resistance metal electrode) should be installed near the top of
intake valve, in the other head of circuit, the heat-resistance
alloy steel wire is installed at the intake valve (unconnected
with intake valve); when the backfire happen, the mixture are
firstly combustible around the detection probe and the alloy
steel wire; because of the air ionization caused by the high
temperature generated by combustion flame, so when the
positive voltage is applied between probe and steel wire, the
current will be generated, when negative, almost no current is
generated. And at this time the flame possess the unilateral
conduction performance like diode. When flame is extinct,
any polar voltage applied between probe and alloy steel wire
can not generate current. Based on this performance of flame,
the backfire phenomenon can be detected.
The specific working process is that: the transistors Q1 and
Q2 sustain the oscillation of transformer B1, and make the
transformer export the alternating current (AC) signals, when
the transformer exports the positive part of AC signal, the
voltage is negative between detection probe and alloy steel
wire, so the circuit is nonconductive, when the transformer
exports the negative part of AC signal, the voltage is positive
between detection probe and alloy steel wire, so the circuit is
conductive, and the capacitor C4, C5 at the left of probe is full
with charge, so a negative voltage can be generated, and
after the voltage comparison of comparator LM3936, the
comparator exports the low level, which make the I/O port of
the single-chip high level change into low level, thus obtain
a falling edge, single-chip can complete the precise detection
count of backfire signal through interruption detection of
the falling edge. When backfire disappears, the I/O port
changes back high level until the next detection of backfire
happens.
5.2. Sensors and its processing circuit
5.2.1. Crankshaft position sensor
Crankshaft position sensor is a kind of electromagnetic
sensor. Crankshaft position signal is the basement for the ECU
of hydrogen engine to run normally, it has significant influence
on accuracy of injection timing and ignition timing in
each of cylinders. Because the voltage signal output by the
electromagnetic sensor is sine wave, in order to change the
sine wave into square wave. To improve the calculation
precision, the 36 pulses generated by the fluted disc per