JP5435807B2 - Structural analysis method of screw fastening part - Google Patents

Description

  The present invention relates to a structure analysis method for a screw fastening portion, and more particularly to a structure analysis method for a screw fastening portion suitable for reducing the number of man-hours for modeling a screw fastening portion in FEM (finite element method) analysis and improving efficiency.

  An analysis method for analyzing the strength and the like of a fastening structure using FEM analysis software is known. In Patent Document 1, a global mesh and a local mesh are generated from the respective models of the entire portion of the fastening structure to be analyzed and the vicinity of the thread of the bolt and the female screw member. A superposition mesh method is described in which a numerical calculation is performed based on the results and a structural analysis is performed by superimposing the two calculation results. In the superposition mesh method, an analysis is performed once with the global model, and the screw fastening portion is calculated again with the local model.

JP 2009-87218 A

  As described above, the analysis method described in Patent Document 1 requires at least two calculations, and if a detailed mesh is set for the entire screw fastening portion that is the analysis target part, a huge amount of processing time is required. Therefore, there is a problem that analysis time increases.

  An object of the present invention is to provide a structure analysis method for a screw fastening portion using a finite element method that can solve the above-described problems of the prior art, can reduce processing time, and can improve analysis accuracy. is there.

  In order to achieve the above object, according to the present invention, the other member to be fastened (for example, a cylinder block) is passed through a female screw portion formed in one of the two fastened members (for example, a crankcase). A structural analysis method for modeling a screw fastening portion having a structure in which a fastening member (for example, a stud bolt) is screwed to fasten two members to be fastened to each other, and evaluating the strength of the screw fastening portion with respect to an external force using a finite element method The first feature is that the mesh in the modeling region set in the vicinity of the engagement end portion of the screw engagement portion of the bolt with respect to the female screw portion is created with a finer mesh size than the other regions. is there.

  In addition, the present invention has a second feature in that the modeling area is set in a range including a plurality of screw threads of the female screw portion.

  In addition, the present invention has a third feature in that the modeling area includes a detailed modeling area having a predetermined depth provided in a curvature portion of a valley portion of the female screw included in the modeling area.

  Further, the present invention includes a cartridge in which the model of the female screw portion is a model created separately from a model of one of the members to be fastened (for example, a crankcase), and one of the members to be fastened (for example, The crankcase model has a fourth feature in that a space region having the same shape as the outer shape of the cartridge is formed in order to fit the cartridge.

  In addition, the present invention has a fifth feature in that the external shape of the cartridge is a polygonal prism shape such as an octagonal prism.

  In the present invention, the detailed modeling region is a region sandwiched between two perpendiculars extending from the two curvature start points of the screw valley bottom to the side surface of the cartridge, and along the screw valley bottom, The sixth feature is that the region extends from the curvature start point to the lowest point of the screw valley bottom in the depth direction and extends over the entire circumference of the screw valley bottom.

  In addition, the present invention has a seventh feature in that the model of the female screw portion is a three-dimensional model having an axisymmetric shape.

  In addition, the present invention has an eighth feature in that a model of a stud bolt as a fastening member is a cylindrical model having no thread.

  In the actual machine durability test, when damage occurs around the screw fastening part, the bottom part of the female screw near the engaging end (bolt tip) of the engaging part of the female screw and the bolt as the fastening member may be the starting point. Many. Therefore, in the present invention having the first, third, and sixth features, the engagement end portion is used as a modeling region, and in particular, the detailed modeling region is set to a predetermined depth at the bottom of the female screw valley, and modeling is performed. Meshes outside the modeling area have been simplified. Therefore, it is possible to reduce the analysis time while reducing the processing man-hours, and to make it practical for practical machine development.

  According to the present invention having the second feature, the modeling region can be set including a plurality of screw threads, and for example, how many threads of the female screw can be arbitrarily selected as the modeling region. There is no need to set a detailed mesh over the entire thread. Therefore, the efficiency of model creation can be increased and processing can be performed for a short time.

  According to the present invention having the fourth feature, the cartridge having the female thread portion is applied to the crankcase model that is one of the fastened members, so that the cartridge can be replaced even when the design of the crankcase is changed. This can reduce the man-hours for model creation. Moreover, versatility also increases.

  According to the present invention having the fifth feature, the cartridge and the crankcase model side have a flat mating surface in the case of a cartridge having a polygonal column shape (for example, an octagonal column shape), unlike the cylindrical outer shape of the cartridge. Analysis accuracy is improved because there is no difference in strain between the two. In addition, when the cartridge is made into an octagonal column shape and a 1/4 model is created by dividing the column shape into four equal shapes along the axis, the calculation is made with this 1/4 model and the calculation result is simply multiplied by four. Since it can be analyzed, calculation is quick and easy.

  According to the present invention having the seventh feature, since the female screw model has an axisymmetric shape different from the actual screw shape, the number of man-hours for model creation is reduced as compared with the case of using the spiral shape model. It is possible to reduce the man-hours required for screw processing in actual machine development. According to the present invention having the eighth feature, the model of the stud bolt as the fastening member is a cylindrical model having no thread, so that the calculation is simplified and the processing time can be shortened.

It is a principal part expanded sectional view which shows the model of the screw fastening part to which the structural analysis which concerns on one Embodiment of this invention is applied. It is a flowchart which shows the structure analysis procedure which concerns on one Embodiment of this invention. It is a flowchart of cartridge mesh creation. It is a figure which shows a cartridge. It is a figure which shows the cartridge accommodated in the crankcase model. It is principal part sectional drawing of a crankcase model. It is sectional drawing of the crankcase model in which the cartridge was accommodated. It is principal part sectional drawing of the cartridge which shows the mesh produced in the internal thread of a cartridge. 1 is a cross-sectional view of a main part of a motorcycle engine to which a structural analysis method according to an embodiment of the present invention is applied. It is a figure which shows 1/4 shape of a cartridge. It is a schematic diagram showing a combination of a model of a female screw cartridge and a stud bolt screwed into the female screw. 3 is a schematic diagram showing a model of a screw fastening portion including a stud bolt and a female screw portion of a crankcase 1. FIG. It is a schematic diagram which shows the cylindrical shape model of a stud bolt. It is a figure which shows the stress distribution which acts on the engaging part of the screw fastening part which consists of a stud bolt and an internal thread. It is a figure which shows the example of the mesh set to the engagement end part of a female screw. It is a figure which shows the example of the mesh set except the engagement end part of a female screw.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a screw fastening portion for assembling a cylinder block to a crankcase of a motorcycle engine is assumed as a structural analysis target. FIG. 9 is a sectional view of an essential part of the engine. In FIG. 9, the engine 9 is composed of a crankcase 1 and a cylinder part 10, and the cylinder part 10 includes a cylinder block 2 and a cylinder head 12, and the crankcase 1 is composed of an upper part 1a and a lower part 1b. An oil pan 11 is coupled to the lower portion 1 b of the crankcase 1.

  A stud bolt fixed to the crankcase 1 is formed by screwing a bolt 4 into a female screw 3 formed on the upper portion 1a side of the crankcase 1, and the crankcase 1, the cylinder portion 10, Assemble. The stud bolt 4 is passed through the cylinder block 2 and the cylinder head 12, and the cylinder block 2 is assembled to the crankcase 1 by fastening a nut 6 to the end of the stud bolt 4 protruding upward from the cylinder head 12.

  In addition, stud bolts 13 and 14 are fixed to the upper portion 1a of the crankcase 1 by being screwed into female screws 15 and 16, respectively. The stud bolts 13 and 14 protrude downward through the lower portion 1b of the crankcase 1. Then, the nuts 20 and 21 are fastened to the lower end portion, whereby the upper portion 1a and the lower portion 1b of the crankcase 1 are assembled. Further, the upper part 1a and the lower part 1b of the crankcase 1 are screwed into the lower part 1b with bolts 18 that pass through the upper part 1a, and screwed into the upper part 1a with bolts 19 that pass through the lower part 1b of the crankcase 1. It is firmly fixed.

  The structural analysis includes the fastening portion between the female screw 3 and the stud bolt 4, the fastening portion between the stud bolts 13 and 14 and the female screws 15 and 16, the stud bolt 4 and the nut 6, and the stud bolts 13 and 14 and the nut 20. The strength evaluation for each fastening part with 21 is performed.

  The object of the structural analysis according to the present invention is not limited to the screw fastening portion related to the stud bolt of the engine 9 described here. For example, the present invention is also applied to structural analysis relating to a screw fastening portion between the bolt 18 and the lower portion 1b of the crankcase 1 and a screw fastening portion between the bolt 19 and the upper portion 1a of the crankcase 1 of the crankcase 1. However, since structural analysis using a mesh of screw fastening portions requires a lot of analysis time even if a plurality of CPUs are used, it is not appropriate to apply this embodiment to structural analysis of all screw fastening portions. In the engine, the effect can be obtained by applying the present embodiment to the fastening portion between the stud bolt and the female screw portion.

  FIG. 2 is a flowchart showing an analysis procedure of the structure analysis method of the screw fastening portion according to the embodiment of the present invention. This analysis procedure is performed using a general purpose computer. In step S1 of FIG. 2, a three-dimensional CAD model of the screw fastening portion is created. In step S2, cartridge outer shape processing is performed on the model of the fastened portion. The parts to be fastened are the crankcase 1 and the cylinder part 10. Here, the outer shape of the cartridge is processed into a model (crankcase model) of the crankcase 1 (upper part 1a) which is one of the fastened parts into which the bolts 4 are screwed. Processing is performed. The “cartridge” is an octagonal column model model prepared in advance and includes a female screw portion.

  When the cartridge is formed in a cylindrical shape, if a mesh is created for a surface having a curvature, an error due to discretization occurs, and the mesh on the outer surface on the cartridge side and the surface of the model on the crankcase side do not match, resulting in a strain difference. On the other hand, according to the study by the present inventors, it has been confirmed that by making the cartridge into an octagonal column shape, there is no distortion difference at the mating surface between the cartridge and the crankcase model side. Adopted the shape. In addition, by making the cartridge into an octagonal column shape, as will be described later, when a 1/4 model is created by dividing this column shape into four equal shapes along its axis, calculation is performed with this 1/4 model, Since the analysis can be performed simply by multiplying the calculation result by four times, the calculation is quick and easy.

  Therefore, the cartridge outer shape processing in step S2 refers to creating an area portion on the crankcase model side in the three-dimensional CAD model where a female screw is formed in a space having the same shape as the outer shape of the cartridge. By applying the cartridge having the female thread portion to the crankcase model in this way, even when a design change occurs in the crankcase, it is possible to cope with the replacement of the cartridge, so that the model creation man-hour can be reduced.

  In step S3, a mesh for each surface of the analysis model is created. In step S4, the mesh of each surface created in step S3 and the cartridge mesh are assembled (mesh model assembly). A cartridge mesh is created for a model model of the cartridge. A model model of the cartridge can be prepared for each bolt size, and the bolt length and cost are corrected from the layout information (design information).

  In step S5, analysis conditions are set. Analysis conditions include in-cylinder pressure, piston thrust load, load information such as crankshaft and transmission and balancer bearing reaction forces, and configuration information such as stud bolt axial force and engine restraint position (mounting position on the vehicle body). Including.

  In step S6, structural analysis (strength analysis of the screw fastening portion) using FEM analysis software is performed. In step S7, the analysis result is evaluated according to a preset evaluation criterion. If the evaluation result conforms to the standard (OK), the process is terminated. If the evaluation result does not conform to the standard (NG), the process proceeds to step S8.

  In step S8, it is determined whether or not the screw fastening portion needs to be changed. If step S8 is negative, the process returns to step S3. If step S8 is positive, the screw fastening portion is changed in step S9. Changes are made for bolt length and cost. If the screw fastening portion is changed, the process proceeds to step S10, and a cartridge mesh is created according to the changed screw fastening portion.

  FIG. 3 is a flowchart for creating a cartridge mesh. In step S101, a model model for each bolt size is acquired according to the bolt size (diameter) from a storage unit previously stored. In step S102, the evaluation unit is corrected based on the changed bolt length and cost of the screw fastening unit. In step S103, a cartridge mesh is generated.

  FIG. 11 is a schematic diagram showing a combination of a cartridge of the female screw 3 and a model of the stud bolt 4 screwed into the female screw. The cartridge 50 has a cylindrical shape embedded in a space formed in the upper portion 1 a of the crankcase 1, and the stud bolt 4 is formed as a thread model 40. The thread model 40 of the stud bolt 4 is a standard model created in advance according to the bolt diameter, and only the portion that is screwed with the cartridge 50 is created, and the portion that is not screwed with the cartridge 50 is omitted.

  FIG. 12 is a schematic view showing a model of a screw fastening portion including the stud bolt 13 and the female screw portion 16 of the upper portion 1 a of the crankcase 1. Here, the cartridge 51 is a cylindrical model corresponding to the female screw portion 16, and the stud bolt 13 is formed as a thread model 131. The thread model 131 of the stud bolt 13 is the same as the thread model 40 and is a standard model created in advance according to the bolt diameter. The model 201 of the nut 20 screwed to the stud bolt 13 is also a standard model created in advance.

  FIG. 13 is a schematic diagram showing a cylindrical model of the stud bolt 4. In the example shown in FIG. 13, the stud bolt 4 and the nut 6 are modeled as simple cylindrical models 42 and 61 having no threads, respectively.

  FIG. 4 shows the cartridge. The cartridge 5 has an octagonal prism shape, and a female screw 3 that fits the stud bolt 4 is formed. In the cartridge 5, meshes are made on the outer peripheral surface, both end surfaces, and each surface of the female screw 3. In FIG. 4, in order to avoid complication of the drawing, a part of the mesh appearing on the outer peripheral surface and the female screw are formed. 3 shows only a part of the created mesh. A two-dot chain line D in the figure is a line that divides the cartridge into four parts, and indicates a parting line of the cartridge as a specular target model to be described later. The female screw 3 may have the same spiral shape as the actual screw shape, but is modeled in an axially symmetric shape in order to reduce the man-hours for model creation and the man-hours for screw processing in actual machine development. When the present inventors conducted an experiment using a test piece for strain measurement, there was almost no difference in strain values between the axially symmetric screw shape and the spiral shape, and the strain distribution was in good agreement with the analysis results. There was no problem in terms of accuracy.

  FIG. 5 is a view showing a cartridge housed in the crankcase model, FIG. 6 is a cross-sectional view of the main part of the crankcase model, and FIG. 7 is a cross-sectional view of the crankcase model containing the cartridge. In each of the drawings, only a substantial part of the mesh that is sufficient for understanding the present invention is shown in a simplified manner. In FIG. 6, the crankcase model 7 has a space (space region) 8 that coincides with the outer shape of the cartridge 5, and a mesh is created on the surface of the space 8. Further, as shown in FIGS. 5 and 7, the cartridge 5 is fitted into the crankcase model 7, and a mesh is formed on the female screw 3 formed on the cartridge 5.

  FIG. 8 is a view showing a three-dimensional model of a cross section of the main part of the cartridge showing a mesh formed on the female screw of the cartridge, and FIG. 1 is an enlarged view of the main part of FIG. In FIG. 8, the mesh 17 at the bottom of the threaded portion of the female screw portion in the distal end region of the stud bolt 4, that is, the engagement end portion of the opposed portion (hereinafter referred to as “engagement portion”) of the female screw portion of the cartridge 5 and the stud bolt 4 is involved. Since the size is extremely smaller than the region other than the end portion of the part, it is shown in a state of being filled in black.

  FIG. 14 is a diagram showing the distribution of stress acting on the engaging portion of the screw fastening portion including the stud bolt 4 and the female screw 3. According to FIG. 14, it is understood that when the stud bolt 4 is screwed into the female screw 3 and tightened with the nut 6, the amplitude stress is remarkably increased at the engagement end portion as compared with other portions of the engagement portion. The In such a stress distribution, it is predicted that a crack Cr will start from the root C1 of the thread corresponding to this stress increasing portion. Therefore, a region in the vicinity of the engagement end portion of the engagement portion with the stud bolt 4 (for example, three peaks from the tip of the bolt 4) is set as a modeling region R, and the mesh is made finer in the modeling region R than in other regions. By performing analysis, efficient analysis processing becomes possible.

  For the reason described with reference to FIG. 14, as shown in FIG. 1, the mesh size of the modeling region R is made smaller than that of the other regions in order to obtain a strain value with high accuracy for the curvature portion of the valley bottom of the female screw 3 with respect to the engagement end portion. doing. A predetermined detailed modeling area Am is set in the vicinity of the thread bottom of the model of the female screw 3 in the modeling area, and the mesh in that area is created with a mesh size that is particularly finer than the other areas.

  The detailed modeling area Am is an area sandwiched by perpendicular lines L1 and L2 extending from the curvature start points a1 and a2 of the curvature portion of the valley bottom of the female screw 3 to the side surface 5s of the cartridge 5, and along the valley bottom of the female screw 3. This is a region extending in the depth direction by a length L corresponding to the length L from the curvature start point a1, a2 of the screw valley bottom to the lowest point b of the screw valley bottom, and extending over the entire circumference of the screw valley bottom.

  Specifically, the length of the curvature portion of the valley of the female screw 3 (the length from the curvature start point a to the lowest point b of the valley bottom (that is, half the length of the curvature portion) L is divided into n (for example, divided into 4). A mesh is created and an n-divided mesh is created in the depth direction (the direction extending from the bottom of the screw valley to the side surface 5S of the cartridge) in the range of the length L. The region Am of the female screw 3 is also circumferential. Similarly, it is preferable to create a mesh having a size obtained by dividing the length L into n.

  FIG. 15 is a diagram showing an example of a mesh set at the engagement end portion of the female screw, and FIG. 16 is a diagram showing an example of a mesh set at a region other than the engagement end portion of the female screw. As shown in FIG. 15, the mesh size is 20 to 30 μm in the detailed modeling region Am of the engagement end portion, that is, the screw end portion, among the engagement portions of the female screw 3 and the stud bolt 4. On the other hand, as shown in FIG. 16, the mesh size is set to 100 μm or more in the region other than the engagement end portion of the screw engagement portion, that is, the region Am1 near the screw engagement start portion. The mesh size is defined by the length of each side of the triangle forming each mesh.

  In this way, only the mesh evaluation part of the cartridge is created in detail, and the mesh other than the evaluation part is roughened and simplified, thereby reducing the calculation time and maintaining the analysis accuracy. As an example, the analysis process of the screw fastening portion of the engine, which was calculated over 24 hours by a CPU with a predetermined number of predetermined processing speeds using the conventional method of simply making the mesh fine, is the screw engagement end portion, that is, the screw tip portion. According to the present embodiment in which only the mesh is made finer than the mesh in other regions and is applied only to the stud bolt, the processing can be performed in 9 hours using the same number and the same processing speed of the CPU. It became possible.

  Note that a quarter-shaped cartridge model may be created, and an octagonal cartridge model may be created using the mirror symmetry of the quarter model. Thereby, the modeling man-hour can be reduced. When creating such a ¼ shape model, a cartridge having an octagonal prism shape is advantageous. This is because the calculation time is easily shortened because it is only necessary to multiply the result calculated using the ¼ shape model by four.

  FIG. 10 is a diagram illustrating a ¼ shape model. FIG. 10 shows that a fine mesh is created on the surface (valley bottom) of the female screw 3. The mesh appearing in the cross section is the same as that shown in FIGS. 1 and 8, and is not shown in order to avoid complication.

  As described above, according to the present embodiment, the analysis location according to the actual situation is used as the detailed modeling area, and a finer mesh is created than the other areas. Therefore, the analysis accuracy is improved while reducing the processing man-hours for the analysis. Can be achieved.

  In addition, since the female screw is modeled in an axially symmetric shape, the number of man-hours for screw processing can be reduced. In addition, the adaptability to the design change can be improved by adopting the cartridge.

  The present invention is not limited to the above embodiment, and can be modified within the scope of the matters described in the claims and the well-known technology. For example, the detailed modeling region is created by dividing the predetermined distance L into four in each of the two directions, but the number of divisions is not limited to this. In short, the mesh of the detailed modeling area Am set according to the actual state of the damaged part may be made finer than the meshes of other areas.

  DESCRIPTION OF SYMBOLS 1 ... Crankcase, 2 ... Cylinder block, 3 ... Female screw, 4 ... Bolt, 5 ... Cartridge, 6 ... Crankcase model, 8 ... Spatial area, Am ... Detailed modeling area

Claims (7)

The computer screws the bolt (4) passing through the other fastening member (2) into the female screw part (3) formed in one (1) of the two fastening members (1, 2). In a structural analysis method for modeling a screw fastening part having a structure for inserting and fastening two fastened members (1, 2) to each other, and evaluating the strength of the screw fastening part against external force using a finite element method,
The female screw portion (3) of the screw engaging portion of the bolt (4) with respect to the mesh in the modeling area (R) to be set in dependency end portion vicinity are created with a fine mesh size than other regions ,
The modeling region (R) includes a detailed modeling region (Am) having a predetermined depth (L) provided in a curvature portion of a valley portion of the female screw included in the modeling region (R),
The model of the female screw part (3) is included in the cartridge (5) which is a model created separately from the model of one (1) of the fastened members,
A space region (8) having the same shape as the outer shape of the cartridge (5) is formed in the model (1) of the fastened member in order to fit the cartridge (5),
The detailed modeling region (Am) is a region sandwiched by two perpendicular lines (L1, L2) extending from the two curvature start points (a1, a2) of the screw valley bottom to the side surface (5S) of the cartridge (5). Then, along the bottom of the screw valley, it extends in the depth direction with a length (L) from the curvature start point (a1, a2) of the screw valley bottom to the lowest point (b) of the screw valley bottom. An area that spans the circumference,
While creating a mesh that divides the length (L) from the curvature start point (a1, a2) of the screw valley bottom to the lowest point (b) of the screw valley bottom, the range of the length (L) also in the depth direction A structure analysis method for a screw fastening portion, wherein a mesh divided into n is created .   The structure analysis method for a screw fastening portion according to claim 1, wherein the modeling region (R) is set in a range including a plurality of screw threads of the female screw portion (3). The structure analysis method for a screw fastening portion according to claim 1 or 2, wherein the external shape of the cartridge (5) is a polygonal prism shape. The external shape of the cartridge (5) has the structure analysis method of the screw fastening portion of claim 1, wherein it is octagonal prism shape. The structural analysis method for a screw fastening portion according to any one of claims 1 to 4 , wherein the model of the female screw portion (3) is an axially symmetrical three-dimensional model. The two workpieces is a crankcase and a cylinder block of a vehicle engine, wherein the bolt, to any one of claims 1 to 5, characterized in that a stud bolt which is erected on the crankcase The structure analysis method of the screw fastening part of description. The structural analysis method for a screw fastening portion according to claim 6 , wherein the model of the stud bolt is a cylindrical model having no thread.

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