Lesson 1/Learning Event 1
FOURWHEEL DRIVING AND STEERING
Four-wheel drive
A construction in which all four wheels of the vehicle drive is used on many
military vehicles. A universal joint is used at the end of the axle shaft
so that the wheel is free to pivot at the end of the axle while being driven
through the axle. The end of the axle housing encloses this universal joint
and has vertical trunnion pins that act as a steering knuckle pivot. The
wheels, mounted on steering knuckles attached to these trunnion pivots, are
free to turn around the pivots at the same time they are driven through
universal joints on the inner axle shaft. Steering knuckle arms are mounted
on the steering knuckles so that the wheels can be turned around the
trunnion steering pivots by the steering linkage.
Four-wheel steering
All four wheels can be steered from the steering wheel by connecting the
steering linkage of these wheels to the pitman arm. The rear wheels are
connected by knuckle arms and a tie rod. Because the rear wheels must be
turned in the opposite direction to the front wheels to travel in the same
arcs around the center of rotation, the drag links to the front and rear
wheel steering linkage cannot be connected directly to the steering gear
arm. The drag link to the front wheels must move forward while the drag
link to the rear wheels moves rearward and vice versa. To accomplish this,
an intermediate steering gear arm is pivoted on the frame sidemember near
the middle of the vehicle. The drag links are connected to opposite ends of
this arm. As it is turned by direct connection to the pinion arm (by means
of an intermediate link), the front and rear drag links are moved in
opposite directions.
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