Threaded connection pair and internal thread

Abstract

The invention provides a threaded connection pair and an internal thread, and belongs to the technical field of threaded connection. The thread profile of the internal thread comprises a crest, a flank, a root and a flank which are connected in sequence, the flank comprises a linear section close to the crest and a linear section close to the root, the included angle between the linear section close to the crest and the plane perpendicular to the axis of the internal thread is 30 degrees, the included angle between the linear section close to the root and the plane perpendicular to the axis of the internal thread is beta, beta is larger than 0 degree and smaller than 30 degrees, and beta is larger than 0 degree and smaller than 30 degrees. The height of the straight section close to the crest in the radial direction of the internal thread is hp, the thread pitch of the internal thread is P, the thread height of the internal thread is hn, and hp is larger than or equal to 0.075 P and smaller than hn. The equivalent action points of the internal thread teeth and the external thread teeth are closer to the tooth bottoms of the external threads, the tooth widths and the rigidity of the external thread teeth at the equivalent action points are larger, meanwhile, equivalent force arms from the equivalent action points to the tooth bottoms of the external threads are shorter, the torque borne by the external thread teeth is reduced, the opening effect of the internal thread teeth on the external thread teeth can be weakened, and the service life of the internal thread teeth is prolonged. External thread root stress concentration is reduced, and the fatigue performance of the external threads is improved.

Description

Technical Field

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

[0002] Metric thread and MJ thread are currently the most widely used thread connection structures. The tooth profiles of standard metric internal thread and MJ internal thread are the same, such as Figure 1 As shown, the tooth profile of the internal thread includes the tooth top 11, the tooth side straight line segment 12, the tooth bottom 13, and the tooth side straight line segment 2 14 connected in sequence. In the figure, D is the major diameter of the internal thread, D2 is the middle diameter of the internal thread, D1 is the minor diameter of the internal thread, P is the pitch, and h is the pitch. n C is the internal thread height, n is the tooth top width, α w is the tooth profile angle, that is, the angle between the tooth side straight line segment 12 and the tooth side straight line segment 2 14, tooth profile angle α w is 60°.

[0003] External threads are compatible with internal threads, and the external thread profile angle is also 60°. The thread height is equal to the internal thread height. Therefore, when the internal and external threads are subjected to load, the straight segments of the internal and external threads contact simultaneously, making the equivalent application point of the internal and external threads closer to the external thread crest. If the external thread is regarded as a cantilever beam, the distance between the equivalent application point and the external thread root is the equivalent effective arm. The equivalent effective arm has a certain length, causing the external thread to be subjected to a larger torque, which in turn causes the internal thread to exert a greater opening effect on the external thread, resulting in significant stress concentration at the external thread root.

[0004] At the same time, since the equivalent action points of the internal and external threads are closer to the top of the external thread, and the tooth width at the top of the external thread is smaller, the tooth width of the internal thread at the equivalent action point is larger, resulting in the stiffness of the external thread being smaller than that of the internal thread. When the internal and external threads are subjected to alternating loads, the inertia force between the internal and external threads is in an unbalanced state. The external thread with smaller thread stiffness acts as an energy absorption box for the internal thread with larger stiffness, absorbing the inertia force between the internal and external threads, which increases the average stress at the bottom of the external thread, resulting in poor fatigue performance of the external thread. Summary of the Invention

[0005] The purpose of the present invention is to provide an internal thread to solve the problem that the existing internal thread causes poor fatigue performance of the external thread; the purpose of the present invention is also to provide a threaded connection pair to solve the above problem.

[0006] To achieve the above purpose, the internal thread in the present invention adopts the following technical solutions:

[0007] An internal thread, which is a metric thread or an MJ thread, wherein the tooth profile of the internal thread includes a crest, a flank, a root, and a flank connected in sequence, at least one flank in the tooth profile includes a near-crest straight line segment and a near-bottom straight line segment connected at an angle, the near-crest straight line segment is connected to the crest, the near-bottom straight line segment is connected to the bottom, the angle between the near-crest straight line segment and a plane perpendicular to the axis of the internal thread is α, α=30°, the angle between the near-bottom straight line segment and a plane perpendicular to the axis of the internal thread is β, 0°<β<30°, and the height of the near-crest straight line segment in the radial direction of the internal thread is h p , the pitch of the internal thread is P, and the tooth height of the internal thread is h n , 0.075P≤h p <h n .

[0008] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further defines the tooth profile structure of the internal thread, and at least one tooth side in the tooth profile includes a near-tooth top straight line segment and a near-tooth bottom straight line segment connected at an angle, the angle between the near-tooth top straight line segment and the plane perpendicular to the axis of the internal thread is α, α=30°, and the angle between the near-tooth bottom straight line segment and the plane perpendicular to the axis of the internal thread is β, 0°<β<30°. In this way, when the internal thread is used with a standard metric external thread or MJ external thread, only the near-tooth top straight line segment of the internal thread contacts the tooth side straight line segment of the external thread, while the near-tooth bottom straight line segment does not contact the tooth side straight line segment of the external thread, and the present invention limits the height of the near-tooth top straight line segment in the radial direction of the internal thread to h p , the pitch of the internal thread is P, and the tooth height of the internal thread is h n , 0.075P≤h p <h n , ensuring that the straight line segment near the tooth top has a certain height to meet the normal contact requirements with the external thread teeth, so that the equivalent action point between the internal and external thread teeth is closer to the tooth bottom position of the external thread. Therefore, the equivalent force arm between the equivalent action point and the tooth bottom of the external thread is shorter, which reduces the torque borne by the external thread teeth, weakens the opening effect of the internal thread teeth on the external thread teeth, and reduces the stress concentration at the tooth bottom of the external thread teeth. At the same time, the closer the equivalent action point is to the tooth bottom of the external thread, the larger the tooth width of the external thread teeth at the equivalent action point, and the greater the stiffness of the external thread teeth. The tooth width of the internal thread at the equivalent action point becomes smaller, and the overall average tooth width of the internal thread becomes smaller. The stiffness of the internal thread teeth is reduced, which can weaken the role of the external thread teeth as an energy absorption box, and even make the internal thread teeth act as an energy absorption box for the external thread teeth, effectively reducing the average stress at the tooth bottom of the external thread teeth and improving the fatigue performance of the external thread.

[0009] Furthermore, the internal thread is a metric thread, 0.075P≤h p ≤0.47P.

[0010] Furthermore, the internal thread is an MJ thread, 0.075P≤h p ≤0.4P.

[0011] Furthermore, 0.075P≤h p ≤0.2P.

[0012] Furthermore, 0°<β≤25°.

[0013] Furthermore, each tooth side near one axial end in the tooth profile of the internal thread is a single straight line segment, and the angle between each single straight line segment and the plane perpendicular to the axis of the internal thread is 30°. Each tooth side near the other axial end in the tooth profile of the internal thread includes the aforementioned straight line segment near the top of the tooth and the straight line segment near the bottom of the tooth, and the angle between the straight line segment near the bottom of each tooth side and the plane perpendicular to the axis of the internal thread is equal.

[0014] Furthermore, each tooth flank close to one axial end and each tooth flank close to the other axial end in the tooth profile of the internal thread includes the aforementioned straight line segment near the tooth top and the straight line segment near the tooth bottom, and adjacent tooth flanks are symmetrical.

[0015] Furthermore, The crest width of the internal thread is C n ,

[0016] Furthermore, The crest width of the internal thread is C n ,

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

[0018] A threaded connection pair comprises an internal thread and an external thread used in conjunction with the internal thread, the external thread being a standard metric thread or MJ thread, the internal thread being an improved metric thread or MJ thread, the tooth profile of the internal thread comprising a crest, a flank, a root and a flank connected in sequence, at least one flank in the tooth profile comprising a near-crest straight line segment and a near-root straight line segment connected at an angle, the near-crest straight line segment being connected to the crest, the near-root straight line segment being connected to the root, the angle between the near-crest straight line segment and a plane perpendicular to the axis of the internal thread being α, α=30°, the angle between the near-root straight line segment and a plane perpendicular to the axis of the internal thread being β, 0°<β<30°, and the height of the near-crest straight line segment in the radial direction of the internal thread being h p , the pitch of the internal thread is P, and the tooth height of the internal thread is h n , 0.075P≤h p <h n .

[0019] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further defines the tooth profile structure of the internal thread, and at least one tooth side in the tooth profile includes a near-tooth top straight line segment and a near-tooth bottom straight line segment connected at an angle, the angle between the near-tooth top straight line segment and the plane perpendicular to the axis of the internal thread is α, α=30°, and the angle between the near-tooth bottom straight line segment and the plane perpendicular to the axis of the internal thread is β, 0°<β<30°. In this way, when the internal thread is used with a standard metric external thread or MJ external thread, only the near-tooth top straight line segment of the internal thread contacts the tooth side straight line segment of the external thread, while the near-tooth bottom straight line segment does not contact the tooth side straight line segment of the external thread, and the present invention limits the height of the near-tooth top straight line segment in the radial direction of the internal thread to h p , the pitch of the internal thread is P, and the tooth height of the internal thread is h n , 0.075P≤h p <h n , ensuring that the straight line segment near the tooth top has a certain height to meet the normal contact requirements with the external thread teeth, so that the equivalent action point between the internal and external thread teeth is closer to the tooth bottom position of the external thread. Therefore, the equivalent force arm between the equivalent action point and the tooth bottom of the external thread is shorter, which reduces the torque borne by the external thread teeth, weakens the opening effect of the internal thread teeth on the external thread teeth, and reduces the stress concentration at the tooth bottom of the external thread teeth. At the same time, the closer the equivalent action point is to the tooth bottom of the external thread, the larger the tooth width of the external thread teeth at the equivalent action point, and the greater the stiffness of the external thread teeth. The tooth width of the internal thread at the equivalent action point becomes smaller, and the overall average tooth width of the internal thread becomes smaller. The stiffness of the internal thread teeth is reduced, which can weaken the role of the external thread teeth as an energy absorption box, and even make the internal thread teeth act as an energy absorption box for the external thread teeth, effectively reducing the average stress at the tooth bottom of the external thread teeth and improving the fatigue performance of the external thread.

[0020] Furthermore, the internal thread is a metric thread, 0.075P≤h p ≤0.47P.

[0021] Furthermore, the internal thread is an MJ thread, 0.075P≤h p ≤0.4P.

[0022] Furthermore, 0.075P≤h p ≤0.2P.

[0023] Furthermore, 0°<β≤25°.

[0024] Furthermore, each tooth side near one axial end in the tooth profile of the internal thread is a single straight line segment, and the angle between each single straight line segment and the plane perpendicular to the axis of the internal thread is 30°. Each tooth side near the other axial end in the tooth profile of the internal thread includes the aforementioned straight line segment near the top of the tooth and the straight line segment near the bottom of the tooth, and the angle between the straight line segment near the bottom of each tooth side and the plane perpendicular to the axis of the internal thread is equal.

[0025] Furthermore, each tooth flank close to one axial end and each tooth flank close to the other axial end in the tooth profile of the internal thread includes the aforementioned straight line segment near the tooth top and the straight line segment near the tooth bottom, and adjacent tooth flanks are symmetrical.

[0026] Furthermore, The crest width of the internal thread is C n ,

[0027] Furthermore, The crest width of the internal thread is C n , BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a tooth profile diagram of metric internal thread and MJ internal thread in the prior art;

[0029] Figure 2 This is a tooth profile diagram of internal thread embodiment 1 of the present invention;

[0030] Figure 3 Schematic diagram of equivalent action points of the internal thread of the present invention and the internal thread of the prior art on the same external thread;

[0031] Figure 4 A schematic diagram of the calibration position of an external thread used in conjunction with the internal thread of the present invention;

[0032] Figure 5 This is a graph showing the change in average stress over time at a calibrated position of an external thread used in conjunction with 17 internal threads with different β values ​​under alternating loads in Example 1 of the internal thread of the present invention;

[0033] Figure 6 This is a graph showing the average stress of an external thread used in conjunction with 17 internal threads of different β values ​​at a specific loading moment as a function of β in Example 1 of the internal thread of the present invention;

[0034] Figure 7 The internal thread embodiment 1 of the present invention and 6 different h p The average stress variation with time of the external thread (major diameter 36mm, pitch 4mm) used in conjunction with the internal thread of the value under the action of alternating load at the calibration position;

[0035] Figure 8 The internal thread embodiment 1 of the present invention and the four different h p The load ratio of each thread circle of the external thread used in conjunction with the internal thread of the value under the action of alternating load at the loading time of 0.0025s;

[0036] Figure 9The internal thread embodiment 1 of the present invention and 6 different h p The average stress variation with time of the external thread (major diameter 42mm, pitch 4.5mm) used in conjunction with the internal thread of the value under the action of alternating load at the calibration position;

[0037] Figure 10 The internal thread embodiment 1 of the present invention and 6 different h p The average stress variation with time of the external thread (large diameter 48mm, pitch 5mm) used in conjunction with the internal thread of the value under the action of alternating load at the calibration position;

[0038] Figure 11 The average stress at the calibrated position at the loading time of 0.0025s in the three groups of external threads with different major diameters and pitches in the internal thread embodiment 1 of the present invention changes with h p / P change curve;

[0039] Figure 12 The average stress at the calibrated position at the loading time of 0.0075s under the action of alternating loads for three groups of external threads with different major diameters and pitches in Example 1 of the internal thread of the present invention varies with h. p / P change curve;

[0040] Figure 13 This is a tooth profile diagram of internal thread embodiment 2 of the present invention;

[0041] Figure 14 This is a graph showing the change in average stress over time at a calibrated position of an external thread used in conjunction with internal threads of 16 different β values ​​under alternating loads in Example 3 of the internal thread of the present invention;

[0042] Figure 15 This is a graph showing the average stress of an external thread used in conjunction with internal threads having 16 different β values ​​at a specific loading moment as a function of β in Example 3 of the internal thread of the present invention;

[0043] Figure 16 The internal thread embodiment 3 of the present invention and the 6 different h p The average stress variation with time of the external thread (major diameter 36mm, pitch 4mm) used in conjunction with the internal thread of the value under the action of alternating load at the calibration position;

[0044] Figure 17 The internal thread embodiment 3 of the present invention and the four different h p The load ratio of each thread circle of the external thread used in conjunction with the internal thread of the value under the action of alternating load at the loading time of 0.0025s;

[0045] Figure 18 The internal thread embodiment 3 of the present invention and the 6 different hp The average stress variation with time of the external thread (major diameter 42mm, pitch 4.5mm) used in conjunction with the internal thread of the value under the action of alternating load at the calibration position;

[0046] Figure 19 The internal thread embodiment 3 of the present invention and the 6 different h p The average stress variation with time of the external thread (large diameter 48mm, pitch 5mm) used in conjunction with the internal thread of the value under the action of alternating load at the calibration position;

[0047] Figure 20 The average stress at the calibrated position at the loading time of 0.0025s in the three groups of external threads with different major diameters and pitches in the internal thread embodiment 3 of the present invention changes with h p / P change curve;

[0048] Figure 21 The average stress at the calibrated position at the loading time of 0.0075s in the three groups of external threads with different major diameters and pitches in the internal thread embodiment 3 of the present invention changes with h p / P change curve.

[0049] In the figure: 11, tooth top; 12, tooth side straight line segment 1; 13, tooth bottom; 14, tooth side straight line segment 2; 2, tooth top; 31, straight line segment near tooth top; 32, straight line segment near tooth bottom; 4, tooth bottom; 5, single straight line segment; 61, straight line segment 1 near tooth top; 62, straight line segment 2 near tooth top; 71, straight line segment 1 near tooth bottom; 72, straight line segment 2 near tooth bottom. DETAILED DESCRIPTION

[0050] In response to the technical problems existing in the prior art, the basic concept of the present invention is to set the tooth side of the internal thread to include two sections, where only the straight line segment near the top of the tooth is in contact with the straight line segment of the tooth side of the external thread, and the straight line segment near the bottom of the tooth is not in contact with the straight line segment of the tooth side of the external thread, so that the equivalent action point between the internal and external thread teeth is closer to the bottom position of the external thread, thereby improving the fatigue performance of the external thread.

[0051] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0052] Embodiment 1 of the internal thread of the present invention:

[0053] The internal thread in this embodiment is a metric thread, and the thread profile of the internal thread is as follows: Figure 2 As shown, the tooth profile of the internal thread includes a tooth top 2, a tooth side, a tooth bottom 4 and a tooth side connected in sequence, and the tooth profile of the internal thread is toward one axial end ( Figure 2Each tooth side (towards the right end in the middle) is a single straight line segment 5, and the angle between each single straight line segment 5 and the plane perpendicular to the axis of the internal thread is 30°, that is, the single straight line segment 5 is the same as the tooth side straight line segment in the tooth profile of the standard metric thread.

[0054] The tooth line of the internal thread faces the other end of the axial direction ( Figure 2 Each tooth flank (facing the left end in the center) includes a proximal tooth crest straight line segment 31 and a proximal tooth root straight line segment 32 connected at an angle. The proximal tooth crest straight line segment 31 is connected to the tooth crest 2, and the proximal tooth root straight line segment 32 is connected to the tooth root 4. The angle between the proximal tooth crest straight line segment 31 and the plane perpendicular to the internal thread axis is α, where α = 30°. The angle between the proximal tooth root straight line segment 32 and the plane perpendicular to the internal thread axis is β, where 0° < β < 30°. The angles between the proximal tooth root straight line segment 32 and the plane perpendicular to the internal thread axis are equal on each tooth flank facing the same axial end.

[0055] The external thread used in conjunction with the internal thread of this embodiment is a standard metric thread. In the external thread profile, except for the crest and root, the rest are flank straight segments. When the internal and external threads are used together, only the crest-near straight segment 31 of the internal thread contacts the flank straight segments of the external thread, while the root-near straight segment 32 does not contact the flank straight segments of the external thread. Figure 3 As shown, the equivalent action point between the internal and external threads is closer to the root of the external thread, that is, position F1. However, the contact area between the straight line segments of the tooth flanks of the standard metric internal thread and the external thread is larger, and the equivalent action point is closer to the top of the external thread, that is, position F2.

[0056] Therefore, after the present invention improves the internal thread profile, the equivalent force arm between the equivalent action point and the external thread bottom 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 external thread bottom, reduces the stress at the external thread bottom, and improves the fatigue performance of the external thread. At the same time, the closer the equivalent action point is to the tooth bottom of the external thread, the larger the tooth width of the external thread at the equivalent action point, and the greater the rigidity of the external thread. The tooth width at the equivalent action point of the internal thread becomes smaller, and the average tooth width of the internal thread as a whole also becomes smaller, and the rigidity of the internal thread is reduced. When subjected to alternating loads, the role of the external thread as an energy absorption box can be weakened, reducing the inertial force borne by the external thread, and even making the internal thread act as an energy absorption box for the external thread, effectively reducing the average stress at the tooth bottom of the external thread and improving the fatigue performance of the external thread.

[0057] In addition, Figure 2 As shown, the major diameter of the internal thread is D, the middle diameter is D2, the minor diameter is D1, the pitch is P, and the crest width of the internal thread is C n , The tooth height of the internal thread is h n According to the geometric relationship, Therefore, the crest width C of the internal thread in this embodiment is n The same as the standard metric internal thread crest width, tooth height h n The tooth height is the same as that of the standard metric internal thread, and only the structure of each tooth side facing the same axial end is changed.

[0058] Furthermore, 0°<β≤25°, within this range, the fatigue performance of the external thread can be further improved. The specific verification process is as follows: This embodiment provides 17 internal threads with different β values ​​for comparison, including 16 improved internal threads with β=5°~29.75° and standard metric threads with β=30°. The major diameter D of all internal threads is selected to be 36mm, and the pitch P is 4mm. The height of the straight line segment near the top of the tooth in the radial direction of the internal thread is h p , select h p =0.5mm,h p <h n =2.165mm. The external threads used with each internal thread are standard metric threads, with a major diameter of 36mm and a pitch of 4mm.

[0059] According to the above parameters, the dynamic analysis of internal and external threads was carried out using general finite element analysis software. That is, a fixed constraint was imposed on the nut and an alternating load that changed with time was imposed on the bolt. Under the same alternating load, the external threads corresponding to the 17 internal threads were obtained at the calibration position (calibration position is Figure 4 The average stress variation curve at the red dot position in the figure, which is the first thread position of the external thread and is usually the position where the stress is most concentrated, is the time curve ( Figure 5 As shown), and the average stress of the external thread at the calibration position at a special loading moment varies with β ( Figure 6 shown).

[0060] from Figure 5 It can be seen that when the 17 types of internal threads are used with the standard metric external threads, the average stress of the external threads at the calibration position increases with the increase of β. Figure 6 It can be seen that at the special loading moments of 0.0025s, 0.005s, and 0.0075s, the average stress decreases with the decrease of β, and when β≤25°, the change trend of the average stress decreases, that is, the influence of β on the average stress at the calibration position decreases.

[0061] Since the height of the straight line segment near the tooth top in the radial direction of the internal thread is h p , the pitch of the internal thread is P, then 0.075P≤h p <h n , ensuring that the straight line segment near the tooth top has a certain height to meet the normal contact requirements with the external thread teeth. Further, since the internal thread in this embodiment is a metric thread, hp The optimization range is 0.075P≤h p ≤0.47P, more preferably, 0.075P≤h p ≤0.2P. Within this range, the external thread can be guaranteed to have better fatigue performance. The specific verification process is as follows:

[0062] This example provides 6 different h p The internal threads with the same value are compared, including five improved internal threads (h p =1mm, 0.75mm, 0.45mm, 0.2mm and 0.1mm) and a standard metric internal thread, the h of the standard metric thread p Right now Select the major diameter D of all internal threads as 36mm and the pitch P as 4mm, then the h of the standard metric thread p The angle β between the straight line segment near the root of the thread and the plane perpendicular to the axis of the thread is set at 20° for all five improved internal threads. The external threads used with each internal thread are all standard metric threads, with a major diameter of 36mm and a pitch of 4mm.

[0063] According to the above parameters, the dynamic analysis of the internal and external threads is carried out using general finite element analysis software, 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 external threads corresponding to the six types of internal threads are obtained at the calibration position (the calibration position is still Figure 4 The curve of the average stress at the position in the middle of the image is as follows: Figure 7 As shown in Table 1, the stress amplitudes of the external threads corresponding to the six types of internal threads at the calibrated positions are shown. The stress amplitude is the difference between the maximum stress and the minimum stress on the stress curve. The smaller the amplitude, the smaller the load amplitude the thread bears when it is subjected to alternating loads, and the better the fatigue performance.

[0064] Table 1 Stress amplitudes at the calibration position of the external threads (major diameter 36 mm, pitch 4 mm) corresponding to the six metric internal threads

[0065] <![CDATA[h p ]]> Standard metric thread 0.25P=1mm 0.1875P=0.75mm Stress amplitude 133.85Mpa 128.86Mpa 126.328Mpa <![CDATA[h p ]]> 0.0875P=0.45mm 0.05P=0.2mm 0.025P=0.1mm Stress amplitude 124.028Mpa 109.464Mpa 107.728Mpa

[0066] Combine Figure 7 As can be seen from Table 1, when h p =1mm, 0.75mm, 0.45mm, 0.2mm and 0.1mm, the average stress at each moment at the calibration position is less than that of the standard metric thread, and the stress amplitude is smaller than that of the standard metric thread. The stress amplitude is related to h p Negatively correlated, that is, h pThe smaller the value, the greater the reduction in stress amplitude. This indicates that compared to standard metric threads, as long as the internal thread is improved so that the tooth flanks of the internal thread profile include a straight line segment near the tooth top and a straight line segment near the tooth bottom connected at an angle, the stress state of the external thread at the calibrated position can be improved.

[0067] like Figure 8 The h shown is for internal thread p =2.165mm, 0.75mm, 0.45mm and 0.2mm, the corresponding external thread load ratio at the loading time of 0.0025s under the alternating load. It can be seen from the figure that the h of the internal thread p The smaller it is, the more uniform the load distribution of each thread circle of the corresponding external thread is. The improvement of load uniformity helps to improve the fatigue performance of the external thread.

[0068] For comparison, this embodiment also provides six different h when the major diameter of the internal and external threads is 42 mm and the pitch is 4.5 mm. p Comparative test results of internal threads with five improved internal threads (h p =1mm, 0.75mm, 0.5mm, 0.2mm and 0.1mm) and a standard metric internal thread. The average stress variation curve of the external thread corresponding to the 6 types of internal threads at the calibration position is as follows Figure 9 As shown in Table 2, the stress amplitudes of the external threads corresponding to the six types of internal threads at the calibrated positions are shown.

[0069] Table 2 Stress amplitudes at the calibration position of the external threads (large diameter 42 mm, pitch 4.5 mm) corresponding to the six metric internal threads

[0070] <![CDATA[h p ]]> Metric thread 0.222P=1mm 0.167P=0.75mm Stress amplitude 158.603Mpa 141.778Mpa 139.585Mpa <![CDATA[h p ]]> 0.111P=0.5mm 0.44P=0.2mm 0.022P=0.1mm Stress amplitude 125.185Mpa 114.568Mpa 113.393Mpa

[0071] In addition, this embodiment also provides 6 different h when the major diameter of the internal and external threads is 48mm and the pitch is 5mm. p Comparative test results of internal threads with five improved internal threads (h p =1mm, 0.75mm, 0.6mm, 0.2mm and 0.1mm) and a standard metric internal thread. The average stress variation curve of the external thread corresponding to the 6 internal threads at the calibration position is as follows Figure 10 As shown in Table 3, the stress amplitudes of the external threads corresponding to the six types of internal threads at the calibrated positions are shown.

[0072] Table 3 Stress amplitudes at the calibration position of the external threads (large diameter 48 mm, pitch 5 mm) corresponding to the six metric internal threads

[0073] <![CDATA[h p ]]> Metric thread 0.2P=1mm 0.15P=0.75mm Stress amplitude 142.701Mpa 135.777Mpa 133.329Mpa <![CDATA[h p ]]> 0.12P=0.6mm 0.04P=0.2mm 0.02P=0.1mm Stress amplitude 125.352Mpa 109.559Mpa 108.648Mpa

[0074] from Figure 9 and Figure 10 It can be seen from Table 2 and Table 3 that the stress amplitude and average stress change trends when the major diameter of the external thread is 42 mm, the pitch is 4.5 mm, and the major diameter is 48 mm, the pitch is 5 mm are the same as those when the major diameter is 36 mm and the pitch is 4 mm.

[0075] Combining the data of the above three groups of tests, we can get the average stress of the external thread at the calibrated position at the loading time of 0.0025s under the action of alternating load with h under three different thread major diameters and pitches. p The change curve of / P, such as Figure 11 As shown, this moment is the moment of maximum stress. In addition, the average stress at the calibrated position of the external thread at the loading time of 0.0075s under the action of alternating load is obtained with h p The change curve of / P, such as Figure 12 As shown, this moment is the moment of minimum stress.

[0076] Combine Figure 11 and Figure 12 It can be seen that in the three groups of test data, the average stress change trend of each group of test data is as h p The average stress decreases first and then increases, but the average stress value after the increase is still lower than h p The average stress value corresponding to the maximum. This is because as long as the tooth side of the internal thread includes a straight line segment near the tooth top and a straight line segment near the tooth bottom connected at an angle, the equivalent action point between the internal thread tooth and the external thread tooth is close to the tooth bottom position of the external thread, which will theoretically improve the fatigue performance of the external thread. Therefore, as h increases p The corresponding average stress value will not exceed h p The average stress value at the maximum. If we look at the number of circles of nut and bolt, such as Figure 8 As shown, h p The reduction can reduce the load ratio of the first circle of thread, thereby reducing the average stress at the nominal position of the external thread.

[0077] And with h p As the contact area between the internal thread and the external thread continues to decrease, it will gradually decrease. When the contact area is too small, it will cause a relatively large contact stress at the contact position. Under the influence of the contact stress, the average stress at the calibration position will increase. This is Figure 11 and Figure 12 The average stress first decreases and then increases, which is why there is a valley value.

[0078] In addition, in h p In the process of gradually decreasing from the maximum value, the average stress at the calibration position first shows a very slow change process. Figure 11 and Figure 12 From the perspective of the change trend, the critical point is h p =0.47P, that is, when h p When >0.47P, the improvement of the internal thread structure has little effect on the average stress at the external thread calibration position, so h p ≤0.47P, so that the average stress at the external thread calibration position can be significantly reduced.

[0079] Furthermore, considering that the mean stress has a valley value, and the valley value varies with the thread major diameter and pitch, and also varies with the load, it is difficult to accurately determine the h corresponding to the valley value. p Therefore, the present invention takes a preferred range, that is, 0.075P≤h p ≤0.2P. Figure 11 and Figure 12 It can be seen that the average stress in this range is relatively low and includes the valley value. p The average stress corresponding to the end value is nearly equal. In addition, h p The lower limit value of 0.075P also takes into account the machinability of the thread, h p If the diameter is too small, it will not only be difficult to process and fail to reflect the structural advantages of the internal thread of the present invention, but also the average stress at the calibrated position of the external thread will increase. Therefore, considering all factors, the above range is the best.

[0080] Embodiment 2 of the internal thread of the present invention:

[0081] The difference between this embodiment and embodiment 1 is that each tooth side facing one axial end and each tooth side facing the other axial end of the tooth profile of the internal thread in this embodiment includes a straight line segment near the tooth top and a straight line segment near the tooth bottom, and adjacent tooth sides are symmetrical. Figure 13 As shown, one of the adjacent flanks includes a proximal crest straight line segment 1 61 and a proximal root straight line segment 1 71 connected at an angle, while the other flank includes a proximal crest straight line segment 2 62 and a proximal root straight line segment 2 72 connected at an angle. Proximal crest straight line segment 1 61 and proximal crest straight line segment 2 62 are respectively connected to the corresponding crest 2, and the proximal crest straight line segment 1 61 and proximal crest straight line segment 2 62 are symmetrical. Proximal root straight line segment 1 71 and proximal root straight line segment 2 72 are respectively connected to the root 4, and the proximal root straight line segment 1 71 and proximal root straight line segment 2 72 are symmetrical. That is, the angle between proximal crest straight line segment 1 61 and a plane perpendicular to the internal thread axis, and the angle between proximal crest straight line segment 2 62 and a plane perpendicular to the internal thread axis are both α, and α = 30°. The angle between the first straight line segment 71 near the tooth bottom and the plane perpendicular to the axis of the internal thread, and the angle between the second straight line segment 72 near the tooth bottom and the plane perpendicular to the axis of the internal thread are both β, and the β values ​​are the same.

[0082] The other parameters of this embodiment are the same as those of Example 1, and the technical effects are also the same as those of Example 1. Compared with Example 1, this embodiment does not need to consider the positive and negative directions of the internal thread during installation, while Example 1 needs to ensure that the straight section near the top of the internal thread is in contact with the external thread after installation.

[0083] Embodiment 3 of the internal thread in the present invention:

[0084] The internal thread in this embodiment is an MJ thread, and the shape of the internal thread profile is the same as in Example 1, that is, the tooth profile of the internal thread also includes the tooth top, tooth side, tooth bottom and tooth side connected in sequence, and each tooth side facing the axial end in the tooth profile of the internal thread is a single straight line segment, and the angle between each single straight line segment and the plane perpendicular to the axis of the internal thread is 30°, that is, the single straight line segment is the same as the tooth side straight line segment in the tooth profile of the standard MJ thread.

[0085] Each flank of the internal thread profile, facing the other axial end, includes an angled segment connecting the crest and root segments. The crest segment connects to the crest, and the root segment connects to the root. The angle between the crest segment and a plane perpendicular to the internal thread axis is α, where α = 30°. The angle between the root segment and a plane perpendicular to the internal thread axis is β, where 0° < β < 30°. The angles between the root segment and the plane perpendicular to the internal thread axis are equal on all flanks facing the same axial end.

[0086] The external thread used with the internal thread of this embodiment is a standard MJ thread. Except for the crest and root of the external thread, the rest of the external thread profile consists of straight flank segments. When the internal and external threads are used together, only the straight segment near the crest of the internal thread contacts the flank segments of the external thread, while the straight segment near the root of the internal thread does not. This places the equivalent point of contact between the internal and external threads closer to the root of the external thread.

[0087] Therefore, the equivalent force arm between the equivalent action 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, reduces the stress at the bottom of the external thread, and improves the fatigue performance of the external thread. At the same time, the closer the equivalent action point is to the bottom of the external thread, the larger the tooth width of the external thread at the equivalent action point, and the greater the stiffness of the external thread. The tooth width of the internal thread at the equivalent action point becomes smaller, and the average tooth width of the internal thread as a whole also becomes smaller, and the stiffness of the internal thread decreases. When subjected to alternating loads, the role of the external thread as an energy absorption box can be weakened, reducing the inertial force borne by the external thread, and even making the internal thread act as an energy absorption box for the external thread, effectively reducing the average stress at the bottom of the external thread and improving the fatigue performance of the external thread.

[0088] The internal thread in this embodiment is an MJ thread, and the crest width of the internal thread is According to the geometric relationship, the tooth height of the internal thread can be known That is, the crest width C of the internal thread in this embodiment n The same as the standard MJ internal thread crest width, tooth height h n The tooth height is the same as that of the standard MJ internal thread, and only the structure of each tooth side facing the same axial end is changed.

[0089] Furthermore, 0°<β≤25°, within this range, the fatigue performance of the external thread can be further improved. The specific verification process is as follows: This embodiment provides 16 internal threads with different β values ​​for comparison, including 15 improved internal threads with β=10°~29.75° and a standard MJ thread with β=30°. The major diameter D of all internal threads is selected to be 36mm, and the pitch P is 4mm. The height of the straight line segment near the tooth top in the radial direction of the internal thread is h p , select h p =0.5mm,h p <h n =1.9485mm. The external threads used with each internal thread are all standard MJ threads, with a major diameter of 36mm and a pitch of 4mm.

[0090] Based on the above parameters, a general finite element analysis software was used to perform dynamic analysis on the internal and external threads. That is, a fixed constraint was imposed on the nut and an alternating load that varied with time was imposed on the bolt. The average stress variation curve of the external threads corresponding to the 16 types of internal threads at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load was obtained ( Figure 14 As shown), and the average stress of the external thread at the calibration position at a special loading moment varies with β ( Figure 15 shown).

[0091] from Figure 14 It can be seen that when the 16 types of internal threads are used with the standard MJ external thread, the average stress of the external thread at the calibration position increases with the increase of β. Figure 15 It can be seen that at the special loading moments of 0.0025s, 0.005s, and 0.0075s, the average stress decreases with the decrease of β, and when β≤25°, the change trend of the average stress decreases, that is, the influence of β on the average stress at the calibration position decreases.

[0092] Since the height of the straight line segment near the tooth top in the radial direction of the internal thread is h p , the pitch of the internal thread is P, then 0.075P≤h p <h n , ensuring that the straight line segment near the tooth top has a certain height to meet the normal contact requirements with the external thread teeth. Further, since the internal thread in this embodiment is an MJ thread, h pThe optimization range is 0.075P≤h p ≤0.4P, more preferably, 0.075P≤h p ≤0.2P. Within this range, the external thread can be guaranteed to have better fatigue performance. The specific verification process is as follows:

[0093] This example provides 6 different h p The internal threads with the same value are compared, including five improved internal threads (h p =1.25mm, 0.75mm, 0.45mm, 0.25mm and 0.1mm) and a standard MJ internal thread, the h of the standard MJ thread p Right now Select all internal threads with a major diameter D of 36 mm and a pitch P of 4 mm, then the h of the standard MJ thread is p The angle β between the straight line segment near the root of the tooth and the plane perpendicular to the axis of the internal thread in each of the five improved internal threads is set at 20°. The external threads used with each internal thread are all standard MJ threads, with a major diameter of 36mm and a pitch of 4mm.

[0094] According to the above parameters, the dynamic analysis of the internal and external threads is carried out using general finite element analysis software. That is, a fixed constraint is imposed on the nut and an alternating load that changes with time is imposed on the bolt. The average stress variation curve of the external thread corresponding to the six types of internal threads at the calibration position (the calibration position is the same as above) under the same alternating load is obtained as shown below: Figure 16 As shown in Table 4, the stress amplitudes of the external threads corresponding to the six types of internal threads at the calibrated positions are shown.

[0095] Table 4 Stress amplitudes at the calibration position of the external threads (major diameter 36 mm, pitch 4 mm) corresponding to the six types of MJ internal threads

[0096] <![CDATA[h p ]]> MJ thread 0.3125P=1.25mm 0.1875P=0.75mm Stress amplitude 133.162Mpa 131.607Mpa 127.301Mpa <![CDATA[h p ]]> 0.0875P=0.45mm 0.0625P=0.25mm 0.025P=0.1mm Stress amplitude 113.139Mpa 108.734Mpa 104.439Mpa

[0097] Combine Figure 16 As can be seen from Table 4, when h p =1.25mm, 0.75mm, 0.45mm, 0.25mm and 0.1mm, the stress amplitude at the calibration position is smaller than that of the standard MJ thread, and the stress amplitude is related to h p Negatively correlated, that is, h p The smaller the value, the greater the reduction in stress amplitude. p =1.25mm, 0.75mm, 0.45mm and 0.25mm, the average stress at each moment at the calibration position is less than that of the standard MJ thread, which shows that compared with the standard MJ thread, the internal thread is improved so that the tooth side includes the straight line segment near the tooth top and the straight line segment near the tooth bottom connected at an angle, while ensuring hp However small, the stress state of the external thread at the calibrated position can be improved.

[0098] like Figure 17 The h shown is for internal thread p =1.9485mm, 0.75mm, 0.45mm and 0.25mm, the corresponding external thread load ratio at the loading time of 0.0025s under the alternating load. It can be seen from the figure that the h of the internal thread p The smaller it is, the more uniform the load distribution of each thread circle of the corresponding external thread is. The improvement of load uniformity helps to improve the fatigue performance of the external thread.

[0099] For comparison, this embodiment also provides six different h when the major diameter of the internal and external threads is 42 mm and the pitch is 4.5 mm. p Comparative test results of internal threads with five improved internal threads (h p =1.25mm, 0.75mm, 0.55mm, 0.25mm and 0.1mm) and a standard MJ internal thread. The average stress variation curve of the external thread corresponding to the 6 internal threads at the calibration position is as follows Figure 18 As shown in Table 5, the stress amplitudes of the external threads corresponding to the six types of internal threads at the calibrated positions are shown.

[0100] Table 5 Stress amplitudes at the calibration position of the external threads (major diameter 42 mm, pitch 4.5 mm) corresponding to the six types of MJ internal threads

[0101] <![CDATA[h p ]]> MJ thread 0.278P=1.25mm 0.167P=0.75mm Stress amplitude 141.329Mpa 138.222Mpa 133.964Mpa <![CDATA[h p ]]> 0.122P=0.55mm 0.056P=0.25mm 0.022P=0.1mm Stress amplitude 128.019Mpa 110.745Mpa 107.81Mpa

[0102] In addition, this embodiment also provides 6 different h when the major diameter of the internal and external threads is 48mm and the pitch is 5mm. p Comparative test results of internal threads with five improved internal threads (h p =1.25mm, 0.75mm, 0.65mm, 0.25mm and 0.1mm) and a standard MJ internal thread. The average stress variation curve of the external thread corresponding to the 6 internal threads at the calibration position is as follows Figure 19 As shown in Table 6, the stress amplitudes of the external threads corresponding to the six types of internal threads at the calibrated positions are shown.

[0103] Table 6 Stress amplitudes at the calibration position of the external threads (large diameter 48 mm, pitch 5 mm) corresponding to the six types of MJ internal threads

[0104] <![CDATA[h p ]]> MJ thread 0.25P=1.25mm 0.15P=0.75mm Stress amplitude 148.983Mpa 144.677Mpa 139.483Mpa <![CDATA[h p ]]> 0.13P=0.65mm 0.05P=0.25mm 0.02P=0.1mm Stress amplitude 138.329Mpa 114.464Mpa 107.81Mpa

[0105] Combining the data of the above three groups of tests, we can get the average stress of the external thread at the calibrated position at the loading time of 0.0025s under the action of alternating load with h under three different thread major diameters and pitches. p The change curve of / P, such as Figure 20 As shown, this moment is the moment of maximum stress. In addition, the average stress at the calibrated position of the external thread at the loading time of 0.0075s under the action of alternating load is obtained with h p The change curve of / P, such as Figure 21 As shown, this moment is the moment of minimum stress.

[0106] Combine Figure 20 and Figure 21 It can be seen that in the three groups of test data, the average stress change trend of each group of test data is as h p The average stress decreases first and then increases. This is because when the tooth side of the internal thread includes a straight line segment near the tooth top and a straight line segment near the tooth bottom connected at an angle, the equivalent action point of the internal and external thread teeth is closer to the tooth bottom position of the external thread, which can improve the fatigue performance of the external thread. Therefore, the average stress decreases with h. p The decrease of h has a downward trend. In addition, according to 17, h p The reduction can reduce the load ratio of the first circle of thread, thereby reducing the average stress at the nominal position of the external thread.

[0107] And with h p As the contact area between the internal thread and the external thread continues to decrease, it will gradually decrease. When the contact area is too small, it will cause a relatively large contact stress at the contact position. Under the influence of the contact stress, the average stress at the calibration position will increase. This is Figure 20 and Figure 21 The average stress first decreases and then increases, which is why there is a valley value.

[0108] In addition, in h p In the process of gradually decreasing from the maximum value, the average stress at the calibration position first shows a very slow change process, and the critical point of this change trend is h p =0.4P, that is, when h p When >0.4P, the improvement of the internal thread structure has little effect on the average stress at the external thread calibration position, so h p ≤0.4P, so that the average stress at the external thread calibration position can be significantly reduced.

[0109] Furthermore, considering that the mean stress has a valley value, and the valley value varies with the thread major diameter and pitch, and also varies with the load, it is difficult to accurately determine the h corresponding to the valley value. pTherefore, the present invention takes a preferred range, that is, 0.075P≤h p ≤0.2P. Figure 20 and Figure 21 It can be seen that the average stress in this range is relatively low and includes the valley value. p The average stress corresponding to the end value is nearly equal. In addition, h p The lower limit value of 0.075P also takes into account the machinability of the thread, h p If the diameter is too small, it will not only be difficult to process and fail to reflect the structural advantages of the internal thread of the present invention, but also the average stress at the calibrated position of the external thread will increase. Therefore, considering all factors, the above range is the best.

[0110] Embodiment 4 of the internal thread of the present invention:

[0111] This embodiment differs from Example 3 in that each flank of the internal thread profile in this embodiment, both toward one axial end and toward the other axial end, includes a proximal crest straight line segment and a proximal root straight line segment, with adjacent flanks symmetrical. All other parameters and technical effects of this embodiment are the same as those of Example 3. However, compared to Example 3, this embodiment does not require consideration of the positive and negative orientation of the internal thread during installation, whereas Example 3 requires ensuring that the proximal crest straight line segment of the internal thread contacts and bears force with the external thread after installation.

[0112] In other embodiments of the internal thread: Different from any of the above embodiments, the tooth height h of the internal thread n The tooth height of the internal thread may not be the same as that of the standard internal thread, but may be greater than that of the standard internal thread. For example, when the internal thread is a metric thread, the tooth height When the internal thread is MJ thread, the tooth height In this case, the stiffness of the internal thread is further reduced, which can further reduce the average stress at the root of the external thread and improve the fatigue performance of the external thread.

[0113] In other embodiments of the internal thread: only the tooth sides of the first three threads of the internal thread and the external thread can be set to include a straight line segment near the tooth top and a straight line segment near the tooth bottom. Because the first three threads are where the stress is relatively concentrated, only improving the stress conditions of the first three threads can also improve the fatigue performance of the external thread, that is, there is no need for each tooth side toward one axial end in the internal thread tooth profile to include a straight line segment near the tooth top and a straight line segment near the tooth bottom.

[0114] In other embodiments of the internal thread, the optimized upper limit value of β may also be 28°.

[0115] In other embodiments of the internal thread: h p The optimal range can also be 0.075P≤h p ≤0.3P, that is, h pThe upper limit value is larger, and the two h p The consistency of the stress values ​​corresponding to the end values.

[0116] In other embodiments of the internal thread: h p The optimal range can also be 0.15P≤h p ≤0.3P, that is, h p The range no longer includes the valley value, h p The stress value corresponding to the range is in an increasing trend, but is lower than the stress value corresponding to the standard internal thread, which has achieved the purpose of improving the fatigue performance of the external thread.

[0117] In other embodiments of the internal thread: when the internal thread is a metric thread, h p The maximum upper limit value can also be 0.48P, 0.49P or 0.5P.

[0118] In other embodiments of the internal thread: when the internal thread is an MJ thread, h p The maximum upper limit value can also be 0.41P, 0.42P, 0.43P, 0.44P or 0.45P.

[0119] The 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 external thread is a standard metric thread or MJ thread, and the structure of the internal thread is the same as the internal thread of the above embodiment, which will not be repeated here.

[0120] 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. An internal thread, which is a metric thread or an MJ thread, wherein the thread profile of the internal thread includes a crest, a flank, a root and a flank connected in sequence, characterized in that: At least one tooth side in the tooth profile includes a straight line segment near the tooth top and a straight line segment near the tooth bottom connected at an angle, the straight line segment near the tooth top is connected to the tooth top, the straight line segment near the tooth bottom is connected to the tooth bottom, the angle between the straight line segment near the tooth top and the plane perpendicular to the axis of the internal thread is α, α = 30°, the angle between the straight line segment near the tooth bottom and the plane perpendicular to the axis of the internal thread is β, 0° < β < 30°, and the height of the straight line segment near the tooth top in the radial direction of the internal thread is h p , the pitch of the internal thread is P, and the tooth height of the internal thread is h n , 0.075P≤h p <h n .

2. The internal thread according to claim 1, characterized in that The internal thread is metric thread, 0.075P≤ h p ≤0.47P。 3. The internal thread according to claim 1, characterized in that The internal thread is MJ thread, the internal thread pitch is P, 0.075P≤h p ≤0.4P.

4. The internal thread according to claim 2 or 3, characterized in that 0.075P≤h p ≤0.2P 5. The internal thread according to any one of claims 1 to 3, characterized in that: 0°＜β≤25°。 6. The internal thread according to any one of claims 1 to 3, characterized in that: Each tooth side close to one axial end in the tooth profile of the internal thread is a single straight line segment, and the angle between each single straight line segment and the plane perpendicular to the axis of the internal thread is 30°. Each tooth side close to the other axial end in the tooth profile of the internal thread includes the aforementioned straight line segment near the top of the tooth and the straight line segment near the bottom of the tooth, and the angle between the straight line segment near the bottom of each tooth side and the plane perpendicular to the axis of the internal thread is equal.

7. The internal thread according to any one of claims 1 to 3, characterized in that: Each tooth flank close to one axial end and each tooth flank close to the other axial end in the tooth profile of the internal thread includes the straight line segment near the tooth top and the straight line segment near the tooth bottom, and adjacent tooth flanks are symmetrical.

8. The internal thread according to claim 2, wherein: The crest width of the internal thread is C n , 9. The internal thread according to claim 3, wherein: The crest width of the internal thread is C n , 10. A threaded connection pair, comprising an internal thread and an external thread used in conjunction with the internal thread, wherein the external thread is a standard metric thread or MJ thread, characterized in that: The internal thread is the internal thread according to any one of claims 1 to 9.

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