6/7/11

BWI Magneride

BWI is a Chinese-based multinational. In 2009 it bought Delphi Chassis Systems, and with the new acquisition came an early version of Magneride.

Magneride is a mechanically simple system for adjusting damper rates steplessly and very quickly. The system uses fixed-orifice monotube dampers containing magneto-rheological (M.R.) fluid. A sensor set and an electronic control unit operate the system, monitoring and reacting to body and wheel motions and driver control inputs.

Range Rover Evoque uses Magneride Generation 3.

M.R. fluid is a suspension of magnetically ‘soft’ (easily but temporarily magnetised) particles in a synthetic hydrocarbon base fluid.

The piston in each damper contains a coil; the M.R. fluid flows back and forth through the coil as the wheel is deflected. When the coil is not energised, the M.R. fluid is not magnetised: the magnetically soft particles within the fluid exhibit a random pattern and the fluid behaves like conventional damper fluid, flowing easily through the piston orifice. When the coil is energised, the magnetic field causes the particles to align into fibrous structures in the direction of the magnetic flux. The strength of the bond between the particles in the structures is proportional to the strength of the magnetic field. The result is a variable resistance to fluid flow within the damper piston, which provides a variable damping rate. Adjustments are stepless.

Changing the current supplied to the coil in the damper piston allows the generation of a wide range of damping forces. Changes in the damping force occur nearly instantaneously, providing continuously variable real-time damping. The power requirement of the system is no more than 20W per damper, plus the requirements of the sensors and ECU.

Magneride first appeared on the 2002 Cadillac Seville STS and, soon afterwards, on the Chevrolet Corvette. Data from these early applications was used to develop the system. The most recent applications, using ‘Generation 2’ Magneride, are the Ferrari 458 Italia, the Audi R8 and — as an option — premium Audi A3 models. Additionally, a version of Magneride has been developed with Porsche to provide active powertrain mounting, and was deployed on various 2010 models.

A wide range of rebound and jounce damping is possible, and the electronic control means that it is relatively straightforward to tailor a vehicle’s ride and handling. Sporting cars are not the only possible application, of course, particularly given that enthusiasts tend to put up with a rather hard ride anyway: the real potential of Magneride is that it can be applied to any car, off-roader or MPV to improve the ride-handling compromise.

Standard monotube damper configuration:
36mm piston for suspension struts
46mm piston for dampers
Internal piston coil
Airlift configuration available
Dead-length minimisation
Air/oil separation
Two-wire electrically isolated flying lead connection

As a consequence of Magneride’s mechanical simplicity, it is also quite compact, being no bulkier than most conventional setups. This means that it can be installed as a direct replacement for passive dampers in a lot of vehicles. It can also be mated with self-levelling systems.

The high-pressure gas charge monotube configuration offers good heat dissipation and no damping force lag.

Generation 3

The third incarnation of Magneride replaces the single electrical coil in each damper with two smaller coils and introduces a new, bespoke ECU with new control algorithms. By providing quicker ‘current off’ performance, the new system delivers a faster transient response. The new dual-coil architecture also contributes to providing an even higher dynamic range — a ‘softer soft’ and a ‘harder hard’ — even at the low relative body velocities that are difficult to control with conventional damping technologies. As well as directly improving comfort and handling, these improvements also allow the authority of the anti-roll bar and the springs to be reduced, improving another area of the ride-handling compromise.

Magneride damper for Range Rover Evoque.

To extend Magneride’s range of applications to heavier vehicles such as premium SUVs, the system’s resistance to side loads has been increased and seals and bearings have been uprated.

Beyond Magneride

For many years BWI has been investigating how vehicle dynamics, particularly response to emergency situations, can be improved by sharing data with other vehicle systems. In a ‘global chassis control’ system, a supervisory computer manages an array of subsystem controllers, covering anti-lock braking, electronic stability control, engine torque, roll control, dampers and active steering.

The main barrier to this level of integration is the need for a standard high-speed com­muni­ca­tions protocol to be implemented by manufacturers. BWI is participating in various consortia, such as Flexray, to develop the infrastructure that will support a safe and reliable integration of the multitude of chassis subsystems used in modern vehicles.

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