| Summary: | Air pollution, global warming, and rising gasoline prices have lead governments,
environmental organizations, and consumers to pressure the automotive
industry to improve the fuel efficiency of cars.
Since alternative fuels such as hydrogen are still quite far from being
commercially viable, improving the existing internal combustion engine is
still an important priority. Traditional internal combustion engines use a
camshaft to control valve timing. Since the camshaft is rigidly linked to
the crankshaft, engineers can optimize the camshaft only for one particular
speed torque combination. All other engine operating points will suffer from
a suboptimal compromise of torque output, fuel efficiency, and emissions. In
an engine with a camless valve actuation system, valve events are controlled
independently of crankshaft rotation. As a result, fuel consumption and
emissions may be reduced by 15%~20% and torque output is enhanced in
a wide range of engine speeds.
The Fully Flexible Valve Actuation (FFVA) system is our approach to
construct a camless valve actuation system. Within the limits of the dynamic
bandwidth of the system, it allows for fully user definable valve trajectories
that can be adapted to any need of the combustion process. The system
is able to achieve 8mm valve lift in 3.4ms, which is suitable for an engine
operating at 6000RPM. The valve seating velocity is similar to conventional
valve trains that achieve 0.2m/s at high engine speeds and 0.05m/s at engine
idle conditions. Finally, the energy consumption measured in an experimental
test bed matches the friction losses of conventional valve trains and it
can further be improved by using an optimized motor.
This thesis describes the progress that has been made towards designing
this technology. A design methodology is derived and important operation
features of the mechanism are explained. Modeling and simulation results
show significant advantages of the FFVA over previously designed electromagnetic
engine valve drives.
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