Novel approaches for quickly measuring engine speed applied to gasoline engine diagnostics

The parameter of engine speed plays an important role to recognize the engine's condition while working. By using this parameter, it is possible to diagnose engine's malfunctions. In this study, in case of the gasoline engine, we introduce two efficient methods for measuring the engine speed without extracting electrical signals from conventional engine speed sensors. For the first approach, based on the signal pin of the sensor, the engine speed was determined from the frequency of manifold absolute pressure. For the second approach, the frequency of the voltage drop measured at the battery positive terminal caused by ignition operation is the key to calculate the engine speed. The noise filter circuits and the amplifier circuits are used to refine signal, Besides, a Schmitt Trigger circuit using a NE555 timer IC was designed to reshape the oscillation signal from either of these sources into a square wave of which frequency was measured and converted to the engine speed by a microprocessor and display the result on the LCD screen.Compared to engine speed measured by a conventional inductive sensor, the proposed methods provide a competitive result with fast response. The second approach was highly promising due to its simplicity involving in direct voltage measurement at the battery positive terminal.