Kistler RoaDyn WFT approved for microcar road testing in Japan

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Thanks to a new approval from the Japanese government, Kistler’s RoaDyn S635, a six-component wheel force transducer (WFT), can now be used for testing on the country’s roads.

According to Kistler, the system passed a comprehensive series of tests to prove compliance with the local JWL (Japan Light Wheel Alloy) standard, meaning it can now be used for tests in local road traffic on microcars from Japanese manufacturers.

The WFTs are used for test driving on public roads and test tracks, off-road testing, and also on vehicle test benches. They detect the load applied to the wheel by connecting a series of load cells to the wheel rim and hub, with the help of a vehicle-specific adapter. The signals are amplified directly in the load cells, and then filtered, digitized and coded by the hub electronics.

Next, the data is transmitted using a telemetry system, via a rotor/stator pair mounted on the inner side of the wheel (rotor) and wheel suspension (stator); this is followed by processing with the onboard electronics, and output to a data acquisition device.

With the RoaDyn S635, the telemetry system is located on the inner side of the wheel to minimize projection over the wheel contour. This allows the WFT to be used on public roads. All structural parts and wheel rims are designed and manufactured by Kistler.

The JWL norm was introduced by the Japanese Ministry of Land, Infrastructure, Transport and Tourism as a standard to improve the safety of light alloy wheels. Use on public roads is permitted only if the requirements set by this standard are met. To comply with the JWL standard, the RoaDyn S635 from Kistler had to undergo three extensive tests. After successfully meeting the criteria, the six-component WFT from Kistler was granted JWL certification.

The first stage of the approval process was a rotary bending test, focusing on the rotational loads and moments that act on the wheel during driving. A clamping device on the rim flange was used to clamp the wheel force transducer – comprising load cells, structural elements, and the aluminum rim – onto the test equipment. The transducer was then exposed to a rotary bending moment over the mounting surface of the wheel hub and 120,000 cycles were completed.

Next came a radial load endurance test, using a machine equipped with a drum: in this case, over 600,000 cycles were performed. The final hurdle was an impact test, where the wheel was placed on a mounting plate, fixed, and inclined by 13°. A free-falling weight was dropped onto the edge of the rim flange, and the wheel was then examined for cracks, deformations and air leaks. After each of the three tests, a dye penetrant inspection was carried out to check for cracks.

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Lawrence has been covering engineering subjects – with a focus on motorsport technology – since 2007 and has edited and contributed to a variety of international titles. Currently, he oversees Automotive Powertrain Technology International and Professional Motorsport World magazines as editor.

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