Actuation systems on turbochargers began with simple boost
pressure operated wastegates. However, the amount of control
achievable with these is limited to how the spring and diaphragm
actuator is matched to the turbocharger. With variable geometry
turbochargers (VGTTM), the need for infinitely variable control
was essential. First generation VGTTM for heavy-duty trucks
have used pneumatic actuation by modulating brake air supply
via an electro-pneumatic control valve. This provides a robust,
low cost solution for such vehicles, but of course not all
applications have such a high pressure air supply.
We have introduced electrical actuation systems for
VGTTM for our Holset E-range. Whilst such systems
have been successfully used on passenger cars, they face
a much more severe operating environment on a large diesel
engine (whether a stationary, industrial, marine or on-highway
application).
Key to providing accurate control is a comprehensive knowledge
of the performance of the system. In many cases the engine
is capable of performing real time diagnostics of its emissions capability. Sensors
on the turbocharger can monitor temperatures, pressures, actuator position (for
wastegate and VGTTM) and turbocharger speed. Some of these are used
for primary feedback in the engine management system, some for protection
or safety algorithms, and some for active diagnostics of
other sensors or other components.
Every new turbocharger design takes into account the need
and desire for sensors and a range of sensors
have been developed.
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