CN116412038A

CN116412038A - Piston crown, piston skirt and combined piston

Info

Publication number: CN116412038A
Application number: CN202211281360.4A
Authority: CN
Inventors: 汤义虎; 张国勇; 李梅; 李丽婷; 梁刚
Original assignee: 711th Research Institute of CSIC
Current assignee: 711th Research Institute of CSIC
Priority date: 2022-10-19
Filing date: 2022-10-19
Publication date: 2023-07-11

Abstract

The utility model provides a piston top, a piston skirt and a combined piston, and relates to the technical field of reciprocating engine parts. According to the piston top and the piston skirt provided by the embodiment of the utility model, the vertical oil holes extending to the contact surface are arranged to guide lubricating oil to the contact surface, so that a lubricating oil film is formed on the contact surface, a certain thrust bearing effect is achieved, the abrasion of the contact surface is reduced, and the risk of micro-cracking is reduced.

Description

Piston crown, piston skirt and combined piston

Technical Field

The utility model relates to the technical field of reciprocating engine parts, in particular to a piston top, a piston skirt and a combined piston.

Background

The combined piston is formed by assembling and connecting a piston top and a piston skirt through bolts, and in the working process, the piston top and the piston skirt connecting surface slide relatively, namely micro-motion exists on the surfaces of the piston top and the piston skirt under the action of alternating load. Under the explosion pressure working condition, the contact pressure of the contact surface of the piston top and the piston skirt is higher, and under the inertia force working condition, the contact surface of the piston top and the piston skirt, which is lower in contact pressure, is partially separated. The contact surface is worn due to the fretting action of the piston crown skirt contact surface, and worn abrasive particles participate in subsequent contact and wear in the sealing surface, so that the surface of the contact surface is roughened, and serious wear and even fatigue cracking are caused on the contact surface of the piston crown skirt along with the time, namely fretting wear and fretting fatigue are caused.

In order to reduce wear of the contact surfaces of the crown and skirt, a wear-resistant coating may be provided between the crown-skirt contact surfaces, the coating material may be chromium, tungsten carbide, or the like, and the coating is applied to the crown or skirt contact surface by a surface process, for example, as disclosed in the patent publication CN 202039963U. Because the coating material is harder than the matrix material and has low toughness, in the area of high local stress of micro-contact, the matrix material can be subjected to plastic deformation, so that cracks are generated on the surface coating. In addition, both coating materials and surface processing costs are relatively expensive.

Therefore, a scheme capable of reducing the abrasion of the contact surface of the combined piston and reducing micro-cracking is urgently needed.

Disclosure of Invention

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

The object of the utility model consists in providing a piston crown which contributes to a reduction of wear of the contact surfaces of the combined piston, while at the same time reducing the risk of micro-cracks.

It is also an object of the present utility model to provide a piston skirt that helps reduce wear of the combined piston interface while reducing the risk of micro-cracking.

It is also an object of the present utility model to provide a combination piston that reduces contact surface wear while reducing the risk of micro-cracking.

Embodiments of the present utility model may be implemented by:

the piston top is used for being fixedly connected with a piston skirt to form a combined piston, the piston top is provided with a first contact surface used for being in contact with the piston skirt, the piston top is provided with a first inner cavity and a first outer cavity, the first outer cavity is distributed around the first inner cavity, the first contact surface is positioned between the first inner cavity and the first outer cavity, the piston top is also provided with a first vertical oil hole and a communication hole, and two ends of the communication hole are respectively communicated with the first inner cavity and the first outer cavity so as to enable lubricating oil to flow between the first inner cavity and the first outer cavity; one end of the first vertical oil hole is communicated with the communication hole, and the other end of the first vertical oil hole extends downwards to the first contact surface so as to guide lubricating oil in the communication hole to flow to the first contact surface.

Optionally, a first oil distribution groove is formed in the first contact surface, the first vertical oil holes extend downwards and are communicated with the first oil distribution groove, and the cross-sectional area of the first oil distribution groove is larger than that of the first vertical oil holes.

Optionally, the number of the first vertical oil holes is multiple, and the openings of the multiple first vertical oil holes at the first contact surface are uniformly distributed along the circumferential direction of the piston top.

Optionally, the piston crown and the piston skirt are fixedly connected by a connecting bolt; the first contact surface is provided with a threaded hole for being in threaded connection with the connecting bolt; the first contact surface is also provided with a pressure relief groove, and the pressure relief groove and the threaded hole are positioned at the same circumferential position, extend along the radial direction of the piston top and are communicated with the first inner cavity and the first outer cavity.

The piston skirt is used for being fixedly connected with a piston top to form a combined piston, the piston skirt is provided with a second contact surface used for being in contact with a first contact surface of the piston top, the piston skirt is provided with a second inner cavity and a second outer cavity, the second outer cavities are distributed around the second inner cavity, the second contact surface is located between the second inner cavity and the second outer cavity, the piston skirt is further provided with a transverse oil hole and a second vertical oil hole, two ends of the transverse oil hole are respectively communicated with the second inner cavity and the second outer cavity, one end of the second vertical oil hole is communicated with the transverse oil hole, and the other end of the second vertical oil hole extends upwards to the second contact surface.

Optionally, a second oil distribution groove is formed in the second contact surface, the second vertical oil holes extend upwards and are communicated with the second oil distribution groove, and the cross-sectional area of the second oil distribution groove is larger than that of the second vertical oil holes.

Optionally, the second contact surface is provided with a surface texture structure, and the surface texture structure is used for forming a channel for lubricating oil to flow along the circumferential direction of the second contact surface.

Optionally, the second contact surface has a roughness with Rz between 15 μm and 30 μm and with Rsm between 350 μm and 500 μm.

Optionally, the piston top and the piston skirt are fixedly connected through a connecting bolt, the piston skirt is provided with a connecting hole penetrating through the second contact surface, and the connecting hole is used for the connecting bolt to penetrate through; and a pressure relief groove is further formed in the second contact surface, is positioned at the same circumferential position as the connecting hole, extends along the radial direction of the piston skirt and is communicated with the second inner cavity and the second outer cavity.

The combined piston comprises a piston top and a piston skirt part which are fixedly connected with each other, wherein the piston top adopts the piston top; and/or, the piston skirt adopts the piston skirt.

The piston crown, the piston skirt and the combined piston provided by the embodiment of the utility model have the beneficial effects that:

embodiments of the present utility model provide a piston crown for fixedly connecting with a piston skirt to form a composite piston. The piston crown has a first contact surface for contacting the piston skirt and the piston crown has a first inner cavity and a first outer cavity distributed about the first inner cavity with the first contact surface between the first inner cavity and the first outer cavity. The piston crown is also provided with a first vertical oil hole and a communication hole, and two ends of the communication hole are respectively communicated with the first inner cavity and the first outer cavity, so that lubricating oil flows between the first inner cavity and the first outer cavity through the communication hole. One end of the first vertical oil hole is communicated with the communication hole, the other end of the first vertical oil hole downwards extends to the first contact surface, and thus lubricating oil in the first communication hole flows to the first contact surface through the first vertical oil hole, a lubricating oil film is formed on the first contact surface, a certain thrust bearing effect is achieved, abrasion of the contact surface is reduced, and the risk of micro-cracking is reduced.

Embodiments of the present utility model also provide a piston skirt for fixedly connecting with a piston crown to form a composite piston. The piston skirt has a second contact surface for contacting the first contact surface of the piston crown, and the piston skirt has a second inner cavity and a second outer cavity. The second outer cavities are distributed around the second inner cavity with the second contact surface between the second inner cavity and the second outer cavities. The piston skirt portion is further provided with a transverse oil hole and a second vertical oil hole, two ends of the transverse oil hole are respectively communicated with the second inner cavity and the second outer cavity, one end of the second vertical oil hole is communicated with the transverse oil hole, and one end of the second vertical oil hole extends upwards to the second contact surface, so that when the lubricating oil level in the outer cooling cavity of the combined piston is higher, lubricating oil in the second vertical oil hole can flow to the second contact surface to form a lubricating oil film, and meanwhile, if part of lubricating oil flows from the second contact surface to the second vertical oil hole, particles generated by friction are discharged along with the second vertical oil hole, and therefore fretting wear is reduced, and the risk of fretting cracking is reduced.

Embodiments of the present utility model also provide a composite piston comprising the piston crown and/or skirt described above. Therefore, the combined piston also has the beneficial effects of reducing fretting wear and reducing the risk of fretting cracking.

Drawings

The above features and advantages of the present utility model will be better understood after reading the detailed description of embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily to scale and components having similar related features or characteristics may have the same or similar reference numerals.

FIG. 1 illustrates a schematic cross-sectional structure of a composite piston provided in accordance with an aspect of the present utility model;

FIG. 2 illustrates a schematic top view of a piston skirt provided in accordance with an aspect of the present utility model;

FIG. 3 illustrates a schematic cross-sectional structural view of a piston skirt provided in accordance with an aspect of the present utility model.

Reference numerals:

10-a combined piston; 11-an internal cooling cavity; 12-an outer cooling chamber; 100-piston crown; 111-a first lumen; 112-a first outer lumen; 113-a first contact surface; 114-a communication hole; 115-a first vertical oil hole; 116-a first oil distribution groove; 200-piston skirt; 211-a second lumen; 212-a second outer cavity; 213-a second contact surface; 214-a transverse oil hole; 215-a second vertical oil hole; 216-a second oil distribution groove; 217-connecting holes; 218-a pressure relief groove; 219-oil inlet hole.

Detailed Description

The utility model is described in detail below with reference to the drawings and the specific embodiments. It is noted that the aspects described below in connection with the drawings and the specific embodiments are merely exemplary and should not be construed as limiting the scope of the utility model in any way.

In the description of the present utility model, it should be noted that, if the terms "upper," "lower," "inner," "outer," "vertical," and the like indicate an orientation or a positional relationship based on that shown in the drawings or that the product of the present utility model is commonly visited when used, it does not indicate or imply that the device or element to be referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore, the present utility model should not be construed as being limited.

Meanwhile, it should be noted that the terms "first," "second," and the like, if any, are used solely for distinguishing descriptions and not to be construed as indicating or implying relative importance.

In the description of the present utility model, it should also be noted that, unless explicitly specified or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, integrally connected, or detachably connected; can be mechanically or electrically connected; may be directly connected, or may be indirectly connected through an intermediate medium, or may be communicated with the inside of two elements. The specific meaning of the above terms in the present utility model can be understood as appropriate by those of ordinary skill in the art.

Fig. 1 is a schematic cross-sectional structure of a combined piston 10 according to the present embodiment, and fig. 2 is a schematic top view of a piston skirt 200 according to the present embodiment. Referring to fig. 1 and 2 in combination, the present embodiment provides a combined piston 10, the combined piston 10 is formed by fixedly connecting a piston top 100 and a piston skirt 200, lubrication is achieved between contact surfaces of the piston top 100 and the piston skirt 200 by providing a contact surface lubrication structure in the combined piston 10, so as to reduce fretting wear, and accordingly, the present embodiment also provides a piston top 100 and a piston skirt 200, the contact surface lubrication structure is provided on the piston top 100 and the piston skirt 200, in other words, the piston top 100 provided in the present embodiment is an anti-fretting wear piston top, the piston skirt 200 is an anti-fretting wear piston skirt, and the combined piston 10 is an anti-fretting wear combined piston. It should be understood that the present embodiment is not limited to the structure of the composite piston 10, and it should be understood that the composite piston 10 provided by the present utility model may be obtained by connecting the piston crown 100 provided by the present utility model with a piston skirt of another structure, or may be obtained by connecting the piston skirt 200 provided by the present utility model with a piston crown of another structure.

In the present embodiment, the piston crown 100 and the piston skirt 200 are fixedly connected by the connecting bolts, and the piston crown 100 and the piston skirt 200 are disposed substantially coaxially, and the axes of the piston crown 100, the piston skirt 200, and the composite piston 10 are substantially coincident, and therefore, in the description of the present embodiment, "the axis of the piston crown 100", "the axis of the piston skirt 200", and "the axis of the composite piston 10" can be regarded as referring to the same axis. The combined piston 10 has an inner cooling chamber 11 and an outer cooling chamber 12, the inner cooling chamber 11 being located at the axial center of the combined piston 10, the outer cooling chamber 12 being an annular chamber provided around the inner cooling chamber 11, and a top skirt contact surface between the piston crown 100 and the piston skirt 200 being located between the inner cooling chamber 11 and the outer cooling chamber 12.

Specifically, the top skirt contact surface includes a first contact surface 113 disposed on the underside of the piston crown 100 (as viewed in FIG. 1) and a second contact surface 213 disposed on the upper side of the piston skirt 200 (as viewed in FIG. 1), the first contact surface 113 and the second contact surface 213 being slightly inclined, e.g., at an angle less than 3, relative to the cross-section of the composite piston 10. The "cross section of the composite piston 10" is a plane perpendicular to the axis of the composite piston 10.

The first contact surface 113 and the second contact surface 213 are both annular, the piston top 100 has a first inner cavity 111 located inside the first contact surface 113 and a first outer cavity 112 located outside the first contact surface 113, and the first outer cavity 112 is annular; the piston skirt 200 has a second inner cavity 211 located inside the second contact surface 213 and a second outer cavity 212 located outside the second contact surface 213, the second outer cavity 212 being annular. The first inner chamber 111 and the second inner chamber 211 form an inner cooling chamber 11 of the combined piston 10, and the first outer chamber 112 and the second outer chamber 212 form an outer cooling chamber 12 of the combined piston 10. The piston skirt 200 is provided with an oil inlet 219 communicating with the second outer chamber 212 so that the outer cooling chamber 12 is filled with lubricating oil through the oil inlet 219.

The contact surface lubrication structure includes a first vertical oil hole 115 provided on the piston crown 100 and a communication hole 114, both ends of the communication hole 114 being respectively communicated with the first inner chamber 111 and the first outer chamber 112, so that lubricating oil can flow between the outer cooling chamber 12 and the inner cooling chamber 11 through the communication hole 114. Specifically, the communication hole 114 is located on the upper side of the first contact surface 113, and the communication hole 114 gradually decreases in height in the direction from the first outer chamber 112 to the first inner chamber 111, i.e., the communication hole 114 extends obliquely. During the up-and-down movement of the combined piston 10, the lubricating oil in the outer cooling chamber 12 oscillates up and down, so as to flow toward the inner cooling chamber 11 through the communication hole 114.

One end of the first vertical oil hole 115 is communicated with the communication hole 114, and the other end of the first vertical oil hole extends downwards to the first contact surface 113, so that lubricating oil in the communication hole 114 can flow to the first contact surface 113 along the first vertical oil hole 115, and the top skirt contact surface is lubricated and cooled, and a lubricating oil film is formed. Specifically, in the present embodiment, the first vertical oil hole 115 extends vertically downward, that is, the extending direction of the first vertical oil hole 115 is substantially parallel to the axis of the combined piston 10.

Further, the first contact surface 113 is further provided with a first oil distribution groove 116, the first vertical oil hole 115 extends downward and is communicated with the first oil distribution groove 116, and the cross-sectional area of the first oil distribution groove 116 is larger than that of the first vertical oil hole 115, specifically, the first oil distribution groove 116 is tapered with gradually increasing radial dimension along the vertical downward direction, in other words, the first oil distribution groove 116 may also be regarded as being formed by gradually expanding the lower end of the first vertical oil hole 115. It will be appreciated that in other embodiments, the first oil distribution groove 116 may be configured as desired, for example, the first oil distribution groove 116 may be configured as a square groove or the like, or may be configured as a communication groove extending in the circumferential direction of the first contact surface 113, so as to guide the lubricant to flow in the circumferential direction of the first contact surface 113.

In this embodiment, the first contact surface 113 is provided with a threaded hole (not shown) for screwing with a connecting bolt, and the first vertical oil hole 115 and the threaded hole are distributed in a staggered manner in the circumferential direction of the piston crown 100. Further, the number of the first vertical oil holes 115 is plural, and the openings of the plurality of first vertical oil holes 115 at the first contact surface 113 are uniformly distributed along the circumferential direction of the piston crown 100, so that oil is simultaneously supplied to the top skirt contact surface through the plurality of first vertical oil holes 115 (the arrows in the piston crown 100 in fig. 1 show the flow of lubricating oil in the first vertical oil holes 115 and the communication holes 114), and the lubricating effect is ensured. Accordingly, the number of the communication holes 114 on the piston crown 100 is plural, the plurality of communication holes 114 are uniformly distributed along the circumferential direction of the piston crown 100, and each of the first vertical oil holes 115 communicates with the communication hole 114.

In the present embodiment, the contact surface lubrication structure further includes a lateral oil hole 214 and a second vertical oil hole 215 provided at the piston skirt 200. Both ends of the transverse oil hole 214 are respectively communicated with the second inner cavity 211 and the second outer cavity 212, one end of the second vertical oil hole 215 is communicated with the transverse oil hole 214, and the other end of the second vertical oil hole 215 extends upwards to the second contact surface 213.

When more lubricating oil is in the outer cooling cavity 12 of the combined piston 10 (for example, the lubricating oil level in the outer cooling cavity 12 is higher than the second contact surface 213), part of the lubricating oil in the outer cooling cavity 12 flows into the inner cooling cavity 11 through the transverse oil hole 214, and meanwhile, part of the lubricating oil in the transverse oil hole 214 enters the second contact surface 213 upwards through the second vertical oil hole 215, as shown by an arrow in fig. 3, so that the lubricating oil can also play a role of a certain lubricating top skirt contact surface, and fretting wear is reduced; when there is less lubrication oil in the outer cooling gallery 12 of the combined piston 10 (e.g., the level of lubrication oil in the outer cooling gallery 12 is lower than the second contact surface 213, even lower than the height of the transverse oil hole 214), the lubrication oil in the top skirt contact surface can flow through the second vertical oil hole 215 toward the transverse oil hole 214 and eventually back into the inner cooling gallery 11 or the outer cooling gallery 12 (as shown by the arrows in the piston skirt 200 in fig. 1, the flow of lubrication oil in the second vertical oil hole 215 and the transverse oil hole 214 at this time), and at the same time, the particulates in the top skirt contact surface are discharged with the lubrication oil into the inner cooling gallery 11 or the outer cooling gallery 12, thereby achieving particulate discharge, avoiding the problem of increased wear of the top skirt contact surface caused by the collection of particulates in the top skirt contact surface.

Specifically, in the present embodiment, the extending direction of the lateral oil hole 214 is parallel to the cross section of the combined piston 10, in other words, the heights of the lateral oil hole 214 are substantially the same throughout the axis line in the view as shown in fig. 1. The second vertical oil hole 215 extends vertically, that is, the extending direction of the second vertical oil hole 215 is substantially parallel to the axis of the combined piston 10.

Further, the second contact surface 213 is further provided with a second oil distribution groove 216, and the second vertical oil hole 215 extends upward and is communicated with the second oil distribution groove 216, and the cross-sectional area of the second oil distribution groove 216 is larger than that of the second vertical oil hole 215, specifically, the second oil distribution groove 216 is tapered with gradually increasing radial dimension along the vertical upward direction, in other words, the second oil distribution groove 216 may also be regarded as being formed by gradually expanding the lower end of the second vertical oil hole 215. It will be appreciated that in other embodiments, the second oil distribution groove 216 may be configured as needed, for example, the second oil distribution groove 216 may be configured as a square groove or the like, or may be configured as a communication groove extending along the circumferential direction of the second contact surface 213, so as to guide the lubricant flowing along the circumferential direction of the second contact surface 213.

In this embodiment, the number of the second vertical oil holes 215 is plural, the openings of the plurality of second vertical oil holes 215 at the second contact surface 213 are uniformly distributed along the circumferential direction of the piston skirt 200, and similarly, the number of the second oil distribution grooves 216 is plural, and the plurality of second oil distribution grooves 216 are uniformly distributed on the second contact surface 213 along the circumferential direction of the piston skirt 200. Meanwhile, as shown in fig. 1, in the present embodiment, the first vertical oil hole 115 and the second vertical oil hole 215 are disposed opposite to each other. The number of the first vertical oil holes 115 and the second vertical oil holes 215 may be specifically set according to the requirement, specifically, in this embodiment, the number of the first vertical oil holes 115 is greater than that of the second vertical oil holes 215, in other words, the second vertical oil holes 215 are not disposed under a portion of the first vertical oil holes 115. It is understood that in other embodiments, the first and second vertical oil holes 115, 215 may be disposed at an angle offset.

In this embodiment, the piston skirt 200 is provided with connection holes 217 penetrating the second contact surface 213, the connection holes 217 are distributed in one-to-one correspondence with the threaded holes, and the connection bolts penetrate through the connection holes 217 and are screwed with the threaded holes, so as to fixedly connect the piston crown 100 with the piston skirt 200. The second plurality of vertical oil holes 215 and the connecting holes 217 are offset in the circumferential direction of the piston skirt 200.

Further, the second contact surface 213 is further provided with a pressure relief groove 218, the pressure relief groove 218 and the connecting hole 217 are located at the same circumferential position, and extend along the radial direction of the piston skirt 200 and are communicated with the second inner cavity 211 and the second outer cavity 212, so that the surface abrasion of a high stress area can be reduced through the pressure relief groove 218, thereby reducing the risk of surface cracks caused by high stress, and on the other hand, particles generated by friction on the top skirt contact surface can be discharged to the inner cooling cavity 11 or the outer cooling cavity 12 along with lubricating oil from the pressure relief groove 218, thereby improving the particle discharge efficiency. It will be appreciated that in other embodiments, the relief groove 218 may be disposed on the first contact surface 113, and accordingly, the relief groove 218 and the threaded hole are located at the same circumferential position, extend along the radial direction of the piston top 100, and communicate with the first inner cavity 111 and the first outer cavity 112.

In this embodiment, the second contact surface 213 is provided with a surface texture structure, and the micro-channels formed by the surface texture structure enable the lubricating oil to be stored on the second contact surface 213 and flow along the circumferential direction and the radial direction of the second contact surface 213, so that a lubricating oil film is formed on the whole top skirt contact surface, and meanwhile, particles generated by friction can be accommodated in the micro-structures formed by the surface texture structure, which helps to reduce the abrasion of the top skirt contact surface. In particular, the surface texture may be selected from one or more of all surface texture based on GB/T131. Optionally, as shown in fig. 2, the surface texture structure provided on the second contact surface 213 is a C-type texture.

Further, the second contact surface 213 has a roughness with an Rz of between 15 μm and 30 μm and an Rsm of between 350 μm and 500 μm, i.e. 15 μm. Ltoreq.rz.ltoreq.30 μm,350 μm. Ltoreq.Rsm.ltoreq.500 μm.

In the combined piston 10 provided by the embodiment of the utility model, in the working process, a certain amount of lubricating oil is filled in the outer cooling cavity 12 and the inner cooling cavity 11, under the alternate action of inertia force and combustion pressure, the first contact surface 113 and the second contact surface 123 are separated and extruded, under the working condition of inertia force, the contact pressure of the first contact surface 113 and the second contact surface 213 is low, meanwhile, as the piston skirt 200 is provided with a molded line, the top skirt is slightly separated, the lubricating oil in the inner cooling cavity 11 and the outer cooling cavity 12 flows along the communication hole 114, and part of the lubricating oil in the communication hole 114 enters the top skirt contact surface through the first vertical oil hole 115 and the first oil distribution groove 116. Under the combustion condition, the first contact surface 113 and the second contact surface 213 are extruded, and the lubricating oil entering the top skirt contact surface is diffused and flows on the second contact surface 213 through the surface texture structure, so that a lubricating oil film is formed between the first contact surface 113 and the second contact surface 213, and a certain thrust bearing effect is achieved.

Meanwhile, part of the lubricating oil flowing on the second contact surface 213 enters the second oil distribution groove 216 and is discharged through the second vertical oil hole 215 and the transverse oil hole 214, and part of the lubricating oil flowing on the second contact surface 213 enters the pressure relief groove 218 and is discharged along the pressure relief groove 218, so that abrasion of the first contact surface 113 and the second contact surface 213 is reduced, and the risk of micro-cracking is reduced.

The foregoing is merely illustrative of the present utility model, and the present utility model is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the technical scope of the present utility model should be included in the scope of the present utility model.

Claims

1. A piston crown for fixedly connecting with a piston skirt to form a composite piston, the piston crown having a first contact surface for contacting the piston skirt and the piston crown having a first inner cavity and a first outer cavity; the first outer cavity is distributed around the first inner cavity, and the first contact surface is positioned between the first inner cavity and the first outer cavity, and the piston top is characterized by also comprising a first vertical oil hole and a communication hole, wherein two ends of the communication hole are respectively communicated with the first inner cavity and the first outer cavity so as to enable lubricating oil to flow between the first inner cavity and the first outer cavity; one end of the first vertical oil hole is communicated with the communication hole, and the other end of the first vertical oil hole extends downwards to the first contact surface so as to guide lubricating oil in the communication hole to flow to the first contact surface.

2. The piston crown of claim 1, wherein a first oil distribution groove is provided in the first contact surface, the first vertical oil hole extends downward and communicates with the first oil distribution groove, and a cross-sectional area of the first oil distribution groove is greater than a cross-sectional area of the first vertical oil hole.

3. The piston crown of claim 1, wherein the number of first vertical oil holes is plural, and openings of the plural first vertical oil holes at the first contact surface are uniformly distributed along the circumferential direction of the piston crown.

4. The piston crown of claim 1, wherein the piston crown and the piston skirt are fixedly connected by a connecting bolt; the first contact surface is provided with a threaded hole for being in threaded connection with the connecting bolt; the first contact surface is also provided with a pressure relief groove, and the pressure relief groove and the threaded hole are positioned at the same circumferential position, extend along the radial direction of the piston top and are communicated with the first inner cavity and the first outer cavity.

5. The piston skirt is used for being fixedly connected with a piston top to form a combined piston, the piston skirt is provided with a second contact surface used for being in contact with a first contact surface of the piston top, the piston skirt is provided with a second inner cavity and a second outer cavity, the second outer cavities are distributed around the second inner cavity, and the second contact surface is positioned between the second inner cavity and the second outer cavity.

6. The piston skirt of claim 5, wherein a second oil distribution groove is provided in the second contact surface, the second vertical oil hole extends upward and communicates with the second oil distribution groove, and a cross-sectional area of the second oil distribution groove is greater than a cross-sectional area of the second vertical oil hole.

7. The piston skirt of claim 5, wherein the second contact surface is provided with a surface texture for forming a channel for the flow of lubricating oil in the circumferential direction of the second contact surface.

8. The piston skirt of claim 7, wherein the second contact surface has a roughness of between 15 and 30 μιη Rz and between 350 and 500 μιη Rsm.

9. The piston skirt of claim 5, wherein the piston crown and the piston skirt are fixedly connected by a connecting bolt, the piston skirt being provided with a connecting hole through the second contact surface, the connecting hole being for the connecting bolt to pass through; and a pressure relief groove is further formed in the second contact surface, is positioned at the same circumferential position as the connecting hole, extends along the radial direction of the piston skirt and is communicated with the second inner cavity and the second outer cavity.

10. A combination piston comprising a piston crown and a piston skirt fixedly connected to each other, wherein the piston crown employs a piston crown as defined in any one of claims 1-4; and/or the piston skirt employs a piston skirt according to any one of claims 5-9.