INSIDE M xDRIVE.

An interview with Bernd Jacob and Jörg Weidinger about the new BMW M5 with M xDrive.

INSIDE M xDRIVE.

An interview with Bernd Jacob and Jörg Weidinger about the new BMW M5 with M xDrive.

INSIDE M xDRIVE.An interview with Bernd Jacob and Jörg Weidinger about the new BMW M5 with M xDrive.

The passionate and successful motorsports enthusiast Jörg Weidinger closely oversaw the development of the driving dynamic characteristics of the M xDrive. Bernard Jacob was also considerably involved in the technology of M xDrive. In an interview, both go into greater detail about the nature of the M xDrive and the performance potential of the new BMW M5 (Fuel consumption in l/100 km (combined): 10,5; CO2 emissions in g/km (combined): 241).

Jörg Weidinger.

Bernd Jacob.

The new BMW M5 is coming out with the new all-wheel drive system BMW M xDrive. What is the difference in hardware between xDrive and M xDrive?
Bernd Jacob: The xDrive hardware is the same as in M xDrive. For example, the transfer case which distributes the total torque coming from the engine and the transmission to the front and rear axles. However, the drivetrain has been reinforced in terms of stiffness and strength.
 

Jörg Weidinger: In the new BMW M5, this technology is combined with the genes of an M Automobile: the Active M Differential, special kinematics, different track widths, the characteristic M suspension and damper set-up, larger rim widths and special high-performance sports tyres with more grip. This creates an overall system with a whole range of new possibilities.


Bernd Jacob: A key advantage of M xDrive also lies in the fact that all systems relevant to driving dynamics are controlled through a single source – the central driving dynamics management system which operates as the overriding intelligence. Central driving dynamics management is the collection point for a four-digit figure of all the relevant sensor data and the parameters calculated from it, including accelerator pedal position, steering angle, road speed, slip at the front and rear axle, longitudinal and transverse acceleration, friction coefficient, yaw rate, etc. – so it’s a lot of information. This has to be analysed so as to establish the vehicle’s current situation. One simple example is assessing whether the vehicle is currently in oversteering or understeering mode. A comparison with the target response of the vehicle is used to activate the so-called actuators. In the new BMW M5 these particularly include the Active M Differential and the transfer case in the all-wheel drive system.

Why is this central control system so important in a sports car such as the BMW M5?
Bernd Jacob: If you have several independently operating actuators, the driving situation would be individually assessed by each separate control software – and it would only be natural for differing results to emerge if you have different instruments carrying out the assessment. In an extreme case you might even have actuators working against each other. For this reason, the BMW M5 transfer case and Active M Differential are deliberately controlled by a single overriding function. So in M xDrive we have a central driving dynamics management system which defines how the vehicle is intended to respond overall based on what the driver wants.

 

That sounds very complex.

Bernd Jacob: Yes, the development of this control logic is the real secret behind M xDrive. 

 

 

All the driving dynamic relevant systems can be controlled from one source.
Bernd Jacob

How does it feel to drive M xDrive as compared to other all-wheel drive systems?
Jörg Weidinger: Traditionally BMW M comes from standard drive - rear-wheel drive. Our development goal was to clearly retain the character of standard drive but to combine this with the traction response of all-wheel drive. So it’s still possible to “steer the M5 with the accelerator pedal”. This is not necessarily drifting, it’s really about predictability. The idea is that the driver should always be able to clearly feel and control the rear axle.
Many all-wheel drive cars that I know respond indifferently in the threshold range – and sometimes switch surprisingly from oversteering to understeering and back again, which doesn’t inspire a lot of trust in the vehicle. By contrast, our aim is to ensure a clear driving response so that the driver always knows how the M5 is going to react. This is why in some cases we might even do without that last little bit of traction if the price to pay would be an indifferent response. An M Automobile – whether with or without M xDrive – must always respond authentically and predictably into the threshold range.

What are the benefits of M xDrive in the new BMW M5 as compared to rear-wheel drive?
Jörg Weidinger: M xDrive fundamentally offers much higher traction potential. This applies particularly on road surfaces with a low friction coefficient of course. But it also applies on dry roads and race tracks – so as to put the maximum available power from the spontaneous new M TwinPower Turbo V8 engine onto the road in optimum fashion, especially in low gears.
What is more, M xDrive gives the new BMW M5 an advantage you wouldn't initially expect: in the new BMW M5 we’ve been able to achieve a more agile and direct set-up in the lower speed ranges in terms of the mechanical suspension while still providing greater stability at high speeds.
A car with an agile set-up with standard drive and engine performance figures in the 600 hp range can sometimes be a challenge in the threshold range at high speeds, especially if you then have bumps to cope which have the effect of taking the load off the powered rear wheels – as happens again and again on the Nordschleife, for example. Experienced drivers have to react fast in this type of situation. The conflicting aims here are easier to resolve with M xDrive. In the upper speed range, torque is sometimes shifted to the front axle in the new BMW M5 in the threshold range, so the vehicle achieves a higher level of stability.

Can you explain M xDrive with some concrete examples?
Jörg Weidinger: When setting off or accelerating along the straight, all that counts is traction. So here the torque is distributed in optimum fashion between the front and rear axle.
But now let’s say we approach a bend. In the initial braking and steering phase leading up to the turning point we don’t need a powered front axle. Up until that point we generally drive exactly as we would with standard drive. M xDrive doesn't bring in the front axle until we start to accelerate out of the opening bend, when we can transfer longitudinal forces without understeering due to the decreasing transverse acceleration. This occurs gradually, so it’s possible to exit the bend with a slight drift as one would expect of an M automobile. As compared to the predecessor model, the whole thing feels as if we were being catapulted out of the bend. When I go full throttle in second gear and accelerate fully out of the bend in a slight drift – with minimum counter-steering and without having to take my foot off the accelerator again – the experience is truly impressive.


Bernd Jacob: Incidentally, working on this was a nice example of how important it is for the very agile M development team to be able to provide new functions when driving tests show this to be necessary.

Our development aim was to clearly keep the feel of the standard drive, but to combine it with the traction advantages of an all-wheel drive.
Jörg Weidinger

Tell us more.
Jörg Weidinger: As I just described, it’s often better to wait until the bend exit before shifting torque to the front axle. We initially started doing this when the fully depressed accelerator pedal indicated the driver’s desire for full torque. But depending on the bend, the car sometimes responded indifferently or by understeering – none of which we wanted.


Bernd Jacob: When we looked at it more closely we realised that it is not enough to assess the desired torque based on the position of the accelerator pedal. Instead we now use a torque that has been adjusted accordingly so as to achieve the desired effect in terms of driving dynamics. If I go full throttle, it’s not long before the full torque arrives at the rear axle. But when has the turbocharger built up full pressure, when has the transmission transferred everything? It wasn’t until we’d taken all this into account that we arrived at a satisfactory function.


How can M xDrive be adapted to the given situation?
Bernd Jacob: The driver has five different configurations available which are derived from the combinations of two DSC modes (DSC on, MDM) and the three M xDrive modes in DSC off (4WD, 4WD Sport, 2WD). In this way, the new BMW M5 can be perfectly adapted to the driver’s needs and preferences.

In which configuration is the new BMW M5 fastest on the race track?
Jörg Weidinger: Based on our tests on various race tracks, this will always be an all-wheel mode without doubt – so in conjunction with deactivated DSC either 4WD or 4WD Sport, depending on the character of the race track.
In terms of the 4WD mode set-up, the focus was on maximum performance on wet or slippery tracks and generally speaking on extremely tight, winding tracks requiring a lot of traction. By contrast, 4WD Sport was set up and optimised taking the example of a completely dry race track. Incidentally: we assume that the new BMW M5 is able to outdo its predecessor’s lap times even in 2WD mode.


Mr. Jacob, Mr. Weidinger, thank you very much for the interview.

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.