A steering column manufacturer discovers that wave springs not only
perform better than their coil spring counterparts, but also save weight
and manufacturing costs
A UK based company, which manufacturers steering columns for a German
automotive customer, experienced problems when using a conventional
round-wire, helical coil spring to pre-load a narrow-wall bearing. In
particular, tolerance build-up within the confined axial space of the
assembly produced excessive spring forces, leading to unacceptable
'torque-to-turn' forces within the steering column. Clearly what was
needed was a spring that would operate over a wider tolerance band with a
reduced spring rate. Moreover, if the current use of support shims to
eliminate point loading of the bearing could be avoided and weight
savings achieved at the same time, this would offer the added bonus of
reduced manufacturing costs and thus volume cost savings.
TFC proposed a solution to this problem that involved replacing the
conventional helical spring with a special pre-load spring design with
flat turn shim ends. The product considered most suitable for the
application was a Smalley crest-to-crest Spirawave spring from TFC's ring
and spring portfolio. Technical director, Brian Goode picks up the story:
This type of spring develops similar forces to conventional round wire
or helical springs but occupies a third or less of the same space. This
not only allows it to be used in a tight axial space, but such high
performance springs will also maintain the same deflection and load
specifications of a conventional spring. During manufacture, Spirawave is
drawn from a continuous coil of single-filament, pre-tempered round edge
wire. We re-worked the design to include flat turn shim ends and the
final result is a spring that operates to specification and more
effectively in the given space envelope, and which also weighs less.