Two concepts of starter-generator-machines for 8 to 12 cylinder combustion engines

High repute car companies make strong efforts to develop an electrical machine which combines producing energy for the electrical system and starting the combustion engine. The machine should be built as a crankshaft-starter-generator. This concept reduces the number of components and optimizes the complete electrical system due to synergistic effects. Two different machine concepts have been developed, built and tested at our institute. First theoretical results have shown, that it wouldn´t be possible to solve the problem with the generally used 12 V battery. The currents would increase to unrealistic dimensions. A possible solution could be an electrical system with a voltage of 42 V. It isn´t an easy task to realize an electrical machine that produces enough torque to start a big combustion engine within a given current limit even at this voltage. Limitation of currents was a binding condition of our concept to reduce the size of the PWM-converter. One concept uses a switch to change the number of turns in the stator winding of the electrical machine. The other concept uses a torque converter to meet the two contrary requirements of high torque at low speeds and constant power up to high speeds. Both concepts are based on asynchronous machines. The paper describes requirements, arrangements, solutions and test results.