Linear Electromagnetic Actuation System for Active Vehicle Suspension

Clearly, the suspension system is a key component of the modern car having to isolate vibration, optimise road holding and ensure reliable cornering. It does this by absorbing energy and dissipating it while travelling over rough ground. In addition, the suspension system has to maintain the vehicle´s wheel geometry to maximise tyre contact with the road at all times, and react to the weight of the car during cornering to minimise body roll.

There are numerous variations and different configurations of suspension, and a car usually has a different design on the front and back. However, whilst suspension systems are a fundamental element of any vehicle and may appear to be relatively simple, designing and implementing them to balance passenger comfort with handling is a complex task. Soft suspensions provide a smooth ride, but result in body roll or pitch during braking, acceleration and cornering, whilst stiff suspensions minimise body motion and allow cars to be driven more aggressively, albeit at the expense of ride quality.

To overcome the limitations of conventional suspension systems, over the years, various alternative suspension technologies have been developed. For example, hydrostatic, hydro-gas, hydro-pneumatic and hydraulic - an innovation which has previously been exploited in motorsport. However, these also have their limitations and/or are too expensive for production cars.

Recent advances in linear electromagnetic machines, facilitated by advances in magnetic materials, power electronics and digital control systems, may, however, make it possible to introduce a totally new suspension technology. This is the subject of the proposed research, which envisages using a single linear motor at each wheel, Figs. 1 and 2, in place of the conventional shock absorber and spring system.

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

Fig. 1 Schematic of Active Suspension

Fig. 2 Integrated Linear Electromagnetic Actuation Unit

The research programme will address the design optimisation of force-dense, energy-efficient linear electrical motors and the associated mathematical algorithms which will be necessary to provide the required active control of the suspension system. The utility of the developed suspension technology will be demonstrated on a quarter car rig, and the resulting vehicle performance improvements will also be quantified by simulations over the full range of ride, handling and stability.