A self-excited oscillation jet flow drill bit with adjustable cavity length and a jet flow device

Abstract

The present application relates to the technical field of water jet, in particular to a self-excited oscillation jet drill bit with adjustable cavity length and a water jet device, comprising a shaft body, a cylinder body and a rotating body, the shaft body is internally provided with a fluid passage, the outer surface of the shaft body is fixed with a key body, the rear part of the inner surface of the cylinder body is provided with an axial sliding groove corresponding to the part of the key body protruding from the outer surface of the shaft body, and the rear part of the inner surface of the cylinder body is provided with a plurality of radially distributed and axially communicated radial limiting grooves; the rear inner hole of the rotating body is rotationally connected with the outer surface of the cylinder body, the front end of the rotating body is provided with a plurality of nozzles, and the inner surface of the rotating body, the front end surface of the shaft body and the inner surface of the cylinder body jointly form a self-excited oscillation cavity; the key body moves forward and backward along the axial sliding groove inside the cylinder body to different positions and rotates along the radial limiting grooves to the bottom of the radial limiting grooves, so as to realize the adjustment of the cavity length of the self-excited oscillation cavity. The present application is simple to operate, can be adapted to various engineering scenes and different matching equipment, and can obtain the best oscillation effect.

Description

Technical Field

[0001] This invention relates to the field of water jet technology, specifically to a self-excited oscillating jet drill bit and water jet device with adjustable cavity length. Background Technology

[0002] Water jet technology has been widely applied in various fields of daily life and industry. Currently, water jets can be broadly classified into three types: continuous jet, pulsed jet, and cavitation jet. Continuous water jet technology has been widely used in underground rock-breaking drilling projects such as coalbed methane extraction and radial horizontal wells in oil, with water jet drill bits playing a crucial role in both rock breaking and drilling. Drill bits currently used in these projects mainly include: multi-hole direct-jet drill bits, rotary jet drill bits, and hybrid direct-rotation jet drill bits. Multi-hole direct-jet drill bits produce uneven holes, which is detrimental to drilling; hybrid direct-rotation jets have complex structures and significant energy loss; while rotary jet drill bits, due to their rotating characteristics, cause fatigue damage to the rock surface and produce round holes with a large rock-breaking area, making them well-suited for underground rock-breaking drilling projects. However, rotary jets are prone to atomization, have rapid velocity decay, and their rock-breaking effect is significantly affected by the target distance. Pulsed jets are discontinuous jets. Pulsed water jets utilize the enormous transient energy generated by water hammer—the impact of hydraulic pressure—to cut or break materials. An important type of pulsed jet is the self-excited oscillating pulsed jet. Many studies indicate that self-excited oscillating pulsed jets can utilize energy and hammering pressure more effectively, and their rock-breaking performance is superior to continuous water jets. For example, the drill bit described in Chinese patent CN110359855A, "Nose for Self-Rotating Jet Drill Bits with Anti-Stall Device," has a complex structure, is difficult to manufacture, and is too large for use in confined spaces in coal mines. Patent CN103752433A, "A High-Pressure Water Jet Self-Excited Oscillating Nozzle Device," uses a self-excited oscillation chamber to generate a pulsed jet, but the jet orifice is single and cannot be used for rock-breaking drilling.

[0003] Overall, the adjustment of the cavity length of the self-excited oscillation chamber in current self-excited oscillating jet drill bits is inconvenient. For different engineering scenarios or different supporting equipment, the jet drill bit needs to be replaced and readjusted, affecting operational efficiency. Furthermore, the water jet drill bits currently used in underground rock-breaking drilling projects such as coalbed methane extraction and oil reservoir extraction still have the following problems: 1) Although self-rotating jet drill bits produce round holes, the jet energy decays rapidly, easily causing atomization; 2) The jet diameter generated by self-excited oscillating jet drill bits is small, making them unsuitable for underground drilling operations; 3) Existing self-rotating drill bits have complex structures and large dimensions, which are not conducive to drill bit steering; 4) There is no drill bit that can be applied to both coalbed methane extraction in confined spaces in coal mines and radial horizontal well drilling in the oil field. Summary of the Invention

[0004] The purpose of this invention is to provide a self-excited oscillating jet drill bit and water jet device with adjustable cavity length. It can adjust the cavity length of the self-excited oscillating cavity, is easy to operate, and can be adapted to various engineering scenarios and different supporting equipment to obtain the best oscillation effect.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a self-excited oscillating jet drill bit with adjustable cavity length, comprising a shaft, a cylinder, and a rotating body. The shaft has a fluid channel inside, and a key is fixed on the outer surface of the shaft. The inner surface of the cylinder has an axial groove corresponding to the portion of the key protruding from the outer surface of the shaft. The inner surface of the cylinder has several spaced radial limiting grooves that communicate with the axial groove. The inner hole at the rear of the rotating body is rotatably connected to the outer surface of the cylinder. The front end of the rotating body has several nozzles. The inner surface of the rotating body, the front end face of the shaft, and the inner surface of the cylinder together form a self-excited oscillating cavity. The outlet of the fluid channel and the inlet of the nozzles communicate with the self-excited oscillating cavity. After the key moves back and forth to different positions along the axial groove inside the cylinder, it rotates along the radial limiting groove to the bottom of the radial limiting groove, thereby realizing the adjustable cavity length of the self-excited oscillating cavity.

[0007] Furthermore, a sealing ring is fixed between the outer surface of the front part of the shaft and the inner surface of the front part of the cylinder.

[0008] Furthermore, the outer surface of the front part of the cylinder is provided with a plurality of grooves in the circumferential direction, and the plurality of grooves are arranged at intervals along the axial direction of the cylinder.

[0009] Furthermore, the outer surface of the cylinder is uniformly provided with several radial blind holes in the circumference. A base is slidably connected to the radial blind holes through a spring. The free end of the base is supported and connected to a ball bearing. The inner surface of the rear part of the rotating body is provided with a groove that corresponds to and cooperates with the ball bearing.

[0010] Furthermore, the inner surface of the front end of the rotating body is convex toward the self-excited oscillation cavity.

[0011] Furthermore, the nozzle includes a central nozzle, an intermediate nozzle, and a plurality of rotating nozzles circumferentially and evenly arranged at the front end of the rotating body.

[0012] The axis of the central nozzle coincides with the axis of the rotating body;

[0013] The extension of the axis of the intermediate nozzle intersects the axis of the central nozzle and forms a preset angle. The distance between the position where the axis of the intermediate nozzle intersects the rear end face of the rotating body and the axis of the central nozzle is denoted as Lm. The ratio of Lm to the outlet diameter d1 of the fluid channel, i.e., Lm / d1, is between 0.5 and 0.75.

[0014] The axis of the rotating nozzle and the axis of the central nozzle are not in the same plane, and they are separated by a preset distance Le. The axis of the rotating nozzle and the axis of the central nozzle form a preset angle.

[0015] Furthermore, the rear end of the cylinder is provided with a radially outwardly extending limiting protrusion, which corresponds to the position of the rear end of the rotating body. When the self-excited oscillating jet drill bit sprays jet, the recoil force of the jet causes the rear end of the rotating body to contact the limiting protrusion on the cylinder to form a seal.

[0016] Furthermore, the cylinder includes a sleeve and an intermediate component detachably connected to the outer wall of the sleeve, and the rear inner hole of the rotating body is rotatably connected to the outer surface of the intermediate component.

[0017] Furthermore, the rotating body includes a first housing and a second housing. The rear inner hole of the first housing is rotatably connected to the outer surface of the cylinder. The front outer surface of the first housing is detachably connected to the rear inner surface of the second housing. The nozzle is disposed on the second housing.

[0018] Secondly, the present invention provides a water jet device comprising the aforementioned self-excited oscillating jet drill bit with adjustable cavity length.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention provides an axial sliding groove on the rear part of the inner surface of the cylinder that corresponds to the part of the key protruding from the outer surface of the shaft. Several radial limiting grooves are provided at intervals on the rear part of the inner surface of the cylinder and communicate with the axial sliding groove. The key fixed on the outer surface of the shaft can move back and forth to different positions along the axial sliding groove inside the cylinder and then rotate to the bottom of the radial limiting groove. This makes the cavity length of the self-excited oscillation cavity adjustable. The cavity length of the self-excited oscillation cavity can be adjusted by tenon and mortise connection. It is simple to operate and can be adapted to various engineering scenarios and different supporting equipment to obtain the best oscillation effect.

[0021] 2. The nozzles set at the front end of the rotating body in this invention include a central nozzle, an intermediate nozzle, and several rotating nozzles evenly arranged circumferentially at the front end of the rotating body. Combined with the arrangement of the rotating body, the drill bit can achieve self-rotation during operation. It combines the advantages of self-rotating jets in producing round holes and large hole areas with the characteristics of self-excited oscillating pulse jets in making more efficient use of energy and hammering pressure, forming a new jet form of self-excited oscillation-self-rotating jets. This makes up for the disadvantage of rapid energy decay of rotating jets and greatly improves the rock breaking and drilling effect.

[0022] 3. This invention applies tangential and radial forces to the rock through nozzles with different opening and tilt angles, while also applying forces periodically through rotation and oscillation, thereby accelerating rock breaking and improving drilling efficiency.

[0023] 4. The self-excited oscillating jet drill bit with adjustable cavity length described in this invention has a simple structure, is detachable, is easy to process, and its size can be designed specifically according to the application scenario, making it highly applicable. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the self-excited oscillating jet drill bit with adjustable cavity length described in an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the shaft described in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the sleeve structure in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the structure of the middleware described in an embodiment of the present invention;

[0028] Figure 5 for Figure 4 Schematic diagram of AA section;

[0029] Figure 6 This is a schematic diagram illustrating the engagement of the ball bearings in an embodiment of the present invention;

[0030] Figure 7 This is a schematic diagram of the structure of the first housing in an embodiment of the present invention;

[0031] Figure 8 This is a schematic diagram of the structure of the second housing in an embodiment of the present invention;

[0032] Figure 9 This is a schematic cross-sectional view of the self-excited oscillating jet drill bit when the cavity length is adjusted to the maximum in an embodiment of the present invention.

[0033] In the diagram, 1—shaft, 11—fluid channel, 12—first mounting groove, 13—second mounting groove, 2—cylinder, 21—axial groove, 22—radial limiting groove, 23—radial blind hole, 24—groove, 25—limiting protrusion, 26—sleeve, 27—intermediate component, 3—rotating body, 31—first housing, 32—second housing, 33—groove, 4—key, 5—nozzle, 51—center nozzle, 52—intermediate nozzle, 53—rotating nozzle, 6—self-excited oscillation chamber, 7—sealing ring, 8—spring, 9—base, 10—ball bearing. Detailed Implementation

[0034] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0035] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0036] See Figure 1 As shown, a self-excited oscillating jet drill bit with adjustable cavity length includes a shaft 1, a cylinder 2, and a rotating body 3. The shaft 1 has a fluid channel 11 inside, which extends through the front and rear end faces of the shaft 1, allowing fluid to pass through the shaft 1 and enter the self-excited oscillating cavity 6. See also... Figure 2 As shown, two first mounting grooves 12 are symmetrically provided in the middle of the outer surface of the shaft 1. A key body 4 is fixed in the first mounting groove 12. It should be noted that the number of first mounting grooves 12 and key bodies 4 is not limited by the specific embodiment of the present invention, and can be reasonably arranged according to actual conditions.

[0037] See Figure 3 As shown, the rear inner surface of the cylinder 2 is provided with an axial sliding groove 21 that corresponds to the portion of the key body 4 protruding from the outer surface of the shaft body 1. The rear inner surface of the cylinder 2 is provided with four radial limiting grooves 22 that are spaced apart and communicate with the axial sliding grooves 21. The axis of the radial limiting grooves 22 is parallel to the surface of the cylindrical cavity inside the cylinder 2, and the curvatures of the two are the same.

[0038] The rear inner hole of the rotating body 3 is rotatably connected to the outer surface of the cylinder 2. Several nozzles 5 are provided at the front end of the rotating body 3. The inner surface of the rotating body 3, the front end face of the shaft 1, and the inner surface of the cylinder 2 together form a self-excited oscillation chamber 6. The outlet of the fluid channel 11 and the inlet of the nozzles 5 are both connected to the self-excited oscillation chamber 6. The key 4 can move back and forth along the axial sliding groove 21 inside the cylinder 2 to different positions, that is, the key 4 slides along the axial sliding groove 21 inside the cylinder 2 to different positions where the axial sliding groove 21 connects to the radial limiting groove 22, and rotates along the radial limiting groove 22 to the bottom of the radial limiting groove 22, thus achieving adjustable cavity length of the self-excited oscillation chamber 6. The cavity length of the self-excited oscillation chamber 6 can be adjusted through a tenon and mortise connection, that is, the key 4 and the radial limiting groove 22 are correspondingly engaged. This simple operation allows it to adapt to various engineering scenarios and different supporting equipment to obtain the best oscillation effect.

[0039] To ensure the oscillation effect, the ratio of the cavity length to the diameter of the self-excited oscillation cavity 6 is set to 0.2~1.0; the ratio of the cavity length to the outlet diameter of the fluid channel is set to 0.8~6.

[0040] As a preferred embodiment of the present invention, see Figure 1 and Figure 2 As shown, a second mounting groove 13 is provided around the outer surface of the front part of the shaft 1. A sealing ring 7, which corresponds to and mates with the inner surface of the front part of the cylinder 2, is fixed in the second mounting groove 13. This effectively prevents a large amount of fluid from flowing out of the drill bit along the gap between the outer surface of the shaft 1 and the inner surface of the cylinder 2, thus effectively controlling the leakage. It should be noted that, see... Figure 9 As shown, when the cavity length of the self-excited oscillation cavity 6 is adjusted to the maximum, the sealing ring 7 is still located between the radial limiting groove 22 and the self-excited oscillation cavity 6, preventing fluid from entering the radial limiting groove 22.

[0041] As a preferred embodiment of the present invention, see Figure 4 As shown, the outer surface of the front part of the cylinder 2 is provided with a plurality of grooves 24 in the circumferential direction. The plurality of grooves 24 are arranged at intervals along the axial direction of the cylinder. When the fluid in the self-excited oscillation chamber 6 enters the gap between the inner surface of the rotating body 3 and the outer surface of the cylinder 2 to form a liquid film, the grooves 24 enable the liquid film to be evenly distributed, which greatly reduces the rotational friction between the rotating body 3 and the cylinder 2.

[0042] As a preferred embodiment of the present invention, see Figure 4As shown, the outer surface of the cylinder 2 is uniformly provided with several radial blind holes 23. A base 9 is slidably connected to the radial blind holes 23 through a spring 8. The free end of the base 9 supports and connects to a ball bearing 10. The inner surface of the rear part of the rotating body 3 is provided with a groove 33 that corresponds to and cooperates with the ball bearing 10. During installation, the spring 8 is placed into the radial blind hole 23 on the outer surface of the cylinder 2, then the base 9 is placed into the radial blind hole 23, and finally the ball bearing 10 is placed on the base 9. By pressing the ball bearing 10, it can slide along the axial arc track on the inner surface of the rear part of the rotating body 3 into the groove 33. After the ball bearing 10 enters the groove 33, the spring 8 returns to its original shape, and the ball bearing 10 forms a point contact with the circumferential groove 33. The ball bearing 10 can restrict the movement of the rotating body 3, so that it can only rotate and move slightly back and forth.

[0043] As a preferred embodiment of the present invention, see Figure 8 As shown, the inner surface of the front end of the rotating body 3 protrudes towards the self-excited oscillation cavity 6, that is, the inner surface of the front end of the rotating body 3 has a certain angle α, which is between 100 and 180°, so that the fluid can move in different directions after hitting the inner surface of the front end of the rotating body 3, thereby improving the oscillation effect of the fluid in the self-excited oscillation cavity 6.

[0044] As a preferred embodiment of the present invention, see Figure 8 As shown, the nozzle 5 includes a central nozzle 51, an intermediate nozzle 52, and four rotating nozzles 43 evenly arranged circumferentially at the front end of the rotating body 3; the axis of the central nozzle 51 coincides with the axis of the rotating body 3; the extension line of the axis of the intermediate nozzle 52 intersects the axis of the central nozzle 51 and forms a preset angle; the distance between the intersection of the axis of the intermediate nozzle 52 and the rear end face of the rotating body 3 and the axis of the central nozzle is denoted as Lm; the ratio of Lm to the fluid channel outlet diameter d1, i.e., Lm / d1, is between 0.5 and 0.75; the axis of the rotating nozzle 53 is not in the same plane as the axis of the central nozzle 51, and the two are separated by a preset distance Le; the axis of the rotating nozzle 53 forms a preset angle with the axis of the central nozzle 51. By combining the arrangement of nozzle 5 and rotating body 3, the drill bit can achieve self-rotation during operation. This combines the advantages of self-rotating jets in producing round and large holes with the characteristics of self-excited oscillating pulse jets in making more efficient use of energy and hammering pressure, forming a new jet form of self-excited oscillation-self-rotating jet. This makes up for the disadvantage of rapid energy decay of rotating jets and greatly improves the rock breaking and drilling effect.

[0045] As a preferred embodiment of the present invention, see Figure 1 and Figure 3As shown, the rear end of the cylinder 2 is provided with a radially outwardly extending limiting protrusion 25, which corresponds to the rear end position of the rotating body 3. When the self-excited oscillating jet drill bit sprays jet, due to the recoil force of the jet, the rear end of the rotating body 3 contacts the limiting protrusion 25 on the cylinder 2 to form a seal, thereby controlling the leakage of fluid in the self-excited oscillating cavity 6 and improving the spraying efficiency.

[0046] As a preferred embodiment of the present invention, see Figure 1 , Figure 3 and Figure 4 As shown, the cylindrical body 2 includes a sleeve 26 and an intermediate component 27 detachably connected to the outer wall of the sleeve 26. The rear inner hole of the rotating body 3 is rotatably connected to the outer surface of the intermediate component 27. The rear inner hole surface of the sleeve 26 is provided with an axial groove 21 that corresponds to the portion of the key body 4 protruding from the outer surface of the shaft body 1. The rear inner surface of the sleeve 26 is provided with four radially spaced grooves 22 that communicate with the axial grooves 21. The rear end of the sleeve 26 is provided with a radially outwardly extending limiting protrusion 25.

[0047] The intermediate component 27 is cylindrical, with its rear inner hole threaded to the outer wall of the sleeve 26, and its rear end abutting against the front side of the limiting protrusion 25. The radial blind hole 23 penetrates the inner and outer surfaces of the intermediate component 27. When the ball bearing 10 is installed, one end of the spring 8 passes through the intermediate component 27 and abuts against the outer surface of the sleeve 26. Because the cylinder 2 is designed as a split structure, different sleeves 26 and intermediate components 27 can be reasonably replaced according to actual conditions to meet the matching of shafts 1 and rotating bodies 3 of different sizes and specifications.

[0048] In a preferred embodiment of the present invention, the rotating body 3 includes a first housing 31 and a second housing 32. The rear inner hole of the first housing 31 is rotatably connected to the outer surface of the cylinder 2, and the front outer surface of the first housing 31 is threadedly connected to the rear inner surface of the second housing 32. The nozzle 5 is disposed on the second housing 32. By replacing the first housing 31 with different sizes and specifications, the connection between the second housing 32 and the cylinder 2 can be better achieved, enhancing the flexibility of matching.

[0049] In specific assembly, the sleeve 26 and the intermediate part 27 are assembled to form the cylinder 2, and the first housing 31 and the second housing 32 are assembled to form the rotating body 3. The spring 8 is placed in the radial blind hole 23 on the outer surface of the cylinder 2, and then the base 9 is placed in the radial blind hole 23. Finally, the ball bearing 10 is placed on the base 9. By pressing the ball bearing 10, it can slide along the axial arc track on the inner surface of the rear hole of the rotating body 3 into the slide groove 33. After the ball bearing 10 enters the slide groove 33, the spring 8 returns to its original shape, and the ball bearing 10 forms a point contact with the circumferential slide groove 33. The ball bearing 10 can restrict the movement of the rotating body 3, so that it can only rotate and move slightly back and forth.

[0050] Finally, the key body 4 is inserted into the first mounting groove 12 of the shaft body 1, and the protruding part of the key body 4 is pushed to slide along the axial sliding groove 21 on the inner surface of the cylinder body 2 to different positions where the axial sliding groove 21 connects with the radial limiting groove 22, and then rotated along the radial limiting groove 22 until it is locked at the bottom of the radial limiting groove 22. It should be noted that the jet recoil force generated by the rotating nozzle 53 on the rotating body 3 makes the direction of the drill bit rotation opposite to the direction of the key body 4 on the shaft body 1 rotating along the radial limiting groove 22. This ensures that the key body 4 is always locked at the bottom of the radial limiting groove 22 during the rotation process.

[0051] In various underground rock-breaking drilling projects, such as underground coalbed methane extraction and radial horizontal well operations in oil, the drill bit shaft 1 is connected to a high-pressure hose. When high-pressure water is ejected from the fluid flow channel 11 inside the shaft 1, the instability of the jet and the disturbance generated by the collision between the jet and the inner surface of the front end of the rotating body 3 will couple together to generate periodic oscillations, thus generating self-excited oscillating pulse jets at the outlets of each nozzle 5. At the same time, the recoil force generated by the jet from the rotating nozzle 53 on the rotating body 3 forms a rotational torque, driving the rotating body 3 to rotate on the ball bearing 10. Simultaneously, due to the recoil force of the jet, the rear end of the rotating body 3 contacts the limiting protrusion 25 at the rear end of the cylinder 2 to form an end-face rotation seal. Since the gap between the outer surface of the intermediate part 27 and the inner surface of the first shell 31 is very small, the leakage can be well controlled. The rock target surface is not only subjected to radial and tangential tensile stress and axial compressive stress generated by each nozzle 5, but also to periodic fatigue damage from rotating jet and oscillating pulse jet. Under multiple effects, the rock is easily broken and a round borehole is formed, which greatly improves the efficiency of rock breaking drilling.

[0052] The present invention also provides a water jet device, which includes the above-described self-excited oscillating jet drill bit with adjustable cavity length.

[0053] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. Based on the technology and solutions disclosed in the present invention, those skilled in the art can make some modifications and changes to some of the technical features without creative effort, according to the technical content disclosed in this patent. All such modifications and changes are within the protection scope of the present invention.

Claims

1. A self-excited oscillating jet drill bit with adjustable cavity length, characterized in that: The device includes a shaft (1), a cylinder (2), and a rotating body (3). The shaft (1) has a fluid channel (11) inside and a key (4) is fixed on the outer surface of the shaft (1). The inner surface of the cylinder (2) has an axial groove (21) that corresponds to the part of the key (4) that protrudes from the outer surface of the shaft (1). The inner surface of the cylinder (2) has several radial limiting grooves (22) that are spaced apart and communicate with the axial grooves (21). The rear inner hole of the rotating body (3) is rotatably connected to the outer surface of the cylinder (2). The front end of the rotating body (3) is provided with several nozzles (5). The inner surface of the rotating body (3), the front end face of the shaft (1) and the inner surface of the cylinder (2) together form a self-excited oscillation cavity (6). The outlet of the fluid channel (11) and the inlet of the nozzles (5) are connected to the self-excited oscillation cavity (6). After the key body (4) moves back and forth to different positions along the axial sliding groove (21) inside the cylinder (2), it rotates along the radial limiting groove (22) to the bottom of the radial limiting groove (22), so that the cavity length of the self-excited oscillation cavity (6) can be adjusted.

2. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1, characterized in that: A sealing ring (7) is fixed between the outer front surface of the shaft (1) and the inner front surface of the cylinder (2).

3. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The outer surface of the front part of the cylinder (2) is provided with a plurality of grooves (24) in the circumferential direction, and the plurality of grooves (24) are arranged at intervals along the axial direction of the cylinder (2).

4. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The outer surface of the cylinder (2) is uniformly provided with a number of radial blind holes (23). A base (9) is slidably connected to the radial blind hole (23) by a spring (8). The free end of the base (9) is supported and connected to a ball (10). The inner surface of the rear part of the rotating body (3) is provided with a groove (33) that corresponds to and cooperates with the ball (10).

5. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The inner surface of the front end of the rotating body (3) protrudes towards the self-excited oscillation cavity (6).

6. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The nozzle (5) includes a central nozzle (51), an intermediate nozzle (52) and several rotating nozzles (53) evenly arranged circumferentially at the front end of the rotating body (3). The axis of the central nozzle (51) coincides with the axis of the rotating body (3); The extension line of the axis of the intermediate nozzle (52) intersects the axis of the central nozzle (51) and forms a preset angle. The distance between the position where the axis of the intermediate nozzle (52) intersects the rear end face of the rotating body (3) and the axis of the central nozzle (51) is denoted as Lm. The ratio of Lm to the outlet diameter d1 of the fluid channel, i.e., Lm / d1, is between 0.5 and 0.

75. The axis of the rotating nozzle (53) and the axis of the central nozzle (51) are not in the same plane, and the two are separated by a preset distance Le. The axis of the rotating nozzle (53) and the axis of the central nozzle (51) form a preset angle.

7. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The rear end of the cylinder (2) is provided with a radially outwardly extending limiting protrusion (25), which corresponds to the rear end position of the rotating body (3). When the self-excited oscillating jet drill bit sprays jet, due to the recoil force of the jet, the rear end of the rotating body (3) contacts the limiting protrusion (25) on the cylinder (2) to form a seal.

8. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The cylinder (2) includes a sleeve (26) and an intermediate piece (27) detachably connected to the outer wall of the sleeve (26). The rear inner hole of the rotating body (3) is rotatably connected to the outer surface of the intermediate piece (27).

9. The self-excited oscillating jet drill bit with adjustable cavity length according to claim 1 or 2, characterized in that: The rotating body (3) includes a first housing (31) and a second housing (32). The rear inner hole of the first housing (31) is rotatably connected to the outer surface of the cylinder (2). The front outer surface of the first housing (31) is detachably connected to the rear inner surface of the second housing (32). The nozzle (5) is disposed on the second housing (32).

10. A water jet device, characterized in that: Includes the self-excited oscillating jet drill bit with adjustable cavity length as described in any one of claims 1 to 9.

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