1. Knock Sensor

2. What Is Knocking ?
 High frequency vibrations giving
rise to ping like sound inside an
Engine.
 Caused By :
 Low Quality Fuel
 Deposits on Cylinder Wall
 Wrong Spark Plug.

3. How Can It Be Prevented?
 Why do we care??
Knocks can rob power from the
engine and worst, destroy the
engine itself.
 How can we prevent knocking??
lower compression ratio, higher
octane fuel, change driving
habits
or……MECHATRONICS! Need a
tow??

4. 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
Piezoelectric Crystal

5. 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

6. 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.
ECU

7. Benefits
 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.

8. Application
 Piezoelectric effect is found in many applications but
knock sensors seem associated with the automotive
industry.
 Knock control for internal combustion engines.
 Machine tool protection.
 Cavitations detection.
 Monitoring of pivot bearings.
 Anti theft systems.

9. Challenges (knocks)
 Piezoelectric elements can be sensitive to more than one
physical dimension.
 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.

10. References
 “Automotive approach” by system approach by Jack Erjavec.
 “ Design of Knock sensor” by Alexander A.Bazhenoy.
 “Total Automotive Technology” by Anthony E. Schaller.

11. THANK YOU
Any Questions..?