Power Train Selection for Optimum Performance and Efficiency

Methods for evaluating vehicle power train components and their effect on optimum vehicle performance and efficiency are considered. The assessment of overall vehicle costs includes the evaluation of each component, and optimizing power train components and performance to provide the most cost-effective vehicle for a given job. Medium and heavy duty trucks and buses involve a great variety of vocations and performance requirements. Any effort to evaluate power train specifications must include an understanding of key parameters defining performance requirements: gross vehicle weight; on-grade startability; and capability to negotiate a given grade at a selected speed. In general, power train components include the engine, transmission, drive shafts, auxiliary transmission or transfer case, and drive axle (s). Engine characteristics critical to vehicle performance and efficiency are power and governed speed, peak torque and corresponding speed, and brake-specific fuel consumption. The transmission must match engine characteristics to the duty cycle. Changes in vehicle operations and components are occurring rapidly; they encompass the desire for bigger and heavier loads, more axles and double-triple trailers, more diesel engines, larger engines, low-speed engines, and new buses, transmissions, and axles. The computer simulation method is replacing obsolete and costly methods such as trial-and-error and actual testing for analyzing vehicle vocation variables and different types of power trains and components. Using computers should bring closer an optimum match of vehicle, engine, transmission, axle, and tire parameters for a given vocation.