The next-generation platform of Subaru (Fuji Heavy Industries) was presented on March 7, 2016. It is called Subaru Global Platform, but what are its further details? Hereafter, it will be explained based on the presentation of Corporate Senior Vice President Tetsuo Onuki (Subaru Technology Headquarters Deputy General Manager), who is in charge mainly of technology-related announcements.
According to Onuki, the aim of this next-generation platform, which focuses on application and electric technology by 2025, is to enhance its dynamic material feel. The dynamic material feel doesn’t only refer to performances expressed in numerical value such as specifications and the like, but it is also expressed through its smooth and pleasant quality. It makes driving easy through the difference of the operability of its steering wheel and pedals, its response, the movement of the car, its sound and the like. It is difficult to express it in numbers and illustrations, like for example, when differentiating its 1/10-second movement towards a certain operation.
In Subaru, a new design has been added to a simulation model from the existing cars, and aside from that, the simulation model was also added with measurements and evaluations of sensors that measure the movement of each part at 1/1,000 milliseconds; actual on-road driving that swerves at 200 points; as well as test benches that were exclusively developed in order to achieve a quantified and visualized dynamic feel. They set forth direct driving, noise and vibration control, and pleasant ride quality as sensory indexes. “In aiming for this goal, we will actualize the development of cars that have the same price range with the existing cars, but have dynamic material feel, just like European cars,” said Onuki. And it is said that in order to achieve this, they improved its rigidity by 70 to 100% compared to the existing cars through this next-generation platform by raising the rigidity of the chassis, lowering its ground balance, and enhancing its suspension system.
For example, the rigidity of the following parts has been improved: the rigidity of its side-bending towards the front part is 90%; the rigidity of its front suspension is 70%, the rigidity of its body torsion is 70%, and the rigidity of its rear sub-room is now 100%. By increasing the rigidity of its chassis, there is only little possibility of the car to swerve when turning to another side or changing lanes, and it can turn easily as well as trace the target line as expected. The resonant frequency piled in the suspension and chassis were already eliminated, and it is already possible to control excess vibrations.
There are also several points with regards to the structure. In addition to spot welding, its full body also adopts structural adhesives, which is linked to its higher rigidity. The two frame structures that go through from the front side member of the auto body, floor, and up to its rear sub-frame are continuously connected. As for the existing Subaru cars, these frame structures turn perpendicularly as they arrive in the fuel tank, so it would seem like these frames were separated. They are making huge revisions from its A-pillar up to the side inner panel. This system has also been applied to the chassis of the Levorg, but in the next-generation platform, its combined parts are enhanced further. The revision of the inner panel part is commonly applied in race machines, but it is unusual for production-based cars.
As for its suspension system, the kingpin’s mass offset (the gap between the center part of the wheel and the suspension strut) was made smaller by 15% compared to the existing cars. Besides, through the revision of its upper mount and the shape of its tire house, the rigidity of its suspension mounting was also further enhanced. Through these improvements, the suspension system functions accordingly when the car enters the road. Even if the suspension movement is being considered and geometrically designed, it does not move according to its performance on actual driving if its body and installation area are distorted.
Its rear stabilizer links the left and right suspensions, restrains vibration, and controls the ground pressure in its left and right tires towards the vibrations that make the car body have the tendency to roll. Normally, by only connecting the suspension-linked parts, it gets fixed in the suspension body (strut & members), but at the rear part of the next-generation platform, it gets fixed in the chassis.
In the improvement of its handling stability and responsiveness, one of its points is its low balance. Its horizontally-opposed engine greatly contributes to its low balance, but it is said that with the next-generation platform, it was made lower by 5mm than the existing cars. Its power unit and rear differential have been made lower by 10mm as well. In addition, some parts were also made lower, such as 10mm in the front seats, and 20mm for the heel parts where the pedals are placed. Some of its road clearance would become non-secure when some parts aren’t made lower, but it can influence towards guaranteeing a good view (if the roof still has the same height).
The next-generation platform is not just about the improvement of its rigidity and running performance. As for their aim by 2025, Onuki said, “We will not only focus on the car types, autonomous driving, and electric technology, but we will also be focusing on improving safety performances by 2025.”
As for the improvement of its running stability and operability, it contributes to safety through danger avoidance and stable driving, but they are also thoroughly considering passenger and pedestrian protection during collision through the optimization of high-intensity materials such as the reinforcement of the structure frame, hot press, and the like. As for the passenger protection, systems that correspond with more complicated collision situations are being demanded globally. Furthermore, it is also necessary to consider various passengers, from infants to elderly passengers. This is also the same for pedestrian protection.
Subaru has already been conducting oblique crash tests. An oblique crash refers to the crashing of a car from a frontal direction in a slanting position. In the video of the crash test being shown in the presentation, the test model was thrown more than 10 meters backwards after being hit by a huge SUV, but even so, its cabin space remained intact.
(Translated by Claire Marie Sausora)