BMW 3: Voltage supply for other high-voltage consumers

The Electrical Machine Electronics supplies voltage not only to the electrical machine. The convenience charging electronics are directly connected with the Electrical Machine Electronics and ensure the voltage supply at high-voltage level to the electric A/C compressor and electrical heating.

However, there is no complex control function in the convenience charging electronics for this. Instead, the Electrical Machine Electronics serves as a simple distributor of the high-voltage direct current voltage which is provided by the high-voltage battery unit. In order to protect the high-voltage cable to the two high-voltage consumers against overloading in the event of a short circuit, the Electrical Machine Electronics contain a high-voltage fuse for the electric A/C compressor and a high-voltage fuse for the electrical heating. The high-voltage fuse has a nominal current level of 90 A.

This high-voltage fuse cannot be replaced separately. The EME must always be replaced.

Activating the electrical vacuum pump

The brake vacuum sensor is located on the housing of the brake booster and is mainly known from conventionally powered vehicles with an automatic engine start-stop function. The sensor is supplied with voltage from the Dynamic Stability Control (DSC) and returns a voltage signal depending on the vacuum in the brake booster.

The Electrical Machine Electronics (EME) receive signals for the brake vacuum, driving speed and brake pedal actuation from the Dynamic Stability Control (DSC).

The Electrical Machine Electronics control unit evaluates these signals and determines whether or not to switch on the electrical vacuum pump based on them. In addition, the function logic takes a hysteresis into account so that the electrical vacuum pump is not continuously switched on and off.

Instead, it remains switched on until a requested minimum level of the brake vacuum is reached.

The Electrical Machine Electronics contains an output stage (semiconductor relay), with which the voltage supply of the electrical vacuum pump can be switched on and off. Upon request the output voltage of the DC/DC converter can be shifted through directly to the electrical vacuum pump. Switch- on currents of up to 30 A can occur in the process. The current level is restricted electronically to protect the output stage and the line. There is no control of the power or speed for the electrical vacuum pump - it is simply switched on and off.

A malfunction of the electrical vacuum pump is identified using the brake vacuum sensor by means of the no longer available vacuum. The legally prescribed deceleration (increased brake pedal force) is available. The DSC will realize a type of hydraulic brake-booster assistance, i.e. depending on the driver pressure a hydraulically reinforced circuit pressure is generated.

• Advantage: Lower brake pedal force also in this fault scenario.
• Disadvantage: Altered pedal feedback.

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