Requiem For the Camshaft?
REQUIEM FOR THE CAMSHAFT?
IT HAS BEEN A DREAM OF ENgine designers for decades: Replace the camshaft and its fixed, compromised timing with something far more flexible. Honda was the first to achieve such flexibility in production with its automotive VTEC designs, which allow the choice of two different cam profiles—highspeed and low-speed. But that's nothing like the hope offered by directly controlling the valves with electric actuators as promised by companies such as Aura. Almost every automobile company has a development contract with Aura, and both BMW and Chrysler have shown prototype camless engines with Aura actuators.
So far, though, the pure electric approach has failed to prove itself, requiring too much electric power and failing to move valves quickly enough to keep up with high-speed engines. The dream remained a dream, at least until tins past April, when big diesel manufacturer International
Truck and Engine (parent of Navistar) announced that it will begin building camless diesels for the 2007 model year.
The breakthrough was to forget about a purely electric approach, and use a high-speed, electrically triggered hydraulic actuator originally developed for NASA applications and patented by is already using small versions of this electro-hydraulic actuator to inject fuel on current production engines, and has a demonstration engine running with the Sturman actuators controlling the valves. International indicates that the testing program before production will be unusually extensive, which is why the 2007 model year is the earliest that the new technology will appear.
Does electro-hydraulic valve actuation have any potential for motorcycle application? Certainly, but not in high-speed sportbike engines. It’s questionable whether the Sturman actuators can keep up with 8000-rpm engines, not to mention those that redline at 15,000 rpm. Rather, camless actuation might first find a home in relatively slowturning engines with big cylinders-those that power cruisers or Thumpers, for example. The infinite flexibility of valve timing and lift provided by eliminating the cam would allow valves to be cracked open slightly during start-up, so a smaller starter motor could be used. It would allow very short valve timing at low speeds for a rock-solid idle and outstanding offthe-line torque. Timing could then be increased to allow an engine with stump-pulling low-end torque to also rev out strongly. Timing could also be adjusted to optimize fuel economy during cruising, and power when full throttle is applied.
In addition, engine mechanicals would benefit. Without rocker arms or cams, hot cylinder-head crowns could be more easily in reach of cooling air, and crankcases could be made narrower if the cam drive was eliminated.
And whom do we have to thank for this potential new technology? None other than the EPA, whose proposed 2006 emission rules for diesels have sent manufacturers scrambling for advanced technology, technology that may someday show up in motorcycles.
Steve Anderson
