Science & technology | Magic carpet ride

A new type of smooth car suspension

Taking care of bumps and potholes

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WHEN unveiled at the Paris Motor Show in 1955, the Citroën DS caused a sensation. It was not just the car’s elegant lines that encouraged 12,000 customers to place immediate orders, but also its mechanical innovations. Chief among these was that instead of steel springs, the DS rode on a self-levelling hydropneumatic suspension. This used spheres, filled with nitrogen, connected to each wheel. When started, the car’s engine pumped hydraulic fluid into the spheres, lifting the vehicle’s body. Bumps in the road were dampened by the incompressible fluid squeezing the compressible gas in the spheres. It made the DS appear to glide over France’s then badly damaged post-war roads.

French roads are now in good shape. Instead, it is to Britain that test drivers look to find some of the most “demanding” roads in Europe. Being plagued with pot holes, humps and choppy surfaces makes them an ideal proving ground for vehicle engineers. Which is why Shakeel Avadhany has opened a development base at the MIRA Technology Park, an automotive-research centre in the English Midlands. Mr Avadhany is the boss of ClearMotion, an American firm that has come up with a novel means of suspension designed to give cars a magic-carpet ride.

Despite hydropneumatics’ famous smoothness, Citroën dropped the technology in 2015. Other, better systems had superseded it. Mr Avadhany now hopes to do to them what they did to Citroën, and run them off the road.

When he and his colleagues spun ClearMotion out of the Massachusetts Institute of Technology in 2008, their intention was to use bumps in the road to generate electricity. They had developed a device designed to be attached to the side of a standard shock absorber. As the suspension moved up and down, hydraulic fluid from the absorber would be forced through their device, turning a rotor that generated electricity. But, just as a generator and an electric motor are essentially the same, except that they run in opposite directions, so ClearMotion’s engineers realised that running their bump-powered generator backwards would turn it into an ideal form of suspension. And that seemed a much better line of business. They therefore designed a version in which the rotor is electrically powered and pumps hydraulic fluid rapidly into and out of the shock absorber. The effect is to level out a rough road by pushing the wheels down into dips and pulling them up over bumps.

This is helped by knowing when the dips and bumps are coming. The system is able to do that by tapping into the increasingly sophisticated network of sensors employed in modern vehicles. Its algorithms use these sensors to learn within millimetres the profile of the road being travelled. They then share the results, via a computing cloud, with other vehicles using the same process. This means that the next time any vehicle in the fleet travels the same route, the system’s software is able to anticipate the road’s topography and control the car’s suspension appropriately.

According to Mr Avadhany, ClearMotion is working with a number of parts suppliers and is close to bringing the system to market. He expects it will be particularly useful for autonomous vehicles, in which passengers are likely to want to use their journey time to work or read. Or, if it is really comfy, to take a quick nap.

This article appeared in the Science & technology section of the print edition under the headline "Riding a magic carpet"

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