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Suspension And Steering Systems Operation
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| Suspension And SteeringSystems Operation |
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| Updated |
Jul 7, 2004 20:29:38 |
| Rating |
 180 ( -20 -11.11% ) |
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Description:
Below is an overview of the suspension and steering
systems
The Steering/Suspension
System
(Overview)
"Suspension," when discussing cars, refers to the use of front and rear
springs to suspend a vehicle's "sprung" weight. The springs used on
today's cars and trucks are constructed in a variety of types, shapes,
sizes, rates, and capacities. Types include leaf springs, coil springs,
air springs, and torsion bars. These are used in sets of four for each
vehicle, or they may be paired off in various combinations and are
attached by several different mounting techniques. The suspension system
also includes shocks and/or struts, and sway bars.
Back in the earliest days of automobile development, when most of the
car's weight (including the engine) was on the rear axle, steering was a
simple matter of turning a tiller that pivoted the entire front axle. When
the engine was moved to the front of the car, complex steering systems had
to evolve. The modern automobile has come a long way since the days when
"being self-propelled" was enough to satisfy the car owner. Improvements
in suspension and steering, increased strength and durability of
components, and advances in tire design and construction have made large
contributions to riding comfort and to safe driving.
Cadillac allegedly produced the first American car to use a steering
wheel instead of a tiller.
Two of the most common steering mechanisms are the "rack and pinion"
and the standard (or recirculating-ball) systems, that can be either
manual or assisted by power. The rack and pinion was designed for sports
cars and requires too much driver muscle at low speeds to be very useful
in larger, heavier cars. However, power steering makes a heavy car respond
easily to the steering wheel, whether at highway speeds or inching into a
narrow parking place, and it is normal equipment for large automobiles.
The suspension system has two basic functions, to keep the car's wheels
in firm contact with the road and to provide a comfortable ride for the
passengers. A lot of the system's work is done by the springs. Under
normal conditions, the springs support the body of the car evenly by
compressing and rebounding with every up-and-down movement. This
up-and-down movement, however, causes bouncing and swaying after each bump
and is very uncomfortable to the passenger. These undesirable effects are
reduced by the shock absorbers.
Steering Systems
The manual steering system incorporates: 1. steering wheel and column,
2. a manual gearbox and pitman arm or a rack and pinion assembly, 3.
linkages; steering knuckles and ball joints; and 4. the wheel spindle
assemblies.
In Pittman arm systems, the movement inside the steering box causes the
Pitman shaft and arm to rotate, applying leverage to the relay rod, which
passes the movement to the tie rods.
Power steering systems add a hydraulic pump; fluid reservoir; hoses;
lines; and either a power assist unit mounted on, or integral with, a
power steering gear assembly.
There are several different manual steering gears in current use. The
"rack and pinion" type is the choice of most manufacturers. The
"recirculating ball" type is a past favorite because the balls act as a
rolling thread between the wormshaft and the ball nut. Another manual
steering gear once popular in imported cars is the "worm and sector" type.
Other manual gears are the "worm and tapered pin steering gear" and the
"worm and roller steering gear."
The steering wheel and column are a major source of injury to the
driver, and a range of energy-absorbing and non-intrusion designs have
been developed. There is great variation in these designs, some of which
are now thought to be not fully effective.
Energy-absorbing columns have to serve two functions. First, they must
stop the steering wheel and column from being pushed to the rear as the
front of the car is crushed in an impact. Before such designs were
invented, a common feature of driver injury was for the chest to be
impaled by the steering column. The energy-absorbing column must also
provide the driver with a tolerable impact as he moves forward and strikes
the wheel with his chest. At that point in the crash, the column should
build up the load on the driver's chest to a tolerable level, and then
deform under that load to give a "ride-down" for the driver.
Several design problems are presented in providing this system. One
major problem is that collapse of the column due to the frontal crush of
the car should not hinder its performance for providing ride-down for the
driver's chest. The system must also be so designed that under crash
conditions, the wheel stays in such a position that it will strike the
driver's chest and not move upwards into the region of his face, or
downwards into his abdomen.
Steering Linkage
The steering linkage is made of interconnected parts which move every
time the steering wheel is turned. The rotating movement of the steering
column activates mechanisms inside the steering box. Tie rod ends, which
join the key parts, pass on the steering wheel's motion no matter what the
angle of the linkage or the vibration from the road. In a pitman arm
steering setup, the movement inside the steering box causes the Pitman
shaft and arm to rotate, applying leverage to the relay rod, which passes
the movement to the tie rods. The steering arms pick up the motion from
the tie rods and cause the steering knuckles to turn the wheels. The
steering linkages need regular maintenance for safe operation, such as
lubrication and inspection. Faulty steering links can cause tire wear at
the least, and complete loss of control of the vehicle at worst. "Popping"
noises (when turning the wheels) usually indicate worn out steering
linkages.
Manual Rack and Pinion Steering
A typical rack and pinion steering gear assembly consists of a pinion
shaft and bearing assembly, rack gear, gear housing, two tie rod
assemblies, an adjuster assembly, dust boots and boot clamps, and grommet
mountings and bolts. When the steering wheel is turned, this manual
movement is relayed to the steering shaft and shaft joint, and then to the
pinion shaft. Since the pinion teeth mesh with the teeth on the rack gear,
the rotary motion is changed to transverse movement of the rack gear. The
tie rods and tie rod ends then transmit this movement to the steering
knuckles and wheels.
Manual Recirculating Ball Steering
With the manual recirculating ball steering gear, turning forces are
transmitted through ball bearings from a "worm gear" on the steering shaft
to a sector gear on the pitman arm shaft. A ball nut assembly is filled
with ball bearings, which "roll" along grooves between the worm teeth and
grooves inside the ball nut. When the steering wheel is turned, the worm
gear on the end of the steering shaft rotates, and movement of the
recirculating balls causes the ball nut to move up and down along the
worm. Movement of the ball nut is carried to the sector gear by teeth on
the side of the ball nut. The sector gear then moves with the ball nut to
rotate the pitman arm shaft and activate the steering linkage. The balls
recirculate from one end of the ball nut to the other through ball return
guides.
Manual Worm and Sector Steering
The manual worm and sector steering gear assembly uses a steering shaft
with a three-turn worm gear supported and straddled by ball bearing
assemblies. The worm meshes with a 14-tooth sector attached to the top end
of the pitman arm shaft. In operation, a turn of the steering wheel causes
the worm gear to rotate the sector and the pitman arm shaft. This movement
is transmitted to the pitman arm and throughout the steering train to the
wheel spindles.
Worm and Tapered Peg Steering
The manual worm and tapered peg steering gear has a three-turn worm
gear at the lower end of the steering shaft supported by ball bearing
assemblies. The pitman shaft has a lever end with a tapered peg that rides
in the worm grooves. When the movement of the steering wheel revolves the
worm gear, it causes the tapered peg to follow the worm gear grooves.
Movement of the peg moves the lever on the pitman shaft which in turn
moves the pitman arm and the steering linkage.
Manual Worm and Roller Steering
The manual worm and roller steering gear is used by various
manufacturers. This steering gear has a three-turn worm gear at the lower
end of the steering shaft. Instead of a sector or tapered peg on the
pitman arm shaft, the gearbox has a roller assembly (usually with two
roller teeth) that engages the worm gear. The assembly is mounted on
anti-frictional bearings. When the roller teeth follow the worm, the
rotary motion is transmitted to the pitman arm shaft, pitman arm and into
the steering linkage.
Power Steering
Over the years, power steering has become a standard equipment item on
many automobiles. The demand for this system has caused power steering to
be installed on over 90%% of all domestic new car production. All systems
require a power steering pump attached to the engine and driven by a belt,
a pressure hose assembly, and a return line. Also, a control valve is
incorporated somewhere in the hydraulic circuit. "Power steering" is
really "power assisted steering." All systems are constructed so that the
car can be steered manually when the engine is not running or if any
failure occurs in the power source.
Most power steering pumps contain a flow control valve, which limits
fluid flow to the power cylinder to about two gallons per minute, and a
relief valve which limits pressure according to system demands.
Power Rack and Pinion
Power rack and pinion steering assemblies are hydraulic/ mechanical
unit with an integral piston and rack assembly. An internal rotary valve
directs power steering fluid flow and controls pressure to reduce steering
effort. The rack and pinion is used to steer the car in the event of power
steering failure, or if the engine (which drives the pump) stalls.
When the steering wheel is turned, resistance is created by the weight
of the car and tire-to-road friction, causing a torsion bar in the rotary
valve to deflect. This changes the position of the valve spool and sleeve,
thereby directing fluid under pressure to the proper end of the power
cylinder. The difference in pressure on either side of the piston (which
is attached to the rack) helps move the rack to reduce turning effort. The
fluid in the other end of the power cylinder is forced to the control
valve and back to the pump reservoir. When the steering effort stops, the
control valve is centered by the twisting force of the torsion bar,
pressure is equalized on both sides of the piston, and the front wheels
return to a straight ahead position.
Integral Power Steering Gears
A representative of an integral power steering gear is used on certain
General Motors rear-wheel drive cars and on American Motors four-wheel
drive. This power steering gear uses a recirculating ball system in which
steel balls act as rolling threads between the steering worm shaft and the
rack piston. The key to its operation is a rotary valve that directs power
steering fluid under pressure to either side of the rack piston. The rack
piston converts hydraulic power to mechanical force. The rack piston moves
up inside the gear when the worm shaft turns right. It moves down when the
worm shaft turns left. During these actions, the steel balls recirculate
within the rack piston, which is power assisted in movement by hydraulic
pressure. (See also Manual Recirculating Ball Steering)
Power Steering Hoses
The power steering hoses are used to transmit hydraulic fluid under
pressure from the pump to the power cylinder and to return. Besides this,
the hoses must provide the proper amount of expansion to absorb any shock
surge and offer enough restriction to the fluid flow to keep the pump
cavity full of fluid at all times.
Power steering hoses are specially designed rubber hoses with metal
fittings at each end which screw together with your power steering system.
They contain power steering fluid at high pressures, and allow the system
to circulate the fluids between the pump and the power
cylinders.
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