MELROSE PARK, Ill. International Truck and Engine Corp. is poised to take a huge step forward in engine design, announcing this week that it will eliminate camshafts from its diesel engines and replacing them with electronic-valve timing systems.
The change, which is set to take effect in the 2007 model year, would make International, the operating company of Navistar, the first manufacturer to electronically control the valves that manage airflow in its internal combustion engines. It would have a profound effect not only on International's own truck lines, but also on medium-duty trucks, school buses and pickups made by other manufacturers.
"It's a big, big step forward for the industry," said David Cole, director of the University of Michigan's Office for the Study of Automotive Transportation (Ann Arbor). "Everybody's been looking at electronic timing, but no one has been able to bring it to production."
International Truck and Engine's Patrick Charbonneau expects to apply electronic valve control across the company's line of diesel engines by 2007. |
Indeed, every major auto and truck maker in the world is now said to be considering a switch to electronically controlled valve timing. Electronic timing offers vehicle manufacturers a myriad of advantages, the main ones being better performance and lower emissions.
Greater flexibility, and performance
"This is going to give our engines greater operating flexibility," said 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."
The change can't come sooner than the 2007 model year because electronic-based systems require more on-site testing than mechanical systems. Where mechanical systems can be put on a dynomometer and tested for a couple of thousand hours, electronic testing must be done in such places as Alaska, Death Valley and Bimidji, Minn., for temperature extremes. Engineers say they need two summers and two winters of testing to be satisfied that they've gotten all the bugs out.
International plans to use the technology across its engine line, in time for new federal emissions regulations in 2007. Besides being used in the company's own truck line, International's diesel engines are currently used in 60 percent of school buses, 40 percent of medium-size trucks and 65 percent of pickups above 8,500 pounds.
For manufacturers of engines and vehicles around the world, International's announcement could signal a first step toward the elimination of the camshaft the mechanical device that opens and closes the valves inside an engine's cylinders. Camshafts, which have served in internal combustion engines since the beginning of the 20th century, enable engines to draw in an air-fuel mixture for the combustion cycle, and then dispose of the exhaust afterward. By working off a chain connected to the engine's crankshaft, camshafts precisely synchronize the opening and closing of the valves to the movement of the pistons. That timing, however, can never be changed.
Edge on emissions
In contrast, electronic control will enable engines to change valve timing on the fly. If, for example, a vehicle's powertrain module senses that an engine is cold, or that a vehicle is struggling up a mountain road, it can call for a change in the valve timing. And because engines emit the majority of their pollutants immediately after the ignition is switched on and they're still cold, electronic timing gives vehicle manufacturers a leg up in their efforts to reduce emissions. It could also help with fuel economy by shutting down one of the engine's cylinders when it is not needed.
"It's like the difference between the typewriter and the computer," said Eddie Sturman, inventor of the digital electrohydraulic valve that is the key to the technology. "The typewriter is fixed; the computer is flexible. Electronic-valve timing brings the same kind of flexibility to your engine."
The electrohydraulic valve operates in conjunction with the engine's valves. Originally created for the Apollo space program, the valve works by sending pressurized hydraulic fluid to the engine valve to move it up and down.
Its primary feature is speed. The valve, developed by Sturman Industries (Woodland Park, Colo.), is about six times faster than conventional hydraulic valves. To achieve that speed, it uses a tiny spool sandwiched between two electrical coils.
By passing current back and forth between the coils, a microprocessor-based controller can quickly move the spool back and forth, and thereby actuate the engine valves in accordance with incoming signals from the engine's sensors. That way, the controller can collect data about the engine's temperature, speed and emissions levels, and then move the valves in response to that information.
International is using the electrohydraulic valve to control movement of its engines' valves and fuel injectors. Control for both systems is currently provided by a Siemens electronics module containing two Infineon 167 microprocessors. The Infineon processors, which operate at 24 MHz, use a reduced instruction set (RISC) and a sophisticated interrupt structure to enable real-time operation.
"In an automotive environment, you have to have real-time operation," said Kregg Wiggins, director of powertrain electronics for Siemens Automotive North America (Auburn Hills, Mich.). "Unlike a PC, everything has to happen in real-time here, because if your fuel injector fires a half-second late, you'll notice it."
Industry observers say that International's effort differs from those of other engine manufacturers primarily in its actuation technique. For decades, they say, the vast majority of the 3,000-plus patents on file for camless engine technology have used electromagnetic actuation techniques.
"There's a long history of people who have tried to develop electromagnetic engine valving systems," said Cole of the University of Michigan. "But power draw, cost and packaging have always been issues that couldn't be solved. It's a tough thing to do."
Engineers involved in the International project, however, believe they've solved the problem with electrohydraulics. Because the hydraulic technology uses International's existing fuel rail systems, the company says it can leverage some of the extra cost of an electronically controlled valve system.
Equally important, engineers say that the electrohydraulic system offers better control and higher actuation forces than electromagnetic technology. "We can get 20 times the pressure and we can control the position more effectively because hydraulics are linear, whereas magnetics are nonlinear," said Sturman.
The company demonstrated the technology on an International 8100 truck equipped with its 530E diesel engine. Engineers said the camless technology let them vary valve timing, valve lift and the engine's compression ratio.
It also let them deactivate valves and cylinders, thus improving fuel efficiency and reducing emissions.
Whether the technology could be used in passenger cars is still unknown. Some experts believe that power draw could be an issue, especially for vehicles that continue to use 12-volt electrical systems, rather than next-generation 42-V systems.
Experts also wonder whether electrohydraulic technology will have the speed needed for passenger car engines, which, unlike the engines in heavy-duty trucks, operate up to 7,000 rpm.