Chapter 25 Steering Systems 515
systems, a magnetic rack-and-pinion spool valve
assembly is used instead of a fl ow control sole-
noid to vary steering assist.
Note
In the near future, some vehicles will be
equipped with fully electronic steering. With
fully electronic steering, there will be no
mechanical connection between the steering
wheel and the steering gear. Sensors in the
steering wheel will operate motors that turn
the wheels.
Electric Power Steering Systems
On some late-model vehicles, the power
steering system is operated by an electric
motor. This type of system is known as electric
power steering. There are four kinds of elec-
tric power steering, as shown in Figure 25-33.
Figure 25-33A shows an electrohydraulic
system. The power steering is a conventional
hydraulic type, but the pump is driven by an
electric motor instead of an engine-driven belt.
The other three designs are electromechanical
systems, which have no hydraulic components.
Figure 25-33B shows an electric motor that is
installed in the steering gear and moves the rack
directly. In Figure 25-33C, the electric motor
is mounted on the steering column. The motor
operates a pinion gear meshed with a ring gear
attached to the steering shaft. The system shown
in Figure 25-33D uses an electric motor that is
mounted on the rack. The motor meshes directly
with the steering gear pinion.
All electric power steering systems operate
on the same principles. A computer is used to
control overall system operation based on inputs
from several sensors. A sensor on the steering col-
umn provides inputs on the turning effort and the
speed of steering wheel movement. Speed sensors
Power steering
dipstick
B A
Dipstick
O-ring seal
Power steering
fluid reservoir
This dipstick has two sides:
“full cold” and “full hot”
Front of
vehicle
Full cold
Full hot
Figure 25-32.
Power steering fl uid reservoir. A—Power steering pump reservoir and dipstick location on one engine. B—Sometimes
the full cold and the full hot fl uid level marks are on opposite sides of the dipstick.
Ford Motor Co.