As the electric/hybrid vehicle market starts to gain momentum worldwide, many suppliers are giving sound advice to OEMs—literally. NVH levels of electric vehicles will be very different from those powered by internal-combustion engines (ICEs), and components that have moving parts may be heard within the cabin.
The technology that this trend is engendering, however, will also benefit ICE vehicles. Power steering is an example. While electric power steering (EPS) systems may not be particularly noisy in operation, they can present an NVH challenge, as column-mounted architectures are generally regarded as being the most cost beneficial and are commonly used across the car segment span.
To help overcome this issue, Nexteer Automotive has developed a lightweight, flexible plastic coupling as an alternative to a steel type. It will be used on the forthcoming Citroën DS3.
Nexteer is a global business focusing solely on electric and hydraulic steering systems, steering columns, and driveline products for OEMs. Improving NVH performance is an important part of its R&D programs.
Column-mounted EPS systems commonly position the electric motor and associated control electronics inside the passenger compartment away from the hostile under-hood environment, which would demand expensive seals for such systems.
Rigid steel couplings that many suppliers use in connection with EPS can act as noise transmitters to the interior, and the widespread use of low-profile, low-rolling-resistance tires can accentuate the situation.
The Nexteer flexible thermoplastic coupling significantly reduces noise transmission and has the added bonus of being lighter weight, explained Kevin Ross, its co-inventor and the Global Engineering Manager of Nexteer Automotive. He believes Nexteer has created the quietest column EPS on the market and that it will find further applications.
The design uses a system of flexible, ribbed pads that connect and transfer torque from one rotating shaft to another. Ross explained that the coupling stretches and compresses to give the required axial stroke while providing a fully compliant constant velocity (CV) joint.
The finished part is some 17% lighter than its steel equivalent and with 50% lower cost. Due to reduced friction, steering feel is also said to be improved.
The thermoplastic is a high-performance, high-temperature polyamide, with glass fiber reinforcement, said Paul Poirel, Nexteer Automotive’s Chief Product Engineer, Europe. “Our EPS technology features in benchmark vehicles such as the Fiat 500 Abarth and soon the Citroën DS3. We are looking forward to further applications as European manufacturers introduce more premium compact cars,” he said.
Nexteer manufactures single- and dual-pinion steering systems plus rack assistance systems for large cars and SUVs. It was a pioneer of EPS systems more than a decade ago; production has now topped 12 million units.