READ MUST...

1. Suspension

2. Outline
• Introduction
• Suspension
components
• Suspension type
examples
– Solid axle
– Double Wishbone
– MacPherson Strut
• Introduce basic
geometry

3. Suspension Purpose
• Isolate passengers
and cargo from
vibration and shock
• Improve mobility
• Improve vehicle
control

4. Basic Terminology
• Sprung Mass
– Mass of all components
that do not move much
when suspension is
displaced. (given the
frame as a fixed
reference)
– (Frame, engine,
passengers, etc,)
– Some suspension
components are
actually partially sprung
mass

5. Basic Terminology
• Unsprung Mass
– Mass of components
that move when
suspension is
displaced
– Minimizing the
unsprung mass allows
for more optimal
suspension operation

6. Basic Terminology
• Bump
– Vertical displacement of entire sprung mass

7. Basic Terminology
• Roll
– Front View angular
rotation of the sprung
vehicle mass

8. Basic Terminology
• Pitch
– Side View angular rotation of the sprung
vehicle mass

9. Basic Terminology
• Roll Center
– Center at which the sprung
mass pivots about during a
roll situation (lateral
acceleration)
– This is a dynamic point:
moves around throughout
suspension travel

10. Basic Terminology
• Pitch Center
– Center at which the sprung mass pivots about during
a Pitch situation (fore/aft acceleration)
– This is a dynamic point: moves around throughout
suspension travel

11. Basic Terminology
Camber
Front View tilt of the tire.
Leaning the top of the
tire inboard adds
negative camber

12. Basic Terminology
Toe
Top view angle of the
tire in a static situation
Turning the front of the
tire in is referred to as
adding “toe in”
Important for both front
and rear tires

13. Basic Terminology
Steering Axis
Axis about which the
wheel/Tire rotate
about during steering
inputs
Also known as “King
Pin Axis”

14. Basic Terminology
Caster Angle
Side view tilt of the
steering axis.
Creates camber
change with steering
input
Creates a restoring
force for centering
steering wheel

15. Basic Terminology
Caster Trail
Side view distance from
the steering axis ground
plain intersection and the
contact patch center point
Creates a restoring force
for centering steering
wheel

16. Basic Terminology
Scrub Radius
Distance From which the
ground plain intersection
of the Steering axis and
the center of the tire
contact patch
Large effect on drivers
feel and steering effort

17. Basic Terminology
Steering Arm
Line between the
steering axis and there
steering linkage “tie rod”

18. Basic Terminology
Bump Travel
Vertical distance wheel is
able to move up from static
position, with reference to
vehicles sprung mass
Droop Travel
Vertical distance wheel is
able to move down from
static position with reference
to vehicles sprung mass

19. Passenger Comfort
The perception of vehicle comfort is very
subjective. Much depends on the cabin
conditions. The main objective of the
designer is to minimize the rate of change
of acceleration (jerk).

20. Trophy truck video
• Front Independent
double wishbone
Suspension
•Rear Solid axle
•High horse power vehicle

21. Baja Buggy
•Front Independent double
wishbone Suspension
•Rear Independent double
wishbone Suspension
•Light weigh low
horsepower vehicle

22. Extreme mobility
•Control in extreme
maneuvers

23. Simplified Quarter Car Model
• Two Degree-of-
Freedom System
– However the longitudinal
and lateral stiffness of
most suspension cannot
be totally disregarded

24. Simplified Half Car Model
• Two Degree-of-Freedom System
– However the longitudinal and lateral stiffness of most
suspension cannot be totally disregarded

25. Components of Suspension
• Tire
• Linkage
• Bearings, Bushings
• Springs
• Dampers
• Sprung / Unsprung
Mass

26. Tire
• Acts as both a spring
and a damper
• These rates are
affected by air
pressure and tire
construction.

27. Pivot Joints
• Spherical & Roller
bearings
– High performance
applications
– Minimal Compliance
– High Precision
– Low Stiction/Friction
• Bushings
– Low Cost
– Offers compliance

28. Spring Types
• Leaf Springs
– Used in many early
applications
– Internal friction provides
damping
– Provide Fore/Aft/Lateral
location for the axle
– Heavy
– Prone to weaken over time

29. Spring Types
• Torsion Bars
– Little to no internal
damping
– Low cost
– Often difficult to
package

30. Spring Types
• Coil Springs
– Little to no internal
damping
– Low cost
– Compact Size
– Used in many
Suspension types

31. Solid Axle Suspensions
Applications:
-Pick Up Trucks (Rear)
-Stock Cars (Rear)
-Rock Crawlers (Front &
Rear)

32. Advantages
• Fewer Individual Components
– Easier to cheaply
manufacture and assemble
– Simplified drivetrain layout
• High Load Capacity
• Axle Components are
protected
• Can use leaf or coil springs
– Also can accept many
different types of linkages to
gain desired geometry
• Solid wheel attachment
– Minimal alignment eminence

33. Disadvantages
Disadvantages:
• Higher Unsprung Weight
– Can lead to “wheel hop”
• Axle wrap when in a leaf
spring configuration
• High Roll Center Height
• Not an Independent
Design
– Corners are coupled
• Fixed Camber Angles

34. Camber Change
• The diagram below shows how the camber is
statically fixed, and does not change in rebound
• The middle diagram shows how the camber of
the two wheels are linked to one another

35. Solid axle adjustability
• As far as the static
characteristics of the
suspension the camber
and castor are preset in
the manufacturing of the
axle housing
– However the dynamic
characteristics of the
suspension are highly
adjustable with various
forms or bar linkages
– There are many different
linkage designs for a solid
axle ranging from leaf
springs to multi-link
suspension systems

36. Truck, NASCAR applications

37. Double Wishbone Suspension
With Unequal Length Upper and Lower Arms
Found On:
-Stock Cars (Front)
-Corvettes (C5 &C6)
(Front and Rear)
-Honda Civics (‘88-’00)
(Front)
-Most Modern Sports
Cars

38. Advantages
• Arguably the best handling suspension design
– Wheel gains negative camber in bump
– Low Unsprung Weight
• Packaging does not compromise styling
– Low Height
• Many different geometry characteristics possible
– Designer can design suspension with minimal
compromises
– Infinite adjustability, with the most ease
– Vehicles roll centers can be placed almost anywhere

39. Disadvantages
• More expensive
– More components to make and assemble
– Alignment and fitment are critical to vehicle performance, large
area of adjustment
– Tolerance of parts must be smaller
– Requires constant alignment checks for optimum performance
• More complex
– Design often becomes more complex because all suspension
parameters are variable
– Frame has to be able to pick up a-arm inboard points
• Tire scrub occurs with vertical wheel displacement
– However this can be minimized during design

40. Double Wishbone Tuning
• The double wishbones
complexity enables it to be
adjusted quite readily
• The suspension geometry can
be adjusted in two distinct
ways
– Move the location of the inner
Chassis attachment points
– Adjust the inclination of the
upright and the pick-up
locations on the upright
• The camber, castor, roll
center, etc…. can all be
individually adjusted on this
type of suspension relatively
easily.

41. Formula 1 Application

42. Suspension Types: MacPherson Strut
• Invented by Earl S.
MacPherson
• First used on the
1951 Ford Consul
• Ford held the patent
for the Macpherson
strut system by many
rival companies
invented similar
systems to avoid Ford
royalties

43. Suspension Types: MacPherson Strut
Advantages
– Low production costs
• Stamped construction
– Preassembled
• Strut body carries spring
assembly
– Compact
• Simple mounting and no need
for an upper control arm
– Simplicity
• Reduction in fasteners and
alignment of vehicle suspension
components.

44. Suspension Types: McPherson Strut
Disadvantages
– Large camber variation
• Body roll and wheel
movement contribute to
camber attitude
– Vertically tall mounting
position
• This compromises vehicle
styling
– Rough ride
• Some ride comfort may be
lost, as it is hard to move
smoothly because of bending
input force
– Dangerous replacement
• The spring must be
compressed and assembled
on the strut body, this causes
the handling of a charged
spring.

45. Associated forces in the strut
• Since the strut serves
as the upper control
arm as well as the
damper it is required
to provide the force to
hold the wheel at the
desired camber
attitude.

46. Adjustment of MacPherson Strut
• Since the strut governs
the King pin axis as well
as the camber of the tire,
these two parameters are
linked
• The adjustability of the
MacPherson strut is
limited, due to its
simplicity
• Most adjustability of the
suspension is achieved
by modifying the location
of the upper strut
mounting location.

47. Suspension Types: MacPherson Strut
• MacPherson Struts
are widely used on a
variety of cars today
from the everyday
road car to world
class race cars