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Four-by-four (4x4) refers to the general class of vehicles. The first figure is normally the total wheels (more precisely, axle ends, which may have multiple wheels), and the second, the number that are powered. Syntactically, 4×2 means a four-wheel vehicle that transmits engine power to only two axle-ends: the front two in front-wheel drive or the rear two in rear-wheel drive.
Four wheel drive (4WD) refers to vehicles that have a transfer case, not a differential, between the front and rear axles, meaning that the front and rear drive shafts will be locked together when engaged. This provides maximum torque transfer to the axle with the most traction, but can cause binding in high traction turning situations. They are also either full-time or part-time 4WD selectable. 4WD is not intended for high speeds without a limited-slip mechanism.
All wheel drive (AWD) refers to a drive train system that includes a differential between the front and rear drive shafts. This is normally coupled with some sort of anti-slip technology that will allow differentials to spin at different speeds, but still maintain the ability to transfer torque from one wheel in case of loss of traction at that wheel. AWD may work well with all surfaces, but is not intended for all terrains.
Individual-wheel drive (IWD) was coined to identify those electric vehicles whereby each wheel is driven by its own individual electric motor. This system essentially has inherent characteristics that would be generally attributed to four-wheel drive systems like the distribution of the available power to the wheels. However, because of the inherent characteristics of electric motors, torque can be negative, as seen in the Rimac Concept One and SLS AMG Electric. This can have drastic effects, as in better handling in tight corners.
The term IWD can refer to a vehicle with any number of wheels. For example, the Mars Rovers are 6-wheel IWD.
When powering two wheels simultaneously the wheels must be allowed to rotate at different speeds as the vehicle goes around curves. This is accomplished with a differential. A differential allows one input shaft (e.g., the driveshaft of car or truck) to drive two output shafts (e.g. - axles shafts that go from the differential to the wheel) independently with different speeds. The differential distributes torque (angular force) evenly, while distributing angular velocity (turning speed) such that the average for the two output shafts is equal to that of the differential ring gear. Each powered axle requires a differential to distribute power between the left and the right sides. When all four wheels are driven, a third or 'center' differential can be used to distribute power between the front and the rear axles.
The described system handles extremely well, as it is able to accommodate various forces of movement and distribute power evenly and smoothly, making slippage unlikely. Once it does slip, however, recovery is difficult. If the left front wheel of a 4WD vehicle slips on an icy patch of road, for instance, the slipping wheel will spin faster than the other wheels due to the lower traction at that wheel. Since a differential applies equal torque to each half-shaft, power is reduced at the other wheels, even if they have good traction. This problem can happen in both 2WD and 4WD vehicles, whenever a driven wheel is placed on a surface with little traction or raised off the ground. The simplistic design works acceptably well for 2WD vehicles. It is much less acceptable for 4WD vehicles, because 4WD vehicles have twice as many wheels with which to lose traction, increasing the likelihood that it may happen. 4WD vehicles may also be more likely to drive on surfaces with reduced traction. However, since torque is divided amongst four wheels rather than two, each wheel receives approximately half the torque of a 2WD vehicle, reducing the potential for wheelslip.
Many differentials have no way of limiting the amount of engine power that gets sent to its attached output shafts. As a result, if a tire loses traction on acceleration, either because of a low-traction situation (e.g. - driving on gravel or ice) or the engine power overcomes available traction, the tire that is not slipping receives little or no power from the engine. In very low traction situations, this can prevent the vehicle from moving at all. To overcome this, there are several designs of differentials that can either limit the amount of slip (these are called 'limited-slip' differentials) or temporarily lock the two output shafts together to ensure that engine power reaches all driven wheels equally.
Locking differentials work by temporarily locking together a differential's output shafts, causing all wheels to turn at the same rate, providing torque in case of slippage. This is generally used for the center differential, which distributes power between the front and the rear axles. While a drivetrain that turns all wheels equally would normally fight the driver and cause handling problems, this is not a concern when wheels are slipping.
The two most common factory-installed locking differentials use either a computer-controlled multi-plate clutch or viscous coupling unit to join the shafts, while other differentials more commonly used on off-road vehicles generally use manually operated locking devices. In the multi-plate clutch the vehicle's computer senses slippage and locks the shafts, causing a small jolt when it activates, which can disturb the driver or cause additional traction loss. In the viscous coupling differentials the shear stress of high shaft speed differences causes a dilatant fluid in the differential to become solid, linking the two shafts. This design suffers from fluid degradation with age and from exponential locking behavior. Some designs use gearing to create a small rotational difference that hastens torque transfer.
A third approach to limiting slippage is taken by a Torsen differential. A Torsen differential allows the output shafts to receive different amounts of torque. This design does not provide for traction when one wheel is spinning freely, where there is no torque, but provides excellent handling in less extreme situations. A typical Torsen II differential can deliver up to twice as much torque to the high traction side before traction is exceeded at the lower tractive side.
A fairly recent innovation in automobiles is electronic traction control. Traction control typically uses a vehicle's braking system to slow a spinning wheel. This forced slowing emulates the function of a limited-slip differential, and, by using the brakes more aggressively to ensure wheels are being driven at the same speed, can also emulate a locking differential. It should be noted that this technique normally requires wheel sensors to detect when a wheel is slipping, and only activates when wheel slip is detected. Therefore, there is typically no mechanism to actively prevent wheel slip (i.e. you can't "lock the differential" in advance of wheel slip), rather the system is designed to expressly permit wheel slip to occur, and then attempt to send torque to the wheels with the best traction. This is a limiting design if preventing all wheel slip is a requirement.
In 1893, before the establishment of a modern automotive industry in Britain, English engineer Bramah Joseph Diplock patented a four-wheel-drive system for a traction engine, including four-wheel steering and three differentials, which was subsequently built. The development also incorporated Bramah's Pedrail wheel system in what was one of the first four-wheel-drive automobiles to display an intentional ability to travel on challenging road surfaces. It stemmed from Bramagh's previous idea of developing an engine that would reduce the amount of damage to public roads.
Ferdinand Porsche designed and built a four-wheel-driven electric vehicle for the k. u. k. Hofwagenfabrik Ludwig Lohner & Co. at Vienna in 1899, presented to the public during the 1900 World Exhibition at Paris. An electric hub motor at each wheel powered the vehicle. Although clumsily heavy, the vehicle proved a powerful sprinter and record-breaker in the hands of its owner E.W. Hart. Due to its unusual status the so-called Lohner-Porsche is not widely credited as the first four-wheel-driven automobile.
The first four-wheel-drive car, as well as hill-climb racer, with internal combustion engine, the Spyker 60 H.P., was presented in 1903 by Dutch brothers Jacobus and Hendrik-Jan Spijker of Amsterdam. The two-seat sports car, which was also the first ever car equipped with a six-cylinder engine, is now an exhibit in the Louwman Collection (the former Nationaal Automobiel Museum) at the Hague in The Netherlands.
Designs for four-wheel drive in the U.S., came from the Twyford Company of Brookville, Pennsylvania in 1905, six were made there around 1906; one still exists and is displayed annually. The second U.S. four-wheel-drive vehicle was built in 1908 by (what became) the Four Wheel Drive Auto Company (FWD) of Wisconsin (not to be confused with the term "FWD" as an acronym for front-wheel drive). FWD would later produce around 15,000 of its four-wheel-drive Model B trucks for the British and American armies during World War I. Approximately 11,500 of the Jeffery or Nash Quad models (1913–1919) were similarly used. The Quad not only came with four-wheel drive and four-wheel brakes, but also featured four-wheel steering.
The Reynolds-Alberta Museum has a four-wheel-drive "Michigan" car from about 1905 in unrestored storage. The Marmon-Herrington Company was founded in 1931 to serve a growing market for moderately priced four-wheel-drive vehicles. Marmon-Herrington specialized in converting Ford trucks to four-wheel drive and got off to a successful start by procuring contracts for military aircraft refueling trucks, 4×4 chassis for towing light weaponry, commercial aircraft refueling trucks, and an order from the Iraqi Pipeline Company for what were the largest trucks ever built at the time.
Daimler-Benz also has a history in four-wheel drive. In 1907 the Daimler Motoren Gesellschaft had built a four-wheel-driven vehicle called Dernburg-Wagen, also equipped with four-wheel steering, that was used by German colonial civil servant, Bernhard Dernburg, in Namibia. Mercedes and BMW, in 1926, introduced a rather sophisticated four-wheel drive, the G1, the G4 and G4 following. The 1937 Mercedes-Benz G5 and BMW 325 4×4 featured full-time four-wheel drive, four-wheel steering, three locking differentials, and fully independent suspension. They were produced because of a government demand for a four-wheel-drive passenger vehicle. The modern G-series/Wolf such as the G500 and G55 AMG still feature some of the attributes, with the exception of fully independent suspension since it hinders suspension articulation. The Unimog is another Mercedes truck.
Possibly the first four-wheel-drive vehicle produced for civilian use was the GAZ-61, developed in the USSR in 1938. "Civilian use" may be a bit of a misnomer, as most if not all were used by the Soviet government and military (as command cars), but the GAZ-61-73 version is the first four wheel drive vehicle with a normal closed sedan body. Elements of the chassis were used in military vehicles such as the GAZ-64, GAZ-67, GAZ-69, and also the properly civilian GAZ-M-72 (based on the rear-wheel drive GAZ-20 "Victory" and built from 1955-1958). Soviet civilian life did not allow the proliferation of civilian products such as the Jeep in the United States, but through the 1960s the technology of Soviet 4x4 vehicles stayed on par with British, German, and American models, even exceeding it in some aspects, and for military purposes just as actively developed, produced and used.
It was not until "go-anywhere" vehicles were needed for the military that four-wheel drive found its place. The Jeep, originally developed by American Bantam but mass-produced by Willys and Ford, became the best-known four-wheel-drive vehicle in the world during World War II.
Willys (since 1950 owner of the Jeep name) introduced the CJ-2A in 1945 as the first full-production four-wheel-drive vehicle for sale in the general marketplace. It set the pattern for many other four-wheel drive vehicles.
The Land Rover appeared at the Amsterdam Motor Show in 1948, originally conceived as a stop-gap product for the struggling Rover car company, and despite chronic under-investment succeeded far better than the passenger cars. Land Rover developed a luxury 4WD with the Range Rover in the 1970s, which, unlike some offerings from other manufacturers, was capable of serious off-road use. The inspiration was a Willys MB that was frequently run off-road on the farm belonging to chief engineer Maurice Wilks, and was felt that it needed some refinement.
Kaiser Jeep, the successor to Willys, introduced a 4WD wagon called the Wagoneer in 1963. It was revolutionary at the time, not only because of its technical innovations such as an independent front suspension and the first automatic transmission with 4WD, but also because it was equipped and finished as a regular passenger automobile. The Super Wagoneer (1966 to 1969) was powered by Rambler or Buick V8s. Its high level of equipment made it the first "luxury" SUV.
Jensen applied the Formula Ferguson (FF) full-time all-wheel-drive system to 318 units of their Jensen FF built from 1966 to 1971, marking the first time 4WD was used in a production GT sports car. While most 4WD systems split torque evenly, the Jensen split torque roughly 40% front, 60% rear by gearing the front and rear at different ratios.
American Motors (AMC) acquired Kaiser's Jeep Division in 1970 and quickly upgraded and expanded the entire line of serious off-road 4WD vehicles. The top range full-size Grand Wagoneer continued to compete with traditional luxury cars. It was relatively unchanged during its production through 1991, even after Chrysler's buyout of AMC.
Subaru introduced the mass-produced Leone in 1972 featuring a part-time four-wheel-drive system that could not be engaged on dry pavement. The American Motors Corporation (AMC) introduced a full-time AWD vehicle the same year as the Subaru in the Jeep Cherokee and Wagoneer with Quadra Trac (1973 model year models were for sale starting September 1972). It dominated all other makes in FIA rally competition, due to the performance of the full-time AWD, which did not require the driver to get out of the vehicle to lock hubs or manually select between 2WD and 4WD modes in the car like other American four-wheel-drive vehicles of the period. Drivers Gene Henderson and Ken Pogue won the Press-on-Regardless Rally FIA championship with a Quadra Trac equipped Jeep in 1972.
American Motors introduced the innovative Eagle for the 1980 model year. These were the first mass production cars to use the complete FF system. The AMC Eagle was the world's first complete line (sedan, coupe, and station wagon) of permanent automatic all-wheel-drive passenger models. The new Eagles combined Jeep technology with an existing and proven AMC passenger automobile platform. They ushered a whole new product category of "sport-utility" or crossover SUV. AMC's Eagles came with the comfort and high-level appointments expected of regular passenger models and used the off-road technology for an extra margin of safety and traction.
The Eagle's thick viscous fluid center differential provided quiet and smooth transfer of power that was directed proportionally to the axle with the greatest traction. This was a true full-time system operating only in four-wheel drive without undue wear on suspension or driveline components. There was no low range in the transfer case. This became the forerunner of the designs that followed from other manufacturers. The automobile press at the time tested the traction of the Eagles and described it as far superior to the Subaru's and that it could beat many so-called off-road vehicles. Four Wheeler magazine concluded that the AMC Eagle was "The beginning of a new generation of cars."
The Eagles were popular (particularly in the snowbelt), had towing capacity, and came in several equipment levels including sport and luxury trims. Two additional models were added in 1981, the sub-compact SX/4 and Kammback. A manual transmission and a front axle-disconnect feature were also made available for greater fuel economy. During 1981 and 1982 a unique convertible was added to the line. The Eagle's monocoque body was reinforced for the conversion and had a steel targa bar with a removable fiberglass roof section. The Eagle station wagon remained in production for one model year after Chrysler acquired AMC in 1987.
Audi also introduced a permanently all-wheel-driven road-going car, the Audi Quattro, in 1980. Audi's chassis engineer, Jorg Bensinger, had noticed in winter tests in Scandinavia that a vehicle used by the German Army, the Volkswagen Iltis, could beat any high-performance Audi. He proposed developing a four-wheel-drive car, that would also be used for rallying to improve Audi's conservative image. The Audi Quattro system became a feature on production cars.
In 1987, Toyota also developed a car built for competition in rally campaigns. A limited number of road-going FIA Homologation Special Vehicle Celica GT-Fours (otherwise known as Toyota Celica All-Trac Turbo in some markets) were produced. The All-Trac system was later available on serial production Toyota Camry, Toyota Corolla, and Toyota Previa models.
Some of the earliest mid-engined four-wheel-drive cars were the various road-legal rally cars made for Group B homologation, such as the Ford RS200 made from 1984 to 1986. In 1989, niche maker Panther Westwinds created a mid-engined four-wheel-drive, the Panther Solo 2.
In 2008, Nissan introduced the GT-R featuring a rear mounted transaxle. The AWD system requires two drive shafts, one main shaft from the engine to the transaxle and differential and a second drive shaft from the transaxle to the front wheels.
The Ferrari FF introduced in 2011 features a unique system called 4RM, which does away with the heavy center differential and instead attaches a smaller, second transaxle that draws power from the front of the engine. This allows the car to keep the traditional rear transaxle design without the need for a second drive-shaft for the front wheels.
Today, sophisticated all-wheel-drive systems are found in many passenger vehicles and some exotic sports cars and supercars. Mainstream luxury and near-luxury vehicles which can absorb the extra cost involved, and for which the fuel economy penalty of some 5% is not an issue, are offered with AWD (or "4x4" or "4WD") as a safety enhancement to meet owners' expectations for a full complement of up-to-date technology.
Miller produced the first 4WD car to qualify for the Indianapolis 500, the 1938 Miller Gulf Special.
Ferguson Research Ltd. built the front-engine P99 Formula One car that actually won a non-World Championship race with Stirling Moss in 1961. In 1969, Team Lotus raced cars in the Indy 500 and two years later in Formula 1 with the Lotus 56, that had both turbine engines and 4WD, as well as the 4WD-Lotus 63 that had the standard 3-litre V8 Ford Cosworth engine. Matra also raced a similar MS84, and McLaren entered their M9A in the British Grand Prix, while engine manufacturers Ford-Cosworth produced their own version which was tested but never raced. All these F1 cars were considered inferior to their RWD counterparts, as the advent of aerodynamic downforce meant that adequate traction could be obtained in a lighter and more mechanically efficient manner, and the idea was discontinued, even though Lotus tried repeatedly.
Nissan and Audi had success with all-wheel drive in road racing with the former's advent of the Nissan Skyline GT-R in 1989. So successful was the car that it dominated the Japanese circuit for the first years of production, going on to bigger and more impressive wins in Australia before weight penalties eventually levied a de facto ban on the car. Most controversially was the win pulled off at the 1990 Macau Grand Prix where the car led from start to finish. Audi's dominance in the Trans-Am Series in 1988 was equally controversial as it led to a weight penalty mid season and to a rule revision banning all-AWD cars, its dominance in Supertouring eventually led to a FIA ban on AWD system in 1998.
New 2011 24 Hours of Le Mans regulations may revive AWD/4WD in road racing, though such systems are only allowed in new hybrid-powered Le Mans Prototypes. One example is the Audi R18 e-tron quattro (winner of 2012 race, the first ever hybrid/4WD to win Le Mans), utilizing an electric motor in the front axle while combining the engine motor in the rear.
Medium duty trucks and Heavy duty trucks have recently adopted 4x4 drive-trains. 4x4 Medium duty trucks became common after Ford Motor Company began selling Ford Super Duty trucks. The Super Duty trucks shared many parts between the light duty and medium duty reducing production costs. The Dana 60 front axle is used on both medium and light duty Super Duty trucks. Furthermore the Big Three share/shared parts between the companies reducing costs. The Dana S 110 is currently being used for the rear drive, under Ford and Ram's medium duty trucks. The Dana 110 was also used on the General Motors 4x4's as well. Ram Trucks began selling medium duty trucks, 4x4 and 4x2, in 2008. General Motors sold a 4x4 for model years 2005-2009.
During the late 1980s, there was a movement by construction equipment builders to find a way for their equipment to handle any terrain they can drive across. The first to utilize a 4WD system was Case Corporation (then known as J.I. Case Co.),[dubious ] who designed a hearty four-wheel-drive system that was instantly tested, and placed on several models of their Loader/Backhoe line. This system was first used in 1987, and has become somewhat of a benchmark in construction equipment. Today, several construction equipment manufacturers offer a 4WD system as an option on their equipment, mostly backhoes.
The 4WD systems on construction equipment are much stronger and larger than their automobile counterparts, incorporating several redundancies in their design. The change in outer appearance of a loader–backhoe equipped with 4WD is instantly noticeable, mostly in the difference of the front hubs, which are flat in design. The second noticeable difference is the design of the front tires, which have a tread on them similar to that of the rear tires, but in smaller scale.
Even though in the general context, the term "four-wheel drive" usually refers to an ability that a vehicle may have, it is also used to designate the entire vehicle itself. In Australia, vehicles without significant off-road abilities are often referred to as All-Wheel Drives (AWD) or SUVs, while those with off-road abilities are referred to as "four-wheel drives". This term is sometimes also used in North America, somewhat interchangeably for SUVs and pickup trucks and is sometimes mistakenly applied to two-wheel-drive variants of these vehicles.
The term 4×4 (read: four by four) was in use to describe North American military four-wheel-drive vehicles as early as the 1940s, with the first number indicating the total number of wheels on a vehicle and the second indicating the number of driven wheels. Today, the term 4×4 is common in North America, and is generally used when marketing a new or used vehicle, and is sometimes applied as badging on a vehicle equipped with four-wheel drive. Similarly, 4×2 would be appropriate for most two-wheel-drive vehicles, and is often used to describe them as a two-wheel drive. In Australia the term is often used to refer to a ute that sits very high on its suspension. This is to avoid the confusion that the vehicle might be a 4×4 because it appears otherwise suited to off-road applications.
Large American trucks with dual tires on the rear axles and two driven axles are officially designated as 4×4s, despite having six driven wheels, because the "dual" wheels behave as a single wheel for traction and classification purposes, and are not individually powered. True 6x6 vehicles with three powered axles such as the famous M35 2½ ton cargo truck used by the U.S. Army has three axles (two rear, one front), all of them driven. This vehicle is a true 6×6, as is the Pinzgauer, which is popular with defense forces around the globe.
Another related term is 4-wheeler (or four-wheeler). This generally refers to all-terrain vehicles with four wheels, and does not indicate the number of driven wheels; a "four-wheeler" may have two- or four-wheel drive. (In CB slang, truckers refer to any two-axled vehicle as a "four-wheeler", sometimes in a derogatory context, as distinguished from an "eighteen-wheeler" or tractor/trailer.)
Prompted by a perceived need for a simple, inexpensive all-terrain vehicle for oil exploration in North Africa, the French motor manufacturer Citroën developed the 2CV Sahara. Unlike other 4×4 vehicles which use a conventional transfer case to drive the front and rear axle, the Sahara had two engines, each independently driving a separate axle, with the rear engine facing backwards. The two throttles, clutches and gear change mechanisms could be linked, so the two 12 hp (9 kW) 425 cc (26 cu in) engines could run together, or they could be split and the car driven solely by either engine. Combined with twin fuel tanks and twin batteries (which could be set up to run either or both engines), the redundancy of two separate drive trains meant that they could make it back to civilization even after major mechanical failures. Only around 700 of these cars were built, and only 27 are known to exist today.
BMC experimented with a twin-engine Mini Moke (dubbed the "Twini Moke") in the mid-1960s, but never put it into production. This made advantage of the Mini's 'power pack' layout, with a transverse engine and the gearbox in the engine sump. Simply by fitting a second engine/gearbox unit across the rear, a rudimentary 4×4 system could be produced. Early prototypes had separate gear levers and clutch systems for each engine. Later versions sent for evaluation by the British Army had more user-friendly linked systems.
In 1965, A. J. M. Chadwick patented a 4WD system, GB 1113068, that used hemispherical wheels for an all-terrain vehicle. Twenty years later, B. T. E. Warne, patented, GB 2172558, an improvement on Chadwick's design that did not use differential gear assemblies. By using near-spherical wheels with provision to tilt and turn each wheel co-ordinatively, the driven wheels maintain constant traction. Furthermore, all driven wheels steer and, as pairing of wheels is not necessary, vehicles with an odd number of wheels are possible without affecting the system's integrity. Progressive deceleration is made possible by dynamically changing the front-to-rear effective wheel diameter ratios.
Suzuki Motors introduced the Suzuki Escudo Pikes Peak Edition in 1996. Earlier Suzuki versions were twin engined, from 1996 on the engine is a twin-turbocharged 2.0 L V6, mated to a sequential 6-speed manual transmission.
Nissan Motors has developed a system called E-4WD. It is designed for cars that are normally front-wheel drive, however the rear wheels are powered by electric motors. This system was introduced in some variants of the Nissan Cube and Tiida. (This is similar to the system used on the Ford Escape Hybrid AWD.)
Chrysler's Jeep Division debuted the twin engine, 670 hp (500 kW) Jeep Hurricane concept at the 2005 North American International Auto Show in Detroit. This vehicle has a unique "crab crawl" capability, which allows it to rotate 360° in place. This is accomplished by driving the left wheels as a pair and right wheels as a pair, as opposed to driving the front and rear pairs. A central gearbox allows one side to drive in the opposite direction to the other. It also has dual Hemi V8s.
Some hybrid vehicles such as the Lexus RX400h provide power to an AWD system through a pair of electric motors, one to the front wheels and one to the rear. In the case of the AWD model version of the Lexus RX400h (and its Toyota-branded counterpart, the Harrier hybrid), the front wheels can also receive drive power directly from the vehicle's gasoline engine as well as via the electric motors, whereas the rear wheels derive power only from the second electric motor. Transfer of power is managed automatically by internal electronics based on traction conditions and need, making this an all-wheel-drive system.
The 4RM system used in the Ferrari FF is unique in that it uses two gearboxes, in addition to the traditional Ferrari rear transaxle behind the engine, the system also uses a smaller transaxle drawing power from the front of the engine, sending it to the front wheels as needed. To save space and weight the front transaxle only has three forward speeds (and no reverse). Drive to the front wheels is transmitted through two infinitely-variable clutch packs which are allowed to 'slip' to give the required road wheel speeds. The system usually operates in the rear-drive only mode and only engages the clutches for the front transaxle when the rear wheels start losing grip.
|1933||Mitsubishi Motors||Mitsubishi PX33||x|
|1941||Volkswagen||Typ 128 Schwimmwagen||Military|
|1948||Rover||Land Rover Series||x|
|1951||Alfa Romeo||Alfa Romeo Matta||Military|
|1951||Austin Motor Company||Austin Champ||Military|
|1956||Auto Union||DKW Munga||Military|
|1970||British Leyland||Range Rover||x|
|1966||Jensen||Jensen FF||x (320 units)|
|1980||American Motors||AMC Eagle||x|
|1982||Renault||Renault 18 Combi 4×4||x|
|1984||Alfa Romeo||Alfa 33 4×4||x|
|1984||Mitsubishi||Mitsubishi Cordia 4WD Turbo||x|
|1984||Volkswagen||Volkswagen Passat Syncro||x|
|1984||Peugeot||Peugeot 205 T16||x (200 units)|
|1985||Lancia||Lancia Delta HF 4WD||x|
|1985||Mazda||Mazda 323 4WD||x|
|1986||Toyota||Toyota Celica GT-Four All-Trac Turbo||x|
|1986||Ford||Ford RS200||x (220 units)|
|1987||Mercedes-Benz||Mercedes W124 4MATIC||x|
|1987||Porsche||Porsche 959||x (292 units)|
|1988||Opel||Opel Vectra 4×4||x|
|1990||Chevrolet||Chevrolet Astro Full-time AWD||x|
|1991||Lamborghini||Lamborghini Diablo VT||x|
|1991||Bugatti||Bugatti EB110||x (ca. 300 units)|
|2008||Saab||Saab 9-3 Turbo X||x|
|2011||Ferrari||Ferrari FF||x (ca. 800 units)|
The above systems ending with "#" function by selectively using the traction control system (via ABS) to brake a slipping wheel.
Note: the above all function like 2WD when multi-plate clutch coupling is not engaged (with exception of Subaru models), and like 4WD highrange in a part-time 4WD system when the clutch is engaged (usually by computer although some allow manual control). Some in this category have varying degrees of control in the torque distribution between front and rear by allowing some of the clutches in a multi-plate clutch coupling to engage and slip varying amounts. An example of a system like this is the BorgWarner i-Trac(TM) system. Note: the Haldex Traction-based car list was created from the list on Haldex Traction corporate web site: Haldex Cars[dead link]. A version of the BorgWarner ITM3e system is used on 2006 and up Porsche 911TT's. The Borg-Warner ITM 3e is also used in the 2006-now Hyundai Santa Fe and the Hyundai Tucson. In the Hyundais, the ITM 3e acts like a full-time AWD with 95:5 normal torque split. In extreme conditions, the system can be locked in a 50:50 split via the 4WD LOCK button.
In Ferrari's 4RM (so far the only system of this type), the engine is set between the traditional Ferrari rear transaxle and a secondary front transaxle (PTU - "power take off unit"). The car itself operates primarily as a rear wheel drive vehicle, clutches in the front transaxle only engage when the rear wheels begin to slip. The front transaxle itself only has 3 gears equivalent to 2nd, 4th and reverse in the rear transaxle (with gear ratios 6% taller than the corresponding ratios in the main gearbox), so the system is only active in 1st to 4th gears. The connection between this gearbox and each front wheel is via independent haldex-type clutches, without a differential. Due to the difference in ratios "the clutches continually slip" and only transmit, at most, 20% of the engine's torque.
These are vehicles that have no center differential. Since there is no center differential to allow for speed differences between the front and rear wheels when turning, a small amount of tire slippage must occur during turns. When used on slick surfaces, this is not a problem, but when turning on dry pavement, the tires grip, then are forced to slip, then grip again, and so on, until the turn is completed. This causes the vehicle to exhibit a 'hopping' sensation. Using part-time 4WD systems on dry pavement is not recommended, as damage to the drive-line eventually occurs.
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