User Guide

3.6 Arc springs
Single spring
The basic version of the arc spring is a single spring. This
is characterised by its large spring volume and resulting
high damping capacity. Because of its simple design,
however, it only offers limited possibilities for satisfying
rising demands for comfort. For this reason, today’s
DMFs are seldom fitted with single springs.
Single-step parallel spring
The arc springs in most frequent use today are single-
stage parallel springs. It consists of an external and in-
ternal spring, of about the same length. The two springs
are arranged in parallel. Their individual characteristics
add up to the spring set curve.
Two-stage parallel spring
In two-stage parallel springs, two arc springs are again
arranged one inside the other. The internal spring, how-
ever, is shorter, thus engaged later. The wind-up curve
of the external spring is matched to the requirements of
the vehicle when the engine starts. Here, load is applied
only on the softer external spring, enabling the system
to pass the critical resonance speed range faster. In the
higher and maximum torque ranges, load is exerted on
the internal spring as well. Both external and internal
springs work together in the second stage. The interplay
of both springs provides good damping at all engine
speeds.
Three-stage arc spring
This type of arc spring consists of one external spring
and two internal springs of different lengths arranged
in-line. This design combines the benefits of the parallel
and in-line arrangements and therefore allows for optimum
torsion damping at each engine torque.
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