Front-engine, front-wheel-drive layout

Front-engine, rear-wheel-drive layout

Historically, this designation was used regardless of whether the entire engine was behind the front axle line. In recent times, the manufacturers of some cars have added to the designation with the term front-mid which describes a car in which the engine is in front of the passenger compartment but behind the front axle. The engine positions of most pre–World-War-II cars are front-mid or on the front axle.

This layout is the most traditional form and remains a popular, practical design. The engine, which takes up a great deal of space, is packaged in a location passengers and luggage typically would not use. The main deficit is weight distribution—the heaviest component is at one end of the vehicle. Car handling is not ideal, but usually predictable.

In contrast with the front-engine, rear-wheel-drive layout (RWD), the FWD layout eliminates the need for a central tunnel or a higher chassis clearance to accommodate a driveshaft providing power to the rear wheels. Like the rear-engine, rear-wheel-drive layout (RR) and rear mid-engine, rear-wheel-drive layout (RMR) layouts, it places the engine over the drive wheels, improving traction in many applications. As the steered wheels are also the driven wheels, FWD cars are generally considered superior to RWD cars in conditions in which there is low traction such as snow, mud, gravel or wet tarmac. When hill climbing in low-traction conditions RR is considered the best two-wheel-drive layout, primarily due to the shift of weight to the rear wheels when climbing. The cornering ability of an FWD vehicle is generally better, because the engine is placed over the steered wheels.^[1] However, as the driven wheels have the additional demands of steering, if a vehicle accelerates quickly, less grip is available for cornering, which can result in understeer.^[2] High-performance vehicles rarely use the FWD layout because weight is transferred to the rear wheels under acceleration, while unloading the front wheels and sharply reducing their grip, effectively putting a cap on the amount of power which could realistically be utilized; in addition, the high power of high-performance cars can result in torque steer. Electronic traction control can avoid wheel-spin but largely negates the benefit of extra power.^[3] This was a reason for the adoption of the all-wheel-drive quattro system in the high performance Jensen FF and Audi Quattro road cars.

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World War II

World War II

World War II or the Second World War, often abbreviated as WWII or WW2, was a global conflict that lasted from 1939 to 1945. The vast majority of the world's countries, including all of the great powers, fought as part of two opposing military alliances: the Allies and the Axis. Many participants threw their economic, industrial, and scientific capabilities behind this total war, blurring the distinction between civilian and military resources. Aircraft played a major role, enabling the strategic bombing of population centres and the delivery of the only two nuclear weapons ever used in war.

Axle

Axle

An axle or axletree 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, especially on bicycles, the latter type of axle is referred to as a spindle.

Weight distribution

Weight distribution

Weight distribution is the apportioning of weight within a vehicle, especially cars, airplanes, and trains. Typically, it is written in the form x/y, where x is the percentage of weight in the front, and y is the percentage in the back.

Front-engine, rear-wheel-drive layout

Front-engine, rear-wheel-drive layout

A front-engine, rear-wheel-drive layout (FR) is an automotive design with an engine in front and rear-wheel-drive, connected via a drive shaft. This arrangement, with the engine straddling the front axle, was the traditional automobile layout for most of the 20th century.It is also used in trucks, pickups, and high-floor buses and school buses.

Rear-engine, rear-wheel-drive layout

Rear-engine, rear-wheel-drive layout

In automotive design, an RR, or rear-engine, rear-wheel-drive layout places both the engine and drive wheels at the rear of the vehicle. In contrast to the RMR layout, the center of mass of the engine is between the rear axle and the rear bumper. Although very common in transit buses and coaches due to the elimination of the drive shaft with low-floor buses, this layout has become increasingly rare in passenger cars.

Rear mid-engine, rear-wheel-drive layout

Rear mid-engine, rear-wheel-drive layout

In automotive design, an RMR, or rear mid-engine, rear-wheel-drive layout is one in which the rear wheels are driven by an engine placed with its center of gravity in front of the rear axle, and thus right behind the passenger compartment. Nowadays more frequently called 'RMR', to acknowledge that certain sporty or performance focused front-engined cars are also "mid-engined", by having the main engine mass behind the front axle, RMR layout cars were previously just called MR, or mid-engine, rear-wheel-drive layout), because the nuance between distinctly front-engined vs. front mid-engined cars often remained undiscussed.

Traction (engineering)

Traction (engineering)

Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction, though the use of shear force of the surface is also commonly used.

Torque steer

Torque steer

Torque steer is the unintended influence of engine torque on the steering, especially in front-wheel-drive vehicles. For example, during heavy acceleration, the steering may pull to one side, which may be disturbing to the driver. The effect is manifested either as a tugging sensation in the steering wheel, or a veering of the vehicle from the intended path. Torque steer is directly related to differences in the forces in the contact patches of the left and right drive wheels. The effect becomes more evident when high torques are applied to the drive wheels because of a high overall reduction ratio between the engine and wheels, high engine torque, or some combination of the two. Torque steer is distinct from steering kickback.

Jensen FF

Jensen FF

The Jensen FF is a four-wheel drive grand tourer produced by British car manufacturer Jensen Motors between 1966 and 1971. It was the first non all-terrain production car equipped with four-wheel drive and an anti-lock braking system. The powertrain was sourced from Chrysler, installing the second generation 6,277 cc V8 engine and 3-speed TorqueFlite A727 automatic transmission.

Audi Quattro

Audi Quattro

The Audi Quattro is a road and rally car, produced by the German automobile manufacturer Audi, part of the Volkswagen Group. It was first shown at the 1980 Geneva Motor Show on 3 March. Production continued through 1991.

Early cars using the FWD layout include the 1925 Alvis, 1929 Cord L-29, 1931 DKW F1, the 1948 Citroën 2CV, 1949 Saab 92, the 1957 Trabant P50, and the 1959 Mini. In the 1980s, the traction and packaging advantages of this layout caused many compact and mid-sized vehicle makers to adopt it in the US. Most European and Japanese manufacturers switched to front wheel drive for the majority of their cars in the 1960s and 1970s, the last to change being VW, Ford of Europe, and General Motors (Vauxhall - UK and Opel - Germany). Toyota was the last Japanese company to switch in the early 1980s. BMW, focused on luxury vehicles, however retained the rear-wheel-drive layout in even their smaller cars,^[4] though their MINI marque are FWD.

There are four different arrangements for this basic layout, depending on the location of the engine, which is the heaviest component of the drivetrain.

Mid-engine / Front-wheel drive

The earliest such arrangement was not technically FF, but rather mid-engine, front-wheel-drive layout (MF). The engine was mounted longitudinally (fore-and-aft, or north–south) behind the wheels, with the transmission ahead of the engine and differential at the very front of the car. With the engine so far back, the weight distribution of such cars as the Cord L-29 was not ideal; the driven wheels did not carry a large enough proportion of weight for good traction and handling. The 1934 Citroën Traction Avant solved the weight distribution issue by placing the transmission at the front of the car with the differential between it and the engine. Combined with the car's low slung unibody design, this resulted in handling which was remarkable for the era. Renault is the most recent user of this format - having used it on the Renault 4, and the first generation Renault 5, but it has since fallen out of favor since it encroaches into the interior space.

Longitudinally mounted front-engine and front-wheel drive

A 1975 Alfa Romeo Alfasud Sprint Veloce using a Longitudinally mounted front-engine and front-wheel drive.

The 1946 Panhard Dyna X, designed by Jean-Albert Grégoire, had the engine longitudinally in front of the front wheels, with the transmission behind the engine and the differential at the rear of the assembly. This arrangement, used by Panhard until 1967, potentially had a weight distribution problem analogous to that of the Cord L29 mentioned above. However, the Panhard's air-cooled flat twin engine was very light, and mounted low down with a low centre of gravity reducing the effect. The air-cooled flat twin engine of the Citroën 2CV was also mounted very low, in front of the front wheels, with the transmission behind the axle line and the differential between the two. This became quite popular; cars using this layout included the German Ford Taunus 12M and the Lancia Flavia and Fulvia. This is the standard configuration of Audi and Subaru front-wheel-drive vehicles. In 1979, Toyota introduced and launched their first front-wheel-drive car, the Tercel, and it had its engine longitudinally mounted, unlike most other front-wheel-drive cars on the market at that time. This arrangement continued also on the second-generation Tercel, until 1987, the third generation received a new, transversely mounted engine. Other front-wheel-drive Toyota models, such as Camry, and Corolla, had transversely mounted engines from the beginning on.

The 1966 Oldsmobile Toronado (along with its sister model the Cadillac Eldorado) used a novel arrangement which had the engine and transmission in a 'side-by-side' arrangement with power being transmitted between the two via a heavy-duty chain, and a specially designed intermediate driveshaft that passed under the engine sump. This family has the distinction of being the highest engine capacity (8.2 L) front-wheel-drive vehicles ever built. The Saab 99 and “classic” Saab 900 also used a similar arrangement. The Eagle Premier used a similar powertrain arrangement found in the Renault 21 and 25 – later becoming the basis for the Chrysler LH sedans produced until the 2004 model year.

Today, Audi is the most prominent user of this mechanical layout, having used it since the 1950s in its predecessor companies DKW and Auto Union, and it can be found in its larger models from the A4 upward. The latest evolution of the format in Audi's MLB platform attempts to address the long-standing drawback of uneven weight distribution. This is done by packaging the differential in front of the clutch, allowing the axle line to be further forward in relation to the rear face of the engine block.

Front-engine transversely mounted / Front-wheel drive

The bonnet on this original Mini is open, showing the transversely mounted engine that drives the front wheels.

The first popular transverse engined FWD cars were the DKW 'Front' made from 1931, which had a twin cylinder two-stroke engine. Saab copied this design on their first car, the 1949 Saab 92. The Trabant in 1957 was also one of the only cars to have a transverse mounted engine, being a sort of DKW successor. This was a novelty, especially for a car being made in a communist country.

Issigonis's Mini of 1959 and related cars such as the Maxi, Austin 1100/1300 and Allegro had the four-cylinder inline water-cooled engine transversely mounted. The transmission was located in the sump below the crankshaft, with power transmitted by transfer gears. Other models that used the "transmission-in-sump" layout included the Datsun 100A (Cherry) and various applications of the PSA-Renault X-Type engine such as the Peugeot 104 and Renault 14. The 1955 Suzuki Suzulight also introduced a front engine with a transversely installed two-stroke twin-cylinder engine (using DKW technology) in a city car/kei car application, based on the German Lloyd LP400.

Dante Giacosa's Autobianchi Primula of 1964, Fiat 128 and Fiat 127, put the transmission on one side of the transversely mounted engine, and doubled back the drivetrain to put the differential just behind the transmission, but offset to one side. Hence the driveshafts to the wheels are longer on one side than the other. This located the weight just a bit in front of the wheels. It is this system which dominates worldwide at present.

Front-wheel-drive vehicles tend to suffer from torque steer under heavy acceleration.^[5] This is caused by differing drive shaft lengths which in turn results in different incident angles at the joints of the driveshaft. The farther these joints are articulate, the less effective they are at delivering torque to the wheels.

Front-wheel drive design characteristics

• 

  Mid-engine, front-wheel drive (MF layout): Renault 4 mid-engine, front-wheel-drive layout allows greater distance between front doors and wheelwells, and short front overhang.

• 

  Longitudinally front-mounted engine, front-wheel drive (FF longitudinal layout): The Auto Union 1000, (today Audi) longitudinal layout superseded the DKW F89 front transverse engines in the 1950s.

• 

  Transverse front-mounted engine, front-wheel drive (FF transverse layout): Fiat 128, followed the footsteps of the Autobianchi Primula.

Front-wheel drive shafts

In front wheel drive vehicles, the drive shafts transfer the drive directly from the differential to the front wheels. A short inner stub shaft is splined to the differential side gear and an outer stub shaft is splined to the front wheel hub. Each stub shaft has a yoke, or housing, to accommodate a universal joint, at each end of a connecting intermediate shaft.

Universal joints let the shaft keep rotating while allowing for changes due to suspension movement, such as shaft length and horizontal angle, and shaft angle as the steering turns. Constant-velocity universal joints are normally used to transfer power smoothly between the components. The inner universal can be a plunge or tripod type joint. The tripod is splined to the intermediate shaft and held by a circlip. A ball, supported on needle roller bearings, is fitted to each post of the tripod, and these slide in a trunion inside the yoke. This caters for changes in shaft length and horizontal angle. The drive is transferred through the trunion and balls to rotate the shaft.

The outer universal joint allows greater angular changes but not changes in shaft length. It is normally a ball and cage type with an inner race splined to the intermediate shaft. An outer race is formed in the yoke. The cage retains the balls in location in grooves in both races. The balls transfer the drive from the shaft to the hub and allow for changes in horizontal angle and for a wide steering angle to be achieved. A flexible rubber boot fitted to each joint retains grease and keeps out dirt and moisture.

Where the differential is not located in the center line of the vehicle, an intermediate shaft can be fitted to maintain equal length drive shafts on each side. This keeps drive shaft angles equal on both sides and helps prevent steering irregularities and vibration. The outer end of the intermediate shaft is supported by a bearing secured to the transaxle case and a universal joint assists with alignment. In some cases a longer drive shaft is used on one side. A rubber dynamic damper may be fitted to absorb vibrations.

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DKW

DKW

DKW was a German car- and motorcycle-marque. DKW was one of the four companies that formed Auto Union in 1932 and thus became an ancestor of the modern-day Audi company.

Citroën 2CV

Citroën 2CV

The Citroën 2CV is an air-cooled front-engine, front-wheel-drive, economy family car, introduced at the 1948 Paris Mondial de l'Automobile, and manufactured by Citroën for model years 1948–1990.

Mini

Mini

The Mini is a small, two-door, four-seat car, developed as ADO15, and produced by the British Motor Corporation (BMC) and its successors, from 1959 until 2000. Minus a brief hiatus, original Minis were built for four decades and sold during six, from the last year of the 1950s into the last year of the 20th century, over a single generation, as fastbacks, estates, and convertibles.

BMW

BMW

Bayerische Motoren Werke AG, abbreviated as BMW, is a German multinational manufacturer of luxury vehicles and motorcycles headquartered in Munich, Bavaria. The corporation was founded in 1916 as a manufacturer of aircraft engines, which it produced from 1917 until 1918 and again from 1933 to 1945.

Mini (marque)

Mini (marque)

Mini is a British automotive marque founded in 1969, owned by German automotive company BMW since 2000, and used by them for a range of small cars assembled in the United Kingdom, Austria and the Netherlands. The word Mini has been used in car model names since 1959, and in 1969 it became a marque in its own right when the name "Mini" replaced the separate "Austin Mini" and "Morris Mini" car model names. BMW acquired the marque in 1994 when it bought Rover Group, which owned Mini, among other brands.

Citroën Traction Avant

Citroën Traction Avant

The Citroën Traction Avant is the world’s first unibody front-wheel-drive car. A range of mostly 4-door saloons and executive cars, were made with four or six-cylinder engines, produced by the French manufacturer Citroën from 1934 to 1957. Approximately 760,000 units were produced.

Renault

Renault

Groupe Renault is a French multinational automobile manufacturer established in 1899. The company produces a range of cars and vans, and in the past has manufactured trucks, tractors, tanks, buses/coaches, aircraft and aircraft engines, and autorail vehicles.

Panhard Dyna X

Panhard Dyna X

The Panhard Dyna X was a lightweight berline designed by the visionary engineer Jean Albert Grégoire and first exhibited as the AFG (Aluminium Français Grégoire) Dyna at the Paris Motor Show in 1946.

Jean-Albert Grégoire

Jean-Albert Grégoire

Jean-Albert Grégoire was one of the great pioneers of the front-wheel-drive car. He contributed to the development of front-wheel-drive vehicles in two ways. The first way was in developing and promoting the Tracta joint, which was, until manufacturing techniques had progressed sufficiently to allow the successful manufacture of the constant velocity joints commonly in use today, the preferred choice of most manufactures of vehicles that had driven front wheels. Tracta joints were used by many of the pioneers of front-wheel drive, including DKW between 1929 and 1936 and Adler from 1932 to 1939 as well as the cars designed by J A Grégoire that will be mentioned later. The Tracta joint was fitted to most of the military vehicles that had driven front wheels used by most of the combatants in the Second World War. They included Laffly and Panhard in France, Alvis and Daimler in the UK and Willys in the United States that used the joint in a quarter of a million Jeeps and many others. This was to continue after the war, the first Land Rover being so fitted.

Ford Taunus

Ford Taunus

The Ford Taunus is a family car that was sold by Ford Germany throughout Europe. Models from 1970 onward were built on the same basic construction as the Ford Cortina MkIII in the United Kingdom, and later on, the two car models were essentially the same, differing almost only in the placement of the steering wheel. The model line was named after the Taunus mountain range in Germany, and was first made in 1939, and continued through several versions until 1994.

Lancia Flavia

Lancia Flavia

The Lancia Flavia is an executive car produced by Lancia in Italy from 1961 to 1971. Production continued as the Lancia 2000 from 1971 to 1975.

Lancia Fulvia

Lancia Fulvia

The Lancia Fulvia is an automobile produced by Lancia between 1963 and 1976. Named after Via Fulvia, the Roman road leading from Tortona to Turin, it was introduced at the Geneva Motor Show in 1963 and manufactured in three variants: Berlina 4-door saloon, 2-door Coupé, and Sport, an alternative fastback coupé designed and built by Zagato on the Coupé floorpan.