The steering is perhaps the most crucial connection between an M automobile and its driver. Benedikt Nussstein is responsible for the newly developed M Servotronic in the BMW M3 and M4. We spoke with him.
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 fitted with 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.
Benedikt Nussstein, responsible for the development of the new M Servotronic in the BMW M3 and BMW M4.
” The precise steering feel comes from the perfect interaction of the stiff chassis, axle kinematics, wheels, mount harmonisation, stabiliser and steering. ”
The most important components of the M Servotronic with Electro Power Steering.
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 (Fuel consumption in l/100 km (combined): 8.8 to 8.3 CO2 emissions in g/km (combined): 204 to 194) and the new BMW M4 Coupé (Fuel consumption in l/100 km (combined): 8.8 to 8.3 CO2 emissions in g/km (combined): 204 to 194) both have high-performance suspensions, which are consistently dimensioned for optimum vehicle dynamics. 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. 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.
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 didnt 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 DTM racing drivers although Bruno Spengler and Timo Glock are very impressed with the 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.
This 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 steerings 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.
Further information about the official fuel consumption and the official specific CO2 emissions for new passenger automobiles can be found in the 'New Passenger Vehicle Fuel Consumption and CO2 Emission Guidelines', which are available free of charge at all sales outlets, from Deutsche Automobil Treuhand GmbH (DAT), Hellmuth-Hirth-Str. 1, 73760 Ostfildern, Germany, or under http://www.dat.de/en/offers/publications/guideline-for-fuel-consumption.html. The figures are not based on an individual vehicle and do not constitute part of the product offer; they are provided solely for the purposes of comparison between different vehicle types. CO2 emissions caused by the production and provision of fuel or other energy sources are not taken into account in the determination of CO2 emissions pursuant to Directive 1999/94/EC.
All vehicles, equipment, combination possibilities and varieties shown here are examples and can differ in your country. In no way do they constitute a binding offer by the BMW M GmbH. Visit your local BMW website or see your authorised BMW M Retailer for accurate details on the offers in your country.
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