Easy rider

The TV show Pimp My Ride, in which cars are modified into macho showboats, often reveals that the suspension is a key to vehicle appeal. The fact that this system is also commonly altered to change the appearance and ride characteristics confirms there has been little significant change in car suspension for decades.

But a different approach from researchers, in collaboration with car manufacturer Jaguar, could give suspension a new spring. They foresee using linear electromagnetic actuators to provide all the functions of the conventional shock absorber and spring system. They envisage a single linear motor in each wheel.

Isolating vibrations

Suspension systems have to isolate vibration, optimise road holding and ensure reliable cornering. They attempt to achieve this by absorbing energy while travelling over rough ground and dissipating it, maintaining wheel geometry to maximise tyre contact with the ground, and reacting to the weight of the car during cornering to minimise body roll. These functions are provided by a combination of springs, shock absorbers and anti-roll bars. The team, based at Sheffield and Loughborough universities, believes linear motors may do the job better.

‘The main benefit of employing linear motors is that they can move much faster than conventional fluid-based damper suspension systems,’ it said.

‘They can, therefore, respond quickly enough to virtually eliminate all movement and vibration of the body of a car under all driving and road conditions and to counter body roll by automatically stiffening the suspension when cornering, thereby giving the driver a greater sense of control and, hence, improving safety.’

But there is some way to go before this can be realised. Dr Kais Atallah of Sheffield‘s electronic and electrical engineering department, a core investigator, explained some of the challenges the team faces during the next three years. ‘Apart from optimising the system’s efficiency, there are constraints on the weight and space that the units can have,’ he said. ‘There are a few topologies out there and we will have to look at ones that give the highest force density.’

Previous work by Sheffield‘s Dr Jiabin Wang with rare earth magnets made from neodymium iron boron (NdFeB) showed it is possible to produce topologies with a force density of 0.6 megaNewtons pcm.

Ride quality

But the researchers will have to turn to their industrial partner, Jaguar, to learn if this is good enough. ‘Jaguar will be the one to specify the performance because it is the potential end user,’ said Atallah. ‘Jaguar has to tell us where the goal posts are. The car maker knows the costs, too, and whether our systems will be able to compete on those terms, as well as on the ride quality the new system provides.’

There is another, unpredictable but crucial, factor that the engineers must consider when adjusting suspension – passenger comfort. Scientists have suggested that occupants experience car sickness when the vehicle does not behave as they are led to expect by what they see through the windows. In other words, passengers may expect a car to roll as they see it travel around a bend. If, instead, the suspension keeps it level, it can trigger nausea.

The university team is not the first to consider the potential of linear actuators. NdFeB magnets are also used in loudspeakers, which may explain why speaker maker Bose has been investigating the use of linear actuators for vehicle suspension since 1980. Two years ago it demonstrated their use on a series of vehicles, including a Lexus saloon car and a Porsche.

While new technologies are often introduced to the automotive market in high-end models, the biggest returns come when they can be added to the ones that sell in the largest quantities and these frequently have greater weight, space and cost constraints.

That is the target the Sheffield and Loughborough teams must meet before they can be confident that their suspension systems based on linear actuators in each wheel will pimp Jaguar’s ride.