Patent ID: 8109254

Claim:
A method of controlling the spark lead of an internal combustion engine comprising at least one cylinder fitted with a spark plug; the method comprising the steps of: determining a standard spark lead value; determining an engine knock index in the cylinder for each of a plurality of combustions for the cylinder, the engine knock index representing an engine knock level of the combustion in the cylinder that is calculated from a signal from at least one engine knock sensor; calculating a correction factor as a function of the engine knock indexes; determining a modified spark lead value by applying the correction factor to the standard spark lead value; and controlling the spark plug using the modified spark lead value; wherein the step of calculating the correction factor comprises the further steps of: statistically analyzing at least thirty-two consecutive engine knock indexes to calculate a cumulative distribution of the engine knock indexes; determining the percentage of engine knock indexes below a threshold value; comparing the percentage of engine knock indexes below the threshold value with a target value indicating a desired percentage of engine knock indexes; and modifying the current correction factor value as a function of the comparison between the cumulative distribution and the target value to ensure the percentage of engine knock indexes below the threshold value equals the target value.