Steering system 1

Copyright by Kia Motors. All rights reserved.

Steering system 1

Index

Subject Page
Steering general 3
Hydraulic power steering 5
Oil pump, pressure and flow control valve 7
Hydraulic control valve 9
Operating principle 10
Service and maintenance 11

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Steering system 1

Steering general

In automobiles, steering wheel, gears, linkages, and other components are used to control the
direction of a vehicle’s motion. Because of friction between the front tires and the road, especially
in parking, effort is required to turn the steering wheel. To lessen the effort required, the wheel is
connected through a system of gears to components that position the front tires. The gears give
the driver a mechanical advantage, i.e., they multiply the force he applies, but they also increase
the distance through which he must turn the wheel in order to turn the tires a given amount. For a
car to turn smoothly, each wheel must follow a different circle. Since the inside wheel is following a
circle with a smaller radius, it is actually making a tighter turn than the outside wheel. If you draw a
line perpendicular to each wheel, the lines will intersect at the center point of the turn. The
geometry of the steering linkage makes the inside wheel turn more than the outside wheel.
Various types of gear assemblies are used. Rack-and-pinion steering is the most common. A
rack-and-pinion gear set is enclosed in a metal tube, with each end of the rack protruding from the
tube. A rod, called a tie rod, connects to each end of the rack. The pinion gear is attached to the
steering shaft. When you turn the steering wheel, the gear spins, moving the rack. The tie rod at
each end of the rack connects to the steering arm on the spindle. The rack-and-pinion gear set
converts the rotational motion of the steering wheel into the linear motion needed to turn the
wheels and provides a gear reduction, making it easier to turn the wheels.

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The recirculation-ball steering gear contains a worm gear. You can image the gear in two parts.
The first part is a block of metal with a threaded hole in it. This block has gear teeth cut into the
outside of it, which engage a gear that moves the pitman arm. The steering wheel connects to a
threaded rod, similar to a bolt, which sticks into the hole in the block. When the steering wheel
turns, it turns the bolt. Instead of twisting further into the block the way a regular bolt would, this
bolt is held fixed so that when it spins, it moves the block, which moves the gear that turns the
wheels.
Instead of the bolt directly engaging the threads in the block, all of the threads are filled with ball
bearings that recirculate through the gear as it turns. The balls actually serve two purposes: First,
they reduce friction and wear in the gear; second, they reduce slop in the gear. Slop would be felt
when you change the direction of the steering wheel -- without the balls in the steering gear, the
teeth would come out of contact with each other for a moment, making the steering wheel feel
loose. On most cars, it takes three to four complete revolutions of the steering wheel to make the
wheels turn from lock to lock (from far left to far right). In faster, heavier cars the amount of force
required to turn the tires can be very great. Many of these cars use a hydraulic or electric power-
steering system. As a safety feature in many modern cars the column on which the steering wheel
is mounted will collapse if the driver is thrown against the wheel in a collision.

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Steering system 1

Hydraulic power steering

The power assisted steering gear system of the rack and pinion type, consisting of the control
valve and servo cylinder. Together with the power steering pump, power steering fluid reservoir,
pressure and return hoses these are the main components of the system. Power steering uses
hydraulic pressure for reduction of steering effort, enabling the driver to easily operate the steering
wheel. Steering effort is generally 20N to 39N. In addition to that, power steering systems offer
higher stability during driving and prevention of shock from road surface irregularities that may
otherwise be transmitted to the steering wheel. Power steering fluid is pumped from the power
steering pump to the passage changeover valve where, depending on which way the steering
wheel is turned, it is directed to either the right or left side of the servo cylinder. This passage
changeover valve is referred to as Hydraulic Control Valve. The steering servo fluid inside the
cylinder acts on the rack's piston (2.), thus providing power assistance to the rack and pinion
steering gear. The mechanical components of the steering gear are lubricated by high viscosity
grease and are sealed from the hydraulic circuit and other parts of the system by seals and rubber
gaiters. Some systems incorporate special considerations to reduce steering effort during low
speed operation and increase steering effort during high speed operation. These systems are
referred to as Electronic Power Steering System (EPS).

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The hydraulic control valve housing, which is attached to the steering gear housing, has four
connections for the flow of power steering fluid: Servo delivery from the power steering pump (A),
return to the power steering fluid reservoir (B), to the servo cylinder when turning right or from the
servo cylinder when turning left (C) and to the servo cylinder when turning left or from the servo
cylinder when turning right (D).The cylinder is part of the steering gear housing. The rack (1.) is
equipped with a piston (2.) complete with seals. For the flow of power steering fluid to and from the
control valve there are two connections on the servo cylinder, one on each side of the piston.
When turning right, power steering fluid is pumped to the right hand section of the servo cylinder.
Piston and rack are forced to the left and power steering fluid is discharged from the left hand
section of the servo cylinder. The rubber gaiter on the left hand side is distended at the same time
as the one on the right side is compressed. Movement of the rack is transferred via the inner ball
joints (3.), track rod and outer track rod ends to the steering arms of the steering swivel member.
Both the inner ball joints and the outer track rod ends are lubricated for life and self-adjusting, with
no further lubrication or adjustment being necessary or possible.

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Oil pump, pressure and flow control valve

Oil Pump
The hydraulic power for the steering is provided by a rotary-vane pump. This pump is driven by the
car's engine via a belt and pulley. The pump element consists of a rotor with a number of slits, a
vane for each slit, a pump ring and two end plates with inlet and outlet ports for power steering fluid.
Due to the oval shape of the pump ring, the volume between vanes increases and decreases twice
during each revolution of the rotor. Inlet ports lead to the areas in which the volume increases and
outlet ports lead from those in which the volume decreases, thereby producing a pumping effect.
Apart from being forced outwards by centrifugal force, the vanes are also pressed outwards
against the pump ring by the pressure of the fluid. The fluid is directed into the slots inside the
vanes.
Pressure and Flow Control Valve
The purpose of the control valve is to regulate the flow from the pump so that it remains constant,
regardless of engine/pump rpm. The control valve sits on one side, directly connected to the pump
flow (A). At the outlet passage (B) of the pump, a restrictor is situated from which a connecting
passage (1) leads to the other side of the valve, which contains a spring (2). When un-actuated,
the valve presses against the outlet side. When pressure is high, an overflow valve (3) housed in
the control valve is actuated by the power steering fluid pressure on the spring loaded control valve.
For the control valve to operate, a certain amount of power steering fluid must circulate through it
continuously at (A) and (C), although not when the steering wheel is at full lock.

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Steering and parking at low engine speed: The pressure produced by the pump is slightly reduced
over the restrictor at the pump outlet. The reduced pressure is led to the spring loaded side of the
control valve, at which time there is a minor pressure difference between the two sides of the valve.
Due to the low pump speed, however, this pressure difference is not enough to actuate the valve.
Steering at high engine speed (pump in flow control mode): The flow of power steering fluid inside
the pump increases with increasing engine rpm and owing to the restrictor in the pump outlet the
flow velocity also increases. This reduces the pressure in the connecting passage, with the result
that the pressure on the spring loaded side of the control valve will be lower than that acting on the
outlet side of the valve. The valve therefore overcomes the force of the spring, opening a port to
the suction side of the pump and allowing a certain amount of internal recirculation of the fluid to
take place so that the flow from the pump is maintained at constant rate, regardless of engine
/pump rpm.
Steering wheel turned to full lock: Pump speed in this case is often low. When the steering wheel is
turned to full lock, the control valve of the steering gear closes. The flow of fluid from the pump will
then be zero. The resulting high pressure is directed via the connection passage to the spring
loaded side of the control valve. The pressure opens the overflow valve and allows the fluid to pass
to the inlet side of the pump. The pressure difference across the control valve forces it to move
against the spring and thus open the port for recirculation of the full delivery flow from the pump.
The predetermined maximum pressure is maintained as long as the control valve remains closed.

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Steering system 1

Hydraulic control valve

Hydraulic Control Valve

The hydraulic control valve consists of a valve spool (1.), a sleeve (2.) , a torsion bar (3.) and a
pinion (4.). The steering column's intermediate shaft is connected to the valve by means of a
universal joint. The torsion bar is connected to the upper end of the valve by means of a pin (5.).
The other end of the torsion bar is press fit in the pinion. The sleeve is connected to the pinion by a
pin (6.) and follows the rotation of the pinion exactly. There is also a fail safe connection between
the valve spool and the pinion required to maintain steer ability in case the torsion bar is broken.
The sleeve has three radial grooves (7.), the power steering fluid being pumped to the middle one.
When the steering wheel is in straight ahead position, the control valve is open and the fluid flows
up through the valve and back to the power steering reservoir via the chamber above the sleeve.
The upper end of the pinion is mounted in a needle bearing while the lower end is mounted in a
ball bearing. A spring loaded plunger presses the rack against the pinion. When the steering wheel
is turned, the movement is transferred via the torsion bar to the pinion. Since the torsion bar is
somewhat elastic, there will be a difference between the degree of rotation of the valve spool
(which follows the rotation of the intermediate shaft) and the sleeve which is fixed to the pinion. As
a result, the fluid can no longer flow through the control valve and back to the power steering fluid
reservoir directly. Instead, delivery and return passages open for the servo cylinder.

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Operating principle

In straight ahead position, pressurized oil is delivered through port „a“ and to the right (port b) and
left (port „c”) servo cylinder. The pressure in both, the left and right servo cylinders are equal, and
the oil is drained through the open port „d“back to the reservoir. When turning left, power steering
fluid is pumped to the left hand side of the servo cylinder via the upper radial groove (port „b“) of
the sleeve. At the same time, the left hand side of the servo cylinder is emptied via the lower radial
groove (port „c”) of the sleeve. Power steering fluid is led up through the valve to the chamber
above the spool and on back to the power steering fluid reservoir. When turning right, the process
is reversed. As long as the torsion bar is twisted, power steering fluid presses on the rack so that
servo effect is obtained. The difference between the valve spool and the sleeve reduces when the
power steering fluid actuates the rack in the same direction as the pinion. When there is no longer
a difference, the valve opens the passage returning power steering fluid to the reservoir. Some
power steering fluid continually circulates in the valve except when the steering wheel is turned to
an end position. This makes it possible for the control valve in the power steering pump to work
while circulation cools the power steering fluid.

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Steering system 1

Service and maintenance

Checking steering wheel free play:

Start the engine with the steering wheel in the straight forward direction. Measure the play while
turning the steering wheel to the left and right. The specifications are given in the workshop
manual. If the play exceeds the standard value, the connection between the steering shaft and tie
rod ends should be checked.
Checking steering wheel return:
The force required for turning the steering wheel and the wheel return should be the same for both,
moderate and sharp turns. When the steering wheel is turned 90° and held or a couple of seconds
while the vehicle is being driven at 20-30 km/h (12-19mph), the steering wheel should return at
least 20° from its central position when it is released. If the steering wheel is turned very quickly,
steering may be momentarily difficult. This is not a malfunction because the oil pump output will be
somewhat decreased.

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Checking Power Steering fluid level:

Position the vehicle on a level surface and start the engine. With the vehicle kept stationary, turn
the steering wheel several times continuously to raise the fluid temperature to 50-60°C (122-140°
F). With the engine at idle, turn the steering wheel fully clockwise and counter-clockwise several
times. Make sure that there is no foaming or cloudiness in the reservoir fluid. Stop the engine and
check for any difference in fluid level between a stationary and a running engine. If the fluid level
varies 5 mm (0.2 in) or more, bleed the system. If the fluid level suddenly rises after stopping the
engine, further bleeding is required. Incomplete bleeding will produce a chattering sound in the
pump and noise in the flow control valve, and lead to decreased durability of the pump.
Replacing Power Steering fluid:
Jack up the front wheels and support them with jack stands. Disconnect the return hose from the
oil reservoir and plug the oil reservoir. Connect a vinyl hose to the disconnected return hose, and
drain the oil into a container. Remove the fuel pump fuse, then start the engine and wait for the
engine to stall. Next, while operating the starting motor intermittently, turn the steering wheel all the
way to the left and then to the right several times to drain the fluid. Connect the return hoses, then
fill the oil reservoir with the specified fluid.

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Air bleeding:
Remove the fuel pump fuse, then start the engine and wait for the engine to stall. Next, while
operating the starting motor intermittently (for 15 ~ 20 seconds), turn the steering wheel all the way
to the left and then to the right five or six times. During air bleeding, replenish the fluid supply so
that the level never falls below the lower position of the filter. If air bleeding is done while the
vehicle is idling, there is a risk that the air causes foaming of the fluid. Be sure to do the bleeding
only while cranking. Reinstall the fuel pump fuse, and start the engine (idling). Turn the steering
wheel to the left and the right until there are no air bubbles in the oil reservoir. Do not hold the
steering wheel turned all the way to either side for more than ten seconds. Confirm that the fluid is
not milky, and that the level is up to the position specified on the level gauge. Confirm that there is
little change in the surface of the fluid when the steering wheel is turned left and right. If the surface
of the fluid changes considerably, air bleeding should be done again. If the fluid level rises
suddenly when the engine is stopped, it indicates that there is still air in the system. If there is air in
the system, a jingling noise may be heard from the pump and the control valve may also produce
unusual noises. Air in the system will shorten the life of the pump and other parts.

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