Smooth operator

A semi-active suspension control system first used in truck seating is making its world debut in a production car’s engine mounts. Christopher Sell reports.

Delphi used the Paris motor show to announce two production contracts with European car manufacturers to supply its real-time suspension Magneride technology.

The semi-active suspension control system, based on magneto-rheological (MR) fluid technology, first seen in truck seating, will be used in engine mounts for the first time – although Delphi was unwilling to name either the manufacturers or when the system will go into production.

In a magneto-rheological fluid, soft particles such as ion microspheres are magnetically suspended in a synthetic hydrocarbon base fluid. When current is applied to an electromagnetic coil inside the damper’s piston, the resulting magnetic field changes the rheology (or resistance to flow) of the fluid.

The particles react to the field by forming a dense network of chains, changing the fluid from a liquid to a near solid and back to a liquid in milliseconds. An onboard controller continually adjusts the damping forces up to once every millisecond based on four suspension displacement sensors, a lateral accelerometer and a steering wheel angle sensor.

Traditional dampers contain oil rather than silicon-based fluid and the valve is a single size. Customers wanting semi-active damping control would require varying damper characteristics and valve sizes to achieve a comparable result in performance, which can be complicated and expensive.

Jocelyn Marchaind, engineering supervisor for Controlled Dampers at Delphi, said that the key advantage of MR fluid is response time. He claimed that because the character of the fluid changes almost instantaneously it is far superior to any current technology.

He said that the damping technology is ideal for engine mounts, as it will control engine vibration and adapt under a variety of driving conditions to prevent damage. This will also reduce the noise and harsh action, which passengers can experience in a car.

Nick Jones, chief engineer of Delphi’s innovation centre in Paris believes that the technology can be adapted to other applications, such as machine tools – or anywhere that requires dampingproperties. ‘The applications are limited only by your imagination, because the fluid can produce a condition very close to a full lock almost immediately. Clearly, actuators that will allow such a movement on demand will be popular.’

Jones is quick to point out that just because technology is new it may not be better or cheaper and must fulfil the cost-value equation – the most scrutinised in the motor industry.

‘We are focused on the fact that there is plenty of wonderful technology, but it has to do something that the simpler technology doesn’t — otherwise there is no point in having it. We are looking for applications that require intelligence – in other words fine control – rather than just a basic function.’

While the technology been around for several years (US company, Lord corporation, which supplies the MR fluid to Delphi, first used it in 1999 as a seat damper for trucks, while Delphi developed a semi-active suspension system, CV-RTD, in 2000) Jones said that some changes had to be made to the basic fluid to adapt it for use in vehicle suspension. These included a very high resistance to temperature variation, and durability, as well as ensuring the metallurgy of the valve would cope with all the various stresses placed upon it.

Jones explained that essentially it is a carrier fluid, with several key ingredients in various proportions — one of which is a very specialised iron-based fluid.

‘The ingredients are mixed very carefully in the proportions that will provide the combinations of behaviour we are looking for across the temperature range, and at the same time produce the ability to switch from very low forces to high forces almost instantly,’ he said.The main challenge after the fluid, according to Jones, was bringing the production costs to a manageable level.

‘So much high technology is involved, that a large part of the engineering effort goes into making this an affordable technology,’ he said, adding that he feels the two contracts announced in Paris show the effort is paying off.

Other people are working on the technology, but Jones believes that the sheer technological effort involved in bringing the system to operating level is a huge barrier to other companies looking to enter the market.

‘We have been developing this for more than a decade, but the technical difficulties in getting it to work in real-world applications are significant. And it has taken that long and all the resources that Delphi can put towards it to get to this stage.’

<b>The roots of the technology</b>

Rheonetic magnetic fluid suspension systems use technology first discovered in the 1940s.

Researchers discovered that by creating a suspension of magnetically polarised particles it would be possible to change fluid viscosity by subjecting the fluid to a magnetic field.

These fluids were called magneto-rheological fluids – or MR fluids. But until recently the challenges involving particle settling and research into other fully active systems had kept the magnetic fluids from finding a market.

As well as being installed initially in truck seats in the US in 1999, the potential of the technology is wide ranging.

The Lord corporation, which pioneered rheonetic systems, applied the technology to the medical field in prosthetic devices. Here the real-time control achieved through MR particles responding to a magnetic field in milliseconds has proved particularly beneficial. Lord joined forces with Biedermann Motech, a German manufacturer of spinal implants and prosthetic components, to produce a device that improves the mobility of leg amputees by recreating a natural gait.

Lord’s MR damper – hailed by many as providing the nearest thing to natural leg muscles – is designed to perform in combination with sensors and software, calculating the changes in walking speed, uphill and downhill motion, high and low roads, ramps, stairs and terrain adjustments.

As well as prosthetic limbs and heavy vehicle seating, MR technology can be seen in numerous applications. In telerobotic surgery, for instance, the Da Vinci system uses MR fluid to allow the surgeon to differentiate between soft and rigid flesh. Its damping qualities can be used in seismic and wind mitigation devices to counteract the negative effects of strong winds and earthquakes.

As a result, civil engineers are incorporating MR technology into buildings and bridges to work similarly to an automotive shock absorber.

Other applications developed by the Lord corporation include control-by-wire, automotive primary suspensions, washing machine vibration detection, passenger protection systems as a component in airbag systems, steering column dampers, seatbelt retractors and bumpers.

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