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介绍了一种在线估计内燃机平均指示压力的方法，通过分析作用于曲轴上的各种扭矩，得出估计平均指示压力的公式，并用最小二乘法拟合出pi和pg的关系式，从循环内转达波动估计平均指示压力。采用光电轴角编码器和自行设计的40MHz计数器进行瞬时转速的精确测量，内燃机每转进行360点瞬时转速的测量，并设计了和转速测量完全同步的示功图测录系统。最后，针对四缸汽油机进行了台架试验，结果表明，在中低转速范围内，这种方法具有较高的精度。
A method for on - line estimation of average indicated pressure of internal combustion engine is introduced. By analyzing various torques acting on the crankshaft, a formula for estimating the average indicated pressure is obtained and the relation between pi and pg is fitted by the least square method. Transmit fluctuations to estimate average indicated pressure. The photoelectric rotary encoder and self-designed 40MHz counter were used to measure the instantaneous speed. The internal combustion engine was used to measure the instantaneous rotation speed of 360 points per revolution. A dynamometer system was designed which was completely synchronized with the speed measurement. Finally, a bench test was carried out on a four-cylinder gasoline engine. The results show that this method has higher accuracy at low speed and medium speed.