Research On Engine Speed Measurement Technology Based On Vibration

Rotational speed is one of the important parameters of engine working state,and rotational speed measurement is an indispensable part of engine running state monitoring.A speed sensor is generally installed inside the engine,and the speed information is provided to the outside by the electronic control unit(ECU).However,fast and portable speed measurement methods are often required in the experimental tests of engine and vehicle emissions,energy consumption,durability and so on.The ECU is fixed in the interior of the vehicle,so the interface connection is inconvenient,and the speed information output by ECU should not be used as the speed standard for engine testing.Based on the relationship between engine vibration signal and rotational speed,a speed measurement method based on engine vibration signal is studied to realize the indirect measurement of engine speed.The main research contents are as follows:(1)Aiming at the deficiency of empirical wavelet transform in spectrum adaptive segmentation,a vibration signal fundamental frequency extraction method based on maximum inter-class variance empirical wavelet transform(Otsu-EWT)is studied by combining maximum inter-class variance(Otsu)and empirical wavelet transform(EWT),which improves the accuracy of fundamental frequency extraction of nonstationary vibration signals.According to the characteristics of the engine vibration signal,the vibration simulation signal is constructed,the fundamental frequency of the vibration signal is extracted by cepstrum method and Otsu-EWT method,the engine speed is calculated,and the engine speed measurements under different working conditions are simulated and compared.(2)An engine parameter extraction method based on engine vibration vector is studied,and the automatic identification of engine cylinder number and main vibration direction is realized.The frequency characteristic of the engine vibration signal is closely related to the number of engine cylinders,the arrangement type and the installation position of the vibration sensor.In this method,the vibration sensor can be installed in any position of the engine,and the cylinder number information needed by the speed measurement model can be identified by using the engine vibration vector signal.The experiment of parameter extraction of four-cylinder engine based on engine vibration vector is completed,and the feasibility of this method is verified.A three-axis vibration signal acquisition unit combined with the TMS320F28335 digital signal processor and host computer software is designed to build an engine vibration signal acquisition and processing system.(3)The field test experiment of engine speed is completed by using the developed speed measurement experimental device.The cepstrum method and Otsu-EWT method are used to measure the speed of single-cylinder,two-cylinder and four-cylinder engines under different speed conditions,and the two operating conditions of the steady-state and unsteady-state are compared.The experimental results show that the relative errors of cepstrum method and Otsu-EWT method are less than 1.5% under steady conditions,and the maximum relative errors of cepstrum method and Otsu-EWT method under unsteady conditions are 4.78% and 2.33%,respectively.