Mild hybrid electric vehicles seek to improve fuel economy over conventional vehicles by providing electrical assist during pull-away and by implementing regenerative braking.  They are based closely around the original vehicle and require the integrated motor/generator and flywheel/clutch arrangement to fit within the existing space between the engine and gearbox.

Switched Reluctance Drives Ltd has worked with Volvo, Fiat Auto and other partners on a European project to produce a mild hybrid-electric powertrain.  An SR Drive^® motor/generator with a novel dual clutch arrangement is integrated between the engine and transmission to provide pull-away assist and regenerative braking.  The exceptionally compact design utilizes the high-specific output and flexible format of switched reluctance machines and allows one of the clutches to be integrated into the centre of the rotor of the SR Drive^® motor/generator.

The result is a design which meets all of the performance requirements and has been demonstrated to be the most cost-effective solution when compared with other electric drive technologies, costing some 25% less than alternative systems.  The 15kW SR Drive^® motor/generator provides up to 120Nm torque assist during launch and yields an anticipated 10% improvement in fuel economy.

Key performance data for the SR Drive^® motor/generator unit is as follows:

Stator lamination diameter = 284mm.
Stator active length = 55mm.
Rotor lamination bore = 197mm.
Air-gap length = 0.4mm radial.
Minimum battery voltage for full performance = 107V.
Low speed peak torque = 120Nm for 60s.
Low speed continuous torque = 70Nm.
Base speed for 15kW motoring = 1200rpm.
Maximum design speed = 6000rpm.

EC funded project ELMAS, “New High Efficiency Electric Machines Solutions for Mild Hybrid Applications” – Project Number NNE5-1999-000675.