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A heterodyne interferometry system with a fiber-optic sensor was developed to measure the temperature history of unburned gas in an engine cylinder. A polarization-preserving fiber and metal mirror were used as the fiber-optic sensor to deliver the test beam to and from the measurement region. This fiber-optic sensor can be assembled in the engine cylinder or the cylinder head without a lot of improvements of an actual engine. The feasibility of our system was sufficient to be applied to temperature history measurement of an unburned gas compressed by flame propagation in an engine cylinder. The resolution of the temperature measurement is approximately 0.7 K, and is dependent on both the sampling clock speed of the A/D converter and the length of the measurement region.

Four-, five- and six-valve engines having two, three and four intake valves, respectively, were fabricated. Fifteen types of output characteristics were then investigated using these engines by varying the intake specifications to examine the relationship of the intake valve mean effective area and the number of valves needed to attain the required maximum output. Improvement of combustion in the light load range at low speeds was also examined by comparing the cylinder flow of four- and five-valve engines. As a result, it was found that the maximum output of multi-valve engines is generated at essentially the same mean intake Mach number regardless of the number of valves, and proportional to the intake valve mean effective area for an identical single cylinder volume. In addition, the result of five-valve engines with the larger intake valve mean effective area than four-valve engines showed that they could attain both the satisfactory mean flow coefficient and tumble.

We attempt to improve the feeling of acceleration by considering the change in instantaneous torque when the throttle is opened in motorcycles equipped with parallel two cylinder engines. Feeling of acceleration and vibrations for motorcycles with five types of 400cc engines, including 3 types of engines with different crankpin phase angles varying by 90° each along with two variations in the firing interval were assessed by sensory evaluation and instruments. As the result, it was found that there is a correlation between the feeling of acceleration and the change in instantaneous torque caused by alteration of the crankpin phase angle. It was therefore determined that the feeling of acceleration could be improved by using a crankpin phase angle of 270° relative to crankpin phase angle of 180 or 360° conventionally used in parallel two cylinder engines.

We compared motoring friction loss, output performance at WOT (wide open throttle) and specific fuel consumption of big-end bearings on engines having identical specifications between the case of using plain bearings and rolling bearings to investigate the effect of the lubricating oil supply rate on these parameters in an attempt to improve output through reduction of friction loss for big-end bearings of small, high-output motorcycle engines. Testing was performed using a 125 cc, 4-cycle, single cylinder engine at high engine speeds mainly above 10,000 rpm.

Connecting rod design factors, such as geometric shape, capscrew torque and materials can significantly affect bore distortion and assembly stress. In this paper, experiments using different materials were conducted on several connecting rod big-ends with various shapes, bosses and bolts. The results show that the distortion of the big-end bore and the bolt stress are influenced considerably by the big-end shape, the bolt axial tension and the material under inertia force. It was also observed that the bolt bending stress and the load separating the big-end joint surface could be calculated with high accuracy using three-dimensional FEM in the initial connecting rod design.

The purpose of this paper is to investigate the effect of the piston shape and weight on the friction losses. The motoring test was conducted on pistons with various shapes, rigidities, and weights at 3000-16000 rpm. The test results suggested that the piston friction loss would be abruptly increased mainly because of the increase in the skirt friction caused by the change of the piston attitude. Then, the piston behavioral simulation was conducted using a two-dimensional rigid model in consideration of the skirt rigidity, which proved the above suggestion. This paper consists of the paper presented at 1990 JSAE Autumn Convention and the results of the investigation we conducted based on the calculation of piston behavioral simulation.