Knock Control on Small Four-Two-Wheeler Engines 2012-32-0052
Today, knock control is part of standard automotive engine
management systems. The structure-borne noise of the knock sensor
signal is evaluated in the electronic control unit (ECU). In case
of knocking combustions the ignition angle is first retarded and
then subsequently advanced again.
The small-sized combustion chamber of small two-wheeler engines,
uncritical compression ratios and strong enrichment decrease the
knock tendency. Nevertheless, knock control can effectuate higher
performance, lower fuel consumption, compliance with lower legally
demanded emission limits, and the possibility of using different
fuel qualities.
The Knock-Intensity-Detector 2 (KID2) and the Bosch knock
control tool chain, based on many years of experience gained on
automotive engines, provides an efficient calibration method that
can also be used for two-wheeler engines. The raw signal of the
structure-borne noise is used for signal analysis and simulation of
different filter settings.
A feasibility quick test was executed on a water-cooled 125cc
small engine of a mass-produced two-wheeler. Although the knock
sensor position was not optimized, a satisfactory knock detection
quality was achieved across the entire engine speed range up to
10,000 rpm. Without knock control an ignition safety margin of 6°CA
to the knock limit is necessary due to tolerances of the
compression ratio and different fuel qualities.
With active knock control, the following benefits could be
achieved at the engine's standard load point of 7,500 rpm: - At
moderate ambient temperature (25°C intake-air), a torque increase
of 3% with original enrichment or equal torque with 10% less
specific fuel consumption at lambda 1. - At high ambient
temperature (60°C intake air), the specific fuel consumption could
be reduced by 16% - at lambda equals unity and original torque.
The benefits that are achieved by merely including knock control
to an already existing engine are only given at full load
operation. The objective for the near future is to increase the
compression ratio of the engine to attain higher performance and
reduce the fuel consumption especially at part load, by finding a
compromise between performance and fuel economy.
