Four Wheel Driving And Steering

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.