A high accuracy dynamical measurement method for engine rotation speed based on vibration

Without encoder and phase discriminator a transient measurement method for rotation speed of the reciprocating engine is proposed in the paper. The coarse rotation speed of the engine is obtained from the components of the lowest harmonic frequency in its vibration signals. When the engine speed has little fluctuation, a discrete spectrum correction technique is employed to improve measurement precision of the speed. When there is a large speed variation, such as in its speed-up and speed-down stages, the vibration signals are re-sampled corresponding to the coarse rotation speed. By the order-tracking technique based on the re-sampling data, a correction factor and the transient rotation speed of the engine are obtained accordingly. Results from the tests on bench and real engines with different number of cylinders prove that the proposed method can achieve a high precision. Comparing to the other usual measurement methods with encoder, the proposed method is simple in hardware, does not need any pre-knowledge of the cylinder number of the tested engine, and is particularly suitable for routine inspection and maintenance of the vehicles.