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Issue
103, February 1999
Truck
Speed Limiter Control
by
Constantin von Altrock
Is
your teen learning to drive? Are you worried? If you think
they lack logic, maybe you
should consider fuzzy logic. Constantin uses fuzzy rules
to consistently limit the speed of commercial trucks, despite
weight variables and truck type.
Start
•
Control
Requirements •
Mechanical
Design •
Fuzzy-Logic
Controller •
Implementation
•
Results
•
References
& Sources
In Europe, commercial trucks with a maximum load of over 12 tons are
legally required to be equipped with a device that limits
their maximum speed to 53.3 mph (86 km/h). Designing an
algorithm for this control problem was no easy task.
The speed-limiter device
needed to be compatible with a variety of trucks, all
of which exhibit different behaviors. Additionally, the
dynamic behavior of a truck varies depending on whether
it is fully loaded or empty.
Conventional control algorithms,
like PID controls, assume a linear model of the process
under control, so they couldn’t be used. A mathematical
model of the truck would be tough to build and would require
too much computational effort from an 8-bit micro. So,
the designers turned to fuzzy logic.
This article focuses on the
electropneumatic design of the speed limiter. The pneumatic
cylinder mechanically limits the throttle-opening angle
of the fuel-pump arm, and a pulse-proportional electromechanical
valve controls the cylinder pressure. The electromechanical
valve connects to an electronic control unit that uses
a microcontroller to drive the valve according to the
speed of the truck.
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