|Nexteer’s eccentric rack bearing reduces EPS systems’ noise and friction, important factors in a vehicle’s perceived quality. Click to enlarge.|
Electric power steering specialist Nexteer Automotive has developed a polyamide eccentric rack bearing that has superior NVH (noise, vibration and harshness) performance compared to conventional yoke-style bearings. It will help vehicle manufacturers improve the feel and noise of electric power steering (EPS) systems in vehicles of all sizes.
The need to cut CO2 is making electric power steering a key technology. According to Nexteer, replacing hydraulic steering with an on-demand electrically powered system can reduce a vehicle’s CO2 emissions by 5-6 g/km. The technology can contribute significantly to an automaker’s CO2 reduction targets for 2015 when the European Commission is due to levy steep penalties.
However, as manufacturers improve their vehicles’ efficiency they must also maintain excellent steering feel. Steering friction is a key factor in this, determining the purity of the feedback. A system with lower friction makes the drive feel more assured, communicating what’s happening at the contact patch to the driver’s fingertips and allowing them to place the car on the road more precisely.
Controlling lash, the play between mating components, in EPS systems is a significant part of our advanced development work. A balance between tight tolerances and low friction is what gives steering systems a feeling of directness. The new bearing’s reduced friction ensures that feel is not lost in the system; it also noticeably improves steering noise. As vehicle manufacturers create more premium models for new market segments and reduce vehicle weights, it will help to ensure the perceived quality of vehicles continues to meet customers’ expectations for their brand.
The bearing is the result of our close cooperation with scientists at materials specialists that produced a premium polyamide grade that displays excellent dimensional properties across all operating temperatures. It then underwent countless painstaking iterations to produce a mechanical design that is both simple and robust. It has to absorb shocks and be insensitive to moisture.
—Paul Poirel, Nexteer’s chief product engineer, Europe
Nexteer’s solution eliminates traditional yoke-style bearings that use a spring-loaded bushing to protect against lash, but which can resonate, creating rattles and other NVH problems. Nexteer’s polyamide bearing makes the steering system quieter, more durable and easier to package. Reducing the friction also makes it quicker and easier to fine-tune the system to suit customers’ requirements.
Nexteer is the only Tier One supplier focused entirely on the development of electric power steering systems. It has the industry’s broadest EPS portfolio, offering systems that can benefit every class of passenger vehicle from city cars to luxury limousines and SUVs.
Nexteer is receiving considerable interest in the development. Our eccentric rack bearing recently entered production in the EPS system for the premium B-segment Citroën DS3. The eccentric rack bearing is compatible with all our EPS systems that are based on a rack and pinion gear, whether it’s single-pinion, dual-pinion or belt-drive. We expect other applications to follow.
—Laurent Bresson, Nexteer Automotive’s Executive Director, Europe
Nexteer recently invested more than €40 million (US$52 million) to upgrade its state-of-the-art factory in Poland as part of its preparations for EPS contracts with PSA Peugeot Citroën. It supplies the Citroën C3 and DS3, benchmark vehicles in their class.