Couleurs et véhicules - Les motos - Comptines et chansons titounis (Mai 2024)
Motocyclette, tout véhicule à moteur à deux roues ou, plus rarement, à trois roues, généralement propulsé par un moteur à combustion interne.
L'histoire
Tout comme l'automobile était la réponse au rêve du 19e siècle d'auto-propulser la calèche, l'invention de la moto a créé le vélo automoteur. Le premier modèle commercial était un trois-roues construit par Edward Butler en Grande-Bretagne en 1884. Il employait un moteur à essence monocylindre horizontal monté entre deux roues avant directrices et relié par une chaîne d'entraînement à la roue arrière.
En 1900, de nombreux fabricants convertissaient les vélos - ou cycles à pédales, comme on les appelait parfois - en ajoutant de petits moteurs à allumage commandé montés au centre. Le besoin de constructions fiables a conduit à des essais d'essais de motos routières et à une concurrence entre constructeurs. Les courses de motos Tourist Trophy originales ont eu lieu sur l'île de Man en 1907 en tant que courses de fiabilité ou d'endurance. De tels événements ont été le terrain d'essai de nombreuses nouvelles idées, des premières conceptions à deux temps aux moteurs multivalves suralimentés montés sur une carrosserie aérodynamique renforcée de fibre de carbone.
Composants
Motorcycles are produced with both two-stroke- and four-stroke-cycle engines and with up to four cylinders. Most are air-cooled, though a few are water-cooled. Engines are generally limited to displacements of about 1,800 cc. The smallest designs, termed mopeds (from “motor pedal”), have very small engines (50 cc) with fuel economies of as much as 2.4 litres per 100 km (100 miles per gallon). Such units are not permitted on limited-access public roads because of their low speed capability. In order of increasing power capacity and engine displacements, the other five classifications are child bikes, trail bikes, road bikes, touring bikes, and racing bikes. A subcategory of racing bikes is known as superbikes. These are motorcycles that displace more than 900 cc and in which the seat is tilted forward so that the rider is hunched over the frame, creating a more aerodynamic profile.
The motorcycle frame is often of steel, usually a combination of tubes and sheets. The wheels are generally aluminum or steel rims with spokes, although some cast wheels are used. Graphite, composite, and magnesium parts are increasingly in use because of their high strength-to-weight characteristics. Tires are similar to those used on automobiles but are smaller and rounded to permit leaning to lower the centre of gravity in a turn without losing traction. The gyroscopic effect of motorcycle wheels rotating at high speed significantly improves stability and cornering ability. Inertia and steering geometry are also significant factors. Front-wheel suspension is provided by coil springs on a telescopic fork; rear-wheel springs are often mounted on shock absorbers similar to those used in automobiles.
Transmissions on motorcycles typically have four to six speeds, although small bikes may have as few as two. Power is normally transmitted to the rear-wheel sprockets by a chain, though occasionally belts or shafts are used.
The clutch and throttle, which control engine speed, are operated by twist-type controls on the handgrips. The front-wheel brake is controlled by a lever near the handgrip; the rear-wheel brake is engaged by a foot pedal. Except on very small machines, the front brake is usually of the hydraulic disc type. The rear brake may be disc or drum. The kick starter has been mostly replaced by an electric push-button starter.
Emissions standards
Tailpipe emissions standards for motorcycles continue to be strengthened. In 1980 the U.S. Environmental Protection Agency (EPA) first regulated new motorcycle hydrocarbon emissions, requiring motorcycles to emit less than 5.0 grams per km (0.3 ounce per mile) of highway driving. California and the European Union (EU) imposed stricter limits on hydrocarbons and added restrictions on nitric oxides and carbon monoxide. In 2006 emissions from new motorcycles sold in the United States were limited to a combined 1.4 grams of hydrocarbons and nitric oxides and 12.0 grams of carbon monoxide per km. The EPA decreased the limit on combined emissions of hydrocarbons and nitric oxides to 0.8 gram in 2010. The EU reduced emissions from new motorcycles in 2004 to 1.0 gram of hydrocarbons, 0.3 gram of nitric oxides, and 5.5 grams of carbon monoxide per km; in 2007 these levels were further reduced to 0.3 gram of hydrocarbons, 0.15 gram of nitric oxides, and 2.0 grams of carbon monoxide per km. The EU did a further emission reduction in 2016 to 0.17 gram of hydrocarbons, 0.09 gram of nitric oxides, and 1.14 grams of carbon monoxide, with a further reduction to 0.1 gram of hydrocarbons, 0.06 gram of nitric oxides, and 1 gram of carbon monoxide planned for 2020. Although U.S. limits for carbon monoxide were not lowered by law, the required reductions in other pollutants effectively lowered carbon monoxide emissions in fact. In order to meet these “clean-air regulations,” manufacturers installed more sophisticated catalytic converters and fuel-injection systems.
