Electric 4WD Unit Represents a New Concept in Four-Wheel Drive
In January 2016, efforts to strengthen collaboration within the AISIN Group led to a major breakthrough when three companies—Aisin Seiki, Aisin AW (AW) and Aisin AI (AI)—jointly developed an electric 4WD unit. In contrast to conventional 4WDs used for extreme driving in mountainous regions and on rough roads, this electric 4WD unit was developed based on a new concept of providing safe and comfortable driving by activating when the vehicle starts to move forward in areas with heavy snowfall and cold weather and for low-speed driving on extreme grades.
The new electric 4WD unit has three main features. First, the motor and differential gear are installed in the same axial line, and a two-axis structure with a reduction gear has been adopted to realize a compact unit. Second, to completely eliminate drag resistance when operating with front-wheel drive, a rear-wheel drive induction motor with no permanent magnetic force was adopted to cut energy loss when operating using front-wheel drive. Third, we adopted a new structure that can reduce oil-stirring loss caused by the rotation of the gears and motor inside the unit. These features contributed contributed to the successful debut of the new-model E-Four Prius that pursues high fuel efficiency and comfort despite being a 4WD vehicle.
In undertaking the collaborative effort, Aisin Seiki handled the development project coordination and the housing that encases the unit, AW was responsible for the induction motor and AI handled the reduction gears.
Yuki Tojima of Aisin Seiki’s Powertrain Products Division, Powertrain Systems Development Department explains the efforts required during development to solve several difficult issues, noting, “We sought to ensure the safety of a 4WD vehicle operating on snow-covered roads and frozen road surfaces during winter while raising fuel efficiency and curbing costs during other seasons.”
Yoshihisa Yamamoto of AW’s Technology Division comments: “AW is well known as a manufacturer of automatic transmissions. Besides these products, however, we also develop and produce original hybrid transmissions, gears and motors. Our motor development and technological competencies played a huge role in the recent development of the electric 4WD unit.” Yuichi Fukuhara of the Technology Coordination Department of AI, which handled the reduction gears, adds, “I was confident we could contribute significantly by deploying our strong manual transmission development technologies, which are AI’s forte, together with our precision gear technologies that assure quiet driving.”
Three Companies Share Goals and Passion and Leverage Their Strengths
The three companies began joint-development efforts in March 2011. Reflecting back on that time, Yamamoto recalls: “A new technology center was completed at AW, which happens to be situated midway between the three companies. To undertake jointdevelopment projects, we set up a structure enabling engineers from all three companies to be permanently stationed at the center. With the establishment of this structure, along with focusing on technologies, we were able to proceed with development as we shared our goals and passion.”
This project skillfully blended the features and strengths of the technologies of the three companies and proceeded smoothly. “Although AW was able to fully leverage its strengths in motor development and production, AI’s manual transmission technologies and its unique ideas, which we ourselves lacked, in fact helped us immensely,” Yamamoto explains. “Induction motors represented an entirely new challenge for us and successfully developing a compact highperformance induction motor has instilled us with confidence.” Fukuhara notes, “In developing two-shaft parallel gears, we are currently using mass-produced parts and processing methods to reduce costs, and I’m also proud that we contributed to the realization of quietness and successful evaluation tests.”
“We were able to simultaneously proceed with the development of the entire unit and individual parts as well as undertake reviews and adjustments and this contributed to shortening development times and lowering costs,” Tojima proudly points out. “Even though all three companies had an abundance of unique attributes, I think it’s truly meaningful that we were able to undertake the project smoothly in a variety of areas utilizing the experiences gained from our collaboration to the present.”
Tojima adds: “We could operate and evaluate a test vehicle integrating the unit at Aisin Seiki’s proving ground in Toyokoro-cho, Hokkaido. This not only helped speed development but raised reliability and the degree of perfection.” As testimony to its high acclaim, the E-Four accounts for a large portion of the volume of orders for the new-model Prius in Hokkaido.
An Era of Full-Fledged Group Collaboration has Begun
“It was a real pleasure for engineers involved in this project to produce results that were far more satisfying than any hardships we encountered, which was made possible by mobilizing the unique attributes of the three companies,” Yamamoto recounts. “I think engineers themselves achieved growth not only by joining forces but also by competing against each other.” “This joint development also created more synergies than we had originally envisioned,” says Tojima, “such as broadening our knowledge in totally new fields.”
By combining the abilities of the three companies, there is no doubt we clearly produced results that exceeded the expectations of customers in such areas as compactness, weight savings, fuel efficiency, and costs. On top of this, the project served as a major springboard for further raising and vigorously deploying collaboration in the future. Undeniably, our achievement in this recent joint development sets the stage for the AISIN Group to compete in this field globally. The successful completion of the project, which focused on the trend toward electrification technologies in powertrains and on system products rather than separate components, will surely provide a major incentive for engineers who are currently strengthening competitiveness at the three companies and at other companies throughout the Group. Other Group development bases spanning regions across the world are also expected to proceed with the development of a number of products recognized by customers.
The electric 4WD unit has contributed to the creation of new appeal for the latest-model Prius. We will accelerate efforts to solidify collaboration within the AISIN Group and expect that further growth and development will be a symbol for the integration of technological strengths.