In automotive design, an FWD, or front-engine, front-wheel-drive
layout places both the internal combustion engine and driven
roadwheels at the front of the vehicle.
1 Usage implications
2 Historical arrangements
2.1 Mid-engine / Front-wheel drive
2.2 Longitudinally mounted front-engine and front-wheel drive
2.3 Front-engine transversely mounted / Front-wheel drive
Front-wheel drive design characteristics
Front-wheel drive shafts
3 See also
5 Further reading
Automobile layout and Front-wheel-drive
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 where the engine is in front of the
passenger compartment but behind the front axle. Most pre-World War II
front engine cars would qualify as front-mid engine, using the
front-mid designation, 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
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 where 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 a FWD vehicle is
generally better, because the engine is placed over the steered
wheels. 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. 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 horsepower of high-performance cars can result in the
sensation of torque steer. Electronic traction control can avoid
wheel-spin but largely negates the benefit of extra power. This was
a reason for the adoption of the four-wheel-drive quattro system in
the high performance
Jensen FF and
Audi Quattro road cars.
Early cars using the FWD layout include the 1929 Cord L-29, 1931 DKW
F1, the 1948 Citroën 2CV, 1949
Saab 92 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 -
Toyota was the last Japanese company to switch in the early
1980s. BMW, focussed on luxury vehicles, however retained the
rear-wheel-drive layout in even their smaller cars, 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
Mid-engine / Front-wheel drive
The earliest such arrangement was not technically FWD, 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
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
but it has since fallen out of favor since it encroaches into the
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
Ford Taunus 12M and the
Lancia Flavia and Fulvia. This is the
standard configuration of
Audi and Subaru front-wheel-drive vehicles.
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.
Oldsmobile Toronado (along with its sister models the
Cadillac Eldorado and Buick Riviera) 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.
Audi is the most prominent user of this mechanical layout,
having used it since the 1950s in its predecessor companies
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 1970s Giugiaro styled hatchback coupe
VW Scirocco based on the
contemporary Giugiaro Golf was in MK1 and MK2 forms the most
successful VW coupe with 800,000 made.
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
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, beind a sort of
DKW precursor . This was a novelty, especially
for a car being made in a comunist country.
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.
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. 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
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.
^ Hillier, Victor; Peter Coombes (2004). Fundamentals of motor vehicle
technology. Nelson Thornes. p. 9.
^ "Engine & Driveline Layouts". Drivingfast.net. Retrieved 6
^ www.motortrend.com Road Test: Rear Drive vs. Front Drive vs.
BMW Technology Guide: Rear wheel drive". Retrieved 1 September
^ www.oneighturbo.com Archived 2011-07-15 at the Wayback Machine.
Comeback of a sports car legend: Volkswagen Scirocco - accessed 14
^ "What the heck is torque steer?".
Sedgwick, Michael Cars of the 50s and 60s. Gothenburg, Sweden: A B
Nordbok, 1983. (Includes pictures of the engine layouts of the
Traction Avant and other designs.)
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