An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes on bicycles, the latter type axle is referred to as a spindle. On cars and trucks, several senses of the word axle occur in casual usage, referring to the shaft itself, its housing, or any transverse pair of wheels. Speaking, a shaft which rotates with the wheel, being either bolted or splined in fixed relation to it, is called an axle or axle shaft. However, in looser usage, an entire assembly including the surrounding axle housing is called an axle. An broader sense of the word refers to every pair of parallel wheels on opposite sides of a vehicle, regardless of their mechanical connection to each other and to the vehicle frame or body.
Thus, transverse pairs of wheels in an independent suspension may be called an axle in some contexts. This loose definition of "axle" is used in assessing toll roads or vehicle taxes, is taken as a rough proxy for the overall weight-bearing capacity of a vehicle, its potential for causing wear or damage to roadway surfaces. Axles are an integral component of most practical wheeled vehicles. In a live-axle suspension system, the axles serve to transmit driving torque to the wheel, as well as to maintain the position of the wheels relative to each other and to the vehicle body; the axles in this system must bear the weight of the vehicle plus any cargo. A non-driving axle, such as the front beam axle in heavy duty trucks and some two-wheel drive light trucks and vans, will have no shaft, serves only as a suspension and steering component. Conversely, many front-wheel drive cars have a solid rear beam axle. In other types of suspension systems, the axles serve only to transmit driving torque to the wheels.
This is typical of the independent suspensions found on most newer cars and SUVs, on the front of many light trucks. These systems still will not have attached axle housing tubes, they may be attached to integral in a transaxle. The axle shafts transmit driving torque to the wheels. Like a full floating axle system, the drive shafts in a front-wheel drive independent suspension system do not support any vehicle weight A straight axle is a single rigid shaft connecting a wheel on the left side of the vehicle to a wheel on the right side; the axis of rotation fixed by the axle is common to both wheels. Such a design can keep the wheel positions steady under heavy stress, can therefore support heavy loads. Straight axles are used on trains, for the rear axles of commercial trucks, on heavy duty off-road vehicles; the axle can optionally be protected and further reinforced by enclosing the length of the axle in a housing. In split-axle designs, the wheel on each side is attached to a separate shaft.
Modern passenger cars have split drive axles. In some designs, this allows independent suspension of the left and right wheels, therefore a smoother ride; when the suspension is not independent, split axles permit the use of a differential, allowing the left and right drive wheels to be driven at different speeds as the automobile turns, improving traction and extending tire life. A tandem axle is a group of two or more axles situated close together. Truck designs use such a configuration to provide a greater weight capacity than a single axle. Semi trailers have a tandem axle at the rear. Axles are made from SAE grade 41xx steel or SAE grade 10xx steel. SAE grade 41xx steel is known as "chrome-molybdenum steel" while SAE grade 10xx steel is known as "carbon steel"; the primary differences between the two are that chrome-moly steel is more resistant to bending or breaking, is difficult to weld with tools found outside a professional welding shop. An axle, driven by the engine or prime mover is called a drive axle.
Modern front-wheel drive cars combine the transmission and front axle into a single unit called a transaxle. The drive axle is universal joints between the two half axles; each half axle connects to the wheel by use of a constant velocity joint which allows the wheel assembly to move vertically as well as to pivot when making turns. In rear-wheel drive cars and trucks, the engine turns a driveshaft which transmits rotational force to a drive axle at the rear of the vehicle; the drive axle may be a live axle, but modern rear wheel drive automobiles use a split axle with a differential. In this case, one half-axle or half-shaft connects the differential with the left rear wheel, a second half-shaft does the same with the right rear wheel; some simple vehicle designs, such as leisure go-karts, may have a single driven wheel where the drive axle is a split axle with only one of the two shafts driven by the engine, or else have both wheels connected to one shaft without a differential. However, other go-karts have two rear drive wheels too.
A dead axle called a lazy axle, is not part of the drivetrain, but is instead free-rotating
A three-wheeler is a vehicle with three wheels. Some are motorized tricycles, which may be classed as motorcycles, while others are tricycles without a motor, some of which are human-powered vehicles and animal-powered vehicles. Many three-wheelers which exist in the form of motorcycle-based machines are called trikes and have the front single wheel and mechanics similar to that of a motorcycle and the rear axle similar to that of a car; such vehicles are owner-constructed using a portion of a rear-engine, rear-drive Volkswagen Beetle in combination with a motorcycle front end. Other trikes include ATVs. Three-wheelers can have either one wheel at the back and two at the front, or one wheel at the front and two at the back. Due to better safety when braking, an popular form is the front-steering "tadpole" or "reverse trike" sometimes with front drive but with rear drive. A variant on the'one at the front' layout was the Scott Sociable, which resembled a four-wheeler with a front wheel missing.
Three-wheelers, including some cyclecars, bubble cars and microcars, are built for economic and legal reasons: in the UK for tax advantages, or in the US to take advantage of lower safety regulations, being classed as motorcycles. As a result of their light construction and potential better streamlining, three-wheeled cars are less expensive to operate. Three-wheeler transport vehicles known as auto rickshaws are a common means of public transportation in many countries in the world, are an essential form of urban transport in many developing countries such as India and the Philippines. Auto rickshaws are a form of novelty transport in many Eastern countries. Early automotive pioneer Karl Benz developed a number of three-wheeled models. One of these, the Benz Patent Motorwagen, is regarded as the first purpose-built automobile, it was made in 1885. In 1896, John Henry Knight showed a tri-car at The Great Exhibition. In 1897, Edward Butler made another three-wheeled car. A Conti 6 hp Tri-car competed in a 1907 Peking to Paris race sponsored by a French newspaper, Le Matin.
A configuration of two wheels in the front and one wheel at the back presents two advantages: it has improved aerodynamics, that it enables the use of a small lightweight motorcycle powerplant and rear wheel. This approach was used by the Messerschmitt BMW Isetta. Alternatively, a more conventional front-engine, front wheel drive layout as is common in four-wheeled cars can be used, with subsequent advantages for transversal stability and traction; some vehicles have a front engine driving the single rear wheel, similar to the rear engine driving the rear wheel. The wheel must support acceleration loads as well as lateral forces when in a turn, loss of traction can be a challenge. A new tadpole configuration has been proposed with a rear engine driving the front wheels; this concept claims both traction, as well as a unique driving experience. With two wheels in the front the vehicle is far more stable in braking turns, but remains more prone to overturning in normal turns compared to an equivalent four-wheeled vehicle, unless the center of mass is lower and/or further forward.
Motorcycle-derived designs suffer from most of the weight being towards the rear of the vehicle. For lower wind resistance, a teardrop shape is used. A teardrop is round at the front, tapering at the back; the three-wheel configuration allows the two front wheels to create the wide round surface of the vehicle. The single rear wheel allows the vehicle to taper at the back. Examples include the Aptera 2 Series and Myers Motors NmG. Having one wheel in front and two in the rear for power reduces the cost of the steering mechanism but decreases lateral stability when cornering while braking; when the single wheel is in the front, the vehicle is inherently unstable in a braking turn, as the combined tipping forces at the center of mass from turning and braking can extend beyond the triangle formed by the contact patches of the wheels. This type, if not tipped has a greater tendency to spin out when handled roughly; the disadvantage of a three-wheel configuration is lateral instability—the car will tip over in a turn before it will slide.
This can be prevented in three ways: by placing the center of mass closer to the ground by placing the center of mass closer to the axle with two wheels by increasing the track widthIn the case of a three-wheeled ATV, tipping may be avoided by the rider leaning into turns. To improve stability some three-wheelers are designed to tilt while cornering like a motorcyclist would do; the tilt may be controlled manually, mechanically or by computer. A tilting three-wheeler's body or wheels, or both, tilt in the direction of the turn; such vehicles can corner safely with a narrow track. Some tilting three-wheelers could be considered to be forms of feet forwards motorcycles or cabin motorcycles or both. Three-wheeled battery powered designs include: Aptera 2 Series Arcimoto CityEl Commuter Cars Tango Cree SAM Myers Motors NmG Toyota i-Road Triac Vanderhall Edison2 ZAP Xebra The world's fastest solar-powered vehicle, Ashiya University's Sky Ace TIGA, is a three-wheeler, it achieved 91.332 kilometres per hour at Shimojishima Airport, in Miyakojima, Japan, to win the Guinness World Record, on 20 August 2014.
An electric vehicle called an EV, uses one or more electric motors or traction motors for propulsion. An electric vehicle may be powered through a collector system by electricity from off-vehicle sources, or may be self-contained with a battery, solar panels or an electric generator to convert fuel to electricity. EVs include, but are not limited to, road and rail vehicles and underwater vessels, electric aircraft and electric spacecraft. EVs first came into existence in the mid-19th century, when electricity was among the preferred methods for motor vehicle propulsion, providing a level of comfort and ease of operation that could not be achieved by the gasoline cars of the time. Modern internal combustion engines have been the dominant propulsion method for motor vehicles for 100 years, but electric power has remained commonplace in other vehicle types, such as trains and smaller vehicles of all types. In the 21st century, EVs saw a resurgence due to technological developments, an increased focus on renewable energy.
A great deal of demand for electric vehicles developed and a small core of do-it-yourself engineers began sharing technical details for doing electric vehicle conversions. Government incentives to increase adoptions were introduced, including in the United States and the European Union. Electric vehicles are expected to increase from 2% of global share in 2016 to 22% in 2030. Electric motive power started in 1827, when Hungarian priest Ányos Jedlik built the first crude but viable electric motor, provided with stator and commutator, the year after he used it to power a tiny car. A few years in 1835, professor Sibrandus Stratingh of the University of Groningen, the Netherlands, built a small-scale electric car, between 1832 and 1839, Robert Anderson of Scotland invented the first crude electric carriage, powered by non-rechargeable primary cells. Around the same period, early experimental electrical cars were moving on rails, too. American blacksmith and inventor Thomas Davenport built a toy electric locomotive, powered by a primitive electric motor, in 1835.
In 1838, a Scotsman named Robert Davidson built an electric locomotive that attained a speed of four miles per hour. In England a patent was granted in 1840 for the use of rails as conductors of electric current, similar American patents were issued to Lilley and Colten in 1847; the first mass-produced electric vehicles appeared in America in the early 1900s. In 1902, "Studebaker Automobile Company" entered the automotive business with electric vehicles, though it entered the gasoline vehicles market in 1904. However, with the advent of cheap assembly line cars by Ford, electric cars fell to the waysideDue to the limitations of storage batteries at that time, electric cars did not gain much popularity, however electric trains gained immense popularity due to their economies and fast speeds achievable. By the 20th century, electric rail transport became commonplace. Over time their general-purpose commercial use reduced to specialist roles, as platform trucks, forklift trucks, tow tractors and urban delivery vehicles, such as the iconic British milk float.
Electrified trains were used for coal transport, as the motors did not use precious oxygen in the mines. Switzerland's lack of natural fossil resources forced the rapid electrification of their rail network. One of the earliest rechargeable batteries - the nickel-iron battery - was favored by Edison for use in electric cars. EVs were among the earliest automobiles, before the preeminence of light, powerful internal combustion engines, electric automobiles held many vehicle land speed and distance records in the early 1900s, they were produced by Baker Electric, Columbia Electric, Detroit Electric, others, at one point in history out-sold gasoline-powered vehicles. In fact, in 1900, 28 percent of the cars on the road in the USA were electric. EVs were so popular that President Woodrow Wilson and his secret service agents toured Washington, DC, in their Milburn Electrics, which covered 60–70 mi per charge. A number of developments contributed to decline of electric cars. Improved road infrastructure required a greater range than that offered by electric cars, the discovery of large reserves of petroleum in Texas and California led to the wide availability of affordable gasoline/petrol, making internal combustion powered cars cheaper to operate over long distances.
Internal combustion powered cars became easier to operate thanks to the invention of the electric starter by Charles Kettering in 1912, which eliminated the need of a hand crank for starting a gasoline engine, the noise emitted by ICE cars became more bearable thanks to the use of the muffler, which Hiram Percy Maxim had invented in 1897. As roads were improved outside urban areas electric vehicle range could not compete with the ICE; the initiation of mass production of gasoline-powered vehicles by Henry Ford in 1913 reduced the cost of gasoline cars as compared to electric cars. In the 1930s, National City Lines, a partnership of General Motors and Standard Oil of California purchased many electric tram networks across the country to dismantle them and replace them with GM buses; the partnership was convicted of conspiring to monopolize the sale of equipment and supplies to their subsidiary companies, but were acquitted of conspiring to monopolize the provision of transportation services.
In January 1990, General Motors' President introduced its EV concept two-seater, the "Impact", at the Los Angeles Auto Show. That September, the California Air Resources Board mandated major-automaker sales of EVs, in phases
Paris is the capital and most populous city of France, with an area of 105 square kilometres and an official estimated population of 2,140,526 residents as of 1 January 2019. Since the 17th century, Paris has been one of Europe's major centres of finance, commerce, fashion and the arts; the City of Paris is the centre and seat of government of the Île-de-France, or Paris Region, which has an estimated official 2019 population of 12,213,364, or about 18 percent of the population of France. The Paris Region had a GDP of €681 billion in 2016, accounting for 31 percent of the GDP of France, was the 5th largest region by GDP in the world. According to the Economist Intelligence Unit Worldwide Cost of Living Survey in 2018, Paris was the second most expensive city in the world, after Singapore, ahead of Zurich, Hong Kong and Geneva. Another source ranked Paris as most expensive, on a par with Singapore and Hong-Kong, in 2018; the city is a major rail and air-transport hub served by two international airports: Paris-Charles de Gaulle and Paris-Orly.
Opened in 1900, the city's subway system, the Paris Métro, serves 5.23 million passengers daily, is the second busiest metro system in Europe after Moscow Metro. Gare du Nord is the 24th busiest railway station in the world, the first located outside Japan, with 262 million passengers in 2015. Paris is known for its museums and architectural landmarks: the Louvre was the most visited art museum in the world in 2018, with 10.2 million visitors. The Musée d'Orsay and Musée de l'Orangerie are noted for their collections of French Impressionist art, the Pompidou Centre Musée National d'Art Moderne has the largest collection of modern and contemporary art in Europe; the historical district along the Seine in the city centre is classified as a UNESCO Heritage Site. Popular landmarks in the centre of the city include the Cathedral of Notre Dame de Paris and the Gothic royal chapel of Sainte-Chapelle, both on the Île de la Cité. Paris received 23 million visitors in 2017, measured by hotel stays, with the largest numbers of foreign visitors coming from the United States, the UK, Germany and China.
It was ranked as the third most visited travel destination in the world in 2017, after Bangkok and London. The football club Paris Saint-Germain and the rugby union club Stade Français are based in Paris; the 80,000-seat Stade de France, built for the 1998 FIFA World Cup, is located just north of Paris in the neighbouring commune of Saint-Denis. Paris hosts the annual French Open Grand Slam tennis tournament on the red clay of Roland Garros. Paris will host the 2024 Summer Olympics; the 1938 and 1998 FIFA World Cups, the 2007 Rugby World Cup, the 1960, 1984, 2016 UEFA European Championships were held in the city and, every July, the Tour de France bicycle race finishes there. The name "Paris" is derived from the Celtic Parisii tribe; the city's name is not related to the Paris of Greek mythology. Paris is referred to as the City of Light, both because of its leading role during the Age of Enlightenment and more because Paris was one of the first large European cities to use gas street lighting on a grand scale on its boulevards and monuments.
Gas lights were installed on the Place du Carousel, Rue de Rivoli and Place Vendome in 1829. By 1857, the Grand boulevards were lit. By the 1860s, the boulevards and streets of Paris were illuminated by 56,000 gas lamps. Since the late 19th century, Paris has been known as Panam in French slang. Inhabitants are known in French as Parisiens, they are pejoratively called Parigots. The Parisii, a sub-tribe of the Celtic Senones, inhabited the Paris area from around the middle of the 3rd century BC. One of the area's major north–south trade routes crossed the Seine on the île de la Cité; the Parisii minted their own coins for that purpose. The Romans began their settlement on Paris' Left Bank; the Roman town was called Lutetia. It became a prosperous city with a forum, temples, an amphitheatre. By the end of the Western Roman Empire, the town was known as Parisius, a Latin name that would become Paris in French. Christianity was introduced in the middle of the 3rd century AD by Saint Denis, the first Bishop of Paris: according to legend, when he refused to renounce his faith before the Roman occupiers, he was beheaded on the hill which became known as Mons Martyrum "Montmartre", from where he walked headless to the north of the city.
Clovis the Frank, the first king of the Merovingian dynasty, made the city his capital from 508. As the Frankish domination of Gaul began, there was a gradual immigration by the Franks to Paris and the Parisian Francien dialects were born. Fortification of the Île-de-la-Citie failed to avert sacking by Vikings in 845, but Paris' strategic importance—with its bridges prevent