Functional description

Stepless power control is possible in the air conditioning compressor. Within the A/C compressor, the delivery volume and thus the pressure in the refrigerant circuit is generated by pistons. The piston stroke is controlled by a swash plate. The swash plate is adjusted with the help of this movement:

• Minimum displacement (below 3 %)

  The electrical control valve is open when de-energized. In this position, the compressor capacity drops to nearly 0 %, in order to reduce the fuel consumption. During a switched on Air conditioning, the minimal compressor capacity lies between 0 % and 3 %, which helps maintain the inner lubrication. A pressure build-up is also enabled, even if liquid refrigerant has accumulated in the air conditioning compressor (physically related).

• Maximum displacement (100 %)
• Control range (0 % to 100 %)

The electric control valve on the A/C compressor influences the balance of forces on the swash plate and thus the adjustment of the displacement.

F0x, F1x, F25 and F26: The junction box electronics (JBE) controls the control valve with a clocked voltage. The IHKA control unit prompts the activation.

F15, F16: The Body Domain Controller (BDC) controls the control valve with a pulsed voltage. The IHKA control unit prompts the activation.

F2x, F3x: The front electronic module (FEM) controls the control valve using a pulsed voltage. The IHKA control unit prompts the activation.

For the purpose of load reduction, only the cooling power that is directly needed is generated. The rules and criterion for switching it on/off are:

• Speed of the air conditioning compressor (engine speed)
• Load torque of the air conditioning compressor (CAN message from the IHKA control unit to the engine control unit)
• Limit of torque (CAN message from the engine control unit to the IHKA control unit) restriction of the load torque of the air conditioning compressor during kick-down position or at a higher coolant temperature.
• Limit of the refrigerant pressure
• Ambient temperature

The following graphic shows an example of an air conditioning compressor.

Courtesy of BMW OF NORTH AMERICA, INC.