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PROGRESS IN TIRES. FHWA Workshop 25 Oct 2007 John Melson Michelin Americas R&D. Topics. In the beginning – rough roads and early tires The bias tire, how it works, and how it led to The radial tire

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progress in tires

PROGRESS IN TIRES

FHWA Workshop

25 Oct 2007

John Melson

Michelin Americas R&D

topics
Topics
  • In the beginning – rough roads and early tires
  • The bias tire, how it works, and how it led to
  • The radial tire
  • Truck tires and how they perform- why radials hit the sweet spot for modern vehicles and roads
  • Why low aspect ratio radial tires are difficult
  • The new hybrid and how it advances design one step further

© Michelin Tire Corporation

slide3

Early days: Rough roads

Rigid wheel no tire: the wheel is forced to mount the obstacle and then drop

Rigid wheel response

Tire with high inflation pressure

Tire with low inflation pressure

Wheel with tire: the tire deforms over the obstacle, less vertical motion, more energy recoverd

  • A 1888 patent by J.B. Dunlop described how a pneumatic tube attached to a rigid rim could ease rolling over rough ground significantly.

© Michelin Tire Corporation

membrane equilibrium shape

φ

Θ

Membrane Equilibrium Shape

r

Radius of curvature is determined by

BIAS CASING

Curvature and casing cord length determine shape

Shape of casing + mechanical properties of casing section determine footprint/contact pressures and thus performance in wear, traction,

© Michelin Tire Corporation

slide5

Bias Construction Parameters and Inflated Shape

r

r0

Building on drum

Conformed to larger radius

ply angles decrease

Rolling direction

Contact Patch progression

High H/W to Low H/W

© Michelin Tire Corporation

bias casing properties
Bias Casing Properties
  • Simple construction, many reinforcing materials can be used
  • Lower bias angles provide higher cornering stiffness because more of the length of the casing is involved in steering or braking
    • Pure radial has poor performance – contact patch shape / contact stress distribution bad, cornering stiffness is very low
  • Shearing between plies in sidewall where large deformation imposes high displacements between cables which are close to each other.
  • Cord paths (except for radial) are non – geodesic with normal building methods so static shears between plies are induced with inflation
  • Contact area shape and stress are largely determined by bias angle. Some level of adjustment can be made by varying rubber thickness

© Michelin Tire Corporation

slide7

φ, p

Crown Belts (2)

Casing Ply (900)

Shear Coupling

r

Bead Wire

BELTED RADIAL CONSTRUCTION, LOAD BEARING STRUCTURES

NΘ/Nφ parameter

Crown Belt to Carcass Shear

Rφ large

Rφ small

© Michelin Tire Corporation

radial casing properties
Radial Casing Properties
  • Flat crown, flexible sidewall
  • Geodesic casing -> less fatigue, lower rolling losses
  • Casing shape has more design parameters variability
    • better contact area shape, better contact stress distribution
    • better wear life, traction, rolling losses

© Michelin Tire Corporation

slide9

Typical Radial Contact Stresses

Radial construction can distribute normal stresses more evenly.

Allows tuning of tangential stresses to improve abnormal wear resistance

tire treads and tread compounds have evolved rapidly
Tire Treads and Tread Compounds have evolved rapidly
  • Tread patterns and compounds needed to deal with wet traction and soft soil conditions.
  • Wear forms and wear rate must be optimized
  • Tread compounds and mechanics interact – the most effective designs optimize the two together
  • The casing evolves slowly, the tread evolves rapidly
  • Customer perception important – if it doesn’t look “traction” it hasn’t got traction.

© Michelin Tire Corporation

slide11

A recent tread innovation example:

Using interlocking sipes to modify

contact stresses

© Michelin Tire Corporation

slide12

Another major change: Rims and Wheels & Tires

Truck Rims:

Tube Type/Flat Seat/Multipiece:

Rim flange removable, rim pieces locked in place by tire pressure and mechanical engagement.

Subject to explosive failure throwing metal pieces.

Tube increases tire running temperature

Sealing Pressure

Casing Tension

Rim Load

150 slope

Tubeless/150 Drop Center

Single piece rim, casing ply forces provide leverage to seal tire on rim. Lower operating tire operating temperature, higher bead stresses, low probability of thrown metal fragments from rim or tire failure.

© Michelin Tire Corporation

truck tire naming by epoch
Truck tire naming by epoch

Tube Type Bias Ply Tires – almost always on multi-piece rims

10.00-20/22/24 XXX

Tire type – usually a tread name

Rim Diameter

even integers 20,22,24 = tube type multi-piece rim

Tire width in inches(10,11, 12..)

Tubeless Tires – almost always on single piece rims (150 drop center for truck)

10.00R 20/22/24 XXX

R =Radial

(different load/pressure)

Rim Diameter

half inch sizes

11R22.5 / 24.5 XXX

Tires were ~ 90 series

Tire width in inches(10,11, 12..) no decimal

Most recently metric width and aspect ratio added

Tire Section Height/Width

275/80R22.5 / 24.5 XXX

h w what limits
H/W – what limits?
  • Trucking profits from lower H/W:
    • Double wide tire (275/80 -> 445/50 or 455/45) NA trucking
    • Lower diameter tires (315/80 -> 315/60) European evolution
  • Belted radial constructions have most endurance when 70 < H/W < 90.
  • Low H/W in belted construction pushed towards higher inflation pressures to control endurance side effects -> greater contact stress level, less even stress distribution in contact.

© Michelin Tire Corporation

slide15

The answer: Circumferential reinforcement

Rφ -> ∞

Circumferential (00) reinforcing

Height constant with respect to dual equivalent tire

Increase width, lower H/W

A 445/50R22.5 casing

  • Three way hybrid of radial casing, small angle bias belt at shoulder and circumferential (00) reinforcing at center
    • Reduces shear stresses at shoulder -> lower inflation pressure for equal crown endurance
    • Better contact stress distribution in wide casing construction

© Michelin Tire Corporation

slide16

Rolling Resistance Evolution 1910 - 2002

Rolling Resistance (10-3)

Bandage plein

30

25

20

15

10

5

0

First tires

Pass Tire Truck Tire Railroad wheel Metro/subway tire Research materials (Shell eco marathon)

First cable reinforced tires

First Radial tires

Green X

First Metalique Tires

Energy 3

Energy

Xone

1880

1900

1920

1940

1960

1980

2000

2020

  • Order of magnitude in 2002 :
  • Passenger car : 8,5 -13 x10-3
  • Truck Tires : 4,5 (Xone) - 10 x10-3
  • - Motorcycle : 2,5 - 5x10-3

© Michelin Tire Corporation

slide17

Rolling Resistance Behavior:

α, β Determined by combination of mechanical effects of tread and casing behavior.

Rubber Compounds vary magnitude of R0 at P0 and Fz0

α~ -0.2

β~ -0.1

for a dual truck tire at road velocities

Xone/duals

R/R0

Fz/Fz0

P/P0

RR behavior: pressure effect is strong, Load effect weaker

© Michelin Tire Corporation

center reinforced low h w xone design goals
Center Reinforced Low H/W (Xone) Design Goals
  • Equivalent vehicle handling (braking, acceleration, cornering, stability) in all situations.
  • Better optimization of vehicle gross weight/volume, wear, rolling resistance and endurance than 80 H/W tire & rim

=

lower cost of ownership

  • Equal operating temperature (short term endurance)

Modified axle shown -> better roll over

Standard axle + 2” off set wheel -> equal roll over

© Michelin Tire Corporation

what customers want
What customers want
  • Safety
    • Vehicle stability – stopping, cornering, emergency maneuvers

© Michelin Tire Corporation

what customers want1
What customers want
  • Life cycle cost minimized
    • Purchase cost
    • Wear life
    • Fuel consumption
    • Payload maximization
    • Maintenance
    • Vehicle down time
      • Pressure maintenance
      • Repairability / Retreadability

© Michelin Tire Corporation