Transcript 投影片 1

高等診斷技術
學生報告
Knock Sensor
The Knock Sensor detects engine knock and sends a voltage signal to the
ECM. The ECM uses the Knock Sensor signal to control timing. Engine knock
occurs within a specific frequency range. The Knock Sensor, located in the
engine block, cylinder head, or intake manifold is tuned to detect that
frequency. In a 4 cylinder it will be between the second and the third cylinder.
6 cylinder engines may have 2 knock sensors.
Inside the knock sensor is a piezoelectric element. Piezoelectric elements
generate a voltage when pressure or a vibration is applied to them. The
piezoelectric element in the knock sensor is tuned to the engine knock
frequency.
This is an AC voltage. The pizo crystals gets crushed due to the noise and
releases electrons. The voltage decreases as the vibration decreases. The
voltage is mV.
The vibrations from engine knocking vibrate the piezoelectric element
generating a voltage. The voltage output from the Knock Sensor is highest
at this time.
Knock Sensor Voltage Generation when knock occurs, the voltage output
increases.
The vibrations from engine knocking vibrate the piezoelectric element
generating a voltage. The voltage output from the Knock Sensor is highest at
this time.
We connected an oscilloscope to the knock sensor to see the wave form and
voltage it was putting out. We hit the knock sensor to cause vibration.We
saved this image from the oscilloscope. The image shows clearly when we hit
the knock sensor and gradually the voltage is decreasing as to the noise
vibration getting weaker. This is an Ac voltage.