Disturbances during engine starts and stops can propagate to the drive wheels with minimal damping in the power split hybrid transaxle due to the system architecture. One such disturbance is the engine cranking torque from pumping & compression during the motoring phase of engine starts and stops before fueling. This paper proposes a control system to compensate for the engine disturbance and reduce the magnitude of the disturbance on the driveline. A high fidelity model of the power split transaxle is developed and validated with test data for NVH analysis. A simple model of a four cylinder engine is developed that can run in real-time and accurately estimate the cranking torque disturbance from the engine. It is show that the engine speed in the power split transaxle is controlled via a generator speed feedback loop. Performing a linear system analysis reveals that the addition of a feedforward term in the loop which is based on the engine cranking torque can reduce the driveline disturbance. It is shown through simulation that the proposed engine model with the feedforward controller can reduce the engine disturbance on the driveline. The engine model and feedforward controller are finally implemented on the production control module of a test vehicle and it is shown that the proposed control strategy can reduce the driveline disturbance by as much a 65% during engine starts. Moreover, it shown that the engine model can run in real-time and correlates well with in-cylinder pressure data measured from the engine.

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