Dong-Chul Han

Oil Film Thickness in Engine Main Bearings: Comparison Between Calculation and Experiment by Total Capacitance Method

The minimum oil film thicknesses (MOFT) in the crankshaft main bearings of a 1.5 liter, L-4, gasoline engine are measured and calculated to study the dynamically loaded engine bearing. The MOFT are measured simultaneously at each of the five main bearings using the total capacitance method(TCM). To improve the reliability of the TCM, a reasonable determination method of bearing clearance is introduced and the effects of bearing cavitation and aeration on the test results are analyzed. Also the crankshaft is grounded by means of a slip ring instead of the friction contact method to improve the test precision. The calculation is based on the model of statically determinate beam, short bearing approximation and Mobility method From the comparison between the measured and calculated MOFT curves, it is found that a qualitative similarity exists between them, but in all cases, measured MOFT are smaller than that of calculated The crankshaft vibration and the imbalance of the load distribution between the engine bearings have important influence upon the MOFT curve. So. it is found that the calculation result from the model of the statically determinate beam has a limitation in predicting bearing performance.

Oil Film Thickness in Engine Connecting-Rod Bearing With Consideration of Thermal Effects: Comparison Between Theory and Experiment

The aim of this paper is to study the thermal ejfects on minimum oil film, thickness in a connecting-rod bearing. A comparison between the theoretical and experimental results of minimum oil film thickness in a connecting-rod bearing is presented. The transient energy equation is solved by adapting the adiahatic boundary condition for considering the thermal effects. The minimum oil film thicknesses are measured by the total capacitance method. The minimum oil film thickness over an engine cycle estimated with consideration of thermal effects is closer to that measures than that estimated by using the iso-viscous lubrication theory.

Oil Film Thickness In Engine Connecting-Rod Bearing: Comparison Between Calculation and Experiment

The minimum oil film thicknesses(MOFT) in the connecting-rod bearings of a 1.5 liter, L-4, gasoline engine are measured up to 5500 rpm and calculated to study the dynamically loaded engine bearings. Short bearing approximation and Mobility methods are used for theoretical analysis of oil film characteristics. Also cylinder pressure, crank-pin surface temperature and bearing temperature are measured and used as the input data of theoretical analysis. The MOFT are measured by the total capacitance method(TCM). To improve the reliability of the test results, a reasonable determination method of bearing clearance is introduced and used, and the effects of cavitation and aeration on the test results are neglected. Also the crankshaft is grounded by means of a slip ring. A scissor type linkage system was developed to measure the MOFT and bearing temperature. The effects of engine speed, load and oil viscosity on the measured and calculated minimum oil film thicknesses are investigated at 1500 to 5500 rpm. From the comparison between the measured and calculated MOFT, it is found that a qualitative similarity exists between them, but in all cases, the measured MOFT are smaller than those calculated.

Theoretical evaluation of the effects of crank offset on the reduction of engine friction

Abstract This study discusses the effects of crankshaft offsets to the piston thrust side on engine friction. An analytical model to interpret some key friction parts of an engine, such as crankshaft bearings, pistons and piston rings, is considered, and the effects of a crankshaft offset on the moving parts is calculated using numerical analysis. Analytical results show that the crankshaft offset has some influence mainly on the side force upon the piston and effects variation in the piston sliding speed. The crankshaft offset can reduce significantly friction loss of the piston skirt, whereas friction loss in other parts is negligible. The optimum offset to minimize skirt friction loss depends on the operating conditions. Upon calculation and measurement it is determined that reduction in friction loss occurs mainly at low engine speed and low engine load. When the speed and load increase, benefit is confined to the lowest offsets, and at higher offsets the friction increases. Analytical and experimental results indicate that crank offset is effective in reducing engine friction and improving fuel economy in the low and medium engine speed region.

The Effects of Additional Factors on the Engine Friction Characteristics

This paper reports on the effects of additional factors on the engine friction characteristics. The total friction loss of engine is composed of pumping and mechanical friction loss. The pumping loss was calculated from the cylinder pressure, and the mechanical friction loss was measured by strip-down method under the motoring condition. The various parameters were tested. The engine friction loss was much affected by oil and coolant temperature. The low viscosity oil was very effective to reduce the friction loss, and friction modifier was very useful to reduce the friction loss at lower engine speed. The engine friction loss was varied with engine running time because of surface roughness decreasing and oil degradation. To prevent oil-churning effect, it was very important to maintain the proper oil level. The presented results will be very useful to understand friction characteristics of engine.

The Problem of Engine Friction Test by Strip Down Method

The aim of this paper is to investigate the problem of strip down method, which is usually used to evaluate the engine friction level. The validity of strip down method was investigated by theoretical analysis of friction in crank and piston assembly. The friction of cylinder and piston assembly was analyzed under the various test conditions. The measured cylinder pressure was used as boundary conditions of friction torque and loss calculation. The friction loss of crank and piston assembly was influenced by test conditions that resulted from the variation of load condition. From the results, we have known that the strip down method could be possible to distort the friction loss of engine moving components.

An Experimental Study on the Tappet Spin for a Direct Acting Valve Train System

The technique for measuring the rotational speed of tappet in direct acting type valve train system has been developed. The optic signal monitoring system with laser and optic fiber was designed to follow the signal of tappet rotation. The system was based on ON/OFF signal generation from the additional encoder teeth under the tappet with optic fibers attached photo transistor. The data showed that tappet rotation was affected by offset, oil temperature and cam shaft operating speed. Also it was found that tappet rotation increases with oil temperature. Tappet spin was delayed 10∼s20 cam angle after valve opening. The instantaneous rotational speed of tappet was reciprocal to cam shaft speed and the tappet and the cam angle ratio was located in the range of 0.1∼0.3.

Friction Characteristics of Piston Assembly (II) -Experiment-

The aim of this paper is to investigate the friction characteristics of piston assembly, which composed of ring pack and piston skirt. The friction force of piston assembly was measured by using the movable liner in the single cylinder engine, and the various parameters were tested. The friction force was suddenly increased at the expansion stroke due to higher cylinder pressure. The viscous friction was dominant at the mid stroke, but the boundary friction was dominant at the top and bottom dead centers. Through the experiment, we could validate previous theoretical study, and confirm that th e radial clearance and ring tension were very effective to reduce friction loss of piston assembly.

Tooth Durability Evaluation of n Cylindrical Worm Gear by Contact Line Analysis

Applying the conjugate contact condition, contact lines of a cylindrical worm gear has been calculated. The characteristics of tooth contact were analyzed and the pitting resistance were also assessed. It has been verified that: i) the length of contact is shortest on the 1st tooth of the front region, ii) the contact region is more narrow in the recess side than in the access side, iii) the contact region is more narrow in worm than in worm wheel. Hence, the pitting resistance is weakest in the recess side of the 1st contacting worm tooth.

Lateral vibration characteristics of a rotor system supported by hydrodynamic journal bearings considering the effect of a bearing width

This paper presents the characteristics of lateral vibrations of rotor system supported by hydrodynamic journal bearings. Finite element model is developed for the dynamic analysis of rotor system. Hydrodynamic bearings are modeled with the distributed springs and dampers in shape of the 2nd order polynomials in the direction of bearing width. Experiments are conducted to measure the natural frequency, and experimental results are compared with the theoretical results that are calculated using the point model and distributed model. Theoretical results using the distributed model agrees better with the measured results as bearing width increases. Also, this method is applied to actual three-stage turbo blower model. Then, critical speed and forced vibration analysis are performed.