In an engine controller, using only the ratio between the engine and transmission output shaft and the position of the clutch pedal can sometimes result in an incorrect determination of the gear state of a manual transmission. For example, if a driver has the clutch pedal released, and is coasting with the transmission in Neutral, the combination of the clutch pedal position and engine/transmission ratio may incorrectly indicate that the transmission is engaged in a gear. For certain features such as instrument cluster gear display and gear-based engine speed matching, among others, this is undesirable. A more robust gear determination method combines the above logic with clutch torque information, which, if higher than a predefined "drive" torque level or lower than a predefined "coast" torque level, provides additional confidence that the transmission is engaged in a gear. This clutch torque is calculated by taking the reported engine torque and offsetting it by any torque which is being used to accelerate or decelerate the engine. This "inertia" torque is calculated by multiplying engine acceleration by a predefined, constant inertia factor, which is a characteristic of the engine/flywheel/clutch hardware.
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