SAE J2601 Appendix M Optional Rationality Check Method 23

APPENDIX M - Optional Rationality Check Method

M.1 INTRODUCTION

There may be potential circumstances (roadside fueling, equipment malfunctions, service procedures, certain ambient temperature fill protocols, etc.) where the initial start-of-fill temperature of the CHSS might be above the boundaries expected in the protocols defined in SAE J2601. Station developers may wish to consider methods to detect such circumstances to ensure the safe interaction of protocols and equipment as hydrogen fueling infrastructure becomes more prevalent and interactions between fills become more common.

This appendix describes a non-normative method which may be implemented as a means to check whether there may be a problem with the temperature signal being communicated indicating that the starting conditions of the CHSS cannot be detected. This method may only be implemented during communications fueling, as it relies upon the data communicated by the vehicle. Given the use of communications in this methods, consideration must be given to how to proceed in a non-communication fill when data is not available to confirm start-of-fill temperature. For example, non-communication fills might consider the use of an alternative fill rate or alternative target pressure which might have the effect of reducing the heat introduced into the CHSS but also of extending the fill time under some circumstances or reducing the end-of-fill state of charge (SOC). See descripton below for discussion of actions that a dispenser manufacturer might take.

The optional rationality check method below was conceived as a way to assess prior to starting a fill whether the start-of-fill temperature is within the range expected by the fueling protocols defined in SAE J2601 prior to starting the fill. This method can only be used when valid communication (refer to SAE J2799) is established between the vehicle and the dispenser. The rationality check method examines potential TV and MT errors during the startup time portion of the protocol before gas is flowing into the CHSS.

M.2 DESCRIPTION OF OPTIONAL RATIONALITY CHECK METHOD

Since both HRS and vehicle measure/calculate the same variables, a consistency check, or rationality check can be made by using the following logic:

1. Has valid communication been established (e.g., physical layer check)?

2. Is there an active abort request being communicated by the vehicle?

3. Compare CHSS volume (communicated by the vehicle) to CHSS volume (calculated by the station). Are they in agreement within a ±15% range?

4. Compare CHSS pressure (communicated by the vehicle) to CHSS pressure (measured by the station). Are they in agreement within a range which takes into account the potential sensor/calculation errors of the sensing systems?

If all four tests result in a “yes” answer, then rationality of the communication data is established, and a logic flag indicating rationality may be set. If, for example, the test is being used to detect whether CHSS temperature represented by MT is within an expected range, and the MT reported is not in that range, the dispenser might decide either to assume that an unexpected set of conditions has arisen or not to trust the MT value.

Figure M1 illustrates an example of a possible logic implementation of a rationality check.