Voltage Supply Integral Active Steering (SA 2VH)

Voltage Supply Integral Active Steering (SA 2VH)

Auxiliary battery, charging controller for auxiliary battery and cut-off relay
With several vehicle types (motorization with high weight), for the optional equipment Integral Active Steering (SA 2VH) ,due to higher front axle load, a more powerful electromechanical power steering is installed which requires a supply voltage of 24 volts. An auxiliary battery is installed for the voltage supply of this EPS; it can be switched using a cut-off relay in series with the main battery. A charger unit controls the cut-off relay and supply voltage of the EPS.
For the other vehicle types, the voltage supply for the EPS occurs in combination with SA 2VH from the positive battery connection point. To reduce the ripple in vehicle voltage caused by the alternator, an ignition capacitor is installed. Capacitor, fuses and power distribution box together form the capacitor box.

Brief component description
The following components for voltage supply are described:
- Auxiliary battery (EPS with 24 V)
- Charging controller for auxiliary battery (EPS with 24 V)
- Component with cut-off relay (EPS with 24 V)
- Electromechanical Power Steering (EPS)
- Capacitor box (EPS with 12 V)







Auxiliary battery (EPS with 24 V)







An auxiliary battery (AGM battery with a 12 Ah capacity) is installed for the voltage supply of the EPS (24 volts).
The auxiliary battery is located with the main battery in the spare wheel well.

Charging controller for auxiliary battery (EPS with 24 V)







The main component of the charging controller for the auxiliary battery is a DC/DC converter (150 W). The charger unit controls the cut-off relay and the EPS supply voltage.
The charging controller for the auxiliary battery monitors the shielding of the supply line for the EPS, the cut-off relay, and the other lines between the cut-off relay and the auxiliary battery.
For data transfer, the charging controller for the auxiliary battery is connected to the Digital Engine Electronics or Digital Diesel Electronics via a local interconnect network bus (LIN bus). The charging controller for the auxiliary battery is connected to terminal 30F via the rear power distribution box.

Component with cut-off relay (EPS with 24 V)
The cut-off relay protects the auxiliary battery and provides a fall-back to 12 volts for the voltage supply of the EPS. The cut-off relay is controlled by the charging controller for the auxiliary battery via a control line and has two switch positions:
- Switch position 12 V: The positive terminal of the auxiliary battery is open. The supply voltage for the EPS is 12 V.
- Switch position 24 V: The main battery and auxiliary battery are switched in series for the voltage supply of the EPS.

Electromechanical Power Steering (EPS)
The electromechanical power steering (EPS) differs from conventional hydraulic steering in that it has steering power assistance. The EPS supports the driver using an electrical servomotor instead of a hydraulic electric motor. The servomotor is only active when the vehicle is being steered. This means that the servomotor consumes no power during straight-ahead driving.
The use of the EPS is a CO2 measure.

Capacitor box (EPS with 12 V)
For the vehicle types, where no 24 V for the voltage supply of the EPS is required, the voltage supply comes from the positive battery connection point. To reduce the ripple in vehicle voltage caused by the alternator, an ignition capacitor is installed. Capacitor, fuses and power distribution box together form the capacitor box.
The capacitor box is installed in the front near the positive battery connection point.
The EPS monitors the state of the capacitor. If the ripple of the vehicle voltage is too high, the EPS then reports a fault to the engine electronics via bus signal. The power management then stores the following fault entry: Ripple in vehicle voltage too high.

System functions
The following system functions are specified for the voltage supply of the EPS (24 V):
- Voltage supply of the EPS with 24 V.
- Auxiliary battery: monitoring of the battery condition.

Voltage supply of the EPS with 24 V
If the charging controller for the auxiliary battery does not determine a fault (e.g. a short circuit or line disconnection), it actuates the cut-off relay once terminal 15 has been connected so that the auxiliary battery is switched in series with the main battery. The charging controller for the auxiliary battery then controls the charging voltage and monitors the charge current accordingly.

Auxiliary battery: monitoring of the battery condition
The monitoring of the battery condition takes place in the electromechanical power steering unit (EPS) by means of the evaluation of the measured supply voltage, the measured current and of the signals sent from the charging controller for the auxiliary battery by means of a message. The EPS stores the results of the last evaluations and calculates the battery condition of the auxiliary battery.

Notes for Service department

General notes

NOTICE: Charging the auxiliary battery

The auxiliary battery can be charged along with the main battery using a charger approved by BMW via the jump start terminal points. If the terminal 15 is switched on, the charging unit recognizes the connected charger and then controls the cut-off relay automatically so that the auxiliary battery is also charged.

Diagnosis instruction

NOTICE: Register battery replacement

Following the installation of a new auxiliary battery, the following service function must be performed: "Auxiliary battery (24 volt EPS): register battery replacement". The registration of the battery replacement is required to inform the electromechanical power steering (EPS) that a new auxiliary battery has been installed in the vehicle. The EPS is then available for use at full power again and the measured data on the battery condition is reset.

NOTICE: Register the change of the capacitor box

Following the installation of a new capacitor box, the following service function must be performed: "Capacitor box: Register change". The registration of the capacitor box change is required to inform the electromechanical power steering (EPS) that a new capacitor box has been installed in the vehicle. The EPS is then available for use at full power again and the measured data on the state of the capacitor is reset. The fault entry from the power management ("Ripple in vehicle voltage too high ) in the engine electronics can be deleted.

We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.