Front Wheel Drive
Front Wheel Drive
In front wheel drive both the engine and transmission system are assembled in one unit, which is mounted at the front of the vehicle. This arrangement provides the following advantages.
(i) Compact construction is obtained.
(ii) Flat floor of passenger compartment is possible in absence of propeller shaft tunnel or gearbox bulge.
(iii) Good traction is provided as majority of weight is taken by the driving wheels.
(iv) Engine can be mounted transversely so that either bonnet length is reduced or the size of the passenger compartment is increased.
(v) Good steering stability is exhibited as driving thrust of the wheels is aimed in the direction that the vehicle is intended to follow. Also the layout rarely suffers from the oversteer characteristics.
The front wheel drive vehicles require more complicated drive shafts, but in view of the many advantages the layout is very suitable for small cars. In the typical front wheel drive layout shown in Fig. 26.59, the transversely mounted engine is bolted to a unit called a transaxle. This name is obtained from the two words transmission and axle.
The four-speed gearbox in Fig. 26.59 uses two shafts i.e. an input shaft splined to the clutch and a mainshaft connected to the final drive pinion. When the engine is mounted longitudinally a bevel gear final drive is necessary. However, in the layout shown in the figure, location of the engine permits the use of normal helical gears. From the final drive through the differential the drive is transmitted to the two drive shafts. At each end of the shaft a constant velocity universal joint is used to prevent the speed variation due to drive shaft angularity.
The inboard joint at each side of the shaft is through the plunge type.
(i) Compact construction is obtained.
(ii) Flat floor of passenger compartment is possible in absence of propeller shaft tunnel or gearbox bulge.
(iii) Good traction is provided as majority of weight is taken by the driving wheels.
(iv) Engine can be mounted transversely so that either bonnet length is reduced or the size of the passenger compartment is increased.
(v) Good steering stability is exhibited as driving thrust of the wheels is aimed in the direction that the vehicle is intended to follow. Also the layout rarely suffers from the oversteer characteristics.
The front wheel drive vehicles require more complicated drive shafts, but in view of the many advantages the layout is very suitable for small cars. In the typical front wheel drive layout shown in Fig. 26.59, the transversely mounted engine is bolted to a unit called a transaxle. This name is obtained from the two words transmission and axle.
The four-speed gearbox in Fig. 26.59 uses two shafts i.e. an input shaft splined to the clutch and a mainshaft connected to the final drive pinion. When the engine is mounted longitudinally a bevel gear final drive is necessary. However, in the layout shown in the figure, location of the engine permits the use of normal helical gears. From the final drive through the differential the drive is transmitted to the two drive shafts. At each end of the shaft a constant velocity universal joint is used to prevent the speed variation due to drive shaft angularity.
The inboard joint at each side of the shaft is through the plunge type.
During acceleration, or if the engine is used as a brake, torque reaction causes the engine to rotate about the crankshaft. Therefore, engine mountings are suitably located and secured to resist this movement. The thrust and braking torque are taken by the suspension members, specifically the tie bar joining the track control arm to the body.
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