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Several types of hybrid-electric vehicles have been developed at Ford Research Laboratory. Among the parallel hybrid systems with a single electric motor, two types were studied. In the first type, the electric motor was attached directly to the crankshaft (mild hybrid) [1], to enable the engine start-stop and regeneration functions. In the second type (full hybrid) the electric motor was connected to the engine through the use of a clutch to allow electric launch of the vehicle and pure electric driving at low speeds. The full hybrid powertrain described in this paper uses a more powerful electric motor for enhanced regenerative braking and engine power assist. An engine-disconnecting clutch saves energy during both the electric propulsion and during vehicle braking. When the clutch is disengaged the engine is shut-off, which eliminates the energy otherwise spent on motoring the engine during electric propulsion.

The idea of using a single electrical machine for both starting the engine and generating electrical power is not new. However, the real benefits, that justify the higher cost of a combined starter-alternator, become apparent when it is used as part of a hybrid powerplant. This powerplant allows a substantial improvement in fuel economy by a variety of methods (i.e. the engine shut-down during deceleration and idle, regenerative braking, etc.), as well as enhancements to engine performance, emissions, and vehicle driveability. This paper describes the analysis of the structure supporting the starter-alternator on the end of the engine crankshaft (Figure 1). It deals with the requirement to maintain a small radial gap between the rotor and stator, and it discusses how the rotor affects the loading on the crankshaft. In addition, thermal deformations of the rotor/clutch assembly are analyzed with three light-weight materials.