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Front Wheel Drive

Chapter Eight Front Wheel Drive Configurations.

The layout of the main components of a front wheel drive cars power train can be in many configurations. The main components are the engine, gearbox and final drive assembly (differential and drive shafts,).  The FWD cars of the nineteen twenties and thirties located the engine well behind the front axle line, as was common practice at that time. At first with the gearbox in front of it, with the final drive between the front wheels. Inline, as in the case of the "Tracta"," Cord", "BSA", "Alvis", "Audi", "Adler" and "Amilcar".
  1932 BSA T9
Or Transverse across the car, connected by chains or spur gears as in the DKW. This layout took up a lot of space and didn't make full use of the possible advantages of FWD, a compact power train and good weight distribution.  J.A.Gregoire stated in his book "Front Wheel Drive", "Technical honesty obliges me, therefore, to recognize that one of the principle advantages of front wheel drive does not derive from the system itself, but from of it's secondary consequences; the predominance of front axle loading".  Citroen made a small step forward with "Traction Avante", by locating the gearbox ahead of the final drive assembly, making a limited improvement in weight distribution and space utilization (See picture in part three). The "DKW", F9 was the first car ready for production in 1939, but not produced until 1950, that had a layout that took full advantage of a front wheel drive configuration, with the engine in line ahead of the final drive assembly with the gearbox behind.  This is the layout that has been used in most of  "DKW"/AUTO UNION/AUDI cars since.
DKW F-91 Power unit.
After practical experience J.A. Gregiore came to the conclusion that this was the way to go. His Aluminium Francais-Gregiore, developed during the Second World War and produced in the form of the Panhard "Dyna", in 1946 and all his later FWD designs had the engine out front.
The Citroen" 2CV", designers also adopted this layout as it suited the installation of horizontally opposed, air-cooled engines perfectly. Citroen went on to produce the AMI 6/8, the Dyane 4/6, also the GS/GSA, and smallest of the VISA models with the same layout.
Citroen 2CV Power Unit.
The transverse engine configuration had not been forgotten. In 1946 a prototype of the first SAAB, the 92, was produced with a transversely mounted twin cylinder, two-stroke engine with the clutch and gearbox located inline with the crankshaft and these components located ahead of the final drive assembly. The 92 went into production at the end of 1949,

     Saab 92 layout,                                 Saab 92 Power Unit.
In their first post war model the F89, DKW moved the engine to a position in front of the final drive, In production by 1950. This was the last of the two-stroke twins from DKW. The last transverse engined vehicle from DKW was the three cylinder F-91/4 Munga, four wheel drive utility made for the German arm forces in 1955.
  DKW F-89.
Not until the advent of the AUDI 50 in 1974 that they fitted a transverse engine again. The next innovation, was the mounting of a four-cylinder engine transversely in a front wheel drive car. This came with the MINI in 1959. The difficulty with the use of a four-cylinder engine in this way was that it was longer than the engines fitted previously, which wouldn't allow the final drive to be located an equal distance between the driven wheels. As unequal length drive shafts cause transmission fluctuations.  The answer to this problem was solved in the MINI by incorporating the gearbox into the engine sump. The drawback to this arrangement is that the engine/gearbox unit is tall, also the gears run in a lubricant that is not ideal. Almost 10 million cars with this arrangement were produced by the British Motor Corporation/BLMC.
BMC Mini Power Unit.

The advantages of the transverse engine arrangement in improving the packaging of a car became apparent with the MINI, so a means of using a four-cylinder engine with a separate gearbox mounted inline with it and overcoming the drawbacks of the MINI arrangement was sought. The answer was to find a way of using unequal length drive shafts without the associated drive problems. The solution was to make the unequal length drive shafts of equal torsional stiffness, this was achieved by Dante Giacosa of FIAT, first in the Autobianchi "Primula", of 1964 which was a stepping stone to his big breakthrough the FIAT 128.
Autobianchi A111 similar to the Primula.
The 128, was the first front wheel drive FIAT. By incorporating features, not new but not used in combination with front wheel drive before, such as a transverse engine (utilizing his new layout and drive shaft arrangement). Adding Mac-Pherson strut front suspension and rack and pinion steering, he produced the layout that is almost universal at the beginning of the this century.
Another configuration used by Triumph in the 1300 and Saab in the 99. It consisted of the engine mounted inline with a separate gearbox and final drive located underneath the engine with it's own lubrication system (As opposed to the shared lubrication used by Issigonis.). The advantages of this system were a compact layout for an inline engines and equal lenght drive shafts. The disadvantage is a tall engine /gearbox assembly. To overcome this, the engine was inclined. The Triumph 1300 was not a success, but the Saab went on to a long production run.

Saab 99 Power unit.
The only other layout in use at this time is that with the engine mounted inline ahead of the final drive unit and the gearbox behind, as used by AUDI and SAAB.
The earlier front wheel drive layouts didn't fall into disuse with the advent of the more compact systems for a long time. Citroen with the DS and ID series (1955 to 1975) continued to produce cars with the engine inline behind the final drive and the gearbox in front. Renault used the same layout for their early front wheel drive cars, the "4" (1961 to 1991) the first "5" (1972 to 1984) and the "6" (1968 to 1980).
Front Wheel Drive Links
GTM CARS LTD April 1981 to March 2003
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