Abstract One primary concern with applying an AWD system to a front wheel drive (FWD) vehicle architecture is the additional weight and drag associated with the AWD drivetrain components, resulting in an increase in fuel consumption compared to FWD-only models. Therefore, Honda recently developed a next-generation integrated AWD unit that reduces weight and drag loss, and increases the SH-AWD cornering performance while maintaining the performance requirements of the previous rear drive unit. These targets were achieved primarily through the application of hydraulically-actuated clutches and an increase in the “speed-increasing ratio”. This paper describes the development, system validation and future technology implications of this recent advancement. Introduction Honda introduced the world's first Super-Handling All Wheel Drive (SH-AWD) system in the 2005 Acura RL. It provided variable torque distribution between the left and right rear wheels through the application of left and right planetary gear sets with electromagnetic clutches. Additionally, the outstanding cornering performance was enhanced through the application of an accelerator device which, when engaged, created a “speed-increasing ratio” of 5.7%. In 2006, the SH-AWD system architecture was simplified and the “speed- increasing ratio” was reduced to 1.7%. In order to further minimize the additional weight and drag associated with AWD systems, Honda recently developed an all-new SH-AWD unit, focusing on improving performance, and reducing both weight and friction. The main change points are: 1. Hydraulically-actuated, multi-disk clutches deliver power to the rear axles and replace the previous system's electromagnetic clutches and planetary gear sets. This change produces a weight reduction of more than 10kg and up to a 50% reduction in mechanical friction. 2. The constant “speed-increasing ratio” is increased from 1.7% to 2.7%, speeding-up the rear axles and enabling faster and more effective SH-AWD performance across a wider range of cornering situations. The different solutions for the weight and mechanical friction reduction were applied while maintaining the performance and durability of the newly developed rear drive unit. Development Goals The following hardware optimization targets were set for the development of a high efficiency next-generation SH-AWD rear differential unit: 1. Improve everyday vectoring capability 2. Reduce drag torque 3. Reduce system weight The hypoid gear ratio selection has been optimized to improve the torque vectoring capability so that the effect can be felt more often, such as when accelerating aggressively through a standard corner. The constantly overdriven front to back speed ratio has been increased from 1.7% to 2.7% enabling a torque vectoring effect that is more pronounced and effective even in corners with a radius of as small as 49.2 feet (15 meters). Figure 1. Speed-Increasing Ratio Optimization benefitDevelopment of High Efficiency Next-Generation SH-AWD Rear Drive Unit2015-01-1098 Published 04/14/2015 Nor Hairuddin Mohd Zainal Abidin and Satoshi Imamori Honda R&D Co., Ltd. Aaron Alexander Honda R & D Americas Inc CITATION: Mohd Zainal Abidin, N., Imamori, S., and Alexander, A., "Development of High Efficiency Next-Generation SH-AWD Rear Drive Unit," SAE Technical Paper 2015-01-1098, 2015, doi:10.4271/2015-01-1098. Copyright © 2015 SAE InternationalDownloaded from SAE International by Brought to you by the University of Kansas (Technical reports: 1998 to Present), Saturday, August 25, 2018Figure 2. Torque vectoring capability comparison between previous and new SH-AWD hardware The gear reduction structure has been simplified from a two-step reduction (hypoid gear and planetary gear sets) to a single hypoid gear reduction. The adoption of a hydraulically-actuated clutch system allows the electric oil pump to be used as a lubrication device instead of the mechanical pump applied in th