JP2008254631A - Fuel tank manufacturing method, and fuel tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel tank manufacturing method capable of improving fatigue life by avoiding concentration of stress to a joining part of a flange of a fuel tank. <P>SOLUTION: When applying bending to a flange part of a fuel tank structured of a fuel tank upper shell 1, a lower shell 2 and a joining part 3 formed by overlapping them and joining them with one another, this fuel tank manufacturing method excellent in fatigue resistant performance applies bending so that angle θ of the joining surface to the horizontal line 4 becomes 45 degrees or more in order to avoid concentration of stress to the joining part to be caused when the inner pressure is applied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a fuel tank having excellent fatigue resistance.

  The fuel tank attached to the vehicle is affected by changes in the outside air temperature, etc., and the fuel vaporized therein repeatedly expands and contracts. Along with this, the fuel tank itself repeatedly expands and contracts. Therefore, if the rigidity of the fuel tank is insufficient, the amount of deformation when the internal pressure changes and the fuel tank expands and contracts increases.

  At this time, in the flange portion where the upper shell and the lower shell are joined, the amount of deformation in the direction in which they are separated increases, a notch effect is added at the joined portion, strain concentration occurs, and repeated fatigue accumulates. .

  As a method of dealing with such repeated fatigue, there is a method of increasing the rigidity of the fuel tank itself, suppressing the deformation amount when subjected to repeated pressure changes, and suppressing the strain at a portion where the strain is easily concentrated, such as a joint. is there.

  As a specific method for increasing the rigidity of the fuel tank, there are a method for increasing the thickness of the fuel tank and a method for introducing beads. Japanese Laid-Open Patent Publication No. 2005-162010 discloses a method for suppressing deformation of a tank when an internal pressure is applied by connecting the bottom surfaces of an upper case and a lower case with stays.

Japanese Patent Application Laid-Open No. 9-309347 discloses a fuel tank that has improved pressure resistance by making the fuel tank into a donut shape. In these conventional techniques, the rigidity of the fuel tank is ensured within a range that does not cause a safety problem.
Japanese Unexamined Patent Publication No. 2005-162010 JP-A-9-309347

  If the thickness of the material is increased in order to increase the rigidity of the fuel tank, the rigidity of the entire tank can be reliably increased, but there is a problem that the weight of the tank and the cost of the material are increased.

  Also, when increasing the rigidity of the tank by introducing a bead, it is necessary to introduce a deep bead to increase the rigidity of the tank, but the deeper the bead, the smaller the capacity of the tank, so the effect is Limited.

  Also, when designing a bead, it is necessary to predict where the amount of deformation will increase when pressure is applied, and to design the position, width, depth, etc. of the bead on a trial and error basis. If it is found out that this is the case, there is a problem that the manufacturing load is high, for example, it is necessary to review the design again.

  In the method disclosed in Japanese Patent Laid-Open No. 2005-162010 (Patent Document 1), it is necessary to connect the bottom surfaces of the upper case and the lower case with stays, which increases the cost of the tank and receives internal pressure. In some cases, distortion may concentrate on the connecting portion of the stay.

  Further, in the method disclosed in Japanese Patent Application Laid-Open No. 9-309347 (Patent Document 2), it is necessary to make the fuel tank shape into a donut shape, the degree of freedom of the shape of the fuel tank is low, and the center portion is hollow. Therefore, this means that the capacity of the tank is reduced by that amount, and it is inefficient in a fuel tank that is required to secure the maximum capacity in a limited space.

  The present invention has been made in view of the above-described problems, and is a fuel capable of improving the fatigue life by a relatively simple method without causing an increase in the weight of the fuel tank and a decrease in the degree of freedom of shape. It aims at providing a tank and its manufacturing method.

  The flange parts of the fuel tank upper shell and the lower shell are overlapped and joined, and when bending is applied to the flange part, bending is performed so that the angle of the joining surface with respect to the horizontal line is 45 degrees or more. , A fuel tank and a manufacturing method thereof.

  Here, it is preferable that the radius of curvature of the bent portion of the flange portion bent by the bending is set to ½ or more of the total plate thickness of the fuel tank upper shell and the lower shell in the flange portion.

  According to the present invention, it is possible to alleviate the concentration of strain at the joint portion that occurs when the fuel tank expands or contracts due to a change in internal pressure, and withstands the resistance near the joint portion without increasing the material plate thickness. A fuel tank with improved fatigue characteristics can be provided at low cost.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross-sectional view of a flange portion of a conventional fuel tank before the bending forming according to claim 1 is performed. As a method for joining the flange joint portion 3 formed by superposing the upper shell 1 and the lower shell 2, methods such as seam welding, laser welding, brazing, and adhesive are used.

  Considering a case where an internal pressure is applied in the direction of expanding the tank, a force is applied in a direction in which the upper shell 1 and the lower shell 2 are separated from each other.

  At this time, a notch effect is added to the joint portion, and strain concentration occurs at the position shown in FIG. Therefore, a fuel tank with higher reliability can be provided by increasing the strength of the joint portion.

  The present invention does not increase the rigidity of the entire tank by increasing the thickness of the material, but inexpensively manufactures a fuel tank with excellent fatigue resistance against repeated changes in internal pressure, even for thin materials. As a result of intensive research on these, the following conclusions were reached.

  FIG. 2 shows an example of the present invention. By applying bending to a flange having a joint portion where strain concentration occurs, strain at the joint portion when the internal pressure is applied and the tank expands can be dispersed.

  As a result, the concentration of strain at the joint is relaxed, so that the fatigue resistance can be improved. As a method of adding such bending, the punch is moved from the upper side to the lower side with a die having an R corresponding to the target bending R pressed against the lower side of the flange, thereby bending the flange portion. There is a method of adding molding, but the bending method is not particularly limited.

  However, it is necessary to add bending so that the angle θ1 of the joint surface with respect to the horizontal line is 45 degrees or more.

  FIG. 2 shows an example in which bending is performed so that θ1 is 90 degrees. In this method, bending is applied so that the flange tip is positioned on the lower side, but bending may be applied so that the flange tip is positioned on the upper side.

  On the other hand, as comparative example 1, FIG. 3 shows a flange cross-sectional view when the flange portion is bent and the angle θ2 of the joint surface with respect to the horizontal line is less than 45 degrees. Thus, when the internal pressure is applied to the fuel tank having a short bending angle, the concentration of strain is promoted rather than the case where bending is not applied at all as shown in FIG. .

  The reason for this is that when internal pressure is applied to a flange that has not been bent at all as shown in FIG. 1, the concentration of strain is distributed almost evenly on the upper side and the lower side, whereas as shown in FIG. This is because when the bending angle is small, the strain concentrates on one side (upper side when the flange tip is bent to the lower side as shown in FIG. 3).

  As shown in FIG. 3, when the joint portion is bent, it is determined whether or not the bending angle is 45 degrees or more with reference to the joint surface at the center of the joint portion.

  Therefore, the bending angle needs to be 45 degrees or more. Further, as Comparative Example 2, a flange cross-sectional view when the bending R (curvature radius) of the bent portion is small although bending is added so that the angle θ3 of the joint surface with respect to the horizontal line is 45 degrees or more is shown in FIG. It shows.

  In this way, when the bending R is small, the strain does not concentrate on the joint portion, but there is a possibility that the strain concentrates on the bent portion instead. Therefore, it is desirable that the bend R of the bent portion is R equal to or greater than the material plate thickness. That is, the bending R of the bent portion is preferably set to 1/2 or more of the total thickness of the tank upper shell and the lower shell in the flange portion.

  Examples of the present invention will be described below. The material of the fuel tank used for the test is a 0.9 mm thick steel sheet with a tensile strength of 270 MPa class mild steel plate. The steel sheet was drawn by press to form an upper shell and a lower shell, and these flange portions were overlapped and joined by seam welding to form a fuel tank. The created tank has a bowl-like shape and has a flange having the same shape as in FIG.

  The tank flange was bent so that the angle of the joint surface with respect to the horizontal line was 32, 45, 56, 78, and 90 degrees. For comparison, a tank in which the flange was not bent at all was also prepared.

  When bending the flange, move the punch from the upper side to the lower side with a die having a curved surface of R5 pressed against the lower side so that the bending R of the flange is 5. Bending was added at

  It is known that the fuel tank undergoes fatigue due to repeated changes in internal pressure, and the fuel tank is low cycle fatigue.

  In other words, by determining the strain range at the risk of fracture when repeated pressure load is applied (the position corresponding to the strain concentration occurrence position in FIG. 1 when no bending is applied and FIG. 3 when bending is applied). You can know the fatigue life of the fuel tank.

  Therefore, the strain range of the risk of fracture was measured when the internal pressure load of 0 kPa → 18 kPa was repeatedly applied to the fuel tank. FIG. 5 shows the result of plotting the relationship between the angle of the joint surface with respect to the horizontal line and the strain range. When the angle of the joint surface with respect to the horizontal line is less than 45 degrees, it is out of the scope of the present invention, and the strain range becomes rather larger than that when the conventional bending is not applied, and the fatigue life is reduced.

  On the other hand, the range of the present invention is the case where bending is performed so that the angle of the joint surface with respect to the horizontal line is 45 degrees or more, and the strain range is smaller and the fatigue life is improved than when the conventional bending is not applied. did.

  In addition, bending up to 90 degrees gave the effect of reducing the maximum strain range. At this time, the fatigue life of the fuel tank was greatly improved.

Cross section of flange of conventional fuel tank Sectional view of a flange of a fuel tank according to an embodiment of the present invention Comparative example 1 flange sectional view Comparative example 2 flange sectional view Graph showing the relationship between the bending angle of the joint surface and the strain range relative to the horizontal line

Explanation of symbols

1 Upper shell 2 Lower shell 3 Joint 4 Horizontal line

Claims (3)

  The flange parts of the fuel tank upper shell and the lower shell are overlapped and joined, and when bending is applied to the flange part, bending is performed so that the angle of the joining surface with respect to the horizontal line is 45 degrees or more. And fuel tank manufacturing method.   2. The radius of curvature of the bent portion of the flange portion bent by the bending is not less than 1/2 of the total plate thickness of the fuel tank upper shell and lower shell in the flange portion. The manufacturing method of the fuel tank of description. A fuel tank manufactured by the method according to claim 1.

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