The (red) solenoid valve regulates oil pressure that opens the intake valves (FIAT500USA photo)
by Jacques Gordon
Remember the HEUI system? It stands for Hydraulically actuated Electronically controlled Unit Injection, a fuel injection system developed by Caterpillar and licensed by International Harvester (now Navistar) and used in the first-generation Ford Powerstroke engine (got all that?). In the past, unit injectors were operated mechanically by a dedicated cam lobe on the engine’s camshaft. The HEUI system operates the injectors with hydraulic pressure, supplied by a high-pressure oil pump and controlled with a solenoid valve. With this system, timing and duration of each injection event can be controlled electronically instead of being literally carved in steel.
FIAT is using a similar idea to operate the intake valves in their MultiAir engine. The single overhead camshaft has three lobes per cylinder, two for the exhaust valves and one that operates a tiny high-pressure oil pump. The oil pressure is supplied to a solenoid valve, which regulates and uses the pressure to open that pair of intake valves. With this system, intake valve timing and duration are electronically controlled.
During start-up and idle, the intake valves open late and close early. Under full load, valve opening follows the cam profile to provide maximum lift and duration. At part load, timing and duration are adjusted to minimize emissions, and under some conditions there are multiple valve opening/closing events on each intake stroke, thus the name MultiAir. This generates turbulence in the cylinder and helps to produce a flat torque curve that reaches over 90% of its peak by 2000 rpm. Overall, the MultiAir system returns a 10% improvement in emissions and fuel economy and a 15% boost in torque. Under certain operating conditions manifold vacuum will be extremely low, so the cam also operates a vacuum pump for the brake booster.
This technology was ten years in development, and today the 1.4-liter MultiAir engine is built in the U.S. for the FIAT 500 (assembled in Mexico). FIAT’s U.S. partner Chrysler is using the same technology in the new 2.0L and 2.4L Tigershark engines. While no further applications have been announced, FIAT has made a serious investment in this technology, and it can easily be used for cylinder deactivation and to eliminate the throttle, which would dramatically improve efficiency. It’s reasonable to believe we’ll see the MultiAir system in many more engines in the future.
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