Copyright Joseph Greene 2001 3 Introduction History –The wheel is one of the most important inventions that has a wide range of applications. Transportation vehicles, construction equipment, internal parts of machines –Invented during the Bronze age over 5000 years ago Sumeria in 3500 BCE used in wheeled vehicles Assyria in 3000 BCE Central Europe in 1000 BCE 1500BCS: 4- wheeled wagons using swiveling front axle. –Use in military applications in Mesopotamia with a spoked wheel and a tire from leather and then later copper and iron binding. –1839: Vulcanization invented by Charles Goodyear –1846: RW Thompson invented elastomeric air tube to be fixed on wheel.
Copyright Joseph Greene 2001 4 Tire Types and Performance 9 Categories for tire applications –Racing vehicles, passenger vehicles, light trucks Use a lot of fabric as reinforcement –Heavy trucks, farm and agricultural vehicles, earthmoving equipment, large aircraft tend to comprise both steel wire and fabric reinforcements. –Specialty tires for fork lift trucks, light aircraft, light construction, golf carts. Tires must fulfill set of conditions –Provide load-carrying capacity and cushioning and dampening –Transmit driving and braking torque –Provide cornering force and dimensional stability –Resist abrasion and generate steering response –Have low rolling resistance and provide minimum noise and minimum vibration –Be durable throughout the expected life span. Dampening characteristics, elastic properties and unique deformability and recovery of tires make tires unique in satisfying conditions.
Copyright Joseph Greene 2001 5 Tire Types and Performance Three performance parameters govern tire’s functions –Vehicle mission profile –Mechanical properties and wear performance –Esthetics, comfort, and behavioral characteristics for steering Mechanical performance describes a tires performance is response to forces and loads applied to it, including torque, load, steering input, etc. Results in a complex set of forces acting on tire. Fig 1. Tire functions include –Forward direction: performance –Lateral direction: vehicle control –Vertical direction: esthetics and comfort
Copyright Joseph Greene 2001 6 Basic Tire Design Tire is a cord/rubber composite –Tires have plies of reinforced cords extending transversely from the bead to bead, on top of which is a belt located below the tread –Belt cords have low extensibility and are made of steel and fabric depending on the application. –Belt cords are at a low angle of 12° and 25°, and serve as restrictions to the 90° casings. Tire construction –Range of specialized components are found in a tire Meet performance requirements –Examples, »Nylon overlays over the belt package, which restrict and control tire growth due to the centrifugal forces created at high speeds. »Ply turnup, which describes the manner in which the body ply wraps around the bead wire and turns up the sidewall, anchors the body ply to the bead bundle and further reinforces the lower sidewall region »Toe guard is a nylon-reinforced rubber that protects the bead toe from tearing during mounting and dismounting. Above the toe guard the chafer further protects the bead area from abrading against the rim flange during use –Fig 3
Copyright Joseph Greene 2001 7 Basic Tire Design Tire components –Assembly of components with a specific function Figure 4 Tread Tread shoulder Tread base Sidewall Curb Guard Beads Bead area components Plies Belts Shoulder belt wedge Liner
Copyright Joseph Greene 2001 8 Tire Engineering Tire is a composite of complex elastomer formulations –Fibers, textile, and steel cord. –Tire structure defines the number, location, and dimensions of the various components used in its composition. –Tire performance governed by Casing plies, bead construction, belts, sidewall, and tread. –Secondary components are Chafers, flippers, and overlays (strips of fabric located in the bead and crown areas) protect the primary components by minimizing stress concentrations Tire nomenclature and Dimensions –Terminology to describe tire and rim dimensions Figure 5 Common throughout industry to describe size, growth, and wheel well clearance factors in addition to load capacity and revolutions per unit distance
Copyright Joseph Greene 2001 9 Tire Engineering Tire nomenclature and Dimensions –Aspect ratio –Cord angle –Overall diameter –Section width –Static loaded radius Minimum dual spacing –Footprint length –Footprint width –Gross contact area –Net contact area –Asymmetrical –Load rating
Copyright Joseph Greene 2001 10 Tire Engineering Tire nomenclature and Dimensions –Three Basic tire size designations Conventional-size tires used on flat base rims- Tube tires Conventional-size tires used on 15° rims or tubeless Metric sizes used on 15° rims; tubeless –Lettering R for radial; D or (_) for bias; ML for mining and logging tire applications P for passenger vehicle tires; LT for light truck Example, –P195/75R14: Passenger car tire; 195 approx. section width in mm; 75 Aspect ratio; R for radial construction; 14 for nominal rim diameter in inches. –Heavy duty truck tire can have 11R24.5 for a conventional tubeless tire; where 11 = nominal section diameter in inches, R = radial, 24.5 Rim diameter in, standard aspect raio of 80 –Low profile metric tire would be sized 295/75R22.5
Copyright Joseph Greene 2001 11 Tire Engineering Tire nomenclature and Dimensions –Designing a tire Determination of required size. –Governed by »Rim dimensions, wheel well envelope, service load, service speed, and inflation –For metric heavy-duty truck tire, these are related as »L = (6.075 x 10 –5 ) K x P 0.7 x S d 1.1 (D r +S d ) »Where, L = load at 100 kph (kg); P = pressure (kPa); S d = dimensional factor; D r = rim diameter; K = constant from wheel speed. »Table I Load values for single mounted 11R24.5 Radial