With current demands on the automotive industry including climate change and changing consumer trends, manufacturers are always seeking new ways to increase efficiency whilst keeping the development of new technology cost effective to ensure vehicles remain affordable.
A leading Asian headquartered OEM has been developing a new vehicle with the aim of maximising efficiency, while still maintaining an acceptable degree of engine performance and all within strict budget constraints. Therefore, developing a highly fuel-efficient engine without losing mid-range driveability was crucial.
Delivering an engine with excellent fuel consumption over a very broad operating area is not a simple task and requires the use of innovative technology. The main focus was to reduce the pumping losses of the engine – one of the most parasitic areas of energy loss. The specific problem areas where the potential for great gains can be realised are in frictional, fluid circuits and throttling losses.
Our approach was to minimise all three forms of these pumping losses, but the greatest benefit to giving a broad operating area of low BSFC (Brake Specific Fuel Consumption) was de-throttling.
De-throttling removes the throttle valve (usually found in the form of a throttle body) from the intake side of the engine, thus the engine speed and load are now controlled using another method. We considered several systems to achieve this, such as Fiat’s Multi-air and BMW’s Valvetronic solutions, but we ultimately decided to use the Pierburg UpValve system developed by Rheinmetall Automotive.
The Pierburg UpValve system is mechanical and similar to the BMW Valvetronic solution; the significant differences are the additional ability to control cylinder deactivation whist using fewer components. This gives us two forms of de-throttling with one system, the major benefit being the ability to compound the two: for finite load control and a further decrease in BSFC.
To tackle the frictional and fluid circuit losses we focused our efforts on minimising the amount of oil required by the engine and its flow rate. This sounds counterintuitive as with less oil you’d assume to see an increase in friction. However, if the oil quantity and the rate at which it needs to flow can be calculated accurately, there will be no need for excessive amounts of oil being stored in the sump (leading to less fluid weight) and the oil flow can be kept at its optimal rate (leading to less energy being required by the oil pump). Both of these factors result in lower fuel consumption.
We have also derived benefits from our in-house Oerlikon-Metco SUMEBore plasma coating machine, which melts down metal powder and sprays it using a rotating torch onto engine block cylinder walls. To reduce frictional losses, we not only optimised the conrod and crankshaft geometry, but also used our plasma coating capabilities. Not only do we benefit from reduction friction between pistons, rings and the cylinder bore walls with this technology, but we also make the need for heavy cylinder liners redundant, reducing the weight of the engine block, and subsequently resulting in a further increase in efficiency.
All of these efforts have resulted in a 2.0 litre inline 4 engine producing 210kW of power and capable of maintaining a BSFC of less than 230 g/kW.h at a thermal efficiency of around 36%, exceeding even our own exacting standards and high expectations.