Resin pipe body

Abstract

A resin pipe body for cooling an electric vehicle is provided, which is provided with a bellows portion having a novel shape characteristic that can improve pressure resistance while avoiding an increase in the thickness of the pipe body. [Solution] A resin pipe body 10 used for cooling piping in an electric vehicle, in which the radius of curvature Ra of the center of the outer surface of a valley portion 22 in a bellows portion 12 is larger than the radius of curvature Rb of the center of the inner surface, and the pipe thickness of the valley portion 22 is larger than the pipe thickness of the boundary portion 34 between the peak portion 20 and the valley portion 22.

Description

[Technical field]

[0001] The present invention relates to a resin pipe used as a cooling piping for an electric vehicle, and more particularly to a resin pipe having a bellows portion in which peaks and valleys are alternately provided in the pipe length direction. [Background technology]

[0002] In electric vehicles, as described in, for example, Patent Document 1 (JP 2022-135796 A), a non-conductive resin pipe is used as a pipe that forms a flow path for a cooling medium in a cooling system for a heat generating body such as a battery. In this invention, an electric vehicle refers to a self-propelled vehicle equipped with an electric motor as a driving means, and includes, in addition to BEVs (battery electric vehicles), for example, PHEVs (plug-in hybrid vehicles), HEVs (hybrid vehicles), and FCEVs (fuel cell vehicles).

[0003] In an electric vehicle, many devices such as an electric motor and a battery are arranged in a limited space, and cooling piping must be routed to pass through the gaps between these various devices.

[0004] Therefore, in order to improve the degree of freedom in routing the cooling piping and to facilitate the installation work, it is conceivable to use a resin pipe body with a bellows section in which peaks and valleys extending in the circumferential direction are alternately provided in the pipe length direction as the cooling piping. Since such a resin pipe body can be curved by utilizing the expansion and contraction deformation of the bellows section, using it as a cooling piping makes it easy to realize curved routing to connect limited spaces. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-135796 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventor conducted a detailed study of the resin pipe body with the bellows section using a stress analysis by the finite element method and found that the concentration of stress in a specific area may make it difficult to ensure durability and reliability. For example, when the pressure of the cooling medium flowing through the pipe increases in order to further improve the cooling performance, there is a concern that the problem of locally concentrated stress may become even more serious.

[0007] Of course, such problems can be addressed by increasing the thickness of the plastic pipe body to ensure durability and reliability, but solving the problems by thickening the plastic pipe body not only inevitably increases costs and weight, but also increases the bending resistance in the bellows section, making it difficult to avoid adverse effects on the handling and installation of the cooling piping.

[0008] Here, the problem to be solved by the present invention is to provide a resin pipe body equipped with a bellows portion having novel geometric characteristics that can improve pressure resistance while avoiding thickening of the pipe body by reducing or eliminating local stress concentration in the bellows portion. [Means for solving the problem]

[0009] In the following, several aspects of the present invention made to solve such problems will be described. The components employed in each aspect described below can be employed in any combination possible. It should be understood that the aspects or technical features of the present invention are not limited to those described below, but are recognized based on the idea of ​​the invention described in the entire specification and drawings, or that a person skilled in the art can grasp from those descriptions.

[0010] The first aspect of the present invention is as follows. A resin pipe body used for cooling piping of an electric vehicle, the resin pipe body having a bellows portion in which peaks and valleys extending in a circumferential direction are alternately provided in a pipe length direction, The radius of curvature Ra of the outer surface center of the valley portion is greater than the radius of curvature Rb of the inner surface center of the valley portion, and A resin pipe body in which the thickness of the valley portion is greater than the thickness of the boundary portion between the peak portion and the valley portion.

[0011] According to the inventor's research, in a conventional resin pipe, the radius of curvature of the inner surface of the pipe is generally larger than the radius of curvature of the outer surface of the pipe at the valley portion, and the pipe thickness of the valley portion is generally constant throughout. In such a conventional resin pipe, it was found that the stress generated in the pipe wall due to the internal pressure of the coolant tends to concentrate in the approximately central portion of the valley portion, which is the bottom of the bellows portion.

[0012] Therefore, in the resin pipe according to the present embodiment, the radius of curvature Ra of the outer surface of the pipe at the valley bottom is made larger than the radius of curvature Rb of the inner surface of the pipe, so that the pipe thickness of the valley part is made larger at the center than at both sides. This is found to be effective in dispersing the stress generated at the valley bottom (center of the valley part) to both sides, thereby reducing the generated stress.

[0013] In addition, in the resin pipe according to this embodiment, the pipe thickness of the valley portion is made larger than the pipe thickness of the boundary portion between the peak portion and the valley portion over the entire pipe, which makes it possible to expand the stress dispersion at the bottom of the valley portion, which is achieved by the above-mentioned Ra>Rb, to a wider region of the valley portion, up to the vicinity of the boundary portion with the peak portion.

[0014] According to the present invention, which provides a resin pipe body with a bellows portion having such a novel shape characteristic of the valley portion, it is possible to improve the pressure resistance and durability performance while avoiding thickening of the pipe body by reducing the local stress concentration in the valley portion. Therefore, it is possible to realize a resin pipe body for cooling electric vehicles that can easily meet the demand for improved pressure resistance performance while ensuring good bending deformation characteristics and piping handling characteristics in the bellows portion without a significant increase in cost or weight.

[0015] In this embodiment, preferably, both the inner and outer surfaces of the bellows portion of the resin pipe body are formed to have a surface shape that extends smoothly in the pipe length direction without corners, connecting curved surfaces or connecting curved surfaces and straight lines, thereby making it possible to avoid sudden changes or concentrations of deformation and stress at corners.

[0016] A second aspect of the present invention is a resin pipe body according to the first aspect, The radius of curvature Ra at the center of the outer surface of the valley portion is set to be infinite.

[0017] In this embodiment, the radius of curvature Ra at the center of the outer surface of the valley portion is set to infinity, thereby providing a straight valley surface extending a predetermined length lv (≠0) in the pipe length direction. On the other hand, the radius of curvature Rb at the center of the inner surface of the valley portion is set to a curved surface that is not straight due to the above-mentioned condition of Ra>Rb.

[0018] A third aspect of the present invention is a resin pipe body according to the second aspect, In the central part of the outer surface of the valley portion, the radius of curvature Ra is set to infinity, so that the straight surface of the valley portion extending in the pipe length direction for a length lv extends for a length that is 10% or more of the distance La between the inflection points on both sides located at the boundary with the adjacent peak portions on both sides in the pipe length direction on the outer surface.

[0019] A fourth aspect of the present invention is a resin pipe body according to any one of the first to third aspects, Regarding the boundary dimension, which is the distance in the pipe length direction between boundary portions corresponding to the inflection points that are the boundaries between the peaks and valleys adjacent in the pipe length direction on the pipe thickness center line connecting the centers of the pipe thickness, The dimension Lv between the boundaries sandwiching the valley portions is larger than the dimension Lm between the boundaries sandwiching the peak portions.

[0020] In this embodiment, the dimensions (Lm, Lv) between the boundaries between the peaks and valleys on the pipe thickness center line connecting the center of the thickness of the member are as follows: Lm <Lvとされることとなる。

[0021] A fifth aspect of the present invention is a resin pipe body according to any one of the first to fourth aspects, The pipe thickness of the valley portion is greatest at the center point of the outer surface and gradually decreases toward both sides in the pipe length direction.

[0022] A sixth aspect of the present invention is a resin pipe body according to any one of the first to fifth aspects, The radius of curvature Rc at the center of the outer surface of the ridge is set to be infinite.

[0023] In the resin pipe according to this embodiment, the radius of curvature Rc is infinite at the center of the outer surface of the ridge, so that a straight ridge surface is provided extending a predetermined length lm (≠0) in the pipe length direction.

[0024] A seventh aspect of the present invention is a resin pipe body according to the sixth aspect, The radius of curvature Rd at the center of the inner surface of the ridge is set to a finite number.

[0025] An eighth aspect of the present invention is a resin pipe body according to the sixth or seventh aspect, The radius of curvature Ra is infinite at the center of the outer surface of the valley portion, thereby forming a valley portion straight surface extending in the pipe length direction by a length lv, The length lv of the straight surface of the valley portion is set within the range of 100 to 140% of the length lm of the straight surface of the peak portion extending in the pipe length direction by making the radius of curvature Rc infinite at the center of the outer surface of the peak portion.

[0026] A ninth aspect of the present invention is a resin pipe body according to any one of the first to eighth aspects, a straight pipe portion extending with a constant inner and outer diameter at a position outside the bellows portion in a pipe length direction; The minimum inner diameter of the tube at the valley portion is smaller than the inner diameter of the straight tube portion.

[0027] A tenth aspect of the present invention is a resin pipe body according to any one of the first to ninth aspects, The bellows portion has straight pipe portions extending with constant inner and outer diameters on both sides in the longitudinal direction, The ridges are provided at both ends of the bellows portion in the longitudinal direction thereof which are connected to the straight pipe portions.

[0028] An eleventh aspect of the present invention is a resin pipe body according to any one of the first to tenth aspects, a straight pipe portion extending with a constant inner and outer diameter at a position outside the bellows portion in a pipe length direction; The pipe thickness Tc of the bellows portion relative to the pipe thickness Ts of the straight pipe portion satisfies 50%≦Tc<100% over the entire bellows portion.

[0029] That is, in the resin pipe body according to this embodiment, the pipe thickness Tc of the bellows portion is relative to the pipe thickness Ts of the straight pipe portion in the range of 0.5Ts≦Tc<1.0Ts.

[0030] A twelfth aspect of the present invention is a resin pipe body according to any one of the first to eleventh aspects, At the center line of the pipe thickness, The minimum value of the radius of curvature rv at the valley portions is set to be larger than the minimum value of the radius of curvature rm at the peak portions. Effect of the Invention

[0031] According to the present invention, it is possible to reduce the stress generated at the bottom of the valley, where it is known that stress concentration is likely to occur, by dispersing the stress to both sides. As a result, it is possible to realize a plastic pipe body for cooling electric vehicles that can easily meet requirements for improved pressure resistance while maintaining good bending deformation characteristics in the bellows section. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram showing a resin pipe according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the resin pipe body shown in FIG. [Diagram 3]An enlarged explanatory diagram of part III in FIG. 2. [Figure 4] Stress distribution diagram when internal pressure acts on the resin pipe shown in Figure 3 [Diagram 5] Stress distribution diagram when internal pressure is applied in the comparative example of the resin pipe body DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0034] 1 shows an overall side view of a plastic pipe 10 according to an embodiment of the present invention. The plastic pipe 10 is used as a piping for a cooling device of an electric vehicle, for example, as a member constituting a flow path of a refrigerant in a battery cooling mechanism.

[0035] The resin pipe body 10 has a bellows portion 12 located at the middle part in the longitudinal direction and extending for a predetermined length, and straight pipe portions 14, 14 each extending with a constant inner and outer diameter are integrally formed on both sides in the longitudinal direction of the bellows portion 12. The diameter and length of the bellows portion 12 and the straight pipe portion 14 are not limited, and can be appropriately set according to the performance and flow path shape required for each vehicle to which the pipe body 10 is applied. The bellows portion 12 may be provided at a plurality of locations in the longitudinal direction of the pipe body 10, separated from each other by the straight pipe portion 14.

[0036] The material of the resin pipe body 10 is not limited, and various resin materials can be used in consideration of the refrigerant to be used and environmental conditions such as temperature under the usage conditions. For example, general-purpose resins such as polypropylene resins and polyamide resins can be used, and vinyl alcohol resins such as EVOH can also be used. The structure is not limited to a single layer structure, and a multi-layer structure may also be used.

[0037] Here, the bellows portion 12 has a structure in which peaks 20 and valleys 22, each of which extends in the circumferential direction with a constant cross-sectional shape, are alternately provided in succession in the pipe length direction. That is, the peaks 20 have a cross-sectional shape that is convex toward the outer circumferential surface side, and the valleys 22 have a cross-sectional shape that is concave toward the outer circumferential surface side.

[0038] Moreover, both the peaks 20 and valleys 22 on the inner surface 26 and the outer surface 28 of the pipe have no bending points in the pipe length direction (left and right direction in the figure), i.e., even at points where the inclination angles are different, they are connected by a common tangent line, forming a smoothly continuous curved surface shape, and in this embodiment in particular, the surface shape is a smoothly connected curved line and a straight line. Furthermore, the pipe thickness center line 30 connecting the center of the pipe thickness also has a smoothly continuous curved shape without bending points over the entire pipe length direction connecting the peaks 20 and valleys 22, and in this embodiment in particular, the surface shape is a smoothly connected curved line and a straight line.

[0039] Furthermore, the peaks 20 and valleys 22 have specific shapes as follows.

[0040] (1) The radius of curvature Ra of the center of the outer surface of the valley portion 22 is larger than the radius of curvature Rb of the center of the inner surface of the valley portion 22. That is, Ra>Rb. In addition, since Ra and Rb are the radii of curvature of valley portion 22, it is assumed that the center of curvature is on the outer side of the resin pipe body 10 (the side opposite to the central axis 32) with respect to valley portion 22, and the values ​​are positive in the direction convex toward the inside of the pipe body where the central axis 32 of the resin pipe body 10 (see Figure 2) is located, and are not negative.

[0041] (2) The pipe thickness of the valley portion 22 is made larger than the pipe thickness of the boundary portion 34 between the peak portion 20 and the valley portion 22. In other words, the valley portion 22, which has a shape that is convex toward the inside of the pipe, has a minimum pipe thickness at both ends of the valley portion 22, which are the boundary portions 34, and is formed to have a pipe thickness equal to or greater than those at both ends over the entire valley portion 22. The boundary portion 34 can be objectively specified as an inflection point located between the peak portion 20 that is convex toward the outside of the tube and the valley portion 22 that is concave toward the inside of the tube. That is, the pipe thickness at the boundary portion 34 is defined as the pipe thickness passing through the inflection point Bc on the pipe thickness center line 30. Such inflection point Bc can also be generally understood as the center point on a line connecting the inflection point Ba on the outer surface 28 of the tube and the inflection point Bb on the inner surface 26 of the tube.

[0042] By combining and adopting the geometric features of (1) and (2), it is possible to disperse the large stress that tends to occur at the bottom of the valley (the central part of the valley portion 22) over a wide area on both sides, thereby reducing the generated stress. By reducing the local stress concentration in the valley portion 22, it is possible to improve the pressure resistance and durability while avoiding an increase in the thickness of the resin pipe body 10.

[0043] (3) The radius of curvature Ra at the center of the outer surface of the valley portion 22 is set to infinity (∞). That is, in this embodiment, a valley portion straight surface 40 is provided at the center of the outer surface of the valley portion 22, extending a predetermined length lv (≠0) in the pipe length direction (left and right direction in FIG. 3 ). Note that the radius of curvature Rb at the center of the inner surface of the valley portion 22 is set to a curved surface that is not straight due to the condition Ra>Rb described in (1) above.

[0044] By adopting the shape feature (3) and providing a valley straight surface 40 at the center of the outer surface of the valley portion 22, the pressure resistance of the valley portion can be more effectively improved, and it becomes possible to easily design the degree of thickness change in the pipe length direction at the bottom central part of the valley portion 22 by adjusting the radius of curvature Rb of the pipe inner surface 26.

[0045] (4) The straight surface 40 of the valley portion having the length lv described in (3) above is formed to have a length extending for a length equal to or greater than 10% of the straight-line distance La between the inflection points Ba, Ba on both sides located at the boundaries between the adjacent ridge portions 20, 20 on both sides of the pipe length direction on the pipe outer surface 28. Note that the inflection point is a point where the center of curvature is located on the opposite side, that is, it is a sign change point of the second derivative in the function representing the shape of the outer surface 28 of the tube in the tube length direction. When the boundary portion between the peak portion 20 and the valley portion 22 extends along a straight line composed of a linear function inclined with respect to the tube central axis 32, the center in the length direction of the straight line is taken as the inflection point.

[0046] By adopting the shape feature of (4) above, the length of the straight surface of the valley portion can be ensured, and further improvement in the pressure resistance improvement effect of the valley portion as described in (3) above can be achieved.

[0047] (5) Regarding the dimension between the boundary portions of the peak portion 20 and the valley portion 22 on the tube thickness center line 30, the dimension Lv between the boundary portions sandwiching the valley portion 22 is larger than the dimension Lm between the boundary portions sandwiching the peak portion 20. That is, Lm < Lv.

[0048] By adopting the shape feature of (5) above, the dimensions (Lm, Lv) between the respective boundary portions of the peak-peak and valley-valley on the tube thickness center line 30 are such that Lm < Lv, and the dimension in the tube length direction of the valley portion 22 can be advantageously ensured. Therefore, it becomes possible to disperse the generated stress in a wider region in the tube length direction in the valley portion 22 where the stress tends to be larger than in the peak portion 20, and further improvement in durability and the like can be achieved. Moreover, even in the valley portion 22 where the deformation rigidity tends to increase due to its small diameter, it is also possible to improve the flexibility and thus the ease of bending deformation by increasing the length in the tube length direction. Note that the dimension between the boundary portions Ba, Ba on the outer surface 28 of the resin tube body 10 may be substantially the same for the boundary portion tube dimensions located on both sides sandwiching the peak portion 20 and the dimension between the boundary portions located on both sides sandwiching the valley portion 22.

[0049] (6) The tube thickness Tv of the valley portion 22 is maximized at the outer surface center point Ps in the tube axis direction, and gradually decreases from such outer surface center point Ps toward both sides in the tube length direction. Note that the tube thickness Tv of the valley portion 22 is the tube wall thickness dimension in the direction orthogonal to the tube wall in the valley portion 22, and is generally the tube wall thickness dimension in the direction orthogonal to the inner surface 26 or the outer surface 28 of the tube.

[0050] By adopting the shape feature (6), it is possible to ensure a large pipe thickness at the outer surface midpoint Ps, where stress is most likely to concentrate, even in the valley portion 22, and thereby ensure pressure resistance and durability more efficiently. In addition, by continuously changing and gradually decreasing the pipe thickness of the valley portion 22 from the outer surface midpoint Ps toward both sides in the pipe length direction, it is possible to prevent the deformation rigidity in the valley portion 22 from becoming excessively large, and it is also easy to ensure the bending deformation performance of the bellows portion 12.

[0051] (7) The radius of curvature Rc at the center of the pipe outer surface 28 of the ridge portion 20 is set to infinity (∞). That is, in this embodiment, a ridge-portion straight surface 42 is provided at the center of the outer surface of the ridge portion 20, extending in the pipe length direction (left-right direction in FIG. 3) for a predetermined length lm (≠0).

[0052] By adopting the shape feature (7), for example, by suppressing local thinning in the central part of the ridge portion 20, it is possible to avoid stress concentration in the ridge portion and further improve the bending deformation characteristics in the ridge portion.

[0053] (8) The radius of curvature Rd at the center of the inner surface of the ridge portion 20 is a finite number.

[0054] By adopting the shape feature of (8), the thickness dimension of the ridge portion 20 can be adjusted by the shape of the inner peripheral surface, for example, it is possible to suppress excessive stiffness of the ridge portion 20 and further improve the bending deformation characteristics of the bellows portion 12. In particular, by combining with the above embodiment of (7) and making the inner surface of the ridge portion 20 corresponding to the outer straight surface 42 a curved surface that is convex outward from the tube, at least in the portion where the straight surface 42 is formed, the tube thickness Tm of the ridge portion 20 is smallest at the center point of the outer surface and gradually increases toward both sides in the tube length direction. This can also disperse deformation and stress in the central portion of the ridge portion 20.

[0055] In addition, since Rc and Rd are the radii of curvature of the ridge portions 20, it is assumed that the center of curvature is located on the inner side of the resin pipe body 10 relative to the ridge portions 20 (the side where the central axis 32 is located), and the values ​​are positive in the direction convex toward the outside of the pipe body, which is the opposite side to the central axis 32 of the resin pipe body 10, and do not take negative values.

[0056] (9) On the outer pipe surface of the ridge portion 20, the straight ridge surface 42 described in (7) above is provided with a length lm, and at the center point Ps of the outer surface of the valley portion 22, the radius of curvature Ra is made infinite, thereby providing a straight valley surface 40 extending in the pipe length direction with a length lv, and the length lv of the straight valley surface 40 is set within the range of 100 to 140% of the length lm of the straight ridge surface.

[0057] By adopting the shape feature (9), the length lm of the straight peak surface 42 and the length lv of the straight valley surface 40 are formed to be relatively close to each other. As a result, it is possible to more effectively enjoy the synergistic effects of improving pressure resistance and durability due to the dispersion of stress in the peaks 20 and valleys 22, and it is also possible to improve favorable bending deformation characteristics.

[0058] (10) Compared to the pipe inner diameter Ds in the straight pipe portion 14 that extends outside the bellows portion 12 in the pipe length direction with a constant inner and outer diameter, the minimum value of the pipe inner diameter Dc in the bellows portion 12, i.e., the minimum pipe inner diameter in the central portion of the valley portion 22, is made smaller.

[0059] By adopting the shape feature (10), even when, for example, a straight pipe having a certain inner and outer diameter previously formed by a known forming method such as extrusion is used and a predetermined length portion in the pipe length direction is deformed by heat or the like to form the bellows portion 12, it is possible to ensure a large pipe thickness Tc of the valley portion 22 by making the minimum inner diameter of the valley portion 22 in the bellows portion 12 smaller than the pipe inner diameter Ds of the straight pipe portion 14. As a result, it is possible to further improve pressure resistance and durability by ensuring the pipe thickness of the valley portion 22 where stress is likely to concentrate.

[0060] However, the molding method of the resin tube body 10 according to the present invention is not limited. For example, in the extrusion molding of a straight tube obtained in advance as described above, for the straight tube immediately after extrusion molding, while circulating an outer mold surrounding the outer peripheral surface in a thermoplastic state and continuously overlapping, while subjecting the outer peripheral surface of the straight tube to negative pressure suction with respect to the molding surface of the outer mold, by transferably attaching the bellows shape formed on the molding surface of the outer mold, it is also possible to continuously form the target bellows portion 12 in the tube length direction.

[0061] Preferably, a straight tube extruded with the inner and outer diameter dimensions of the straight tube portion 14 of the target resin tube body 10 is used. With respect to the inner diameter Ds of the straight tube portion 14, the inner diameter Dc of the bellows portion 12 is made smaller at the trough portion 22 (Ds > Dc), while being made larger at the peak portion 20 (Dc < Dm). Also, with respect to the wall thickness of the peripheral wall of the resin tube body 10, the wall thickness Tc of the bellows portion 12 is made smaller than or equal to Ts at both the trough portion 22 and the peak portion 20 (Tc ≦ Ts). More preferably, the wall thickness Tc of the bellows portion 12 is made smaller than the wall thickness Ts of the straight tube portion 14 over the entire length excluding the connection points with the straight tube portion 14 at both ends in the tube length direction (Tc < Ts).

[0062] (11) It has straight tube portions 14, 14 extending with a constant inner and outer diameter on both sides in the length direction of the bellows portion 12, and peak portions 20 are provided at the connection end portions with each straight tube portion 14 on both sides in the length direction of the bellows portion 12.

[0063] By adopting the shape feature (11), it is possible to more effectively reduce the concentration of stress in the valley portion when the bellows portion 12 is curved in accordance with the piping form of the vehicle. That is, when the bellows portion 12 is curved in accordance with the piping space, the straight pipe portion 14 having a large deformation rigidity exerts a deformation restraining force on both ends of the bellows portion 12 in the pipe length direction, and stress is likely to concentrate. Therefore, by arranging the peak portion 20, which is more likely to be curved and deformed than the valley portion 22 and is more likely to suppress the generated stress, in such parts (both ends of the bellows portion 12 in the pipe length direction), it is possible to improve the bending performance of the bellows portion 12 while reducing the generated stress in the bellows portion 12. And by arranging the valley portion 22 in this way to avoid the connection end portion of the bellows portion 12 with the straight pipe portion 14, it is possible to more effectively reduce the generated stress in the valley portion 22 when the piping is curved, in combination with the stress dispersion effect of the valley portion 22 due to the shape action of the present invention as described above.

[0064] (12) A straight pipe portion 14 extends with a constant inner and outer diameter at a position outside the bellows portion 12 in the pipe length direction, and the pipe thickness Tc of the bellows portion 12 relative to the pipe thickness Ts of the straight pipe portion 14 satisfies 50%≦Tc<100% throughout the entire bellows portion.

[0065] In the resin pipe body 10 employing the geometric feature (12), the pipe thickness Tc of the bellows portion 12 is set to 0.5Ts≦Tc<1.0Ts relative to the pipe thickness Ts of the straight pipe portion 14. This, combined with the stress dispersion effect of the valley portion 22 due to the geometric action of the valley portion 22 of the present invention as described above, makes it possible to more effectively achieve improvements in the pressure resistance and durability of the bellows portion 12 while avoiding an increase in the thickness of the bellows portion 12 and realizing good deformation characteristics.

[0066] In the bellows portion 12, it is desirable to set the position where the tube thickness Tc is minimum in the central portion of the peak portion 20. In the bellows portion 12, it is desirable to set the position where the tube thickness Tc is maximum in the central portion of the valley portion 22. This makes it easier to simultaneously improve the pressure resistance and durability in the valley portion 22 where stress is likely to concentrate, and ensure the bending deformation characteristics in the peak portion 20 where the problem of stress concentration is more easily avoided than in the valley portion 22.

[0067] (13) In the pipe thickness center line 30 that connects the center of the pipe thickness, the minimum value of the radius of curvature rv in the valley portion 22 is made larger than the minimum value of the radius of curvature rm in the peak portion 20.

[0068] In the resin pipe body 10 that adopts the geometric feature (13), stress can be distributed more efficiently over a wide area in the valley portion 22 where stress concentration is likely to be a problem, and buckling deformation can be prevented, while the bending deformation characteristics of the peak portion 20 can be further improved.

[0069] Incidentally, Fig. 4 shows, as an example, the results of a simulation in which stress distribution caused by pressure action inside a plastic pipe body 10 having the geometric features described in (1) to (13) above and structured according to the present embodiment shown in Figs. 1 to 3 was obtained. Fig. 5 shows, as a comparative example, the results of a simulation in which stress distribution was obtained under the same conditions for a plastic pipe body having a conventional structure not having the geometric features according to the present invention as described in (1) above. In both the example and comparative example, the plastic pipe body was made of a single-layer polypropylene structure, and the simulation was performed under the operating conditions of an internal pipe pressure of 120 KPa under atmospheric pressure.

[0070] The simulation results shown in Figures 4 and 5 are difficult to see because they are color originals converted into gray displays, but the areas of difference in shading observed in the valleys in the comparative example shown in Figure 5 are hardly observed in the embodiment shown in Figure 4. Also, from the specific calculation results, the value of the maximum stress generated in the valleys was able to be suppressed to 70% or less in the embodiment shown in Figure 4 compared to the comparative example shown in Figure 5. From this, it can be confirmed that stress dispersion is achieved in the valleys where stress is particularly likely to concentrate.

[0071] Although specific and preferred aspects of the present invention have been described in detail above based on the embodiments, the present invention should not be interpreted as being limited by the above specific descriptions and aspects. In particular, the shape features described in (3) to (13) above are preferred in the present invention, but they may be adopted as desired and are not essential aspects.

[0072] For example, the specific dimensions such as length, thickness, and radius of curvature of each part of the bellows portion 12, including the pitch of the peaks 20 and valleys 22, are not limited and are appropriately designed taking into consideration the required characteristics of the resin pipe body 10, such as pressure resistance and bending performance, as well as sizes such as inner and outer diameters.

[0073] In addition, in the above embodiment, a ridge portion 20 was provided at each end in the pipe length direction of the bellows portion 12, which is the connection portion to the straight pipe portion 14, but a valley portion 22 may be provided at either one end or both ends.

[0074] In addition, it is desirable that the maximum thickness Tc of the bellows portion 12 is within 200% of the minimum thickness, and in general, it is desirable that the maximum thickness Tmmax of the pipe thickness Tm at the ridge portion 20 is Tmmax≦200·Tvmin, where Tv is the minimum value Tvmin of the pipe thickness Tv at the valley portion 22.

[0075] Also, the straight ridge surface 42 set on the ridge portion 20 is not essential, and the entire outer pipe surface 28 of the ridge portion 20 may be curved.

[0076] In addition, although not listed one by one, the present invention can be embodied in various forms with various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art, and it goes without saying that all such embodiments are included within the scope of the present invention as long as they do not deviate from the spirit of the present invention. [Explanation of symbols]

[0077] 10 Resin pipe body 12 Bellows section 14 Straight pipe section 20 Yamabe 22 Valley 26 Tube inner surface 28 Pipe outer surface 30 Pipe thickness center line 32 Pipe center axis 34 Boundary 40 Straight surface of valley 42 Straight surface of mountain Ra: Radius of curvature at the center of the outer surface of the valley Rb Radius of curvature at the center of the inner surface of the valley Inflection point on the outer surface of Ba tube Inflection point on the inner surface of the Bb Bc Inflection point on the center line of the pipe La: Distance between adjacent Ba and Ba across the valley Ps: Outer center point of valley Tv Pipe thickness at valley Tm Pipe thickness at the crest Ts: Thickness of straight pipe (constant) Tc Bellows pipe thickness (Tv and Tm) lv Length of the straight surface of the valley lm Length of the straight surface of the peak Ds: Inner diameter of straight pipe Dc Bellows pipe inner diameter

Claims

1. A resin pipe body used for cooling piping of an electric vehicle, the resin pipe body having a bellows portion in which peaks and valleys extending in a circumferential direction are alternately provided in a pipe length direction, The radius of curvature Ra of the outer surface center of the valley portion is greater than the radius of curvature Rb of the inner surface center of the valley portion, and A resin pipe body in which the thickness of the valley portion is greater than the thickness of the boundary portion between the peak portion and the valley portion.

2. 2. The resin pipe according to claim 1, wherein the radius of curvature Ra at the center of the outer surface of the valley portion is infinite.

3. 3. A resin pipe body as described in claim 2, wherein the radius of curvature Ra is infinite in the central portion of the outer surface of the valley portion, so that the straight surface of the valley portion extending in the pipe length direction by a length lv extends for a length that is 10% or more of the distance between the inflection points on both sides located at the boundary between the adjacent peak portions on both sides in the pipe length direction on the outer surface.

4. Regarding the boundary dimension, which is the distance in the pipe length direction between boundary portions corresponding to the inflection points that are the boundaries between the peaks and valleys adjacent in the pipe length direction on the pipe thickness center line connecting the centers of the pipe thickness, 3. The resin pipe according to claim 1, wherein a dimension Lv between the boundaries sandwiching the valley portions is larger than a dimension Lm between the boundaries sandwiching the peak portions.

5. 3. The resin pipe body according to claim 1, wherein the thickness of said valley portion is maximum at the center point of the outer surface and gradually decreases toward both sides in the direction of the pipe length.

6. 3. The resin pipe body according to claim 1, wherein a radius of curvature Rc at a center of an outer surface of the ridge portion is infinite.

7. 7. The resin pipe body according to claim 6, wherein a radius of curvature Rd at a center of an inner surface of said ridge portion is a finite number.

8. The radius of curvature Ra is infinite at the center of the outer surface of the valley portion, thereby forming a valley portion straight surface extending in the pipe length direction by a length lv, The resin pipe body according to claim 6, wherein the length lv of the straight surface of the valley portion is set within a range of 100 to 140% of the length lm of the straight surface of the peak portion extending in the pipe length direction by making the radius of curvature Rc infinite at the center of the outer surface of the peak portion.

9. a straight pipe portion extending with a constant inner and outer diameter at a position outside the bellows portion in a pipe length direction; 3. The resin pipe body according to claim 1, wherein a minimum inner diameter of said valley portion is smaller than an inner diameter of said straight pipe portion.

10. The bellows portion has straight pipe portions extending with constant inner and outer diameters on both sides in the longitudinal direction, 3. The resin pipe body according to claim 1, wherein the ridges are provided at both ends of the bellows portion in the longitudinal direction thereof that are connected to the straight pipe portions.

11. a straight pipe portion extending with a constant inner and outer diameter at a position outside the bellows portion in a pipe length direction; 3. The resin pipe body according to claim 1, wherein a pipe thickness Tc of the bellows portion relative to a pipe thickness Ts of the straight pipe portion satisfies 50%≦Tc<100% over the entire bellows portion.

12. At the center line of the pipe thickness, 3. The resin pipe body according to claim 1, wherein a minimum value of the radius of curvature rv at the valley portions is greater than a minimum value of the radius of curvature rm at the peak portions.

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