CAD aids design of multilink suspension

When Mike Pilbeam set out to develop a rear suspension for Peugeot 406 sedans raced in the British Touring Car Championship, he turned to a new program in his arsenal: Working Model from Working Model Inc. (San Mateo, CA). Multilink suspensions are complex contraptions, and the software let him look at the effect various loads would have on the chassis in a new way.

His company, Pilbeam Racing Designs (Lincoln-shire, England), has been designing and building race cars and subcomponents for the past two decades. His MP series of single-seat hillclimb cars has won the RAC British Hillclimb Championship 17 times in the past 20 years. The Peugeot 406 project involved development of the entire car in conjunction with Peugeot's competition department, but Pilbeam was to manufacture the suspension in-house.

"More than any other factor, you want a suspension with predictable characteristics," says Pilbeam. Once the car leans into a corner and takes a set, it shouldn't change its handling suddenly due to a small change in cornering forces. A driver can never press such a car to its limits."

To create a suspension with the best roll center and handling, Pilbeam engineers built a simple version of it in Working Model. Unlike some custom analysis programs the company had developed over the years to analyze specific suspension designs, Working Model works with any suspension arrangement.

On the Peugeot, rules require the suspension be the same configuration as the stock vehicle--multi-link with three transverse links, and a radius rod from the chassis to the wheel upright to take out braking torque. However, attachment points can be moved, and engineers developed a Working Model that output such things as wheel movement, toe angle, and camber change as a function of suspension travel and steering angle.

How well do the computer results correlate to the real world? "Nicely," says Pilbeam. "We aren't to the point where we can define spring rates and damping characteristics. But there's no reason we won't get there some day."

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