A return oil hole structure for suppressing oil film cavitation in main bearings

Abstract

This invention relates to the field of sliding bearing technology, specifically to an oil return hole structure for suppressing oil film cavitation in the main bearing of an internal combustion engine. It includes an oil return hole disposed on the crankshaft main journal; both ends of the oil return hole are located on the circumferential surface of the main journal and communicate with the oil film gap of the main bearing bush; the oil return hole is perpendicularly connected to an inclined oil hole, the main journal axis is spatially perpendicular, and its geometric center is radially eccentric relative to the journal's rotation center; the two openings of the oil return hole are respectively machined with rounded corners; this invention can guide the lubricating oil to transition smoothly, suppress the flow separation phenomenon at the end of the oil reservoir, and reduce the cavitation intensity; it enables the oil hole to periodically relieve pressure in the high-pressure area of ​​the oil film convergence section when rotating with the journal, reducing the cavitation intensity in the divergence area; through the above dual mechanisms, the risk of cavitation damage to the inner wall of the bearing bush is effectively reduced, further improving the operating efficiency, working stability, and service life of the main bearing of the internal combustion engine.

Description

Technical Field

[0001] This invention relates to the field of sliding bearing technology, and more specifically to an oil return hole structure for suppressing oil film cavitation in the main bearing of an internal combustion engine. Background Technology

[0002] With the continuous increase in power density of internal combustion engines and other equipment, the problem of oil film cavitation in main bearings is becoming increasingly prominent. This not only weakens the oil film's load-bearing capacity but also generates shock waves and micro-jet streams when bubbles collapse, inducing cavitation erosion on the bearing surface and even leading to bearing failure, severely impacting the service life and operational reliability of main bearings. Cavitation in main bearings mainly occurs in two typical flow channel structures: first, when the journal oil hole passes the end of the oil reservoir, the flow channel suddenly contracts, forming a high-speed jet, causing a sudden drop in local pressure and leading to cavitation; second, the oil film gradually contracting-expanding flow channel caused by journal eccentricity, where the pressure gradient drops sharply when the oil film pressure transitions from the convergence zone to the divergence zone, generating cavitation. The superposition of these two types of cavitation further exacerbates the risk of bearing damage. To address these problems, existing technologies typically employ the following solutions: micro-texturing of the bearing surface, using micro-pits or micro-grooves to suppress the development of cavitation bubbles. However, micro-texturing requires high precision, and its suppression effect is greatly affected by changes in operating conditions, resulting in insufficient stability. Regulating the oil supply system pressure increases the pressure level in the low-pressure zone of the oil film, but this increases the energy consumption of the internal combustion engine lubrication system and cannot eliminate cavitation caused by abrupt changes in the flow path. Using high-strength, high-toughness, and corrosion-resistant materials or surface modification technologies improves the bearing surface's resistance to cavitation erosion, but this is a passive protection measure; cavitation itself can still occur, and the materials are expensive and the surface modification process is complex. Optimizing the bearing surface profile or multi-oil wedge structure alleviates cavitation in the divergence zone by adjusting the oil film pressure distribution, but these modifications are concentrated on the main bearing surface structure, requiring significant changes. Furthermore, they are limited by the assembly space and processes of the internal combustion engine's main bearings, making their engineering application difficult. Summary of the Invention

[0003] The purpose of this invention is to address the problems in existing technologies where solutions to the problem of oil film cavitation in main bearings are mostly concentrated on the bearing bush side, resulting in a single suppression effect and large modifications. This invention provides an oil return hole structure that addresses the issue from the journal side, simultaneously suppressing cavitation downstream of the oil groove and cavitation in the divergence zone, with minimal structural modifications, and meets the requirements of long life and high reliability for high-power-density internal combustion engines.

[0004] To achieve the above objectives, the present invention adopts the following technical solution.

[0005] An oil return hole structure for suppressing cavitation of the main bearing oil film includes an oil return hole 4 disposed on the crankshaft main journal; the oil return hole 4 is a circular through hole of equal diameter with smooth hole wall, and the openings at both ends are located on the circumferential surface of the main journal 3 and communicate with the oil film gap of the main bearing 1.

[0006] The oil return hole 4 is vertically connected to the inclined oil hole 7 inside the crankshaft, forming a return channel for lubricating oil from the main bearing to the connecting rod bearing 15; the axis of the oil return hole 4 is spatially perpendicular to the axis of the main journal 3, and its geometric center is radially eccentric relative to the journal rotation center.

[0007] The oil return hole 4 has rounded corners on both sides, including a gradually expanding streamlined transition rounded corner pointing in the direction of journal rotation and a first conventional rounded corner 10 facing away from the direction of journal rotation; the gradually expanding streamlined transition rounded corner is composed of a streamlined guide surface 8 and a second conventional rounded corner 9;

[0008] The streamlined guide surface 8 extends from the journal to the oil return hole in the opposite direction of the journal rotation direction and the depth increases from shallow to deep, and is connected to the oil return hole opening through the second conventional fillet 9.

[0009] The depth of the streamlined guide surface is 1% to 2% of the main journal diameter, and the corresponding rotation angle of the streamlined guide surface is 8 to 15 degrees.

[0010] The curved surfaces of the streamlined guide surface 8, the second conventional fillet 9, and the first conventional fillet 10 are smoothly tangent to the inner wall of the oil return hole 4 and the outer surface 6 of the main journal.

[0011] A further improvement or preferred embodiment of the aforementioned oil return hole structure for suppressing cavitation of the main bearing oil film is provided, wherein the inner diameter of the central bearing bush is applicable to a range of 100mm to 200mm, and the rated speed is between 1400 and 2000 rpm.

[0012] In a further improvement or preferred embodiment of the aforementioned oil return hole structure for suppressing cavitation of the main bearing oil film, the diameter of the oil return hole 4 is... In the formula, μ is the dynamic viscosity of the lubricating oil. ; Main journal diameter. The main journal width is in mm; Q represents the oil supply flow requirement for connecting rod bearing 15. ∆p is the pressure difference between the supply and return oil, in Pa; , This is an empirical constant.

[0013] In a further improved or preferred embodiment of the aforementioned oil return hole structure for suppressing cavitation of the main bearing oil film, with A as the starting point of the guide surface profile, connecting to the outer surface 6 of the journal; B as the ending point of the guide surface profile, transitioning to the opening of the oil return hole 4 via the second fillet 9; with point O as the center of the journal and point O1 as the center of the oil return hole 4, in a coordinate system with point A as the origin of the coordinate axis, AO as the x-axis, and the tangent direction of the journal surface as the y-axis, the oil return hole structure and its associated structural parameters satisfy:

[0014] The angle between the starting point A and the ending point B of the guide surface profile about the center point O of the journal. ;

[0015] Distance between the end point B of the guide surface profile and the outer surface of the journal ;

[0016] The angle between the y-axis and the tangent at the starting point A of the guide surface profile. ;

[0017] The angle between the y-axis and the tangent at the endpoint B of the guide surface profile ;

[0018] The functional expression for the guide surface profile is: ;

[0019] and ;

[0020] Where d is the designed oil return hole diameter, and c is the radial clearance of the main journal, in mm; The value is an empirical constant; Pin represents the inlet pressure of the oil inlet hole, in Pa. These are empirical constants; These are empirical constants; The introduced compressive viscosity coefficient; The density of the lubricating oil is expressed in kg / m³. 3 ; , is an empirical constant; ∆x and ∆y are the projected lengths of the guide surface profile on the x and y axes, respectively, in mm; , , , are the slopes of the tangent lines to the guide surface profile at points A and B, respectively, and a and b are polynomial coefficients.

[0021] In a further improvement or preferred embodiment of the aforementioned oil return hole structure for suppressing cavitation of the main bearing oil film, the radius of the second fillet 9 is... The radius of the first fillet 10 ; Eccentricity of return oil hole 4 ;

[0022] In the formula, The linear velocity of the journal surface is in mm / s; , These are empirical constants; This is an empirical constant.

[0023] Its beneficial effects are as follows:

[0024] This invention provides a return oil hole structure to suppress cavitation in the oil film of an internal combustion engine main bearing. By rationally optimizing the orifice configuration of the return oil hole, the cavitation characteristics of the oil film flow field are improved. On the one hand, the streamlined guide surface of the outer orifice of the return oil hole can guide the lubricating oil to transition smoothly, suppressing the flow separation phenomenon at the end of the oil reservoir and reducing the cavitation intensity. On the other hand, the designed guide surface configuration of the return oil hole orifice allows the oil hole to periodically relieve pressure in the high-pressure area of ​​the oil film convergence section when rotating with the journal, reducing the cavitation intensity in the divergence zone. Through the above dual mechanisms, the risk of cavitation damage to the inner wall of the bearing is effectively reduced, further improving the operating efficiency, working stability, and service life of the internal combustion engine main bearing. Attached Figure Description

[0025] Figure 1 Schematic diagram of the location of the oil return hole to suppress oil film cavitation in the main bearing of an internal combustion engine

[0026] Figure 2 A cross-sectional view of the main journal section;

[0027] Figure 3 This is a front view of the oil hole opening;

[0028] Figure 4 Schematic diagram of oil orifice structure Figure 1 ;

[0029] Figure 5 Schematic diagram of oil orifice structure Figure 2 ;

[0030] Figure 6 This is a schematic diagram showing the distribution of the cavitation-prone area at the end of the oil tank and the downstream cavitation area;

[0031] Figure 7 It optimizes the cavitation volume fraction of the region before and after optimization;

[0032] Figure 8 It is the volume fraction of cavitation in the region before and after optimization.

[0033] Figure 9 It optimizes the cavitation range of the divergence zone when the oil holes pass through. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] To address the shortcomings of the prior art, this invention provides an oil return hole structure that suppresses oil film cavitation in the main bearing of an internal combustion engine. By optimizing the orifice configuration of the oil return hole, the cavitation intensity at the end of the oil reservoir and in the oil film dispersion zone is simultaneously reduced, thereby improving the operational stability and service life of the main bearing of the internal combustion engine.

[0036] like Figure 1 , Figure 2 , Figure 3 As shown, the present invention provides an oil return hole structure for suppressing oil film cavitation in the main bearing of an internal combustion engine, which is disposed on the crankshaft main journal 3. An oil return hole 4 penetrating the journal is provided on the main journal 3;

[0037] The two ends of the oil return hole 4 are located on the circumferential surface of the main journal 3 and are connected to the oil film gap of the main bearing 1.

[0038] The oil return hole 4 is vertically connected to the inclined oil hole 7 inside the crankshaft, forming a return channel for lubricating oil from the main bearing to the connecting rod bearing 15.

[0039] Oil return hole 4 is a circular through hole of equal diameter with smooth walls;

[0040] The axis of the oil return hole 4 is spatially perpendicular to the axis of the main journal 3, and its geometric center is radially eccentric relative to the rotation center of the journal.

[0041] The oil return hole 4 has rounded corners on both sides, including a gradually expanding streamlined transition rounded corner pointing in the direction of journal rotation, and a first conventional rounded corner 10 facing away from the direction of journal rotation.

[0042] The gradually expanding streamlined transition fillet is composed of a streamlined guide surface 8 and a second conventional fillet 9;

[0043] The streamlined guide surface 8 extends from the journal to the oil return hole in the opposite direction of the journal rotation direction and the depth increases from shallow to deep, and is connected to the oil return hole opening through the second conventional fillet 9.

[0044] In a general implementation, the applicable range of the inner diameter of the bearing bush in this application is about 100mm to 200mm, and the rated speed is 1400-2000rpm;

[0045] The depth of the streamlined guide surface is 1% to 2% of the main journal diameter, and the corresponding rotation angle of the streamlined guide surface is 8 to 15 degrees.

[0046] The curved surfaces of the streamlined guide surface 8, the second conventional fillet 9, and the first conventional fillet 10 are smoothly tangent to the inner wall of the oil return hole 4 and the outer surface 6 of the main journal.

[0047] The oil return hole structure designed in this invention changes the position of the low-pressure zone caused by the high-speed jet formed by the flow channel contraction when the journal oil hole passes through the end of the oil tank, which triggers flow separation and local pressure drop. At the same time, it changes the cavitation distribution in the oil film dispersion zone caused by the pressure drop.

[0048] This structure, on the one hand, guides the lubricating oil through the streamlined, rounded corners of the outer orifice of the return oil hole, causing the low-pressure zone of the jet cavitation to contract and move downstream, thus reducing the cavitation intensity at the end of the oil tank. On the other hand, the design of the guide surface at the orifice of the return oil hole allows the oil hole to periodically relieve pressure in the high-pressure region of the oil film convergence section as it rotates with the journal, reducing the cavitation intensity in the divergence zone.

[0049] To facilitate the determination of the specific parameters of the oil return hole structure in this application, the present invention further provides a method for determining the specific configuration parameters of the oil return hole structure for suppressing oil film cavitation in the main bearing of an internal combustion engine.

[0050] For ease of explanation and analysis, a structural coordinate system is first established, such as... Figure 4 , Figure 5 As shown, along the direction of journal rotation, A is the starting point of the guide surface profile, connecting to the outer surface 6 of the journal; B is the ending point of the guide surface profile, transitioning to the oil return hole opening via the second fillet 9; point O is the center of the journal, point O1 is the center of the oil return hole 4, the structural coordinate system takes point A as the origin of the coordinate axis, the AO direction as the x-axis, and the tangent direction of the journal surface as the y-axis.

[0051] 1. Determine the diameter d of the oil return hole 4 using the following formula:

[0052]

[0053] In the formula: μ is the dynamic viscosity of the lubricating oil. D is the main journal diameter, B is the main journal width, in mm; Q is the oil supply flow requirement for connecting rod bearing 15, in mm. 3 / s; ∆p is the pressure difference between the oil supply and return, in Pa; k1 and k2 are empirical constants, with k1 ranging from 7 to 9 and k2 ranging from 0.9 to 1.2. The viscosity of the lubricating oil is determined by the grade of lubricating oil selected for the internal combustion engine, while the diameter, width, and pressure difference of the main journal can be determined by the design specifications of the internal combustion engine.

[0054] Oil supply flow requirements for connecting rod bearings The empirically corrected form of the leakage flow rate of the sliding bearing is estimated as follows: ;

[0055] In the formula: This refers to the radius clearance of the connecting rod journal. The diameter of the connecting rod journal. Width of the connecting rod journal, in mm; The journal angular velocity, n is the bearing speed, in rpm; It is an empirical constant, with a value range of 2 to 4.

[0056] 2. Determine the parameters of the guide surface profile (8-shaped profile): including the angle α between the start point A and end point B of the guide surface profile with respect to the journal center O, the distance L between the end point B of the guide surface profile and the outer surface of the journal, the angle β1 between the y-axis and the tangent to the start point A of the guide surface profile, the angle β2 between the y-axis and the tangent to the end point B of the guide surface profile, and the functional expression of the guide surface profile. ;

[0057] The included angle is calculated using the following formula.

[0058] In the formula: d is the designed oil return hole diameter, c is the radial clearance of the main journal, mm; k4 is an empirical constant, with a value range of 0.4~0.5.

[0059] Calculate the distance using the following formula ;

[0060] In the formula: The oil inlet pressure is the pressure at the oil inlet port. ; It is an empirical constant, with a value range of 16 to 22.

[0061] To ensure that the oil film's load-bearing capacity is not affected, the dimensions of the guide surface must be controlled, and the following conditions must be met during the design phase:

[0062]

[0063] In the formula: k6 is an empirical constant, with a value range of 0.5 to 0.6.

[0064] The following formulas are used to calculate the tangent angle β1 between the y-axis and the tangent at the starting point A of the guide surface profile, and the tangent angle β2 between the y-axis and the ending point B of the guide surface profile:

[0065]

[0066] In the formula: The introduced compressive viscosity coefficient; The density of the lubricating oil is expressed in kg / m³. 3 The value of k7 is determined by the grade of lubricating oil selected for the internal combustion engine; k7 and k8 are empirical constants, with k7 ranging from 1.0 to 1.6 and k8 ranging from 0.45 to 0.55, ensuring the design... .

[0067] To avoid boundary layer separation and eddy current losses caused by abrupt changes in the guide surface profile, this invention employs a cubic polynomial to fit the guide surface profile. This profile is constructed based on preset tangent angles at the inlet and outlet, enabling a smooth transition of the fluid along the profile, effectively suppressing flow separation, and thus reducing cavitation intensity.

[0068] The functional expression for the guide surface profile is determined by the following formula:

[0069]

[0070]

[0071] In the formula: in the established coordinate axes, ∆x and ∆y are the projected lengths of the guide surface profile on the x and y axes, respectively, in mm; s1 and s2 are the tangent slopes of the guide surface profile at points A and B, respectively, and a and b are polynomial coefficients.

[0072] Based on the above configuration design, the return oil orifice configuration designed in this invention can periodically relieve pressure in the high-pressure region of the oil film convergence section, reduce local pressure accumulation, smooth the pressure gradient in the downstream divergence region, and disrupt the initial conditions for cavitation, thereby reducing the degree of cavitation in the oil film in the divergence region. The structural dimensions of the return oil orifice guide surface are based on the oil film bearing capacity requirements, ensuring that the geometric parameters of the guide surface meet the pressure relief requirements without weakening the bearing capacity and stability of the oil film, thus ensuring that the bearing maintains sufficient bearing capacity while suppressing cavitation.

[0073] 3. Determine the fillet radius dimensions (9-12):

[0074] This invention designs the fillet dimensions at the upper and lower ends of the oil return hole based on factors such as rotational speed, main journal diameter, oil film clearance, and return hole diameter, ensuring that the fillets match the journal surface linear velocity, oil film thickness, and return hole size. Specifically, the lower fillet aligns with the incoming flow direction to reduce flow impact, while the upper fillet smoothly connects to the guide surface, achieving a geometrically continuous transition. The fillets reduce geometric discontinuities at the sharp edge of the orifice, preventing flow separation and sudden pressure drops caused by abrupt changes in the flow channel, thereby suppressing cavitation. The upper fillet further reduces the velocity and pressure gradients near the orifice, resulting in a more uniform flow field distribution when lubricating oil flows into the return hole, which is beneficial for downstream pressure recovery and reduces cavitation intensity at the orifice. The synergistic effect of the upper and lower fillets ensures a stable and effective flow cross-section for the oil return channel, preventing flow separation caused by sharp structures occupying the flow area.

[0075] Specifically: the radii R1 and R2 of the second fillet 9 and the first fillet 10 are calculated using the following formulas: ; ;

[0076] In the formula, The linear velocity of the journal surface is in mm / s; k9, k10 As an empirical constant, k9 ranges from 20 to 30. 10 The value range is 0.2 to 0.3.

[0077] For the third fillet 11 and the fourth fillet 12, their dimensions are adaptively adjusted according to the actual structural space, and the structural edges are blunted to eliminate sharp protrusions.

[0078] 4. Determine the eccentricity of return oil hole 4. ;

[0079] In the formula, k 11 It is an empirical constant, with a value range of 0.4 to 0.5.

[0080] Based on the aforementioned optimized design method, this application designs the return oil hole diameter by considering factors such as the main bearing oil supply pressure, lubricating oil viscosity, connecting rod bearing oil supply flow requirements, and main journal diameter. This ensures that the return oil flow matches the main bearing oil inlet flow, thereby guaranteeing the stability of oil supply from the inclined oil hole inside the crankshaft to the connecting rod bearing. This avoids the temperature rise caused by lubricating oil stagnation in the main bearing due to poor oil return, reducing the impact of fluctuations in the connecting rod bearing oil supply pressure. Simultaneously, it prevents excessive reduction in the main bearing oil film pressure due to an excessively large hole diameter, mitigating the cavitation tendency caused by sudden pressure drops and playing a positive role in suppressing cavitation in the main bearing.

[0081] The streamlined guide surface profile at the upper end of the return oil hole orifice is designed by considering factors such as inlet pressure, oil film clearance, lubricating oil viscosity, return oil hole diameter, main journal diameter, and rotational speed, ensuring it matches the lubricating oil flow and journal structural dimensions. When the lubricating oil flows through the throttling throat and enters the downstream gradually expanding section, the flow channel cross-section expands gently, the flow velocity gradually decreases, and some kinetic energy is smoothly converted into pressure energy, significantly reducing the pressure gradient and pressure drop near the orifice. As the pressure energy recovers and the flow velocity decreases, the low-pressure region is effectively confined to the throttling throat and downstream near-field region, preventing high-speed jets from penetrating deep into the return oil hole and causing excessive diffusion of the low-pressure region into the oil hole. The low-pressure region's spatial range shrinks significantly, thus limiting the occurrence and development of cavitation. The optimized guide surface profile can guide the jet to flow close to the wall, effectively avoiding flow separation caused by high-speed flow and adverse pressure gradient, reducing backflow vortices and secondary flows caused by flow separation, reducing the risk of cavitation promoted by the low-pressure area in the vortex core, and reducing turbulence intensity and pressure pulsation, making the flow field distribution more uniform and stable.

[0082] Implementation and verification:

[0083] Based on finite element analysis simulation, the following results were obtained: Figure 6 The diagram shows the distribution of the cavitation erosion zone at the end of the oil tank and the downstream cavitation zone; points 1 and 2 and zone 1 are the cavitation erosion zone at the end of the oil tank, and zone 2 is the downstream cavitation zone at the end of the oil tank.

[0084] Figure 7 , Figure 8 , Figure 9 The figure shows a comparison of the cavitation state of the present invention with that of the conventional internal combustion engine main bearing oil return hole structure. As can be seen from the figure, after optimizing the main bearing oil return hole structure based on the technical solution of this application, the cavitation volume fraction, cavitation intensity (cavitation quality) and cavitation range ratio in the cavitation-prone area at the end of the oil tank, the cavitation area downstream of the end of the oil tank, and the oil film dispersion area are significantly reduced.

[0085] Depend on Figure 8 It can be seen that, compared with the conventional oil return hole structure of the main bearing of the internal combustion engine, the cavitation position of the present invention is concentrated near the guide surface wall, and the cavitation cloud moves downstream, which reduces the risk of cavitation erosion on the bearing side after the oil tank enters the oil film area, thereby further improving the operating stability and service life of the main bearing of the internal combustion engine.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A return oil hole structure for suppressing cavitation of the main bearing oil film, characterized in that, Including the oil return hole (4) set on the crankshaft main journal; the oil return hole (4) is a circular through hole of equal diameter with smooth hole wall, and the openings at both ends are located on the circumferential surface of the main journal (3) and are connected to the oil film gap of the main bearing (1); The oil return hole (4) is vertically connected to the inclined oil hole (7) inside the crankshaft, forming a return channel for lubricating oil from the main bearing to the connecting rod bearing (15); the axis of the oil return hole (4) is spatially perpendicular to the axis of the main journal (3), and its geometric center is radially eccentric relative to the rotation center of the journal. The oil return hole (4) has rounded corners on both sides, including a gradually expanding streamlined transition rounded corner pointing in the direction of journal rotation and a first conventional rounded corner (10) facing away from the direction of journal rotation; the gradually expanding streamlined transition rounded corner is composed of a streamlined guide surface (8) and a second conventional rounded corner (9); The streamlined guide surface (8) extends from the journal to the return oil hole in the opposite direction of the journal rotation and the depth increases from shallow to deep, and is connected to the return oil hole opening through the second conventional fillet (9); The depth of the streamlined guide surface is 1% to 2% of the main journal diameter, and the corresponding rotation angle of the streamlined guide surface is 8 to 15 degrees. The curved surfaces of the streamlined guide surface (8), the second conventional fillet (9), and the first conventional fillet (10) are smoothly tangent to the inner wall of the oil return hole (4) and the outer surface (6) of the main journal.

2. The oil return hole structure for suppressing cavitation of the main bearing oil film according to claim 1, characterized in that, The inner diameter of the central bearing is applicable in the range of 100mm to 200mm, and the rated speed is 1400 to 2000rpm.

3. The oil return hole structure for suppressing cavitation of the main bearing oil film according to claim 1, characterized in that, The diameter of the return oil hole (4) ; In the formula, μ is the dynamic viscosity of the lubricating oil. ; Main journal diameter. Main journal width, mm; For the oil supply flow requirements of the connecting rod bearing (15), ; The journal angular velocity, ; The pressure difference between the supply and return oil, in Pa; This is an empirical constant.

4. The oil return hole structure for suppressing cavitation of the main bearing oil film according to claim 3, characterized in that, With A as the starting point of the guide surface profile, it connects to the outer surface of the journal (6); B is the ending point of the guide surface profile, transitioning to the opening of the return oil hole (4) via the second fillet (9); point O is the center of the journal, and point O1 is the center of the return oil hole (4). In a coordinate system with point A as the origin of the coordinate axis, AO as the x-axis, and the tangent direction of the journal surface as the y-axis, the return oil hole structure and its associated structural parameters satisfy: The angle between the starting point A and the ending point B of the guide surface profile about the center point O of the journal. ; Distance between the end point B of the guide surface profile and the outer surface of the journal ; The angle between the y-axis and the tangent at the starting point A of the guide surface profile. ; The angle between the y-axis and the tangent at the endpoint B of the guide surface profile ; The functional expression for the guide surface profile is: ; and ; Where d is the designed oil return hole diameter, and c is the radial clearance of the main journal, in mm; The value is an empirical constant; Pin represents the inlet pressure of the oil inlet hole, in Pa. These are empirical constants; C is an empirical constant; d ρ is the introduced compressive viscosity coefficient; ρ is the density of the lubricating oil, kg / m³ 3 ; , These are empirical constants; , These are the projected lengths of the guide surface profile on the x and y axes, respectively, in mm; , , , are the slopes of the tangent lines to the guide surface profile at points A and B, respectively, and a and b are polynomial coefficients.

5. The oil return hole structure for suppressing cavitation of the main bearing oil film according to claim 4, characterized in that, The radius of the second fillet (9) The radius of the first fillet 10 ; Eccentricity of return oil hole (4) ; In the formula, The linear velocity of the journal surface is in mm / s; , These are empirical constants; This is an empirical constant.

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