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Issue
103, February 1999
Truck
Speed Limiter Control
by
Constantin von Altrock
Start
•
Control
Requirements •
Mechanical
Design •
Fuzzy-Logic
Controller •
Implementation
•
Results
•
References
& Sources
MECHANICAL DESIGN
Figure
2 shows the outline of the mechanical design for the speed
limiter. An electronic control unit (ECU) compares the
digital pulse signal from the speedometer with the maximum
speed value preset in the device.
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Figure 2—The
speed limiter consists of an electronic control
unit (ECU) that reads in the speedometer signal
and controls the pulse proportional valve (PPV).
The PPV manipulates the air pressure in the
cylinder connecting the accelerator pedal and
fuel-pump arm.
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Based
on this comparison, the ECU computes the command value
for the pulse-proportional valve (PPV) that controls the
air pressure in the cylinder. The air stems from the vehicle’s
pressured-air system. In a nonlinear but proportional
ratio, the cylinder shortens the arm linking the accelerator
pedal to the fuel pump, thereby throttling the fuel pump.
The
ECU is designed as a mixed digital and analog circuit.
Speedometer signal processing, diagnosis functions, and
the fuzzy-logic control algorithm are all computed by
an 8-bit PIC. The MCU uses an external EEPROM to store
parameters of the truck and speedometer such as the maximum
velocity and diagnosis variables.
The
MCU generates a PWM signal that is amplified by a power
stage to drive the PPV. The analog part is responsible
for preprocessing and filtering the speedometer signal.
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