Self-Study Programme 34 Fabia power assisted steering.pdf

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Electrically Powered Hydraulic
Steering EPHS
SP34_13
The new EPHS (
E
lectrically
P
owered
H
ydraulic
S
teering) system manufactured
by TRW Chassis Systems is used for the
first time within the Group in the
Š
KODA
FABIA.
The new steering system, while retaining
the excellent steering properties of the
conventional hydraulic power steering,
offers a wide range of advantages.
This system is used in the
Š
KODA FABIA
on models fitted with 14” and 15” running
gear.
It is available as a left-hand drive and right-
hand drive version.
Advantages of the electrically powered
hydraulic steering are:
Improvement in comfort,
easier operation when parking and
manoeuvring, while offering a taught
steering at high speeds (safety factor).
Fuel savings,
as the energy consumption is based on
demand - irrespective of the operating
state of the internal combustion engine.
In this self-study programme we wish to
familiarise you with the design and operation
of this steering system and provide you with
initial information regarding service.
2
GB
Contents
System Overview
Engine-Pump Unit
Power Steering Control Unit
Power Steering Sensor
Power Steering Gear
Service
Self-Diagnosis
Function Diagram
4
7
8
9
10
12
14
15
Service
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You will find notes on inspection and maintenance,
setting and repair instructions in the Workshop
Manual.
GB
3
System Overview
Power steering sensor G250
Steering gear
Reservoir
Gear pump
Power steering control unit J500
Pump motor
SP34_17
The system pressure which is required for the
steering force assistance, is produced by a
hydraulic pump.
In the conventional power steering system,
familiar, for example, from the FELICIA and
OCTAVIA, this pump is driven directly by the
vehicle engine.
In other words, part of the power output of the
engine is therefore required for driving the
pump.
Engine speed is at its lowest, however, at the
moment at which the greatest servo
assistance is required for the steering - in
other words when parking or manoeuvring.
Consequently, the pump capacity must be
designed for such cases.
When the engine is operating at higher revs,
the pump capacity which is not required, is
dumped over a bypass.
In the new steering system, the hydraulics
continue assisting the human steering effort,
but the hydraulic pump - a gear pump - is
driven in this case by an electric motor, and is
therefore mechanically separate from the
vehicle engine.
The electrically powered hydraulic steering
system is similar to a conventional one.
The hydraulic control is also basically
identical.
A new feature is that the steering servo
assistance depends on the steering angle.
That is why a steering angle sensor is
provided additionally above the steering
housing, to detect the steering angle rate and
transmit this information to the electronic
control.
The steering angle information flows along a
sensor cable directly to the control unit.
In addition, the vehicle speed is detected in
the control unit for analysis.
This information flows over the CAN bus.
The overview on the page opposite shows the
system design.
4
GB
System overview, schematic
diagram
Note:
The system overview is not the
electrical connection diagram.
Refer to the function diagram for this
information.
Vehicle speed
sender
Engine control unit
Control unit in dash
panel insert J285
Servotronic
warning lamp K92
Power steering
sensor G250
Signal of steering
angle rate
Vehicle speed signal
Non-return valve
Hydraulic fluid
reservoir
Pressure limiting valve
Gear pump
Power steering
control unit J500
Power steering terminal
+30
Power steering terminal
+15
Earth
–
M
CAN
CAN
Engine speed signal
CAN
Pump motor
SP34_05
Technical data
System pressure max. 10
±
0.4 MPa (100
±
4 bar)
Volume flow at max. pressure and corresponding
steering angle rate 3 l/min
Power demand max. 70 A
Power demand in standby mode 2.5 A
Volume flow at 0˚ steering angle 2 l/min max.
i.e. at v > 0 km/h, Q < 2 l/min.
Operational readiness –40 to 100˚C
GB
5
System Overview
Advantages of the electrically
powered hydraulic steering
Average power consumption in [watts]
600
500
400
300
200
100
0
Standard power
steering
EPHS
SP34_16
Driving on motorway
Driving on main road
Driving in town
In comparison to the traditional conventional
power steering system, as used in the FELICIA
and OCTAVIA, the newly developed
electrically powered hydraulic steering offers
a wide range of benefits:
–
Energy savings of as much as 85 %
When driving only on motorways, a
conventional power steering system produces
a high power loss at the bypass valve because
of the high engine revs, in other words the
power steering pump supplies an excess
volume flow at low steering angle rates and
high engine speeds.
The new electrically powered hydraulic
steering system offers the greatest savings as
a result of the low steering angle rate when
driving on fast roads and from the fact that the
volume flow is matched to the vehicle speed.
Even driving in towns, it is still possible to
achieve significant savings (refer to chart).
– Enhanced environmental compatibility as a
result of reduced energy demand and
energy input, as well as a smaller volume
of oil in hydraulic system.
–
Realistic driving cycles produce fuel
savings of about 0.2 ltr./100 km in
comparison with a conventional system.
Improvement in active safety as the
steering is easier to operate when parking,
while taught at high speeds.
–
6
GB

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