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. Published analysis is used to show that the equivalent of recovered brake energy is almost completely used up in carrying the extra weight of the full hybrid system, without any net benefit - except high torque at low speeds and more optimum operation of the downsized engine.
It is proposed that a light hybrid powertrain combined with (electrically) assisted turbocharging can get the same benefits without the extra weight and cost. Assisted turbocharging can be used to shape the torque curve and downsize the engine. Light hybrid configuration can be used for fuel cut-off during coasting and stopping/idling. A methodical optimization between turbo assist and light hybrid functionality can be used to optimize the benefits and minimize the impact on weight and cost. Experimental results showing the torque shaping capabilities of one example of assisted turbocharging - using an e-Turbo™ are presented. Published data on full and light hybrids are used to analyze the proposed configuration. It is shown that the “new” concept can give the same or better fuel consumption reduction than full hybrid systems without the added weight or cost.