INSIDE M xDRIVE.

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. 

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.

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.