On January 26th, Toyota Motor Corporation announced that the development catch-phrase for the new Alphard and Vellfire is ‘large-space luxury saloon’. In order to achieve a high-quality riding performance and an excellent running stability to compare favorably with a luxury sedan, they used the double wishbone suspension referred to as the newly developed ‘trailing wishbone’ in the rear.
It is common for many minivans to use multi-links and axles in the rear when it comes to widening the interior space. The Nissan Elgrand uses multi-link and the Honda Odyssey uses axle (FF vehicle); both are large minivans.
Kenichi Yoshioka, development chief in Toyota’s product planning head office, was interviewed regarding the reason for the use of the disadvantageous double wishbone suspension despite the number of other parts available for creating a large indoor space.
“We decided to use it to achieve both riding comfort and driving stability suitable for a luxury saloon. Although it is possible to improve the riding comfort with the conventional torsion beam, its lateral force would absolutely be weakened; it would be a necessary sacrifice for such an improvement. Meanwhile, the independent suspension gives it an advantage when we talk of strength, which in turn also strengthens the lateral force.” (Yoshioka).
Specifically, what do we mean by a strong lateral force? According to Yoshioka, they can improve the line traceability to reduce the fear when driving with a stronger lateral force.
“Upon receiving the lateral force, the suspension has been established to set into toe-in angle to perform an understeer. After all, the lateral force will provide a slight feel of oversteer were we to use a torsion beam suspension. Oversteering may create an image of fear of the vehicle spinning out of control.” (Yoshioka).
Yoshioka said at the presentation that they are focused on achieving a flat floor in the development. They can only imagine the difficulty of confining the complicated structure under the flat floor. Yoshioka said, “We adjusted it by 1mm and we were able to fit it by distributing each of the three arms that receives lateral force from the trailing arm. We provided a storage space below the three rows and we have created three rows of sliding seats.”
(Translated by Natassia Jeronne D. Martinez)