ABSTRACT A new 6-speed automatic transmission (AT) has been developed with the aim of enhancing fuel economy, raising efficiency, and achieving greater compactness. The unit was built on a parallel-shaft structure similar to the previous Honda AT, which has high torque transmission efficiency. The new AT was given more gear speeds and the ability to handle higher input torque from the engine. On the one hand, bolt structure for shaft tightening was implemented, the forward-reverse shift mechanism was placed on the input shaft and common gear trains are provided. As a result of these and other measures, the total length of the new transmission is 18 mm shorter than the previous model 5- speed AT. A multi-plate lock-up clutch (LC) structure with a separate chamber in the torque converter was also adopted so that the lock-up torque capacity could be increased and the LC control range expanded. In combination with decreased friction loss torque and improved transmission efficiency by the new hydraulic control system, lubrication oil management and improvement of the gear contacts, this new configuration achieves a 5% or greater increase in fuel economy over that of the previous model 5-speed AT, while realizing greater power and driving performance with enhanced direct feeling. INTRODUCTION The world today is faced with the issue of global warming caused by an increase in greenhouse gases, and various industries are required to come up with measures for this problem. To reduce CO 2 emissions, there is a growing need for automobiles to have better fuel economy, and the automotive industry must act quickly to meet this demand. On the other hand, higher product quality and a better driving feel are also much in demand.In the area of transmission technologies for higher fuel efficiency, Honda has introduced continuously variable automatic transmissions (CVT)(1), (2), integrated motor assist (IMA)(3) technology, and wider LC ranges, mainly in small and mid-size vehicles. The new 6-speed AT structure reported in this paper was developed to improve the fuel economy of large vehicles. The new 6-speed AT achieves both better fuel economy and a shorter length, and on top of that it delivers greater driving performance and a better driving feel. The following describes the development objectives and major technologies employed in this 6-speed AT. DEVELOPMENT AIMS Reducing the engine rpm change while shifting stabilizes the engine combustion, so increasing gear speeds is an effective means to improve fuel economy. However, adding clutches and gears to a conventional parallel-shaft transmission will increase its overall length and reduce clearances between the transmission and body frame. There is concern that this will affect crash safety and reduce the flexibility of installation in car bodies. For this reason, a requirement for this project was to both increase gear speeds and achieve a shorter length. In the design of the transmission torque capacity, the maximum target torque allowed in structure must be set in consideration of the higher torque expected of next- generation engines. Attention must also be paid to needs for not only higher fuel efficiency but also enhanced driving performance and commercial appeal. High Efficiency 6-speed Automatic Transmission2010-01-0858 Published 04/12/2010 Isamu Shinbori, Akio Muto, Hiroyuki Takeo, Tooru Takahashi, Yoshiharu Saito and Yoshimichi Tsubata Honda R&D Co.,Ltd. Copyright © 2010 SAE InternationalDownloaded from SAE International by Univ of Nottingham - Kings Meadow Campus, Tuesday, September 18, 2018Based on these requirements, the development aims of the new 6-speed AT structure were set as follows: 1). Balance between an increase in gear speeds and a shorter length 2). Greater torque capacity to match the specifications of next-generation engines 3). Good balance between higher fuel economy and a better driving feel BASIC STRUCTURE AND MAJOR SPECIFICATIONS Fig. 1 shows the main sec