A piston crown, a piston skirt and a combined piston

Abstract

The application provides a piston crown, a piston skirt and a combined piston, and relates to the technical field of reciprocating engine components. The piston crown and the piston skirt provided by the embodiment of the application guide lubricating oil to a contact surface by arranging a vertical oil hole extending to the contact surface, so that a lubricating oil film is formed on the contact surface, a certain thrust bearing effect is achieved, and the wear of the contact surface is reduced, and the risk of fretting cracking is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reciprocating engine components, in particular to a piston crown, a piston skirt and a combined piston. BACKGROUND

[0002] The combined piston is connected by the piston crown and the piston skirt through bolt assembly. In the working process, the piston crown and the piston skirt connection surface is under the action of alternating load, and the piston crown and the piston skirt surface exists relative sliding, that is, fretting. In the explosion pressure condition, the contact pressure of the piston crown and the piston skirt contact surface is high, and in the inertia force condition, the contact pressure of the piston crown and the piston skirt contact surface is low, and the contact surface exists partial separation. Due to the fretting effect of the piston crown and the skirt contact surface, the contact surface is worn, and the wear particles participate in the subsequent contact and wear in the closed surface, resulting in the roughening of the contact surface, and with the passage of time, the piston crown and the skirt contact surface is seriously worn and even the fatigue cracking damage mode is induced, that is, fretting wear and fretting fatigue.

[0003] In order to reduce the wear of the piston crown and the piston skirt contact surface, a wear-resistant coating can be arranged between the piston crown and the skirt contact surface, and the coating material can be chromium, tungsten carbide and the like. The coating is coated on the piston crown or the piston skirt contact surface through surface process, for example, the scheme disclosed in the utility model patent with publication number CN202039963U. Since the coating material is harder and less ductile than the base material, in the local area with high stress under the micro-motion contact, the base material will be plastically deformed, causing cracks in the surface coating. In addition, the coating material and the surface process cost are relatively high.

[0004] Therefore, there is an urgent need for a scheme capable of reducing the wear of the combined piston contact surface and the risk of fretting cracking. SUMMARY

[0005] The following gives a brief overview of one or more aspects to provide a basic understanding of these aspects. This overview is not an extensive overview of all contemplated aspects, and is neither intended to identify key or critical elements of all aspects nor to 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 to be given later.

[0006] The purposes of the present application include providing a piston crown which helps to reduce the wear of the combined piston contact surface and the risk of fretting cracking.

[0007] The purposes of the present application also include providing a piston skirt which helps to reduce the wear of the combined piston contact surface and the risk of fretting cracking.

[0008] The purposes of the present application also include providing a combined piston which can reduce the wear of the contact surface and the risk of fretting cracking.

[0009] Embodiments of the present application can be implemented in the following ways:

[0010] A piston crown is used to be fixedly connected with a piston skirt to form a combined piston, the piston crown has a first contact surface used to contact the piston skirt, and the piston crown has 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 located between the first inner cavity and the first outer cavity, the piston crown further has a first vertical oil hole and a communication hole, two ends of the communication hole are respectively communicated with the first inner cavity and the first outer cavity to allow 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 downward to the first contact surface to guide the lubricating oil in the communication hole to flow to the first contact surface.

[0011] Optionally, a first oil distribution groove is arranged on the first contact surface, the first vertical oil hole extends downward and is communicated 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.

[0012] Optionally, the number of the first vertical oil holes is a plurality, and openings of the plurality of first vertical oil holes at the first contact surface are uniformly distributed along a circumference of the piston crown.

[0013] Optionally, the piston crown is fixedly connected with the piston skirt through a connecting bolt, a threaded hole used to be screwed with the connecting bolt is arranged on the first contact surface, a pressure relief groove is further arranged on the first contact surface, the pressure relief groove is located at the same circumferential position as the threaded hole, and extends along a radial direction of the piston crown and communicates the first inner cavity and the first outer cavity.

[0014] A piston skirt is used to be fixedly connected with a piston crown to form a combined piston, the piston skirt has a second contact surface used to contact a first contact surface of the piston crown, the piston skirt has a second inner cavity and a second outer cavity, the second outer cavity is distributed around the second inner cavity, and the second contact surface is located between the second inner cavity and the second outer cavity, the piston skirt further has 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 upward to the second contact surface.

[0015] Optionally, a second oil distribution groove is arranged on the second contact surface, the second vertical oil hole extends upward and is communicated 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.

[0016] Optionally, a surface texture structure is arranged on the second contact surface, and the surface texture structure is used to form a channel for the lubricating oil to flow along the circumference of the second contact surface.

[0017] Optionally, the second contact surface has a roughness with Rz between 15 μm and 30 μm and Rsm between 350 μm and 500 μm.

[0018] Optionally, the piston crown and the piston skirt are fixedly connected by a connecting bolt, the piston skirt is provided with a connecting hole penetrating through the second contact surface, the connecting hole is used for the connecting bolt to pass through, and the second contact surface is further provided with a pressure relief groove, the pressure relief groove is located at the same circumferential position as the connecting hole, and extends along the radial direction of the piston skirt and communicates the second inner cavity and the second outer cavity.

[0019] A combined piston comprises a piston crown and a piston skirt fixedly connected with each other, the piston crown is the piston crown described above, and / or the piston skirt is the piston skirt described above.

[0020] The piston crown, the piston skirt and the combined piston provided by the embodiments of the present application have the following beneficial effects:

[0021] The embodiments of the present application provide a piston crown which is used to be fixedly connected with a piston skirt to form a combined piston. The piston crown has a first contact surface which is used to contact with the piston skirt, and the piston crown has 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 located between the first inner cavity and the first outer cavity. The piston crown further has a first vertical oil hole and a communication hole, two ends of the communication hole are communicated with the first inner cavity and the first outer cavity respectively, so that the 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, and the other end extends downward to the first contact surface, so that the lubricating oil in the first communication hole flows to the first contact surface through the first vertical oil hole, thereby forming a lubricating oil film on the first contact surface, playing a certain effect of thrust bearing, thereby reducing the wear of the contact surface and reducing the risk of fretting cracking.

[0022] The embodiment of the present application also provides a piston skirt used to be fixedly connected with a piston crown to form a combined piston. The piston skirt has a second contact surface used to be in contact with a first contact surface of the piston crown, and the piston skirt has a second inner cavity and a second outer cavity. The second outer cavity is distributed around the second inner cavity, and the second contact surface is located between the second inner cavity and the second outer cavity. The piston skirt also has a transverse oil hole and a second vertical oil hole, two ends of the transverse oil hole are in communication with the second inner cavity and the second outer cavity respectively, one end of the second vertical oil hole is in communication with the transverse oil hole, and the other end of the second vertical oil hole extends upward to the second contact surface, so that when the lubricating oil level in the outer cooling cavity of the combined piston is high, the lubricating oil in the second vertical oil hole can flow to the second contact surface, thereby forming a lubricating oil film, and meanwhile, if part of the lubricating oil flows from the second contact surface to the second vertical oil hole, the particles generated by friction are discharged, which helps to reduce the fretting wear and reduce the risk of fretting cracking.

[0023] The embodiment of the present application also provides a combined piston comprising the piston crown and / or the piston skirt described above. Therefore, the combined piston also has the beneficial effect of being able to reduce the fretting wear and reduce the risk of fretting cracking. BRIEF DESCRIPTION OF DRAWINGS

[0024] The above features and advantages of the present application can be better understood by reading the detailed description of embodiments of the present application in conjunction with the following drawings, in which the components are not necessarily drawn to scale and components of similar or identical function or structure can have the same or similar reference numbers.

[0025] Figure 1 A cross-sectional structural schematic diagram of a combined piston provided according to an aspect of the present application is shown;

[0026] Figure 2 A top view structural schematic diagram of a piston skirt provided according to an aspect of the present application is shown;

[0027] Figure 3 A cross-sectional structural schematic diagram of a piston skirt provided according to an aspect of the present application is shown.

[0028] LIST OF REFERENCE NUMBERS

[0029] 10-combined piston; 11-inner cooling cavity; 12-outer cooling cavity; 100-piston crown; 111-first inner cavity; 112-first outer cavity; 113-first contact surface; 114-communication hole; 115-first vertical oil hole; 116-first oil distribution groove; 200-piston skirt; 211-second inner cavity; 212-second outer cavity; 213-second contact surface; 214-transverse oil hole; 215-second vertical oil hole; 216-second oil distribution groove; 217-connection hole; 218-pressure relief groove; 219-oil inlet hole. DETAILED DESCRIPTION

[0030] The present application will be described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the aspects described below in conjunction with the accompanying drawings and specific embodiments are merely exemplary and should not be understood as limiting the scope of protection of the present application in any way.

[0031] In the description of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer", "vertical" and the like indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, or the orientation or position relationship commonly encountered when the product of the present application is used, and are not indicative or suggestive of the device or element referred to having a particular orientation or being constructed and operated in a particular orientation, and therefore should not be understood as limiting the present application.

[0032] At the same time, it should be noted that if the terms "first", "second" and the like are used only for differentiation and description, and should not be understood as indicative or suggestive of relative importance.

[0033] In the description of the present application, it should also be noted that unless otherwise explicitly specified or limited, the terms "mounting", "connection", "connecting" should be understood broadly, for example, it can be fixedly connected, integrally connected, or detachably connected; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium, or the connection between two elements inside, etc. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0034] Figure 1 A cross-sectional structure schematic diagram of the combined piston 10 provided in the present embodiment is shown in the figure, Figure 2 A top view structure schematic diagram of the piston skirt 200 provided in the present embodiment is shown in the figure. Please refer to Figure 1 and Figure 2 The present embodiment provides a combined piston 10 formed by fixedly connecting a piston crown 100 and a piston skirt 200, and achieves lubrication between the contact surface of the piston crown 100 and the piston skirt 200 by setting a contact surface lubrication structure in the combined piston 10 to reduce the fretting wear, accordingly, the present embodiment also provides a piston crown 100 and a piston skirt 200, and the contact surface lubrication structure is set in the piston crown 100 and the piston skirt 200, in other words, the piston crown 100 provided in the present embodiment is a fretting wear resistant piston crown, the piston skirt 200 is a fretting wear resistant piston skirt, and the combined piston 10 is a fretting wear resistant combined piston. It can be understood that the present embodiment does not limit the structure of the combined piston 10, it can be understood that the combined piston 10 provided in the present application can be obtained by connecting the piston crown 100 provided in the present application with a piston skirt of other structure, or can be obtained by connecting the piston skirt 200 provided in the present application with a piston crown of other structure.

[0035] In this embodiment, the piston top 100 and the piston skirt 200 are fixedly connected by connecting bolts, and the piston top 100 and the piston skirt 200 are substantially coaxially arranged. The axes of the piston top 100, the piston skirt 200, and the combined piston 10 are substantially coincident. Therefore, in the description of this embodiment, "axis of piston top 100", "axis of piston skirt 200", and "axis of combined piston 10" can be regarded as referring to the same axis. The combined piston 10 has an inner cooling cavity 11 and an outer cooling cavity 12. The inner cooling cavity 11 is located at the axis of the combined piston 10, and the outer cooling cavity 12 is an annular chamber arranged around the inner cooling cavity 11. The top skirt contact surface between the piston top 100 and the piston skirt 200 is located between the inner cooling cavity 11 and the outer cooling cavity 12.

[0036] Specifically, the top skirt contact surface includes a surface located on the lower side of the piston top 100 (e.g., Figure 1 The first contact surface 113 (as shown in the view) and the first contact surface 113 located on the upper side of the piston skirt 200 (as shown in the view) Figure 1 The second contact surface 213 (as shown in the viewpoint) is slightly inclined relative to the cross-section of the combined piston 10, for example, the inclination angle is less than 3°. The "cross-section of the combined piston 10" is the plane perpendicular to the axis of the combined piston 10.

[0037] Both the first contact surface 113 and the second contact surface 213 are 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, the first outer cavity 112 being 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 cavity 111 and the second inner cavity 211 form the inner cooling cavity 11 of the combined piston 10, and the first outer cavity 112 and the second outer cavity 212 form the outer cooling cavity 12 of the combined piston 10. The piston skirt 200 is provided with an oil inlet hole 219 communicating with the second outer cavity 212, thereby filling the outer cooling cavity 12 with lubricating oil through the oil inlet hole 219.

[0038] The contact surface lubrication structure includes a first vertical oil hole 115 and a connecting hole 114 disposed on the piston top 100. The two ends of the connecting hole 114 are connected to the first inner cavity 111 and the first outer cavity 112, respectively, allowing lubricating oil to flow between the outer cooling cavity 12 and the inner cooling cavity 11 through the connecting hole 114. Specifically, the connecting hole 114 is located above the first contact surface 113, and its height gradually decreases along the direction from the first outer cavity 112 to the first inner cavity 111, meaning the connecting hole 114 extends obliquely. During the up-and-down movement of the combined piston 10, the lubricating oil in the outer cooling cavity 12 oscillates up and down, thereby flowing into the inner cooling cavity 11 through the connecting hole 114.

[0039] One end of the first vertical oil hole 115 is connected to the connecting hole 114, and the other end extends downward to the first contact surface 113, so that the lubricating oil in the connecting hole 114 can flow along the first vertical oil hole 115 to the first contact surface 113, thereby lubricating and cooling the top skirt contact surface and forming a lubricating oil film. Specifically, in this embodiment, the first vertical oil hole 115 extends vertically downward, that is, the extension direction of the first vertical oil hole 115 is approximately parallel to the axis of the combined piston 10.

[0040] Furthermore, a first oil distribution groove 116 is also provided on the first contact surface 113. The first vertical oil hole 115 extends downward and communicates with the first oil distribution groove 116. The cross-sectional area of ​​the first oil distribution groove 116 is larger than the cross-sectional area of ​​the first vertical oil hole 115. Specifically, the first oil distribution groove 116 is a cone shape with its radial dimension gradually increasing in the vertically downward direction. In other words, the first oil distribution groove 116 can also be regarded as the lower end of the first vertical oil hole 115 gradually expanding. It is understood that in other embodiments, the structure of the first oil distribution groove 116 can also be set according to needs. For example, the first oil distribution groove 116 can be set as a square groove, or as a connecting groove extending circumferentially along the first contact surface 113, thereby guiding the lubricating oil to flow circumferentially along the first contact surface 113.

[0041] In this embodiment, a threaded hole (not shown) for screwing with a connecting bolt is provided on the first contact surface 113. The first vertical oil holes 115 and the threaded hole are staggered in the circumferential direction of the piston top 100. Furthermore, there are multiple first vertical oil holes 115, and the openings of these multiple first vertical oil holes 115 at the first contact surface 113 are evenly distributed along the circumferential direction of the piston top 100, thereby synchronously supplying oil to the top skirt contact surface through the multiple first vertical oil holes 115. Figure 1 The arrows in the piston top 100 indicate the flow of lubricating oil in the first vertical oil hole 115 and the connecting hole 114, ensuring lubrication. Accordingly, there are multiple connecting holes 114 on the piston top 100, which are evenly distributed along the circumference of the piston top 100, and each first vertical oil hole 115 is connected to a connecting hole 114.

[0042] In this embodiment, the contact surface lubrication structure further includes a transverse oil hole 214 and a second vertical oil hole 215 disposed on the piston skirt 200. The two ends of the transverse oil hole 214 are respectively connected to the second inner cavity 211 and the second outer cavity 212, one end of the second vertical oil hole 215 is connected to the transverse oil hole 214, and the other end of the second vertical oil hole 215 extends upward to the second contact surface 213.

[0043] When there is a large amount of lubricating oil in the outer cooling chamber 12 of the combined piston 10 (for example, the lubricating oil level in the outer cooling chamber 12 is higher than the second contact surface 213), some of the lubricating oil in the outer cooling chamber 12 flows into the inner cooling chamber 11 through the transverse oil hole 214, while some of the lubricating oil in the transverse oil hole 214 enters the second contact surface 213 upwards through the second vertical oil hole 215. Figure 3 As indicated by the middle arrow, this also serves to lubricate the top skirt contact surface, reducing fretting wear. When the lubricating oil in the outer cooling chamber 12 of the combined piston 10 is low (for example, the lubricating oil level in the outer cooling chamber 12 is lower than the second contact surface 213, or even lower than the height of the transverse oil hole 214), the lubricating oil in the top skirt contact surface can flow through the second vertical oil hole 215 to the transverse oil hole 214, and eventually flow back to the inner cooling chamber 11 or the outer cooling chamber 12 (e.g., ...). Figure 1 The arrows in the piston skirt 200 indicate the flow of lubricating oil in the second vertical oil hole 215 and the lateral oil hole 214 at this time. At the same time, the particles in the top skirt contact surface are discharged with the lubricating oil into the inner cooling chamber 11 or the outer cooling chamber 12, thereby realizing the discharge of particles and avoiding the problem of increased wear of the top skirt contact surface caused by the accumulation of particles in the top skirt contact surface.

[0044] Specifically, in this embodiment, the extension direction of the transverse oil hole 214 is parallel to the cross-section of the combined piston 10; in other words, in such a case... Figure 1 From the perspective shown, the height of the axis of the transverse oil hole 214 is approximately the same at all points. The second vertical oil hole 215 extends vertically, that is, the extension direction of the second vertical oil hole 215 is approximately parallel to the axis of the combined piston 10.

[0045] Furthermore, a second oil distribution groove 216 is also provided on the second contact surface 213. The second vertical oil hole 215 extends upward and communicates with the second oil distribution groove 216. The cross-sectional area of ​​the second oil distribution groove 216 is larger than the cross-sectional area of ​​the second vertical oil hole 215. Specifically, the second oil distribution groove 216 is a cone shape with its radial dimension gradually increasing in the vertical upward direction. In other words, the second oil distribution groove 216 can also be regarded as the lower end of the second vertical oil hole 215 gradually expanding. It is understood that in other embodiments, the structure of the second oil distribution groove 216 can also be set according to needs. For example, the second oil distribution groove 216 can be set as a square groove, or as a connecting groove extending circumferentially along the second contact surface 213, thereby guiding the lubricating oil to flow circumferentially along the second contact surface 213.

[0046] In this embodiment, there are multiple second vertical oil holes 215, and the openings of the multiple second vertical oil holes 215 at the second contact surface 213 are evenly distributed along the circumference of the piston skirt 200. Similarly, there are multiple second oil distribution grooves 216, and the multiple second oil distribution grooves 216 are evenly distributed along the circumference of the piston skirt 200 on the second contact surface 213. Meanwhile, as...Figure 1 As shown, in this embodiment, the first vertical oil hole 115 and the second vertical oil hole 215 are arranged opposite each other. The number of the first vertical oil hole 115 and the second vertical oil hole 215 can be specifically set according to requirements. Specifically, in this embodiment, the number of first vertical oil holes 115 is greater than the number of second vertical oil holes 215. In other words, some of the first vertical oil holes 115 are not directly below the second vertical oil holes 215. It is understood that in other embodiments, the first vertical oil holes 115 and the second vertical oil holes 215 can also be arranged at a certain angle.

[0047] In this embodiment, the piston skirt 200 has a connecting hole 217 that penetrates the second contact surface 213. The connecting holes 217 are distributed one-to-one with the threaded holes. The connecting bolt passes through the connecting hole 217 and is screwed into the threaded hole, thereby fixing the piston top 100 to the piston skirt 200. A plurality of second vertical oil holes 215 are staggered with the connecting holes 217 in the circumferential direction of the piston skirt 200.

[0048] Furthermore, a pressure relief groove 218 is also provided on the second contact surface 213. The pressure relief groove 218 is located in the same circumferential position as the connecting hole 217, and extends radially along the piston skirt 200, connecting the second inner cavity 211 and the second outer cavity 212. In this way, the pressure relief groove 218 can reduce surface wear in the high-stress area, thereby reducing the risk of surface cracks caused by high stress. On the other hand, the particles generated by friction on the top skirt contact surface can be discharged from the pressure relief groove 218 with the lubricating oil to the inner cooling cavity 11 or the outer cooling cavity 12, thereby improving the particle discharge efficiency. It is understood that in other embodiments, the pressure relief groove 218 can also be provided on the first contact surface 113. Accordingly, in this case, the pressure relief groove 218 is located in the same circumferential position as the threaded hole, and extends radially along the piston top 100, connecting the first inner cavity 111 and the first outer cavity 112.

[0049] In this embodiment, a surface texture structure is provided on the second contact surface 213. The micro-channels formed by the surface texture structure allow lubricating oil to be stored on the second contact surface 213 and flow along its circumferential and radial directions, thereby forming a lubricating oil film across the entire top skirt contact surface. Simultaneously, friction-generated particles can be contained within the micro-structure formed by the surface texture structure, helping to reduce wear on the top skirt contact surface. Specifically, this surface texture structure can be selected from one or more of all surface processing textures based on GB / T 131. Optionally, such as... Figure 2 As shown, the surface texture structure set on the second contact surface 213 is a C-type texture.

[0050] Furthermore, the second contact surface 213 has a roughness Rz between 15 μm and 30 μm and Rsm between 350 μm and 500 μm, i.e., 15 μm ≤ Rz ≤ 30 μm and 350 μm ≤ Rsm ≤ 500 μm.

[0051] The combined piston 10 provided in the embodiments of the present invention, during operation, contains a certain amount of lubricating oil in the outer cooling chamber 12 and the inner cooling chamber 11. Under the alternating action of inertial force and combustion pressure, the first contact surface 113 and the second contact surface 123 separate and are squeezed. Under the inertial force condition, the contact pressure between the first contact surface 113 and the second contact surface 213 is low. At the same time, due to the profile provided on the piston skirt 200, the top skirt undergoes slight separation. The lubricating oil in the inner cooling chamber 11 and the outer cooling chamber 12 flows along the connecting hole 114. Part of the lubricating oil in the connecting 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 is squeezed against the second contact surface 213. The lubricating oil that enters the top skirt contact surface diffuses and flows on the second contact surface 213 through the surface texture structure, thereby forming a lubricating oil film between the first contact surface 113 and the second contact surface 213, which plays a certain thrust bearing role.

[0052] Meanwhile, a portion 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. A portion 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, thereby reducing the wear between the first contact surface 113 and the second contact surface 213 and reducing the risk of fretting cracking.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A combined piston, comprising a piston top and a piston skirt fixedly connected to each other, characterized in that, The piston top has a first contact surface for contacting the piston skirt, and the piston top has 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 located between the first inner cavity and the first outer cavity; the piston top also has a first vertical oil hole and a connecting hole, the two ends of the connecting hole being connected to the first inner cavity and the first outer cavity respectively, so as to allow lubricating oil to flow between the first inner cavity and the first outer cavity; One end of the first vertical oil hole communicates with the connecting hole, and the other end of the first vertical oil hole extends downward to the first contact surface to guide the lubricating oil in the connecting hole to flow to the first contact surface and form a lubricating oil film on the first contact surface; the piston skirt has a second contact surface for contacting the first contact surface of the piston top, the piston skirt has a second inner cavity and a second outer cavity, the second outer cavity is distributed around the second inner cavity, and the second contact surface is located between the second inner cavity and the second outer cavity; the piston skirt also has a transverse oil hole and a second vertical oil hole, the two ends of the transverse oil hole communicate with the second inner cavity and the second outer cavity respectively, one end of the second vertical oil hole communicates with the transverse oil hole, and the other end of the second vertical oil hole extends upward to the second contact surface; the first contact surface and the second contact surface are inclined relative to the cross-section of the combined piston; The second vertical oil hole is used to guide lubricating oil to the second contact surface to form a lubricating oil film on the second contact surface; or, the second vertical oil hole is used to discharge lubricating oil from the second contact surface. At least part of the first vertical oil hole is not provided directly below the second vertical oil hole.

2. The combined piston according to claim 1, characterized in that, A first oil distribution groove is provided on the first contact surface, and the first vertical oil hole extends downward and communicates with the first oil distribution groove. The cross-sectional area of ​​the first oil distribution groove is larger than the cross-sectional area of ​​the first vertical oil hole.

3. The combined piston according to claim 1, characterized in that, 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 evenly distributed along the circumference of the piston top.

4. The combined piston according to claim 1, characterized in that, The piston top and the piston skirt are fixedly connected by connecting bolts; a threaded hole for screwing the connecting bolt is provided on the first contact surface; a pressure relief groove is also provided on the first contact surface, the pressure relief groove and the threaded hole are located in the same circumferential position, and extend radially along the piston top and connect the first inner cavity and the first outer cavity.

5. The combined piston according to claim 1, characterized in that, A second oil distribution groove is provided on the second contact surface, and the second vertical oil hole extends upward and communicates with the second oil distribution groove. The cross-sectional area of ​​the second oil distribution groove is larger than the cross-sectional area of ​​the second vertical oil hole.

6. The combined piston according to claim 1, characterized in that, The second contact surface is provided with a surface texture structure, which is used to form a channel for lubricating oil to flow circumferentially along the second contact surface.

7. The combined piston according to claim 6, characterized in that, The second contact surface has a roughness Rz between 15 μm and 30 μm and Rsm between 350 μm and 500 μm.

8. The combined piston according to claim 1, characterized in that, The piston top and the piston skirt are fixedly connected by connecting bolts. The piston skirt has a connecting hole that penetrates the second contact surface for the connecting bolt to pass through. A pressure relief groove is also provided on the second contact surface. The pressure relief groove and the connecting hole are located in the same circumferential position and extend radially along the piston skirt and connect the second inner cavity and the second outer cavity.

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