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Suspension
Outline
• Introduction
• Suspension
components
• Suspension type
examples
– Solid axle
– Double Wishbone
– MacPherson Stru...
Suspension Purpose
• Isolate passengers
and cargo from
vibration and shock
• Improve mobility
• Improve vehicle
control
Basic Terminology
• Sprung Mass
– Mass of all components
that do not move much
when suspension is
displaced. (given the
fr...
Basic Terminology
• Unsprung Mass
– Mass of components
that move when
suspension is
displaced
– Minimizing the
unsprung ma...
Basic Terminology
• Bump
– Vertical displacement of entire sprung mass
Basic Terminology
• Roll
– Front View angular
rotation of the sprung
vehicle mass
Basic Terminology
• Pitch
– Side View angular rotation of the sprung
vehicle mass
Basic Terminology
• Roll Center
– Center at which the sprung
mass pivots about during a
roll situation (lateral
accelerati...
Basic Terminology
• Pitch Center
– Center at which the sprung mass pivots about during
a Pitch situation (fore/aft acceler...
Basic Terminology
Camber
Front View tilt of the tire.
Leaning the top of the
tire inboard adds
negative camber
Basic Terminology
Toe
Top view angle of the tire
in a static situation
Turning the front of the
tire in is referred to as
...
Basic Terminology
Steering Axis
Axis about which the
wheel/Tire rotate
about during steering
inputs
Also known as “King
Pi...
Basic Terminology
Caster Angle
Side view tilt of the
steering axis.
Creates camber
change with steering
input
Creates a re...
Basic Terminology
Caster Trail
Side view distance from
the steering axis ground
plain intersection and the
contact patch c...
Basic Terminology
Scrub Radius
Distance From which the
ground plain intersection
of the Steering axis and
the center of th...
Basic Terminology
Steering Arm
Line between the
steering axis and there
steering linkage “tie rod”
Basic Terminology
Bump Travel
Vertical distance wheel is
able to move up from static
position, with reference to
vehicles ...
Passenger Comfort
The perception of vehicle comfort is very
subjective. Much depends on the cabin
conditions. The main obj...
Simplified Quarter Car Model
• Two Degree-of-
Freedom System
– However the longitudinal
and lateral stiffness of
most susp...
Simplified Half Car Model
• Two Degree-of-Freedom System
– However the longitudinal and lateral stiffness of most
suspensi...
Components of Suspension
• Tire
• Linkage
• Bearings, Bushings
• Springs
• Dampers
• Sprung / Unsprung
Mass
Tire
• Acts as both a spring
and a damper
• These rates are
affected by air
pressure and tire
construction.
Pivot Joints
• Spherical & Roller
bearings
– High performance
applications
– Minimal Compliance
– High Precision
– Low Sti...
Spring Types
• Leaf Springs
– Used in many early
applications
– Internal friction provides
damping
– Provide Fore/Aft/Late...
Spring Types
• Torsion Bars
– Little to no internal
damping
– Low cost
– Often difficult to
package
Spring Types
• Coil Springs
– Little to no internal
damping
– Low cost
– Compact Size
– Used in many
Suspension types
Solid Axle Suspensions
Applications:
-Pick Up Trucks (Rear)
-Stock Cars (Rear)
-Rock Crawlers (Front &
Rear)
Advantages
• Fewer Individual Components
– Easier to cheaply
manufacture and assemble
– Simplified drivetrain layout
• Hig...
Disadvantages
Disadvantages:
• Higher Unsprung Weight
– Can lead to “wheel hop”
• Axle wrap when in a leaf
spring configur...
Camber Change
• The diagram below shows how the camber is
statically fixed, and does not change in rebound
• The middle di...
Solid axle adjustability
• As far as the static
characteristics of the
suspension the camber
and castor are preset in
the ...
Truck, NASCAR applications
Double Wishbone Suspension
With Unequal Length Upper and Lower Arms
Found On:
-Stock Cars (Front)
-Corvettes (C5 &C6)
(Fro...
Advantages
• Arguably the best handling suspension design
– Wheel gains negative camber in bump
– Low Unsprung Weight
• Pa...
Disadvantages
• More expensive
– More components to make and assemble
– Alignment and fitment are critical to vehicle perf...
Double Wishbone Tuning
• The double wishbones
complexity enables it to be
adjusted quite readily
• The suspension geometry...
Formula 1 Application
Suspension Types: MacPherson Strut
• Invented by Earl S.
MacPherson
• First used on the
1951 Ford Consul
• Ford held the p...
Suspension Types: MacPherson Strut
Advantages
– Low production costs
• Stamped construction
– Preassembled
• Strut body ca...
Suspension Types: McPherson Strut
Disadvantages
– Large camber variation
• Body roll and wheel
movement contribute to
camb...
Associated forces in the strut
• Since the strut serves
as the upper control
arm as well as the
damper it is required
to p...
Adjustment of MacPherson Strut
• Since the strut governs
the King pin axis as well
as the camber of the tire,
these two pa...
Suspension Types: MacPherson Strut
• MacPherson Struts
are widely used on a
variety of cars today
from the everyday
road c...
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Suspension system

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Suspension system

  1. 1. Suspension
  2. 2. Outline • Introduction • Suspension components • Suspension type examples – Solid axle – Double Wishbone – MacPherson Strut • Introduce basic geometry
  3. 3. Suspension Purpose • Isolate passengers and cargo from vibration and shock • Improve mobility • Improve vehicle control
  4. 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. 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. 6. Basic Terminology • Bump – Vertical displacement of entire sprung mass
  7. 7. Basic Terminology • Roll – Front View angular rotation of the sprung vehicle mass
  8. 8. Basic Terminology • Pitch – Side View angular rotation of the sprung vehicle mass
  9. 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. 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. 11. Basic Terminology Camber Front View tilt of the tire. Leaning the top of the tire inboard adds negative camber
  12. 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. 13. Basic Terminology Steering Axis Axis about which the wheel/Tire rotate about during steering inputs Also known as “King Pin Axis”
  14. 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. 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. 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. 17. Basic Terminology Steering Arm Line between the steering axis and there steering linkage “tie rod”
  18. 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. 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.
  20. 20. Simplified Quarter Car Model • Two Degree-of- Freedom System – However the longitudinal and lateral stiffness of most suspension cannot be totally disregarded
  21. 21. Simplified Half Car Model • Two Degree-of-Freedom System – However the longitudinal and lateral stiffness of most suspension cannot be totally disregarded
  22. 22. Components of Suspension • Tire • Linkage • Bearings, Bushings • Springs • Dampers • Sprung / Unsprung Mass
  23. 23. Tire • Acts as both a spring and a damper • These rates are affected by air pressure and tire construction.
  24. 24. Pivot Joints • Spherical & Roller bearings – High performance applications – Minimal Compliance – High Precision – Low Stiction/Friction • Bushings – Low Cost – Offers compliance
  25. 25. 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
  26. 26. Spring Types • Torsion Bars – Little to no internal damping – Low cost – Often difficult to package
  27. 27. Spring Types • Coil Springs – Little to no internal damping – Low cost – Compact Size – Used in many Suspension types
  28. 28. Solid Axle Suspensions Applications: -Pick Up Trucks (Rear) -Stock Cars (Rear) -Rock Crawlers (Front & Rear)
  29. 29. 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
  30. 30. 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
  31. 31. 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
  32. 32. 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
  33. 33. Truck, NASCAR applications
  34. 34. 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)
  35. 35. 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
  36. 36. 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
  37. 37. 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.
  38. 38. Formula 1 Application
  39. 39. 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
  40. 40. 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.
  41. 41. 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.
  42. 42. 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.
  43. 43. 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.
  44. 44. 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

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