Variable valve actuation, especially timing, has been readily available for light passenger engines for years. Problems in introducing the technology to heavy-duty diesel engines include the vastly different thermodynamics at play and the durability required. With already high compression ratios, clearance between the piston and valve in diesels can be an issue. Since a diesel is typically unthrottled, it is more difficult to improve efficiency compared to a gasoline engine. Constant switching in engines that run continuously means building reliable gadgets that can run for thousands of hours.
However, with the continued push for both fuel efficiency and criterion emissions control, IAV thinks it is time for heavy-duty applications to consider it. An engine with a fixed valve lift and timing must balance high-speed engine performance and low-speed fuel economy. Low speed and cold start exhaust temperatures also affect aftertreatment devices, especially important as regulatory pressures continue.
The IAV SlideCam system, available under licensing agreement from the company, toggles between two cam lobes, according to Robert Dolan, Director, Commercial Vehicle and Government Programs, which can vary timing or lift or both. “It is a switchable system, with two settings on the hot side and two settings on the cold side,” he explained. “That allows, for example, a Miller cycle and a retarder function.”
One device produces two benefits. Using it to produce a Miller cycle operation makes combustion more efficient, meaning better fuel economy. The other is improving aftertreatment.
SlideCam’s ability to open the exhaust valve earlier when needed means it can hold the temperature of the aftertreatment devices at a higher temperature without lowering combustion process efficiency. Standard techniques with fixed cams include post-injection of fuel during low load operation, which can entrain fuel and lead to more frequent oil changes, as well as impacting fuel efficiency.
Dolan reports that IAV is currently working with an on-highway OEM to transfer the technology through a patent arrangement. “It could also see off-highway utility as well,” he said.