Overallsize & vehicle integration

Compactness of an engine must be estimated while taking into account its power density from several points of view:

		kW per cm3,
		kW per kilogram,
		kW per centimeter of engine length, width and height.

It is the only valid method: ideally everybody would like an engine with an infinite power density, but this engine does not exist. However, main automotive trends are for engines that are as small as possible.

Small engines permit liberating vehicle designers’ pencil, provide better results on crash test, and facilitate peripherals implementation such as air-conditionning, power steering or intake unit. They also permit several engine positions and orientation for implementation into vehicles. In addition, the smaller an engine, the wider the vehicle range it covers.

In theory, power density is a strong point for VCR engines thanks to downsizing. However, even in the case of FCR engines, a downsizing ratio of 50% does not divide by two the engine volume. In practice, as VCR engines are more complex than conventional ones, their benefit for engine overallsize and weight can be lower than expected. In addition, downsized engines need a turbocharger and an intercooler, which have to be taken into account to establish the final judgement.

Some VCR engine designs need specific connections to pipes and peripherals, or specific transmission devices located between the crankshaft and the gearbox. These additional components not only generate additional size and cost for no technical benefit, they also reduce the powertrain reliability.

Conclusion

Even if they present a high power-per-capacity, VCR engines complexity can lead to less overallsize reduction than expected.

To be easily integrated into all existing vehicles with a minimum need for adaptation, VCR engines’ architecture must be as conventional as possible. Additional technical artifacts for vehicle integration must be avoided: they lead to powertrain oversizing, useless costs, and reliability reduction.

(see: The MCE-5 technology response to VCR engines’ overallsize & vehicle integration challenges)