The operating principle of the system, applied to intake valves, is the following: a piston, moved by a mechanical intake camshaft, is connected to the intake valve through a hydraulic chamber, which is controlled by a normally open on/off solenoid valve. When the solenoid valve is closed, the oil in the hydraulic chamber behaves like a solid body and transmits to the intake valves the lift schedule imposed by the mechanical intake camshaft. When the solenoid valve is open, the hydraulic chamber and the intake valves are de-coupled; the intake valves do not follow the intake camshaft anymore and close under the valve spring action.
The final part of the valve closing stroke is controlled by a dedicated hydraulic brake, to ensure a soft and regular landing phase in any engine operating conditions. Through solenoid valve opening and closing time control, a wide range of optimum intake valve opening schedules can be easily obtained. For maximum power, the solenoid valve is always closed and full valve opening is achieved following completely the mechanical camshaft, which is specifically designed to maximise power at high engine speed (long opening time).
For low-rpm torque, the solenoid valve is opened near the end of the camshaft profile, leading to early intake valve closing. This eliminates unwanted backflow into the manifold and maximises the air mass trapped in the cylinders. In engine part-load, the solenoid valve is opened earlier, causing partial valve openings to control the trapped air mass as a function of the required torque. Alternatively the intake valves can be partially opened by closing the solenoid valve once the mechanical camshaft action has already started. In this case the air stream into the cylinder is faster and results in higher in-cylinder turbulence. The last two actuation modes can be combined in the same intake stroke, generating a so-called Multilift mode that enhances turbulence and combustion rate at very low loads.
MultiJet for multiple injections, small diesel engines, and the recent Modular Injection technology, soon to be
Similarly, MultiAir technology will pave the way to further technological evolutions for petrol engines:
Integration of the MultiAir Direct air mass control with direct petrol Injection to further improve transient response and fuel economy. Introduction of more advanced multiple valve opening strategies to further reduce emissions. Innovative engine-turbocharger matching to control trapped air mass through a combination of optimum boost pressure and valve opening strategies.
While electronic petrol injection developed in the '70s and Common Rail developed in the '90s were fuel-specific breakthrough technologies, MultiAir Electronic Valve Control technology can be applied to all internal combustion engines whatever fuel they burn.
MultiAir, initially developed for spark ignition engines burning light fuel ranging from petrol to natural gas and hydrogen, also has wide potential for diesel engine emissions reduction
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