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Toyota Motor Corporation has developed a dedicated compressed natural gas (CNG) powered vehicle “Camry” sedan to achieve near zero emissions and to meet rising demand for alternative fuel. A new engine that uses CNG as fuel has been developed by modifying the base 2.2 liter gasoline engine. In the unmodified base engine, torque and power for CNG decrease compared to gasoline. The new engine has adopted a high compression ratio, intake valves with early closed timing, intake and exhaust valves with increased lift and a low back pressure muffler, which thereby restored the loss of engine power. In order to greatly reduce exhaust emissions, a multi port injection system was chosen, and the injectors and pressure regulator have been newly developed. At the same time, precise A/F ratio control and special catalysts for CNG exhaust gas have been utilized.

Efficiency of a supercharger mainly depends on the clearances between the rotors and the housing, but it has hitherto proved impossible to reduce the clearances without a strong possibility of seizure. A two lobe Roots type supercharger has been developed which overcomes this problem by means of a special resin coating on the rotors. As a result, an increase of 18% in volumetric efficiency of the supercharger is achieved. Engine torque is increased by 30%. Drive power loss resulting from the operation of a supercharger at partial load when boost was not required caused fuel consumption to increase by about 10%. An electro magnetic clutch and an air by-pass valve controlled by the onboard computer were used in the new supercharger to eliminate this fuel economy loss. A passenger car equipped with the new supercharged 2-liter engine demonstrated about the same acceleration performance as a 3-liter class car without sacrificing fuel economy.