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The internal combustion engine and associated powertrain are likely to remain the mainstay of mobility over the next twenty years and to remain a significant portion of the portfolio of technologies employed over a much longer period of time. Efficient combustion of all fuels (petroleum based or alternative) requires copious amounts of air particularly with downsized engines. Turbocharging technology thus becomes an even more critical part of reducing both global warming gas and urban pollutant emissions from IC engines. Gasoline engine downsizing and turbocharging have been shown to improve fuel economy by ∼20% in production vehicles. In addition to data over a wide range of engines/vehicles, the results of a simple analysis done on vehicles/engines/drive cycles are presented to show the benefits of turbocharging and downsizing in a parametric variation of downsizing in combination with other technologies.

Data on several hundred family sedan production vehicles over a ten-year period are analyzed to compare turbocharged with non-turbocharged engines. It is shown that for the same power turbocharging enables gasoline engine downsizing by about 30%, improves fuel economy by 8-10% while improving torque and acceleration performance. Data with experimental turbocharged, downsized gasoline engines also shows that in the same vehicle, for the same power and performance, downsized turbocharged engines can give about 18% improvement in fuel economy. The paper discusses these data and analyzes the benefits of engine downsizing and turbocharging and the possible mechanisms of these effects. It is shown that the same basic small engine can be turbocharged using a wide range of turbocharger matching to cover a power range normally covered by 4-5 engine families of progressively increasing displacement. Thus additional benefits can be obtained by rationalizing the engine product lines.

A “new” concept combining existing technologies of engine downsizing, electrically assisted turbocharging and light hybrid powertrain is proposed. Published analysis of hybrid technology and data of production hybrid vehicles are used to show that much of the benefit is derived from engine downsizing. Engine downsizing results in operation more often at wider open throttle with reduced pumping work and higher efficiency conditions. Results from vehicles using turbocharged, downsized engines are used to further corroborate this conclusion. Fuel shut off during coasting and vehicle stopping/idling also contributes positively to fuel economy improvement. In a “full hybrid” configuration, electric motor and battery energy is used to compensate for engine downsizing to get high torque at low speeds. Brake energy recovery is used to charge batteries.