The transformation of the commercial vehicle sector is in full swing, driven by two factors in particular: the need to reduce emissions, and the demand for e-mobility and automated driving. In both cases, one of the key technologies is all-electric steering, slated for series production in 2025, when Knorr-Bremse will install it in the fleet of a leading truck manufacturer. But how does Knorr-Bremse’s “Electric Power Steering” actually work? And what are its market prospects?
Anyone who has ever struggled to park an old VW Beetle knows just how useful power steering really is. Of course, those muscle-straining days are long behind us. And in much the same way as the VW Beetle gradually disappeared from our streets, the internal combustion (IC) engine will also decline and eventually vanish. Will power steering also disappear? Certainly not. But the steering systems in modern electric commercial vehicles are very different from those we have become used to in past decades. Conventional power steering is directly powered by the IC engine – and that is not an option for commercial e-vehicles.
The solution goes by the name of Electric Power Steering, or EPS for short. Knorr-Bremse is the first supplier in the commercial vehicle sector to bring this electric power steering system to market – and the market is looking forward to it! Behind this demand is the shift to e-mobility, with the EU’s Green Deal playing an especially important role in Europe. Compared with 2019 as the baseline, the European Commission recently proposed that mandatory carbon emission levels for all new heavy-duty commercial vehicles should be reduced by 45 percent by 2030, 65 percent by 2035, and an ambitious 90 percent by 2040.
EPS has real strengths when it comes to meeting carbon emission targets. Whenever the EU assesses the levels of pollutants emitted by commercial vehicles, EPS earns significantly more points than any other system.
Peter Heimbrock – Director Global Technical Sales Steering & Lead Location in Düsseldorf
EPS does not just help to reduce emissions indirectly, by acting as an enabling technology for e-mobility. It is also suitable for use in commercial vehicles powered by IC engines, where it systematically reduces fuel consumption.
Why is that? Peter Heimbrock, Director Global Technical Sales Steering & Lead Location in Düsseldorf, explains: “In a conventional commercial vehicle’s steering system, a separate hydraulic pump produces the energy that helps the driver steer. To provide a constant flow of hydraulic fluid through the steering system, this pump is permanently powered by the IC engine. The fluid is used to transfer the pressure that helps the driver move the steering wheel. But in Knorr-Bremse’s EPS, a built-in electric motor produces the necessary energy. While the e-motor also actuates a hydraulic transmission, the big difference – and the major advantage – of this approach is that the motor doesn’t have to maintain a permanent flow of oil through the system. The electric motor that powers the assisted steering is only activated when the driver moves the steering wheel, following the ‘power-on-demand’ principle. The rest of the time – when the truck is driving in a straight line along a highway, for example – EPS doesn’t use any energy at all, unlike the hydraulic pump in a conventional system.”
The resulting savings can be quantified. According to Knorr-Bremse’s tests, the level of fuel consumption accounted for by the steering system falls from 0.22 liters per 100 km when using a conventional hydraulic system down to just 0.06 liters per 100 km when using Knorr-Bremse’s EPS – a 73-percent drop in fuel consumption. Lawmakers are delighted. “EPS has real strengths when it comes to meeting carbon emission targets. Whenever the EU assesses the levels of pollutants emitted by commercial vehicles, EPS earns significantly more points than any other system,” continues Heimbrock, adding that: “Of course the energy saved by EPS also has a positive impact on electric vehicles, by extending their range.”
In terms of savings, Knorr-Bremse’s Electric Power Steering system has further benefits to offer: “Our EPS is a standalone solution,” says Peter Heimbrock. “It doesn’t need external components such as hydraulic pumps, hoses or oil reservoirs. So EPS fits into less space, and is easier to assemble and maintain.” For commercial vehicle manufacturers and operators, this means lower costs all round.
There are good reasons why Knorr-Bremse’s developers opted to integrate hydraulics into the EPS system when seeking to scale up the electric motor’s power to the levels required for assisted steering. “The alternative would have been a mechanical transmission. But building a durable steering transmission that isn’t prone to vibration or rattling is very challenging. And in any case, it wouldn’t be modular enough to fit into the available space,” explains Heimbrock.
The decision to opt for a hydraulic transmission was taken in 2021, after both concepts had been intensively evaluated and tested. This pre-development stage started back in 2017, led by the steering team at the Schwieberdingen facility with the support of teams in Düsseldorf and Budapest. And the decision in favor of hydraulics has turned out to be the right one: Following successful B-sample tests, and with new sample stages impending (including winter trials), the launch of series production is slated for 2025.
However advantageous the EPS steering system may be for e-mobility and fuel efficiency, it would be wrong to believe it has no other benefits. EPS also has a key role to play in support of another commercial vehicle industry trend: automated driving.
“With EPS, the steering can be controlled independently of the driver – by an active lane-keeping function, for example,” explains Peter Heimbrock. Of course this is already possible today, thanks to what is known as Torque Overlay Steering (TOS). Here, a steering system that normally relies exclusively on hydraulics is given additional assistance when required by an auxiliary system that electrically reinforces (“overlays”) the steering movement. “But EPS goes a step further, because it no longer relies on other, external systems for torque overlay. It can be directly controlled, while at the same time bringing all the emission-reducing benefits we’ve just been discussing,” adds Heimbrock. It goes without saying that EPS is also ready for the final big step forward in the evolution of automated driving: steer-by-wire technology.
In a steer-by-wire system, unlike the steering systems we still use today, the steering wheel is no longer mechanically connected to the steered axle via the steering column. Instead, the steering wheel electronically captures the driver’s steering movements and transmits them to the axle in the form of electronic signals. There, actuators – such as Knorr-Bremse’s EPS – perform the actual physical movement. “With this steering system, you don’t really need a steering wheel. Eventually the vehicle could be steered by algorithm, without involving the steering wheel at all.”
No more solid, mechanical link between steering wheel and steered axle? Just signals transmitted over wires? Anyone encountering this concept for the first time may well feel a little uneasy. What happens if the electronic control system malfunctions or fails? The driver no longer has any way to intervene!
To safely implement the steer-by-wire approach, a steering system must have emergency options – subsystems ready to leap into action if the main system should fail. In techspeak, this is known as redundancy.
Peter Heimbrock is reassuring on the subject: “Knorr-Bremse’s EPS provides all the necessary redundancy. There’s a redundant electric motor installed, as well as a redundant electronic control system – and both of them are duplicated in hardware and software, so there are two microcontrollers. One system can take over if the other one fails,” he confirms.
I’m certain that EPS will gain significant market share, and in the medium term, become the industry standard for large swathes of commercial vehicle applications.
Fabian Stambrau – Vice President Global Steering at Knorr-Bremse
Electric Power Steering supports and enables the two most important developments in the commercial vehicle industry: electrification and automated driving. This raises an interesting question – will it become the industry standard? To this Fabian Stambrau, Vice President Global Steering at Knorr-Bremse, gives an optimistic reply: “I’m certain that EPS will gain significant market share, and in the medium term, become the industry standard for large swathes of commercial vehicle applications. In certain areas, however, there’s no doubt it will still make sense to use conventional steering systems.” And when we ask the Head of the Global CoC for Commercial Vehicle Steering what other factors lie behind the system’s appeal, he is equally confident about Knorr-Bremse’s prospects. “As far as steer-by-wire is concerned, one of the things we’re currently exploring in a pre-development project is what redundancies will be required across the system as a whole – including the onboard electrical system – to safely deliver this technology in the field.” And what will this be based on? “EPS, of course.”