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The technology to estimate engine load using the amplitude of crankshaft angular velocity variation during a cycle, which is referred to as “Δω (delta omega)”, in a four-stroke single-cylinder gasoline engine has been established in our former studies. This study was aimed to apply this technology to the spark advance control system for small motorcycles. The cyclic variation of the Δω signal, which affects engine load detection accuracy, was a crucial issue when developing the system. To solve this issue, filtering functions that can cope with various running conditions were incorporated into the computation process that estimates engine loads from Δω signals. In addition, the system made it possible to classify engine load into two levels without a throttle sensor currently used. We have thus successfully developed the new spark advance system that is controlled in accordance with the engine speed and load.

The auto-ignition attracts researchers as an ultimate combustion method that could simultaneously reduce fuel consumption and NOx emissions. The authors have studied auto-ignition combustion in the two-stroke gasoline engines aiming at vehicle engine applications. However, our attempts were in an impasse with the onset of irregular combustion in the lower speed and the extremely lower load range. As a solution for this problem, this paper proposes a new auto-ignition concept, i.e. Stratified Charge Auto-Ignition (SCAI), which focuses on the thermal distribution and mixture formation in the combustion chamber. Visualization of the direct injection spray formation was conducted first, and then a combustion chamber design was determined by using a CFD simulation, so as to form a mixture at the hottest spot in the combustion chamber.

From the environmental conscious point of view, subjects of conventional two-stroke engines will be irregular combustion and new mixture shortcut. Concerning for the irregular combustion, our previous papers has however proven that timing controlled auto-ignition, namely Activated Radical (AR) Combustion, was an effective solution. Meanwhile for the new mixture shortcut, no solution is mentioned in those papers. This time, a low pressure pneumatic direct fuel injection engine has been experimented. This engine is however intended to perform homogeneous combustion, the A R Combustion solves irregular combustion effectively in the light load range. Fuel is pneumatically injected into the cylinder by using accumulated in-cylinder gas pressure, after the scavenging process performed by the air only. A mechanically driven rotary type injector is installed in the cylinder wall.

The centrifugal-weight-type V-belt automatic transmission is widely used for the light engines of scooters and agricultural machines, etc. for being compact, efficient and comparatively cheap. The operating section of this centrifugal weight, which contains the metal weight coated with thermoplastic resins in its movable pulley, is lubricated with grease to provide stability and life (reliability) for its operation. However, the grease filling work not only requires a substantial number of man-hours but also various seal parts to prevent, during running, the grease from being splashed about by the centrifugal force and dust particles from intruding. To overcome these restrictions, research has been conducted on how to free the centrifugal weight from the grease by experimenting with various self-lubricant resin compositions as the coating materials for this metal weight.

We have successfully developed a system to estimate Indicated Mean Effective Pressure (hereafter "IMEP") by detecting the crankshaft angular velocity variation during one cycle of a four-stroke single-cylinder gasoline engine. The system has been commercially applied to the spark-ignition timing control system for small-displacement motorcycle engines. The determined amplitude of crankshaft angular velocity variation during one cycle is defined as "delta omega (Δω)." The relationship between Δω and IMEP has been experimentally examined using engine unit bench tests and actual motorcycles. From the experimental results, it was confirmed that Δω represents IMEP. This paper discusses the experimental study on the estimation of IMEP using crankshaft angular velocity variation.