UWE Bristol Engineering showcase 2015

Oliver de Garston
MEng Motorsport Engineering
Formula Student Car Suspension Design
Deciding Basic Parameters
The start of the design process begins with
deciding on the best wheelbase and track as these
have great consequence on the longitudinal and
lateral weight transfer. A wheel base was chosen
with a near 50/50 weight distribution from the
estimated centre of gravity and vehicle mass.
Track was chosen on the basis on lateral load
transfer and course width at the event, too wide
would mean manoeuvres need to be larger to
negotiate obstacles, to narrow and load transfer
become too great.
Upright Geometry
The starting point for
upright geometry is
making sure any braking
system fits inside the
chosen wheel, this will
then give the brake disc
offset to the wheel and
then consequently the
best possible position
for the lower outer
pivot point is as close to the brake disc as possible
as low down as possible.
Suspension Geometry
Once outboard pivot points are chosen, attention
can then turn toward the inboard points. Vsusp
was used to design from this point, as it gave a real
time look at the roll centre and shape of the
suspension.
Once the desired design was formed in Vsusp this
was moved over to Solidworks to create a 3D
design below is shown the front suspension
geometry.
This was repeated for the rear to give the overall
suspension geometry seen below. The lines
extending out the front are the anti-squat lines for
the rear suspension. 30% anti-squat was included
in the design.
Bellcrank Geometry
Once the front and rear wishbone and upright
geometry is decided, the pushrod and bellcrank
geometry is next on the list. Below is a graph of
the front bellcrank motion ratio. As seen the ratio
is nearly linear, this is an ideal situation as it means
the shock has a smooth actuation.
Analysis
The system was then built in MSC Adams,
although the program was not used to its full
potential it was still used for some basic analysis.
A key area of analysis was the movement of the
roll centre below is the graph of roll centre
movement due to body roll.
The system geometry was then turned into a CAD
design for the UWE Formula Student team to
manufacture for the new 2015 car.
Project Supervisor
Dr. Rohitha Weerasinghe
Project summary
The aim of this work is to design from scratch a
suspension system for the University’s race car to suit
the needs of the event and to analyse its
performance though computer simulation. This
design will be one of the key features of this year’s
car being built by students participating in the UWE
Formula Student team. The suspension system will be
of a classical unequal length double wishbone design.
This suspension type has the most adjustability in
characteristics and should meet all demands.
Project Objectives
• A kingpin inclination angle of between 0° and 8°
• A scrub radius between 0mm and 100mm
• A caster angle between 3° and 7°
• Static camber of around -2° but adjustable
between 0°and -4°
• Camber gain of between 0.2° and 0.5° at the front
axle
• Camber gain of between 0.5° and 0.8° at the rear
axle
• A maximum roll of about 2°
• A roll centre height between 25mm below ground
and 50mm above ground at the front and
marginally higher at the rear
• Controlled and predictable movement of the roll
axis
• A swing arm length of between 1250mm and
2500mm at the front
• A swing arm length of between 1016mm and
1778mm at the rear
• Minimal bump steer
• 50% - 65% of the roll stiffness on the rear axle
Project Conclusion
This system should be practical and possible for the
UWE Formula Student team to manufacture and
construct, to within reasonable tolerances the
system, to enable the team to go to Silverstone with a
complete and accurate suspension system that
complies with all the rules. The author believes that
the basic geometry of the system is good, and
enables there to be space for all the vehicles other
subsystems.