Toyota’s New Driveline for FR Passenger Vehicles 2017-01-1130

The renewed platform of the upcoming flagship front-engine, rear-wheel drive (FR) vehicles demands high levels of driving performance, fuel efficiency and noise-vibration performance. The newly developed driveline system must balance these conflicting performance attributes by adopting new technologies. This article focuses on several technologies that were needed in order to meet the demand for noise-vibration performance and fuel efficiency.

For noise-vibration performance, this article will focus on propeller shaft low frequency noise (booming noise). This noise level is determined by the propeller shaft’s excitation force and the sensitivity of differential mounting system. In regards to the propeller shaft’s excitation force, the contribution of the axial excitation force was clarified. This excitation force was decreased by adopting a double offset joint (DOJ) as the propeller shaft’s second joint and low stiffness rubber couplings as the first and third joints. The input to the body and its sensitivity were decreased by separating the pitching resonances of body mount bushings and differential mount bushings.

For improving fuel efficiency, the differential hypoid gear (D/F) efficiency improvement is described in this article. The hypoid gear specifications, bearings, and oil lubrication system were optimized to improve fuel efficiency. Thus, new D/F efficiency is superior to the previous model in spite of the bigger size, and it achieves its vehicle efficiency development target. A low pinion offset and the low spiral angle of the hypoid gears enable meshing loss reduction. Adoption of ball bearings for the drive pinion axis further enables the reduction in losses compared to conventional taper bearings. Optimization of the carrier lubrication structure and a low oil volume and fill level enable additional reduction in losses and improve the life of the ball bearings by limiting an excessive oil supply to the bearings.