The torsion beam type of rear suspension has been adopted by most manufacturers of small to medium front wheel drive passenger cars. This is primarily for reasons of cost, packaging and functionality. However, with a torsion beam, there is a compromise between handling performance and ride refinement. A typical torsion beam set to give optimum handling has insufficient longitudinal wheel compliance to give good ride and NVH performance, and when set to give optimum ride and NVH performance suffers from significant levels of lateral compliance oversteer.
Some of the compromises inherent in a simple torsion beam rear suspension may be ameliorated by the addition of extra links into the system; such solutions include the addition of a panhard rod or of toe-control links. However, such solutions incur additional cost, and the additional space used may be unacceptable from a packaging viewpoint. With this in mind, the Ford Motor Company decided to investigate how the performance of the torsion beam rear suspension could be improved whilst retaining its simple, basic layout.
Ford chose MIRA as its partner to develop a concept torsion beam design, which would deliver some of the performance benefits of a multi-link suspension, without significantly increasing the cost of the torsion beam or changing the packaging requirements. Using the latest CAE techniques, MIRA/Ford designed a torsion beam axle that includes compliant hubs. A prototype implementation of this arrangement displayed excellent handling characteristics, whilst achieving improvements in ride refinement.