In this paper, an Electronic Control System (ECS) is designed to
manage a 125 cc single-cylinder air-cooled motorcycle engine. The
aim of this study was to accomplish low cost, high reliability and
mainly meet the motorcycle engine emission standard of China Stage
III.
The intake port fuel injection mode was chosen with a redesigned
part of intake pipe. Gathering information of speed, throttle
position (TP), inlet temperature and pressure, cylinder
temperature, switch-type exhaust gas oxygen sensor and the battery
voltage, an Engine Control Unit (ECU) was devised to calculate fuel
injecting pulse width, advance ignition angle and control the
working conditions of the fuel pump and the exhaust gas oxygen
sensor. Additionally, a three-way catalytic converter (TWC) was
used to reduce exhaust gas emissions.
The basic fuel injection table and ignition advance angles table
according to the speed-TP were calibrated accurately through bench
test with consideration to engine performance, emission and AFR.
Taking account of the cylinder temperature correction term, air
pressure correction term, the inlet air temperature and pressure
correction terms and the battery voltage term, the AFR in
stationery on a feedback control constantly fluctuated around the
stoichiometric ratio. In terms of transient AFR control, a
nonlinear compensator based on the fueling dynamics parameters x
and τ was designed and the x Table and τ Table were acquired
through the method of pulse-changing the fuel injection rate and
recording the AFR response. As for the fact that either x or τ
varies among speed, TP and cylinder temperature, the final value of
each other was calculated by timing the MAP-searching value and the
cylinder temperature coefficient. For startup conditions, cold or
hot, an approach by reducing the enriching fuel gradually rather
than the nonlinear compensator was applied to ensure the success of
start.
The following bench tests demonstrated that the fuel economy,
exhaust gas emission and output torque under low-medial load
conditions all showed great improvement while less than 5% decrease
in maximum power compared to the original motorcycle engine
equipped with a carburetor.