Elsevier

Engineering Failure Analysis

Volume 90, August 2018, Pages 277-289
Engineering Failure Analysis

Lubrication performance analysis of crankshaft bush in compressor

https://doi.org/10.1016/j.engfailanal.2018.03.014Get rights and content

Highlights

  • Lubrication performance of the crankshaft bush in compressor was investigated.

  • Parameters of the bush lubrication are studied during the stable rotation of crankshaft.

  • Speed and width diameter ratio affect the maximum pressure value of oil film.

  • Max pressure and carrying capacity decrease with min oil film thickness increases.

Abstract

The instability of lubricating oil film has a great effect on the wear of friction pairs and carrying capacity of the parts as well as smooth running of the machine. The lubrication system of crankshaft bush plays an important role in the good operation of compressor unit, reduces production cost while improving production efficiency. In this paper, lubrication performance of the crankshaft bush in compressor was investigated. Parameters involved in the lubrication of bush are studied and analyzed systematically during the stable rotation of crankshaft. Effects of lubrication parameters, such as width diameter ratio, crankshaft speed, inlet pressure, attitude angle and the minimum oil film thickness, on the pressure and distribution of lubricant film were discussed. At last, the optimum value and recommended range of some parameters of bush are determined, and the quantization is carried out within a certain range. The results show that two symmetrical distributions of positive and negative high pressure concentrated areas on both sides of bush oil groove can be formed when the crankshaft is stable. The speed and width diameter ratio have a great effect on the maximum pressure value of oil film. The inlet oil pressure and the minimum oil film thickness are the second, and the inlet attitude angle has little effect. With the increase of width diameter ratio, the maximum pressure value of the positive high pressure concentrated area increases, and the negative areas decreases. With the increase of oil inlet pressure, the maximum oil film pressure increases too but the influence is small. With the increasing of minimum oil film thickness, the maximum pressure and carrying capacity of oil film decrease. If the clearance between crankshaft and bush is too small, oil film can't be formed. For the analysis model in this paper, it is recommended that the radius clearance of bush is 0.04 mm. The inlet oil pressure range of lubricating oil is 0.32–0.36 MPa. Those results can be used in the design, testing and evaluation of the crankshaft system in compressor.

Introduction

Compressor is an important equipment in many production processes, provides the necessary power for the whole process (as shown in Fig.1). The crankshaft is used as the transmission part of the compressor to convert its rotational motion into reciprocating motion. In the course of rotation, the crankshaft is subjected to great mechanical load and thermal load. In some bad conditions, it is easy to be damaged and even cause accidents.

In order to reduce the accident cost, the special sliding bearing and crankshaft bush are attached to the crankcase seat to support and transfer the motion. In the process of compressor operation, the bush is affected by friction, connecting rod force and crankshaft gravity. If without timely and effective lubrication, it is likely to cause early failure damage, and even lead to crankshaft strain, fracture and so on. Crankshaft bearing lubrication description can adopt the theory of sliding bearing lubrication. When the bush is working, it is attacked by a dynamic load that varies in size and direction. So the crankshaft bush can be regarded as a kind of special sliding bearing [1].

In 1886, Reynolds, a British physicist, successfully deduced the Reynolds equation by fluid mechanics, and explained the formation mechanism of fluid pressure perfectly [2,3]. In 1965, Booker put forward the Mobility method on the basis of Hahn method, and obtained the approximate analytic solution of oil film pressure with infinite narrow bearing lubrication theory [4]. In the 1960s, with the development of the internal combustion engine manufacturing industry, China's bearing production gradually started. Since then, the rapid development of China's railway industry, the use of internal combustion engine continues to increase, the bush is also more and more widely used. S Bukovnik et al. [5] studied the relationship between the maximum oil film pressure of the crankshaft main bearing and connecting rod big end bearing, and the minimum oil film thickness and the flow rate of lubricating oil, based on the numerical method of hydrodynamics and the theory of thermoelastic lubrication. On the premise of the change of dynamic lubrication characteristics for the crankshaft bush caused by crankshaft deformation, Jun Sun et al. [6]analyzed the influence of the oil film distribution on its lubrication performance, and deduced the oil film thickness expression of the inclined sliding bearing.

At present, most of the researches on the lubrication performance of bush are limited to qualitative analysis, but there has not been a range of quantification for the studied parameters. The formation and distribution of lubricating film are affected by many factors. In this paper, the influence of the main lubrication factors on the formation and pressure value of the crankshaft bush lubricating oil film are studied, which provides a theoretical guidance for its field application.

Section snippets

Structure of crankshaft bush

Compressor lubrication system is divided into three categories, pre-lubrication system, cylinder lubrication system and crankshaft connecting rod lubrication system. The oil circuit diagram [7] of crankshaft connecting rod lubrication system is shown in Fig. 2. The lubrication range of crankshaft connecting rod lubrication system mainly includes crankshaft bush, connecting rod bush and crosshead.

The lubricating oil flows from the crankcase oil tank through the coarse filter, and then enters the

CFD theories

When a viscous fluid enters the wedge gap, it can produce a steady fluid pressure effect, which is called the wedge effect of hydrodynamic lubrication. The following Eq. [10] can be obtained from the schematic diagram of the oil film micro cell force in Fig. 5, that is:pdydz+τdxdzp+pxdxdydzτ+τydxdxdz=0

After calculating, the px=τy. According to Newton's law of viscosity, τ=ηuy. To simplify (3), the relationship of the pressure in the X direction and velocity along the Y direction

Attitude angle

When the compressor is running stable, the center of crankshaft has a certain distance from the center of bush. And the connection between the two centers and the vertical direction has a certain angle, defined as the attitude angle. The radius clearance of model is 0.03 mm, the inlet oil pressure is 0.3 MPa and the rotational speed of its inner wall is 960 r/min.

The attitude angle of analysis model is simulated from 0–45°, and the oil film pressure nephograms are shown in Fig. 11. It can be

Conclusions

In this paper, the lubrication performance of crankshaft bush was studied, and the formation law of oil film in the bush clearance can be clearly displayed. By analyzing the main lubricating parameters, the following conclusions are obtained.

  • (1)

    When the crankshaft is stable, thickness of the oil film is close to the minimum value. Two symmetrical distributions of positive and negative high pressure concentrated areas on both sides of bush oil groove are formed. By analyzing the main lubricating

Acknowledgements

This paper is supported by the Scientific Research Starting Project of SWPU (2017QHZ011), Project of Sichuan Education Hall (17ZA0423) and National Natural Science Foundation of China (51474180).

References (17)

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