Tooth Time-Based Engine Misfire Detection Index for Multicylinder Engines of Vehicles Not Affected by Various Deviations between Cylinders
ISSN: 1946-3936, e-ISSN: 1946-3944
Published September 28, 2021 by SAE International in United States
This article proposes a new misfire detection index, the ΔGap slope, for a four-cylinder engine. However, the proposed index is not limited to four-cylinder engines. The ΔGap slope uses the tooth time measured using the existing crankshaft position sensor; therefore, an additional sensor is not required, which makes it economical. The ΔGap slope is defined as the difference between the gap slopes of the same cylinder for two adjacent cycles. Various factors that cause deviations in gap slopes between cylinders can be eliminated in the process of determining the difference between two gap slopes. Hence, in contrast with the existing engine roughness method, the ΔGap slope has the advantage of not requiring compensation for deviations between the cylinders. The conventional gap slope method must use different sets of thresholds for each cylinder located at the same position on the sensor wheel, which results in multiple thresholds being applied. In contrast, the ΔGap slope can use the same set of thresholds for all the cylinders as the deviations between the cylinders are eliminated. Although a set of thresholds is required for diagnosing the start and end of misfire, the values are characterized by the same absolute magnitude and opposite signs; this is another merit of the ΔGap slope. It was found that the average misfire detection rate of the ΔGap slope is 90.2% for all the test conditions of idle to 6,000 rpm and neutral to 100% load, and this increased to 93% and 98% between 1,500 rpm and 4,000 rpm. However, the misfire detection rate tends to decrease below the average value as the load approaches neutral and the engine speed exceeds 4,000 rpm.