TS-139
Oil Film Pressure Measurement & Fatigue Evaluation of the Large Scale Diesel Engine
Main Bearing under Fluctuating Load by the Test Rig
Kazuhiko YAMASHITA*, Masayoshi KATSUMI** and Katsuhiko SAKAGUCHI**
ABSTRACT
The main bearing for large bore marine diesel engines are usually operated under fluctuating load. Especially under extremely heavy load, misalignment-driven uneven contact between journal and bearing metal causes very thin operating film, which leads high oil film pressure in the bearing. As this high pressure (about 100MPa) increases the possibility of White Metal failure, evaluation of the oil film pressure is indispensable for designing and developing main bearings. To answer this, original zero-dead volume high response pressure sensor has been developed and the following results are obtained;
(1) Measuring technology for high oil film pressure is established by elemental test with newly developed highly responsive sensor to detect axial force strain. With this sensor, high oil film pressure in clearance of under 10mm can be measured.
(2) Loading of fluctuating load by simulation of actual unit is made possible by development of three dimensional bearing load test equipment which controls load and position.
(3) The maximum oil film pressure of approximately 100-150MPa is measured in specimen bearing with bearing inner diameter of 300mm to prove high oil film pressure generation and fatigue faiilure by endurance test. In addition, oil film pressure reduction is achieved (reduced to 61MPa) by improvement of bearing, to verify oil film pressure distribution in bearing agrees with EHD analysis.
Key Words : Engine, Bearing, Fatigue, Pressure, Measurement, Sensor
NOMENCLATURE
Cr : Bearing radius clearance
ex, ey : Shaft center eccentricity
Fx, Fy : Oil film strength
f1 : Reynolds number remainder
f2, 3 : Equilibrium of forces remainder
H : Oil film thickness
L : Compliance matrix
p : Oil film pressure
t : Time
U : Sliding velocity
Wx,Wy : Load
x, y, z : Coordinates
α : Pressure coefficient of viscosity
αx , αy : Uneven contact angle of shaft
μ : Viscosity (μ=μ0 exp(αp))
Ω : Regional area
θ : Angle
1. INTRODUCTION
Recently, more powerful and more efficient large bore marine diesel engines have been developed to respond the market demand. MHI takes the lead in this tendancy with its UEC-LS II Diesel Engines, which are in progress for more power, efficiency and compactness [1]. As the greater power and efficiency mean heavier load and severity to each engine part, it is inevitable to establish evaluation technology to assure the reliability.
Before discussing this technology, UEC-LS II Engine should be outlined. As seen from the cross section (Fig. 1) [2] and the main bearing structure (Fig.2), main bearing consists of bedplate saddle, bearing cap and main bearing upper and lower metals to accept fluctuating load from crankshaft [2]. Please refer to Table 1 for the dimensions.
The fluctuating load causes fatigue failure in main bearing's white metal. This process may be analyzed into the three factors as shown in Fig.3. Among them, excessive oil film pressure occurs due to severe operating condition, such as fluctuating load and uneven contact, or due to bearing configuration. According to numerical analysis, this oil film pressure of the order of 100MPa occurs in micro-thin oil film of under 10μm, though it has not been verified yet.
For measuring oil film pressure, a thin film sensor with Manganin was developed by Someya et al. [3] to make a success in measuring pressure of approximately 50MPa, as Piezoelectric sensor by Jones et al. also did. Both sensors are susccessful in measuring from bearing metal side on static side, not in measuring three dimensional pressure distribution on bearing surface under fluctuating load.
* Takasago R&D Center. Mitsubishi Heavy Industries, Ltd.
2-1-1 Shinhama Arai-Cho Takasago, Hyogo Pref. 676-8686 Japan
Fax: +81-794-45-6081 E-mail:kazuhiko_yamashita@n.trdc.mhi.co. jp
** Mitsubishi Heavy Industries, Ltd.
