Engine sliding bearing lubrication coordination evaluation method

Abstract

The present application relates to a kind of engine sliding bearing lubrication coordination evaluation method, according to bearing lubrication state and proportion, bearing peak oil film pressure average, axial oil film pressure load uniformity and total friction loss power consumption of friction pair per cycle, sliding bearing lubrication coordination factor Λ3 is calculated, the coordination of the sliding bearing lubrication of engine is evaluated.The present application introduces lubrication coordination factor, considers the boundary lubrication of bearing, mixed lubrication and rough hydrodynamic lubrication state distribution, axial oil film load uniformity, bearing peak oil film pressure and total friction loss power consumption of friction pair per cycle, the coordination of the sliding bearing lubrication of engine is described and evaluated using the above four indicators.

Description

Technical Field

[0001] This invention belongs to the field of engine technology, specifically relating to a method for evaluating the lubrication coordination of engine sliding bearings. Background Technology

[0002] The increase in engine power density will inevitably lead to a significant increase in load and speed, which will correspondingly cause the working environment of sliding bearings to deteriorate. Traditional lubrication assessment methods cannot evaluate engine lubrication from multiple dimensions and cannot provide support for the lubrication improvement design of diesel engines, thus failing to meet the requirements of lubrication assessment.

[0003] Traditional lubrication evaluation uses minimum oil film thickness and maximum oil film pressure. This requires lubrication conditions to meet certain requirements under all operating conditions, typically requiring the bearing to avoid boundary lubrication states, which is quantified by minimum oil film thickness. Besides worst-case lubrication conditions, peak oil film pressure also reflects bearing load in engineering applications, usually requiring it not to exceed a specified value. Meeting both of these requirements indicates the bearing is usable. However, with increasing power density, this evaluation method is no longer applicable.

[0004] Traditional lubrication evaluation has two main drawbacks:

[0005] 1. With the increase in power density, the lubrication state of the main friction pairs of the engine, such as piston ring friction pairs, connecting rod small end friction pairs, main bearing and connecting rod bearing friction pairs, is inevitably in the boundary lubrication state. Rough contact exists at a certain time, and the traditional minimum oil film thickness assessment is no longer applicable.

[0006] 2. The maximum oil film pressure cannot fully reflect the lubrication status of a sliding bearing. Even if the evaluation criteria for sliding bearings are met, there are still risks of failure such as uneven wear, large frictional losses, and even adhesive wear. Summary of the Invention

[0007] This invention provides a method for evaluating the lubrication compatibility of engine sliding bearings, overcoming the shortcomings of existing technologies.

[0008] To address the above technical problems, this invention provides a method for evaluating the lubrication coordination of engine sliding bearings. The method is characterized by calculating the sliding bearing lubrication coordination factor Λ3 based on the bearing lubrication state and ratio, the average value of the bearing peak oil film pressure, the uniformity of the axial oil film pressure load, and the total friction loss power consumption per cycle of the friction pair, thereby evaluating the coordination of the engine's sliding bearing lubrication.

[0009] Beneficial effects: This invention introduces a lubrication coordination factor, which takes into account the distribution of boundary lubrication, mixed lubrication and rough hydraulic lubrication states of the bearing, the uniformity of axial oil film load, the peak oil film pressure of the bearing and the total friction loss power consumption per cycle of the friction pair. The above four indicators are used to describe and evaluate the coordination of the sliding bearing lubrication of the engine. Attached Figure Description

[0010] Figure 1 This invention provides a schematic diagram of the principle for evaluating the lubrication coordination of engine sliding bearings. Detailed Implementation

[0011] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below.

[0012] The present invention proposes an evaluation method for the lubrication coordination of engine sliding bearings, which considers the bearing lubrication state and ratio, the average oil film pressure, the uniformity of axial oil film pressure load, and the total friction loss power consumption per cycle of the friction pair. The above four indicators are used to describe and evaluate the lubrication coordination of the engine sliding bearings.

[0013] The bearing lubrication conditions and proportions include the distribution of boundary lubrication, mixed lubrication, and rough hydraulic lubrication conditions of the bearing;

[0014] The average oil film pressure includes the circumferential average pressure and the total average bearing pressure;

[0015] Axial oil film load uniformity is the average value of the bearing's peak oil film pressure;

[0016] The total frictional work loss per cycle of the friction pair.

[0017] The lubrication state is determined by the film thickness ratio. However, when the minimum oil film thickness decreases linearly, the impact of different lubrication states on lubrication performance is not linear. Performance deteriorates rapidly when the film thickness is small, and when the film thickness ratio is less than 1 (the boundary lubrication state), lubrication performance significantly decreases. Therefore, directly using the minimum film thickness to evaluate lubrication performance reduces the impact of poor lubrication states and cannot fully reflect the adhesive wear of the friction pair. Therefore, different influence coefficients *c* are set according to the degree of influence of different lubrication states on oil film stability and friction wear. The minimum film thickness within the cycle is weighted to obtain a comprehensive lubrication state coefficient to quantitatively evaluate lubrication adhesive wear failure.

[0018] When the film thickness ratio is greater than 4, it is a fluid lubrication state. In this state, the oil film can form well, the pressure is stable, the frictional work is small, and there is no significant frictional wear. The specific gravity coefficient is set to ch. When the film thickness ratio is between 1 and 4, it is a mixed lubrication state. In this state, the surface roughness and elastic deformation of the bearing have a greater impact on the lubrication profile, the frictional work increases, and the wear phenomenon is obvious when in mixed lubrication for a long time. The specific gravity coefficient is set to c.m When the film thickness ratio is less than 1, indicating boundary lubrication, there is essentially no macroscopic hydraulic lubrication. Contact action is dominated by solid elasto-plasticity, leading to a sharp decline in lubrication performance, significant wear and loss, a large instantaneous temperature rise, and a decrease in lubricating oil viscosity, further damaging lubrication performance. The specific gravity coefficient is set to c. b .

[0019] h b h m and h h The upper limit oil film thicknesses for boundary lubrication, mixed lubrication, and rough hydraulic lubrication states are respectively obtained by multiplying the roughness of the journal and bearing by the film thickness ratio of each state. The state coefficient function is divided into three segments, each a linear function, passing through four points: (0, c b ), (h b c m ), (h m C h ), (h h The function expression is obtained through Lagrange interpolation:

[0020]

[0021] h b =σ s h m =4·σ s h h =10·σ s (2)

[0022] σ s =σ1+σ2 (3)

[0023] In the formula, h is the minimum oil film thickness at different circulation angles, and x is the lubrication state coefficient. θ It is negatively correlated with the oil film thickness. σ1 is the roughness value of the first contact surface of the friction pair, and σ2 is the roughness value of the second contact surface of the friction pair. The mean value of the lubrication state coefficient is calculated, and the reciprocal is taken to make the coefficient positively correlated with the lubrication state, so as to obtain the comprehensive lubrication state coefficient X as shown in the formula, where n is the number of discrete angles in one cycle.

[0024]

[0025] Axial oil film load uniformity is represented by the average of the absolute values ​​of the differences between the average circumferential pressure at each cross-section of the bearing along the axial direction and the total average pressure at the maximum pressure. A larger value indicates a more pronounced variation in axial load and poorer uniformity. This value is normalized, and maximum and minimum values ​​are set. To ensure a positive correlation between this value and the direction of uniformity variation, 1 is subtracted from this value to represent the axial load uniformity, expressed as:

[0026]

[0027] Where m is the number of axial sections of the bearing, P j Let P be the average pressure at the j-th axial section. mean P is the total average pressure of the bearing. min With P max These represent the maximum and minimum values ​​of the difference, respectively.

[0028] The lubrication coordination factor is expressed as:

[0029]

[0030] Where Λ3 is the lubrication friction coordination factor, P a P represents the average peak oil film pressure of the bearing. a，li P represents the maximum limit of the average peak pressure of the oil film. a，min The minimum average value of the peak oil film pressure is the optimal value. L a L represents the total frictional loss power consumption per cycle of the friction pair. a，li This is the limit value for power consumption due to friction loss, L a，min This represents the minimum frictional power loss. α, β, γ, and δ are the weighted influence coefficients of each indicator, summing to 1. These coefficients are obtained using the entropy weighting method, as shown in Table 1. When the average peak oil film pressure exceeds the allowable value, or the actual frictional power loss exceeds the limit, or dry friction occurs due to zero oil film thickness, the performance of the main bearing lubrication system deteriorates significantly, and the coordination factor is 0. Improved lubrication conditions, increased load uniformity, and reduced total pressure all enhance lubrication coordination.

[0031] Table 1 Weighting coefficients of lubrication coordination factor

[0032]

[0033]

[0034] When the lubrication friction coordination factor is 0, the sliding bearing cannot meet the usage requirements and needs to be improved in terms of structure, bearing material, and process. The lubrication factor is between 0 and 1. The closer it is to 1, the better the lubrication coordination of the sliding bearing. The factor can only approach 1 infinitely and will not be greater than or equal to 1.

[0035] This invention introduces a lubrication friction coordination factor to determine lubrication coordination evaluation indicators and methods from the perspective of sliding bearing failure modes. For example, crankshaft main journals and crank pins move at high speeds under high specific pressure, and the decreased lubrication performance or even failure of main bearings and connecting rod big end bearings is one of the main failure modes of engines. Bearing failure is mainly caused by abrasive wear failure, adhesive failure, surface fatigue failure, corrosion failure, cavitation failure, etc. Adhesive wear failure is caused by insufficient lubrication, bearing hole deformation, etc., resulting in too small bearing clearance, excessive frictional heat generation, causing the surface metal of the bearing shell to overheat and melt and be scraped off, or even leading to bearing seizure. When adhesive wear occurs, the oil film thickness is small, and the lubrication state changes, so the adhesive wear condition can be reflected by the lubrication state. At the same time, due to the bending of the main journal under load, the bearing edge stress is high, and uneven wear is prone to occur. Improving the uniformity of bearing surface load can effectively improve bearing reliability. In summary, lubrication state and ratio, peak oil film pressure, axial oil film pressure load uniformity, and friction loss work are used as lubrication response evaluation indicators.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the lubrication compatibility of engine sliding bearings, characterized in that: Based on the bearing lubrication condition and ratio, the average peak oil film pressure of the bearing, the uniformity of axial oil film pressure load, and the total friction loss power consumption per cycle of the friction pair, the lubrication coordination factor of the sliding bearing is calculated. To evaluate the coordination of lubrication of the engine's sliding bearings; The average oil film pressure includes the circumferential average pressure and the total average bearing pressure; the axial oil film load uniformity is the average peak oil film pressure of the bearing. Lubrication Coordination Factor for Sliding Bearings The definition is as follows: X represents the overall lubrication condition parameter. Here, η is the lubrication condition coefficient, and η is the uniformity of axial oil film load. This represents the average value of the bearing's peak oil film pressure. This represents the maximum limit of the average peak pressure of the oil film. The minimum average value of the peak oil film pressure is the optimal value. The total frictional loss power consumption per cycle of the friction pair This is the limit value for power consumption due to friction loss. It is the minimum value of frictional power loss; , , , These are the influence coefficients for the comprehensive lubrication condition weight, axial load uniformity weight, peak oil film pressure weight, and total friction loss power consumption, respectively. The closer the value is to 1, the better the lubrication coordination; the closer it is to 0, the worse the lubrication coordination.

2. The method for evaluating the lubrication compatibility of an engine sliding bearing according to claim 1, characterized in that: The comprehensive lubrication condition parameter X is: In the formula The number of discrete angles in a cycle.

3. The method for evaluating the lubrication compatibility of an engine sliding bearing according to claim 1, characterized in that: Lubrication condition coefficient for: In the formula, , and These represent the upper limit oil film thickness corresponding to boundary lubrication, mixed lubrication, and rough hydraulic lubrication states, respectively. Minimum oil film thickness at different circulation angles. Let be the roughness value of the first contact surface of the friction pair. This represents the roughness value of the second contact surface of the friction pair; , , Here, represents the influence coefficient corresponding to different lubrication conditions, where The specific gravity coefficient under boundary lubrication conditions. This is the specific gravity coefficient under fluid lubrication conditions. This is the specific gravity coefficient under mixed lubrication conditions.

4. The method for evaluating the lubrication compatibility of an engine sliding bearing according to claim 1, characterized in that: The axial oil film load uniformity η is: in, The number of axial sections of the bearing. For the first Average pressure at each axial section; This represents the total average pressure of the bearing. and These represent the maximum and minimum differences, respectively.

5. The method for evaluating the lubrication compatibility of an engine sliding bearing according to claim 1, characterized in that: α=0.2439,β=0.2299,γ=0.2840, =0.2422.

6. The method for evaluating the lubrication compatibility of an engine sliding bearing according to claim 1, characterized in that: When the lubrication compatibility factor is 0, the sliding bearing cannot meet the usage requirements and needs to be improved in terms of structure, bearing materials, and manufacturing process.

7. The method for evaluating the lubrication compatibility of an engine sliding bearing according to claim 3, characterized in that: When the film thickness ratio is greater than 4, it is in fluid lubrication state; when the film thickness ratio is between 1 and 4, it is in mixed lubrication state; and when the film thickness ratio is less than 1, it is in boundary lubrication state.

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