AFMNA0AA – EPS-BLI HYG – User Manual
Page – 11/75
4.2 Coordination between SCM and other modules in the truck
This chapter gives a list of possible solutions for coordinating the modules in the truck.
Acronyms:
SCM:
Steering control module.
VCM:
Vehicle control master (also VMC).
TCM:
Traction control module.
PCM:
Pump control module.
MC:
Main contactor.
SC:
Steering contactor.
MuC
: Master microcontroller.
SuC
: Slave microcontroller.
4.2.1
Bringing TCM to a safe state
Coordination between SCM and other modules performs the safety-related function of
leading the traction to a safe state when the SCM is lost. This safety function is not in
charge of the steering system, instead it involves others modules in the truck.
Coordination between SCM and other modules performs the safety-related function of
leading the traction to a safe state when the SCM is lost. This safety function is not in
charge of the steering system, instead it involves others modules in the truck.
Whatever the connecting diagram to coordinate SCM and other modules in the truck is,
the following inquiry raises up.
An error in the SCM stops the steering, but the traction is commanded to a safe state
via CAN bus only. As a consequence, transmission of the SCM errors has a proper
redundancy (MuC and SuC in the SCM check that the error information has been
transmitted over CAN bus); however the correct reception and the action of leading the
TCM to a safe state are not demanded to the steering system.
Even if the event “error in the SCM together with TCM fails to lead the truck to a safe
state” could represent an accumulation of faults, it is better the OEM is informed about
this safety issue and involved for possibly taking countermeasures. Countermeasures
to upgrade this external process (from SCM error to TCM in a safe state) to a better
controlled handling could be:
a) Supplying the positive to the coil of the MC or of the EB via the high-side driver in
the E-steering motor controller (CNA#14). Another module shall supply the low-
side driver of the coil. This handling has the drawback that sudden engagement
of the EB leads to an uncomfortable violent braking of the traction while the truck
is travelling fast.
b) Using redundancy in both VCM and TCM (VCM and TCM should be designed
with a category #3 architecture) to ensure that the SCM error is received by the
destination and that the traction is taken to a safe state.
c) In case the TCM directly picks up the SCM error frame from CAN bus (without
using VCM as a gateway), only the TCM should be designed with a category #3
architecture to ensure the SCM error is received by the destination and the
traction is taken to a safe state.
