Although autonomous vehicles (AVs) are on the horizon, steering wheels will be fitted as standard to new cars for a while yet. Continuing just-auto/QUBE's series of interviews with global automotive component suppliers, we spoke to Thilo Bitzer, Senior Vice President, Steering Engineering, ZF Active and Passive Safety Division, about steering systems for AVs as well as active front steering and dual-pinion electric power steering systems.
In terms of the autonomous vehicle, in what ways will it impact the steering system?
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The global race to Automated Driving (AD) that we are witnessing is one of the key influencing factors in steering development today.
The global race to Automated Driving (AD) that we are witnessing is also one of the key influencing factors in steering development today. This is because the steering system is the key actuator for both driver-assisted and automated vehicle lateral control. Specifically, AD is leading to steering product roadmaps for systems to support requirements of the various levels of automation (as defined by the SAE) and their associated Use Cases.
One of the biggest immediate impacts of AD (together with safety trends) is the development and introduction of high availability electronics architectures (with redundant, fault-tolerant and low failure rate designs), as well as enhanced crash capabilities in the steering mechanics.
The fully autonomous vehicle will also, by definition, require some form of steer-by-wire system and in the steps towards full autonomy, we will see novel steering HMI concepts integrated into new forms of cockpit design as well as a proliferation of AD functions and features actuated by the steering system.
Steer-by-wire systems have also been talked about for years. What's your view on its prospects?
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By GlobalDataIn ZF we believe it's a very exciting time to be working in the automotive sector because there are many such technologies which, having been talked about for years, are now beginning to become a reality. These include electric powertrains, automated driving, V2x connectivity and of course steer-by-wire (among many others). Limited authority RWS steer-by-wire systems (including ZF's AKC® system) are already relatively well-established and the market is growing extremely rapidly.
The future outlook for full authority FWS steer-by-wire depends largely on the success of AD.
On the other hand, full authority FWS steer-by-wire is less mature, having entered the market only in the last 3-4 years and with quite limited market penetration to date. ZF believes that the future outlook for full authority FWS steer-by-wire depends largely on the success of AD. Level 5 AD demands some form of steer-by-wire steering system by definition, since there is no human driver to turn the wheel. However, there is also likely to be a percentage of Level 4 and even Level 3 vehicles that will adopt steer-by-wire solutions to avoid automatically rotating steering wheels in AD mode.
AFS is said to make steering more comfortable and safer. Yet do you think that such steering technology and associated systems will become a necessity rather than a luxury?
To date, AFS has seen limited market penetration largely due to its underlying cost and overall value proposition.
Active Front Steer (AFS, or mechanical angle overlay) has historically been used primarily to provide an overall steering ratio that varies with vehicle speed. By this means, the steering system can make low speed parking manoeuvres more comfortable by requiring fewer turns of the steering wheel, while simultaneously improving understeer and oversteer characteristics through an increased steering ratio at higher vehicle speeds. To date, the technology has seen limited market penetration largely due to its underlying cost and overall value proposition.
Going forward, AFS is seemingly another steering technology whose future outlook could be largely linked to the AD megatrend. Automated driving modes typically require the steering system to servo-control to a steering angle demand in order to track the vehicle to a desired trajectory. This functionality can be achieved with a traditional EPS system alone, but the side-effect is motion of the steering wheel caused by the AD system and not the human driver. With increasing functionality and automation levels, this steering wheel motion may become intrusive or even considered a safety concern.
AFS provides one mechanism to reduce or even eliminate steering wheel motion while moving the road wheels. On the other hand, some steering wheel motion in vehicles with AD features is already accepted today. In addition, steer-by-wire systems can deliver all the functionality of AFS (and more), and as the AD megatrend drives more and more capability and functionality into EPS systems, both the cost and conceptual gaps to full steer-by-wire are diminished. Therefore, it is unlikely that AFS will ever become an absolute necessity in the future.
EPS has evolved through a number of technology generations. What could OEMs expect from the next generation? And will motorists notice the difference?
From an OEM perspective, one of the fundamental developments that the next generation of EPS steering systems can be expected to incorporate will be increased fault tolerance and orders of magnitude reduction in the statistical probability of loss of assist in the event of a fault.
This improvement in system availability will be as great (if not greater) than that offered by the current generation of EPS steering systems over traditional HPS. Even when the system does experience a component failure and the dashboard MIL has to be illuminated, the EPS will in virtually every case, be able to continue to provide assistance to the driver (or AD system actuation) – albeit at a reduced level in some circumstances.
Next generation EPS systems will also provide greater assist levels, enhanced steering feel, improved NVH characteristics, support for high-speed data communication networks, electro-magnetic immunity levels suitable for operation in EVs and hardware and software infrastructures to support AD feature actuation.
Perhaps the most noticeable change for the motorist will be the increasing array of both ADAS and AD features that the steering system will support – and which will increasingly be upgraded and updated on-demand and over the air.
I guess EPS systems are pushing hydraulic steering-assist systems off the road. How do you see the hydraulic steering sector evolving over the next few years?
EPS represents around 80 percent of the light vehicle steering system market. So yes, it is clearly the dominant technology for the sector today. However, the residual HPS market looks remarkably resilient and although we do expect to some further decline in market share, at least over the next 4-5 years or so we do not foresee a seismic shift from the overall picture as it currently stands.
What is the appetite for EPS in some newer markets such as India and China? How do you see this application being used in emerging markets?
ZF has been selling steering systems for light vehicle applications into China for more than 10 years. These sales are now almost exclusively EPS. In our experience, the market is highly dynamic and maturing rapidly, with the time lag of technical requirements between EU, NA and China virtually gone. Therefore, the appetite for EPS in China is second to none from our perspective.
The EPS market in India is somewhat different. It is smaller now than the China market was 10 years ago and roughly half of the systems are deployed on applications with simple, low-power, limited capability technological requirements. However, the organic growth rate in India is now roughly twice that of China, and the market for more mainstream EPS technologies could double in volume if only three key OEMs made the technical leap. Therefore, the appetite for EPS in India could be described as lagging currently, but could also undergo a significant shift in the medium term.
We believe that dual-pinion EPS systems are used for upper-midsize cars and small SUVs. Do you see any strategic shifts in terms of greater or less use of single or dual pinion steering systems?
We see dual-pinion EPS consolidating and growing in C and D-segment vehicles because these are seemingly well matched to the price point and technical requirements of these segments.
Within ZF, we see dual-pinion EPS consolidating and growing in C and D-segment vehicles because these are seemingly well matched to the price point and technical requirements of these segments. We believe that growth in dual-pinion deployment is linked to an increasing global popularity of small and mid-sized SUVs, particularly in China. Single-pinion EPS is more suited to smaller B-segment vehicles with specific packaging requirements where it overlaps, but generally has not been able to compete with column-drive EPS on the grounds of cost.
