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Old 05-02-2009, 08:56 AM   #2
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Pneumatic valves. Sweden's Cargine Engineering reckons it may have cracked the camless engine concept to provide infinitely variable valve timing and lift (within limits), using air pressure to shoot the valve open while hydraulic pressure holds it open and cushions its closing. The system reportedly requires air pressure of 3-16 bar (44-232 psi) and can provide 8mm lift for 5 milliseconds of duration, with a max lift of 14mm, and can operate at engine speeds of up to 8000 rpm. The setup consumes 50 percent less space than a conventional DOHC 4-valve setup and reduces mass by 30 percent. It doesn't require 42-volt electricity, and net power consumption of the air compressor needed to run the system is said to average out about the same as a camshaft over the entire driving range, consuming more power at high rpm (reportedly 4kW at 6000 rpm for a 2.0-liter 16-valve four) and less at lower rpm. Several development partners have signed on, including supercar-maker Koenigsegg and the Split-Cycle engine folks at the Scuderi Group.
Split-Cycle Engine. We've covered the Scuderi Group's innovative concept, splitting the four traditional combustion strokes between two different cylinders, with one handling intake and compression, the other combustion and exhaust. At this year's SAE show, the company announced that its first running prototype will be operational in May 2009, and revealed more details. The first prototype will be naturally aspirated, and will be followed shortly by a turbocharged variant (because the split-cycle engine fires after the cylinder passes top dead center, the risk of predetonation is very low, so higher boost pressures can be tolerated for greater efficiency), followed by the air-hybrid concept (in which a tank recovers surplus compressed air during overrun and braking, then gives it back under acceleration-another significant efficiency-booster).
The inlet and exhaust valves are likely to be operated by conventional camshafts, but the smaller valves that admit air from the crossover tubes (two per cylinder pair) will be likely be pneumatic. They open upward, into the crossover, not down into the cylinder, and timing will be critical, hence the exotic valvetrain. Fuel will be injected in the crossover tubes just before entering the combustion cylinder, but because of the high pressures in those tubes, a direct-injection type Bosch injection system will be used. The Scuderi folks say they've signed their first licensees this year, and three to five years of development will be needed for production. Stay tuned.
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