Detection of irregularities in engine cylinder firing

A method for controlling a powertrain assembly having an engine with at least one cylinder, at least one electric machine, a motor speed sensor operatively connected to and configured to obtain motor speed data of the at least one electric machine, and a controller having a processor and tangible, non-transitory memory, the method comprising:

• obtaining the motor speed data at a predefined time interval from the motor speed sensor, until a predefined time window is reached;
• obtaining a fast Fourier transform of the motor speed data during the predefined time window, via the controller;
• detecting firing irregularities in the at least one cylinder based at least partially on the fast Fourier transform, including:
• obtaining a calculated engine firing frequency as a product of an average engine speed during the predefined time window and a factor, wherein the factor is a number of the one or more cylinders in the engine divided by two (ncyl/2);
• obtaining an engine firing frequency (EFF) from the fast Fourier transform, the engine firing frequency (EFF) being a relative maximum within a predefined range of the calculated engine firing frequency;
• obtaining a first amplitude (AF1) at a first reference frequency (F1) from the fast Fourier transform, the first reference frequency (F1) being half the engine firing frequency (EFF);
• obtaining a third amplitude (AEFF) at the engine firing frequency (EFF) from the fast Fourier transform and a first ratio (AF1/AFF) of the first amplitude and the third amplitude;
• and
• controlling the engine based at least partially on a comparison of the first ratio (AF1/AFF) and the first threshold (T1).

A vehicle comprising:

• an engine having one or more cylinders;
• an electric machine operatively connected to the engine;
• a motor speed sensor operatively connected to and configured to obtain motor speed data of the electric machine;
• a controller operatively connected to the motor speed sensor, the controller including a processor and tangible, non-transitory memory on which is recorded instructions for executing a method for detection of irregularities in firing of the one or more cylinders;
• wherein execution of the instructions by the processor causes the controller to:
• obtain the motor speed data at a predefined time interval from the motor speed sensor, until a predefined time window is reached;
• obtain a fast Fourier transform of the motor speed data during the predefined time window;
• obtain a calculated engine firing frequency as a product of an average engine speed during the predefined time window and a factor, wherein the factor is a number of the one or more cylinders in the engine divided by two (ncyl/2);
• obtain an engine firing frequency (EFF) from the fast Fourier transform, the engine firing frequency (EFF) being a relative maximum within a predefined range of the calculated engine firing frequency;
• obtain a first amplitude (AF1) at a first reference frequency (F1) from the fast Fourier transform, the first reference frequency (F1) being half the engine firing frequency (EFF);
• obtain a second amplitude (AF2) at a second reference frequency (F2) from the fast Fourier transform, the second reference frequency (F2) being half the first reference frequency (F1);
• obtain a third amplitude (AEFF) at the engine firing frequency (EFF) from the fast Fourier transform;
• determine if a first ratio (AF1/AFF) of the first amplitude and the third amplitude is at or above a first threshold (T1);
• determine if a second ratio (AF2/AFF) of the second amplitude and the third amplitude is at or above a second threshold (T2);
• and
• wherein the controller is configured to control the engine based at least partially on a comparison of the first ratio (AF1/AFF) and the second ratio (AF2/AFF) to the first threshold (T1) and the second threshold (T2), respectively.