Continued from Toyota Intentionally Increases Damper Friction for 'Corolla Sport' (1)

By decreasing the speed of the change of the load applied to the right and left wheels at the time of turning the vehicle, it becomes easier for the driver to turn the vehicle as he or she wishes, Toyota said. Also, the company said, "The resistance of the steering wheel increases, improving steering feeling."

On the other hand, if the friction is simply increased, it affects ride comfort. So, Toyota enabled to reduce friction (in accordance with the "theory") to improve ride comfort when the vehicle is just traveling and not making a turn.

At the time of turning the vehicle, the lateral force applied from the road surface to the wheel is transmitted to the damper. Toyota and KYB newly developed parts that increases the friction on the piston sliding surface when the lateral force is applied and reduces the friction when the vehicle is running straight.

Specifically, Toyota and KYB developed (1) a bush to be wrapped around the piston and (2) oil to be put in the cylinder. When the lateral force is applied, friction increases between the bush and the sliding surface of the inner wall of the cylinder. For this purpose, they increased flatness by reducing fine irregularities on the surface of the bush made of Teflon resin.

A resin bush was newly developed for the piston.

With the improved flatness of the bush's surface, when the bush is pressed against the inner wall by the lateral force, its contact area increases, increasing friction. On the other hand, with the high flatness, friction becomes small when the lateral force is not being applied. The two companies made improvements to the method to form the bush.

The newly-developed oil is general mineral oil. But an additive was added so that friction increases when a force is applied. KYB found out the additive, and an oil maker produces the new oil. The viscosity of the oil is equivalent to that of an existing product. So, the damping force characteristics were not changed.

Original Japanese article