Dynamic Pressure Ratio Allocation for Electric Supercharger and Turbocharger Coordination

To improve transient torque response of an aggressively downsized turbocharged spark-ignition engine, a series sequential boosting configuration that utilizes an electrically driven supercharger to assist the main turbocharger compressor is considered. The system is over-actuated with two actuators (i.e. turbocharger wastegate, electric supercharger motor) and one output, the total boost pressure. A dynamic pressure ratio allocation method is designed that apportions the control reference to each actuator. The method is based on the characteristics of each actuator, i.e., the turbocharger is generally more efficient but has a slower dynamic response relative to the electrical supercharger. Therefore, the turbocharger is always asked to deliver the desired boost pressure while the electrical supercharger is utilized only as necessary in transients to make up for any deficit. The control design is validated in a test vehicle and good performance is observed. Transitions between the electric supercharger and turbocharger are smooth and without noticeable disturbances.