Input: Inputs into the ECU are readable signals that the ECU
will then compare to its read only memory chip. The inputs come from many different sensors
around the engine and relay information in different ways, (but that are still
readable by the the ECU), e.g. Air flow sensors use resistance (ohms) in
accordance to the position of the air vane which can then be translated into a
readable form for the ECU. Another example would be Hot Wire air flow sensors
which use voltage outputs to relay information to the ECU.
Actuator Output: Actuator outputs are responses made by the
ECU in order to reach Lambda1 (a good air to fuel ratio for emission) in the
specific running range of the engine at a said point in time. Measuring
actuator output can be achieved simply with a multimeter and the right setting.
Different outputs are read according to different readings, i.e. certain
sensors like fuel injector’s duty cycle will be measured in % whilst others
like coolant temp, throttle position sensor and crank sensors are measured
according to DC volts, and CAM sensors are measured in AC volts & hertz.
Relationship between the two: Inputs are the initial step or
at the start of the chain. The ECU acts as a translator as it reads the inputs
and sends signals to the outputs accordingly. And the output is the end of the
line man. E.g. When the TPS sends a signal that it is fully open and that a
reasonable amount of air is entering and heading for the combustion chamber,
the ECU will read that and tell the injector to stay open for longer to
compensate for the huge amount of air entering.
Closed loop: Inputs are the initial step or at the start of
the chain. The ECU acts as a translator as it reads the inputs and sends
signals to the outputs accordingly. And the output is the end of the line man.
Now in a closed loop that is not the full story. The ECU will then go behind
the bakers back and check if everything is well by taking information from the
EGO (exhaust gas oxygen sensor) located in the exhaust manifold behind most of
the output sensors. An input sends information to the ECU about the engine
running condition in a way in which the ECU can read them. The ECU then reads
the input signals and refers to its read only memory chip to cross check the
running condition of the engine. It then sends a signal to the output actuators
to get the engine to run at Lambda1, if it were driving at across the range of
driving speeds.
