A low speed two-stroke engine piston

Abstract

The application discloses a low-speed two-stroke engine piston, which comprises a piston rod, a piston head, a piston skirt, a distribution block, a jet disc and an oil return pipe; a central cooling cavity of the piston head is communicated with a cooling blind hole; the oil return pipe is arranged in the piston rod and is provided with an oil return channel, and an oil inlet channel is formed between the oil return channel and the piston rod; the distribution block is arranged at one end of the oil return pipe and is provided with an oil inlet hole, an oil return groove and an oil return hole; the jet disc is provided with a through hole, a side cooling hole and a top cooling hole, a strong convection cavity is formed between the jet disc and the central cooling cavity, and a distribution oil cavity is formed between the jet disc and the distribution block; a gap is reserved at a transition position of the piston head and the jet disc; the oil inlet channel is communicated with the distribution oil cavity through the oil inlet hole, the distribution oil cavity is communicated with the central cooling cavity through the side cooling hole, and the distribution oil cavity is communicated with the strong convection cavity through the top cooling hole; the strong convection cavity is communicated with the central cooling cavity through the gap, the central cooling cavity is communicated with the oil return groove through the through hole, and the oil return groove is communicated with the oil return channel through the oil return hole. The low-speed two-stroke engine piston meets the cooling and heat exchange requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of engine technology, in particular to a low-speed two-stroke engine piston. BACKGROUND

[0002] The piston is an important component of the combustion chamber and one of the core components of the engine, and plays a crucial role in the reliable operation of the engine. The working environment of the piston is extremely harsh, directly contacting with the high-temperature and high-pressure gas in the combustion chamber, while bearing the mechanical load and high thermal load transmitted by the combustion chamber, which can easily cause problems such as poor lubrication and difficult cooling. When the piston is not sufficiently cooled, it may cause the temperature of the piston to be too high, the mechanical properties of the material to decrease, and the piston to locally break or crack, which seriously threatens the reliable operation of the engine; the lubricating oil between the piston and the cylinder sleeve is gelled, which induces serious failures such as piston seizure and piston ring jamming; the oil on the top surface is carbonized, which causes the local temperature to be too high, the thermal stress of the piston to increase, and a series of problems such as top surface ablation and increased emissions.

[0003] With the development of larger and larger ships, the mean effective pressure and explosion pressure of the low-speed two-stroke engine are continuously increasing, which makes the pressure and temperature in the combustion chamber higher and higher, which puts higher requirements on the cooling and heat exchange of the piston. SUMMARY

[0004] The mean effective pressure and explosion pressure of the low-speed two-stroke engine are continuously increasing, which makes the pressure and temperature in the combustion chamber higher and higher, and the present application provides a low-speed two-stroke engine piston to meet the higher demand of the piston for cooling and heat exchange.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is:

[0006] A low-speed two-stroke engine piston, comprising a piston head mounted at the top of a piston rod and a piston skirt arranged around the piston rod and closely connected with the piston head, further comprising a distribution block, a jet disc and an oil return pipe;

[0007] The piston head is provided with a central cooling cavity and a cooling blind hole obliquely arranged at the transition of the inner top wall and the side wall of the piston head, and the central cooling cavity is communicated with the cooling blind hole;

[0008] The oil return pipe is arranged inside the piston rod, the oil return pipe is provided with an oil return channel, and the oil return pipe and the piston rod form an oil inlet channel therebetween;

[0009] The distribution block is arranged at one end of the oil return pipe and fixedly connected with the piston rod, and the distribution block is provided with an oil inlet hole, an oil return groove and an oil return hole;

[0010] The injection disc is provided with a through hole, a side cooling hole and a top cooling hole, the injection disc is fixedly connected with the distribution block, a strong convection cavity is formed between the top wall of the injection disc and the top wall of the central cooling cavity, and a distribution oil cavity is formed between the injection disc and the distribution block;

[0011] A gap is left between the transition of the inner top wall of the piston head and the side wall and the transition of the top wall of the injection disc and the side wall;

[0012] The oil inlet channel is communicated with the distribution oil cavity through an oil inlet hole, the distribution oil cavity is communicated with the central cooling cavity through the side cooling hole towards the bottom of the cooling blind hole along the axis, and the distribution oil cavity is communicated with the strong convection cavity through the top cooling hole;

[0013] The strong convection cavity is communicated with the central cooling cavity through the gap, the central cooling cavity is communicated with the oil return groove through the through hole, and the oil return groove is communicated with the oil return channel through an oil return hole.

[0014] Further, the axis of the top cooling hole is perpendicular to the top wall of the central cooling cavity.

[0015] Further, the side cooling hole and the cooling blind hole are on the same axis.

[0016] Further, the axis of the side cooling hole is offset relative to the axis of the cooling blind hole, and the axis of the side cooling hole points to the side wall of the piston head.

[0017] Further, the axis of the side cooling hole is offset relative to the axis of the cooling blind hole, and the axis of the side cooling hole points to the top wall of the piston head.

[0018] Further, the center of the distribution block is arched towards the top wall of the piston head.

[0019] Further, the distance between the top outer wall of the injection disc and the top wall of the central cooling cavity is 15-25 mm, and the gap is 5-10 mm.

[0020] Further, the diameter of the side cooling hole is 2-5 mm, and the diameter of the top cooling hole is 2-5 mm.

[0021] Further, the end of the oil return pipe close to the distribution block is a flared opening, and the inner hole of the end of the piston rod close to the distribution block is flared.

[0022] Further, the through hole is a waist-shaped hole, and the cross-sectional shape of the oil return groove is the same as the cross-sectional shape of the through hole.

[0023] The present application has the following beneficial effects:

[0024] Compared with the prior art, the low-speed two-stroke engine piston provided by the application has a combined structure of a spray disc and a distribution block, a distribution oil cavity is arranged in a central cooling cavity of a piston head, side / top cooling holes communicating with the distribution oil cavity are arranged on the spray disc, spray cooling is realized without the need of installing a spray pipe, the position, angle and number of the side / top cooling holes arranged on the spray disc are not limited by space size and can be set according to actual cooling requirements, the structure is simpler, the cooling mode is more flexible, meanwhile, the number of parts is effectively reduced, and the manufacturing difficulty of the piston is reduced.

[0025] After the cooling oil enters the distribution oil cavity, part of the cooling oil impacts the cooling blind hole on the piston head along the side cooling hole, heat exchange of the side surface and the top edge of the piston is strengthened through free spray cooling, and the other part of the cooling oil enters the strong convection cavity along the top cooling hole, impacts the wall surface of the central cooling cavity, is limited by the top wall of the central cooling cavity and the top wall of the spray disc, constantly collides, rebounds and collides again between the two walls, and simultaneously has a mutual coupling effect with the cooling liquid in the strong convection cavity, forms extremely strong turbulent flow, and the heat exchange of the top surface of the piston is strengthened through the limited submerged jet flow, the cooling heat exchange of the piston is greatly strengthened through the combination of the limited submerged jet flow cooling and the free spray cooling, the failure of the engine piston caused by excessively high thermal load can be effectively avoided, and it is ensured that the engine can be safely and reliably operated. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative labor under the premise of the drawings.

[0027] Figure 1 is a whole front view of embodiment 1 of the low-speed two-stroke engine piston disclosed by the application;

[0028] Figure 2 is a whole side view of embodiment 1 of the low-speed two-stroke engine piston disclosed by the application;

[0029] Figure 3 is a whole top view of embodiment 1 of the low-speed two-stroke engine piston disclosed by the application;

[0030] Figure 4 is a structure schematic view of the spray disc of embodiment 1 of the low-speed two-stroke engine piston disclosed by the application;

[0031] Figure 5 is a cooling oil flow path of embodiment 1 of the low-speed two-stroke engine piston disclosed by the applicationFigure 1 ;

[0032] Figure 6 is a cooling oil flow path of embodiment 1 of a low-speed two-stroke engine piston disclosed by the present application Figure 2 ;

[0033] Figure 7 is a jet cooling schematic of embodiment 1 of a low-speed two-stroke engine piston disclosed by the present application

[0034] Figure 8 is a jet cooling schematic of embodiment 2 of a low-speed two-stroke engine piston disclosed by the present application

[0035] Figure 9 is a jet cooling schematic of embodiment 3 of a low-speed two-stroke engine piston disclosed by the present application

[0036] Figure 10 is a partial enlarged sectional view of embodiment 4 of a low-speed two-stroke engine piston disclosed by the present application.

[0037] In the figure: 1, piston head; 11, central cooling cavity; 12, cooling blind hole;

[0038] 2, piston skirt;

[0039] 3, piston rod; 31, oil inlet channel;

[0040] 4, distribution block; 41, oil inlet hole; 42, oil return groove; 43, oil return hole; 44, distribution oil cavity;

[0041] 5, jet disc; 51, through hole; 52, side cooling hole; 53, top cooling hole; 54, strong convection cavity;

[0042] 6, bolt;

[0043] 7, oil return pipe; 71, oil return channel. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0045] Embodiment 1

[0046] The present embodiment provides a low-speed two-stroke engine piston, such as Figure 1 andFigure 2 As shown, it includes a piston head 1 mounted on top of the piston rod 3 and a piston skirt 2 arranged around the piston rod 3 and tightly connected to the piston head 1, as well as a distribution block 4, an injection disc 5 and a return oil pipe 7;

[0047] The piston head 1 is provided with a central cooling chamber 11 and a cooling blind hole 12 inclinedly disposed at the transition between the top wall and the side wall inside the piston head 1. The central cooling chamber 11 is connected to the cooling blind hole 12 (in this embodiment, the cooling blind hole 12 is a flat-bottomed blind hole).

[0048] The oil return pipe 7 is installed inside the piston rod 3, and the oil return pipe 7 is provided with an oil return channel 71. An oil inlet channel 31 is formed between the oil return pipe 7 and the piston rod 3.

[0049] The distribution block 4 is located at one end of the return oil pipe 7 and is fixedly connected to the piston rod 3, such as Figure 3 As shown, the distribution block 4 is provided with an oil inlet 41, an oil return groove 42 and an oil return hole 43;

[0050] like Figure 4 As shown, the spray disk 5 is provided with through holes 51, side cooling holes 52 and top cooling holes 53. The spray disk 5 is fixedly connected to the distribution block 4. A strong convection cavity 54 is formed between the top wall of the spray disk 5 and the top wall of the central cooling cavity 11. An oil distribution cavity 44 is formed between the spray disk 5 and the distribution block 4.

[0051] A gap is left between the transition between the inner top wall and the side wall of the piston head 1 and the transition between the top wall and the side wall of the injection disc 5;

[0052] The oil inlet channel 31 is connected to the oil distribution chamber 44 through the oil inlet hole 41. The oil distribution chamber 44 is connected to the central cooling chamber 11 through the side cooling hole 52 with the axis facing the bottom of the cooling blind hole 12. The oil distribution chamber 44 is connected to the strong convection chamber 54 through the top cooling hole 53.

[0053] The strong convection cavity 54 is connected to the central cooling cavity 11 through a gap. The central cooling cavity 11 is connected to the oil return groove 42 through a through hole 51. The oil return groove 42 is connected to the oil return channel 71 through an oil return hole 43.

[0054] Compared with the prior art, the present invention provides a low-speed two-stroke engine piston. Through the combined structure of injection disc 5 and distribution block 4, a distribution oil chamber 44 is set in the central cooling chamber 11 of the piston head 1. Side cooling holes 52 and top cooling holes 53 are opened on the injection disc 5 to connect the distribution oil chamber 44. Spray cooling can be achieved without the need to install a nozzle. The position, angle and number of side / top cooling holes on the injection disc are not limited by the space size and can be set according to the actual cooling needs. The structure is simpler and the cooling method is more flexible, effectively reducing the number of parts and reducing the manufacturing difficulty of the piston.

[0055] In the prior art, the piston is usually cooled by oscillation cooling, and the heat exchange effect of oscillation cooling is greatly affected by the rotating speed, the higher the rotating speed, the better the heat exchange effect, for a low-speed two-stroke engine, the rotating speed is lower than 300r / min, and the heat exchange effect of oscillation cooling cannot be enhanced by increasing the rotating speed, when the piston is close to the bottom dead center, the cooling oil is gathered at the bottom of the oil chamber of the piston due to the action of the inertial force, so that the high-temperature top surface is separated from the cooling oil and cannot be effectively cooled, therefore, the conventional oscillation cooling cannot meet the increasing heat load demand of the piston;

[0056] The application provides a piston for a low-speed two-stroke engine, as shown in Figure 5 and Figure 6 The cooling oil enters through the oil inlet channel 31, enters the distribution oil chamber 44 through the oil inlet hole 41, a part of the cooling oil impacts the cooling blind hole 12 on the piston head 1 along the side cooling hole 52, the heat exchange of the side surface and the top edge of the piston head 1 is strengthened by free jet cooling, and sufficient heat exchange of the piston in the vicinity of the bottom dead center is ensured.

[0057] Another part of the cooling oil enters the strong convection cavity 54 along the top cooling hole 53, impacts the wall surface of the central cooling cavity 11, is limited by the top wall of the central cooling cavity 11 and the top wall of the jet disc 5, constantly collides, rebounds and collides again between the two wall surfaces, and constantly couples with the cooling oil in the strong convection cavity 54, so that a strong turbulent flow is formed in the strong convection cavity 54, and the heat exchange of the top surface of the piston is strengthened by limited submerged jet cooling.

[0058] The cooling oil after completing the heat exchange flows out through the gap, is accumulated at the bottom of the central cooling cavity 11 under the action of gravity, and finally enters the oil return channel 71 through the through hole 51, the oil return groove 42 and the oil return hole 43 and flows out.

[0059] The application effectively strengthens the cooling heat exchange of the piston by combining limited submerged jet cooling and free jet cooling, meets the high demand of the piston of the low-speed two-stroke engine for cooling heat exchange, can effectively avoid the failure of the engine piston caused by excessively high heat load, and ensures that the engine can be safely and reliably operated.

[0060] In specific embodiments, the piston rod 3, the distribution block 4 and the jet disc are fixedly connected through bolts 6, and the oil return pipe 7 is fixedly welded to the distribution block 4.

[0061] In specific embodiments, the axis of the side cooling hole 52 is offset relative to the axis of the cooling blind hole 12, and the axis of the side cooling hole 52 points to the side wall of the piston head 1.

[0062] In the embodiment, as shown in Figure 7As shown, after the cooling oil impacts the bottom of the cooling blind hole 12 through the side cooling hole 52, the cooling oil flows downward along the side wall of the cooling blind hole 12 and flows from the bottom of the cooling blind hole 12 near the side wall of the piston head 1 to the side near the top wall. It continuously collides in the cooling blind hole 12, which can simultaneously enhance the heat exchange of the top edge and the side of the piston head 1. In this embodiment, the axis of the side cooling hole 52 points to the side wall of the piston head 1, so the jet points to the bottom of the cooling blind hole 12 near the side wall of the piston head 1, which is better for cooling and heat exchange of the side wall of the piston head 1.

[0063] In a specific embodiment, the center of the distribution block 4 arches towards the top wall of the piston head 1, thereby reducing the weight of the distribution block 4 and decreasing the volume of the distribution oil chamber 44 between the distribution block 4 and the injection disc 5. This allows the cooling oil to quickly fill the distribution oil chamber 44 and pass through it rapidly, while also reducing the weight of the cooling oil accumulated in the distribution oil chamber 44. By reducing the weight of the distribution block 4 and the cooling oil accumulated in the distribution oil chamber 44, the piston weight is reduced, thereby reducing the piston inertial force, which in turn reduces the friction between the piston and the cylinder liner, reduces the load on the connecting rod assembly, and improves the engine's durability. At the same time, the overall engine weight is reduced, improving fuel economy.

[0064] In practical applications, the top wall and side wall of the distribution block 4 are chamfered at the transition, the top wall and side wall of the piston head 1 are chamfered at the transition, and the top wall and side wall of the injection disc 5 are chamfered at the transition, in order to avoid stress concentration.

[0065] In a specific embodiment, the distance between the outer top wall of the spray disc 5 and the inner top wall of the central cooling cavity 11 is 15-25 mm (see...). Figure 10 (H1), the gap is 5-10mm (see H1). Figure 10 The gap H2 is narrower than the distance H1 between the top outer wall of the spray disc 5 and the top wall of the central cooling cavity 11, so as to ensure that the strong convection cavity 54 can be filled with cooling oil by reducing the flow rate of cooling oil out of this area.

[0066] In a specific embodiment, the diameter of the side cooling hole 52 is 2-5mm, and the diameter of the top cooling hole 53 is 2-5mm. The small diameter ensures that the cooling oil is ejected from the hole at a faster flow rate under the same pressure.

[0067] In a specific embodiment, the axis of the cooling blind hole 12 is offset relative to the central axis of the piston head 1, and the included angle between the two is 15° to 30°. Within this angle range, the depth of the cooling blind hole 12 can be ensured without affecting the strength of the piston head 1, so as to ensure good heat exchange effect.

[0068] In a specific embodiment, the end of the oil return pipe 7 near the distribution block 4 is a flared opening, and the inner hole of the piston rod 3 near the distribution block 4 is flared. The flared shape with its inclined angle can make the return of cooling oil smoother.

[0069] In a specific embodiment, the through hole 51 is an oblong hole, and the cross-sectional shape of the oil return groove 42 is the same as that of the through hole 51. The oblong hole increases the passable area, making the cooling oil return smooth.

[0070] In a specific embodiment, a plurality of cooling blind holes 12 are arranged in a circular array around the central axis of the piston head 1 on the piston head 1, a plurality of oil inlet holes 41, a plurality of oil return grooves 42 and a plurality of oil return holes 43 are arranged in a circular array around the central axis of the piston head 1 on the distribution block 4, and a plurality of through holes 51, a plurality of side cooling holes 52 and a plurality of top cooling holes 53 are arranged in a circular array around the central axis of the piston head 1 on the injection disc 5;

[0071] Multiple sets of pressurized cooling oil are continuously and at high speed injected into the central cooling chamber 11 and the strong convection chamber 54. Restricted by the top wall of the central cooling chamber 11 and the top wall of the injection disk 5, the oil collides, bounces, and collides again between the two walls, and couples with the cooling oil in the strong convection chamber 54, generating strong turbulent flow, which greatly enhances the convective heat transfer on the top surface of the piston head 1.

[0072] In practical applications, the piston head 1, piston skirt 2, and piston rod 3 are fixedly connected by threaded fasteners.

[0073] Example 2

[0074] This embodiment provides a low-speed two-stroke engine piston. The working principle and main structure of this embodiment are the same as those of Embodiment 1. The difference between this embodiment and Embodiment 1 is as follows:

[0075] In Embodiment 1, the axis of the side cooling hole 52 is offset relative to the axis of the cooling blind hole 12, and the axis of the side cooling hole 52 points towards the side wall of the piston head 1.

[0076] In this embodiment, as Figure 8 As shown, the side cooling hole 52 and the cooling blind hole 12 are on the same axis;

[0077] In this embodiment, after the cooling oil impacts the bottom of the cooling blind hole 12 through the side cooling hole 52, the cooling oil flows downward along the side wall of the cooling blind hole 12 and flows from the center of the bottom of the cooling blind hole 12 to the outside of the bottom of the cooling blind hole 12. It continuously collides within the cooling blind hole 12, which can simultaneously enhance the heat exchange of the piston top and side. In this embodiment, the side cooling hole 52 and the cooling blind hole 12 are on the same axis, so the jet points to the center of the bottom of the cooling blind hole 12, and the cooling heat exchange of the side wall and top wall of the piston head 1 is relatively uniform.

[0078] Example 3

[0079] This embodiment provides a low-speed two-stroke engine piston. The working principle and main structure of this embodiment are the same as those of Embodiment 1. The difference between this embodiment and Embodiment 1 is as follows:

[0080] In Embodiment 1, the axis of the side cooling hole 52 is offset relative to the axis of the cooling blind hole 12, and the axis of the side cooling hole 52 points towards the side wall of the piston head 1.

[0081] In this embodiment, as Figure 9 As shown, the axis of the side cooling hole 52 is offset relative to the axis of the cooling blind hole 12, and the axis of the side cooling hole 52 points towards the top wall of the piston head 1.

[0082] In this embodiment, after the cooling oil impacts the bottom of the cooling blind hole 12 through the side cooling hole 52, the cooling oil flows downward along the side wall of the cooling blind hole 12 and flows from the bottom of the cooling blind hole 12 near the top wall of the piston head 1 to the side wall. It continuously collides within the cooling blind hole 12, which can simultaneously enhance the heat exchange of the piston top and side. In this embodiment, the axis of the side cooling hole 52 points to the top wall of the piston head 1, so the jet points to the bottom of the cooling blind hole 12 near the top wall of the piston head 1, which provides better cooling and heat exchange for the top wall of the piston head 1.

[0083] Example 4

[0084] This embodiment provides a low-speed two-stroke engine piston. The working principle and main structure of this embodiment are the same as those of Embodiment 1. The difference between this embodiment and Embodiment 1 is as follows:

[0085] In Embodiment 1, the orientation of the top cooling hole 53 is not limited.

[0086] In this embodiment, as Figure 10 As shown, the axis of the top cooling hole 53 is perpendicular to the top wall of the central cooling cavity 11, so that the angle of inclination of the jet emitted by the top cooling hole 53 and the angle of the heat exchange surface of the top wall of the central cooling cavity 11 are 90 degrees. At this time, the maximum heat transfer coefficient can be obtained and the heat exchange effect is the best.

[0087] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A piston for a low-speed two-stroke engine, comprising a piston head (1) mounted on top of a piston rod (3) and a piston skirt (2) arranged around the piston rod (3) and in close connection with the piston head (1), characterized in that It also comprises a distribution block (4), a spray disc (5) and an oil return pipe (7); The piston head (1) is internally provided with a central cooling cavity (11) and a cooling blind hole (12) obliquely arranged at the transition between the internal top wall and the side wall of the piston head (1), and the central cooling cavity (11) is communicated with the cooling blind hole (12); The oil return pipe (7) is arranged inside the piston rod (3), the oil return pipe (7) is internally provided with an oil return channel (71), and the oil return pipe (7) and the piston rod (3) form an oil inlet channel (31) therebetween; The distribution block (4) is arranged at one end of the oil return pipe (7) and is fixedly connected with the piston rod (3), the distribution block (4) is provided with an oil inlet hole (41), an oil return groove (42) and an oil return hole (43); The spray disc (5) is provided with a through hole (51), a side cooling hole (52) and a top cooling hole (53), the spray disc (5) is fixedly connected with the distribution block (4), a strong convection cavity (54) is formed between the top wall of the spray disc (5) and the top wall of the central cooling cavity (11), and a distribution oil cavity (44) is formed between the spray disc (5) and the distribution block (4); A gap is left between the transition between the internal top wall and the side wall of the piston head (1) and the transition between the top wall and the side wall of the spray disc (5); The oil inlet channel (31) is communicated with the distribution oil cavity (44) through the oil inlet hole (41), the distribution oil cavity (44) is communicated with the central cooling cavity (11) through the side cooling hole (52) which is axially directed to the bottom of the cooling blind hole (12), and the distribution oil cavity (44) is communicated with the strong convection cavity (54) through the top cooling hole (53); The strong convection cavity (54) is communicated with the central cooling cavity (11) through the gap, the central cooling cavity (11) is communicated with the oil return groove (42) through the through hole (51), and the oil return groove (42) is communicated with the oil return channel (71) through the oil return hole (43).

2. A low speed two-stroke engine piston according to claim 1, characterized in that The axis of the top cooling hole (53) is perpendicular to the top wall of the central cooling cavity (11).

3. A low speed two-stroke engine piston according to claim 1, characterized in that The side cooling hole (52) and the cooling blind hole (12) are on the same axis.

4. A low speed two-stroke engine piston according to claim 1, characterized in that The axis of the side cooling hole (52) is offset relative to the axis of the cooling blind hole (12), and the axis of the side cooling hole (52) is directed to the side wall of the piston head (1).

5. A low speed two-stroke engine piston according to claim 1, characterized in that The axis of the side cooling hole (52) is offset relative to the axis of the cooling blind hole (12), and the axis of the side cooling hole (52) is directed to the top wall of the piston head (1).

6. A low speed two-stroke engine piston according to claim 1, characterized in that The distribution block (4) is arched towards the top wall of the piston head (1).

7. A low speed two-stroke engine piston according to claim 1, characterized in that The distance between the top outer wall of the spray disc (5) and the top wall of the central cooling cavity (11) is 15-25 mm, and the gap is 5-10 mm.

8. A low speed two-stroke engine piston according to claim 1, characterized in that The diameter of the side cooling hole (52) is 2-5 mm, and the diameter of the top cooling hole (53) is 2-5 mm.

9. A low speed two-stroke engine piston according to claim 1, characterized in that The end of the oil return pipe (7) close to the distribution block (4) is a flared end, and the inner hole of the end of the piston rod (3) close to the distribution block (4) is flared.

10. A low speed two-stroke engine piston according to claim 1, characterized in that The through hole (51) is a waist-shaped hole, and the cross-sectional shape of the oil return groove (42) is the same as that of the through hole (51).

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