200 Auto Suspension and Steering
Summary
The steering system is a system of parts that transmit
the movement of the steering wheel to the front wheels of
the vehicle. All steering systems contain some of the same
parts, including the steering wheel, steering shaft and
column, flexible coupler, universal joints, ball sockets, and
steering arms. The steering wheel hub is splined to the
steering shaft. A large nut holds the hub to the steering
shaft. Steering wheel size affects steering effort. Steering
wheels contain the horn button and, when used, air bags.
The steering shaft is installed inside the steering
column. Bearings hold the shaft in position and reduce
friction. Steering shafts are made of two sections of steel
rod held in place by shear pins. A steering coupler is
installed on the bottom of the shaft. Universal joints are
used on some steering shafts. The steering column usually
contains the turn signal indicator, and may contain the
gearshift selector. Some steering columns can be tilted to
change the position of the steering wheel.
Vehicles have steering arms to convert linear motion
of the steering linkage to rotation at the steering knuckle.
Ball sockets resemble ball joints but transmit horizontal
steering motion instead of transmitting vehicle weight
vertically. Ball sockets used to connect the steering linkage
to the steering knuckle are called tie rod ends. Other ball
sockets are used on other parts of the steering linkage.
Rack-and-pinion steering transmits the rotation of the
steering wheel and converts it to straight line movement at
the wheels. Major rack-and-pinion components are the
pinion, rack, and housing. Simple and direct linkage
consisting of inner and outer tie rods connects the rack to
the steering arms.
The conventional steering system has more
components than the rack-and-pinion system. All conven-
tional steering gears are similar in appearance and
operation. The use of a worm gear and sector reduces
steering efforts by increasing the steering ratio.
The recirculating-ball steering gear uses a nut that is
moved back and forth as the worm gear turns. Teeth on the
nut engage teeth on the sector gear. The worm-and-roller
steering gear uses a roller assembly installed on the sector
gear instead of a ball nut. The worm-and-follower steering
gear uses a pin or peg to directly engage the worm gear.
Pitman arms connect the conventional steering gear to
the other steering linkage. A relay rod connects the two
sides of the steering system. An idler arm supports the
steering linkage on the side opposite of the pitman arm.
Rack-and-pinion and conventional power steering
systems are operated by hydraulic pressure. The basic
operating principle of power steering is that the power
steering fluid cannot be compressed. Pressure is created in
the pump and transmitted to the rest of the power steering
system. Modern power steering systems use special power
steering fluid.
The power steering reservoir stores extra fluid for use
by the other system components. The engine operates the
power steering pump through a belt and pulley arrange-
ment. Most power steering pumps are vane type pumps. A
few pumps are slipper or gear pumps. Output of the pump
is controlled by flow and pressure regulators. Flow control
valves keep the flow at about the same value no matter
how fast the pump is turning, and pressure regulators
prevent the development of excessively high pressures.
Power steering hoses connect various parts of the sys-
tem. They must be able to withstand system pressures.
High pressure hoses have tubing fittings while low pressure
hoses may be clamped to the steering gear and reservoir
fittings.
Some vehicles have a pressure switch installed on the
high pressure side of the system. This switch signals the
ECM when the power steering system is producing maxi-
mum pressure.
Power steering coolers remove the heat created by
pressurizing the power steering fluid. Simple coolers
consist of an extra length of tubing under the vehicle. More
elaborate coolers are finned and installed in front of the
radiator.
The rack-and-pinion power steering unit resembles a
manual rack-and-pinion system. An inner power piston
receives hydraulic pressure to help move the rack. The
control valve is a rotary valve consisting of an inner spool
valve in a valve body. The turning effort from the steering
wheel passes through the valve assembly before reaching
the pinion gear. The spool valve moves in relation to the
valve body before the turning effort passes through the
valve body to the pinion gear. This action directs pressure
to the proper power piston chamber as necessary. The valve
permits fluid in the other chamber to exit to the reservoir.
Conventional linkage power steering usually uses
a self-contained steering gear. The self-contained power
steering gear is a recirculating-ball gear with a
power piston and a control valve. The power piston divides
the steering gear into two pressure chambers. The piston is
connected to the ball nut. Pressure to one chamber or the
other moved the piston and therefore the ball nut. The
control valve used on most self-contained recirculating-
ball steering gears is a rotary valve similar to that used on
rack-and-pinion power steering. A few older steering gears
use a linear valve that moves back and forth in a valve
body. A lever connected to the steering shaft moves the
valve.
Linkage-mounted power steering consists of a power
piston and control valve mounted on the linkage of a
conventional steering system. The system uses a manual
steering gear, a power cylinder and a control valve mounted
on the end of the pitman arm. The valve is a
linear type. High pressure hoses connect the components.
A few vehicles have four-wheel steering. Input from
front steering system is used to control the rear steering.
Some four-wheel steering systems use hydraulic pressure
from the front power steering to operate the rear wheel
steering system. The hydraulic pressure is controlled by an
electronic control system. Other four-wheel steering
systems consist of electrical motors operated by a control
module. Input to the control module comes from front and
rear wheel position sensors.