Cosworth has a long heritage in developing and building high-performance engines for motorsports as well as road-going applications. Nowadays, the UK-based company is utilising its knowledge more and more to support the development of highly efficient combustion engines. We sat down with its Managing Director Powertrain, Bruce Wood, to discuss the potential and technologies to further optimise gas exchange as well as supercharging systems.
MTZ: In a joint development project, Cosworth and further partners have developed a highly efficient gasoline engine. The reduction of pumping losses was one major goal. Which measures have you taken?
Bruce Wood: “I guess you are referring to the ME engine project we undertook in collaboration with CEC / Haitec, for which we have recently published some of the very exciting results we achieved.
“At the beginning, Cosworth undertook an extensive concept study to look at all the technologies available to reduce parasitic losses within engines. The focus here was to provide our customers with an engine that delivered excellent fuel consumption over a very broad operating area.
“In this respect, we looked at several measures to minimise friction and fluid circuit losses, but the greatest benefit to giving a broad operating area of low BSFC was through dethrottling. We considered several systems to achieve this, such as Fiat’s Multi-air and BMW’s Valvetronic, but in the end decided to use the Pierburg UpValve system being developed by Rheinmetall Automotive.
“This is a mechanical valve actuation system similar to the BMW Valvetronic arrangement, but with fewer components and also capable of providing cylinder deactivation. In this way, with one valvetrain system, two methods of dethrottling could be used, and the compound and synergistic benefits of both systems could be explored.”
Variable inlet valve timing is currently in high demand to realise Miller timing under part load. Do you see any realistic road-going approaches other than mechanically-actuated systems?
“Early- or late-intake valve closing can be used to very good effect in controlling engine load through regulating the trapped charge without throttling the intake air. In this way, we have demonstrated that pumping losses can be significantly reduced – although not entirely eliminated – at light load. The degree to which this can be achieved depends on the extent to which throttling across the intake valve can be avoided.
“The problem with mechanical actuation systems is that the valve lift has to be controlled together with duration in order to maintain acceptable dynamics, and with early intake valve closing (EIVC) systems you reach a point where for very low charge mass the valve lift reduces to the extent that irreversible pumping losses are incurred. Despite this, in our experience these systems offer the best methods for providing charge control through variable valve duration.”