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auto ignition(خوداشتعالی)
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auto ignition(خوداشتعالی)


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  • 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..?