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Powertrain torsional vibration has become a subject of increasing concern for the heavy duty truck industry in recent years. This is due in part to truck and diesel engine developments, and to drivetrain system trends. A computer simulation is an effective tool in analyzing this problem. A powertrain vibration analysis program has been developed by the authors. It has been used extensively in the evaluation and optimization of powertrain system performance. In this paper, first the heavy duty powertrain is characterized as a vibrating system. Its natural frequencies, mode shapes and frequency response characteristics are reviewed. Second, the theory of torsional vibration and its application in the simulation are described. The drivetrain is described as a discreet model. An undamped modal analysis is given as an eigenvalue problem.

In recent years, several transit agencies have tested buses equipped with hybrid powertrain systems. It has been reported that hybrid powertrains have significant advantages over conventional diesel engine systems, in the area of emissions and fuel economy performance. Presented in this paper are engineering issues and suggestions from an auto component supplier point of view in the design of such a powertrain system. The particular system being considered consists of a downsized diesel engine, a generator, a battery package, two identical AC induction motors, and gearbox systems for the left and right driven wheels. The assembly is supported by an H-shaped suspension sub-structure uniquely designed to achieve the “ultra-low floor” configuration. Our discussion covers the system performance, as well as the durability issues. In particular, the presentation focuses on the durability and the design layout of the gearbox and suspension substructure.

The uniqueness and challenge of heavy and medium duty vehicle manufacturing is that the vehicle&s subsystems and major components are procured from different suppliers. As a consequence, engineering task coordination for total vehicle performance optimization is required even if the intended design modification is only on one component. In the case of suspension design, related subsystems such as the drive axle, driveline, brake system, steering system, and engine mounts should all be included for review. The related potential problems for study fall into three categories, namely: function, durability, and NVH. The effective approach in addressing all these issues early in the design stage is through computer modeling and dynamic system simulation of the suspension system and related subsystems.

Contact stress analysis or surface fatigue life prediction is a subject frequently encountered in powertrain component designs. Examples are the design of gears, bearings, cams, and load ramps. In many cases, design evaluations rely on simple analysis, component supplier's suggestions, and prototype testing. One viable technology trend in modern engineering, however, is to use computer simulation and analysis as a design guide. It is universally acknowledged that up-front computer-aided-engineering (CAE) will reduce the product development cycle time and cost, and improve product quality. In addition, this approach provides a good platform for technology growth. Scattered examples on surface durability analytical modeling techniques are available in the literature. But, the most suitable engineering tools for routine product design support are yet to be developed. Currently, a semi-empirical approach is widely used in the industry.