Modern steering systems: Convenience, safety and energy efficiency

A review of the current state of development of modern steering systems, electric steering systems and Steer-by-Wire systems.

As CEO Division Steering Gear, Siegfried Dejaco is, among other things, responsible for the development of steering gears in Thyssen-Krupp’s steering business. In this role, he is helping to shape the transition from hydraulic to electric steering systems. In addition to already available functions, further trends are emerging, including speed-dependent steering assistance or crosswind compensation. “Additional automated driving functions, convenience functions, including lane keeping assist, imbalance and road gradient compensation, or even individual steering force settings, are specifically called for. And automatic maneuvering functions for trucks will also become available, which will make it safer and faster for trucks to approach ramps.”

Avoiding malfunctions due to interactions

Today, we already have similar parking functions available in cars, where the on-board electronics are networked to the steering system. More and more electronics, sensors and actuators from other subsystems, such as brakes and shock absorbers, are interacting with the steering system. “Linking all this together is highly complex and one of the greatest challenges in modern vehicles,” explains Dejaco. Around 1,000 software developers at Thyssen-Krupp are working on developing safe steering systems.

However, the cost-benefit ratio always needs to be taken into account with all the technical possibilities available. Purely electric steering is hardly more expensive than electrohydraulic steering for cars when you consider the overall package of steering functions, including the servo pumps for the steering hydraulics. “But this is primarily due to the high volumes in the automotive industry. At the start, electric steering was almost twice as expensive,” explains Dejaco. Electromechanical steering systems are currently used in around 70 percent of all cars. We still tend to use electrohydraulic or purely hydraulic systems in commercial vehicles with high rack-and-pinion forces.

ZF is working on the steering revolution. Photo: ZF

Steering revolution

But that will change. In 2018, ZF presented the ReAX EPS, the prototype of a purely electric steering system for commercial vehicles; since then, nothing more has been heard of the project. However, behind the scenes, ZF continued to work on the “steering revolution,” as Dan Williams explains. “We are still in development, but will be launching electric steering very soon. Initially, this will only be in certain series, not across the board.” Williams is Director of Advanced Driver Assist Systems (ADAS) and Autonomy Commercial Vehicle Technology at ZF in the USA. Together with his team, he is developing driver assistance functions connected to the steering system. An electric steering system is of real interest particularly in view of the even stricter CO2 limits coming in future. Electric steering offers major potential fuel savings, even if the powerful electric motor of the steering system is an electrical consumer that might necessitate changes to the vehicle’s electrical system. However, the 48-volt on-board power supplies mean that the requirements are already in place for its use in newer and future vehicles.

Meanwhile, Dan Williams’ team continues to work on driver assistance systems that interact with the steering system. “Above a certain level of technical detail, it may be enough to just add a sensor to enable a new function,” Williams says, citing an example. Adding a side short-range sensor to an existing lane departure warning system would enable a lane change function to be implemented relatively easily. This is already operating in cars, but, according to the ZF expert: “You can’t just adopt technology from cars. Commercial vehicles have different dimensions and a completely different dynamic. We need to develop this from scratch.”

Production process at Thyssen-Krupp’s Eschen plant. Photo: Thyssen-Krupp

ZF cooperation with Locomation

A few weeks ago, ZF in the USA announced a collaboration with Locomation, a start-up that develops autonomous driving functions for commercial vehicles. The companies will work together to develop and test the ZF Level-4-capable ReAX electro­hydraulic steering system under real driving conditions. Locomation is continuing to develop the platooning principle, unlike in Germany where several truck OEMs are withdrawing from platooning for now. Platooning is where the second vehicle is designed to follow the first vehicle autonomously. Locomation plans to be using its first product line, Autonomous Relay Convoy, by the end of 2022. It already has contracts with two customers for a total of 2,120 trucks to be equipped with the system.

Siegfried Dejaco of Thyssen-Krupp is not aware of any increased interest in platooning in Germany. However, he has seen a marked trend towards Steer-by-Wire (SbW) systems in the car sector, at least as an option or for niche segments. In SbW steering, the steering commands are solely electronically detected and transmitted by a cable to the actuator. SbW steering systems are already in series production today, where the steering wheel is still present but merely as a redundant component. “It means that the entire front of a car can be developed more cost-effectively. Simpler packaging and more modern interior design become possible, and crash safety is increased,” explains Dejaco, summarizing the benefits.