A down-the-hole hammer with an annular transition band cylinder

Abstract

This invention discloses a down-the-hole impactor with an annular transition zone cylinder, specifically relating to the field of pneumatic rock-breaking equipment. It includes a down-the-hole impactor body comprising a cylinder body and a piston. The cylinder body has an axial inner bore for accommodating the piston, and at least one air distribution channel is provided on the side wall of the cylinder body. This air distribution channel works in conjunction with an air distribution groove on the piston to achieve the reversal of air intake and exhaust directions in the air chamber. This invention, by setting an annular transition zone at the critical opening and closing boundary of the rear air chamber air distribution, transforms the abrupt change in flow cross-sectional area caused by the original straight step or short transition structure into a gradual process with a certain buffer length. This weakens the velocity gradient and local eddy intensity of the gas near the inlet and step, reduces local pressure loss and pressure gradient peaks, thereby reducing the flow dissipation of gas energy and improving the effective driving capability of compressed air on the piston.

Description

Technical Field

[0001] This invention relates to the field of pneumatic impact rock breaking equipment technology, and more specifically, to a down-the-hole impactor with an annular transition zone cylinder. Background Technology

[0002] Down-the-hole (DH) hammers are pneumatic rock-breaking equipment widely used in open-pit mines, underground mines, water well drilling, foundation engineering, and geological exploration. Their typical operating principle is as follows: compressed air enters the hammer through the intake channel, alternating between the front and rear chambers formed by the cylinder and piston to complete the processes of intake, expansion, exhaust, and depressurization. This causes the piston to achieve high-frequency reciprocating motion driven by the gas pressure difference, generating periodic impacts on the drill bit or intermediate body at the end of the stroke, thus achieving efficient rock breaking. Engineering evaluation indicators for this type of equipment typically include impact frequency, single impact energy, impact power, air consumption, and the service life of key components. Among these, the efficiency of converting gas pressure energy into piston mechanical energy directly determines the drilling efficiency and overall economic performance of the equipment.

[0003] In down-the-hole impactors, the valve timing process is the core element determining their performance. The valve timing process refers to the sequential combination of stages—intake pressurization, closed compression, and depressurization / exhaust—that occur in the front and rear chambers within a single working cycle. The variation of chamber pressure with time and piston stroke directly determines the piston's force state, acceleration, reversal timing, and final impact velocity, ultimately affecting the impact frequency and impact power. In terms of engineering structure, down-the-hole impactors do not rely on complex external valve assemblies but instead employ compact and highly reliable "orifice-groove" or valveless / minimal-valve valve timing methods. Specifically, this involves setting valve channels and annular grooves / windows on the inner wall of the cylinder (or inner cylinder) and valve grooves on the outer surface of the piston. The relative shielding and connection of the orifices and grooves during the piston's reciprocating motion precisely controls the opening and closing of the intake and exhaust passages. Therefore, it can be seen that the location and duration (i.e. stroke length) of the connection and shielding of the valve train are essentially determined by the geometric relationship between the cylinder and the piston, which is a timing control mechanism with strong geometric coupling.

[0004] To meet multiple requirements such as guidance, sealing, gas distribution, and structural strength, the cylinders of existing down-the-hole impactors typically employ a multi-section diameter combined with stepped structures for their inner bores, incorporating channels, annular grooves, and local diameter variation zones in key gas distribution sections. However, a common inherent drawback hinders further performance improvement: in the critical gas distribution area of ​​the rear chamber, especially near the opening and closing boundary of the rear chamber intake channel, the flow cross-sectional area often undergoes abrupt changes within a very short stroke as the piston moves. For example, using a straight step or short-distance transition inner wall structure means that the connection and disconnection of the gas distribution channel depend entirely on the shielding relationship between the piston and the cylinder bore and annular groove. This geometric abrupt change leads to the formation of strong velocity gradients and local vortices at the inlet of the intake channel and near the step, resulting in concentrated local pressure losses and pronounced pressure gradient peaks. This gas energy is dissipated in flow losses and fails to be effectively converted into driving pressure energy for the piston, thus reducing the effective driving capability of the chamber on the piston. Meanwhile, at geometric abrupt changes such as the edge of the step and the entrance boundary, peak concentrations of wall shear stress will appear. Under the long-term scouring of high pressure and high speed airflow, the material is easily eroded and worn, which in turn leads to deterioration of the sealing fit, out-of-tolerance inner wall dimensions, and ultimately causes the impactor's performance to decline and its service life to be reduced.

[0005] On the other hand, the comprehensive performance indicators of down-the-hole impactors, such as impact frequency, impact power, and air consumption, are significantly sensitive to the "effective intake length" (i.e., equivalent gas distribution length) of the rear chamber. The effective intake length of the rear chamber refers to the effective piston stroke window from the start of connection to the re-blocking of the rear chamber intake channel within one working cycle. However, in existing cylinder structures, this key parameter is often determined by the coupling of multiple geometric elements, such as the axial position of the gas distribution channel, the length of the annular groove and window, the relative position of the steps, and the starting position of the piston boundary. This multi-factor coupling means that designers lack an independent, manufacturable, and parameterizable geometric adjustment method to finely change the continuous gas distribution stroke. Structural optimization often relies on modifying a small number of discrete parameters (such as orifice diameter and groove width) or conducting "trial and error" experiments, making it difficult to quickly and accurately determine the optimal gas distribution length and efficiency range applicable to different air supply pressures and drilling conditions.

[0006] Therefore, based on existing technology, there is an urgent need to propose a new cylinder structure improvement scheme. This scheme should be able to effectively solve the geometric change problem at the key opening and closing boundary of the rear air chamber without significantly increasing the overall structural complexity of the cylinder, without significantly increasing the processing and manufacturing difficulty, and without changing the original overall assembly relationship and basic air distribution principle of the down-the-hole impactor as much as possible. It should also achieve controllable and parameterizable adjustment of the effective air intake length of the rear air chamber. Summary of the Invention

[0007] To overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a down-the-hole impactor with an annular transition cylinder. The technical problem to be solved by the present invention is: how to smooth the geometric abrupt change in the key area of ​​the rear air chamber air distribution by a manufacturable and parameterizable structural improvement while maintaining the original compact structure and high reliability of the down-the-hole impactor, reduce local flow loss and wall erosion risk, and achieve independent and precise adjustment of the effective air intake length of the rear air chamber.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a down-the-hole impactor with an annular transition zone cylinder, comprising a down-the-hole impactor body, the down-the-hole impactor body comprising a cylinder body and a piston, the cylinder body having an axial inner hole for accommodating the piston, and the side wall of the cylinder body having at least one air distribution channel, the air distribution channel being used to cooperate with the air distribution groove on the piston to realize the reversal of air intake and exhaust in the air chamber;

[0009] On the inner wall of the cylinder body, near the opening and closing boundary of the rear air chamber intake passage, there is an annular transition zone; the annular transition zone is an axially extending annular buffer area with a smooth inner diameter transition, which is used to replace the straight step or short-distance transition structure in the prior art at this position.

[0010] The annular transition zone is located at at least one of the following key areas on the cylinder inner wall: the starting boundary position where the rear chamber intake passage begins to connect, the ending boundary position where the rear chamber intake passage ends to connect, and the sensitive area where the valve distribution channel and the valve distribution groove on the piston undergo a change in their shielding and connection relationship.

[0011] The length of the annular transition zone along the cylinder body axis is defined as Lt, in millimeters (mm). The length Lt is an independently adjustable geometric parameter. By changing its value, the duration of the connection and shielding process of the rear air chamber intake channel can be adjusted, thereby changing the effective intake length of the rear air chamber, i.e., the equivalent valve length.

[0012] In a preferred embodiment, the inner wall of the annular transition zone is a smooth curved surface, and its axial cross-sectional profile is a straight line or a curve, so as to form a conical or arcuate surface on the inner wall of the cylinder body that smoothly transitions from the first inner diameter to the second inner diameter.

[0013] In a preferred embodiment, a fitting gap is formed between the inner wall surface of the annular transition zone and the outer circular surface of the piston. When the piston reciprocates in the cylinder, the annular transition zone moves relative to the sealing strip, guide strip or end face edge on the piston, so that the flow cross-sectional area between the air distribution channel and the air distribution groove on the piston gradually changes with the piston stroke.

[0014] In a preferred embodiment, the length Lt of the annular transition band ranges from 2 mm to 12 mm to accommodate different gas supply pressures and operating loads.

[0015] In a preferred embodiment, the annular transition band is disposed near the axial opening of the air distribution channel. By changing the length Lt of the annular transition band, the axial stroke range of the air distribution channel being blocked or opened by the piston can be adjusted.

[0016] In a preferred embodiment, the annular transition zone is provided at the step or shoulder position of the cylinder inner wall to replace the original right-angle step and form a smooth transition area.

[0017] In a preferred embodiment, the cylinder body is provided with a plurality of air distribution channels, and the annular transition zone is located near at least one air distribution channel related to the intake of the rear air chamber.

[0018] In a preferred embodiment, the annular transition zone and the cylinder body are an integral structure, formed by machining (such as turning, milling) or precision casting.

[0019] In a preferred embodiment, the surface of the annular transition zone has a wear-resistant coating to further enhance its resistance to airflow erosion.

[0020] The technical effects and advantages of this invention are as follows:

[0021] 1. This invention, by setting an annular transition zone at the critical opening and closing boundary of the rear air chamber, transforms the abrupt change in flow cross-sectional area caused by the original straight step or short transition structure into a gradual process with a certain buffer length; it weakens the velocity gradient and local eddy intensity of the gas near the inlet and step, reduces local pressure loss and pressure gradient peaks, thereby reducing the flow dissipation of gas energy and improving the effective driving capability of compressed air on the piston; at the same time, due to the improvement of the flow field, the peak value of wall shear stress is effectively suppressed and dispersed, significantly reducing the risk of scouring and wear in critical areas, which helps to extend the service life of the impactor and maintain performance stability.

[0022] 2. This invention uses the axial length Lt of the annular transition zone as an independently adjustable geometric parameter, achieving precise and controllable adjustment of the effective air intake length of the rear air chamber. It transforms a complex parameter that was originally determined by multiple coupled geometric elements and was difficult to optimize individually into an object that can be designed, verified, and optimized through a single main parameter. Designers can quickly perform parametric comparison and optimization by adjusting the Lt value according to different air supply pressures, drilling conditions, and performance requirements, thereby finding the optimal air distribution matching scheme more efficiently and significantly improving the flexibility of structural design and adaptability to working conditions.

[0023] 3. The structural modifications of this invention are highly concentrated in a local area of ​​the cylinder inner wall, without changing the overall configuration, basic valve distribution principle and main assembly relationship of the down-the-hole impactor, nor introducing complex external valve groups or adding new precision components. This localized improvement scheme has the advantages of simple processing technology, low manufacturing cost, easy implementation and promotion, and can be well compatible with the existing cylinder manufacturing system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structural model of the down-the-hole impactor body of the present invention.

[0025] Figure 2 This is a schematic diagram of the exploded structure of the down-the-hole impactor body of the present invention.

[0026] Figure 3 This is a schematic diagram of the cylinder body structure of the present invention.

[0027] Figure 4 This is a schematic diagram comparing the annular transition zone of the present invention with the reference structure (Lt=0).

[0028] Figure 5 The following are flow field simulation results cloud maps under the Lt=0 structure in the embodiment of the present invention; where (a) is the velocity cloud map, (b) is the pressure cloud map, and (c) is the wall shear rate cloud map.

[0029] Figure 6 The following are flow field simulation results cloud maps under the Lt=6 structure in the embodiment of the present invention; where (a) is the velocity cloud map, (b) is the pressure cloud map, and (c) is the wall shear rate cloud map.

[0030] Figure 7 The following are flow field simulation results cloud maps under the Lt=12 structure in the embodiment of the present invention; where (a) is the velocity cloud map, (b) is the pressure cloud map, and (c) is the wall shear rate cloud map.

[0031] The attached diagram is labeled: 100 down-the-hole impactor;

[0032] 110 rear connector;

[0033] 120 Cylinder body, 121 Axial inner bore, 122 Air distribution channel, 123 Annular transition zone, 124 Positioning pin;

[0034] 130 piston, 131 valve train;

[0035] 140 front connector;

[0036] 150 drill bit;

[0037] 160 outer sleeve;

[0038] 170 check valve. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1:

[0041] This invention provides a down-the-hole impactor with an annular transition belt cylinder, such as... Figure 1 and Figure 2 As shown, the down-the-hole impactor 100 of this invention comprises a rear connector 110, a cylinder body 120, a piston 130, a front connector 140, a drill bit 150, and an outer sleeve 160, among other main components. The cylinder body 120, as the core component, has an axial inner bore 121 within which the piston 130 is axially slidably accommodated. The piston 130 divides the internal space of the cylinder body 120 into a front chamber (near the front connector 140 and the drill bit 150) and a rear chamber (near the rear connector 110 and the air inlet). The rear connector 110 has a main air inlet channel through which compressed air enters the impactor.

[0042] like Figure 3 As shown, at least one air distribution channel 122 is provided on the side wall of the cylinder body 120. This air distribution channel 122 works in conjunction with the air distribution groove 131 provided on the piston 130 to control the intake and exhaust reversal of the front and rear air chambers. On the inner wall of the cylinder body 120, near the opening and closing boundary of the rear air chamber intake passage, an annular transition zone 123 is provided. This annular transition zone 123 is an axially extending annular buffer area with a smooth inner diameter transition, used to replace the straight steps or short-distance transition structures in the prior art.

[0043] Specifically, the annular transition zone 123 is disposed in a critical area of ​​the cylinder inner wall, such as the starting boundary where the rear air chamber intake passage begins to connect, the ending boundary where the rear air chamber intake passage ends to connect, or the sensitive area where the shielding and connection relationship between the valve distribution channel 122 and the valve distribution groove 131 on the piston 130 changes. The length of the annular transition zone 123 along the axial direction of the cylinder body 120 is defined as Lt (in mm), and this length Lt is an independently adjustable geometric parameter in this invention.

[0044] like Figure 4As shown, a comparison with the baseline structure (Lt=0, i.e., the existing straight step structure without a transition zone) reveals that the annular transition zone 123 of this invention transforms a geometric abrupt change point into a gradual buffer zone with an axial length Lt. When the piston 130 moves within the cylinder, the flow cross-sectional area between the valve port 122 and the valve groove 131 on the piston 130 no longer opens or closes instantaneously within a very short stroke, but rather undergoes a smooth, gradual transition as the piston 130 gradually passes the length Lt of the annular transition zone 123. This process directly alters the duration of the connection and obstruction of the rear chamber intake passage, thereby precisely adjusting the effective intake length (i.e., the equivalent valve length) of the rear chamber.

[0045] Example 2:

[0046] This embodiment uses numerical simulation to compare and analyze the three structures Lt=0, Lt=6, and Lt=12, revealing the influence of the annular transition zone length Lt on the internal flow field characteristics of the cylinder.

[0047] Simulation Model and Settings

[0048] The simulation model does not directly solve for the solid metal cylinder, but rather extracts the space inside the cylinder actually occupied and traversed by gas as a separate fluid domain solid model. This ensures that the simulated object is highly consistent with the real fluid flow region, thus enabling more accurate analysis of flow field characteristics. All three models (Lt=0, Lt=6, Lt=12) use the same main channel structure, the same air distribution port location, and the same outlet end face structure, only changing the axial length Lt of the annular transition zone in the key inlet region.

[0049] The simulation software used was COMSOL Multiphysics 6.3, the physics field was a laminar flow model, and the study type was steady-state analysis. Boundary conditions were set as follows: the large circular opening with an annular transition zone at the left end was designated as the velocity inlet, with the inlet velocity set to the same value; the circular end face at the right end and the two side orifice faces near the right end were designated as the pressure outlet, with the outlet pressure set to 0 Pa (gauge pressure); all other boundaries except the inlet and outlet were designated as no-slip walls. A consistent mesh level and the same local refinement principles were used to ensure the comparability of calculation results from different Lt models.

[0050] The simulation results mainly output velocity contour maps, pressure contour maps, and wall shear rate contour maps, which are used to characterize the velocity distribution of the flow field, the pressure decay process, and the concentrated region of the wall flow gradient (potential scour risk region), respectively.

[0051] like Figure 5As shown, for the baseline structure with Lt=0, the velocity contour map (a) shows a significant high-speed zone at the entrance step, with drastic changes in the velocity gradient; the pressure contour map (b) shows a sharp drop in pressure near the step, with significant local pressure loss; and the wall shear rate contour map (c) shows an extremely high shear rate peak at the edge of the step, forming a scour point.

[0052] like Figure 6 As shown, for the optimized structure with Lt=6, the velocity contour map (a) shows that the velocity gradient in the inlet region is somewhat mitigated and the high-speed region is more evenly distributed; the pressure contour map (b) shows that the pressure drop near the inlet is relatively gentle and the local pressure loss is reduced; the wall shear rate contour map (c) shows that the peak value of the high shear region of the wall is significantly reduced and the distribution range is expanded, no longer a single peak point.

[0053] like Figure 7 As shown, for the optimized structure with Lt=12, the velocity cloud map (a) shows that the velocity change in the inlet region is more gradual and the flow state is more stable; the pressure cloud map (b) shows that the pressure decay curve along the axial direction is smoother and the overall pressure loss is further reduced; the wall shear rate cloud map (c) shows that the range of the high shear region on the wall is wider, but the peak value continues to decrease, and the risk of scouring is effectively dispersed.

[0054] Simulation results from the three structures show that as Lt increases from 0 to 6 and then to 12, the velocity distribution, pressure gradient, and wall shear rate distribution in the inlet transition zone all change significantly. This indicates that the length Lt of the annular transition zone structure proposed in this invention is a key variable that strongly modulates the local flow field. Increasing Lt can effectively smooth the flow, reduce pressure loss, and decrease the degree of high shear concentration at the wall.

[0055] Example 3:

[0056] To further quantitatively analyze the influence of different annular transition zone lengths Lt on the internal flow field of the cylinder, this embodiment simulates seven groups of structures with Lt=0, 2, 4, 6, 8, 10, and 12 mm under the same boundary conditions and solution settings. Key indicators such as maximum velocity, average inlet pressure, average outlet pressure, pressure drop ΔP, and maximum shear rate are extracted and compared. The results are summarized in Table 1 below.

[0057]

[0058] The following patterns can be observed from the data in Table 1:

[0059] When Lt increases from 0 to 2 mm, the maximum velocity, pressure drop, and maximum shear rate all increase significantly. This indicates that introducing a very short transition zone may actually intensify the local flow, possibly due to changes in the airflow incident angle or increased local disturbances.

[0060] However, as Lt continues to increase from 2 mm to 12 mm, the maximum velocity, pressure drop, and maximum shear rate generally show a gradual decreasing trend. This indicates that when the annular transition zone has a sufficient length (Lt≥4 mm), its beneficial effects of smoothing flow, reducing losses, and minimizing wall shear concentration begin to appear and continue to enhance.

[0061] The quantitative analysis results above show that the length Lt of the annular transition zone has a clear parametric sensitivity to the local flow field, and there exists an optimized range of Lt values ​​(e.g., Lt ≥ 4 mm in this embodiment), within which better flow performance can be obtained. This provides a clear quantitative basis for selecting a reasonable Lt range for different operating conditions in engineering practice.

[0062] Example 4:

[0063] Combination Figures 1-7 This paper details the specific implementation method and working process of a down-the-hole impactor with an annular transition zone cylinder according to the present invention.

[0064] like Figure 1 and Figure 2 As shown, during the assembly of the down-the-hole hammer 100, the piston 130 is installed in the axial inner hole 121 of the cylinder body 120, with its rear end adjacent to the rear connector 110 and its front end adjacent to the front connector 140 and the drill bit 150. Compressed air enters from the rear connector 110 and acts on the rear end face (rear chamber) and front end face (front chamber) of the piston 130 through the airflow passage and air distribution port 122 on the cylinder body 120.

[0065] like Figure 3 and Figure 4 As shown, the key structure of this invention lies in the annular transition zone 123 on the inner wall of the cylinder body 120. The axial length Lt of this annular transition zone 123 is a designable parameter. During the stroke and return stroke of the piston 130, when the piston 130 moves to the opening and closing boundary of the rear air chamber intake passage, the connection or obstruction between the valve distribution channel 122 and the valve distribution groove 131 on the piston 130 is no longer completed instantaneously, but gradually as the end face or sealing strip of the piston 130 passes through the annular transition zone 123 of length Lt.

[0066] Working principle:

[0067] Refer to the instruction manual appendix Figures 3-4Taking the stroke stage as an example. Initially, the rear chamber is in the exhaust state, and the front chamber is in the intake state. When the piston 130 moves towards the drill bit 150 under the action of the pressure difference, the valve groove 131 on the piston 130 gradually disengages from the valve passage 122 on the cylinder body 120, and the intake passage of the rear chamber begins to close. Due to the presence of the annular transition zone 123, the opening of the valve passage 122 is not instantly blocked by the cylindrical surface of the piston 130, but rather, as the end face of the piston 130 or the sealing strip moves on the gradually changing inner diameter of the annular transition zone 123, the flow area gradually decreases, thus achieving a smooth closing process. This effectively suppresses pressure fluctuations and eddy current generation, reducing flow losses.

[0068] Further, please refer to the appendix to the instruction manual. Figures 5-7 During the return stroke, as piston 130 moves towards rear connector 110 under gas pressure, the intake passage of the rear chamber needs to reopen. As piston 130 moves, the opening of the distribution port 122 disengages again from the end face or sealing strip of piston 130. Due to the gradually changing inner diameter of the annular transition band 123, the flow area gradually increases, achieving a smooth opening process. This allows gas to enter the rear chamber smoothly, reducing the velocity gradient and pressure loss at the inlet.

[0069] Referring to Table 1, by changing the value of Lt, the duration of the smooth opening and closing process described above can be quantitatively adjusted, thereby precisely controlling the effective air intake length of the rear chamber. For example, when it is necessary to increase the impact frequency, Lt can be appropriately decreased to shorten the air intake time of the rear chamber and make the reversal faster; when it is necessary to increase the single impact power, Lt can be appropriately increased to make the air intake of the rear chamber more complete and the pressure build-up higher. This parameterized adjustment capability is not available in existing technologies.

[0070] This invention transforms the original geometrically abrupt boundary into a gradually transitioning boundary with a buffer length by setting an annular transition zone with a specific axial length Lt at the critical opening and closing boundary of the rear chamber's air distribution on the cylinder inner wall. During piston movement, this structure changes the flow cross-sectional area of ​​the air distribution channel from abrupt to gradual, effectively improving the flow field distribution in the inlet region and reducing local pressure loss and wall shear stress concentration. Simultaneously, by using Lt as an independently adjustable parameter, precise and controllable adjustment of the effective intake length (equivalent air distribution length) of the rear chamber is achieved, providing a clear and quantifiable design path for optimizing the performance of down-the-hole impactors.

[0071] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0072] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0073] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A down-the-hole impactor with an annular transition cylinder, comprising a down-the-hole impactor body (100), characterized in that: The down-the-hole impactor body (100) includes a cylinder body (120) and a piston (130). The cylinder body (120) is provided with an axial inner hole (121) for accommodating the piston (130). At least one air distribution channel (122) is provided on the side wall of the cylinder body (120), and a positioning pin (124) is provided at the air distribution channel (122). On the inner wall of the cylinder body (120), there is an annular transition zone (123) near the opening and closing boundary of the rear air chamber intake passage. The length of the annular transition zone (123) along the axis of the cylinder body (120) is defined as Lt; the length Lt is used as an independently adjustable geometric parameter to change the effective intake length of the rear air chamber.

2. The down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The down-the-hole hammer body (100) also includes a drill bit (150), a front connector (140) and a rear connector (110). A check valve (170) is also provided between the piston (130) and the rear connector (110); one end of the piston (130) has its outer diameter reduced inward to form a gas distribution groove (131).

3. A down-the-hole impactor with an annular transition zone cylinder according to claim 2, characterized in that: The inner wall of the annular transition zone (123) is a smooth curved surface, and its axial cross-sectional profile is a straight line or a curve, so as to form a cone or arc surface with a smooth inner diameter transition on the inner wall of the cylinder body (120). The annular transition zone (123) is set at the starting boundary position where the rear air chamber intake channel begins to connect, at the ending boundary position where the rear air chamber intake channel ends to connect, and in the sensitive area where the shielding and connection relationship between the air distribution channel (122) and the air distribution groove (131) on the piston (130) changes.

4. A down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The inner wall of the annular transition zone (123) and the outer circular surface of the piston (130) form a fitting gap. When the piston (130) reciprocates in the axial inner hole (121), the annular transition zone (123) and the sealing strip, guide strip or end face edge on the piston (130) form relative motion, so that the flow cross-sectional area between the air distribution channel (122) and the air distribution groove (131) on the piston (130) gradually changes with the piston stroke.

5. A down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The annular transition band (123) is located at the axial opening of the air distribution channel (122). By changing the length Lt of the annular transition band (123), the axial stroke range of the air distribution channel (122) being blocked or opened by the piston (130) can be adjusted.

6. A down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The annular transition zone (123) is set at the step or shoulder position of the cylinder inner wall to replace the original right-angle step and form a smooth transition zone.

7. A down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The cylinder body (120) is provided with a plurality of air distribution channels (122), and the annular transition zone (123) is provided at at least one air distribution channel (122) related to the intake of the rear air chamber.

8. A down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The annular transition zone (123) and the cylinder body (120) are an integral structure, formed by machining or precision casting.

9. A down-the-hole impactor with an annular transition zone cylinder according to claim 1, characterized in that: The surface of the annular transition zone (123) has a wear-resistant coating.

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