Melrose Park, IL óOne of the world's biggest diesel engine manufacturers has announced that it will eliminate camshafts and replace them with electronic valve control systems across all its engine lines by 2007.
International Truck and Engine Corp., the operating company of Navistar, is the first manufacturer to say that it will electronically control the valves that manage air flow in its internal combustion engines. The company's move will affect its own trucks, as well as school buses, pick-ups, and medium duty trucks made by other manufacturers.
Conventional engines use a camshaft to open and close engine valves.
By moving to electronic control, experts say that International has solved a problem that has baffled engine designers for decades. Although there are said to be more than 3,500 patents on file for electronic engine control techniques, none has ever gone into large-scale production. Most reportedly have been too complex or used too much power. "This is a big, big step forward for the industry," notes David Cole, director of The Office for the Study of Automotive Transportation at the University of Michigan (Ann Arbor, MI). "Everybody's been looking at electronic timing, but no one has been able to bring it to production."
The key to International's new design is a digital electrohydraulic valve developed by Sturman Industries (Woodland Park, CO). The electrohydraulic valve replaces the camshaft by using hydraulic pressure to open and close the engine valves. A tiny spool in the valve moves in response to electrical current that runs through coils on either side. By energizing either coil, a controller can quickly move the spool back and forth. The lightweight valve mechanism is said to be about six times faster than conventional electrohydraulic valves, thus enabling it to work with electronic controllers.
Control for the system comes from a Siemens electronics module containing two Infineon 167 microprocessors. The Infineon microprocessors, which operate at 24 MHz, collect data about the engine's temperature, speed, and emission levels, and then move the valves in response to that information.
International engineers say that the camless technology will enable them to vary valve timing, valve lift, and the engine's compression ratio. It will also let them deactivate valves and cylinders on demand, thus improving fuel efficiency and emissions.
Up until now, most engine makers have been trying to achieve electronic engine control with electromagnetic technology. But Eddie Sturman, who originally developed the digital valve for the Apollo space program, says that electrohydraulics will succeed in camless applications because it offers better control and higher actuation forces than electromagnetics. "We can get 20 times the pressure and we can control position more effectively because hydraulics are linear, whereas magnetics are nonlinear," Sturman says.
Experts don't yet know whether the new system could be used in passenger cars. Some believe that power draw could be an issue, especially for vehicles that continue to use 12V electrical systems, rather than the 42V systems planned for next-generation vehicles.
International engineers, however, believe that the camless technology is worth the effort of the massive development program. The reason: The new system will help the firm meet new federal emission regulations scheduled for 2007. "This is going to give our engines greater operating flexibility," notes Patrick Charbonneau, vice president of engineering for International's engine and foundry division. "And if we didn't think that flexibility would have a tremendous impact on our diesel engine performance, we wouldn't be doing this."