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Magnetic systems find their niche
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01/03/2007
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Ian Adcock takes a closer look at the future of advanced magnetic fluid suspension systems and how they are developing and being applied in the light of competition from air systems and active dampers.
Probably the biggest compromises a vehicle programme manager has to make concern ride and handling. Few car engineering teams manage to fully balance the needs for deft handling without sacrificing ride quality. In most new cars a comfortable ride usually gives way to superior vehicle dynamics – a situation that can be made even more uncomfortable when a car is tuned for one particular country’s roads at the expense of others.
The search for a suitable balance between the two requirements has intensified in recent decades. There was once much optimism about active suspension systems, with Lotus leading the way, but excessive power consumption and expensive, aerospace-derived components meant it has never fulfilled its potential. Meanwhile advances in electronically controlled dampers (like those, for example, in the Mercedes-Benz C-Class described in our article elsewhere in this issue) and air springs has eroded the potential advantages of fully active systems and at much lower costs.
Now Delphi’s manager of forward engineering, Olivier Raynauld, believes its second generation MagneRide system is poised to leapfrog these technologies and provide the means to deliver ride and handling without compromising either.
The advanced development team is focusing on delivering a higher dynamic range (a ‘softer soft’ and a ‘harder hard’) and a faster transient response. This will allow MagneRide to take more control of the suspension so that the authority of the roll bar and springs (which create ride compromise) can be reduced and transient body motions can be controlled effectively without additional systems. The ability to generate high control forces at low relative body velocities (the speed the body moves up or down on the suspension) is an intrinsic property of MagneRide.
Other mechanical improvements leading to improved efficiency and faster response include friction reduction and superior seal and bearing designs and materials, plus modifications to improve resistance to side loads that will push the application possibilities into heavier vehicles such as large SUVs.
“It’s becoming obvious as we refine MagneRide more and more that it has the potential to offer OEMs a solution to many of their dynamic problems, especially when it comes to vehicles with high centre of gravity such as SUVs and MPVs,” says Raynauld. “Because it is tuned electronically via its sensor network and ECU it also means a manufacturer can have one set of components across a wide range of products that can be individually tuned to reflect the characteristics of a given product whether that is a family saloon or a performance GT. So there’s a potential cost saving to the OEMs as well.”
Now in its fifth year of production, MagneRide is entering a new phase of development and European Automotive Design has driven an Audi A8 and a TT fitted with updated technology.
The principle remains unchanged: monotube dampers using magneto-rheological fluid energised by an electrical current that is controlled via a series of sensors and an ECU to vary stiffness in real time. What Delphi has been concentrating on, says Raynauld, is improving the sophistication of the data used to control the damper’s characteristics.
Vehicles are now equipped with a much wider array of sensors than they were even five years ago and it is the input from these that Delphi is harnessing to refine MagneRide’s potential. For instance, inputs via the CAN network from a brake systems pressure sensor or torque signals from the transmission could be used to modulate the suspension to limit dive and pitch under hard braking or fierce acceleration.
The limiting factor, says Raynauld, is not the quantity of information received but how quickly it can be processed. “ECUs are already too small and slow so improving them would lead to faster response times, although we’re pretty quick already. We need faster computational speeds to process the algorithms as they get bigger and more complex, and to be more precise in the control signals being issued,” he says.
Currently Delphi uses maps and interpolates from them. Although Raynauld says this process is very fast and quite efficient in terms of CPU time, it’s also “a bit crude”.
The A8 development car is a test bed for what Delphi sees as the next generation command system for MagneRide suspension. Equations replace the presently used maps. The inputs remain the same but the new process calculates in real time what the map would have ultimately detailed. The results are more precise and allow the system to schedule the current outputs to control damper rates more accurately.
Raynauld sees no need for self-learning systems that adapt to a given driving style but instead prefers to take inputs from, for example, the transmission that show a particular driver is an especially hard gear-changer. However, it could recognise peculiar road surfaces like severe washboards in Australia and respond accordingly, even if the suspension remained in that mode for 50m after the washboard had finished.
Delphi is also experimenting with the idea of replacing sensors on the A8 with accelerometers. The main challenge with accelerometers is their tendency to respond to the geography of the road so, for instance, they react to each movement as the vehicle goes over a sleeping policeman. Wheel sensors only read suspension displacement and therefore provide the right answers about how the vehicle body is moving regardless of what kind of bump it is negotiating.
The likely outcome of the accelerometer versus sensor debate, predicts Raynauld, will be a fusion with sophisticated controls eliminating the extremes of both to end up doing a better all round job. Some OEMs, says Raynauld, are convinced accelerometers are the way forward. “We don’t want to disappoint by not being able to accommodate them.”
Delphi is also developing asymmetrical response so that when the damper comes off compression most of the energy will be fed through into rebound. This is a constantly shifting pattern, not a series of fixed curves that control the asymmetrical shifts. And this means a system could be designed with a soft compression and hard rebound in different phases.
As well as improving ride comfort – for example by preventing flattening out at the bottom of steep dips – asymmetrical damping behaviour improves handling as individual forces are calculated for each wheel during cornering. Compression-rebound ratio is constantly and subtlety altered for the optimum ride-handling characteristics of a particular car.
Because of the amount of force generated under compression, manufacturers will have to rethink the top mount design to ensure that it is sufficiently robust. However, Raynauld also suggests MagneRide could have a knock-on effect when it comes to vehicle structures as it transmits lower forces. It could also mean, at last, a comfortable ride on large 22 inch wheels fitted with low profile tyres.
It seems MagneRide is about to come of age and make the transition from high performance sports cars to more everyday vehicles.
How it feels on the road
Although I drove both Audis fitted with Delphi’s latest system, the most noticeable difference was in the A8, writes Ian Adcock. Like most German saloons the A8’s composure on British road surfaces peppered with pot holes and ruts is compromised. It might be fine on autobahns and Germany’s ultra smooth roads, but it usually doesn’t take long for crash-through to become evident when driven in the UK.
It came as a pleasant surprise then to detect that had been eliminated in the Delphi mule; the ride was more composed, edging towards what you get in Jaguar’s latest XJ, while the steering was similarly adept meaning the big German saloon could be hustled along at speeds and in comfort that would leave a normally suspended A8 floundering in its wake.
And Roger Bishop reports on the Audi R8 supercar’s MagneRide dampers.
To say that the R8 is assured is an understatement; it is positively gripping both in the sense of its attachment to the road and the thrill of the experience. Yet the ride could not be described as extreme. The dampers respond very quickly indeed to different road surfaces, providing a ride that is both assured and comfortable.
It took a few laps around Le Castellet’s Paul Ricard circuit (in the hands of a professional driver) to appreciate fully how well the dampers combined with the late-intervention ESP 8.0.
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Author
Ian Adcock
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