Bus Transmission Design for Optimum Fuel Economy

Controlled tests undertaken by the Scottish Bus Group show that under the same conditions of service one model of diesel-engined bus may use 25 per cent more than another of the same weight and passenger capacity. One bus may use 17 per cent more than another having the same engine but a different type of transmission. This paper discusses aspects of power train design which can produce such variations in fuel usage. These include the transmission efficiency of driveline components, the working regime presented to the engine, standstill and parasitic losses and the kinetic energy entrained in rotating components. Differences observed between service and test bed (i.e. steady state) results with turbocharged engines are referred to and brief reference is made to systems which aim to recover and conserve the kinetic energy of the vehicle when it stops