What Is Knocking ?
High frequency vibrations giving
rise to ping like sound inside an
Caused By :
Low Quality Fuel
Deposits on Cylinder Wall
Wrong Spark Plug.
How Can It Be Prevented?
Why do we care??
Knocks can rob power from the
engine and worst, destroy the
How can we prevent knocking??
lower compression ratio, higher
octane fuel, change driving
or……MECHATRONICS! Need a
The Sensor : Principle
Knock Sensor Uses Piezoelectric Element.
Works on Piezoelectric Effect.
Piezoelectric elements generate
voltage when pressure or vibration
is applied to them.
Ceramics and single crystal materials:
quartz, tourmaline and gallium phosphate
Working Of the Sensor
Knock Sensors generate a voltage
when vibration is applied to them
utilizing the piezoelectric effect.
Due to the vibration, a counter
weight inside the sensor is
applying pressure on the piezo-
element, this pressure creates an
electric charge in the piezo-
element which is the output signal
of the sensor.
Knock Sensor Circuit
Once signs of detonation are detected (i.e. knocking), the knock
sensor sends a voltage signal to the engine control unit(ECU)
which retards the spark timing slightly to avoid detonation.
Vehicle engines work more efficiently and produce more power
when operating near the detonation limit.
Although simple, knock sensors allow optimum engine
performance and protect the engine from potential damage
caused by detonation.
Piezoelectric effect is found in many applications but
knock sensors seem associated with the automotive
Knock control for internal combustion engines.
Machine tool protection.
Monitoring of pivot bearings.
Anti theft systems.
Piezoelectric elements can be sensitive to more than one
Operate in harsh environment (dirt, grease, moisture, road salt,
etc.) for automotive applications.
Ceramic materials lack long term stability.
Sensor can be fooled by things like bad water pump or
alternator bearing, or a loose rod bearing.
“Automotive approach” by system approach by Jack Erjavec.
“ Design of Knock sensor” by Alexander A.Bazhenoy.
“Total Automotive Technology” by Anthony E. Schaller.