Design and Characterization of an E-booster Driven by an High Speed Brushless DC Motor

Abstract

Engine downsizing has become one of the main strategies to reduce C02 emission. Turbochargers are well-adapted to this purpose but one of their biggest drawbacks is the turbo-lag which reduces the driving comfort especially during acceleration. Electrically driven compressors also known as E-compressor or E-booster could be a well-adapted solution to boost the engine intake pressure in order to reduce the turbo-lag. Since centrifugal compressors operate at high rotational speeds, high speed electric machines are therefore required. To achieve a significant reduction of the turbo-lag, a very fast response time is needed leading to the development of electric machines able to typically spin from idle to 75kRPM in less than 300ms. With 20 years of expertise in the development of innovative brushless DC motors for automotive applications, MMT has recently investigated the design of such high power-high rotation speed motors. After first integrated an electric motor into a turbocharger described in [1], MMT has decided to optimize the complete system in collaboration with SwissAuto Wenko AG, a specialist in the design and characterization of advanced charging systems. The initial specification was an overpressure of 1.3 within 300ms, reached by using a 2kW@80kRPMs electric motor. The motor optimization, the mechanical design of the system as well as experimental measurements are presented. Details about the brushless DC motor design will be given as well as compressor maps and transient response behaviors. Results will also show that the transient state performances are better than expected.