During the past decade the development of slow speed, turbo-charged and intercooled diesel engines with characteristics to match 9 or 12 speed mechanical transmissions, the use of aerodynamic drag reducing devices, the adoption of radial ply tyres and other mechanically efficient devices, the current semi-trailer tractor has approached the peak of realisable efficiency.
The addition of energy storage is perhaps the only method of significantly reducing further the fuel consumption since utilising the potential energy on downhill running for subsequent hill climbing increases the average speed whilst maintaining the same maximum speed. Since energy storage is most, likely to be incorporated with an effective, continuously variable transmission, the engine can always be operated at maximum efficiency and at lower engine speeds, thus reducing the wear rate. A non-conventional transmission also has the potential to reconfigure the standard semi-trailer layout which is necessary to lead to further reductions in the aerodynamic drag.
This paper describes the advantages of reducing aerodynamic drag and incorporating energy storage devices of 5 MJ or more with power ratings in excess of 200 kW. The potential between 15 and 20% for fuel saving has been determined by the use of Monte Carlo simulation and with realistic CVT efficiencies.