Vehicle suspension improves handling and maintains comfort

The suspension has been developed by vehicle dynamicists at MIRA over the past two years and builds on the existing double-wishbone suspension (DWS).

The DWS is most commonly seen in high-performance sports cars — including those made by Lamborghini and Aston Martin — thanks to its ability to provide a low bonnet line and improved handling. However, it has always struggled to achieve the comfort offered by softer suspensions, such as the MacPherson strut suspension.

Ian Willows, a MIRA consultant, told The Engineer: ‘The problem with the existing DWS is that there’s an inherent compromise with its design.’

He explained that there is a trade-off between the longitudinal compliance and the castor compliance of the suspension. The longitudinal compliance allows the wheel to be displaced rearwards if a force is applied in that direction. Meanwhile, the castor compliance relates to the rotational displacement of the steering axis when a braking force is applied.

‘The reason we’d like some longitudinal compliance is because it gives the ability to absorb the longitudinal force input associated with a pothole or a ridge in the tarmac,’ said Willows. ‘But we don’t want the associated castor compliance because that reduces the stability of the steering as the steering axis rotates and the castor angle and castor trail reduce.’

The interlinked DWS overcomes the compromise by effectively decoupling the castor and the longitudinal compliances of the traditional double wishbone suspension — creating a solution that delivers the cornering, handling and steering performance of a double-wishbone design but with the longitudinal isolation associated with a more comfortable suspension design.

‘When you apply a breaking force, there is no loss in castor angle with the new suspension,’ said Willows. ‘This will maintain the stability of the steering axis and eliminate any associated variation in steering feedback through the wheel when you’re cornering and breaking.’

He explained that one of the problems suspensions now have to address is the fact that less isolation is being offered from tyres on new vehicles as the trend towards reducing tyre profiles continues.

The concept is ready to go but the suspension would have to be customised for each individual vehicle model.

‘We’re aiming to advertise the concept advantages and then get some manufacturers or OEM suppliers to develop it for their next model,’ said Willows.

The Society of Motor Manufacturers and Traders (SMMT) told The Engineer: ‘MIRA’s suspension development is another clear example of the high level of innovation and R&D capability within UK industry.’