A drill bit self-rotating pneumatic down-the-hole hammer drill with overload protection

Abstract

The present application relates to the technical field of percussion rotary drilling equipment, and particularly relates to a drill bit self-rotating pneumatic down-the-hole hammer drilling tool with overload protection. The down-the-hole hammer drilling tool comprises a gas distribution assembly, an overload protection assembly, a rotation assembly, an outer cylinder, a lower cylinder body and a drill bit. The outer cylinder is assembled at the upper part of the drilling tool, the lower cylinder body is connected at the bottom of the outer cylinder, the gas distribution assembly is assembled in the outer cylinder, and the overload protection assembly, the rotation assembly and the drill bit are sequentially assembled in the lower cylinder body from top to bottom. The gas distribution assembly drives the drill bit to self-rotate through the rotation assembly, and the rotation assembly performs overload protection on the drill bit through the overload protection assembly. The beneficial effects are as follows: the intermittent self-rotation of the drill bit is realized, the dependence on the external rotation of the drill rod is reduced, the key transmission components such as alloy balls, spiral grooves, transmission bushings and splines are prevented from being worn, deformed or failed due to overload, and thus the working reliability and service life of the drilling tool in hard rock and complex stratum drilling are improved.

Description

Technical Field

[0001] This invention relates to the field of impact rotary drilling equipment technology, and in particular to a self-rotating pneumatic down-the-hole hammer drill bit with overload protection. Background Technology

[0002] Currently, the self-rotating down-the-hole hammer is an impact rotary drilling device that uses an internal transmission assembly to convert the reciprocating motion of the piston into the rotary motion of the drill bit. Compared with traditional rotary drilling and conventional down-the-hole hammers, the self-rotating down-the-hole hammer can reduce the dependence on the external rotation of the drill rod, which is beneficial to improving the rotational stability of the drill bit at the bottom of the hole in complex hole sections such as deep holes, directional holes, and horizontal holes.

[0003] However, during drilling in complex formations, existing self-rotating down-the-hole hammers are susceptible to abnormal conditions such as hard interlayers, blockage, or localized stuck drill bits, which cause a sharp increase in rotational resistance and overload torque on the internal rotational assembly, thereby affecting the stability of the self-rotation function and the overall reliability of the machine.

[0004] Therefore, it is necessary to propose a self-rotating down-the-hole hammer with overload protection function, which can release overload torque under abnormal working conditions while realizing the autonomous rotation of the drill bit, thereby improving the working reliability of the slewing assembly and the whole machine. Summary of the Invention

[0005] The main purpose of this invention is to solve the problem that in the process of drilling in complex formations, the drill bit of the existing self-rotating down-the-hole hammer is easily affected by abnormal working conditions such as hard interlayers, block falling and jamming or local jamming, which leads to a sudden increase in rotation resistance and causes the internal rotation assembly to bear overload torque. Therefore, this invention provides a drill bit self-rotating pneumatic down-the-hole hammer drill tool with overload protection.

[0006] The self-rotating pneumatic down-the-hole hammer drill bit with overload protection provided by the present invention includes an air distribution assembly, an overload protection assembly, a rotation assembly, an outer cylinder, a lower cylinder body, and a drill bit. The outer cylinder is mounted on the upper part of the drill bit, and the lower cylinder body is connected to the bottom of the outer cylinder. The air distribution assembly is mounted inside the outer cylinder. The overload protection assembly, the rotation assembly, and the drill bit are sequentially mounted inside the lower cylinder body from top to bottom. The air distribution assembly drives the drill bit to rotate through the rotation assembly, and the overload protection assembly constrains the rotation assembly to provide overload protection for the drill bit.

[0007] The gas distribution assembly includes an upper connector, a check valve, an adjusting ring, a pressure regulating spring, a gas distribution seat, an inner cylinder, and a piston. The upper connector is mounted on the top of the drill bit, the check valve is mounted on the bottom of the upper connector's inner cavity, the pressure regulating spring is mounted in the gas distribution seat below the check valve, the gas distribution seat is mounted in the inner cylinder, the adjusting ring is fitted on the top of the gas distribution seat, the upper part of the piston cooperates with the gas distribution assembly, and the piston reciprocates under the action of high-pressure gas. A bushing is fitted in the middle of the piston, and the drill bit is mounted on the bottom of the piston. High-pressure gas enters the drill bit through the upper connector, and then enters the piston's narrow end chamber through the gas distribution seat and the inner cylinder. Under high pressure, the piston is driven upward and enters its top cavity as the piston moves, driving the piston downward and impacting the drill bit. With the cooperation of the piston, inner cylinder, gas distribution seat, and bushing, high-pressure gas alternately enters the piston's narrow end chamber and the top cavity, driving the piston to reciprocate.

[0008] The overload protection assembly is located on the top of the lower cylinder block and is fitted onto the piston. The overload protection assembly includes a fixing bolt, an upper fixing ring, an upper pressure plate, a pin, a disc spring, a lower pressure plate, an upper friction plate, a limit sleeve, a lower friction plate, and a lower fixing ring. The upper fixing ring, upper pressure plate, lower pressure plate, and upper friction plate are sequentially assembled on the upper part of the limit sleeve, and the lower friction plate and lower fixing ring are sequentially assembled on the lower part of the limit sleeve. The pin and disc spring are assembled between the upper and lower pressure plates, and the disc spring is fitted onto the pin. The upper fixing ring is screwed to the top of the lower cylinder block. The fixing bolt engages with the threaded hole on the upper fixing ring's circumference to adjust the compression of the disc spring. The disc spring, through the upper and lower pressure plates, protects the upper friction plate, limit sleeve, and lower piston. The friction plates provide axial clamping force, and the upper and lower pressure plates, along with the upper and lower friction plates, enable the limiting sleeve to maintain circumferential stability under normal operating conditions. When the drill bit rotation resistance does not exceed the set value, the limiting sleeve remains circumferentially fixed under the clamping action of the upper and lower friction plates, and the protrusions mounted on the inner circumference of the limiting sleeve restrict the circumferential rotation of the piston, allowing the piston to only perform axial reciprocating motion. When the drill bit rotation resistance exceeds the set value, the counter-torque on the limiting sleeve is greater than the frictional resistance provided by the upper and lower friction plates, causing frictional slippage between the limiting sleeve and the upper and / or lower friction plates, allowing the piston to rotate circumferentially relative to the lower cylinder, thereby releasing the overload torque borne by the rotary assembly.

[0009] The rotary assembly includes a limiting ring, an alloy ball, and a transmission bushing. The transmission bushing is fitted around the lower circumference of the piston, and the alloy ball is assembled between the helical grooves opened on the inner side wall of the transmission bushing and the outer side wall of the lower piston. The limiting ring is installed on the upper part of the lower cylinder, and the bottom surface of the limiting ring abuts against the top surface of the transmission bushing. The limiting ring is used to restrict the axial movement of the transmission bushing and enable the transmission bushing to rotate circumferentially around the piston axis.

[0010] The inner wall of the transmission bushing has an inclined surface, and the alloy ball is assembled between the inclined surface and the spiral groove opened on the lower outer wall of the piston. When the piston moves downward, the alloy ball moves radially inward under the action of the inclined surface and embeds itself in the spiral groove on the lower outer wall of the piston, locking the spiral groove, the alloy ball and the transmission bushing, and transmitting torque to the drill bit. When the piston moves upward, the alloy ball is released from the locking state with the spiral groove under the action of the inclined surface, so that the transmission bushing does not transmit rotational torque.

[0011] The lower outer wall of the piston has several spiral grooves evenly distributed circumferentially. Each spiral groove is equipped with several alloy balls. Each spiral groove includes an upper section, a middle section, and a lower section. When the piston is at the bottom dead center, the alloy balls are located in the upper section of the spiral groove. During the piston's upward movement to the top dead center, the alloy balls enter the lower section of the adjacent spiral groove. During the piston's downward movement, the alloy balls move from the lower section of the adjacent spiral groove through the middle section to the upper section, driving the transmission bushing to rotate circumferentially.

[0012] The lower inner wall of the transmission bushing is provided with a spline groove, and the top of the drill bit is provided with a spline protrusion that mates with the spline groove. The transmission bushing transmits the rotational torque to the drill bit through the spline groove and the spline protrusion at the top of the drill bit.

[0013] The upper part of the drill bit is fitted with a semi-circular clip, and the lower part of the drill bit is connected to the bottom of the lower cylinder through a lower connector.

[0014] Working principle of the invention:

[0015] The air distribution assembly of the self-rotating pneumatic down-the-hole hammer drill bit with overload protection provided by this invention is installed in the outer cylinder. The overload protection assembly, the rotation assembly, and the drill bit are installed sequentially in the lower cylinder from top to bottom. The upper part of the piston cooperates with the air distribution assembly and reciprocates under the action of air drive. The lower outer wall of the piston has a spiral groove around its perimeter, which cooperates with the alloy ball in the rotation assembly. When the piston moves downward, the alloy ball locks and drives the transmission bushing to rotate under the action of the spiral groove and the inclined surface set in the inner side wall of the transmission bushing. The torque generated is transmitted to the drill bit through the spline groove in the lower part of the transmission bushing. In addition, the limiting structure at the bottom of the piston cooperates with the protrusion on the inner side of the limiting sleeve to restrict the piston's rotational freedom under normal working conditions. When the drill bit torque is too large, the counter-torque borne by the limiting sleeve overcomes the friction of the upper and lower friction plates, causing friction slippage, which allows the piston to rotate circumferentially. This releases the overload torque borne by the rotary assembly and prevents key transmission parts such as alloy balls, spiral grooves, inclined surfaces on the inner wall of the transmission bushing, and spline grooves at the bottom of the transmission bushing from wearing, deforming, or failing due to overload, thus protecting the rotary assembly.

[0016] When the drill bit is working, high-pressure gas enters the drill bit through the upper connector, then through the gas distribution seat and inner cylinder into the piston's narrow end chamber. Under high pressure, the piston is driven upwards, and as it moves, it enters the top cavity, driving the piston downwards and impacting the drill bit. With the cooperation of the piston, inner cylinder, gas distribution seat, and bushing, high-pressure gas alternately enters the piston's narrow end chamber and the top cavity, driving the piston to reciprocate.

[0017] As the piston descends, the alloy ball moves radially inward under the action of the inclined surface on the inner wall of the transmission bushing, and embeds itself in the helical groove on the lower outer wall of the piston, forming a locking transmission relationship between the helical groove, the alloy ball, and the transmission bushing. As the piston continues to descend, the alloy ball moves from the lower section, through the middle section, to the upper section of the helical groove, pushing the transmission bushing to rotate circumferentially around the piston axis. The resulting rotational torque is transmitted to the drill bit through the spline groove within the transmission bushing, thereby driving the drill bit to rotate.

[0018] As the piston moves upward, the alloy ball, under the action of the inclined surface within the transmission bushing, releases its locking position against the helical groove. The alloy ball moves upward with the piston and enters the lower section of the adjacent helical groove from the upper section. During this process, the alloy ball does not transmit rotational torque to the transmission bushing, and the transmission bushing does not rotate. When the piston moves downward again, the alloy ball re-locks under the action of the inclined surface within the transmission bushing and moves from the lower section of the helical groove through the middle section to the upper section, driving the transmission bushing to rotate again. Thus, the axial reciprocating motion of the piston is periodically converted into the intermittent rotational motion of the drill bit.

[0019] In application, both the slewing assembly and the overload protection assembly are located inside the down-the-hole hammer, resulting in a compact overall structure and a clear transmission path. Through the cooperation of the piston helical groove, alloy ball, and inclined surface of the transmission bushing, the axial reciprocating motion of the piston is converted into the intermittent slewing motion of the drill bit, reducing reliance on the external rotation of the drill rod. Simultaneously, the overload protection assembly employs a friction-limiting torque mechanism. Under normal operating conditions, it restricts the circumferential rotation of the piston, ensuring stable slewing transmission. When the drill bit's slewing resistance exceeds a set value, the overload protection assembly engages in frictional slippage, allowing the piston to rotate relative to the drill bit and releasing the overload torque. This reduces the risk of overload damage to key transmission components of the slewing assembly, improving the reliability and service life of the drill bit in hard rock and complex formations.

[0020] Figure 6The cycle begins when the piston is at bottom dead center and in contact with the drill bit, at which point the alloy ball is located at position 'a' in the upper section of the helical groove. During the piston's upward return stroke, the alloy ball, under the action of the inclined surface inside the transmission bushing, releases its locking from the helical groove and moves axially from position 'a' to the lower section of the adjacent helical groove, i.e., position 'b'. During this process, the alloy ball does not drive the transmission bushing to rotate. During the piston's downward stroke, the alloy ball, under the action of the inclined surface inside the transmission bushing, moves radially inward and embeds itself in the helical groove. From position 'b', it moves through the middle section of the helical groove to position 'c' in the upper section of the helical groove, pushing the transmission bushing to rotate circumferentially. When the piston moves upward again, the alloy ball enters the lower section of the next adjacent helical groove from position 'c', completing the reset for the next cycle. Thus, the alloy ball periodically completes the unlocking, reset, locking, and rotation driving actions during the piston's reciprocating motion, transforming the axial reciprocating motion of the piston into the intermittent rotational motion of the transmission bushing and the drill bit. The number of helical grooves and alloy balls in the lower part of the piston is adjusted according to the drill string size and torque transmission requirements.

[0021] The beneficial effects of this invention are:

[0022] The self-rotating pneumatic down-the-hole hammer drill bit with overload protection provided by this invention utilizes the reciprocating motion of a piston to drive an alloy ball and a transmission bushing inclined surface to form a locking and unlocking engagement. This allows the piston's downward stroke to convert axial motion into drill bit rotational motion via the alloy ball, spiral groove, and transmission bushing. The piston's upward return stroke does not transmit rotational torque, thus achieving intermittent self-rotation of the drill bit and reducing dependence on external rotation of the drill rod. Simultaneously, the overload protection assembly forms an adjustable friction torque-limiting structure through fixing bolts, disc springs, friction plates, and limit sleeves. Under normal operating conditions, it restricts the circumferential rotation of the piston, ensuring stable rotational transmission. When the drill bit encounters abnormal conditions such as hard interlayers, block jamming, or stuck drill bit, causing the rotational resistance to exceed the set value, the friction plates slip, allowing the piston to rotate relative to the cylinder and release the overload torque. This prevents key transmission components such as the alloy ball, spiral groove, transmission bushing, and spline from wearing, deforming, or failing due to overload, thereby improving the reliability and service life of the drill bit in hard rock and complex formation drilling. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the self-rotating down-the-hole hammer with overload protection assembly described in this invention.

[0024] Figure 2 This is a schematic cross-sectional view of the piston in the limiting sleeve section of the present invention.

[0025] Figure 3 This is a schematic diagram of the lower cross-section of the piston described in this invention.

[0026] Figure 4 This is a schematic diagram of the overall piston structure described in this invention.

[0027] Figure 5 This is a schematic diagram of the overload protection assembly and slewing assembly described in this invention.

[0028] Figure 6 This is a schematic diagram of the movement path of the piston and alloy ball described in this invention.

[0029] The annotations in the above figure are as follows:

[0030] 1. Outer cylinder; 2. Lower cylinder body; 3. Drill bit; 4. Upper connector; 5. Check valve; 6. Adjusting ring sleeve; 7. Pressure regulating spring; 8. Valve seat; 9. Inner cylinder; 10. Piston; 11. Bushing; 12. Fixing bolt; 13. Upper fixing ring; 14. Upper pressure plate; 15. Pin; 16. Disc spring; 17. Lower pressure plate; 18. Upper friction plate; 19. Limiting sleeve; 20. Lower friction plate; 21. Lower fixing ring; 22. Limiting ring; 23. Alloy ball; 24. Transmission bushing; 25. Spiral groove; 26. Inclined surface; 27. Spline groove; 28. Semicircular clip; 29. ​​Lower connector; 30. Overload protection assembly. Detailed Implementation

[0031] Please see Figures 1 to 6 As shown:

[0032] The self-rotating pneumatic down-the-hole hammer drill bit with overload protection provided by the present invention includes an air distribution assembly, an overload protection assembly 30, a rotation assembly, an outer cylinder 1, a lower cylinder body 2, and a drill bit 3. The outer cylinder 1 is mounted on the upper part of the drill bit, and the lower cylinder body 2 is connected to the bottom of the outer cylinder 1. The air distribution assembly is mounted inside the outer cylinder 1. The overload protection assembly 30, the rotation assembly, and the drill bit 3 are sequentially mounted in the lower cylinder body 2 from top to bottom. The air distribution assembly drives the drill bit 3 to rotate through the rotation assembly, and the overload protection assembly 30 constrains the rotation assembly to provide overload protection for the drill bit 3.

[0033] The valve train assembly includes an upper connector 4, a check valve 5, an adjusting ring 6, a pressure regulating spring 7, a valve seat 8, an inner cylinder 9, and a piston 10. The upper connector 4 is mounted on the top of the drill bit. The check valve 5 is mounted at the bottom of the inner cavity of the upper connector 4. The pressure regulating spring 7 is mounted in the valve seat 8 below the check valve 5. The valve seat 8 is mounted in the inner cylinder 9. The adjusting ring 6 is fitted onto the top of the valve seat 8. The upper part of the piston 10 engages with the valve train assembly. The piston 10 reciprocates under the action of high-pressure gas. The part is equipped with a bushing 11, and the drill bit 3 is mounted on the bottom of the piston 10. High pressure gas enters the drill bit through the upper connector 4, and enters the narrow end chamber of the piston 10 through the air distribution seat 8 and the inner cylinder 9. Under the action of high pressure, the piston 10 is driven to move upward, and enters its top cavity as the piston 10 moves, driving the piston 10 downward and impacting the drill bit 3. With the cooperation of the piston 10, the inner cylinder 9, the air distribution seat 8 and the bushing 11, the high pressure gas alternately enters the narrow end chamber and the top cavity of the piston 10, driving the piston 10 to reciprocate.

[0034] The overload protection assembly 30 is located on the top of the lower cylinder 2 and is sleeved on the piston 10. The overload protection assembly 30 includes a fixing bolt 12, an upper fixing ring 13, an upper pressure plate 14, a pin 15, a disc spring 16, a lower pressure plate 17, an upper friction plate 18, a limiting sleeve 19, a lower friction plate 20, and a lower fixing ring 21. The upper fixing ring 13, the upper pressure plate 14, the lower pressure plate 17, and the upper friction plate 18 are sequentially assembled on the piston 10. The upper part of the limiting sleeve 19, the lower friction plate 20 and the lower fixing ring 21 are sequentially assembled on the lower part of the limiting sleeve 19. The pin 15 and the disc spring 16 are assembled between the upper pressure plate 14 and the lower pressure plate 17. The disc spring 16 is sleeved on the pin 15. The upper fixing ring 13 is screwed to the top of the lower cylinder 2. The fixing bolt 12 is engaged with the threaded hole around the upper fixing ring 13 to adjust the compression of the disc spring 16. The disc spring 16 passes through the upper pressure plate 14 and the lower pressure plate 17. Plate 17 provides axial clamping force to the upper friction plate 18, the limiting sleeve 19, and the lower friction plate 20. The upper pressure plate 14, the lower pressure plate 17, the upper friction plate 18, and the lower friction plate 20 enable the limiting sleeve 19 to maintain circumferential stability under normal working conditions. When the rotational resistance of the drill bit 3 does not exceed the set value, the limiting sleeve 19 remains circumferentially fixed under the clamping action of the upper friction plate 18 and the lower friction plate 20. The protrusions assembled on the inner circumference of the limiting sleeve 19 restrict the circumferential rotation of the piston 10, so that the piston 10 only performs axial reciprocating motion. When the rotational resistance of the drill bit 3 exceeds the set value, the counter-torque on the limiting sleeve 19 is greater than the frictional resistance provided by the upper friction plate 18 and the lower friction plate 20. Friction slippage occurs between the limiting sleeve 19 and the upper friction plate 18 and / or the lower friction plate 20, allowing the piston 10 to rotate circumferentially relative to the lower cylinder 2, thereby releasing the overload torque borne by the rotary assembly.

[0035] The rotary assembly includes a limiting ring 22, an alloy ball 23, and a transmission bushing 24. The transmission bushing 24 is sleeved around the lower circumference of the piston 10, and the alloy ball 23 is assembled between the helical groove 25 opened between the inner side wall of the transmission bushing 24 and the outer side wall of the lower part of the piston 10. The limiting ring 22 is installed on the upper part of the lower cylinder 2, and the bottom surface of the limiting ring 22 abuts against the top surface of the transmission bushing 24. The limiting ring 22 is used to restrict the axial movement of the transmission bushing 24 and enable the transmission bushing 24 to rotate circumferentially around the axis of the piston 10.

[0036] The inner wall of the transmission bushing 24 is provided with an inclined surface 26, and the alloy ball 23 is assembled between the inclined surface 26 and the spiral groove 25 opened on the lower outer wall of the piston 10. When the piston 10 moves downward, the alloy ball 23 moves radially inward under the action of the inclined surface 26 and is embedded in the spiral groove 25 on the lower outer wall of the piston 10, so that the spiral groove 25, the alloy ball 23 and the transmission bushing 24 are locked together and the torque is transmitted to the drill bit 3. When the piston 10 moves upward, the alloy ball 23 is released from the locking state with the spiral groove 25 under the action of the inclined surface 26, so that the transmission bushing 24 does not transmit rotational torque.

[0037] The lower outer wall of the piston 10 has several spiral grooves 25 evenly distributed around its circumference. Each spiral groove 25 is provided with several alloy balls 23. Each spiral groove 25 includes an upper section, a middle section and a lower section. When the piston 10 is at the bottom dead center as the starting point of a motion cycle, the alloy balls 23 are located in the upper section of the spiral groove 25. During the piston 10's upward movement to the top dead center, the alloy balls 23 enter the lower section of the adjacent spiral groove 25. During the piston 10's downward movement, the alloy balls 23 move from the lower section of the adjacent spiral groove 25 through the middle section to the upper section, and drive the transmission bushing 24 to rotate circumferentially.

[0038] The lower inner wall of the transmission bushing 24 is provided with a spline groove 27, and the top of the drill bit 3 is provided with a spline protrusion that mates with the spline groove 27. The transmission bushing 24 transmits the rotational torque to the drill bit 3 through the spline groove 27 and the spline protrusion at the top of the drill bit 3.

[0039] The upper part of the drill bit 3 is fitted with a semi-circular clip 28, and the lower part of the drill bit 3 is connected to the bottom of the lower cylinder 2 through a lower connector 29.

[0040] Working principle of the invention:

[0041] The air distribution assembly of the self-rotating pneumatic down-the-hole hammer drill bit with overload protection provided by this invention is installed in the outer cylinder 1. The overload protection assembly 30, the rotation assembly, and the drill bit 3 are installed sequentially from top to bottom in the lower cylinder 2. The upper part of the piston 10 cooperates with the air distribution assembly and reciprocates under the action of air drive. The lower outer wall of the piston 10 is provided with a spiral groove 25, which cooperates with the alloy ball 23 in the rotation assembly. When the piston 10 moves downward, under the action of the spiral groove 25 and the inclined surface 26 provided on the inner side wall of the transmission bushing 24, the alloy ball 23 locks and drives the transmission bushing 24 to rotate. The torque generated is transmitted to the drill bit 3 through the spline groove 27 at the lower part of the transmission bushing 24. In addition, the limiting structure at the lower part of the piston 10 cooperates with the inner protrusion of the limiting sleeve 19 to restrict the rotational freedom of the piston 10 under normal working conditions. When the torque of the drill bit 3 is too large, the counter-torque borne by the limiting sleeve 19 overcomes the friction of the upper friction plate 18 and the lower friction plate 20, causing friction slippage, so that the piston 10 can rotate circumferentially, thereby releasing the overload torque borne by the rotary assembly, and preventing key transmission parts such as the alloy ball 23, the spiral groove 25, the inclined surface 26 on the inner wall of the transmission bushing 24, and the spline groove 27 at the lower part of the transmission bushing 24 from wearing, deforming or failing due to overload, thus protecting the rotary assembly.

[0042] When the drill bit is working, high-pressure gas enters the drill bit through the upper connector 4, then through the gas distribution seat 8 and the inner cylinder 9 into the narrow end chamber of the piston 10. Under high pressure, the piston 10 is driven upward, and as it moves, it enters the top cavity, driving the piston 10 downward and impacting the drill bit 3. With the cooperation of the piston 10, the inner cylinder 9, the gas distribution seat 8, and the bushing 11, high-pressure gas alternately enters the narrow end chamber and the top cavity of the piston 10, driving the piston 10 to reciprocate.

[0043] As the piston 10 descends, the alloy ball 23 moves radially inward under the action of the inclined surface 26 on the inner wall of the transmission bushing 24, and embeds itself in the spiral groove 25 on the lower outer wall of the piston 10, thus forming a locking transmission relationship between the spiral groove 25, the alloy ball 23, and the transmission bushing 24. As the piston 10 continues to descend, the alloy ball 23 moves from the lower section of the spiral groove 25 through the middle section to the upper section of the spiral groove 25, pushing the transmission bushing 24 to rotate circumferentially around the axis of the piston 10. The resulting rotational torque is transmitted to the drill bit 3 through the spline groove 27 in the transmission bushing 24, thereby driving the drill bit 3 to rotate.

[0044] When the piston 10 moves upward, the alloy ball 23, under the action of the inclined surface 26 within the transmission bushing 24, releases its locking state from the spiral groove 25. The alloy ball 23 moves upward with the piston 10 and enters the lower section of the adjacent spiral groove 25 from the upper section. During this process, the alloy ball 23 does not transmit rotational torque to the transmission bushing 24, and the transmission bushing 24 does not rotate. When the piston 10 moves downward again, the alloy ball 23 re-locks under the action of the inclined surface 26 within the transmission bushing 24 and moves from the lower section of the spiral groove 25 through the middle section to the upper section of the spiral groove 25, driving the transmission bushing 24 to rotate again. Thus, the axial reciprocating motion of the piston 10 is periodically converted into the intermittent rotational motion of the drill bit 3.

[0045] In application, both the slewing assembly and the overload protection assembly 30 are arranged inside the down-the-hole hammer, resulting in a compact overall structure and a clear transmission path. Through the cooperation of the helical groove 25 of the piston 10, the alloy ball 23, and the inclined surface 26 of the transmission bushing 24, the axial reciprocating motion of the piston 10 is converted into the intermittent slewing motion of the drill bit 3, reducing reliance on the external rotation of the drill rod. Simultaneously, the overload protection assembly 30 employs a friction-limiting torque method, restricting the circumferential rotation of the piston 10 under normal operating conditions to ensure stable slewing transmission. When the slewing resistance of the drill bit 3 exceeds a set value, the overload protection assembly 30 experiences frictional slippage, allowing the piston 10 to rotate relative to the drill bit and releasing the overload torque. This reduces the risk of overload damage to key transmission components of the slewing assembly, improving the reliability and service life of the drill bit in hard rock and complex formations.

[0046] Figure 6The cycle begins when piston 10 is at bottom dead center and in contact with the drill bit, at which point alloy ball 23 is located at position a in the upper section of spiral groove 25. During the piston 10's upward return stroke, alloy ball 23, under the action of the inclined surface 26 inside the transmission bushing 24, releases its locking from spiral groove 25 and moves axially from position a to the lower section of the adjacent spiral groove 25, i.e., position b. During this process, alloy ball 23 does not drive the transmission bushing 24 to rotate. During the piston 10's downward stroke, alloy ball 23, under the action of the inclined surface 26 inside the transmission bushing 24, moves radially inward and embeds itself in spiral groove 25. From position b, it moves through the middle section of spiral groove 25 to position c in the upper section of spiral groove 25, pushing the transmission bushing 24 to rotate circumferentially. When piston 10 moves upward again, alloy ball 23 enters the next adjacent lower section of spiral groove 25 from position c, completing the reset of the next cycle. Thus, during the reciprocating motion of the piston 10, the alloy ball 23 periodically completes the unlocking, resetting, locking, and driving rotation actions, transforming the axial reciprocating motion of the piston 10 into the intermittent rotational motion of the transmission bushing 24 and the drill bit 3. The number of the lower spiral groove 25 of the piston 10 and the alloy ball 23 are adjusted according to the drill string size and torque transmission requirements.

Claims

1. A pneumatic down-the-hole hammer drill bit with overload protection, comprising an air distribution assembly, an overload protection assembly, a rotation assembly, an outer cylinder, a lower cylinder body, and a drill bit, wherein the outer cylinder is mounted on the upper part of the drill bit, the lower cylinder body is connected to the bottom of the outer cylinder, the air distribution assembly is mounted inside the outer cylinder, and the overload protection assembly, the rotation assembly, and the drill bit are sequentially mounted in the lower cylinder body from top to bottom. The air distribution assembly drives the drill bit to rotate via the rotation assembly, and the overload protection assembly constrains the rotation assembly to provide overload protection for the drill bit. The rotary assembly includes a limiting ring, alloy balls, and a transmission bushing. The transmission bushing is fitted around the lower circumference of the piston, and the alloy balls are assembled between the helical grooves formed on the inner sidewall of the transmission bushing and the outer sidewall of the lower piston. The limiting ring is installed on the upper part of the lower cylinder, with its bottom surface abutting against the top surface of the transmission bushing. The limiting ring restricts the axial movement of the transmission bushing and allows the transmission bushing to rotate circumferentially around the piston axis. Several helical grooves are evenly distributed circumferentially around the outer sidewall of the lower piston, and several alloy balls are correspondingly arranged in each helical groove. Each helical groove includes an upper section, a middle section, and a lower section. When the piston is at the bottom dead center as the starting point of a motion cycle, the alloy balls are located in the upper section of the helical groove. During the piston's upward movement to the top dead center, the alloy balls enter the lower section of the adjacent helical groove. During the piston's downward movement, the alloy balls move from the lower section of the adjacent helical groove through the middle section to the upper section, driving the transmission bushing to rotate circumferentially.

2. The self-rotating pneumatic down-the-hole hammer drill bit with overload protection according to claim 1, characterized in that... The aforementioned gas distribution assembly includes an upper connector, a check valve, an adjusting ring, a pressure regulating spring, a gas distribution seat, an inner cylinder, and a piston. The upper connector is mounted on the top of the drill bit, the check valve is mounted on the bottom of the inner cavity of the upper connector, the pressure regulating spring is mounted in the gas distribution seat below the check valve, the gas distribution seat is mounted in the inner cylinder, the adjusting ring is sleeved on the top of the gas distribution seat, the upper part of the piston cooperates with the gas distribution assembly, and the piston reciprocates under the action of high-pressure gas. A bushing is sleeved in the middle of the piston, and the drill bit is mounted on the bottom of the piston. High-pressure gas enters the drill bit through the upper connector, and enters the piston's narrow end chamber through the gas distribution seat and the inner cylinder. Under the action of high pressure, the piston is driven upward, and as the piston moves, it enters its top cavity, driving the piston downward and impacting the drill bit. With the cooperation of the piston, the inner cylinder, the gas distribution seat, and the bushing, high-pressure gas alternately enters the piston's narrow end chamber and the top cavity, driving the piston to reciprocate.

3. A self-rotating pneumatic down-the-hole hammer drill bit with overload protection according to claim 1 or 2, characterized in that... The overload protection assembly is located on the top of the lower cylinder and is fitted onto the piston. The overload protection assembly includes a fixing bolt, an upper fixing ring, an upper pressure plate, a pin, a disc spring, a lower pressure plate, an upper friction plate, a limiting sleeve, a lower friction plate, and a lower fixing ring. The upper fixing ring, upper pressure plate, lower pressure plate, and upper friction plate are sequentially assembled on the upper part of the limiting sleeve, and the lower friction plate and lower fixing ring are sequentially assembled on the lower part of the limiting sleeve. The pin and disc spring are assembled between the upper and lower pressure plates, and the disc spring is fitted onto the pin. The upper fixing ring is screwed to the top of the lower cylinder. The fixing bolt engages with the threaded hole on the upper fixing ring to adjust the compression of the disc spring. The disc spring passes through the upper and lower pressure plates to the upper friction plate and the limiting sleeve. The upper and lower friction plates provide axial clamping force, and the upper and lower pressure plates, along with the upper and lower friction plates, enable the limiting sleeve to maintain circumferential stability under normal operating conditions. When the drill bit rotation resistance does not exceed the set value, the limiting sleeve remains circumferentially fixed under the clamping action of the upper and lower friction plates, and the protrusions assembled on the inner circumference of the limiting sleeve restrict the circumferential rotation of the piston, so that the piston only performs axial reciprocating motion. When the drill bit rotation resistance exceeds the set value, the counter-torque on the limiting sleeve is greater than the frictional resistance provided by the upper and lower friction plates, and frictional slippage occurs between the limiting sleeve and the upper and / or lower friction plates, allowing the piston to rotate circumferentially relative to the lower cylinder, thereby releasing the overload torque borne by the slewing assembly.

4. A self-rotating pneumatic down-the-hole hammer drill bit with overload protection according to claim 1, characterized in that... The inner wall of the transmission bushing is provided with an inclined surface, and the alloy ball is assembled between the inclined surface and the spiral groove opened on the lower outer wall of the piston. When the piston moves downward, the alloy ball moves radially inward under the action of the inclined surface and embeds itself in the spiral groove on the lower outer wall of the piston, so that the spiral groove, the alloy ball and the transmission bushing are locked together and the torque is transmitted to the drill bit. When the piston moves upward, the alloy ball is released from the locking state with the spiral groove under the action of the inclined surface, so that the transmission bushing does not transmit rotational torque.

5. A self-rotating pneumatic down-the-hole hammer drill bit with overload protection according to claim 1, characterized in that... The transmission bushing has a spline groove on its lower inner sidewall and a spline protrusion at the top of the drill bit that mates with the spline groove. The transmission bushing transmits the rotational torque to the drill bit through the spline groove and the spline protrusion at the top of the drill bit.

6. A self-rotating pneumatic down-the-hole hammer drill bit with overload protection according to claim 1, characterized in that... The upper part of the drill bit is fitted with a semi-circular clip, and the lower part of the drill bit is connected to the bottom of the lower cylinder through a lower connector.

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