01142_17_00878_STT_Electric_Power_Steering_Strategy.doc

01142_17_00878 STT EPS Strategy V1.1 - Page 1 10/05/2024- page 1/24
Functional Specification
Reference: 01142_17_00878 Belchamp, June, 15th 2017
STT Electric Power Steering Strategy
Written by
A. MARCUS DQI/DCTC/ICDV/AFDH/ACSD
R. DELPLACE DQI/DCTC/ICDV/CLDR/EMIN
G. FRAMBOT DQI/DCTC/ICDV/CLDR/EMIN
G. CLAUDE DQI/DSEE/MCDV/RT3E
J.C. HAMEL DQI/DSEE/MCDV/E2TC/SDTC
J.F. MAILLARD DQI/DSEE/MCDV/E2TC/SDTC
A. YAGOUBI DQI/DSEE/MCDV/E2TC/SDTC
B. HUARD (ALTEN) DQI/DCTC/ICDV/CLDR/EMIN
Verified by
D. MEHARZI DQI/DAPF/SFAD/MSD
B. BEAURAIN DQI/DSEE/MC2E/IEPS/COSE
D. VINET DQI/DSEE/MCDV/E2TC/EVTC
C. VALET DQI/DCTC/ICDV/CLDR/EPS

1 MODIFICATION REVISION HISTORY .......................................................................... 3
2 REFERENCED DOCUMENTS ..................................................................................... 4
3 DESCRIPTION / CONDITION ..................................................................................... 4
3.1 Context......................................................................................................... 4
3.2 Architecture et interfaces.............................................................................. 5
3.2.1 Functional breakdown structure.............................................................. 5
3.2.2 External Interfaces.................................................................................. 6
3.2.3 Internal Interfaces ................................................................................... 7
3.3 Mission Profile.............................................................................................. 9
3.4 Voltage Profil................................................................................................ 9
3.4.1 Voltage Profile for DMT Less .................................................................. 9
3.4.2 Voltage Profile for STTa.......................................................................... 9
4 STTD OPERATION ............................................................................................... 10
4.1 Power Steering life phase .......................................................................... 10
4.2 Analysis of the EPS consumption requirement .......................................... 10
4.3 Functional Requirements ........................................................................... 11
4.4 Manage the electric consumption............................................................... 11
4.4.1 Ramp down management..................................................................... 11
4.4.2 Ramp up management ......................................................................... 12
4.4.3 Ramp priority management................................................................... 13
4.4.4 Interpret the power cut request for deactivation.................................... 15
4.4.5 Interpret the power cut request for activation........................................ 16
4.5 Compute the stop authorization and the restarting requests for EPS......... 16
4.5.1 Priority................................................................................................... 16
4.5.2 EPS STTd Defect.................................................................................. 17
4.5.3 Compute Engine stop authorization...................................................... 18
4.5.4 Compute Engine restart request ........................................................... 19
4.5.5 Engine’s flows request illustration......................................................... 20
5 STTA OPERATION................................................................................................ 21
6 FAILURE MODES................................................................................................... 21
6.1 Power cut request inconsistency................................................................ 21
6.2 Power cut request validity .......................................................................... 22
6.3 +APC or RCD information .......................................................................... 23
6.4 CAN bus..................................................................................................... 24

1 MODIFICATION REVISION HISTORY
Version DATE COMMENTS
V1 2017.06.15
Document creation from document 01452_09_00092 « STTd
EPS Steering Monitoring Strategy »
V1.1
2017.06.27
4.1 Power Steering life phase syntax adjustment
STTd_EPS_5.1 (1) syntax adjustment
STTd_EPS_19 (1) graph modification
STTd_EPS_21 Requirement created

2 REFERENCED DOCUMENTS
The following documents were used to define the functional requirement of the steering system:
N° Reference Title Link
1 01552_15_06355
Diversity
Management
EPS Generic
Application
http://docinfogroupe.inetpsa.com/ead/doc/ref.01552_15_0635
5/v.vc/fiche
2 01452_12_00155
Steering
Assistance «
Startup »,
« Hold » and «
Shut down »
EPS
http://docinfogroupe.inetpsa.com/ead/doc/ref.01452_12_0015
5/v.vc/fiche
3 01452_10_00245
STTd Steering
AMDE
http://docinfogroupe.inetpsa.com/ead/doc/ref.01452_10
_00245/v.vc/fiche
4 01551_10_00043
RCD Technical
Specification
http://docinfogroupe.inetpsa.com/ead/doc/ref.01551_10
_00043/v.vc/fiche
3 DESCRIPTION / CONDITION
3.1 Context
The STT €6.1 function is an evolution of the €5.
STT €5:
The STT step1 architecture associates an alternator and a centralized Voltage Holding Device.
This device is used to ensure the minimum voltage profile (10,5V when stopped, 9.5V during 50ms at
restart) for the chassis units by applying a “voltage boost”.
The electrical system voltage moderately constrains steering operation (limited assistance to ensure
the ACV/AEEV/CLDR/EPCT/ inter-service).
STT €6.1:
Two types of STT system exist.
A first architecture that associates an alternator and a Network Voltage Holding Device, whose
operation is identical to that of the STT step1.
The second architecture associates a starter motor and a Network Voltage Holding Device. In this
definition, the voltage profile is only ensure if the LAS units consume virtually no current during
stop and restart phases.
The only possibility to answer at this requirement is to deactivate the steering assistance during the
stop and restart phase.
STT €6.2:
- DMTr replaced by DMTless
- STTd stop entrance vehicle speed up to 3kph
The various STT versions are summed up in the following table:
STT €5 STT €6.1 STT €6.2
2010 2013 2017 
STTa STTa STTd STTa STTd
DMTc DMTc DMTr DMTc DMTless
Alternator Alternator Starter Alternator Starter
This document only describes the operation of the STT 2017 

3.2 Architecture et interfaces
3.2.1 Functional breakdown structure
The use case / physical scenario approach and the detailed conception described in the STTd Design document lead to the following Functional
Breakdown Structure for the steering system:
 Manage the electric consumption
 To compute the stop authorization and the restarting requests for EPS
o Compute Engine stop authorization
o Compute Engine restart request

3.2.2 External Interfaces
I/O From Signal label Type Description Gender
Values list (if boolean or list)
Value (if parameter)
Unit
Minimum
Value
Maximum
value
Accuracy Resolution
max latency
(ms)
Input ESC STEERING_WHEEL_ANGLE info
Steering Wheel Angle
External EPS Flow : ESC ou CAV
Num NA ° -780 780 0.1 10
Input SAS STEERING_WHEEL_SPEED info
Rotational wheel speed
Internal or external EPS Flow
(CAV)
Num NA ° 0 1016 4 10
Output EPS ETAT_ASSIST_DA Info Power steering assistance state List
0 : No activated assistance
1 : Nominal mode activated
assistance
2 : Failure mode activated
assistance
3 : STTa mode activated
assistance
4 : STTd mode activated
assistance
5 : Prohibited value
6 : Prohibited value
7 : Invalid value
- 0 7 1 1 10
Input ESC VITESSE_VEHICULE_ROUES info Vehicle speed Num - Km/h 0 655.34 0.01 10
Input CMM ETAT_MT info Engine State List
0 : Locked
1 : Cut
2 : Starting
3 : Engine running
4 : Stopped
5 : Driven restart
6 : Degraded go
7 : Engine preparing
8 : Reserved
9 : Reserved
10 : Autonomous starting
11 : Reserved
12 : Reserved
13 : Autonomous restart
14 : Reserved
15 : Invalid
- 0 15 1 1 -
Input BSI ETAT_LIGNE_APC info Control wake-up signal Bool
0 : Ignition line is detected
as inactive
1 : Ignition line is detected
as active
- 0 1 1 1 10
Input BSI DMD_DELEST_DA info Power cut request sent by BSI Bool
0 : Not request
1 : Power cut request
- 0 1 1 1
Output EPS DDE_REDEM_DA info
Request of the EPS sub-system to
the engine.
Restart when in stop mode.
Bool
0 : No need of restart
1 : Restart request
- 0 1 1 1 10
Output EPS AUTOR_ARRET_MOT_DA info
Authorization of the EPS sub-
system to the engine to switch to
stop mode.
Bool
0 : No stop authorization
1 : Stop authorization
- 0 1 1 1

3.2.3 Internal Interfaces
Signal label Type Description Gender
Values list (if boolean or list)
Value (if parameter)
Unit
Minimum
Value
Maximum
Value
Precision Resolution
Max
Latency
(ms)
STEERING_WHEEL_TORQUE Info
Steering wheel
torque (Internal EPS
flow)
Num - Nm -10 10 10
Parameters :
System I/O From Parameter label Type Description Gender Values Unit Minimum Value Maximum value Resolution
Steering C Steering Vvh_entree_STT info Vehicle speed to enter in STT mode Num 7,5 km/h 0 655.34 0.01
Steering P Steering Vvh_sortie_STT info Vehicle speed to reactivate the power steering. Num 8,5 km/h 0 655.34 0.01
Steering C Steering Tconf_sortie_STT info Confirmation time to restart the engine Num 3 s 0 1000 0.1
Steering C Steering Tconf_entree_STT info Confirmation time to stop the engine Num 30 ms 0 1000 1
Steering C Steering Wvol_entree info Steering wheel speed to stop the engine Num 20 °/s 0 1016 1
Steering C Steering Cvol_entree_STT info Steering wheel torque to stop the engine Num 1.5 Nm 0 10 0.1
Steering C Steering An_entree_STT info Steering wheel angle to stop the engine Num 90 ° 0 780 1
Steering C/P Steering Ramp_down_STT (*) (**) info
Slope to apply to deactivate the Steering
assistance progressively starting with the
measured steering wheel torque.
Num 3 Nm/s 0 ∞ 10
Steering C/P Steering Ramp_up_STT (*) info Slope to apply to reactivate the power control. Num 20 Nm/s 0 ∞ 10
Steering C Steering Cvol_sortie_STT info Steering wheel torque to restart the engine Num 4.5 Nm 0 10 0.1
Steering C Steering An_sortie_STT info Steering wheel angle to restart the engine Num 100 ° 0 780 1
Steering C Steering Wvol_sortie_STT info Steering wheel speed to restart the engine Num 300 °/s 0 1016 1
Steering C Steering T_tot_ramp_up info Time to apply the ramp up Num 500 ms 0 2000 1
Steering C Steering T_tot_ramp_down info Time to apply the ramp down Num 600 ms 0 2000 1

Steering C Steering T_conf_ramp info Confirmation time to start the ramp Num 70 ms 0 2000 1
C: Calibration
P: Parameter that will be encoded in hardware
(*): Dependending on the supplier’s monitoring conditions
(**): The slope must be ended after 600ms after power cut request

3.3 Mission Profile
The confidence level that is required to validate the components is 75% over the reference period of
15 years or 240 000km
The number of stop/restart powertrain operations over the reference period of 15 years or 240 000km
is 532 000.
3.4 Voltage Profil
3.4.1 Voltage Profile for DMT Less
3.4.2 Voltage Profile for STTa
The voltage supply profile for the power steering is the same as that for the STTa (see following
graph).
U0 11,4V t0
Umin 7,6V t0+1,5ms
7,6V t0+20ms
8,4V t0+50ms
Urestart1 9V t0+80ms
9V t0+230ms
Urestart2 9,5V t0+250ms
9,5V t0+1100ms
U0 11,4V t0+1102ms

4 STTD OPERATION
4.1 Power Steering life phase
The following table summarized the assistance state according to the power cut request state
(DMD_DELEST_DA flow).
Power cut request state (DMD_DELEST_DA)
EPS State (Assistance Mode ON)
regarding the STTd mode
Power cut request, ie no consumption authorization
(DMD_DELEST_DA = 1)
STTd mode = deactivated assistance state
No request ie consumption authorization
(DMD_DELEST_DA = 0)
Nominal mode = activated assistance state
In STTd mode, the DMD_DELEST_DA flow authorizes consumption.
4.2 Analysis of the EPS consumption requirement
The EPS current consumption is lower than 500mA without driver ction or road-feedback: (rack force
and steering wheel speed values are zero, ie: straight line condition).
Applying a zero assist power steering or deactivating the assistance level shall reach (or equal) the
current consumption in straight line.
This EPS current consumption level is nearly the same than in INIT before the activation of the power
stage
The EPS is no longer authorized to consume more than 500mA, 600ms after power cut request
reception.

4.3 Functional Requirements
Requirement no. Requirement
STTd_EPS_5.1 (1)
From the end of ramp down to the beginning of the ramp up, the electrical
consumption of the EPS must be less than 500mA.
STTd_EPS_6.1 (1)
With all engine states/phases, diagnostics functionalities must be operational (in
particular, the information regarding torque, angle and speed).
4.4 Manage the electric consumption
4.4.1 Ramp down management
4.4.1.1 THE FUNCTION USES THE FOLLOWING PARAMETERS:
 T_tot_ramp_down
 T_conf_ramp
STTd_EPS_1.3 (2)
Steering assistance shall be deactivated with a linear ramp and equal to 0 after
T_tot_ramp_down (Default value = 600ms). The T_tot_ramp_down period is
maximum time allowed.
STTd_EPS_4.2
The deactivated assistance state return time shall be less than T_conf_ramp
(Default value = 70ms  2 frames + ECU management time), when vehicle
conditions are fulfilled.
STTd_EPS_19 (1)
The ramp down shall start from the initial torque when T_conf_ramp is over.

4.4.2 Ramp up management
 T_tot_ramp_up
 T_conf_ramp
STTd_EPS_3.3 (1)
Assistance is reactivated with a transition in order to avoid the « steering wheel shot
racket » sensation.
The knowledge of the motor torque in STT mode allows to linearize in the best
possible way.
STTd_EPS_4.1 (4)
The activated assistance state return time shall be less than T_conf_ramp (Default
value = 70ms  2 frames + ECU management time), when vehicle conditions are
fulfilled.
STTd_EPS_17 (2)
The assistance shall be fully effective at the end of T_tot_ramp_up
The maximum duration to provide the full requested assistance when vehicle
conditions are fulfilled shall be T_tot_ramp_up (Default value = 500 ms).

4.4.3 Ramp priority management
 T_tot_ramp_down
 T_tot_ramp_up
 T_conf_ramp
STTd_EPS_20 (1)
The assistance shall start the ramp up even if the ramp down is not finished when
DMD_DELEST_DA (power cut request) flow‘s turns ON

STTd_EPS_21
The assistance shall start the ramp down even if the ramp up is not finished when
DMD_DELEST_DA (power cut request) flow‘s turns ON

4.4.4 Interpret the power cut request for deactivation
THE INPUTS FOR THE FUNCTION ARE:
 DMD_DELEST_DA
 VITESSE_VEHICULE_ROUES
4.4.4.1 THE FUNCTION PRODUCES THE OUTPUTS:
 State Assistance
 Vvh_entree_STT
STTd_EPS_1.2 (2)
If vehicle speed is lower than a given threshold and power supply network authorizes
it, then the assistance is deactivated. The power cut request flow is not reliable, the
vehicle speed flows is combined to achieve a reliable request.
IF
[DMD_DELEST_DA = 1 AND VALID] ) FOR 2 consecutive frames
(Power cut request)
AND [VITESSE_VEHICULE_ROUES < Vvh_entree_STT AND VALID]
THEN
State Assistance = DEACTIVATED

4.4.5 Interpret the power cut request for activation
4.4.5.1 THE INPUTS FOR THE FUNCTION ARE:
 DMD_DELEST_DA
 Vvh_sortie_STT
STTd_EPS_3.2 (3)
The assistance is only reactivated if reactivation condition is true or vehicle speed is
too high.
IF
[DMD_DELEST_DA = 0 AND VALID] FOR 2 consecutive frames
OR [VITESSE_VEHICULE_ROUES > Vvh_sortie_STT AND VALID]
THEN
State Assistance = ACTIVATED
4.5 Compute the stop authorization and the restarting requests
for EPS
4.5.1 Priority
STTd_EPS_16
Engine restart request and engine stop authorization shall not be TRUE in the same
time.

4.5.2 EPS STTd Defect
 AUTOR_ARRET_MOT_DA
 DDE_REDEM_DA
STTd_EPS_7.1 (2)
An internal failure of the EPS shall require inhibition of STTd function.
IF
Electric Power Steering is in failure
THEN
AUTOR_ARRET_MOT_DA = 0
DDE_REDEM_DA = 1

4.5.3 Compute Engine stop authorization
 STEERING_WHEEL_SPEED
 STEERING_WHEEL_TORQUE
 STEERING_WHEEL_ANGLE
 Wvol_entree_STT
 Cvol_entree_STT
 An_entree_STT
 Tconf_entree_STT
STTd_EPS_1.1 (3)
When steering is not used in torque or in speed for a certain time, then the powertrain
is authorized to stop. Regarding the accuracy management of the steering wheel
angle, the supplier shall justify the technical answer.
IF
(+APC = ON OR RCD = Main Wake Up)
AND [STEERING_WHEEL_SPEED< Wvol_entree
AND STEERING_WHEEL_SPEED is VALID]
AND [STEERING_WHEEL_TORQUE < Cvol_entree_STT
AND STEERING_WHEEL_TORQUE is VALID]
AND [{STEERING_WHEEL_ANGLE is Accurate*
AND STEERING_WHEEL_ANGLE < An_entree_STT
AND STEERING_WHEEL_ANGLE is VALID}
OR STEERING_WHEEL_ANGLE is Inaccurate]
DURING Tconf_entree_STT
THEN
ELSE

4.5.4 Compute Engine restart request
 STEERING_WHEEL_SPEED
 STEERING_WHEEL_TORQUE
 STEERING_WHEEL_ANGLE
 DDE_REDEM_DA
 Wvol_sortie_STT
 Cvol_sortie_STT
 An_sortie_STT
 Vvh_sortie_STT
STTd_EPS_3.1 (2)
On the driver’s request (action on the steering wheel), the steering shall require a
restart of the GMP. If the torque threshold or the steering wheel speed is not detected
due to value outside of the sensor range, a restart on driver request is inhibited.
Regarding the accuracy management of the steering wheel angle, the supplier shall
justify the technical answer.
IF
[{ STEERING_WHEEL_TORQUE > Cvol_sortie_STT
AND STEERING_WHEEL_TORQUE is VALID}
OR { STEERING_WHEEL_SPEED > Wvol_sortie_STT
AND STEERING_WHEEL_SPEED is VALID}
OR { STEERING_WHEEL_ANGLE is accurate*
AND STEERING_WHEEL_ANGLE > An_sortie_STT
AND STEERING_WHEEL_ANGLE is VALID}
OR {VITESSE_VEHICULE_ROUES > Vvh_sortie_STT
AND VITESSE_VEHICULE_ROUES is VALID}]
OR {VITESSE_VEHICULE_ROUES is INVALID}
OR { STEERING_WHEEL_SPEED is INVALID }
OR { STEERING_WHEEL_ANGLE is INVALID }
OR { STEERING_WHEEL_TORQUE is INVALID}
THEN
DDE_REDEM_DA = 1
ELSE
DDE_REDEM_DA = 0

4.5.5 Engine’s flows request illustration

5 STTA OPERATION
To be completed
6 FAILURE MODES
The failure modes that are described in this chapter mean the missing, the loss or the invalidity of
the input information
6.1 Power cut request inconsistency
 DMD_DELEST_DA
 DDE_REDEM_DA
6.1.1.3 THE FUNCTION USES THE FOLLOWING PARAMETERS
 Tconf_sortie_STT
STTd_EPS_10.0
(4)
If DMD_DELEST_DA is inconsistent, then the steering assistance will no longer
authorize the engine to be stopped. The steering checks that DMD_DELEST_DA flow
is consistent regarding vehicle speed.
IF
{(DMD_DELEST_DA=1 AND VITESSE_VEHICULE_ROUES >
Vvh_entree_STT) DURING Tconf_sortie_STT }
THEN
default present
DDE_REDEM_DA = 1
IF the assistance = ACTIVATED,
THEN the assistance = ACTIVATED
IF the assistance = DEACTIVATED,
THEN the assistance = ACTIVATED })
UNTIL fault recovery } #The default is recovered with a KEY OFF / KEY ON

6.2 Power cut request validity
 DMD_DELEST_DA
 DDE_REDEM_DA
STTd_EPS_11.0
(3)
If the DMD_DELEST_DA information is confirmed as lost, missing or invalid (in the
communication sense, example: frozen frame), steering assistance will be reactivated
on an engine state condition.
IF DMD_DELEST_DA is confirmed as absent
THEN { Power Steering Power cut request fault is present
DDE_REDEM_DA = 1
AND State Assistance is based on engine state and vehicle speed conditions
following the Startup & shut down requirements specification [2].
UNTIL Power Steering Power cut request fault recovery }
The default is recovered if the Power Cut request DMD_DELEST_DA is
confirmed as valid and available

6.3 +APC or RCD information
 APC or RCD information.
 DDE_REDEM_DA
STTd_EPS_14.0
(1)
The +APC line status loss can lead to a vehicle situation that isn’t clear for the
customer: assistance deactivated, engine running. Even though the indicator lamp
(the vehicle speed threshold is sufficiently low to eliminate the security risk), a P-code
is tracked. The analysis of the associated contexts will justify the situation that
experienced by the customer.
The loss of CAN connection with the steering assistance will light up a red indicator
lamp on the dashboard. Then, the driver is informed of a communication problem with
the steering system by the BSI. The fact that the steering assistance stays
DEACTIVATED is not a problem.
The steering system will have to adopt the usual operation in case of the loss or
missing of +APC or RCD information. This means deactivating of the assistance
below a vehicle speed threshold and a reactivating it above this threshold.
IF +APC or RCD information is confirmed as LOST, MISSING or INVALID
THEN {Regardless power cut request flow state,
DDE_REDEM_DA = 1
AND the steering assistance is activated or deactivated following the Startup
& shut down requirements specification [2] }
UNTIL +APC or RCD information is confirmed as VALID AND AVAILABLE

6.4 CAN bus
 DDE_REDEM_DA
STTd_EPS_15.0
(3)
The loss of CAN connection with the steering assistance will light up a red indicator
lamp on the dashboard. Then, the driver is informed of a communication problem
with the steering system by the BSI. The fact that the steering assistance stays
DEACTIVATED is not a problem. If the EPS has a BUS OFF failure or if mute is
confirmed then the assistance no longer receives any CAN information and the
steering assistance no longer stays in its previous state.
IF CAN Defect
THEN
DDE_REDEM_DA = 1
AND IF [DMD_DELEST_DA = 0 OR INVALID]
THEN the steering assistance switches to a vehicle speed backup
assistance.
ELSE the steering assistance stays DEACTIVATED}
ELSE the steering assistance is activated or deactivated following the Startup &
shut down requirements specification [2]
UNTIL CAN connection restored and usual EPS conditions

01142_17_00878_STT_Electric_Power_Steering_Strategy.doc

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