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 Bushings
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