Automotive electronics power up

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[3] Fuel savings is a direct consequence of eliminating the conventional dc starter motor in favor of a contant-torque machine, such as the integrated starter/alternator. Overall starting time for the engine is shorter, as well.

With a conventional dc starter, fuel is supplied shortly after engine cranking begins, but the engine does not fire until about 500 ms later [red curve]. But a starter/alternator responding to a constant 200-N^.m torque command injects fuel after about 250 ms [yellow curve], at which point the engine immediately fires and only the fuel necessary to maintain idle is supplied.

IEEE Spectrum May 2000 Volume 37 Number 5