PROTOTYPING | DESIGN FLOW
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Wave spring delivers design simplifi cation and space savings
Compact blade brake clutch
design takes advantage of a
multi-turn wave spring to
reduce assembly height and
number of components.
Flat wire wave springs are often used in
compact applications where axial space
is limited and traditional round wire
springs cannot produce the needed
force at the desired work height. As the
spring element of choice for many design
engineers, wave springs are used in a wide
range of applications ranging from bearing
preloads in electric motors over injection
pens to directional drilling devices.
Another application that requires a
compact size is the blade brake clutch as
found under the mower deck of highend
lawn mowers. Originally designed
as a safety feature when emptying the
mower bag, it allows for the mower
engine to run without the mower blade
being engaged and spinning. When the blade
brake clutch is activated, the mower blade
is uncoupled from the mower drive and
simultaneously braked to a stop.
Blade Brake Clutch systems are designed
as either a combination of two main
assemblies, a separate brake and clutch, or as
one compact assembly. The drawback of the
separate assemblies design is its complexity
due to the larger number of parts needed,
making it harder to assemble and maintain.
The larger number of parts also add weight
and take up more room under the mower
deck where the available space is limited. The
single unit design on the other hand reduces
complexity and achieves space savings by
sharing components between the brake and
clutch, which reduces the number of total
parts needed and shrinks the assembly in size
and weight.
The single unit design utilises a multi-turn
wave spring with a free height of 12mm.
When the spring operates at its rst work
height of 8mm (WH1) it holds the brake
member at a prede ned distance away from
the brake actuator.
When the operator engages the blade
brake clutch via the control lever, the wave
spring is further compressed to its second
work height of 6mm (WH2) and allows the
braking surface to connect with the brake
surface, stopping the blade from spinning.
The two main reasons why a wave spring
was chosen for this blade brake clutch design
are space savings and design simpli cation.
The most visible bene t of the wave spring is
its space savings aspect, reducing the overall
height of the assembly under the mower
deck.
In static applications, a wave spring will
typically need just 50% of the work height
of coil spring to deliver an equivalent force.
In dynamic applications, the work height
advantage is typically about 30%, less than
static applications but still substantial.
Design Simplifi cation
Additionally, the wave spring simpli es the
design. Only one component is needed to
achieve the desired spring function, which
usually requires multiple round wire coil
springs. The result is a lighter, less complex,
module that is easier to assemble and
maintain.
As the blade brake clutch example shows,
wave springs can o er the design engineer
advantages when tasked with developing
components and assemblies that need to
be compact, less complex, and yet reliably
perform the functions in safety-critical
applications.
In addition to design simpli cation and
space savings, wave springs o er other design
advantages such as a consistent force over a
wide range of de ections, transmitting those
forces only in the intended axial direction
while improving dimensional tolerances.
Interested in fi nding out if a
wave spring can empower your
application design?
Connect with rotor clip’s
technical sales engineers via
email at info@rotorclip.com
26 WWW.EUREKAMAGAZINE.CO.UK | FEBRUARY 2020
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