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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.

Diesel engines face increasingly stringent emissions regulations worldwide. The trade-off between fuel economy and NOx emissions and between NOx and particulate emissions is becoming more critical. In light of these regulations and design trade-offs among many variables, engine-boosting systems have become increasingly important. An advanced variable nozzle turbocharger (AVNT™) is described. The innovative design is described along with key characteristics. The design features a minimization of additional parts associated with the variable geometry mechanism and electro-hydraulic actuation integrated with the bearing system. The impact of variable geometry turbocharging on diesel engine performance, fuel economy, torque, emissions and braking capability is described. It is shown that significant improvements in all five variables are readily possible with the use of this variable geometry turbocharger.

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.