08-21-2003, 08:03 AM
(free registration required)
"...When Siemens VDO Automotive, in partnership with BMW, built a prototype camless engine four years ago, it came up with a three-part system. In place of cams it used solenoids, electromagnetically controlled plungers that are already widely used in cars for things like electric door locks..."
08-21-2003, 11:17 AM
A Chip-Based Challenge to a Car's Spinning Camshaft
By IAN AUSTEN
F Henry Ford could see the engines now made by the company he founded 100 years ago, he would probably be puzzled by the electronics that control many operations. But the mechanical system operating the valves that bring fuel and air into the engine and let out exhaust would be very familiar.
As in Ford's time, those spring-loaded valves are opened and closed by cams, precisely shaped bumps of steel spinning along a rotating shaft.
But some automotive researchers are working on ways of making mechanical valve controls as obsolete as the Model T Ford. Operating the controls electronically could improve fuel efficiency, reduce emissions and perhaps even eliminate the need for spark plugs in gasoline engines.
The demise of the camshaft would also be welcomed by companies that make electronic parts for cars. "We'd really like to see this technology come along because it requires a huge use of semiconductors," said Ray Cornyn, the manager of Motorola's microcontroller division in Austin, Tex., which supplies the auto industry.
Over the years, electronics have been more of a boon than a threat to camshafts. Computer-controlled manufacturing systems and computer-based designs have improved the quality of camshafts while reducing the cost of their manufacture. But in concept, camshafts remained relatively unchanged from the era of Ford's first assembly lines.
Today it is common for each cylinder of a car's engine to have two pairs of intake and exhaust valves, with each pair sharing a cam on the camshaft. The camshaft is set spinning by a rubber belt or steel chain connected to the engine's crankshaft, the component that ultimately provides the power to the car's wheels. As the camshaft rotates, the high point of each cam first presses against a spring-loaded lifter of an intake valve, gradually opening it, and then closing it as the cam's low side approaches. As it continues to revolve, the high part of the cam repeats the process for the paired exhaust valve.
When Siemens VDO Automotive, in partnership with BMW, built a prototype camless engine four years ago, it came up with a three-part system. In place of cams it used solenoids, electromagnetically controlled plungers that are already widely used in cars for things like electric door locks.
While an electronic valve control system doesn't need mechanical power from the crankshaft, it does need to know what the crankshaft and the pistons driving it are doing. In a normal car, the belt or chain that connects crankshaft to camshaft ensures proper timing; that is, no valve remains open when its cylinder's piston is at the top of its travel. Such a situation would seriously damage a motor.
In its camless version, Siemens prevents such mistiming by using sensors that detect the position of the crankshaft and thus the pistons. Finally, the new engine was given yet another powerful computer to make sure everything works in sequence. "When an eight-cylinder engine with four valves per cylinder is running at 6,000 r.p.m. there's a lot to do," said Michael Gauthier, director of corporate technology in Siemens's automotive division.
The prototype engine was installed in a 3-series BMW sedan. It worked but had several significant shortcomings. For one thing, the solenoids and the additional computer power taxed the car's already overburdened electrical system. Mr. Gauthier said that cars would have to make a long-awaited move to 42-volt electrical systems (from the current 12 volts) before electronic valve control would be practical.
For car makers, the system's least attractive aspect was its price relative to camshafts. And there was a problem that made the engine unattractive to buyers, particularly those who associate BMW with smoothly running engines. As anyone who has opened a car with electric locks knows, solenoids are far from silent. "I saw the vehicle, and all you heard when it was running was slap, slap, slap," Mr. Gauthier said.
Motorola believes that the control computer could be programmed to soften and quiet the action of the solenoids. Other electronic valve-control designs have relied on different parts to push the valves open.
A device that used piezoelectric crystals, which produce electricity when bent, was quiet and cut the power burden. But current piezoelectric devices must be about 8 to 10 inches high to operate engine valves. The result, Mr. Gauthier said, is an engine "that looks something like a porcupine" and will not fit under the hood of most cars.
There are several incentives for trying to perfect electronic valves. Among other things, it would allow engines to reduce their power after getting a car up to speed, an easy way to save fuel. "About 90 percent of the time you need about 20 percent of the engine's output," Mr. Gauthier said. "It's extremely wasteful to put a 200-horsepower engine in a car when you only need 40 horsepower most of the time."
But some car makers have already found several ways to achieve that goal mechanically. Some engines have camshafts that can be raised or lowered between two positions to adjust the valve openings. A more sophisticated system from BMW can make a wider range of valve adjustments to reduce or boost power.
Because of those mechanical advances and the cost issue, Zoran Filipi, an associate research scientist and the assistant director of the University of Michigan's automotive research center, said that electronic control would probably become widespread only if it could change the way engines operate.
A potential way to reduce emissions and improve economy in gasoline engines would be to eliminate spark plugs and, like a diesel engine, ignite fuel through the compression of pistons. Such engines, however, would only be cleaner if they used a carefully blended fuel mix injected at the last moment. Dr. Filipi said that electronic valves might be an effective way to control the engines' operation.
The biggest hurdle for electronic valve controls may be that when it comes to auto parts, age does have its advantages, said Dr. Filipi. "Over the last 100 years or so we've perfected camshaft technologies," he said.
08-22-2003, 10:51 AM
This has been a common thing in Formula 1 engines for quite a while.
The engines turn at such high rpms that springs are too "slow".
So the valves are opened and closed with air controlled by computerised solenoids.
My memory is fading but I think the first use was on Williams/Renault.
vBulletin® v3.8.7, Copyright ©2000-2014, vBulletin Solutions, Inc.