BELIEVE IN HUMAN SENSITIVITY AND WORK TENACIOUSLY. THE ANSWER LIES IN THE FIELD.

As a result, all the magazine staff members noticed a clear reduction in noise and vibration, and also felt an improvement in ride comfort and steering stability. It was as if we had switched to a higher-class vehicle.
How can such a simple part make a huge difference? When asked why, the development team explained that very slight deformation of less than 1 mm is generated in the body of typical moving passenger cars due to the vibration. While suppressing the vehicle body deformation, the damping force of the PD quickly reduces and minimizes the vibration, eventually contributing not just to improving the ride comfort, but also to enhancing the tire grip feel due to the stabilized fluctuation. This also leads to excellent steering stability.

At that time, while working on the development of REAS, the development team, including HARADA and SATOU, who were in charge of the development and testing of REAS, felt that there might be a problem with the body performance of the commercially available cars provided by automakers. In general, to improve vehicle body performance, enhancing the rigidity was considered the standard approach. Thus, the development team was initially focusing on increasing the rigidity of vehicle bodies. However, Harada says, “When we installed a tower bar and patch to the vehicle body to increase rigidity, the vehicle at its cornering limit either slipped and slid or caused repulsion due to the accumulated deformation energy. This may have been acceptable as a racing car, but we were developing for passenger cars. Simply increasing rigidity did not result in a car that was comfortable to drive.”
Then, the development team came up with a hypothesis that it would be better to slowly rather than rapidly release the energy, and they continued testing. But as Harada says, “At that time, as we couldn’t even carry out advanced simulations, we just tried every approach we could think of,” the team had to keep searching for a solution. At some point, a member of development team back then came up with a great idea: “Wouldn’t it be better if we let the energy escape somewhere? What if we give the vehicle body some viscosity along with rigidity?” Then, they started to shift focus from rigidity to viscosity.
Based on this inspiration, the team created a viscoelastic rubber part sandwiched between metal plates, and it perfectly worked as intended. When they drove the vehicle with this new part installed, vibration quickly converged and a smooth ride was obtained even when the vehicle was pushed to the limit.

After further testing, however, another problem with the durability and stability of the rubber emerged. Again, another great idea hit the development team: “What if we add a shock absorber?” and they made a prototype. They initially fitted a single-tube shock absorber for four-wheeled vehicles with some adjustment, but Satou says, “Although the damping characteristics were good, the pressure of the high-pressure gas sealed inside the tube acted on the extension side and pushed the vehicle body, which eventually had a negative impact on both ride comfort and controllability.”
The development team determined that the technical key was to have only the damping force act on the vehicle body without applying pressure on it. By incorporating a rebound spring and balancing the spring force with the reaction force of the high-pressure nitrogen gas to neutralize the piston valve, they achieved eliminating the pressure on the vehicle body. Since damping force responds to minute displacements of the vehicle body, an ultra-low speed piston valve was developed that achieved minute movements with a stroke (displacement) on the order of µm (1/1000 mm), just less than 1 mm. It was generally difficult to control the ultra-low speed range with hydraulic pressure, but the development team realized it through a high-precision mechanism that reduced leakage. This is an important part of the PD.
Furthermore, they started to see some possibility of practical applications of the PD by using existing shock absorbers with appropriate modifications. Another major feature of the PD is that it is a highly cost-effective product.
The team also thoroughly reviewed the location for mounting the damper. Not only did they install the damper on the suspension towers, but also, as Harada says, the team tried everything, such as mounting the damper on the top part of the windshield of an open-top car, under the seat of a sedan, and installing as many as eight dampers in a car. He adds, “as a result of a considerable number of tests on every non-moving part of the body of various types of vehicles, we were able to obtain a consistent effect no matter where the damper was mounted.” In 2000, the development team applied for a patent on the PD. The PD was unveiled as the world’s first vehicle body technology in 2001, and it was finally adopted as a mass-produced product in April 2004.

As a result of their effort, several major automobile manufacturers are now using the PD. This is just because the effect of the PD is perceivable. The development team gradually gained trust by communicating with various people including employees of automobile manufacturers, repeating experiments, and sometimes explaining the effect to them using a handmade experience kit.

Of course, this PD is also adapted for use in motorcycles. In 2011, it was released as a genuine optional part for the TMAX. Currently, Y’S GEAR, one of Yamaha’s group companies, is expanding the range of PD-mountable models as a genuine accessory part. It also started supplying the PD to aftermarket parts manufacturers so that the PD can be fitted to other manufacturers’ motorcycles.
In 2024, a new PD with an aluminum body was also released. “It was originally designed for motorcycles, but repeated testing with an aluminum body eventually resulted in improvement in ride comfort. I was happy to see the PD being adopted for sport type motorcycles such as the XSR900, which places great importance on its maneuverability,” says Iikura with high expectation that the PD will also be used for a wide range of motorcycles.
The design of the new PD including its bracket for motorcycles was entrusted to GK Dynamics. Looking ahead to further sales expansion, this company is currently working on colorful PDs using anodized aluminum and paying extra attention to the coloring method.