Performance control of a motor vehicle engine for consistent high quality transmission shifting

In a motor vehicle including a spark ignition internal combustion engine adapted to drive the vehicle through an automatic shift transmission calibratable to provide acceptable shift quality at a specified engine performance level, and an engine control normally effective to schedule the engine spark timing for producing substantially optimum engine performance, a method of operation which avoids degradation of transmission shift quality due to variations in the engine performance level, the method comprising the steps of:

• calibrating the transmission to provide acceptable shift quality at a less than optimum specified engine performance level;
• predefining engine acceleration levels that would occur during shifting of the transmission at an engine performance level corresponding to said less than optimum specified level;
• measuring an actual engine acceleration level in the course of transmission shifting;
• and
• during shifting of the transmission, retarding the engine spark timing from the value normally scheduled by said engine control so as to bring the actual engine acceleration level into correspondence with the predefined engine acceleration level, thereby bringing the actual engine performance level into correspondence with the less than optimum specified engine performance level for which the transmission is calibrated.