2004 DAEWOO LACETTI Service Repair Manual

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Page 1945 of 2643

DAEWOO LACETTI 2004 Service Repair Manual 6C – 28IPOWER STEERING GEAR
DAEWOO V–121 BL4
2. Install the lower valve assembly bearing and the
bushing.
3. Center the rack in the housing.
4. Install the the valve assembly, the stub shaft be

Page 1946 of 2643

DAEWOO LACETTI 2004 Service Repair Manual POWER STEERING GEAR 6C – 29
DAEWOO V–121 BL4
RACK BEARING
Tools Required
J–42459 Rack Guide Spring Cap Wrench
Disassembly Procedure
1. Remove the rack and pinion steering assembly
from the veh

Page 1947 of 2643

DAEWOO LACETTI 2004 Service Repair Manual 6C – 30IPOWER STEERING GEAR
DAEWOO V–121 BL4
RACK BEARING PRELOAD
ADJUSTMENT
Adjustment Procedure
1. Raise and suitably support the vehicle.
2. Center the steering wheel.
3. Remove the power st

Page 1948 of 2643

DAEWOO LACETTI 2004 Service Repair Manual POWER STEERING GEAR 6C – 31
DAEWOO V–121 BL4
4. With the gear centered, mark the location of the
stub shaft notch on the housing to aid in properly
installing the pinion and valve assembly.
5.

Page 1949 of 2643

DAEWOO LACETTI 2004 Service Repair Manual 6C – 32IPOWER STEERING GEAR
DAEWOO V–121 BL4
Assembly Procedure
Notice : Coat all of the seals and bushings with power
steering fluid to ensure proper sealing.
1. Install the bushing and a new lo

Page 1950 of 2643

DAEWOO LACETTI 2004 Service Repair Manual POWER STEERING GEAR 6C – 33
DAEWOO V–121 BL4
GENERAL DESCRIPTION
AND SYSTEM OPERATION
POWER RACK AND PINION
The power rack and pinion steering system has a rotary
control valve that directs hydra

POWER STEERING GEAR 6C – 33
DAEWOO V–121 BL4
GENERAL DESCRIPTION
AND SYSTEM OPERATION
POWER RACK AND PINION
The power rack and pinion steering system has a rotary
control valve that directs hydraulic fluid coming from the
hydraulic pump to one side or the other side of the rack pis-
ton. The integral rack piston is attached to the rack. The
rack piston converts hydraulic pressure to a linear force
that moves the rack left or right. That force is then trans-
mitted through the tie rods to the steering knuckles, which
turn the wheels.
If power rack and pinion steering is not available, manual
rack and pinion control is used; however, with this system,
more steering effort is required. The movement of the
steering wheel is transferred to the pinion. The rotary
movement of the pinion is then transferred through the pin-
ion threads, which mesh with teeth on the rack, thereby
causing the rack to move in a linear direction.
A vane–type of hydraulic pump provides hydraulic pres-
sure for both steering systems.
SPEED SENSITIVE POWER
STEERING SYSTEM
The speed sensitive power steering (SSPS) system varies
the driver effort required to steer as the vehicle speed
changes. At low speeds, the system provides maximum
power assist for easy turning and parking maneuvers. At
higher speeds, the steering power is reduced to provide
the driver with firmer steering and directional stability. The
SSPS system accomplishes this by reducing the amount
of power steering fluid flow from the power steering pump
to the power steering gear as the vehicle speed increases.
When the vehicle is stationary, the SSPS system provides
maximum fluid flow to the steering gear. As the vehicle
speed increases, the fluid flow to the steering gear is de-
creased.
Control Module
The SSPS control module processes the vehicle speed in-
formation from the engine control module (ECM) and uses
the steering wheel rotation sensor to provide a control sig-
nal to the electronic variable orifice (EVO) actuator located
on the power steering pump.
Electronic Variable Orifice (EVO) Actuator
The electronic variable orifice (EVO) actuator is located on
the power steering pump and contains a solenoid– oper-
ated pintle valve. Fluid leaving the pump passes through
an orifice in the actuator tip. When the EVO actuator is
powered by the SSPS control module, the pintle moves
into the orifice and reduces the power steering fluid flow.As the vehicle speed increases, current from the SSPS
control module increases, and the pintle blocks more and
more of the orifice.
Steering Wheel Rotation Sensor
The steering wheel rotation sensor is located at the end of
the steering column housing and is used to send a signal
to the controller when abrupt or evasive steering maneu-
vers are needed.
Power Steering Pressure Hose
SSPS vehicles have a specific pressure hose assembly
which includes an in–line check valve in the rack and pin-
ion assembly. This reduces the amount of steering wheel
”kick” when driving over irregular road surfaces while oper-
ating at speeds with reduced flow rate and pressure.
Power Rack and Pinion
Except for differences in valve machining, the design of
the SSPS power rack and pinion assembly is the same as
for the a non–SSPS system. The steering wheel move-
ment is transferred to the pinion via the intermediate shaft.
The pinion moves the rack left or right through meshing the
pinion and the rack teeth. The force is then transmitted
through the tie rods and steering knuckle to steer the
wheels.
The power rack and pinion steering system has a rotary
control valve which directs the hydraulic fluid from the
power steering pump to one side or the other side of the
rack piston. The piston is attached to the rack and uses hy-
draulic pressure to move the rack left or right. The rotary
control valve regulates the degree of assist by responding
to the driver’s torque input.
If hydraulic assist is not available, manual control is main-
tained. However, under this condition, more steering effort
is required.
Power Steering Pump
The standard vane–type pump, which provides hydraulic
pressure for the system, incorporates a special discharge
fitting to hold the EVO actuator.
System Operation
System operation originates with input from the vehicle
speed sensor via the engine control module to the SSPS
control module. The SSPS control module sends a signal
to the SSPS actuator to vary the rate of fluid flow output
by the power steering pump.
Circuit Operation
The SSPS system uses inputs from the speed sensor and
steering wheel rotation sensor to the SSPS controller to
determine the desired amount of power steering assist.
The SSPS control module constantly compares the
amount of current flowing through the EVO actuator to the
desired current it has calculated. The EVO actuator has a
pintle that moves in and out of an orifice, regulating power

Page 1951 of 2643

DAEWOO LACETTI 2004 Service Repair Manual 6C – 34IPOWER STEERING GEAR
DAEWOO V–121 BL4
steering fluid flow. The SSPS control module can change
the amount of current flowing through the EVO actuator by
varying the output duty cycle. If the

6C – 34IPOWER STEERING GEAR
DAEWOO V–121 BL4
steering fluid flow. The SSPS control module can change
the amount of current flowing through the EVO actuator by
varying the output duty cycle. If the EVO actuator is dis-
connected, the pintle will be pulled out of the orifice for
maximum power steering assist.
The SSPS control module has the ability to detect faults
in the steering wheel rotation sensor, the EVO actuator, or
the circuitry to those components. Any default detected
will cause the power steering assist to remain at maximum
with the pintle in its normally retracted position for all
speeds.
When the system is operating normally, increasing the ve-
hicle speed will decrease power steering assist, allowing
the driver to have improved road feel and directional stabil-
ity. When sudden steering wheel turns are made, as in
evasive maneuvers, they are detected by the SSPS con-trol module through the steering wheel rotation sensor.
When detected, the SSPS control module reduces current
to the EVO actuator, allowing greater power steering as-
sist.
SSPS (Speed Sensitive Power Steering) is to control pow-
er steering effort properly according to varying conditions
for both convenience and safety.
At low speed or standstill, power steering effort becomes
light to provide easy steering. On the contrary, at high
speed, power steering effort becomes heavy to provide
stable steering.
SSPS offered to LACETTI is EVO (Electric Variable Ori-
fice) type, which controls steering effort by modulating
pressurized fluid supply to the steering unit from the power
steering pump.
Steering wheel rotation sensor is installed at the bottom of
the steering column.
This sensor detects steering wheel rotation which is used
to calculate the angle speed of the steering wheel by
SSPS module.
If the angle speed was big enough for intervention into nor-mal steering force control during high vehicle speed, which
means a driver made an evasive steering maneuver to
avoid an accident, SSPS module would supply enough
steering support.
The sensor consists of a variable resistor.

Page 1952 of 2643

DAEWOO LACETTI 2004 Service Repair Manual POWER STEERING GEAR 6C – 35
DAEWOO V–121 BL4
1. Steering Wheel
2. SSPS control module
3. Steering Wheel Rotation Sensor
4. Steering Column
Checking procedure is as follows;
1. Remove SSPS conn

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