Anti-fatigue external thread and threaded connection pair

Abstract

The invention provides an anti-fatigue external thread and a threaded connection pair, and belongs to the technical field of threaded connection. The external threads are used for being matched with standard metro internal threads or MJ internal threads, the thread height of the external threads is hw, and according to the matching safety of the external threads and the metro internal threads or the MJ internal threads, it is guaranteed that the thread tooth effective coincidence rate of the external threads and the metro internal threads or the MJ internal threads is not lower than 25%; the range of hw is determined to be # imgabs0 #, wherein hn is the standard tooth height of the meter-made internal thread or the MJ internal thread. The thread height of the external threads is reduced, the rigidity of the external threads can be improved, the fatigue performance of the external threads when the external threads bear alternating loads is improved, and meanwhile the matching safety of the external threads and the meter internal threads or the MJ internal threads is guaranteed.

Description

Technical Field

[0001] The invention relates to an anti-fatigue external thread and a threaded connection pair, belonging to the technical field of threaded connection. Background Art

[0002] In the field of engineering, thread fatigue fracture is a particularly critical technical challenge, especially in equipment and components that are subjected to high stress and long service life, and its impact cannot be ignored. As a common connection method, thread has been widely used in many industries such as automobiles, aerospace, petrochemicals, and construction. The strength and stability of the connection are directly related to the safety and reliability of the entire structure.

[0003] Among the common threaded connections, there are metric threads and MJ threads. The tooth profiles of standard metric threads are as follows: Figure 1 As shown in the figure, the tooth profile of both internal and external threads includes the crest, straight line segment, root and straight line segment connected in sequence, where D is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. The crest width of the internal thread is The tooth bottom width is The crest width of the external thread is The tooth bottom width is Since the tooth angle of the internal and external threads is 60°, the tooth height of the internal and external threads can be obtained through geometric calculation. (Right now Figure 1 In ).

[0004] The tooth type of standard MJ thread is as follows Figure 2 As shown in the figure, the tooth profiles of internal and external threads also include the crest, straight line segment, root and straight line segment connected in sequence, where D is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. Unlike metric threads, the crest width of MJ internal threads is The tooth bottom width is The crest width of the MJ external thread is The tooth bottom width is Since the tooth angles of the MJ internal and external threads are both 60°, the tooth heights of the MJ internal and external threads can be obtained through geometric calculations as follows: (Right now Figure 3 In ).

[0005] At present, no matter it is metric thread or MJ thread, due to the influence of the thread structure itself, the average thickness of the external thread teeth is smaller than the average thickness of the internal thread teeth, so the stiffness of the internal thread teeth is greater than the stiffness of the external thread teeth, resulting in the threaded connection pair being subjected to alternating loads. The external thread with smaller thread stiffness acts as an energy absorption box for the internal thread with larger stiffness. The external thread teeth will produce greater deformation to share more inertia force, thereby aggravating the stress concentration phenomenon at the bottom of the external thread teeth, resulting in poor fatigue performance of the external thread. Summary of the invention

[0006] The purpose of the present invention is to provide a fatigue-resistant external thread to solve the problem that the existing external thread teeth have low rigidity and thus have poor fatigue performance when subjected to alternating loads; the purpose of the present invention is also to provide a threaded connection pair to solve the above problem.

[0007] To achieve the above purpose, the fatigue-resistant external thread of the present invention adopts the following technical solution:

[0008] A fatigue-resistant external thread, which is a metric external thread or MJ external thread used to match a standard metric internal thread or MJ internal thread, and the tooth height of the external thread is h w According to the safety of the external thread and the metric internal thread or MJ internal thread, the effective overlap rate of the external thread and the metric internal thread or MJ internal thread is not less than 25%, and h is determined. w The range is where h n It is the standard thread height of metric internal thread or MJ internal thread.

[0009] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further limits the external thread height h w The range is where h w <h n , which is equivalent to reducing the tooth height of the external thread, so that the rigidity of the external thread tooth can be improved, and its fatigue performance when subjected to alternating loads can be improved. At the same time, the tooth height of the external thread cannot have no lower limit, and it must not be less than one-fourth of the standard tooth height of the metric internal thread or the MJ internal thread, thereby ensuring that the effective overlap rate of the thread teeth of the external thread and the metric internal thread or the MJ internal thread is not less than 25%, ensuring the safety of the external thread and the metric internal thread or the MJ internal thread.

[0010] Furthermore, the external thread is a metric external thread, the pitch of the metric external thread is P, the crest width is C w , the tooth bottom width is 0.25P, the tooth angle is 60°, according to the tooth top width C w He Ya Gao w Satisfied geometric relationship: So 0.125P<Cw ≤0.594P, where 0.125P is the standard metric internal thread root width, and 0.594P is C w Value, where

[0011] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the metric external thread are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the standard metric internal thread are simplified, it is concluded that 0.173P≤C w ≤0.594P.

[0012] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the metric external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric internal thread, it is concluded that 0.317P≤C w ≤0.594P.

[0013] Furthermore, the external thread is an MJ external thread, the pitch of the MJ external thread is P, the crest width is C w , tooth bottom width is The tooth angle is 60°, according to the tooth top width C w He Ya Gao w Satisfied geometric relationship: So 0.125P<C w ≤0.547P, where 0.125P is the standard MJ internal thread root width, 0.547P is C w Value, where

[0014] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the MJ external thread are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ internal thread are simplified, it is concluded that 0.193P≤C w ≤0.547P.

[0015] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the MJ external thread are simplified is not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ internal thread are simplified, it is concluded that 0.325P≤C w ≤0.547P.

[0016] Furthermore, the crest of the external thread is a straight line parallel to the thread axis.

[0017] To achieve the above purpose, the threaded connection pair in the present invention adopts the following technical solution:

[0018] A threaded connection pair includes an internal thread and an external thread used in conjunction with the internal thread, wherein the internal thread is a standard metric internal thread or an MJ internal thread, and the external thread is an improved metric external thread or an MJ external thread, and the tooth height of the external thread is h w According to the safety of the external thread and the metric internal thread or MJ internal thread, the effective overlap rate of the external thread and the metric internal thread or MJ internal thread is not less than 25%, and h is determined. w The range is where h n It is the standard thread height of metric internal thread or MJ internal thread.

[0019] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further limits the external thread height h w The range is where h w <h n , which is equivalent to reducing the tooth height of the external thread, so that the rigidity of the external thread tooth can be improved, and its fatigue performance when subjected to alternating loads can be improved. At the same time, the tooth height of the external thread cannot have no lower limit, and it must not be less than one-fourth of the standard tooth height of the metric internal thread or the MJ internal thread, thereby ensuring that the effective overlap rate of the thread teeth of the external thread and the metric internal thread or the MJ internal thread is not less than 25%, ensuring the safety of the external thread and the metric internal thread or the MJ internal thread.

[0020] Furthermore, the external thread is an improved metric external thread, the pitch of the metric external thread is P, the crest width is C w , the tooth bottom width is 0.25P, the tooth angle is 60°, according to the tooth top width C w He Ya Gao w Satisfied geometric relationship: So 0.125P<C w ≤0.594P, where 0.125P is the standard metric internal thread root width, and 0.594P is C w Value, where

[0021] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the metric external thread are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the standard metric internal thread are simplified, it is concluded that 0.173P≤C w ≤0.594P.

[0022] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the metric external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric internal thread, it is concluded that 0.317P≤C w ≤0.594P.

[0023] Furthermore, the external thread is an improved MJ external thread, the pitch of the MJ external thread is P, the crest width is C w , tooth bottom width is The tooth angle is 60°, according to the tooth top width C w He Ya Gao w Satisfied geometric relationship: So 0.125P<C w ≤0.547P, where 0.125P is the standard MJ internal thread root width, 0.547P is C w Value, where

[0024] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the MJ external thread are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ internal thread are simplified, it is concluded that 0.193P≤C w ≤0.547P.

[0025] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the MJ external thread are simplified is not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ internal thread are simplified, it is concluded that 0.325P≤C w ≤0.547P.

[0026] Furthermore, the crest of the external thread is a straight line parallel to the thread axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a tooth profile diagram of a standard metric thread in the prior art;

[0028] Figure 2 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0029] Figure 3 The tooth profile diagram of the anti-fatigue external thread embodiment 1 of the present invention;

[0030] Figure 4 is the crest width C in Example 1 of the fatigue-resistant external thread of the present invention w He Ya Gao w Geometric relationship diagram;

[0031] Figure 5 It is a schematic diagram of the thread profile in Example 1 of the anti-fatigue external thread of the present invention being simplified into a cantilever beam;

[0032] Figure 6 k and C in Example 1 of the fatigue-resistant external thread of the present invention w The change relationship diagram of

[0033] Figure 7This is a thread calibration position diagram in Example 1 of the anti-fatigue external thread of the present invention;

[0034] Figure 8 It is a curve diagram of the average stress variation over time at a calibrated position under the action of an alternating load in Example 1 of the anti-fatigue external thread of the present invention;

[0035] Fig. 9 The tooth profile diagram of the fatigue-resistant external thread embodiment 2 of the present invention;

[0036] Fig.10 It is a schematic diagram of the thread profile in Example 2 of the anti-fatigue external thread of the present invention being simplified into a cantilever beam;

[0037] Fig.11 k and C in Example 2 of the anti-fatigue external thread of the present invention w The change relationship diagram of

[0038] Fig.12 This is a graph showing the change in average stress over time at a calibrated position under an alternating load in Example 2 of the anti-fatigue external thread of the present invention. DETAILED DESCRIPTION

[0039] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0040] In response to the technical problems existing in the prior art, the basic concept of the present invention is to reduce the tooth height of the external thread, thereby increasing the stiffness of the external thread teeth, causing the internal thread teeth to undergo greater bending deformation to absorb the inertia force generated by the alternating load, and improving the fatigue resistance of the external thread.

[0041] Embodiment 1 of the fatigue-resistant external thread of the present invention:

[0042] In this embodiment, the fatigue-resistant external thread is an improved metric external thread, and the internal thread used in conjunction with it is a standard metric internal thread, wherein the tooth profile of the metric external thread is evolved from the tooth profile of the existing standard metric thread, such as Figure 3 As shown, the tooth profile of the metric external thread (hereinafter referred to as the external thread) in this embodiment includes a tooth top 11, a first straight line segment 12, a tooth bottom 13 and a second straight line segment 14 connected in sequence, the pitch of the external thread is P, the major diameter of the external thread is d, the middle diameter of the external thread is d2, the minor diameter of the external thread is d1, the tooth profile angle α=60°, the tooth bottom width is P / 4=0.25P, the tooth top width is C w In this embodiment, the tooth top 11 is a straight line parallel to the thread axis. The tooth top 11 and the straight line segments on both sides have two intersection points, namely A and B. The line segment AB is parallel to the thread axis. The length of the line segment AB is also the tooth top width C. w The tooth height of the external thread is h w , which is the length of the vertical line segment from point A to the bottom of the tooth.

[0043] The present invention reduces the tooth height of the external thread, so the external thread has a width C w , major diameter d, tooth height h w Except for this, the other parameters are the same as those of the existing standard metric external threads. According to the geometric structure, when the tooth height of the external thread is not reduced, the tooth crest width should be P / 8=0.125P; when the tooth height of the external thread is reduced to zero, the tooth crest width should be 3P / 4=0.75P. Therefore, the tooth crest width C of the external thread in this embodiment is w The maximum range is: 0.125P<C w <0.75P. At the same time, when the tooth height of the external thread is not reduced, it can be concluded through geometric calculation that the tooth height should be (This value is also the tooth height of the standard metric internal thread, i.e. ), so the tooth height h of the external thread in this embodiment w The maximum range is:

[0044] Furthermore, if Figure 4 As shown, according to the geometric relationship: After simplification, the tooth height h of the external thread can be obtained w and tooth top width C w The following relations are satisfied:

[0045] Considering the safety of the fit between the external and internal threads, the effective overlap rate of the internal and external threads cannot be less than 25%, that is, the tooth height of the external thread must meet It can be concluded that After simplification, we can get C w ≤0.594P.

[0046] At this point, the crest width C is optimized w The upper limit value of the tooth top width C is obtained w The basic range is: 0.125P<C w ≤0.594P.

[0047] In order to further explore the crest width C w A better lower limit value is convenient for subsequent analysis, such as Figure 5 As shown, in this embodiment, the threads of the external thread and the internal thread are simplified into a set of interacting rectangular cantilever beams, the action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads, and the tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0048] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated.w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0049] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0050] Furthermore, the beam heights h of the cantilever beams after the internal and external threads are simplified are C n1 and C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0051] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0052] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0053]

[0054] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0055]

[0056] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0057]

[0058] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as:

[0059]

[0060] According to the above determined C w Range: 0.125P<C w ≤0.594P, within this range, plot k with respect to C w The curve, such as Figure 6 As shown in the curve, it can be seen that k increases with C w The ratio of the bending deflection of the external thread to the bending deflection of the internal thread decreases with the increase of the tooth width C of the external thread. w As the value of P increases, it gradually decreases. w In the range of ≤0.594P, the external thread of this embodiment can be used in conjunction with the standard metric internal thread to reduce the bending deflection of the external thread teeth, which is equivalent to increasing the bending deflection of the internal thread teeth, so that the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread teeth under the action of the alternating load, and improving the fatigue performance of the external thread.

[0061] Furthermore, when k = 1, the bending deflection of the external thread is equal to the bending deflection of the internal thread, We can find C w =0.173P. Therefore, when k < 1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread teeth begins to be smaller than the bending deflection of the internal thread teeth, that is: C w >0.173P.

[0062] Therefore, the external thread width C can be obtained w The optimized range is: 0.173P≤C w ≤0.594P. Within this range, it can ensure that the effective overlap rate of the internal and external threads is not less than 25% of the internal thread height, ensuring the safety of the internal and external thread matching, and at the same time it can also ensure that the bending deflection of the external thread is not greater than the bending deflection of the internal thread. The internal thread can undergo a larger bending deformation to absorb the inertia force generated by the alternating load.

[0063] Furthermore, when k≤0.1, C w ≥0.317P. in C w In the range of ≥0.317P, the bending deflection of the external thread teeth is reduced to no more than one tenth of the bending deflection of the internal thread teeth, which can further cause the internal thread teeth to undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby further improving the fatigue performance of the external thread. Therefore, the external thread tooth width C can be obtained. w The optimal range is: 0.317P≤C w ≤0.594P.

[0064] In specific applications, the pitch P of the external thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm. Standard metric internal thread

[0065] In order to verify the external thread width C provided in this embodiment w In order to find out the superiority of the test thread, a comparative test was conducted. The parameters of the test thread are shown in Table 1. The pitch P of each test thread is 4 mm, and the root width is 1 mm, that is, C in the table n =1mm. The tooth width of thread 1 to thread 3 is 0.317P<C w <0.594P, within the optimal range; thread 4 tooth width C w =0.25P, in the optimal range 0.173P≤C w ≤0.594P; thread 5 tooth width C w =0.15P, in the basic range 0.125P<C w ≤0.594P internal; the comparison thread is the standard metric external thread.

[0066] Table 1 Thread parameters of Example 1 of the present invention and comparative thread

[0067]

[0068] According to the above setting parameters, the general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is imposed on the bolt. Under the same alternating load, the stress variation curves of threads 1 to 5 and the comparison threads at the calibration position are obtained, as shown in Figure 2. Figure 7 As shown in the figure, the calibration position is the red dot position in the figure, which is the first buckle position of the external thread and the matching internal thread, and is usually the position where the stress is most concentrated. Figure 8 As shown in Figure 2, the average stress at the calibrated position of threads 1 to 5 under the action of alternating load is less than that of the standard metric thread (i.e., the comparison thread). w <0.317P, the average stress of threads 4 and 5 is similar to that of standard metric threads; when C w When >0.317P, the average stress of threads 1 to 3 is significantly reduced.

[0069] Table 2 shows the stress amplitudes of the thread of the present invention and the comparative thread. It can be seen from the table that the average stress amplitudes of the calibrated positions of the thread of the present invention are all smaller than those of the standard metric thread.

[0070] Table 2 Stress amplitude of the thread of Example 1 of the present invention and the comparative thread

[0071] Thread 1 Thread 2 Thread 3 Thread 4 Thread 5 Standard metric thread 199.928MPa 203.648MPa 206.043MPa 212.44Mpa 213.874Mpa 214.258MPa

[0072] From the above test data, it can be seen that in the 0.125P<C w In the basic range of ≤0.594P, the average stress amplitude of threads 1 to 5 is smaller than that of the comparison thread; in the basic range of 0.173P≤C w In the optimization range of ≤0.594P, the average stress amplitude of threads 1 to 4 is smaller; in the optimization range of 0.317P≤C w In the optimal range of ≤0.594P, the average stress amplitude of threads 1 to 3 is smaller, and the tooth width C w The average stress amplitude of the largest thread 1 is the smallest, and the fatigue performance of the thread is the best.

[0073] Embodiment 2 of the fatigue-resistant external thread of the present invention:

[0074] In this embodiment, the fatigue-resistant external thread is an improved MJ external thread, and the internal thread used in conjunction with it is a standard MJ internal thread, wherein the tooth profile of the MJ external thread is evolved from the tooth profile of the existing standard MJ thread, such as Fig. 9 As shown, the tooth profile of the MJ external thread in this embodiment also includes a tooth top, a first straight line segment, a tooth bottom and a second straight line segment connected in sequence. The pitch of the MJ external thread is P, the major diameter is d, the middle diameter is d2, the minor diameter is d1, the tooth profile angle α=60°, and the tooth bottom width is The crest width is C w In this embodiment, the tooth top is also a straight line parallel to the thread axis. The tooth top and the straight line segments on both sides have two intersection points, namely A and B. The line segment AB is parallel to the thread axis. The length of the line segment AB is also the tooth top width C. w The tooth height of the external thread is h w , which is the length of the vertical line segment from point A to the bottom of the tooth.

[0075] The present invention reduces the tooth height of the MJ external thread, so the MJ external thread has a width C w , major diameter d, tooth height h w Except for the above, the other parameters are the same as the existing standard MJ external thread. According to the geometric structure, when the tooth height of the MJ external thread is not reduced, the crest width should be When the tooth height of the MJ external thread is reduced to zero, the crest width should be Therefore, the crest width C of the MJ external thread is w The maximum range is: At the same time, when the tooth height of the MJ external thread is not reduced, it can be concluded through geometric calculation that the tooth height should be (This value is also the tooth height of the standard MJ internal thread, i.e. Therefore, the tooth height h of the MJ external thread in this embodiment is w The maximum range is:

[0076] Furthermore, according to the geometric relationship of the MJ external thread, it can be known that the external thread height h w and tooth top width C w The following relations are satisfied:

[0077] Considering the safety of the MJ external thread and internal thread, the effective overlap rate of the internal and external threads cannot be less than 25%, that is, the tooth height of the MJ external thread must meet It can be concluded that After simplification, we can get C w ≤0.547P.

[0078] At this point, the crest width C is optimized w The upper limit value of the tooth top width C is obtained w The basic range is: 0.125P<C w ≤0.547P.

[0079] In order to further explore the crest width C w A better lower limit value is convenient for subsequent analysis, such as Fig.10 As shown, in this embodiment, the threads of the MJ external thread and the MJ internal thread are simplified into a set of interacting rectangular cantilever beams, the action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads, and the tooth width of the cantilever beam after the external thread is simplified is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0080] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0081] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0082] Furthermore, the beam heights h of the cantilever beams after the internal and external threads are simplified are C n1 and C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0083] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0084] Assume that the material elastic modulus of the MJ external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam simplified by the MJ external thread at the equivalent action point Q is w for:

[0085]

[0086] Assume that the material elastic modulus of the MJ internal thread is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0087]

[0088] Furthermore, the ratio of the MJ external thread deflection to the MJ internal thread deflection is defined as k, then k is:

[0089]

[0090] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as:

[0091]

[0092] According to the above determined C w Range: 0.125P<C w ≤0.547P, within this range, plot k with respect to C w The curve, such as Fig.11 As shown in the curve, it can be seen that k increases with C w The ratio of the bending deflection of the external thread to the bending deflection of the internal thread decreases with the increase of the tooth width C of the external thread. w As the value of P increases, it gradually decreases. wIn the range of ≤0.547P, the MJ external thread of this embodiment can be used in combination with the standard MJ internal thread to reduce the bending deflection of the external thread teeth, which is equivalent to increasing the bending deflection of the internal thread teeth, so that the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress at the bottom of the external thread teeth under the action of the alternating load, and improving the fatigue performance of the external thread.

[0093] Furthermore, when k≤1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread teeth is not greater than the bending deflection of the internal thread teeth, that is: C w ≥0.193P. Therefore, it can be concluded that the MJ external thread tooth width C w The optimized range is: 0.193P≤C w ≤0.547P. Within this range, it can ensure that the effective overlap rate of the internal and external threads is not less than 25% of the internal thread height, ensuring the safety of the internal and external thread matching, and at the same time it can also ensure that the bending deflection of the external thread is not greater than the bending deflection of the internal thread. The internal thread can undergo a larger bending deformation to absorb the inertia force generated by the alternating load.

[0094] Furthermore, when k≤0.1, C w ≥0.325P. in C w In the range of ≥0.325P, the bending deflection of the external thread teeth is reduced to no more than one tenth of the bending deflection of the internal thread teeth, which can further cause the internal thread teeth to undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby further improving the fatigue performance of the external thread. Therefore, the external thread tooth width C can be obtained. w The optimal range is: 0.325P≤C w ≤0.547P.

[0095] In specific applications, the pitch P of the MJ external thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm. Standard MJ internal thread

[0096] In order to verify the external thread width C provided in this embodiment w In order to find out the superiority of the thread, a comparative test was conducted. The parameters of the test threads are shown in Table 3. The pitch P of each test thread is 4 mm, and the root width is 1.25 mm, that is, C in the table n =1.25mm. The tooth width of thread 6 to thread 8 is 0.325P<C w <0.547P, within the optimal range; thread 9 tooth width C w=0.25P, in the optimal range 0.193P≤C w ≤0.547P; thread width C of thread 10 w =0.15P, in the basic range 0.125P<C w ≤0.547P internal thread; the comparison thread is standard MJ external thread.

[0097] Table 3 Thread parameters of Example 2 of the present invention and comparative thread

[0098]

[0099] According to the above setting parameters, the dynamic analysis of the internal and external threads is performed using general finite element analysis software, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt, and the stress variation curve of threads 6 to 10 and the comparison thread at the calibration position (the calibration position is the same as that of Example 1, both are the first buckle position) under the same alternating load is obtained. Fig.12 As shown in Figure 2, the average stress at the calibrated position of threads 6 to 10 under the action of alternating load is less than that of the standard MJ thread (i.e., the comparison thread). w When <0.325P, the average stress of threads 9 and 10 is similar to that of standard MJ threads; when C w When >0.325P, the average stress of threads 6 to 8 is significantly reduced.

[0100] Table 4 shows the stress amplitudes of the thread of the present invention and the comparative thread. It can be seen from the table that the average stress amplitudes of the calibrated positions of the thread of the present invention are all smaller than those of the standard MJ thread.

[0101] Table 4 Stress amplitude of the thread of Example 2 of the present invention and the comparative thread

[0102]

[0103]

[0104] In other embodiments of the fatigue-resistant external thread: when the external thread is a metric thread, the tooth width C is optimized. w In the process of lower limit value, according to the actual situation, it is not necessary to take C when k = 0.1 w =0.317P, for example C w The lower limit can be 0.4P or 0.5P, and of course it can also be 0.3P or 0.2P or 0.25P. When the external thread is an MJ external thread, it is also not necessary to take C when k = 0.1. w =0.325P, for example, it can be 0.4P, 0.5, 0.3P, 0.2P or 0.25P.

[0105] In other embodiments of fatigue-resistant external threads: regardless of whether the external thread is a metric thread or an MJ thread, its tooth top can be an arc. Since the arc does not contact the internal thread teeth, the effective contact length of the internal thread teeth and the external thread teeth remains unchanged, that is, the process of simplifying the external thread and the internal thread teeth into a rectangular cantilever beam to calculate the bending deflection in the above embodiment is also applicable, and the calculation results are the same.

[0106] An embodiment of the threaded connection pair in the present invention is as follows: the threaded connection pair includes an internal thread and an external thread used in conjunction with the internal thread, the internal thread is a standard metric internal thread or an MJ internal thread, and the external thread is an improved metric external thread or an MJ external thread. The specific parameters of the external thread are the same as those of the fatigue-resistant external thread in any of the above embodiments, and will not be repeated here.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the protection scope of the present invention.

Claims

1. A fatigue-resistant external thread, which is a metric external thread or an MJ external thread used to match a standard metric internal thread or an MJ internal thread, and the thread height of the external thread is h w , characterized in that, According to the safety of the external thread and the metric internal thread or MJ internal thread, the effective overlap rate of the external thread and the metric internal thread or MJ internal thread is guaranteed to be not less than 25%, and h is determined. w The range is where h n It is the standard thread height of metric internal thread or MJ internal thread.

2. The fatigue-resistant external thread according to claim 1, characterized in that: The external thread is a metric external thread, the pitch of the metric external thread is P, the crest width is C w , the tooth bottom width is 0.25P, the tooth angle is 60°, according to the tooth top width C w He Ya Gao w Satisfied geometric relationship: So 0.125P<C w ≤0.594P, where 0.125P is the standard metric internal thread root width, and 0.594P is C w Value, where 3. The fatigue-resistant external thread according to claim 2, characterized in that: According to the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the metric external thread is not greater than the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric internal thread, it is concluded that 0.173P≤C w ≤0.594P.

4. The fatigue-resistant external thread according to claim 3, characterized in that: According to the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the metric external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric internal thread, it is concluded that 0.317P≤C w ≤0.594P.

5. The fatigue-resistant external thread according to claim 1, characterized in that: The external thread is an MJ external thread, the pitch of the MJ external thread is P, the crest width is C w , tooth bottom width is The tooth angle is 60°, according to the tooth top width C w He Ya Gao w Satisfied geometric relationship: So 0.125P<C w ≤0.547P, where 0.125P is the standard MJ internal thread root width, 0.547P is C w Value, where 6. The fatigue-resistant external thread according to claim 5, characterized in that: According to the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the MJ external thread is not greater than the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard MJ internal thread, it is concluded that 0.193P≤C w ≤0.547P.

7. The fatigue-resistant external thread according to claim 6, characterized in that: According to the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the MJ external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard MJ internal thread, it is concluded that 0.325P≤C w ≤0.547P.

8. The fatigue-resistant external thread according to any one of claims 1 to 7, characterized in that: The crest of an external thread is a straight line parallel to the axis of the thread.

9. A threaded connection pair, comprising an internal thread and an external thread used in conjunction with the internal thread, wherein the internal thread is a standard metric internal thread or an MJ internal thread, characterized in that: The external thread is the fatigue-resistant external thread as described in any one of claims 1 to 8.

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