Power steering sensor G250 Power steering control unit J500 Gear pump Pump motor Reservoir Steering gear SP34_17... Operational readiness –40 to 100˚C M +30 +15 – Servotronic warning lam
Trang 1Electrically Powered Hydraulic
Steering EPHS
SP34_13
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
The new EPHS (Electrically Powered
Hydraulic Steering) system manufactured
by TRW Chassis Systems is used for the
first time within the Group in the ŠKODA
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 ŠKODA FABIA
on models fitted with 14” and 15” running
gear
It is available as a left-hand drive and
right-hand drive version
Trang 2
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Contents
You will find notes on inspection and maintenance,
setting and repair instructions in the Workshop
Manual.
Trang 3System Overview
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
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
Power steering sensor G250
Power steering control unit J500
Gear pump
Pump motor
Reservoir Steering gear
SP34_17
Trang 4System overview, schematic
diagram
Technical data
System pressure max 10 ± 0.4 MPa (100 ± 4 bar) Power demand max 70 A
Volume flow at max pressure and corresponding
steering angle rate 3 l/min
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
M
+30 +15
–
Servotronic warning lamp K92
Engine control unit
Vehicle speed sender
Control unit in dash panel insert J285
Signal of steering angle rate
Power steering sensor G250
Non-return valve
Hydraulic fluid reservoir Pressure limiting valve
Gear pump
Power steering terminal
Power steering terminal
Earth
Vehicle speed signal Engine speed signal
SP34_05
Pump motor
Power steering
control unit J500
Note:
The system overview is not the
electrical connection diagram
Refer to the function diagram for this
information.
Trang 5200
0
300
400
500
600
System Overview
Advantages of the electrically
powered hydraulic steering
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)
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 %
– 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
SP34_16
Driving on motorway Driving on main road Driving in town
Standard power steering
EPHS
Trang 6Engine-Pump Unit
The motor-pump unit
The motor-pump unit is a self-contained
component
A special bracket for the motor-pump unit is
bolted to the longitudinal member, in the left
of the engine compartment, between bumper
and wheelhouse
The motor-pump unit is flexibly mounted in
rubber bushings on the bracket and
surrounded by a noise-absorbing
encapsulation
The motor-pump unit combines the following
components:
– the hydraulic unit with gear pump,
pressure limiting valve and electric motor,
– the reservoir for the hydraulic fluid,
– the power steering control unit
The motor-pump unit requires no
maintenance It is lubricated internally by the
hydraulic fluid
It cannot be dismantled and no provision is
made for repairs
A pressure line connects the pump to the
power steering gear
The return-flow line of the hydraulic fluid
merges into the reservoir
SP34_18
SP34_14
Screw cap
Reservoir
Return-flow connection
Gear pump
Pressure hose connection
Power steering control unit Electric motor Rubber bushing
Trang 7Power Steering Control Unit
The power steering control unit
J500
is part of the engine-pump unit
Incoming signals
– Engine speed (internal combustion engine)
– Vehicle speed
– Steering angle rate
Task
Converting the signals for powering the gear
pump in line with the steering angle rate and
vehicle speed
Extended functions
– Temperature protection for power steering
– Reactivate protection after faults
Self-diagnosis
The control unit detects faults during
operation and stores these in a permanent
memory
SP34_23
Pump function
assistance
speed = 0
Steering servo assistance
Vehicle
speed
Steering angle rate
Delivery Steering servo
assistance
(light steering)
(taught steering)
CAN
H1 H2 0 C
Trang 8Power Steering Sensor
Task
The power steering sensor G250 is located at
the top in the steering gear and surrounds the
input shaft of the steering gear It detects the
steering wheel angle and computes the
steering angle rate It is not an absolute angle
sensor (steering wheel angle proportional to
steering wheel lock)!
Analysis of signal
The signal is required in the power steering
control unit in order to detect steering
movements
The greater the steering angle rate, the greater
is the pump speed and thus the volume flow
(ignoring the vehicle speed)
Substitute function
If the sensor fails, the power steering moves
into a programmed emergency mode
The steering function is assured
The steering is slightly heavier to operate
Self-diagnosis
The sensor is integrated in the self-diagnosis
The power steering control unit stores
malfunctions of the sensor
In the function 02 - Interrogating fault memory -
it is possible to detect
– short circuit to earth
– open/short circuit to positive
– faults
Electrical circuit
G250 Power steering sensor
J500 Power steering control unit
SP34_19
SP34_10
31
S
J500
G250
30
M
15
CAN L CAN H
CAN L CAN H
31
30 15
CAN CAN 15 +
31
-SP34_08
Input shaft Power steering sensor
Trang 9Power Steering Gear
Initial position
Vehicle running straightahead Engine running
Pump motor running Gear pump delivering
Operating principle
The pressurized oil flows from the gear pump along the pressure line to the hydraulic control unit in the mechanical steering gear
Note:
From a hydraulic aspect, the function
positions of “right lock” and “left
lock” are similar to the familiar power
steering Read more on this in SSP 14.
In the same way as in the conventional power steering system, there is a torsion bar in the hydraulic control unit which is connected at the one side to the rotary slide, and on the other side to the drive pinion and to the control sleeve
c d
b
a
Feed from gear pump
Return flow
SP34_03
Power steering sensor
Non-return valve
Trang 10When driving straightahead, the torsion bar
holds the rotary slide and control sleeve in the
Neutral position The power steering sensor
does not detect any steering angle
The hydraulic fluid flows practically
pressureless through the hydraulic control
unit along the return-flow line and back to the
reservoir
SP34_07
a b
c
d
from pump
Return flow
to power cylinder on left
to power cylinder on right
Hydraulic control unit - schematic diagram
Torsion bar Rotary slide Control sleeve
SP34_04
Trang 11If the unit has overheated, wait, if necessary,
15 minutes to allow it to cool down
If it is not possible to cancel the reactivate protection by starting the engine after this waiting time, there is a fault in the vehicle electrical system, or the motor-pump unit is faulty
Service
The electrically powered hydraulic steering is
maintenance-free
No new special tools are required
No provision is made for repair work on the
power steering gear or on the motor-pump
unit The causes for problems can be detected
by carrying out the pressure and leak test, as
well as self-diagnosis If a problem exists, the
power steering gear or the motor-pump unit
should be replaced
The following parts of the steering gear may
be replaced:
Track rod end, track rod, boot, clamp, spring
strap clamp, seal (sealing power steering gear
to body), clamp, rubber insert and power
steering sensor G250
SP28_04
SP34_15
Left track rod end
Right track rod end The following parts may be replaced at the
motor-pump unit:
Bracket, rubber bush, noise encapsulation and
screw cap with dipstick
Reactivate protection
The motor-pump unit features a reactivate
protection after a fault, failure or a crash
The reactivate protection can be cancelled by
switching the ignition off and starting the
engine again
Note:
When replacing the track rod ends,
pay attention to the marking by
means of letters on the end.
If correctly installed, the track rod end
must be angled to the rear and the
stud of the track rod end facing up.
Carry out a check of chassis
alignment.
Trang 12Pressure line and return-flow line
When reconnecting the pressure line or
return-flow line, replace the existing seals and
clamps
SP34_21
SP34_22
Inspecting hydraulic fluid level
The hydraulic fluid level can be inspected with
the aid of the dipstick at the screw cap of the
reservoir
– When hydraulic fluid is cold:
in area of lower marking
– When hydraulic fluid is warm (from engine
temperature of about 50 ˚C):
approximately in the middle between
bottom and top markings
Note:
Each time the pressure line is
disconnected at the power steering
gear, the banjo bolt and non-return
valve should be replaced On no
account use the banjo bolt without a
non-return valve.
Fit only a genuine replacement part.
Avoid stresses and bends in the
hy-draulic lines.
Note:
Detailed information on the service
aspect can be found in the Workshop
Manual Running Gear and in the
Inspection and Maintenance binder.
bottom marking top marking
Hydraulic fluid reservoir
Screw cap with dipstick
SP34_20
Return-flow line
Power steering gear
Subframe Banjo bolt with
non-return valve Pressure line
Trang 13The system
Diagnosis communication flows over the
CAN The gateway converts the signals from
CAN to the K cable
Self-diagnosis relates to the electrical and
electronic parts of the power steering system
The control unit detects faults during
operation and stores these in a permanent
memory This information is also retained
even if there is no battery voltage
Sporadic faults are not stored in the
permanent memory
The warning lamp
After the ignition is switched on, the
Servotronic warning lamp -K92- comes on An
internal check cycle is completed during this
period
If the warning lamp does not go out after the
engine is started and after completion of the
check cycle, this indicates that faults may be
stored
Faults may be defects in the electrical system
The self-diagnosis
It is necessary to switch on the ignition first in
order to initiate self-diagnosis
Self-diagnosis can be performed with the
vehicle system tester V.A.G 1552, the fault
reader V.A.G 1551 or the vehicle diagnosis,
measuring and information system VAS 5051
It is initiated with the address word
44 - Power steering
Available functions
01 - Interrogating control unit version
02 - Interrogating fault memory
05 - Erasing fault memory
06 - Ending output
07 - Coding control unit
08 - Reading measured value block
SP34_06
Servotronic warning lamp K92
Self-Diagnosis
SP33_73
Trang 14S
J500
G250
J
30
M
15
CAN L
CAN H
CAN L
CAN H
31
J519 J533
30 15
J285
G22
15 +
K92
31
-Function Diagram
Legend
G22 Vehicle speed sender G250 Power steering sensor J… Engine control unit J285 Dash panel insert control unit J500 Power steering control unit J519 Vehicle electrical system control unit
K92 Servotronic warning lamp
The function diagram provides a simplified
representation of the linkages of the system
components of the “electrically powered
hydraulic steering” with other system
components of the vehicle
Communication takes place in this case over
the drive CAN
SP34_09
Note:
The function diagram is not a current
flow diagram.
Positive Negative Output signal Input signal CAN (output and input signals)