1993-03-01

Toyota Lean Combustion System - The Third Generation System 930873

The third generation four valve lean combustion engine controlled by newly designed combustion pressure sensor has been developed. This combustion sensor composed of a metal diaphragm and a thin silicone layer formed on devitron piece detects the combustion pressure in the No.1 cylinder. Comparing with the lean mixture sensor equipped in the first and second generation lean combustion engine, the lean misfire limit was detected directly with this sensor, and the lean operation range was expanded, which realized lower fuel consumption and NOx emission. The output torque fluctuation was minimized by precisely compensating the fuel supplied to individual cylinder based on the crank angle sensor signal. Separated dual intake ports, one with the swirl control valve and the other with helical port shape was designed and a twin spray injection nozzle was equipped between those ports. The swirl ratio was lowered from 2.2 to 1.7. Steeply inclined swirl generated a turbulence level enough to extend the lean limit. The homogeneous and
stable mixture formation was realized by the injection nozzle layout and the connecting passage between two ports which assist the atomization of the fuel spray. The volumetric efficiency in the case of SCV(Swirl Control Valve) closed was increased by the flow path resistance reduction and the utilization of the intake charge inertia effect of narrower cross sectional area port. By these improvements, the lean fuel air mixture operating range with sufficient low NOx level was expanded remarkably and the heavier inertia weight class vehicle (1.25ton) with automatic transmission has been commercialized in the Japanese market

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