The ball nut is fitted with tubular ball guides to
The steering gear case contains the gears that
return the balls diagonally across the nut to recirculate
control the movement of the pitman arm and steering
them. As the nut moves up and down, the pitman arm
linkage. Figure 2-9 shows a typical steering gear
turns, and the vehicle's wheels turn with it.
assembly, the location of the adjustment screw, and the
filler plug for gear lubricant.
On equipment that is steered by the rear wheels,
such as forklifts, the steering components and
The principal parts of any steering gear unit are the
operation are the same except that a longer drag link is
worm gear and sector. A sector is a portion of a full
necessary to permit the driver to face forward. Because
gear. The sector gear and worm provide a ratio between
the steering column must be pointed forward to permit
the number of turns of the steering wheel to one turn of
the operator to face forward, the distance from the
the pitman arm. Because the pitman arm does not turn a
gearbox and pitman arm to the steering knuckle arm is
complete revolution, only a section of one gear is used
greater than on a front steering vehicle. Thus, a longer
in the gear arrangement. The gear ratio of the steering
drag link is required.
column and the cross shaft that carries the pitman arm
varies from 4 to 1 to 18 to 1 in automotive equipment.
The high steering gear ratios are used in vehicles that
are hard to steer or are slow moving. The low steering
Automotive power steering hydraulic systems
consist of three units: the pump (including reservoir),
gear ratios are used in vehicles that are easy to turn.
the power cylinder or cylinders, and the control valve.
To provide easier and more efficient steering,
The power steering pump is driven by the engine or an
roller and ball bearings have been added to the steering
engine-driven accessory, by a belt, a shaft, or gears.
gear units. The design of the worm gear and sector has
Lines and hoses connect the three units, and all systems
been changed, and even the names of these parts are
are constructed so that the vehicle can be steered
different. In figure 2-9, the worm gear is called a cam
manually, should the power steering system fail.
and the sector is called a stud. These parts work on the
One type of power steering system has the power
same principle as a worm gear and sector.
cylinder and control valve built into the gearbox or case
Another form of steering gear is the recirculating
at the base of the steering column. As the steering
ball and nut gear (fig. 2-10). In this assembly the nut is
wheel is turned to the right or left, the control valve
mounted on a continuous row of balls on the worm to
directs hydraulic fluid pressure to one side or the other
of a piston in the power cylinder that is connected to the
Figure 2-9.--Steering gear unit of the cam and lever type.