Innovative Fan Drives for Hybrid Trucks

A2 - Fan Mechanical Design

With ever-increasing fuel prices and forthcoming stringent regulations on the reduction of CO2 emissions, the desire for better fuel economy in the truck sector continues to drive towards an optimisation of energy use. This leads to a need to reduce parasitic losses on the vehicle, including those from the engine accessory drive. Accessory drive losses account for a significant proportion of the engine power and have a direct impact on vehicle fuel consumption.

An additional driver for an evolution in accessory drives is the development of Hybrid Electric Vehicles, where there is a need for accessories to function even when the internal combustion engine is stopped.

This paper addresses, in particular, the need for an evolution of the main engine mounted cooling fan drive, for trucks. Typically, in hybrid vehicles the cooling of the electrical components of the powertrain, such as the energy storage systems, power converters and electric machines, is assured by an auxiliary cooling system. Auxiliary electrically driven fans are used to meet cooling needs in hybrid or electric drive modes, adding cost, weight and additional packaging constraints to the vehicle.

This paper explores the possibilities for using the main engine cooling fan to provide cooling air flow even when the internal combustion engine is stopped. The required functionalities, including fan speed modulation, fan acceleration, noise levels and efficiency in several operating conditions, and fail safe modes, are established and prioritised. Different solutions for the engine cooling fan drive are discussed. The development of an innovative electro-mechanical solution is presented: The working principle, modeling, concept choices and mechanical and electrical dimensioning to reach the required functionalities are detailed.

Finally, the conclusions summarise the main challenges in developing such an electro-mechanical fan drive, as well as the advantages and disadvantages compared to traditional fan drives for both hybrid and non-hybrid applications.