A hydraulic impact sub for underground coal mines

Abstract

The present application relates to a kind of coal mine underground hydraulic impact nipple, belong to drilling tool technical field, including outer tube, coaxial inner tube is equipped in outer tube, fluid passage is equipped between outer tube and inner tube;Impact mechanism is equipped in inner tube, impact mechanism includes transmission shaft, screw motor is connected in one end of transmission shaft, and other end is connected with cam mechanism;Cam mechanism includes cylindrical cam and the driving piston being arranged in the outside of cylindrical cam, the circumferential of cylindrical cam is equipped with the guide groove matching with the protruding structure being arranged in the inside of driving piston to drive driving piston linear reciprocating motion along the axis of inner tube;Driving piston is connected with driving disc located below it;Driving disc below is equipped with impact piston, impact piston below is equipped with punch to impact drill bit.The present application converts the rotary motion of existing mature screw motor into reciprocating linear impact motion, avoids the technical problem of high-pressure seal of hydraulic hammer, has no stringent requirement to water quality, is suitable for coal mine underground impact rotary drilling.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling tools and relates to a hydraulic impact pup joint for underground coal mines. Background Art

[0002] Impact rotary drilling technology is the most effective technology for solving the problem of drilling in hard rock formations. The hydraulic impact device (hereinafter referred to as hydraulic hammer) is an important component of impact rotary drilling tools. The hydraulic hammer is driven by high-pressure water as the working medium, and the generation of impact energy depends on the high-frequency impact force generated by the pressure difference between the front and rear of the piston. The metal seal of the piston sealing surface is the key to the generation of pressure difference. However, the piston sealing surface is severely worn due to its long-term exposure to high-pressure water impact and high temperature environment. When the piston sealing surface is worn to a certain extent, the pressure difference between the front and rear will not be enough to provide sufficient impact force for the piston. At this time, the hydraulic hammer is considered to have failed.

[0003] To extend the service life of hydraulic hammers, improvements to structural design and the use of heat treatment processes such as quenching and nitriding have been used to improve the wear resistance of the piston, with some success. However, in coal mine drilling operations, groundwater is used directly as the drilling fluid. This groundwater contains corrosive substances and tiny particles, which can cause severe wear in the impact, corrosion, and abrasive environment. The piston sealing surface quickly fails, resulting in a decrease in the impact force of the hydraulic hammer. Therefore, in coal mine tunnel environments, it is difficult to extend the service life of hydraulic hammers that rely on high-pressure water at both ends of the piston seal to generate impact force. Summary of the Invention

[0004] In view of this, the purpose of the present application is to provide a hydraulic impact pup joint for underground coal mines to solve the problem of short service life of existing hydraulic hammers in underground coal mines.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A coal mine underground hydraulic impact nipple, comprising an outer tube, an inner tube coaxially arranged inside the outer tube, and a fluid flow channel provided between the outer tube and the inner tube for conveying drilling fluid; an impact mechanism provided inside the inner tube for impacting the drill bit, the impact mechanism comprising a transmission shaft, one end of the transmission shaft being connected to a screw motor for driving its rotation, the other end passing through an end cap located at the top of the inner tube and fixedly connected to the outer tube and being connected to a cam mechanism located below the end cap; the cam mechanism comprising a cylindrical cam and a driving piston arranged outside the cylindrical cam, the cylindrical cam being circumferentially provided with a guide groove matching a raised structure provided inside the driving piston to form a cam transmission, driving the driving piston to perform linear reciprocating motion along the axial direction of the inner tube; the driving piston is slidably connected to a cam located below the cylindrical cam and fixed to the inner tube The cam is connected to the driving plate of the outer tube; the driving plate, the driving piston and the inner tube form a first sealed chamber; an impact piston is provided under the driving plate, and the impact piston, the driving plate and the inner tube form a second sealed chamber; a punch is provided under the impact piston to impact the drill bit located under the punch; the punch comprises an upper section, a middle section and a lower section arranged in sequence from top to bottom; the upper section passes through and extends out of an impact plug arranged at the bottom of the inner tube and fixedly connected to the outer tube, and a return spring is provided on the extended end sleeve; the outer diameter of the middle section is larger than the outer diameters of the upper section and the lower section, and the middle section is slidably connected to the outer tube; pressure balancing holes are provided between the driving plate and the driving piston, and between the impact piston and the impact plug, so that the space between the driving plate and the driving piston and the space between the impact piston and the impact plug are connected.

[0007] Optionally, a limiting device is provided under the punch to prevent empty hitting, and the limiting device includes a limiting buffer pad fixed on the inner side of the outer tube and / or a resistance spring sleeved on the lower section of the punch, and the resistance spring is supported on a spring support seat located below it, and the spring support seat is fixed on the outer tube.

[0008] Optionally, the drive shaft is floatingly connected to the cylindrical cam, and the axial movement of the drive shaft is limited by the drive shaft step surface located below the end cover and the shaft fixing ring located above the end cover and threadedly connected to the drive shaft; the drive shaft and the cylindrical cam are connected by a spline, and the axial position of the cylindrical cam is limited by a spline cover sleeved on the drive shaft, the spline cover is slidingly connected to the drive shaft, the inner hole of the spline cover is smaller than the outer diameter of the spline at the end of the drive shaft, and the spline cover is fixedly connected to the cylindrical cam by threads.

[0009] Optionally, the driving piston is floatingly connected to the driving disk arranged below it through a floating connection structure. The floating connection structure is a spherical floating connection structure. The floating connection structure includes a connecting rod and a ball head connecting rod connected through a spherical surface. The other end of the connecting rod is fixedly connected to the driving piston, and the other end of the ball head connecting rod is fixedly connected to the driving disk.

[0010] Optionally, the driving piston and the inner tube are connected via a spline.

[0011] Optionally, the end cover, the inner tube and the impact plug are provided with a plurality of grooves parallel to the axial direction in the circumferential direction, and the grooves among the end cover, the inner tube and the impact plug are connected to form a fluid flow channel.

[0012] Optionally, the inner tube includes an upper inner tube and a lower inner tube arranged in an upper and lower manner, the top of the upper inner tube is connected to the end cover, the connection position of the upper inner tube and the lower inner tube is not lower than the upper limit position of the drive disk, and the bottom end of the lower inner tube is connected to the impact plug; a slide is provided inside the lower inner tube, and the slide is limited by the upper inner tube and the impact plug respectively arranged at its upper and lower ends.

[0013] Optionally, sealing rings are provided between the driving disc, the impact piston and the inner tube to form a sealed space between the driving disc and the impact piston.

[0014] Optionally, the protruding structure is cylindrical.

[0015] Optionally, the end cover, the impact plug and the outer tube are detachably connected.

[0016] The beneficial effects of the present invention are: converting the rotational motion of the existing mature screw motor into reciprocating linear impact motion, avoiding the technical difficulties of high-pressure sealing of the hydraulic hammer, having no stringent requirements on water quality, and being suitable for impact rotary drilling in coal mines.

[0017] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0019] Figure 1 This is a structural schematic diagram of a hydraulic impact sub for underground coal mines according to the present invention;

[0020] Figure 2 It is a structural diagram of the cam mechanism;

[0021] Figure 3 for Figure 1 AA section view;

[0022] Figure 4 This is the motion trajectory diagram of the cam mechanism.

[0023] Markings in the diagram: transmission shaft 1, spline cover 2, cylindrical cam 3, drive piston 4, connecting rod 5, ball head connecting rod 6, impact piston 7, return spring 8, punch 9, resistance spring 10, spring support seat 11, semicircular clamp 12, drill bit 13, lower outer tube 14, drill bit pressing sleeve 15, limit buffer pad 16, impact plug 17, slide 18, lower inner tube 19, drive disc 20, pressure balance hole 21, fluid flow channel 22, upper outer tube 23, upper inner tube 24, end cover 25, shaft fixing ring 26, guide groove 301, protruding structure 401. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0025] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0026] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0027] See Figures 1-4A hydraulic impact nipple for an underground coal mine comprises an outer tube, an inner tube coaxially arranged therein, and a fluid flow channel 22 provided between the outer tube and the inner tube for conveying drilling fluid; an impact mechanism is provided in the inner tube for impacting a drill bit 13, the impact mechanism comprises a transmission shaft 1, one end of the transmission shaft 1 is connected to a screw motor for driving its rotation, and the other end passes through an end cover 25 located at the top of the inner tube and fixedly connected to the outer tube and is connected to a cam mechanism located below the end cover 25; the cam mechanism comprises a cylindrical cam 3 and a driving piston 4 arranged on the outside of the cylindrical cam 3, a guide groove 301 is provided on the circumference of the cylindrical cam 3 that matches a protruding structure 401 provided on the inner side of the driving piston 4 to form a cam transmission to drive the driving piston 4 to perform a linear reciprocating motion along the axial direction of the inner tube; the driving piston 4 is connected to a driving disk 2 located below it and slidably connected to the inner tube. 0 connection; the drive disc 20, the drive piston 4, and the inner tube form a first sealed chamber; an impact piston 7 is located below the drive disc 20, and the impact piston 7, the drive disc 20, and the inner tube form a second sealed chamber; a punch 9 is located below the impact piston 7 to impact the drill bit 13 located below the punch 9; the punch 9 comprises an upper section, a middle section, and a lower section arranged sequentially from top to bottom; the upper section passes through and extends from an impact plug 17 located at the bottom of the inner tube and fixedly connected to the outer tube, and a return spring 8 is sleeved on the extended end; the middle section has an outer diameter larger than that of the upper and lower sections, and is slidably connected to the outer tube; pressure balancing holes 21 are provided between the drive disc 20 and the drive piston 4, and between the impact piston 7 and the impact plug 17, to connect the space between the drive disc 20 and the drive piston 4 and the space between the impact piston 7 and the impact plug 17. Sealing rings are provided between the drive disc 20, the impact piston 7, and the inner tube to form a sealed space between the drive disc 20 and the impact piston 7.

[0028] Screw motors are already widely used in underground coal mine drilling, with drilling footage reaching tens of thousands of meters. The service life and water quality requirements of screw motors fully meet the requirements of coal mine drilling construction, providing a new approach to solving the seal failure problem of hydraulic hammers. Since screw motors can only provide rotational power, it is necessary to convert the screw motor's rotational motion into linear reciprocating impact motion. The present invention achieves the function of converting the screw motor's rotational motion into linear reciprocating motion by providing a cam mechanism, circumventing the high-pressure sealing structure of the piston. Therefore, the water quality problem of underground coal mine water is no longer a technical limitation of underground coal mine impact rotary drilling. This solves the problem of the short service life of existing hydraulic hammers in underground coal mines, making the present invention have broad engineering application prospects in the coal mining field.

[0029] In order to prevent empty hitting, the present invention provides a limiting device under the punch 9 to prevent empty hitting. The limiting device includes a limiting buffer pad 16 fixed on the inner side of the outer tube and / or a resistance spring 10 sleeved on the lower section of the punch. The resistance spring 10 is supported on a spring support seat 11 located below it, and the spring support seat 11 is fixed on the outer tube.

[0030] To address the issue of misalignment at the input end, the present invention employs a floating connection between the drive shaft 1 and the cylindrical cam 3. The drive shaft 1 is restricted in axial movement by a stepped surface located below the end cap 25 and a shaft retaining ring 26 located above the end cap 25 and threadedly connected to the drive shaft 1. A spline connection is established between the drive shaft 1 and the cylindrical cam 3. The cylindrical cam 3 is axially positioned by a spline gland 2 sleeved on the drive shaft 1. The spline gland 2 is slidably connected to the drive shaft 1. The inner bore of the spline gland 2 is smaller than the outer diameter of the spline at the end of the drive shaft 1. The spline gland 2 is fixedly connected to the cylindrical cam 3 via threads.

[0031] To address the issue of misalignment at the output end, the present invention employs a floating connection between the drive piston 4 and the drive plate 20. The drive piston 4 is connected to the drive plate 20 below it via a floating connection structure. This floating connection is a spherical floating connection structure comprising a connecting rod 5 and a ball-end connecting rod 65 connected via a spherical surface. The other end of the connecting rod 5 is fixedly connected to the drive piston 4, and the other end of the ball-end connecting rod 65 is fixedly connected to the drive plate 20.

[0032] To improve the force applied to the drive piston 4, the present invention employs a spline connection between the drive piston 4 and the inner tube. This connection allows the radial force exerted on the drive piston 4 by the guide groove 301 of the cylindrical cam 3 via the protrusion 401 to be offset by the keyway between the drive piston 4 and the upper inner tube 24, thereby limiting the force applied to the drive piston 4 to the axial component.

[0033] The fluid flow channel 22 of the present invention can be formed by arranging multiple grooves parallel to the axial direction on the circumference of the end cover 25, the inner tube, and the impact plug 17, and connecting the grooves between the end cover 25, the inner tube, and the impact plug 17 to form the fluid flow channel 22.

[0034] To facilitate assembly and manufacturing, the present invention utilizes separate inner and outer tubes. The inner tube comprises an upper inner tube 24 and a lower inner tube 19, arranged vertically. The top of the upper inner tube 24 connects to the end cap 25, and the junction between the upper and lower inner tubes 24 and 19 is no lower than the upper limit of the drive plate 20. The bottom of the lower inner tube 19 connects to the impact plug 17. A slide 18 is located within the lower inner tube 19, which is restrained by the upper inner tube 24 and the impact plug 17, respectively, located at its upper and lower ends. The outer tube comprises an upper outer tube 23 and a lower outer tube 14, arranged vertically.

[0035] The protruding structure 401 of the present invention is preferably cylindrical, and the connection between the end cover 25, the impact plug 17 and the outer tube is preferably a detachable connection, such as a threaded connection.

[0036] Example

[0037] A hydraulic impact pup joint for underground coal mines adopts a layered design, an impact mechanism is arranged in an inner tube, and a fluid flow channel 22 is arranged on the outer periphery of the inner tube. Figures 1-4 As shown, the figure shows a transmission shaft 1, a spline gland 2, a cylindrical cam 3, a driving piston 4, a connecting rod 5, a ball-end connecting rod 6, an impact piston 7, a return spring 8, a punch 9, a resistance spring 10, a spring support seat 11, a semicircular clamp 12, a drill bit 13, a lower outer tube 14, a drill bit pressing sleeve 15, a limit buffer 16, an impact plug 17, a slide 18, a lower inner tube 19, a driving disc 20, a pressure balance hole 21, a fluid flow channel 22, an upper outer tube 23, an upper inner tube 24, an end cap 25, a shaft fixing ring 26, a guide groove 301, and a protruding structure 401. A plurality of grooves are provided on the outer surfaces of the end cap 25, the upper inner tube 24, the lower inner tube 19, and the impact plug 17. The end cap 25, the upper inner tube 24, the lower inner tube 19, and the impact plug 17 are embedded in the upper outer tube 23. The upper and lower grooves are interconnected to form a fluid flow channel 22. A guide groove is provided on the outer surface of the cylindrical cam 3, divided into an impact stroke section, a transition section, a return stroke section, and a transition section. A driving piston 4 is circumferentially disposed around the cylindrical cam 3. A radially extending projection 401 is provided on the inner surface of the driving piston 4. This projection 401 engages within the guide groove of the cylindrical cam 3, creating a cam drive. The driving piston 4 is splined to the upper inner tube 24, limiting its axial movement. The driving piston 4 is floatingly connected to the drive disc 20 via a spherical floating connection, preventing misalignment between the drive disc 20 and the driving piston 4, which could cause the disc 20 and the driving piston 4 to become stuck. A sealing ring is provided on the outer surface of the driving disc 20, as well as on the outer surface of the impact piston 7. A sealed space is formed between the driving disc 20 and the impact piston 7. This sealed space is filled with compressible gas at a certain pressure, which stores the kinetic energy of the impact piston 7. A resistance spring 10 and a limit buffer 16 are located beneath the punch 9. Pressure balancing holes 21 are provided between the drive disc 20 and the drive piston 4 and between the impact piston 7 and the impact plug 17. The pressure balancing holes 21 keep the space between the drive disc 20 and the drive piston 4 and the space between the impact piston 7 and the impact plug 17 connected.

[0038] The operating principle is as follows: the drive shaft 1 is connected to the screw motor, which rotates the drive shaft 1, which in turn rotates the cylindrical cam 3. The guide groove 301 of the cylindrical cam 3 exerts both axial and radial forces on the drive piston 4 via the protrusion 401. The radial force is offset by the keyway between the drive piston 4 and the upper inner tube 24. Therefore, the drive piston 4 is only subject to the axial force component, and the drive piston 4 performs linear reciprocating motion according to the contour of the guide groove 301 of the cylindrical cam 3. Drilling fluid circulates through the fluid flow channel 22 between the upper cover 24, the upper inner tube 24, the lower inner tube 19, the impact plug 17, and the upper outer tube 23, reaching the drill bit 13.

[0039] Impact rock crushing process: The following is combined Figure 4 and Figure 1The process of impact rock crushing is described. The drill bit 13 is pressed against the rock. The drill bit 13 is retracted to the upper limit position. The drill bit 13 is pressed against the punch 9. Figure 4 The zero point is used as the starting position of the rotation of the cylindrical cam 3. The rotation of the cylindrical cam 3 drives the driving piston 4 to move downward, and the driving piston 4 drives the driving plate 20 to move downward. The driving plate 20 compresses the gas in the enclosed space, and the gas pressure increases to push the impact piston 7 downward. The cylindrical cam 3 enters the transition section, and the impact stroke ends at the impact piston 7 just contacts the punch 9. The impact force is transmitted to the rock, and the speed of the impact piston 7 quickly drops to zero. After the cylindrical cam 3 enters the return section, the driving piston 4 drives the driving plate 20 to move upward, and the gas above the driving plate 20 enters the bottom of the impact piston 7 through the pressure balance hole 21. The impact piston 7 moves upward under the combined action of the gas pressure and the return spring 8, and the cylindrical cam 3 enters the transition section. The driving plate 20 stops moving briefly, and the kinetic energy of the impact piston 4 is converted into gas pressure energy between the driving plate 20 and the driving piston 4 for storage. After the cylindrical cam 3 completes the transition section, it enters the next cycle.

[0040] Anti-air strike function: Combined with the following Figure 4 The anti-air striking function is described, the drill bit 13 does not hit the rock, the drill bit 13 does not hit the punch 9, and Figure 4 The zero point is used as the starting position of the rotation of the cylindrical cam 3. The cylindrical cam 3 rotates, and the driving piston 4 drives the driving plate 20 to move downward. The driving plate 20 compresses the gas in the enclosed space. The gas pressure increases and pushes the impact piston 7 downward. At the end of the impact stroke, the impact piston 7 just contacts the punch 9, and the cylindrical cam 3 enters the transition section. The driving plate 20 stops moving briefly. The impact piston 7 and the punch 9 decelerate downward under the action of the resistance spring 10. Finally, the punch 9 contacts the limit buffer pad 16, and the impact piston 7 and the punch 9 decelerate to zero. The cylindrical cam 3 enters the return section, and the driving piston 4 drives the driving plate 20 to move upward. The gas above the driving plate 20 enters the bottom of the impact piston 7 through the pressure balance hole 21. The impact piston 7 moves upward under the combined action of the gas pressure and the return spring 8. The cylindrical cam 3 enters the transition section, and the driving plate 20 stops moving briefly. The kinetic energy of the impact piston 7 is converted into gas pressure energy between the driving plate 20 and the impact piston 7 for storage, and the cylindrical cam enters the next cycle.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A hydraulic impact sub for underground coal mines, characterized by: The invention comprises an outer tube, wherein an inner tube coaxial with the outer tube is provided inside the outer tube, and a fluid flow channel (22) is provided between the outer tube and the inner tube for conveying drilling fluid; an impact mechanism is provided inside the inner tube for impacting a drill bit (13), the impact mechanism comprising a transmission shaft (1), one end of the transmission shaft (1) is connected to a screw motor for driving the rotation thereof, and the other end passes through an end cover (25) located at the top of the inner tube and fixedly connected to the outer tube and is connected to a cam mechanism located below the end cover (25); the cam mechanism comprises a cylindrical cam (3) and a driving piston (4) arranged outside the cylindrical cam (3), a guide groove (301) matching a protrusion structure (401) arranged inside the driving piston (4) is provided on the circumference of the cylindrical cam (3) to form a cam transmission, driving the driving piston (4) to perform linear reciprocating motion along the axial direction of the inner tube; the driving piston (4) is connected to a driving disk (20) located below the driving piston (3) and slidably connected to the inner tube; the driving disk (20), The driving piston (4) and the inner tube form a first sealed cavity; an impact piston (7) is provided below the driving disc (20), and the impact piston (7), the driving disc (20) and the inner tube form a second sealed cavity; a punch (9) is provided below the impact piston (7) to impact a drill bit (13) located below the punch (9); the punch (9) comprises an upper section, a middle section and a lower section arranged in sequence from top to bottom; the upper section passes through and extends out of an impact plug (17) arranged at the bottom of the inner tube and fixedly connected to the outer tube, and a return spring (8) is sleeved on the extended end; the outer diameter of the middle section is larger than the outer diameters of the upper section and the lower section, and the middle section is slidably connected to the outer tube; a pressure balancing hole (21) is provided between the driving disc (20) and the driving piston (4) and between the impact piston (7) and the impact plug (17), so that the space between the driving disc (20) and the driving piston (4) and the space between the impact piston (7) and the impact plug (17) are connected.

2. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: A limiting device is provided below the punch (9) to prevent empty striking. The limiting device comprises a limiting buffer pad (16) fixed on the inner side of the outer tube and / or a resistance spring (10) sleeved on the lower section of the punch. The resistance spring (10) is supported on a spring support seat (11) located below the resistance spring, and the spring support seat (11) is fixed on the outer tube.

3. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The transmission shaft (1) is floatingly connected to the cylindrical cam (3), and the transmission shaft (1) is limited in axial movement by a transmission shaft step surface located below the end cover (25) and a shaft fixing ring (26) located above the end cover (25) and threadedly connected to the transmission shaft (1); the transmission shaft (1) and the cylindrical cam (3) are connected via a spline, and the cylindrical cam (3) is limited in axial position by a spline pressure cover (2) sleeved on the transmission shaft (1), and the spline pressure cover (2) is slidingly connected to the transmission shaft (1), and the inner hole of the spline pressure cover (2) is smaller than the outer diameter of the spline at the end of the transmission shaft (1), and the spline pressure cover (2) is fixedly connected to the cylindrical cam (3) via a thread.

4. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The driving piston (4) is floatingly connected to a driving disk (20) arranged below it via a floating connection structure. The floating connection structure is a spherical floating connection structure. The floating connection structure comprises a connecting rod (5) and a ball-head connecting rod (6) connected via a spherical surface. The other end of the connecting rod (5) is fixedly connected to the driving piston (4), and the other end of the ball-head connecting rod (6) is fixedly connected to the driving disk (20).

5. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The driving piston (4) and the inner tube are connected via a spline.

6. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The end cover (25), the inner tube, and the impact plug (17) are circumferentially provided with a plurality of grooves parallel to the axial direction, and the grooves among the end cover (25), the inner tube, and the impact plug (17) are connected to form a fluid flow channel (22).

7. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The inner tube comprises an upper inner tube (24) and a lower inner tube (19) which are arranged in an upper and lower manner. The top of the upper inner tube (24) is connected to the end cover (25). The connecting position of the upper inner tube (24) and the lower inner tube (19) is not lower than the upper limit position of the driving disk (20). The bottom end of the lower inner tube (19) is connected to the impact plug (17). A slide tube (18) is provided inside the lower inner tube (19). The slide tube (18) is limited by the upper inner tube (24) and the impact plug (17) which are respectively arranged at the upper and lower ends of the slide tube (18).

8. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: Sealing rings are provided between the driving disc (20), the impact piston (7) and the inner tube to form a sealed space between the driving disc (20) and the impact piston (7).

9. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The protruding structure (401) is cylindrical.

10. The coal mine underground hydraulic impact sub according to claim 1, characterized in that: The end cover (25), the impact plug (17) and the outer tube are detachably connected.

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