A new method for measuring engine rotational speed based on the vibration and discrete spectrum correction technique

This paper presents an encoder-less method for measuring the rotational speed of a reciprocating engine. The proposed method obtains the rotational speed of the engine from the lowest harmonic frequency component of its vibration signals, and uses a discrete spectrum correction technique to improve the measurement precision. Results from bench tests and tests on real engines, each having a different number of cylinders, have proven that the proposed method can achieve an extremely high precision when the engine is working in a steady-state or small speed fluctuation condition. As compared to the encoder-based method for measuring engine rotational speed, which is often found in literatures, the proposed method uses a straightforward hardware which is easy to install, and is particularly suitable for use during routine inspection and maintenance of vehicles.