  This paper investigates the optimization of the exhaust gas composition by
applying a velocity-controlled Throttle-by-Wire-System on modern 50 cc scooters
(Euro 5). Nowadays combustion-powered scooters are still inefficiently
restricted, resulting in an unreasonably high fuel consumption and unfavorable
exhaust emissions. The velocity control prevents restriction by negatively
shifting the ignition timing and regulates the throttle valve opening instead.
Injection quantity, engine speed, ignition timing, cylinder wall temperature,
exhaust gas temperature, oxygen sensor data, crankshaft position and
in-cylinder pressure were acquired to measure engine parameters. At the same
time, vehicle data on the CAN bus, such as throttle opening angle, the rider's
acceleration command and vehicle velocity were recorded. For determination of
the exhaust gas composition, five probes were sensing CO, CO2, NOx, O2 and HC
in addition to the temperature and mass flow. A Peugeot Kisbee 50 4T (Euro 5)
serves as test vehicle. The original and the optimized restriction were
subjected to various gradients on a roller dynamometer at top speed. Thus, a
statement can be made about all operating points of restriction. The resistance
parameters required, were previously determined in a coast down test. When
driving on level ground, a difference of 50% in the throttle opening leads to a
17% improvement in fuel economy. By measuring the engine parameters, optimum
ignition timing could be proven with increasing internal cylinder pressure.
Further, 17% reduction in exhaust gas flow was demonstrated. CO emissions
decreased by a factor of 8.4, CO2 by 1.17 and HC by 2.1 while NOx increased by
a factor of 3.
