米其林低滚动阻力轮胎技术

Rolling Resistance Basic Foundation Randall CLARK Rolling Resistance Basic Foundation • Definition and Origins • Relative magnitude –Cars – Trucks – Buses • External Variables What is Rolling Resistance Rolling Resistance • FRR-Tire drag on vehicle montion How can you fell Rolling Resistance? • If you ride a bicycle with tires at low pressure,you have to work harder to overcome the increased rolling resistance. So is it Energy or Force? Both! • Rolling Resistence – =tire rolling energy consumed per unit distance – =work/distance – =[Newstons x meters]/msters • Rolling Resistance – =resistance force of the tires – =force – =Newtons What causes Rolling Resistance? • The main three physical causes of rolling resistance Where is most of the energy consumed in the tire? • Computer Modeling of Energy Loss The Role of Rubber Compounds • Positive: provide grip, resilience, toughness, wear • Negative: waste heat generated when tire flexes; lost energy comes form fuel tank Choosing Rubber Compounds • There are rubber compounds that can redece rolling resistance • The choice depends on many design requirements: –wear; grip; cut resistance…. • Some new high tech compounds can reduce rolling resistance with few compromises Tread Pattern Effects examples: truck tires Lower Rolling Resistance Smooth rib tires Higher Rolling Resistance lug tires Choice of Rubber Compounds & Tread Patterns affect Rolling Resistance & Heat Generation Truck tire images taken with infrared camera while tire rolling; both tires running under identical load and pressure Comparing low rolling resistance to high rolling resistance • You can see the difference in tread pattern and compound By placing different brands/types of tires on similar positions on the vehicle, you can see the heat and therefore RR differences by using an infrared camera at night… Cooler tires have other benefits, also • Truck tires: tire carcass lasts longer for potential retreading – Better use of reources • Car tires: cooler tires reduce chance of failure while running – safety Doses the tire structure play a role? Yes! Radial tires are better The Bias-ply Tire • A casing made of several plies positioned in a criss-cross manner The bias-ply tire HIGH FRICTION=HIGH ROLLING RESISTANCE Bias tire: Crown and sidewalls interdependent • Sidewall flesing is transmitted to the tread resulting in: –Distortion of ground contact area – Scissoring of casing plies that leads to overheating –High friction with the road surface Radials • Casing made of one radial ply • Crown stabilized by several steel plies • Sidewalls and tread function separately Radial Construction LOW FRICTION=LOW ROLLING RESISTANCE Radial: sidewalls and tread function independenly • Sidewall flexing is not transmitted to the tread resulting in: – Less distortion of the ground contact are –Reduced friction with the ground for enhanced ride comfort –Cool running Radial advantages • Improved fuel economy: – from 5% to 10% better • Better puncture resistance – safety • Cooler running casing – safety and retreadabilty • Better wear – two times longer – fewer tires needed per year; fewer to dispose • Less pavement damage than bias Does the tire size matter? Yes!! Larger tire are better. Rolling Resistance Basic Foundation • Definition and Origins • Relative magnitude –Cars – Trucks – Buses • External Variables Relative importance vs other factors Tire RR as a% of all fuel used: highway • Passenger car – form 8 to 20% – or for every 100 liters of fuel, 8 to 20 liters are consumed by the tires as lost energy • Truck and bus – form 25 to 35% – or for every 100 liters of fuel, 25 to 35 liters are consumed by the tires as lost energy Greatly depends on driving cycle Rolling Resistance Basic Foundation • Definition and Origins • Relative magnitude –Cars – Trucks – Buses • External Variables Time of Running • Rolling Resistance drops quickly and then stabilizes Effect of temperature • Warmer days cause a tire to be More Efficient (lower RR) Effect of speed • The tire contribution (FRR) does not change but the % contribution decreases because the areodynamic dray dominates at higher speeds Effect of Pressure Higher Pressure reduces Rolling Resistance Effect of load Complex • The tire becomes more efficient (CRR)- BUT the actual resistive force (FRR) increases because the load in the tire increases Rolling Resistance: key points • It consumes fuel from your fuel tank • It cannot be completely eliminated • Certain tire designs and compounds can lower rolling resistance