AFMNA0AA – EPS-BLI HYG – User Manual
Page – 65/75
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The procedure of taking the traction to a safe state when the steering system
reports an alarm is FULLY UNDER THE RESPONSABILITY OF THE LIFT
TRUCK MNUFACTURER that has to ensure this procedure is 100% effective.
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Furthermore, special care is recommended in case the module designated to
lead the traction to a safe state (traction control module = TMC) IS NOT A ZAPI
UNIT (see 10.1 for properly coordinating the communication between E-
steering motor controller and TMC).
11.2 Vehicle master control (VMC) safety functions
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Together with the safety function to stop the traction (see topic 14.1) the VMC
in general has a second Safety Relevant function: it sends a PDO to the E-
steering motor controller to turn the steering control from rest to Operational.
Typical situation is:
1) A main contactor, driven by the VMC or by another unit in the truck,
supplies the Battery Power to the E-steering motor controller.
2)The E-steering motor controller is expected to stay at rest until the main
contactor will be closed (to avoid unwilling alarms).
3) VMC will communicate on a PDO (VMC -> E-steering motor controller) when
the main contactor has been closed and the E-steering motor controller turns
Operational.
This function is Safety Relevant because, the event with the VMC commands
the traction moving and forgets to command the steering to Operational leads
to an unsafe situation (traction moving and no steer). This is a single fault
leading to a loss of safety. So, for fulfilling with ISO13849, this Safety Function
of the VMC should be designed according the PLd and Category #3
requirements.
A possible countermeasure to avoid the VMC is called to perform the above
safety function could be: DO NOT CONNECT THE E-steering motor controller
UNDER THE MAIN CONTACTOR DRIVEN BY THE VMC.
This rule leads to the following two possibilities:
1) Connect the E-steering motor controller directly to the Battery rail (as a
consequence the E-steering motor controller is always Operational). (This
solution has cons (see 4.2.3) and so alternative 2) below is strongly preferred).
OR
2) Connect the E-steering motor controller under a line contactor that the E-
steering motor controller switches on immediately at key-on (see 4.2.2).
As a consequence, in both cases 1) and 2), E-steering motor controller will be
always Operational independently by the traction is REALLY moving or not.
