Transmission options
Longitudinal and transverse driveline configurations
 Figure 1. The standard driveline for rear-wheel-drive vehicles from Jaguar, BMW, and Mercedes-Benz is a longitudinally installed, inline engine/transmission combination.  Figure 2. The front-longitudinal driveline is composed of a longitudinally installed inline engine/transmission in front-wheel-drive vehicles from OEMs such as Chrysler, Audi, and VW.  Figure 3. The most common of the all-wheel-drive variants is the standard driveline with a flange-mounted transfer case on the transmission output typically found on North American market light trucks and SUVs. Click on an image to enlarge |
A driveshaft transfers output from the transmission to an axle drive with an integrated differential, which transfers the power through the axle shafts to the wheels.
The front-longitudinal driveline is composed of a longitudinally installed inline engine/transmission in front-wheel-drive vehicles (Figure 2). Transmission output is conveyed via gears or chain and a shaft to an axle drive with an integrated differential. This driveline solution is found on many Chrysler, Audi, and Volkswagen cars.
The rear-longitudinal driveline is one with a rear engine/transmission and rear-wheel drive and corresponds to the front-longitudinal driveline in Figure 2, but with the drive direction reversed. The most prominent use of this configuration was for the original VW Beetle, while a variation is the mid-engine installation of the current Porsche Boxster.
All-wheel-drive variants can be derived from all longitudinal drivelines. The most common version today is the standard driveline with a flange-mounted transfer case on the transmission output (Figure 3). A transfer gearbox transmits output via driveshafts to front and rear axle drives and finally to the wheels via axle shafts. Typical examples of this configuration are North American market light trucks and SUVs.
 Figure 4. The front-transverse driveline on cars such as the VW New Beetle, Ford Mondeo, and Saturn models makes use of a transversely installed, inline engine/transmission and front-wheel drive.  Figure 5. A special variation of the front-transverse driveline is the U-drive, in which the transmission lies behind the engine—a common configuration on large GM and Ford cars for North America.  Figure 6. Most all-wheel-drive variants can also be derived from front- and rear-transverse drivelines and use an additional output shaft for power takeoff from the transmission. Click on an image to enlarge |
The front-transverse driveline makes use of a transversely installed, inline engine/transmission and front-wheel drive (Figure 4). The axle drive and differential are integrated in the transmission, with the wheel drive ensuing directly from the flange-mounted axle shafts on both sides of the transmission. The axle position lies behind the crankshaft, an exception being in the Mercedes-Benz A-Class.
Today, this driveline is common on vehicles in the small and mid-range segments and reaches as far up as the upper segment. Examples are the VW New Beetle, Ford Mondeo, and Saturn models.
A special variation of this driveline is the U-drive, in which the transmission lies behind the engine (Figure 5). It is common in the U.S. in vehicles that have a large engine and not enough space for an inline engine/transmission unit. The transmission input is at the crankshaft's center and connected to the transmission via a chain drive. Examples are large GM and Ford cars for North America.
The rear-transverse driveline, with a transversely installed engine/transmission in the rear and rear-wheel drive, corresponds to the front-transverse driveline of Figure 4 but with the driving direction reversed. This driveline is rare and is found today in mini cars such as DaimlerChrysler's Micro Compact Car (MCC) smart.
All-wheel-drive variants can also be derived from front- and rear-transverse drivelines, though the transmission's power takeoff design is dependent on the all-wheel-drive system employed. Most variants use an additional output shaft for power takeoff from the transmission (Figure 6).
In 1999, 6.2 million North American vehicles out of a total car production volume of 7.3 million were equipped with a front-transverse driveline (Figure 7). About 92% of these front-wheel-drive cars were equipped with automatic transmissions. Standard-driveline-equipped vehicles (about 700,000 units) had 82% automatic penetration, and most cars with the front-longitudinal driveline (about 200,000 units) had automatics. All-wheel-drive vehicles accounted for only 2% of production in North America, with an automatic transmission share of nearly 80%.
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Figure 7. Market share data for North America during 1999 show that 6.2 million vehicles were equipped with a front-transverse driveline out of a total car production volume of 7.3 million. Click to enlarge |
