Kei car is the Japanese vehicle category for the smallest highway-legal passenger cars. Similar Japanese categories existing for microvans, Kei trucks; the kei car category was created by the Japanese government in 1949, the regulations have been revised several times since. These regulations specify a maximum vehicle size, engine capacity of 660cc and power output, so that the kei car may enjoy both tax and insurance benefits. In most rural areas are exempted from the requirement to certify that adequate parking is available for the vehicle. Kei cars have become successful in Japan — consisting just over one third of domestic new car sales in fiscal 2016, in spite of dropping from a record 40% market share in 2013, just three years prior. However, in export markets, the genre is too specialized and too small for most models to be profitable. Notable exceptions exist though, for instance the Suzuki Alto and Jimny models, which were exported from ca. 1980. Most kei cars are designed and manufactured in Japan, however there have been overseas models that have been imported into Japan to be sold as kei cars.
Kei cars feature yellow license plates, earning them the name "yellow-plate cars" in English-speaking circles. Japanese government regulations limit the physical size, engine power and engine displacement of kei cars. Kei cars are available with forced-induction engines, automatic and CV transmissions, front-wheel drive and all-wheel drive; the Kei-car legal class originated in the era following the end of the Second World War, when most Japanese could not afford a full-sized car, but many had enough money to buy a motorcycle. To promote the growth of the car industry, as well as to offer an alternative delivery method to small business and shop owners, the kei car category and standards were created. Limited to a displacement of only 150 cc in 1949, dimensions and engine size limitations were expanded to tempt more manufacturers to produce kei cars. In 1955, the displacement limit increased to 360 cc for both two-strokes, as well as four-stroke engines, resulting in several new kei car models beginning production in the following years.
These included the 1955 Suzuki Suzulight and the 1958 Subaru 360, the first mass-produced kei car able to fill people's need for basic transportation without being too compromised. In 1955, the Japanese Ministry of International Trade and Industry set forth goals to develop a "national car", larger than kei cars produced at the time; this goal influenced Japanese automobile manufacturers to determine how best to focus their product development efforts for the smaller kei cars, or the larger "national car". The small exterior dimensions and engine displacement reflected the driving environment in Japan, with speed limits in Japan realistically not exceeding 40 km/h in urban areas; the class went through a period of increasing sophistication, with an automatic transmission appearing in the Honda N360 in August 1968, with front disc brakes becoming available on a number of sporting kei cars, beginning with the Honda Z GS of January 1970. Power outputs kept climbing, reaching a peak in the 40 PS Daihatsu Fellow Max SS of July 1970.
Sales increased reaching a peak of 750,000 in 1970. Throughout the 1970s, the government kept whittling away at the benefits offered to kei vehicles, which combined with stricter emissions standards to lower sales drastically through the first half of the decade. Honda and Mazda withdrew from the contracting passenger kei car market, in 1974 and 1976 although they both maintained a limited offering of commercial vehicles; until 31 December 1974, kei cars used smaller license plates than regular cars 230 mm × 125 mm. As of 1975, kei cars received the medium-sized standard plates. To set them apart from regular passenger cars, the plates were now yellow and black rather than white and green. Sales had been declining, reaching a low-water mark of 150,000 passenger cars in 1975, 80% less than 1970 sales. Many were beginning to doubt the continued existence of the kei car, with both Honda and Mazda withdrawing in the middle of the 1970s. Emissions laws were another problem for the kei car industry in the mid 1970s.
From 1973 to 1978, emissions standards were to be tightened in four steps. Meeting the stricter standards which were to be introduced in 1975 would be problematic for manufacturers of kei cars; this was hard for Daihatsu and Suzuki, which focused on two-stroke engines. Daihatsu, had both the engineering backing and powerful connections of their large owner, Toyota, to aid them in meeting the new requirements. All manufacturers of kei cars were clamoring for increasing the engine displacement and vehicle size limits, claiming that the emissions standards could not be met with a functional 360-cc engine. In the end, the Japanese legislature relented, increasing the overall length and width restrictions by 200 mm and 100 mm respectively. Engine size was increased to 550 cc, taking effect from 1 January 1976; the new standards were announced on 26 August 1975, leaving little time for manufacturers to revise their designs to take advantage of the new limits. Most manufacturers were somewhat surprised by the decision.
The AMC Eagle is a compact-sized four-wheel drive passenger vehicle, produced by American Motors Corporation from 1979 to 1987. Introduced in August 1979 for the 1980 model year, the coupe and station wagon body styles were based on the AMC Concord; the AMC Eagles were the only four-wheel-drive passenger cars produced in the U. S. at the time. They were affordable cars offering a comfortable ride and handling on pavement together with superior traction in light off road use through AMC's innovative engineering and packaging. Although the definition is not precise, the AMC Eagle is today known as one of the first crossover vehicles. All models featured "passenger-car comfort, plus 4wd security for all-weather security." Fuel-thirsty vehicles built for rugged off-road were on the market. Comparable sedan and compact station wagon models were not available from other manufacturers at the Eagle's price point, AMC "predicted that consumers would embrace a vehicle with the comfort of an automobile, but the ride height and foul-weather capabilities of a four-wheel-drive utility vehicle."In 1981, the two-door subcompact-sized AMC Spirit-based models, the SX/4 and Kammback, joined the Eagle line aimed at both first-time buyers and fleet sales.
The Sundancer convertible conversion for the larger Eagle two-door model was available during 1981 and 1982. In March 1987, Chrysler Corporation reached an agreement to acquire AMC. Production of the Eagle continued until December 14, 1987; the initial proposal for production of what would become the AMC Eagle came from Roy Lunn, the chief design engineer for AMC Jeep. "Project 8001 plus Four" was Lunn's code name for a new "line of four-wheel-drive vehicles with the ride and handling conventions of a standard rear wheel drive car" built on a uni-body platform. In February 1977, AMC contracted FF Developments to build a prototype vehicle based on a production V8 powered AMC Hornet with drive torque split 33% front and 66% rear. Testing and further development proved the feasibility of a vehicle with greater ground clearance, larger 15-inch wheels, as well as a torque split closer to 50% - 50%, with Lunn recommending using the AMC straight-6 engine coupled to an automatic transmission. Thus, the AMC Eagle came about when Jeep's chief engineer joined a Concord body with a four-wheel-drive system.
Such a vehicle was a logical step for AMC, according to CEO Gerald C. Meyers, as a second energy crisis had hit in 1979, sales of AMC's profitable truck-based Jeep line dropped, due in part to their low fuel efficiency, leaving AMC in a precarious financial position; the Eagle provided a low-cost way of bridging the gap between AMC's solid and economical, but aging, passenger car line and its well-regarded, but decidedly off-road-focused, Jeep line, as the Eagle used the existing Concord automobile platform. The Eagle bridged the sizable price gap between the low-end imported 4WD Subaru and the large-sized domestic four-wheel-drive vehicles like the Jeep Wagoneer; the Eagle models provided the biggest new boost to the automaker's profit mix. Sales were brisk since Day One, with the manufacturer's suggested retail price for the basic 2-door model starting at $6,999 and the 4-door station wagon at $7,549; the Eagle represented a "burst of AMC's genetic creativity...quickly captured the attention of many American drivers who found its unique union of four-wheel drive safety and security with the comfort of an automobile."A first in mass production passenger cars, the early AMC Eagles came with a true full-time automatic system that operated only in permanent all-wheel drive.
The four-wheel drivetrain added 300 pounds to the Eagle's curb weight. The AMC Eagles were the first mass-produced U. S. four-wheel-drive vehicles with an independent front suspension. The AMC Eagle's central differential behind its TorqueFlite automatic transmission was single-speed and used a viscous fluid coupling for quiet and smooth transfer of power to the axle with the greatest traction, on wet or dry pavement; the central unit consisted of spaced, wavy clutch plates operating in a "honey-like Silicone fluid" performing a "limited-slip function" between the front and rear drives, as well as under adverse driving conditions sending torque to the axle with the most traction. Designed as "reasonably size passenger cars" offering a comfortable ride and handling on pavement, the AMC Eagles "behave more like mountain goats" when off the road; the value of four-wheel drive in the AMC Eagle was apparent when driving in slippery conditions, they were used in America's first ice-driving school.
The Eagle models provided the comfort and appointments expected of passenger models with off-road technology offering an extra margin of safety and traction. The Eagle was designed for customers that "must get through regardless of road or weather conditions" as well as those living areas of bad weather or roads, adventurous hunters and fishermen; the AMC Eagle did not compete with rudimentary four-wheel-drive vehicles. The company did not design the Eagle as an off-pavement recreation vehicle, but rather as a passenger car that offers added benefits. Not built for off-road performance as a Chevrolet Blazer or a Jeep Cherokee, the Eagle "will overcome mud, sand and obstacles that would stop ordinary sedans cold."The AMC Eagle was the first production car to use the complete "Ferguson Formula" full-time all-wheel-drive system from Britain's Ferguson Research. Other four-wheel-drive automobile-type vehicles - the Subaru DL/GL, muc
A tractor unit is a characteristically heavy-duty towing engine that provides motive power for hauling a towed or trailered load. These fall into two categories: heavy and medium duty military and commercial rear-wheel drive "semi tractors" used for hauling semi-trailers, heavy-duty off-road-capable 6×6, military and commercial tractor units, including ballast tractors. Tractor units have large displacement diesel engines for power and economy; the tractor-trailer combination distributes a load across multiple axles while being more maneuverable than an equivalently sized rigid truck. The most common trailer attachment system is a fifth wheel coupling, allowing rapid shift between trailers performing different functions, such as a bulk tipper and box trailer. Trailers containing differing cargos can be swapped between tractors, eliminating downtime while a trailer is unloaded or loaded. Drawbar couplings are found in dedicated exceptionally heavy-duty ballast tractors and as a means to connect intermediate fifth-wheel dollies for pulling multiple semi trailers.
There have been three common cab configurations used in tractors, two are still used. The conventional has an engine and hood over the front axle in front of the cab, as in most automobiles; this style is universal in North America. The cab over engine or cab forward has a flat nose cab with the driver sitting in front of the front axle. Used in the EU and Japan, this style has the advantages of good vision and maneuverability and allows maximum trailer length relative to overall length. In the North America this type of cab can be useful in rigid trucks, but now has little advantage in tractors and is used. A North American style cab over engine, now obsolete, had a flat nose cab located higher over the engine, with the driver sitting above the front axle; this allowed a sleeper compartment in a short tractor, maximum wheelbase relative overall length, important for bridge formula weight restrictions. With the loosening of length restrictions in 1982 this style had limited applications, is no longer manufactured for the U.
S. market. This style is still however popular in Australia where length restrictions still apply on many roads and it is used to maximise the capacity of both single trailer and B double configurations, American companies Freightliner and Kenworth still manufacture trucks in this style for this market. In Australia both styles of cab over engine truck as well as conventionals are in common use. A tractor unit can have many axles depending on axle load legislation; the most common varieties are those of 6 × 2 and 6 × 4 types. However, some manufacturers offer 6×6, 8×6, 8×8, 10×8, 10×10 axle configurations. A 6×4 has three axles an undriven front steer axle and the two rear axles driven. 6×4 units are more common in long distance haulage in larger countries such as the United States and Australia. In Europe, the 4×2 and 6×2 variants are more commonplace. Tractors with three axles or more can have more than one steering axle, which can be driven. Most 6×2 units allow the undriven rear axle to be raised when loaded, or running without a trailer, to save tire wear, save toll road fees, increase traction on the driven axle.
The 6×6 units have three axles, all can be driven, 8×6 units have four axles, with either the rear three driven and the front axle not, or the front and rear-most two axles powered and an unpowered lifting bogie center axle to spread the load when needed. The 8×8 units have four axles, but with all of them driven, 10×8 units have five axles with the rear four driven and the front axle for steering. All five axles of 10×10 units are driven; the front two axles are both steer axles. The axle configurations are based on axle load legislation, maximum gross vehicle weight ratings. Heavier versions of tractor units, such as those used in heavy haulage and road trains, tend to have four or more axles, with more than two axles driven. In certain countries, a certain amount of weight must be spread over driven axles, which led to heavier varieties having six-wheel drive, otherwise another tractor unit would have to be used. Heavy haulage variants of tractor-units are turned into a ballast tractor by fitting temporary ballast, which may require special permitting
Hot rods are old, classic or modern American cars with large engines modified for faster speed. The origin of the term "hot rod" is unclear. For example, some claim. Other origin stories include replacing the engine's camshaft or "rod" with a higher performance version. Hot rods were favorites for greasers The term has broadened to apply to other items that are modified for a particular purpose, such as "hot-rodded amplifier". There are various theories about the origin of the term "hot rod"; the common theme is that "hot" related to "hotting up" a car, which means modifying it for greater performance. One theory is that "rod" means roadster, a lightweight 2-door car, used as the basis for early hot rods. Another theory is that "rod" refers to camshaft, a part of the engine, upgraded in order to increase power output. In the early days, a car modified for increased performance was called a "gow job"; this term morphed into the hot rod in the early to middle 1950s. The term "hot rod" has had various uses in relation to performance cars.
For example, the Ontario Ministry of the Environment in its vehicle emissions regulations, refers to a hot rod as any motorized vehicle that has a replacement engine differing from the factory original. The predecessors to the hotrod were the modified cars used in the Prohibition era by bootleggers to evade revenue agents and other law enforcement. Hot rods first appeared in the late 1930s in southern California, where people raced modified cars on dry lake beds northeast of Los Angeles, under the rules of the Southern California Timing Association, among other groups; this gained popularity after World War II in California, because many returning soldiers had received technical training. The first hot rods were old cars, modified to reduce weight. Engine swaps involved fitting the Ford flathead V8 engine into a different car, for example the common practice in the 1940s of installing the "60 horse" version into a Jeep chassis. Typical modifications were removal of convertible tops, bumpers, and/or fenders.
Wheels and tires were changed for improved handling. Hot rods built before 1945 used'35 Ford wire-spoke wheels. After World War II, many small military airports throughout the country were either abandoned or used, allowing hot rodders across the country to race on marked courses. Drag racing had tracks as long as 1 mi or more, included up to four lanes of racing simultaneously; as some hot rodders raced on the street, a need arose for an organization to promote safety, to provide venues for safe racing. The National Hot Rod Association was founded in 1951, to take drag racing off the streets and into controlled environments. In the'50s and'60s, the Ford flathead. Many hot rods would upgrade the brakes from mechanical to hydraulic and headlights from bulb to sealed-beam. A typical mid-1950s to early 1960s custom Deuce was fenderless and steeply chopped, powered by a Ford or Mercury flathead, with an Edelbrock intake manifold and Collins magneto, Halibrand quick-change differential. Front suspension hairpins were adapted from sprint cars, such as the Kurtis Krafts.
As hot rodding became more popular and associations catering to hot rodders were started, such as the magazine Hot Rod, founded in 1948. As automobiles offered by the major automakers began increasing performance, the lure of hot rods began to wane. With the advent of the muscle car, it was now possible to purchase a high-performance car straight from the showroom; however the 1973 Oil Crisis caused car manufacturers to focus on fuel efficiency over performance, which led to a resurgence of interest in hot rodding. As the focus shifted away from racing, the modified cars became known as "street rods"; the National Street Rod Association began hosting events. By the 1970s, the 350 cu in small-block Chevy V8 was the most common choice of engine for hot rods. Another popular engine choice is the Ford Windsor engine. During the 1980s, many car manufacturers were reducing the displacements of their engines, thus making it harder for hot rod builders to obtain large displacement engines. Instead, engine builders had to modify the smaller engines to obtain larger displacement.
While current production V8s tended to be the most frequent candidates, this applied to others. In the mid-1980s, as stock engine sizes diminished, rodders discovered the 215 cu in aluminum-block Buick or Oldsmobile V8 could be modified for greater displacement, with wrecking yard parts; this trend was not limited to American cars. There is still a vibrant hot rod culture worldwide in Canada, the United States, the United Kingdom and Sweden; the hot rod community has now been subdivided into two main groups: hot rodders. There is a contemporary movement of traditional hot rod builders, car clubs and artists who have returned to the roots of hot rodding as a lifestyle; this includes a new breed of traditional hot rod builders and styles, as well as classic style car clubs. Events like GreaseOrama feature the greaser lifestyle. Magazines like Ol' Skool Rodz and Gals, Rat-Rods and Rust Queens cover events and people. Author Tom Wolfe was
Microcar is a term used for the smallest size of cars, with three or four wheels and an engine smaller than 700 cc. Specific types of microcars include bubble cars, cycle cars and voiturettes, the Japanese equivalent is the kei car. Microcars are covered by separate regulations to normal cars, having relaxed requirements for registration and licensing. Most microcars are powered by petrol or diesel engines, however electric-powered microcars have become more common in recent years. Voiturette is a term used by some small cars and tricycles manufactured from 1895 to 1910. Cyclecars are a type of small and inexpensive car manufactured between 1910 and the late 1920s; the first cars to be described as microcars were built in the United Kingdom and Germany following World War II and remained popular until the 1960s. These cars were called minicars, however they became known as microcars. France produced large numbers of similar tiny vehicles called voiturettes, however these were sold abroad. A common characteristic of these microcars is an engine displacement of less than 700 cc, although several cars with engines up to 1,000 cc are considered to be microcars.
The engine was designed for a motorcycle. Microcars have four wheels; the origin of these microcars is in the years following World War II. To provide better weather protection, three-wheeled microcars began increasing in popularity in the United Kingdom, where they could be driven using a motorcycle licence. Microcars became popular in Europe, due to their greater fuel efficiency than larger cars. One of the first microcars was the 1949 Bond Minicar. Micro cars became popular in Europe at that time as a demand for cheap personal motorised transport emerged and fuel prices were high due in part to the 1956 Suez Crisis. Most of them were three-wheelers, which in many places qualified them for inexpensive taxes and licensing as motorcycles; the microcar boom lasted until the late 1950s, when larger cars regained popularity The 1959 introduction of the Mini, which provided greater size and performance at an affordable price, contributed to the decline in popularity of microcars. Production of microcars had ceased by the end of the 1960s, due to competition from the Mini, Citroen 2CV, Fiat 500 and Renault 4.
Several microcars of the 1950s and 1960s— produced in Germany— were nicknamed bubble cars. This was due to the aircraft-style bubble canopies of cars like the Messerschmitt KR175, Messerschmitt KR200 and the FMR Tg500. Other microcars, such as the Isetta had a bubble-like appearance. German manufacturers bubble cars included former military aircraft manufacturers Messerschmitt and Heinkel. BMW manufactured the Italian Iso Rivolta Isetta under licence, using an engine from one of their own motorcycles; the United Kingdom had licence-built right-hand drive versions of the Isetta. The British version of the Isetta was built with only one rear wheel instead of the narrow-tracked pair of wheels in the normal Isetta design in order to take advantage of the three-wheel vehicle laws in the United Kingdom. There were indigenous British three-wheeled microcars, including the Peel Trident. Examples include the Citroën Prototype C, FMR Tg500, Heinkel Kabine, Messerschmitt KR175, Messerschmitt KR200, Peel P50, Peel Trident and Trojan 200.
Kleinschnittger F125. Recent microcars include the 2001 Aixam 5xx series; the Smart Fortwo is called a microcar in the United States. Electric-powered microcars which have reached production include the 1987 CityEl, the 1990 Automobiles ERAD Spacia, the 1999 Corbin Sparrow, the 2001 REVAi, the 2009 Tazzari Zero and the 2011 Peel P50; the European Union introduced the quadricycle category in 1992. In several European countries since microcars are classified by governments separately to normal cars, sometimes using the same regulations as motorcycles or mopeds. Therefore, compared with normal cars, microcars have relaxed requirements for registration and licensing, can be subject to lower taxes and insurance costs. Kei car is the Japanese legal category for the smallest and most limited power, highway-legal motor vehicles, including passenger cars and Kei trucks. There are a variety of microcar trucks of the "forward control" or van style to provide more cargo room; these might be used for local deliveries on narrow streets.
The Piaggio Ape is a three-wheeled example. Car classification Economy car Neighborhood Electric Vehicle
Subcompact car is the American classification for small cars, broadly equivalent to the B-segment or supermini classifications. According to the U. S. Environmental Protection Agency car size class definition, the subcompact category sits between minicompact and compact categories; the EPA definition of a subcompact is a passenger car with a combined interior and cargo volume of between 85–99 cubic feet. Current examples of subcompact cars are the Ford Chevrolet Sonic; the smaller cars in the A-segment / city car category are sometimes called subcompacts in the U. S. because the EPA's name for this smaller category— minicompact— is not used by the general public. The prevalence of small cars in the United States increased in the 1960s increased imports of cars from Europe and Japan. Widespread use of the term subcompact coincided with the early 1970s increase in subcompact cars built in the United States. Early 1970s subcompacts include Chevrolet Vega and Ford Pinto; the term subcompact originated during the 1960s, however it came into popular use in the early 1970s, as car manufacturers in the United States began to introduce smaller cars into their line-up.
Cars in this size were variously categorized, including "small cars" and "economy cars". Several of these small cars were produced in the U. S. in limited volumes, including the 1930 American Austin and the 1939 Crosley. From the 1950s onwards, various imported small cars were sold in the U. S. including the Nash Metropolitan, Volkswagen Beetle and various small British cars. Due to the increasing populary of small cars imported from Europe and Japan during the late 1960s, the American manufacturers to began releasing competing locally-built models in the early 1970s; the AMC Gremlin was described at its April 1970 introduction as "the first American-built import" and the first U. S. built subcompact car. Introduced in 1970 were the Chevrolet Vega and Ford Pinto. Sales of American-built "low weight cars" accounted for more than 30% of total car sales in 1972 and 1973, despite inventory shortages for several models; the Gremlin and Vega were all rear-wheel drive and available with four-cylinder engines.
The Pontiac Astre, the Canadian-born re-badged Vega variant was released in the U. S. September 1974. Due to falling sales of the larger pony cars in the mid-1970s, the Vega-based Chevrolet Monza was introduced as an upscale subcompact and the Ford Mustang II temporarily downsized from the pony car class to become a subcompact car for its second generation; the Monza with its GM variants Pontiac Sunbird, Buick Skyhawk, Oldsmobile Starfire, the Mustang II continued until the end of the decade. The Chevrolet Chevette was GM's new entry-level subcompact introduced as a 1976 model, it was an ` Americanized' design from GM's German subsidiary. And there were subcompacts that were imported but sold through a domestic manufacturers dealer network Captive imports, the Renault Le Car and the Ford Fiesta In 1977, the U. S. Environmental Protection Agency began to use a new vehicle classification system, based on interior volume instead of exterior size; this resulted in cars classified as subcompact now being classified as compact cars, a smaller group of cars now being classified as subcompact.
In 1978, Volkswagen began producing the "Rabbit" version of the Golf— a modern, front-wheel drive design— in Pennsylvania. In 1982, American Motors began manufacturing the U. S. Renault Alliance— a version of the Renault 9— in Wisconsin. Both models benefiting from European designs and experience. To replace the aging Chevette in the second half of the 1980s, Chevrolet introduced marketed imported front-wheel drive subcompact cars: the Suzuki Cultus and the Isuzu Gemini. During the 1990s GM offered the Geo brand featuring the Suzuki-built Metro subcompact; because of consumer demand for fuel-efficient cars during the late-2000s, sales of subcompact cars made it the fastest growing market category in the U. S; as of 2016, numerous models of subcompacts are sold in North America. As of 2012, the Chevrolet Sonic was the only subcompact assembled in the United States. Imported subcompact cars include Korean models such as Hyundai Accent, Kia Rio along with Japanese models such as Honda Fit, Mazda 2, Nissan Micra, Scion xD, Suzuki Swift, Toyota Yaris and Toyota Prius C.
Car classification Mini SUV Economy car
Differential (mechanical device)
A differential is a gear train with three shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others, or a fixed multiple of that average. In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn; this is necessary when the vehicle turns, making the wheel, travelling around the outside of the turning curve roll farther and faster than the other. The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other; when used in this way, a differential couples the longitudinal input propellor shaft to the pinion, which in turn drives the transverse ring gear of the differential. This usually works as reduction gearing. On rear wheel drive vehicles the differential may connect to half-shafts inside an axle housing, or drive shafts that connect to the rear driving wheels.
Front wheel drive vehicles tend to have the engine crankshaft and the gearbox shafts transverse, with the pinion on the end of the main-shaft of the gearbox and the differential enclosed in the same housing as the gearbox. There are individual drive-shafts to each wheel. A differential consists of one input, the drive shaft, two outputs which are the two drive wheels, however the rotation of the drive wheels are coupled to each other by their connection to the roadway. Under normal conditions, with small tyre slip, the ratio of the speeds of the two driving wheels is defined by the ratio of the radii of the paths around which the two wheels are rolling, which in turn is determined by the track-width of the vehicle and the radius of the turn. Non-automotive uses of differentials include performing analog arithmetic. Two of the differential's three shafts are made to rotate through angles that represent two numbers, the angle of the third shaft's rotation represents the sum or difference of the two input numbers.
The earliest known use of a differential gear is in the Antikythera mechanism, circa 80 BCE, which used a differential gear to control a small sphere representing the moon from the difference between the sun and moon position pointers. The ball was painted black and white in hemispheres, graphically showed the phase of the moon at a particular point in time. An equation clock that used a differential for addition was made in 1720. In the 20th Century, large assemblies of many differentials were used as analog computers, for example, the direction in which a gun should be aimed. However, the development of electronic digital computers has made these uses of differentials obsolete. Military uses may still exist, for example, for a hypothetical computer designed to survive an electromagnetic pulse. All the differentials that are now made are used in automobiles and similar vehicles including offroad vehicles such as ATVs. There are many claims to the invention of the differential gear, but it is possible that it was known, at least in some places, in ancient times.
Some historical milestones of the differential include: 100 BC–70 BC: The Antikythera mechanism has been dated to this period. It was discovered in 1902 on a shipwreck by sponge divers, modern research suggests that it used a differential gear to determine the angle between the ecliptic positions of the Sun and Moon, thus the phase of the Moon. 227–239 AD: Ma Jun from the Kingdom of Wei in China invents the first verifiable south-pointing chariot, which provided cardinal direction as a non-magnetic, mechanized compass. Some such chariots may have used differential gears. 658, 666 AD: two Chinese Buddhist monks and engineers create south-pointing chariots for Emperor Tenji of Japan. 1027, 1107 AD: Documented Chinese reproductions of the south-pointing chariot by Yan Su and Wu Deren, which described in detail the mechanical functions and gear ratios of the device much more so than earlier Chinese records. 1720: Joseph Williamson uses a differential gear in a clock. 1810: Rudolph Ackermann of Germany invents a four-wheel steering system for carriages, which some writers mistakenly report as a differential.
1827: modern automotive differential patented by watchmaker Onésiphore Pecqueur of the Conservatoire National des Arts et Métiers in France for use on a steam wagon. 1832: Richard Roberts of England patents "gear of compensation", a differential for road locomotives. 1874: Aveling and Porter of Rochester, Kent list a crane locomotive in their catalogue fitted with their patent differential gear on the rear axle. 1876: James Starley of Coventry invents chain-drive differential for use on bicycles. 1897: first use of differential on an Australian steam car by David Shearer. 1958: Vernon Gleasman patents the Torsen dual-drive differential, a type of limited-slip differential that relies on the action of gearing, instead of a combination of clutches and gears. An epicyclic differential can use epicyclic gearing to split and apportion torque asymmetrically between the front and rear axles. An epicyclic differential is at the heart of the Toyota Prius automotive drive train, where it interconnects the engine, motor-generators, the drive wheels.
It has the advantage of being compact along the length of its axis. Epicyclic gears are called planetary gears because the axes of the planet gears revolve around the common axis of the sun and ring gears that they mesh with and roll between. In the image, the yellow shaft carries the sun gear, hidden. T