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.
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??
The Sensor : Principle Knock Sensor Uses Piezoelectric Element. Works on Piezoelectric Effect. Piezoelectric elements generate voltage when pressure or vibration is applied to them. Piezoelectric Crystal 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
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
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.
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.
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.
References “Automotive approach” by system approach by Jack Erjavec. “ Design of Knock sensor” by Alexander A.Bazhenoy. “Total Automotive Technology” by Anthony E. Schaller.