Boost Pressure Control in Transient Engine Load with Turbocharger Speed Sensing

The new driving cycles require a greater focus on a wider engine operative area and especially in transient conditions where a proper air path control is a challenging task for emission and drivability. In order to achieve this goal, turbocharger speed measurement can give several benefits during boost pressure transient and for over-speed prevention, allowing the adoption of a smaller turbocharger, that can further reduce turbo-lag, also enabling engine down-speeding. So far, the use of turbocharger speed sensor was considered expensive and rarely affordable in passenger car applications, while it is used on high performance engines with the aim of maximizing engine power and torque, mainly in steady state, eroding the safe-margin for turbocharger reliability. Thanks to the availability of a new cost effective turbocharger speed technology, based on acoustic sensing, turbocharger speed measurement has become affordably also for passengers car application. In this paper, a new model-based boost pressure control employing the speed measurement, is proposed. In particular, a cascade controller based on boost pressure, turbocharger speed and VGT position measurements has been developed. Furthermore, the open loop term and the speed target filtering have been calculated by means of a simplified physical model of the plant. The control has been designed and validated by means of a 1-D model of a small turbocharged Diesel engine for passenger cars. Moreover the achievable benefits have been analyzed.