首先指出了在测量内燃机瞬时转速时所存在的问题：一是缺少一个合理的测量误差计算公式；二是没有合理选择信号齿盘齿数的依据。详细叙述了利用磁电或光电传感器测量瞬时转速的原理和方法，在此基础上提出了测量瞬时转速的新的误差计算公式；分析了影响测量精度的诸因素。研究表明瞬时转速的误差来源主要有３个：角度误差、量化误差和触发误差。试验证明，利用发动机的飞轮齿圈测量瞬时转速是切实可行的 First of all, it points out the problems existing in measuring the instantaneous speed of internal combustion engine. The first one is the lack of a reasonable formula for calculating the measurement error. The second one is that there is no basis for choosing the tooth number of the signal gear rationally. The principle and method of using magnetoelectricity or photoelectric sensor to measure instantaneous speed are described in detail. On this basis, a new error calculation formula for measuring instantaneous speed is put forward and the factors affecting the measurement accuracy are analyzed. Research shows that there are three main sources of error in the instantaneous speed: angle error, quantization error and trigger error. Experiments show that it is practicable to use the flywheel ring of the engine to measure the instantaneous speed