Porsche 911 Carrera, Braking stability 13 Photos Zoom

Technology: control electronics in sports cars: Physical education for ESP

Even for sports cars it has long been the case: without ESP control electronics, there is no more hunting for best times. Bosch is now taking it to the next level, which should help even the professionals to find that extra tenth of a second.sport autotakes a glimpse into the future.

The cold temperatures at this year's 24h race at the Nürburgring did little to cool the heated emotions: once again there we heated discussions regarding dynamics control systems, their pros and cons and with regard to a general ban. Disputes surrounding this topic also quickly arose with regard to street-legal sports cars, with many demanding the ability to deactivate the feature as an essential feature. But one thing remains irrefutable: ESP, the electronic stabilisation programme, is mandatory – for everyone. Which sub-functions the manufacturers use and according to which control strategy they operate, on the other hand, remains at their discretion.

More than stabilisation

A by and large standard BMW 550i flies over the Bosch test grounds Boxberg, in a region that is known just as little for Mediterranean weather as the Eifel region. Water is lying on the driving dynamics course, yet nonetheless the two-tonne saloon weaves through the 18-metre slalom as it is a mere triviality, steering directly into the corner, although understeering slightly. Creaking braking interventions? Abrupt accelerator release? None. And yet, the electronics are in fact activated.

Here, in particular prior to journeys on cordoned-off sections of track, the mother of all questions crops up: can the ESP be completely disabled or not? No, ESP cannot be disabled – not in any vehicle, as too may systems rely on the available software, such as electronically simulated differential locks or the networking with the ABS.

ESP reduces engine performance and applies braking force to the wheels

However, the function for which this technology was initially designed in the early nineties can actually be switched off in many sporty series models – so-called skid protection. Here the electronics reduce the engine power and, if necessary, applies the brakes to individual wheels in order to stabilise a vehicle during an evasive manoeuvre.

This certainly serves the vast majority of car drivers well, however, there are exceptions. "Some drivers know from experience what should be done in certain situations. Under certain circumstances the electronic control can then cause problems," says Lars König, team leader for driving dynamics control systems at Bosch Engineering. He sits on the passenger seat, comparatively relaxed, and swipes cheerfully on his tablet PC with his finger.

Reaction to the driver

In the same moment the BMW appears to want to turn almost at a right angle, steers much more directly and hints at a tendency towards oversteer. So that would be Sport mode. To clarify: In the 550i, Bosch is trying out integrated driving dynamics control. It combines the existing braking system, the ESP hardware and rear axle steering with a new control strategy. "Here we are following the pre-control principle," explains Gert Hägele, Product Area Manager responsible for chassis and driver assistance systems.

In plain text: "Whereas previous systems have reacted to the behaviour of the vehicle, so essentially to oversteer and understeer, the action of the driver is now to be taken into account.“ Depending on the previously selected setting, the software draws conclusions based on the steering impulse, the speed and the coefficient of friction, and adjusts the agility, balance, the required steering angle, the yaw damping and stabilisation accordingly.

Electronics do not brake radically - quite the opposite

Incidentally, the concept vehicle is still a long way from exhausting all possibilities, as the handling could be made even more precise and individual by means of active stabilisers, active differentials, active front axle steering and electric motors at each individual wheel.

Sounds a little disconcerting? Perhaps for those who love mechanical differential locks and masters of the heel-toe technique perhaps. However, with every additional metre driven in the Bosch BMW it becomes clear that the electronics do not brake radically,- quite the opposite: it helps to mobilise the vehicles reserves in a targeted manner.

In so doing it even takes the individual driving style into account, as an individual regulation algorithm can be stored via the stabilisation, balance and steering behaviour control lever. The integrated driving dynamics control even provides a special drift mode. Wild countersteering or pressing hard on the accelerator? Not necessary. Increasing the steering angle alone causes the 5 series to begin to oversteer in lively fashion.

Seven km/h faster through the 36-metre slalom

For Lars König, alongside the software the key lies primarily in the rear-axle steering: "The lateral dynamics all come down to the firm rear axle in particular, which can develop high cornering forces. For this reason, metallic rather than rubber bearings are used, which does, however, remove any suitability for road use from a street car. With the clever control of the rear axle steering, we can build up or relieve the complete cornering force within one tenth of a second“ – a characteristic that the new Porsche 911 GT3 would like to make use of, for example.

And the weight? The components supposedly weigh just five kilograms. Gert Hägele is aware of the doubts of the sports driver fraction: "None of this sounds particularly sporty, but it does make the car go faster." How fast exactly? Engineer König specifies: "In our expert trials, we managed an average top speed that was seven km/h faster in the BMW, in the 36-metre slalom."That said, the active stabilisers are problematic, as they increase the weight by around 80 kilograms.

Even if the ESP intervenes, it doesn't slow down the driver at all

In current models everything that the integrated driving dynamics control could possibly require is already on-board anyway – in the case of the BMW this even includes the rear axle steering – and this alone is more than sufficient to ensure that sports cars are not slowed down. Thus, in ESP Sport mode,a Porsche 911 Carrera with dual clutch transmission and a torque vectoring function glides quickly around the short circuit at Hockenheim as if the stabilisation programme were disabled – in 1:13.3 minutes.

The reason: the electronics leave so much room for manoeuvre that they only have to intervene when there is threat of lift-off or at least excessive rear panning. Put simply: Even if the ESP intervenes, it doesn't slow down the driver at all.

Key issue: continuous load

In the BMW M135i the electronics makes its presence felt in another, positive manner: even when the stabilisation function is disabled, braking interventions simulate a differential lock at the rear wheel that is not under load. With a time of 1:15,7 minutes, the 316 HP 1 series delivers considerable power. On the other hand, once in racing mode the technology reaches its limits on account of the extreme strain on the brakes - in this regard only an additional mechanical component can help.

And the rear axle steering? "That shouldn't be a problem," says König. For in motor sports the advantages of better suitability for everyday driving are of secondary importance. "Therefore in this instance I would rather use electronically controlled differential." The handling track in Boxberg has now dried up, but nonetheless the BMW 550i feistily throws its tail towards the outside of the corner. But one tap of a finger later, the heavy saloon sticks stubbornly and smoothly to its trajectory by means of a little understeer. All of this is still al little disconcerting, to some extent down to the fact that it considerably increases the level of fun when driving. The heated discussions regarding control electronics are not expected to do much in the way of holding the new technology back.

The most important functions of a modern ESP

Braking and accelerating:

1. Dry braking function
2. Preventative pressure build-up
3. Braking assistant
4. Brake servo
5. Back-up brake servo
6. Fading compensation
7. Rear brake force booster
8. Brake jerk avoidance

Special stabilisation functions:

9. Understeer reduction
10. load-dependent characteristics
11. Tilt instability avoidance
12. Roll prevention
13. Trailer stabilisation

Controlled driving:

14. Holding brake function
15. Automatic brake release
16. Speed regulation
17. Selectable acceleration
18. Controlled deceleration
19. Stop-and-go function
20. Automatic parking brake
21. Hill descent control
22. Hill-start assistant

Comprehensive range of sensors:

23. Brake pressure calculation
24. Automatic pressure build-up
25. Automatic full braking
26. Automatic warning brake

Specific torque distribution:

27. Dynamic torque distribution
28. Terrain detection

Monitoring and information:

29. Tyre pressure monitoring



Karl-Heinz Augustin


19 August 2013
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