Functional description

Depending on the request from the master control unit (IHKA control unit), the control electronics in the (electrical) air conditioning compressor control the engine speed of the three-phase motor.

A three-phase motor (outer fan, synchronized) drives the air conditioning compressor. The magnetic field of the rotor is formed by several permanent magnets.

The three-phase motor is operated in a specific engine speed range (e.g. between 2000 and 8600 revolutions per minute). The engine speed can be steplessly adjusted.

A spiral compressor is used to compress the refrigerant (also called a scroll compressor). The spiral compressor works according to the positive displacement principle. The spiral compressor consists of 2 spirals that are nested inside one another. The outer spiral is fixed. The three-phase motor powers the inner spiral via a shaft. The inner spiral moves eccentrically. Due to the eccentric movement, both spirals touch each other many times. This forms numerous chambers that get smaller and smaller inside the coils. As a result, the gaseous refrigerant is drawn in through openings in the static outer spiral. After approx. 2 revolutions (e.g. after 720°), the drawn in refrigerant is compressed. As the process continues (e.g, after 960°), the refrigerant escapes to the capacitor through a central opening in the outer spiral.

If the temperature of the voltage transformer in the (electrical) air conditioning compressor rises above 110°C, the IHKA control unit switches off the electric A/C compressor. A variety of measures have already been tried (e.g. engine speed increase for self-cooling) in an effort to limit the temperature.

For the high-voltage interlock loop, a test lead passes through all connectors of the high-voltage components. A bridge is installed in some connectors. The test lead is arranged in a ring shape (similar to the MOST ring). The following control units in the ring evaluate the test signal (square wave signal with defined frequency) of the test lead:

• Electrical machine electronics (EME)
• Battery management electronics (SME)

If the test lead circuit is interrupted, the EME control unit or the SME control unit switches off the voltage supply for the high-voltage electrical system. Only once the test lead circuit is reclosed can the high-voltage electrical system be supplied with voltage again.

The battery management electronics (SME) generate the test signal. If the high-voltage electrical system is started up, the battery management electronics feed the test signal into the test lead.

The following graphic shows the (electrical) air conditioning compressor using the example of F04.

Courtesy of BMW OF NORTH AMERICA, INC.