stress and the both ends with large stress are divided into sections, and a different steel tube made of a different steel sheet is used as a tubular steel for each section.

In the simplest case, the entire length of a tubular steel can be divided into three sections and each section can be divided into one section. However, the inventors use several stress distribution experiments to determine the torsional stresses (reference stress). According to the beam specification, it was found to be distributed randomly within the range of adding or subtracting the outer diameter of the tubular steel about the baseline which divides the tubular steel into three parts. In the present invention, three sections (S1, S2, S3) are classified according to the above equation (1) based on the experimental results.

In addition, the tubular steel, which is divided into three sections as described above and each section is made of a different steel sheet, is configured to have a different thickness for each section according to the present invention.

Here, to make different steel sheets does not mean that they are made of different steel grades (materials), for example, made of high strength steel and ordinary carbon steel, but also made of different steel sheets with different thickness, strength, etc. It is used in a comprehensive sense to include. Therefore, the present invention also includes welding steel sheets of the same type having different thicknesses from each section.

In addition, to make different steel sheets does not only mean that all three sections are made of steel sheets having different specifications, but to make one of the three sections into steel sheets having different specifications, for example, As can be seen, Sections 1 and 3 are made of steel plate with large thickness and Section 2 is made of steel plate with small thickness.

When manufacturing a tubular torsion beam using a dissimilar steel pipe manufactured according to the Taylor Weld method, it is possible to control the various specifications (physical properties) of the steel sheet to make durable design. For example, sections 1 and 3 located on either side of the highly stressed tubular torsion beam can be made of high strength steel and sections of central stressed section 2 using normal carbon steel.

In the present invention, the purpose of the optimum durability design by controlling the thickness of the steel sheet for each section in the tubular torsion beam manufactured by using different steel pipes. When the strength of the steel sheet in each section is different, it is difficult to process because the steel sheet having a different material must be bonded, and when the shape of the steel sheet in each section is changed, the complexity of the hydroforming mold increases.

Therefore, it is most preferable to control roll strength and roll rigidity by hydroforming using the same mold as in the prior art by using a heterogeneous steel pipe made by joining steel sheets having different thicknesses for each section. While controlling the thickness of the steel sheet for each section, while controlling other specifications such as strength is also included in the technical idea of the present invention.

The thickness control of the present invention is to make the section 1, section 3 is subjected to a large stress to optimize the roll strength and roll stiffness made of a large steel sheet, and the section 2 is applied to a small stressed sheet to reduce the manufacturing cost Direction is made. Preferably, the thickness of the section 1, section 3 is 3 to 4mm, the thickness of the section 2 is composed of 2 to 3mm, wherein when the section 1, section 3 has the same thickness (3mm) as section 2 Is excluded.

When the thickness of the sections 1 and 3 exceeds 4mm, the load of the tubular torsion beam is greatly increased, which causes a problem in weight reduction. This is a very serious problem, considering that the tubular torsion beam suspension is mainly mounted on compact cars. On the other hand, when the thickness of the section 2 is less than 2mm, since the basic bending rigidity is not secured, bending deformation occurs while driving, and thus it may not function as a suspension device. The standard thickness of 3mm, which distinguishes sections 1 and 3 from section 2, is determined by considering the stress distribution and bending deformation of each section.

<Example>

The finite element modeling method is used to show the feasibility of performance improvement by controlling the thickness of the tubular torsion beam using the heterogeneous steel pipe according to the present invention described above.

For finite element modeling, the most important technique is to simulate the best fit with the actual model to find the stresses in the continuum. Finite element modeling used in the present invention is as follows. Meshing was performed with proper adjustment of Quad4, Tria3 and shell / solid elements, and bushes and joints were modeled using rigid elements (RBE2, RBE3). The torsion beam is modeled as a shell element, and the connecting part is applied to the beam element.

As the actual vehicle travels, the suspension system rolls, resulting in repeated torsion and bending loads. In particular, since the torsional load due to the rotation of the vehicle is the largest acting, it is very important to design to prevent the damage caused in advance. Stiffness was applied to the 4 degree roll stiffness test. That is, it is calculated with the reaction force obtained by calculating the displacement load by applying a displacement load to the suspension by converting it into a displacement by rotating the behavior 4 degrees in the vertical direction with respect to the center of the spindle plate 6. Strength can be obtained by applying a boundary condition and a load condition to the fastening part of the suspension system and then solving the linear equations.

Here, dozens of load cases are actually imposed on the suspension device, but the analysis was carried out with 19 load cases which have a great influence on the suspension device. In particular, we focused on torsional jounce and rebound loads where stress is highest due to the torsion beam's characteristics. Inertia relief virtual boundary conditions were used to model the boundary conditions most closely to the actual suspension.

In the case of tubular torsion beams manufactured using dissimilar steel tubes through the finite element modeling, the thicknesses of sections 1, 2, and 3 are respectively 3.4 mm and 2.7 mm 3.4 in the same thickness for each section. In the case of mm (Example 1), the thicknesses of the sections 1, 2, and 3 were each divided into the cases of 3.6 mm, 2.5 mm, and 3.6 mm (Example 2), respectively, to calculate the roll strength and roll rigidity. 2 to 4 show the stress distribution according to each case, and the roll strength and roll stiffness values in each case are shown in Table 1 below.

Roll strength Roll stiffness Comparative Example 1 751 MPa 519 Nm / deg Example 1 711 MPa 492 Nm / deg Example 2 660 Mpa 492 Nm / deg

In tubular torsion beams manufactured using dissimilar steel tubes, the greater the thickness of sections 1 and 3 compared to section 2, the more uniform the stress distribution along the longitudinal direction of the tubular torsion beam, as shown in FIGS. As shown in Table 1, the roll strength becomes smaller. The roll strength refers to the maximum stress on the tubular torsion beam, so the smaller the value, the better the required performance. Roll stiffness, on the other hand, decreases slightly but does not change significantly. Moreover, since the tubular torsion beam has a very high roll rigidity as compared to the plate-shaped torsion beam, the reduction to a certain level is rather helpful for optimal durability design.

Thus, according to the present invention it was possible to obtain the effect of reducing the strength while preventing the change in rigidity to occur as much as possible. The most difficult point in designing a general TBA is that if the thickness and cross-sectional area are increased to reduce the internal stress, the roll stiffness also increases, and if the thickness and cross-sectional area are reduced to reduce the roll rigidity, the suspension cannot be satisfied. Can not satisfy the ride comfort required. According to the present invention, it is possible to solve the above problems and to design a durable tubular torsion beam capable of satisfying the high performance requirements of the suspension system.

1 is a view showing a mounting state of a typical tubular torsion beam.

Figure 2 is a view showing the mounting state of the tubular torsion beam using a dissimilar steel pipe according to the present invention.

3 is a diagram illustrating a stress distribution in the case where the thickness of each section is uniform in FIG. 2;

4 is a view showing a stress distribution in the case of varying the thickness of each section in FIG.

5 is a view showing a stress distribution in another case of varying the thickness of each section in FIG.

※ Explanation of symbols about main part of drawing ※

1: bush sleeve 2: trailing arm

3: spring seat 4: damper bracket

5: wheel carrier 6: spindle plate

10: tubular torsion beam 11: both ends

12: transition part 13: center part

S1 to S3: Section 1 to Section 3

Claims (3)

The tubular steel is press-molded in different shapes over the entire length by hydroforming, thereby forming a closed cross section with a predetermined cross-sectional area, and forming an open cross section having a "V" shape with both ends coupled to the trailing arms for the rear suspension. In the torsion beam consisting of a transition portion connecting the both ends and the central portion while the central portion and the cross section is changed, The tubular steel is composed of a dissimilar steel pipe made by joining different steel sheets to each section divided in the longitudinal direction, and is formed to have a different thickness for each section, Each section is divided into section 1, section 2, section 3 according to the following equation (1), the thickness of the section 1, section 3 is 3 ~ 4mm, the thickness of the section 2 is characterized in that 2 ~ 3mm Tubular torsion beam for rear wheel suspension of automobile using dissimilar steel pipe. 0 ≤ length of section 1 ≤ {(length of tubular steel / 3) ± outer diameter of tubular steel} {(Length of tubular steel / 3) ± outer diameter of tubular steel} ≤ length of section 2 ≤ {(length of tubular steel / 3) × 2 ± outer diameter of tubular steel} {(Length of tubular steel / 3) × 2 ± outer diameter of tubular steel} ≤ length of section 3 ≤ length of tubular steel (1) delete delete

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