Fill level sensor system

Fill level sensor system and Magna control unit

The hydrogen tank in the BMW Hydrogen 7 vehicle serves contains the H2. It is equipped with overfill protection systems that respond when the maximum H2 fill level is reached.

These H2 overfill protection systems (so-called ”Magna control unit”) are only activated during the refuelling phase and during diagnosis.

Communication between the fill level sensor system and the Clean Energy control unit (CESG) takes place across a separate CAN connection, the so-called ”fill level CAN”.

Fill-level-dependent fuel strategy

The strategy for selection of the operating mode (hydrogen mode or petrol mode) of the Hydrogen 7 vehicle depends on the fill level:

• Fill level: ”empty” The vehicle is always started with the petrol emergency start with subsequent petrol mode.
  
• Fill level: ”gaseous” If there is an adequate petrol fill level, the vehicle is started in the hydrogen mode with subsequent petrol mode or initial hydrogen mode with automatic changeover to petrol mode after completion of the warm-up phase.
  
• Fill level: ”liquefied” If there is an adequate petrol fill level, the vehicle is started in the hydrogen mode with subsequent hydrogen mode or with a free choice of the operating mode after completion of the warm-up phase.
  

With a low petrol fill level, the engine start is always a petrol emergency start with subsequent petrol mode.

Component diagnosis

The check for diagnosis of the overfill protection systems takes place via a separate diagnosis interface between the CESG and Magna control unit. Here, both overfill protection systems must respond. If there is no response, there is a fault.

Within the framework of the test modules for these components, the following faults are covered:

• 64DF fill level control unit fill level sensor channel 1
  
• 64E0 fill level control unit fill level sensor channel 2
  
• 64E2 fill level control unit temperature sensor channel 1
  
• 64E3 fill level control unit temperature sensor channel 2
  
• 64A7 overfill protection system 1
  
• 64A8 overfill protection system 2
  
• 64CC fill level control unit CAN message pressure
  
• 64DD fill level control unit protocol incorrect
  
• 64DE fill level control unit mass calculation
  
• CE0B fill level CAN communication fault