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This paper will focus whining noise on rear axles applied in mid-size trucks. Vehicle integration changes during development affect directly the gear noise perception, in which it may be intensified. Also, gear material and heat treatment choices for the rear axle need to be done carefully, taking into consideration the integration changes and also the driver usage. A lessons learned collection over the diverse aspects of a rear axle whining noise will be the basis of this paper.

1 During the development of a new clutch disc damping system and after three months of hard work the engineering team got stuck with unsatisfactory system performance (rattle noise), despite the help of a computer simulation software. The only alternative seemed to be using a more expensive damping concept but, besides the fact that there wasn't much development time left, that option would increase part cost by unacceptable US$ 200, plus development cost. The team then decided to try Taguchi's Robust Engineering optimization approach for the first time. In just two weeks the authors got a 4.6 dB gain on the signal-to-noise ratio. That allowed us to keep the initially proposed system, thus avoiding the cost increase. Besides, the authors were able to keep the development schedule on track.

This paper explains the evolution of Electric and Hybrid propulsion system from its early beginning and the drawbacks faced along the way, explaining why the Internal Combustion Engine turned out to be dominant and the reasons why the fossil fuel model is now in question. It explains the recent developments that allowed its production and the progressive electrification steps leading from conventional Internal Combustion Technology towards the top electrification technologies. It demonstrates how some old-fashioned technologies are reinvented in order to boost performance and efficiency on Hybrid Propulsion systems. The paper explains the evolution on the Hybrid Propulsion Systems architecture in the last 20 years and how it brought a considerable improvement on efficiency and performance leading to the highly advanced hybrid vehicles now in production. It also points out to future new developments on the sector.