Diesel – Electric Parallel Hybrid Traction

For vehicles that live and work in the city and never leave, pure electric traction provides excellent benefits, for the operator and for society as a whole. Where the vehicle is required to leave the city, where range and performance are key operational needs, the Diesel-electric hybrid drive provides an excellent solution. With traction either wholly by electric motor, wholly by Diesel engine or by a combination of the two, what appears at first sight to be a compromise is nonetheless an exciting innovative solution. It brings outstanding benefits both in ease of driving and in fuel economy savings of up to 30%, depending on mission, compared to conventional power train solutions. This is achieved in three important ways:

• Regenerative braking system. The electric traction motor under overrun conditions or vehicle braking functions as a generator and the kinetic energy of motion is converted to electrical energy to charge the traction batteries.
• Stop and Start function. When coming to rest the Diesel engine is automatically switched off. Starting from rest is initially by electric motor only and the Diesel engine is started automatically according to vehicle road speed and driver acceleration demand (indicated by the accelerator position).
• Down-sized Diesel engine. Like most mechanical devices, engine efficiency increases as a function of power demand or load. Usually, the Diesel engine chosen for a particular application will have sufficient power to cater for all needs. With a Diesel-electric parallel hybrid, the use of a down-sized engine covers most needs but the extremes of power required for high rates of acceleration or for the steepest of hills can be met by the Diesel engine working in parallel with the electric motor.

With these features, urban driving in which there is a high degree of stopping and restarting provides the greatest fuel economy savings while the vehicle is equally at home on the motorway between cities, functioning with the flexibility that is expected of a commercial vehicle.


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