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      03-20-2014, 09:49 AM   #1
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Arrow BMW M3 / M4 M Servotronic EPS Steering: Deep Dive and Interview

BMW M3 / M4 M Servotronic EPS Steering: Deep Dive and Interview

The following comes courtesy of

Also see:
BMW M3 and BMW M4 Inside (part 1): The new M Servotronic.
BMW M3 and BMW M4 Inside (part 2): The Brake Systems.
BMW M3 and BMW M4 Inside (part 3): The new engine.
BMW M3 and BMW M4 Inside (part 4): Sound and Exhuast System.
BMW M3 and BMW M4 Inside (part 5): smartly light, rigid, precise.
BMW M3 and BMW M4 Inside (part 6): The new chassis.
BMW M3 and BMW M4 Inside (part 7): The Active M differential.

BMW M3 and BMW M4 Inside (Part 1): The new M Servotronic.
Interview with Benedikt Nussstein.


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Benedikt Nussstein is responsible for the development of the new M Servotronic for the BMW M3 and BMW M4.

Until now, the power steering employed in M automobiles was hydraulic servo-assisted, but both the new BMW M3 Sedan and the new BMW M4 Coupé are set to be the first M automobiles to be fitted with an electrical servo-assisted steering system. What are the reasons behind this development?

Benedikt Nussstein: The new M Servotronic with Electro Power Steering (EPS) weighs about 3.5 kg less than comparable systems with hydraulic servo-assisted steering, which is important when it comes to creating an optimum axle load distribution and in turn ensuring agile handling. The new steering saves approximately 0.3 litres of petrol per 100 km, because energy is only consumed when actually steering, while a hydraulic pump represents a constant drain on power. And by using EPS it is also possible to install the latest driver assistance systems.

Why was it decided to develop a fully new steering system for M automobiles rather than modify an existing one?

The new BMW M3 Sedan and the new BMW M4 Coupé both have high-performance suspensions, which are consistently dimensioned for optimum vehicle dynamics. The special axle kinematics and high degree of grip in the tyres result in high levels of steering rod power to the steering system. As a result, M axles are able to provide better response from the road surface to the steering wheel, and in turn to the driver.

The aim of the new development was to obtain extremely direct and spontaneous responsiveness – especially from the central rest position of the steering wheel. The yardstick here was the last generation of the BMW M3, and our goal was to improve on it.

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Toothed rack with i-Var gear ratios.

The car must respond well to the steering and the steering angle must be right – at both low and high speeds. The vehicle response must not be too sharp at very high speeds. Furthermore, we selected a variable toothed rack with new gear ratios.

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Steering rack with ball screw.

The aim was moreover to avoid any hardening of the steering when performing fast and sporty steering manoeuvres. To enable this, we have employed a larger than usual EPS motor.

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Ball screw with EPS power pack (EPS motor plus EPS controller). The ball screw transforms the rotational motion of the motor into a translational motion of the rack.

In several interviews, Mr Biermann, head of development for M automobiles, has heaped praise on the M Servotronic system used in the new BMW M3 Sedan and the new BMW M4 Coupé. What is it that justifies this evaluation, from your point of view?

EPS systems can often convey a somewhat synthetic feel, and this is precisely what we did not want. The driver of the BMW M3 or BMW M4 should have a good sense of the nature of the road surface. He wants to be able to feel when he is driving over a drain cover in the road or when the surface material changes. This steering is responsive enough to convey these impressions very clearly – when we began its development, I didn’t expect it to be able to do this to the extent it does.

Similarly, the driver is able to immediately feel any transitional responses in the steering, the moment he enters the marginal zone when the car begins to skid due to over or understeering. This makes it possible to drive the car very precisely at its limit: not only by DRM racing drivers – although Bruno Spengler and Timo Glock are very impressed with the steering.

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Torsion bar with rack. The torsion bar measures the torque applied by the driver and in turn controls the EPS motor. The angle is applied by the driver, while the power is provided in part by the EPS motor.

The axle itself has a great deal of potential and returns the steering to its central, zero position, for example, by mechanical means. This means that we can dispense almost entirely with additional functions such as active return motion in the software, which may create a synthetic steering sensation.

Our steering offers all the benefits of a hydraulically assisted system. Nothing has been lost but plenty has been gained.

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What has been gained?

Well we already spoke about the fundamental benefits of EPS.

A further advantage is that the steering can be tuned more precisely to reflect with other optimisations made in the context of the suspension. The precise steering feel is a result of the interplay between a rigid body, axle kinematics, tyres, bearing coordination, stabiliser, and the steering itself, among other factors. This explains why developers employed in suspension coordination at BMW M are so heavily involved in networking, why they need to talk so much about matters such as these. For instance, when the parameters of a stabiliser change in the course of a development process, we are able to perform optimum readjustment of the steering. That is something which is not so easily possible in this form with hydraulically assisted power steering.

What was the greatest challenge in developing this steering?

The biggest challenge was to ensure that the industrial production suited the EPS steering in the way in which we developed it. The steering has very good responsiveness as far as the road surface is concerned. However, this precision places great demands on the production process. It requires a very precisely produced steering system and, in turn, precisely turned out parts and components.

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The driver is able to choose from three different characteristic curves for the steering. Why did you decide to provide this capability?

Our customers have very different tastes. There are drivers who prefer light steering while others prefer to use more manual force. This is why we have included three steering mode settings: Comfort, Sport und Sport plus. Changing from one mode to another will not result in any functional differences and will not, for instance, cause any change in the quality of the steering’s responsiveness. We also have racing drivers in our department; they prefer to apply the Comfort mode curve – while the adaptive M suspension is set to Sport plus. It is really up to the driver to decide which choice best suits his personal preferences.

Mr Nussstein, thank you very much for talking to us.

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      03-20-2014, 10:29 AM   #2

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Thanks for posting, Jason. They've clearly put a lot of work into this new M EPS. I'm sure the doubters will remain until test drives are completed, but hopefully this quashes at least some of the fear.
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      03-20-2014, 12:35 PM   #3
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This is great info, thanks for posting!!! I have guarded optimism about the new ELS after reading this. It seems like an all-out effort to not only keep the benefits of the old system from an enthusiast's perspective, but to take the game to a whole new level. Cool that some of their test drivers preferred the "comfort" setting with the sport plus setting on the shocks when piloting a road course. If the steering lives up to what Nussstein says it will do, we will be privy to a pretty awesome car when we finally get our hands on one.
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      03-20-2014, 12:42 PM   #4
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Great info!!!!
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      03-20-2014, 12:44 PM   #5
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I honestly just can't wait to see reviews of this car so i can finally determine what i want after my M3
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      03-20-2014, 12:51 PM   #6
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Nice read. I'm looking forward to seeing how it really feels.
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      03-20-2014, 12:53 PM   #7
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Overall this sounds positive, I'm a bit concerned over the preference of comfort setting though. It corresponds with my preference of the current EPS system since the sportier settings feels terribly artificial and even more numb. Hopefully this is not the case here but instead it's the lesser fatigue during extended racing from a lighter steering that make them prefer this.
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      03-20-2014, 12:58 PM   #8
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I think the proof is in how the car drives. Just because some implementations of EPS were bad does not mean the system can't be done right. Next thing to drop off the serpentine belt will be the AC compressor.
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      03-20-2014, 01:05 PM   #9
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I have very little doubt that they will get this one right. The fact that they developed a system form the bottom up on the f8x, and did not merely improve on the f3x EPS, is already a great start. However, my f30 steering with the newest software is miles better than it was when initially released. There is improvement and what appears to be constant tweaking on behalf of BMW engineers to get this system right.

I would caution future f8x owners here to not have their expectations too high. Initially it will have a different feel than the hydraulically assisted system, and may take some time getting used to. The good news is that they can always remedy most issues with a software tune. It may take some tweaking and fine tuning immediately after launch, but I have a lot of faith in them to get this as close as possible in the M cars.
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      03-20-2014, 01:08 PM   #10
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Excellent article. This puts to bed much of my worry.
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      03-20-2014, 01:33 PM   #11
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Wow! Great thread.
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      03-20-2014, 02:06 PM   #12
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There's a whole lot of literature talking about the ins and outs, but when will the press get a chance to discuss the end product? I've never seen a car get so much hype; at some point you get the vibe that they're spinning it off as damage control marketing. I'd love to hear about what matters from a third party tester: how it drives. That's all that really matters in the end.
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      03-20-2014, 02:07 PM   #13
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+1000 for this thread, thanks Jason
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      03-20-2014, 02:12 PM   #14
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Thank you, can't wait to feel it myself!!
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      03-20-2014, 02:14 PM   #15
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Very interesting article. It seems the new f8x M cars will provide the feel that most enthusiasts here are looking for in a M car.

I will say, after test driving a M235i and coming from my 135i, I had no problems with the steering system. In Sport+ it was precise and had that heaviness feeling I was used to at higher speeds. It seems that this M EPS will be better than that yet, on top of that you can choose 3 different steering mode settings.

I am very positive that they got this right
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      03-20-2014, 02:16 PM   #16
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I'll just echo what others have said in that there is some good info in there. Thanks for posting, Jason!
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      03-20-2014, 02:20 PM   #17

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Good to hear them address the issue directly. Encouraging to hear things like the return to center will be mechanical. Shows that they really tried hard to emulate hydraulic power. This may be a clever implementation after all.
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      03-20-2014, 02:31 PM   #18
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      03-20-2014, 03:31 PM   #19

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Drove the M235i 6MT today for the first time. Great drive but dull steering - no life through it, very smoothed out. Considering how busy the ride was (as it's tuned to be), it was shocking how little steering feedback there was.

I'd still drive it everyday and love it, don't get me wrong, but good steering is the difference between dating someone with great looks and someone with great looks + personality.
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      03-20-2014, 03:40 PM   #20
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I'll wait for independent reviews rather than someone from BMW telling me how great it is. I mean what is he supposed to say?
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      03-20-2014, 04:15 PM   #21
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That information on steering is pure M Erotica

I love the ability to highly customize the steering feel versus the Suspension and all will have their favorites. I agree that this system will be as good and mostly far superior to any other steering systems found anywhere from the clear emphasis of establish a connection to the road. It's what I loved the most with my 06 330i sport.
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      03-20-2014, 04:24 PM   #22
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It is encouraging that BMW invested that much effort in the steering.

I will reserve final judgment to how good or bad the EPS is to when I get to drive the car this coming July.
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