Arc threaded connection pair

Abstract

The invention provides an arc threaded connection pair, and belongs to the technical field of threaded connection. The arc threaded connection pair comprises an internal thread and an external thread which are both arc threads, the included angle between an external thread side linear section and a plane perpendicular to the axis of the external thread is # imgabs 0 # internal thread, and at least all internal thread side linear sections, close to one axial end, in the thread form of the internal thread are adduction linear sections with the included angle smaller than # imgabs 1 # internal thread and the plane perpendicular to the axis of the internal thread. The intersection point of the adduction straight line section and the inner crest straight line section and the outer tooth side straight line section and the contact point are located on the side, closer to the axis of the outer thread, of the middle point of the outer tooth side straight line section, or the intersection point of the adduction straight line section and the inner crest straight line section is in arc contact with the outer tooth bottom, and the contact point is closer to the tooth bottom of the outer thread; the force arm between the contact point and the external thread root is shorter, so that the torque borne by the external thread tooth is reduced, the opening effect of the internal thread tooth on the external thread tooth can be weakened, the stress concentration of the external thread root is reduced, and the fatigue performance of the external thread is improved.

Description

Technical Field

[0001] The invention relates to an arc thread connection pair, belonging to the technical field of thread connection. Background Art

[0002] The fatigue performance of threads is an important indicator related to the safety and reliability of threaded connection pairs, especially in applications where they are subjected to alternating loads, the fatigue performance of threads is even more important. In order to improve the fatigue performance of threads, the Chinese utility model patent with the authorization announcement number CN209818480U discloses a high-strength arc thread connection pair, which includes a bolt and a nut, and the external thread on the bolt and the internal thread on the nut are both arc threads. The tooth profile angle of the external thread is equal to the tooth profile angle of the internal thread, both of which are 60°. The tooth profile of the external thread includes an external thread bottom arc (referred to as the external thread bottom arc), an external thread tooth side straight line segment (referred to as the external thread side straight line segment), an external thread tooth top arc (i.e., external thread tooth top), and an external thread tooth side straight line segment, and the external thread tooth side straight line segment is tangent to the external thread tooth bottom arc and the external thread tooth top arc, respectively. The tooth profile of the internal thread includes the internal thread bottom arc (referred to as the internal thread bottom arc), the internal thread tooth side straight line segment (referred to as the internal tooth side straight line segment), the internal thread tooth top straight line segment (referred to as the internal tooth top straight line segment), and the internal thread tooth side straight line segment connected in sequence. The internal thread tooth side straight line segment is tangent to the internal thread tooth bottom arc.

[0003] When the aforementioned arc thread connection pair is in use, when the external and internal threads are subjected to load, the outer and inner straight segments simultaneously contact each other, and the equivalent point of action of the external and internal threads (because the outer and inner straight segments fit together, the equivalent point of action can be considered the midpoint of the outer and inner straight segments) is relatively closer to the crest of the external thread. Assuming the external thread is considered a cantilever beam, the distance from the equivalent point of action to the root of the external thread is the equivalent effective arm. The equivalent effective arm has a certain length, causing the external thread to be subjected to a greater torque, which in turn causes the internal thread to exert a greater opening effect on the external thread. This opening effect causes significant stress concentration at the root of the external thread, resulting in poor fatigue performance and susceptibility to fatigue fracture. Summary of the Invention

[0004] The purpose of the present invention is to provide two circular arc thread connection pairs to solve the problem of poor fatigue performance of the external threads in the existing circular arc thread connection pairs.

[0005] To achieve the above objectives, one of the arc thread connection pairs in the present invention adopts the following technical solutions:

[0006] A circular arc thread connection pair includes an internal thread and an external thread that cooperate with each other and are both circular arc threads. The tooth profile of the internal thread includes an inner tooth bottom circular arc, an inner tooth side straight line segment, an inner tooth top straight line segment and an inner tooth side straight line segment connected in sequence. The tooth profile of the external thread includes an outer thread top, an outer tooth side straight line segment, an outer tooth bottom circular arc and an outer tooth side straight line segment connected in sequence. The angle between the outer tooth side straight line segment and a plane perpendicular to the axis of the external thread is In the tooth profile of the internal thread, at least the straight line segments of the internal tooth side near one axial end have an angle with the plane perpendicular to the axis of the internal thread of less than The intersection of the inward-retracted straight line segment and the inner tooth top straight line segment contacts the outer tooth side straight line segment, and the contact point is located on the side of the midpoint of the outer tooth side straight line segment closer to the external thread axis.

[0007] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further defines the angle between the straight line segment on the outer tooth side and the plane perpendicular to the axis of the external thread as In the tooth profile of the internal thread, at least the straight line segments of the internal tooth side near one axial end have an angle with the plane perpendicular to the axis of the internal thread of less than The inward-retracted straight line segment, due to the small angle of the inward-retracted straight line segment, can no longer fit in contact with the outer tooth side straight line segment, but the intersection of the inward-retracted straight line segment and the inner tooth top straight line segment contacts the outer tooth side straight line segment, and the contact point is located on the side of the midpoint of the outer tooth side straight line segment that is closer to the axis of the external thread, that is, the contact point between the internal thread and the external thread is closer to the tooth bottom of the external thread, and the force arm between the contact point and the tooth bottom of the external thread is shorter, so that the torque borne by the external thread tooth is reduced, which can weaken the opening effect of the internal thread tooth on the external thread tooth, reduce the stress concentration at the tooth bottom of the external thread tooth, and improve the fatigue performance of the external thread.

[0008] At the same time, the tooth width of the external thread at the contact point is larger and the rigidity is greater, and the inward straight line segment reduces the average tooth width of the internal thread and reduces the rigidity of the internal thread. Therefore, when the internal and external threads are subjected to alternating loads, the external thread is less likely to deform, but the internal thread is more likely to deform to absorb the inertia force between the internal and external threads, thereby reducing the average stress at the bottom of the external thread and improving the fatigue performance of the external thread.

[0009] Furthermore, the angle between the inward straight line segment and the plane perpendicular to the internal thread axis is defined as but

[0010] Furthermore, each inner tooth side straight line segment close to one axial end and each inner tooth side straight line segment close to the other axial end in the tooth profile of the internal thread are both the inward-retracted straight line segments, and adjacent inward-retracted straight line segments are symmetrical.

[0011] Furthermore, the pitch of both the external and internal threads is defined as P, and the radius of the inner tooth bottom arc is defined as r.

[0012]

[0013] Furthermore, the minor diameter of the internal thread is defined as D1, the minor diameter of the external thread is defined as d1, and the major diameter is defined as d.

[0014]

[0015] To achieve the above-mentioned purpose, another circular arc thread connection pair in the present invention adopts the following technical solution:

[0016] A circular arc thread connection pair, comprising an internal thread and an external thread that cooperate with each other and are both circular arc threads, wherein the tooth profile of the internal thread comprises an inner tooth bottom circular arc, an inner tooth side straight line segment, an inner tooth top straight line segment and an inner tooth side straight line segment connected in sequence, and the tooth profile of the external thread comprises an outer thread top, an outer tooth side straight line segment, an outer tooth bottom circular arc and an outer tooth side straight line segment connected in sequence, wherein the angle between the outer tooth side straight line segment and a plane perpendicular to the axis of the external thread is In the tooth profile of the internal thread, at least the straight line segments of the internal tooth side near one axial end have an angle with the plane perpendicular to the axis of the internal thread of less than The intersection of the inward straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc, and the width of the inner tooth top straight line segment is defined as C n , the radius of the outer tooth bottom arc is R1, the minor diameter of the internal thread is D1, and the minor diameter of the external thread is d1, then

[0017] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further defines the angle between the straight line segment on the outer tooth side and the plane perpendicular to the axis of the external thread as In the tooth profile of the internal thread, at least the straight line segments of the internal tooth side near one axial end have an angle with the plane perpendicular to the axis of the internal thread of less than The inward straight line segment, due to the small angle of the inward straight line segment, the inward straight line segment can no longer fit in contact with the outer tooth side straight line segment, but the intersection of the inward straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc, and it also limits To ensure that the internal and external threads can fit together normally, since the contact point between the internal and external threads is closer to the bottom of the external thread, the force arm between the contact point and the bottom of the external thread is shorter, which reduces the torque borne by the external thread, weakens the opening effect of the internal thread on the external thread, reduces the stress concentration at the bottom of the external thread, and improves the fatigue performance of the external thread.

[0018] At the same time, the tooth width of the external thread at the contact point is larger and the rigidity is greater, and the inward straight line segment reduces the average tooth width of the internal thread and reduces the rigidity of the internal thread. Therefore, when the internal and external threads are subjected to alternating loads, the external thread is less likely to deform, but the internal thread is more likely to deform to absorb the inertia force between the internal and external threads, thereby reducing the average stress at the bottom of the external thread and improving the fatigue performance of the external thread.

[0019] Furthermore, the angle between the inward straight line segment and the plane perpendicular to the internal thread axis is defined as but

[0020] Furthermore, each inner tooth side straight line segment close to one axial end and each inner tooth side straight line segment close to the other axial end in the tooth profile of the internal thread are both the inward-retracted straight line segments, and adjacent inward-retracted straight line segments are symmetrical.

[0021] Furthermore, the pitch of both the external and internal threads is defined as P, and the radius of the inner tooth bottom arc is defined as r. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the tooth profile of the external thread in the first embodiment of the circular arc thread connection pair of the present invention;

[0023] Figure 2 Schematic diagram of the tooth profile of the internal thread in the first embodiment of the circular arc thread connection pair of the present invention;

[0024] Figure 3 Schematic diagram of the tooth profile matching between the internal thread and the external thread in the first embodiment of the circular arc thread connection pair of the present invention;

[0025] Figure 4 Schematic diagram of the equivalent action point of the external thread in the first embodiment of the circular arc thread connection pair of the present invention;

[0026] Figure 5 Schematic diagram of the calibration position of the external thread in the first embodiment of the circular arc thread connection pair of the present invention;

[0027] Figure 6 The internal thread 1 in the first embodiment of the arc thread connection pair of the present invention n Schematic diagram of the calculation;

[0028] Figure 7 This is a graph showing the change in average stress over time at a designated position of seven types of external threads under alternating loads in the first embodiment of the circular arc thread connection pair of the present invention;

[0029] Figure 8This is a graph showing the variation of the average stress at the calibrated position of the external thread in the first embodiment of the circular arc thread connection pair under the action of an alternating load at the loading time of 0.0025s as a function of the tooth profile half-angle difference θ;

[0030] Figure 9 The load ratio of each thread circle of the four types of external threads in the first embodiment of the circular arc thread connection pair of the present invention under the action of alternating load at the loading time of 0.0025s;

[0031] Figure 10 Schematic diagram of the tooth profile matching of the internal thread and the external thread in the second embodiment of the circular arc thread connection pair of the present invention;

[0032] Figure 11 This is a graph showing the average stress variation over time at the calibrated position of seven types of external threads under alternating loads in the second embodiment of the circular arc thread connection pair of the present invention;

[0033] Figure 12 This is a graph showing the variation of the average stress at the calibrated position of the external thread in the second embodiment of the circular arc thread connection pair under the action of an alternating load at the loading time of 0.0025s as a function of the tooth profile half-angle difference θ;

[0034] Figure 13 It is the load ratio of each thread circle of the four types of external threads in the first embodiment of the circular arc thread connection pair of the present invention under the action of alternating load at the loading time of 0.0025s.

[0035] In the figure: 1, external thread; 11, external thread top; 12, external tooth side straight segment; 13, external tooth bottom arc; 2, internal thread; 21, internal tooth bottom arc; 22, internal tooth side straight segment; 23, internal tooth top straight segment. DETAILED DESCRIPTION

[0036] In response to the technical problems existing in the prior art, the basic concept of the present invention is to change the tooth profile angle of the internal thread so that the straight line segment on the inner tooth side is retracted inward to form an inward straight line segment. The angle between the inward straight line segment and the plane perpendicular to the axis of the internal thread is smaller than the angle between the straight line segment on the outer tooth side and the plane perpendicular to the axis of the external thread, so that the intersection of the inward straight line segment and the straight line segment on the inner tooth top contacts the straight line segment on the outer tooth side or the arc of the outer tooth bottom, the contact point is closer to the tooth bottom of the external thread, and the force arm between the contact point and the tooth bottom of the external thread is shorter, so that the torque borne by the external thread tooth is reduced, the stress concentration at the tooth bottom of the external thread is reduced, and the fatigue performance of the external thread is improved.

[0037] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0038] Implementation method 1 of the arc thread connection pair in the present invention:

[0039] like Figure 5As shown, a circular arc thread connection pair includes an outer thread 1 and an inner thread 2, both of which are circular arc threads. The outer thread 1 is provided on a bolt or stud, and the inner thread 2 is provided on a nut. Therefore, the circular arc thread connection pair can be a common bolt connection pair consisting of a bolt and a nut, a high-strength bolt connection pair consisting of a bolt, a nut, and a washer, or a stud connection pair consisting of a stud and nuts at both ends.

[0040] like Figure 1 As shown, the tooth profile of the external thread 1 includes an external thread crest 11, an external flank straight segment 12, an external root arc 13, and an external flank straight segment 12, which are connected in sequence. In this embodiment, the external thread crest 11 is arc-shaped, and the external flank straight segment 12 is tangent to the external thread crest 11 and the external root arc 13, respectively. In other embodiments, the external thread crest 11 may also extend in a straight line, in which case the external flank straight segment 12 is tangent only to the external root arc 13.

[0041] The angle α between two adjacent outer tooth side straight segments 12 is the tooth profile angle of the external thread, and the range of α is: 40° to 80°, and is generally preferably 60°. Therefore, the angle between the outer tooth side straight segment 12 and the plane perpendicular to the axis of the external thread is It can also be called the half angle of the external thread. The range is 20° to 40°, with 30° being preferred. Furthermore, the external thread has a pitch of P, a minor diameter of d1, a major diameter of d, a radius of the external thread bottom arc 13 of R1, and a radius of the external thread crest 11 of R2. In reality, the structure of the external thread is based on prior art, and the present invention does not improve upon the external thread.

[0042] like Figure 2 As shown, the tooth profile of the internal thread 2 includes an inner tooth bottom arc 21, an inner tooth side straight line segment 22, an inner tooth top straight line segment 23 and an inner tooth side straight line segment 22 connected in sequence, wherein the inner tooth side straight line segment 22 is tangent to the inner tooth bottom arc 21. In this embodiment, two adjacent inner tooth side straight line segments 22 are symmetrical, and the angle β between the two adjacent inner tooth side straight line segments 22 is the tooth profile angle of the internal thread, so the angle between the inner tooth side straight line segment 22 and the plane perpendicular to the axis of the internal thread is It can also be called the half angle of the internal thread. In addition, the pitch of the internal thread is also P, the minor diameter is D1, the major diameter is D, and the width of the inner tooth top straight section 23 is C n , the radius of the inner tooth bottom arc 21 is r.

[0043] like Figure 3 As shown, Since the tooth profile half angles of the internal and external threads are different, the inner tooth side straight segment 22 can no longer fit with the outer tooth side straight segment 12. The inner tooth side straight segment 22 is equivalent to being retracted inward to form an inward straight segment. Moreover, since the two adjacent inner tooth side straight segments 22 are symmetrical, the inner tooth side straight segments 22 near one axial end and the inner tooth side straight segments 22 near the other axial end of the tooth profile of the internal thread in this embodiment are all formed into inward straight segments. In this way, there is no need to consider the front and back when installing the nut. In other embodiments, only the inner tooth side straight segments near one axial end can be inward straight segments, while the inner tooth side straight segments near the other axial end are not retracted and remain parallel to the corresponding outer tooth side straight segments 12. That is, the adjacent inner tooth side straight segments are not symmetrical. In this case, during installation and use, it is necessary to ensure that the side of the internal thread that is in contact with the external thread and is subjected to force is the side provided with the inward straight segment.

[0044] like Figure 3 As shown, the intersection of the inner tooth side straight segment 22 and the inner tooth top straight segment 23 contacts the outer tooth side straight segment 12, and the contact point is located on the side of the midpoint of the outer tooth side straight segment 12 that is closer to the external thread axis. Figure 4 As shown, the contact point F1 between the internal thread and the external thread in the present invention is closer to the root of the external thread (F2 in the figure is the equivalent action point of the internal thread and the external thread before the improvement), and the force arm between the contact point F1 and the root of the external thread is shorter, so that the torque borne by the external thread is reduced, which can weaken the opening effect of the internal thread on the external thread, reduce the stress concentration at the root of the external thread, and improve the fatigue performance of the external thread.

[0045] At the same time, the tooth width of the external thread at the contact point F1 is larger and the rigidity is greater, and the straight line segment 22 on the inner tooth side is retracted, so that the average tooth width of the internal thread is reduced and the rigidity of the internal thread is reduced. Therefore, when the internal and external threads are subjected to alternating loads, the external thread is less likely to deform, but the internal thread is more likely to deform to absorb the inertia force between the internal and external threads, thereby reducing the average stress at the bottom of the external thread and improving the fatigue performance of the external thread.

[0046] In addition, the load borne by the first three threads of the existing equidistant thread connection pair near the support surface (taking the bolt and nut as an example, the support surface is the end surface of the nut used to compress the connected parts) accounts for 70% of the total load, and the first thread carries the largest load. Because the intersection of the inner tooth side straight segment 22 and the inner tooth top straight segment 23 preferentially contacts the outer tooth side straight segment 12, the stiffness of the internal thread at the contact point is much smaller than that of the external thread. As the axial force of the bolt increases, the internal thread of the present invention is more prone to elastic deformation compared to the existing arc thread structure, especially the first thread. When the internal thread of the present invention and the existing internal thread undergo the same deformation, the stiffness of the internal thread of the present invention is smaller, and the load generated by the first thread of the internal and external threads is smaller. Since the total load between the entire thread is constant, the load on the first thread is reduced, and the load on the other threads is bound to increase accordingly. This can improve the load uniformity of the thread and further enhance the fatigue performance of the thread.

[0047] In order to ensure that there is a certain overlap rate between the internal and external threads, avoid the phenomenon of the internal and external threads being stripped due to the overlap rate being too small, and improve the safety of use, the embodiment of the present invention defines For the case where the external thread crest 11 is an arc and the arc radius is equal to the radius of the external thread bottom arc 13, the midpoint of the external thread side straight line segment 12 is also the midpoint of the entire external thread in the radial direction. The limitation of the contact point between the internal and external threads is located on the side closer to the external thread axis than the midpoint of the external tooth side straight segment 12. However, when the external thread crest 11 is a straight segment, the midpoint of the external tooth side straight segment 12 is not the radial midpoint of the entire external thread. The midpoint of the external tooth side straight segment 12 is located on the side of the radial midpoint of the entire external thread away from the external thread axis. The limitation can ensure the most basic overlap rate between the internal and external threads and avoid the phenomenon of stripping.

[0048] In actual applications, the internal and external threads are in point contact at the beginning. However, due to the low rigidity of the internal thread teeth, deformation is easy to occur. Therefore, as the load continues to increase, the internal and external thread teeth may change from point contact to partial contact, so that there is a certain contact area between the internal and external thread teeth, which can prevent the internal and external thread teeth from generating large contact stresses. Therefore, in order to ensure that the internal and external thread teeth can change from point contact to partial contact, the difference between α and β should not be too large. In this embodiment, α-β < 30°, that is, In other embodiments, and The difference can also be smaller than 16°, 15.5°, 14° or 14.5°.

[0049] like Figure 3As shown, the angle between the outer tooth side straight segment 12 and the inner tooth side straight segment 22 is defined as θ. According to the geometric relationship, it can be seen that: After simplification, we can get θ is the difference between the half angles of the internal and external threads.

[0050] Furthermore, although the internal thread is more easily deformed, it can absorb the inertia force between the internal and external threads, reduce the average stress at the bottom of the external thread, and improve the fatigue performance of the external thread. However, if the rigidity of the internal thread is too small, the thread may break or severely yield. Therefore, from the perspective of thread safety, the thickness of the internal thread cannot be too small. Figure 6 As shown, l n is the thickness at the intersection of the inner tooth bottom arc and the inner tooth side straight line segment. From the geometric relationship, we can know that This embodiment determines l based on experience n >0.2P, so In other embodiments, it is possible to take n is greater than 0.18P, 0.19P, 0.21P or 0.22P, and different relationship equations for r, β, and P are obtained.

[0051] To demonstrate the superiority of the circular arc thread connection pair in this embodiment, seven thread pair structures are described below. Their specific thread parameters are shown in Table 1. Comparative Thread Pair 1 is a conventional circular arc thread connection pair, with both internal and external thread profile angles of 60°. The profile parameters of the external threads in Thread Pairs 1 through 6 are identical to those of conventional external circular arc threads. The profile parameters of the internal threads, except for the profile angle, are identical to those of conventional internal circular arc threads.

[0052] Table 1 Thread structure parameters in embodiment 1

[0053]

[0054]

[0055] According to the above 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 applied to the bolt or stud. Under the same alternating load, the dynamic analysis results of the 7 types of external threads at the calibration position (calibration position is Figure 5 The red position in the figure is the first thread position, which is usually the position where the stress is most concentrated. The average stress at this position changes with time, as shown in the figure. Figure 7As shown in the figure, at each loading moment, the average stress of the external threads in thread pairs 1 to 6 at the calibrated position is lower than the average stress of the external threads in comparison thread pair 1 at the calibrated position. This indicates that by reducing the tooth angle of the internal thread and making the intersection of the inner tooth side straight segment and the inner tooth top straight segment contact the outer tooth side straight segment, the stress concentration at the root of the external thread is indeed reduced, which is consistent with the above theoretical analysis results.

[0056] At the same time from Figure 7 It can also be seen that with the increase of the half-angle difference θ between the internal and external thread profiles, the average stress generated at the bottom of the external thread at different loading times gradually decreases. Figure 8 The figure shows the change curve of the average stress at the calibration position at the loading time of 0.0025s as a function of the tooth profile half-angle difference θ. It can be seen from the figure that when the tooth profile half-angle difference θ is greater than 15°, the average stress at the root of the external thread changes little, and further increasing the difference θ has limited effect on reducing the average stress at the root of the tooth. In addition, as the tooth profile half-angle difference θ continues to increase, obvious tip contact will occur between the internal and external threads, which will generate greater contact stress between the internal and external threads, thereby reducing the fatigue performance of the thread. Therefore, this embodiment takes θ < 15° based on this consideration.

[0057] Figure 9 The figure shows the load ratio of each thread circle of the four types of external threads under the action of alternating load at the loading time of 0.0025s. It can be seen from the figure that compared with the comparison thread pair 1 (θ = 0°), the load distribution of each thread circle of the three external threads with θ = 5°, 10° and 15° is more uniform, and the larger θ is, the better the load uniformity. The improvement of load uniformity is helpful to improve the fatigue performance of the external thread.

[0058] Implementation method 2 of the arc thread connection pair in the present invention:

[0059] The difference between the second embodiment and the first embodiment lies in the contact position of the internal thread and the external thread. In the second embodiment, Figure 10 As shown, line segment AB is the outer tooth side straight line segment 12, point B is the tangent point of the outer tooth side straight line segment 12 and the outer tooth bottom arc 13, the intersection of the inner tooth side straight line segment 22 (i.e., the inward straight line segment) and the inner tooth top straight line segment 23 contacts the outer tooth bottom arc 13, and the contact point is C. Compared with implementation mode one, the contact point of the internal and external threads in implementation mode two is closer to the tooth bottom of the external thread, so the force arm between the contact point and the tooth bottom of the external thread is shorter, so that the torque borne by the external thread is reduced, which can weaken the opening effect of the internal thread on the external thread, reduce the stress concentration at the tooth bottom of the external thread, and improve the fatigue performance of the external thread.

[0060] At the same time, the tooth width of the external thread at the contact point is larger and the rigidity is greater. When the internal and external threads are subjected to alternating loads, the external thread is less likely to deform, while the internal thread is more likely to deform to absorb the inertial force between the internal and external threads, thereby reducing the average stress at the bottom of the external thread and improving the fatigue performance of the external thread. At the same time, because the internal thread is more susceptible to elastic deformation, especially the first circle of threads, when the internal thread of the present invention and the existing internal thread undergo the same amount of deformation, the rigidity of the internal thread of the present invention is smaller, and the load generated by the first circle of internal and external threads is smaller. Since the total load between the entire thread is constant, the load on the first circle of threads is reduced, and the corresponding load on the other circles of threads is bound to increase. This can improve the load uniformity of the thread and further improve the fatigue performance of the thread.

[0061] In order to ensure that the internal and external threads can contact normally in structure, and the contact point is on the arc of the external tooth bottom, such as Figure 10 As shown, the width C of the inner tooth top straight line segment 23 must be ensured. n ≤CC', where C is the contact point of the internal and external threads, and C' is the intersection of the extension line of the internal tooth top straight line segment 23 and the external tooth bottom arc 13. Otherwise, if C n >CC', the inner tooth top straight section 23 cannot be accommodated between CC', and the internal and external threads cannot match.

[0062] In addition, point O in the figure is the center of the outer tooth bottom arc 13, OE is perpendicular to the axis of the external thread, point E is on the outer tooth bottom arc 13, OE is perpendicular to CC', and OE and CC' intersect at point F, OC = OE = R1. According to the geometric relationship, we can know that: so

[0063] The remaining structures and parameters in the second embodiment are the same as those in the first embodiment, including the tooth profile half-angle difference θ between the internal and external threads, the thickness at the intersection of the inner tooth bottom arc and the inner tooth side straight line segment, etc., which will not be repeated here.

[0064] To demonstrate the superiority of the circular arc thread connection pair in this embodiment, seven thread pair structures are described below. Their specific thread parameters are shown in Table 2. Comparative thread pair 2 is a conventional circular arc thread connection pair, with both internal and external thread profile angles of 60°. The profile parameters of the external threads in thread pairs 7 through 12 are identical to those of conventional external circular arc threads. The profile parameters of the internal threads, except for the profile angle, are identical to those of conventional internal circular arc threads.

[0065] Table 2 Thread structure parameters in embodiment 2

[0066]

[0067] Based on the above parameters, a 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 applied to the bolt or stud. Under the same alternating load, the average stress variation curve of the seven types of external threads at the calibration position (the calibration position is the same as in embodiment 1) is obtained. Figure 11 As shown in the figure, at each loading moment, the average stress of the external threads in thread pairs 7 to 12 at the calibrated position is lower than the average stress of the external threads in comparison thread pair 2 at the calibrated position. This indicates that by reducing the tooth profile angle of the internal thread, the intersection of the inner tooth side straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc, which indeed reduces the stress concentration at the outer thread root, which is consistent with the above theoretical analysis results.

[0068] At the same time from Figure 11 It can also be seen that with the increase of the half-angle difference θ between the internal and external thread profiles, the average stress generated at the bottom of the external thread at different loading times gradually decreases. Figure 12 The figure shows the curve of the average stress at the calibration position at the loading time of 0.0025s as a function of the tooth profile half-angle difference θ. It can be seen from the figure that when the tooth profile half-angle difference θ is greater than 15°, the average stress at the root of the external thread changes little, and further increasing the difference θ has limited effect on reducing the average stress at the root of the tooth. In addition, as the tooth profile half-angle difference θ continues to increase, obvious tip contact will occur between the internal and external threads, which will generate greater contact stress between the internal and external threads, thereby reducing the fatigue performance of the thread. Therefore, taking θ < 15° is based on this consideration.

[0069] Figure 13 The figure shows the load ratio of each thread circle of the four types of external threads under the action of alternating load at the loading time of 0.0025s. It can be seen from the figure that compared with the comparison thread pair 2 (θ = 0°), the load distribution of each thread circle of the three external threads with θ = 5°, 10° and 15° is more uniform, and the larger θ is, the better the load uniformity. The improvement of load uniformity is helpful to improve the fatigue performance of the external thread.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the description and drawings of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A circular arc thread connection pair, comprising an internal thread and an external thread that cooperate with each other and are both circular arc threads, wherein the thread profile of the internal thread comprises an inner tooth bottom circular arc, an inner tooth side straight line segment, an inner tooth top straight line segment, and an inner tooth side straight line segment connected in sequence, and the thread profile of the external thread comprises an outer thread top, an outer tooth side straight line segment, an outer tooth bottom circular arc, and an outer tooth side straight line segment connected in sequence, characterized in that: The angle between the straight line segment on the external tooth side and the plane perpendicular to the axis of the external thread is In the tooth profile of the internal thread, at least the straight line segments of the internal tooth side near one axial end have an angle with the plane perpendicular to the axis of the internal thread of less than The intersection of the inward-retracted straight line segment and the inner tooth top straight line segment contacts the outer tooth side straight line segment, and the contact point is located on the side of the midpoint of the outer tooth side straight line segment closer to the external thread axis.

2. The arc thread connection pair according to claim 1, characterized in that: The angle between the inward straight line segment and the plane perpendicular to the internal thread axis is but 3. The arc thread connection pair according to claim 1 or 2, characterized in that: In the tooth profile of the internal thread, each inner tooth side straight line segment close to one axial end and each inner tooth side straight line segment close to the other axial end are both inward-retracted straight line segments, and adjacent inward-retracted straight line segments are symmetrical.

4. The arc thread connection pair according to claim 3, characterized in that: The pitch of both the external and internal threads is P, and the radius of the inner tooth bottom arc is r, then 5. The arc thread connection pair according to claim 1 or 2, characterized in that: The minor diameter of the internal thread is D1, the minor diameter of the external thread is d1, and the major diameter is d, then 6. A circular arc thread connection pair, comprising an internal thread and an external thread that cooperate with each other and are both circular arc threads, the internal thread profile comprising an inner tooth bottom circular arc, an inner tooth side straight segment, an inner tooth top straight segment, and an inner tooth side straight segment connected in sequence, and the external thread profile comprising an outer thread top, an outer tooth side straight segment, an outer tooth bottom circular arc, and an outer tooth side straight segment connected in sequence, characterized in that: The angle between the straight line segment on the external tooth side and the plane perpendicular to the axis of the external thread is In the tooth profile of the internal thread, at least the straight line segments of the internal tooth side near one axial end have an angle with the plane perpendicular to the axis of the internal thread of less than The intersection of the inward straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc, and the width of the inner tooth top straight line segment is defined as C n , the radius of the outer tooth bottom arc is R1, the minor diameter of the internal thread is D1, and the minor diameter of the external thread is d1, then 7. The arc thread connection pair according to claim 6, characterized in that: The angle between the inward straight line segment and the plane perpendicular to the internal thread axis is but 8. The arc thread connection pair according to claim 6 or 7, characterized in that: In the tooth profile of the internal thread, each inner tooth side straight line segment close to one axial end and each inner tooth side straight line segment close to the other axial end are both inward-retracted straight line segments, and adjacent inward-retracted straight line segments are symmetrical.

9. The arc thread connection pair according to claim 8, characterized in that: The pitch of both the external and internal threads is P, and the radius of the inner tooth bottom arc is r, then

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