2427431 - 4110D steering electrical control system
The EPS (Electrical Power Steering)
produced by DELPHI is a power assisted steering system designed
to reduce the effort required on the steering wheel, especially
during steering manouevres at low speed, without, however, making
the steering too light during normal driving.1, EPS power steering
2, Mechanical steering box
3, Battery
4, Engine compartment junction unit (B01)
5, Junction unit under the dashboard (B02)
Electric power assisted steering
offers the following advantages compared with hydraulic power assisted
steering:
- The system has a smaller number of components and therefore
is lighter and less complex
- It takes less time to install and is simpler to service.
- The electric power assisted steering only absorbs energy
when power assisted steering is required, improving the performance
of the vehicle and reducing consumption and emissions.
- Greater driving comfort resulting from less operating
noise.
- There is a reduction in pollution because the electrical
energy used is clean.
- A variation in the power assistance according to the
vehicle speed
- The steering returns to the 'Active return' centre
- Damping steering return fluctuations
- Power assisted selection (Normal / City)
IMPLEMENTATION STRATEGIES
The following figure shows system
operating strategies
BASIC OPERATION
According to the driver's requirements
(force on the steering wheel) and the speed of the vehicle, the
(NGE) control unit operates the electric servomotor which assists
the rotation of the steering column. The motor applies a force to
the actual steering column, by means of a worm screw mechanism,
decreasing the effort required from the driver when steering.
The power assistance varies according to the vehicle
speed
As the speed of the vehicle increases,
the driver proportionally increases the force applied to the steering
wheel also because the force resistant to the wheels decreases as
the speed of the vehicle increases. Consequently, making use of the vehicle
speed signal, the NGE implements less power assistance.
Active return
The return stage refers to the
realignment function normally produced by the geometry of the front
section of the vehicle when the steering is released after a steering
manoeuvre.This function is designed to make this realignment
faster, causing the servo motor to intervene and assist the normal
geometry effect.The active return correction varies
according to the speed of the vehicle:
- Maximum at low speeds
- Minimum at high speeds
The servomotor carries out the active return
of the steering wheel acording to the steering angle in relation
to the centre. The greater the steering angle, the greater the effort
of the motor to realign the wheels
Damping steering return fluctuations
After the steering wheel is released,
following a steering manoeuvre, the vehicle chassis produces oscillations
which, if they persist for a certain length of time, can be tiresome.The servo motor reduces the amplitude of
oscillations (B) during the return to the straight line driving
position and intervenes more at high speed.
Selectable power steering
The user can select between two driving
styles by pressing a button located on the control panel:
- 'Normal' for normal power assistance at medium to high
speeds,
- 'City' for easier driving whilst parking and at low
speeds, thanks to increased power assistance.
The following figure shows unit
components.1, Microprocessor
2, CAN interface
3, Supply circuits
4, Engine timing operating circuit (EBMD)
5, Power electronics (FET)
6, Analogue signals interface
7, Position and torque sensor
8, Servo mechanism
9, Electric motor (with engine position sensor and engine relays
incorporated)
Geared motor
The geared motor unit consists
of an aluminium casting fastened to the vehicle chassis.Positioned at the side of the geared motor
casting, the servomotor supplies a torque with a ratio of 22:1,
by means of a worm screw, to the power assisted gear.The geared motor gear, coaxial and joined
to the steering column, is made of steel, whilst the outer ring
gear is made from pressed plastic. The worm screw and the gear have
been designed so that the angles ensure that the coupling is reversible.The metal part of the gear is fitted on
the output shaft, which transmits the steering forces (in other
words the torques from the servomotor and the driver).The input and output shafts are connected
to one another by a 'calibrated torsion bar' which allows an angular
movement from + 8° to - 8° (mechanical ends of travel prevent
a further increase in torsion).Where there is resistance at the wheels,
the input shaft weakens (NOT irreversibly) the torsion bar, therefore
the input shaft and the output shaft are offset at an angle proportional
to the force applied to the steering wheel.A torque sensor, fitted inside the geared
motor, detects the change in angle, between the input shaft and
the output shaft and supplies an electrical signal to the control
unit proportional to the shift.The geared motor casing also has the task
of retaining the outer part of the 'torque and position sensor'
and, lastly, the input shaft mounting cover is fastened to the casing,
where the flywheel is fitted, and houses both the ignition switch
and the steering column switch unit.On the version with an adjustable column,
the angle and the axial position can be adjusted on the vehicle. | The geared motor casing must not,
under any circumstances, be dismantled. Also, it will NOT be possible
to reassemble this complex system like in the factory |
Control unit
The control unit processes the
input signals received from the sensors and operates the electric
motor, supplying a suitable current for the power assisted force
required. It also handles the CAN network communication and carries
out a continuous autodiagnosis of the system, to ensure correct
operation. It manages communication with the diagnostic equipment
on the CAN.The vehicle and alternator speed values
are read from the CAN line.The position and torque signals coming from
the sensors represent the basic values with which the microprocessor
processes the output data in terms of current supplied to the engine.The control unit for the power assisted
steering is fixed to the actual steering box and has an interface
with the wiring by means of two separate connectors: one 10 pin
and one 2 pin.
CONTROL UNIT PIN-OUT
The diagram below illustrates
the control unit pin out.
CONTROL UNIT PIN-OUT
Connector A:| Pin | Function |
|---|
| A | Batteria + |
| B | Battery - |
Connector B:| Pin | Function |
|---|
| 1 | Ignition |
| 2 | CAN HI 2 |
| 3 | CAN LO 2 |
| 4 | k line |
| 5 | N.C. |
| 6 | N.C. |
| 7 | CAN HI |
| 8 | CAN LO |
| 9 | N.C. |
| 10 | N.C. |
Connector C:| Pin | Operation |
|---|
| 1 | P3 (only VDC) |
| 2 | P1 |
| 3 | Vref |
| 4 | T2 |
| 5 | N.C. |
| 6 | P2 |
| 7 | Earth |
| 8 | T1 |
Driving style selection input signal (normal / city)
(pin 4)
The Normal / City function has
the tsk of varying the assistance torque depending on the speed
of the vehicle. It is possible to switch from a standard (Normal)
configuration to City using the button in the control panel.The system only implements the request when
the button is released, lighting up the signal, after the driver
has applied a force of more than 1 Nm.During the key off / key on cycle, the control
unit maintains the state requested previously by the driver.The power assistance is always operating,
with the CITY function on, it is greater and it decreases as the
speed increases.
C.A.N. serial line
The control unit is capable of
receiving/transmitting information using the CAN network; this interface
is working from the key on to the key off.
Signals received / sent via the C.A.N. network
The following signals are received
via the C.A.N. network from the NGE control unit:
- Car speed
- failure light status
- engine running signal (D+)
- fault diagnosis
- vehicle speed signal error
The following signals are sent to
the C.A.N. network by the NGE control unit:
- system status (failure)
- power assisted steering activated signal (EPS Active)
- driving style selection light (Normal / City)
- fault diagnosis
- steering wheel absolute position
The following figure shows the
system operating layout1, City driving selection
2, Ignition key
3, Alternator voltage
4, Vehicle speed
5, Steering effort
6, Fault warning light and/or City status send
7, Fault warning light and/or City status return
8, Fault warning light and/or City light
9, Steering angular position signal (only with VDC)
10, city/normal signal from NBC
Operating performance
The following table illustrates
system operating performance schematically.| INPUT | OUTPUT |
|---|
| Vehicle speed reading (4) (through CAN network) | Regulates the power assisted steering according
to the speed of the vehicle and the recommended torques for the
steering wheel. |
| Reading (3) Alternator D+ (through CAN network) | By means of this reading, the control module
is able to know whether the engine has been started up |
| System error | Fault warning light on through the CAN network |
| Normal/City selection (included in the system) | According to the driver's request through
the button, the system activates the corresponding strategy (hard/soft)
and lights up the Normal/City warning light through the CAN network. |
| System electrical load (system reading) | The system send this information to the
engine control module through the CAN and the module implements
the appropriate strategy to adjust engine idle speed.The
NGE node control panel can identify time changes in the current
taken up by the node during operation.The control panel recognizes
when the positive and negative thresholds have been exceeded and retransmits
this information via the CAN. |
SPECIFCATIONS
The electric motor is the three
phase, auto-switching, synchronous type (without blades) with a
permanent magnet rotor.The power distribution and the control of
the phases is regulated by the NGE control unit.
COMPOSITION
The following figure shows the
electric motor components.
COMPOSITION
The motor rotor is constructed
using permanent magnetic materialThere is a disc secured to the motor rotor
(1) on which small magnets (2) are fitted, whilst on the fixed,
output shaft side, there are three Hall effect semi-conductors:
they have the task of notifying the control unit of the angular
position of the shaft throughout 360°. Rotor position (orientation)
is therefore measured by the position sensors built into the case
(Hall-effect sensors) to allow the control unit
COMPOSITION
To reduce noise and oscillations
at the steering column, the motor is fitted with three insulators
for the stator and one for the rotor.
Operation
Engine current uptake ranges
from 1A to 75A; the maximum absorption conditions occur when the
steering box is in the end of travel positionThe motor has been designed to provide torque
as required, in other words it has been designed to assist the driver
according to the effort made on the steering wheel,The wheels offer different resistance to
the steering column depending on whether they are resting on ice
or asphalt, for example. As a result, the motor provides the torque
according to requirements.
Operation
The control unit controls each
individual (threephase) winding using a current. As the induction
winding consists of permanent magnets, it tends to reach the centre
of the magnetic field.The control unit controls the position of
the rotor through the signals sent to it by the Hall effect semi-conductors,The exact position of the rotor is used
by the control unit for passing the (operating) current through
the coils concerned and maintaining the motor torqueThe operation of the individual coils is
carried out using the FET bridge illustrated with an operating frequency
of 18 KHz using the PWM (Pulse Width Modular) method for each individual
coil.
Operation
It is possible to see from the
diagram that, when the current is supplied to one winding, it is
requested in another, whilst no current passes through the third
winding. On switching, the current flows passing through the coils
changeThe synchronized, auto-switching motor always
operates at the torque required by the force exerted by the driver
on the steering wheel. As the torque requirement increases, the
current value passing through the windings increases proportionally;
this value is around zero when the motor does not require any torque.
The sensor
The sensor which measures torque
and position is fitted in a single casing secured to the geared
motor whilst the input and output shafts are free to rotate driving
the moving measuring parts.As stated above, the sensor performs two
functions: to measure torque and outlet shaft position. The torque
sensor function can be compared to a potentiometer, where the resistive
support is secured to the output shaft and the cursor is secured
to the input shaft. The torsion movement on the torsion bar between
the two shafts determines the torque value applied between the steering
wheelsThrough the signal from this potentiometer,
the control unit is capable of understanding the effort which the
driver is exerting on the steering wheel and the torque direction.
On the same principle (potentiometer), the sensor measures angular output
shaft position in relation to the centre (wheels straight). Through
a signal, the control unit is capable of understanding how many
degrees the steering wheel has moved in relation to the centre.On versions with ESP, the sensor also acts
as a steering angle sensor and thus computes the number of turns
completed by the steering wheel and the number of degrees per turn.
Information supplied by the torque/position sensor is sent via the
C-CAN from the NGE node to ensure optimum management of the electronic
stability control system managed by the NFR. | it is forbidden to carry out tests
using any sorts of instruments on the sensors: any fault diagnosis
MUST be carried out using the electric steering control unit. |
Lower shaft
The connection between the steering
column output shaft and the steering box pinion takes place through
a telescopic type intermediate shaft, which is attached to the pinion
by means of a splined fork with 26 teeth and a screw.
Electrical steering system protective fuses
There is a 70A power fuse, in
the engine compartment, behind the battery, protecting the system
with the control unit supply direct from the battery. The supply
controlled by the ignition (+15) is protected by a 10A fuse located
on the electro-mechanical control unit connected to the body computer
(NPL dashboard connector).
