48V On-Board Electrical System, Function - GF54.10-P-2008RFM
Model 205, 253 with Engine 264
with Code B01 (48V technology)
48 V on-board electrical system in general
The 48 V on-board electrical system augments the conventional 12 V on-board electrical system. It provides the energy for the combustion engine's starting procedure and it powers additional consumers. The 48 V on-board electrical system is connected through the DC/DC converter control unit (N83/1) to the 12 V on-board electrical system. In other words, the 12 V on-board electrical system replaces the conventional 12-V alternator with the DC/DC converter control unit. Apart from this, the 48 V on-board electrical system together with the 48 V on-board electrical system battery (G1/3) provides additional storage capacity throughout the overall system. The DC/DC converter control unit is the master control unit for energy management in the 48 V on-board electrical system.
The energy management in the 48 V on-board electrical system calculates the current and voltage limits for the power output of the starter-alternator (M1/10) in order to achieve a stable charge balance for the 48 V on-board electrical system battery and ensure starting ability. The drivetrain control unit (N127) is the master control unit for the traction management in the 48 V on-board electrical system. The traction management decides whether the starter-alternator generates drive torque in addition to the combustion engine or works in generator mode.
The 48 V on-board electrical system fulfills the following subfunctions:
- Voltage provision
- Dynamic idle speed control
- Cooling 48 V on-board electrical system battery
Voltage provision
The voltage provision function comprises the following subfunctions:
- Charge 48 V on-board electrical system battery
- Traction management
Charge 48 V on-board electrical system battery
The DC/DC converter control unit reads in the data of the 48 V onboard electrical system battery via the 48 V on-board electrical system LIN (LIN B22) and calculates the permissible current and voltage limits.
Finally, the DC/DC converter control unit sends these values over the interior CAN, electronic ignition lock control unit and the suspension FlexRay to the drivetrain control unit. The drivetrain control unit evaluates this by taking the following input factors (e.g. air conditioning system ON) into account. It calculates the operating mode of the starter-alternator based on the current and voltage limits or by means of the temperature-dependent charging characteristic in order to optimally charge the 48 V on-board electrical system battery. The powertrain control unit then transmits the calculated operating mode via the hybrid CAN (CAN L) to the starter-alternator.
Traction management
The traction management includes, for example, the following tasks:
- Compliance with current and voltage limits of 48 V on-board electrical system battery
- Converting in overrun mode to recuperation
- Converting during acceleration to torque support
- Supporting the combustion engine when balancing speed while changing gear
- Moving the combustion engine into an efficient range by increasing or reducing the load
The drivetrain control unit communicates over the hybrid CAN with the starter-alternator and evaluates its operating rate.
The DC/DC converter control unit reads in the data of the 48 V onboard electrical system battery over the 48 V on-board electrical system LIN. It evaluates all relevant information and calculates the permissible current and voltage limits. Finally, the DC/DC converter control unit sends these values over the interior CAN, electronic ignition lock control unit and the suspension FlexRay to the drivetrain control unit. The drivetrain control unit evaluates these taking into account additional input factors (e.g. air conditioning system ON) and calculates the optimal starter-alternator operating mode. The drivetrain control unit then transmits the calculated operating mode via the hybrid CAN to the starter-alternator that then adopts this mode. The drivetrain control unit also checks the input factors for plausibility, to avoid any overloading or insufficient charging of the 48 V on-board electrical system battery.
The drivetrain control unit compares the optimal starter-alternator operating mode with its actual output and can thus detect the energy state of the 48 V on-board electrical system. The continuous comparison and the corresponding corrections are designated as power management. Where failure to comply with the permissible current and voltage limits is detected, power management is then gradually reduced. The starter-alternator can then make available its full output.
If, because of a fault, the data for the 48 V on-board electrical system battery are not available, the energy management switches to a fixed voltage, whose value is dependent on the last transmitted charge level.
Dynamic idle speed control
The dynamic idle speed control sets the engine's idle speed so that, when idling, an impermissibly high current is never drawn from the 48 V on-board electrical system battery. For a high consumer load, a higher idle speed is set so that the starter-alternator delivers a higher current and the load of the 48 V on-board electrical system battery is reduced.
Function requirements for cooling the 48 V on-board electrical system battery
- Drivetrain operational
- V on-board electrical system battery temperature > 25 °C
Cooling 48 V on-board electrical system battery
The output capacity of the 48 V on-board electrical system battery is dependent on the battery temperature. To enable the 48 V on-board electrical system battery to be used over a wide temperature range, it is cooled through the low-temperature circuit 2 with water. The drivetrain control unit is responsible for temperature control. It regulates the battery temperature with the coolant flow volume. Because of the related thermic coupling, the DC/DC converter control unit is cooled together with the 48 V on-board electrical system battery.
The 48 V on-board electrical system battery sends the following signals over the 48 V on-board electrical system LIN, DC/DC converter control unit, interior CAN, electronic ignition lock control unit and the suspension FlexRay to the drivetrain control unit:
- Minimum temperature of 48 V on-board electrical system battery
- Maximum temperature of 48 V on-board electrical system battery
- Temperature of 48 V on-board electrical system battery
The drivetrain control unit reads in the low-temperature circuit temperature sensor 2 (B10/14) directly.
Schematic diagram of cooling circuits
The drivetrain control unit evaluates the data of the low-temperature circuit 2 temperature sensor and actuates the low-temperature circuit circulation pump 2 over the drivetrain LIN (LIN C3) to meet requirements. An increase in pump output here increases the coolant flow volume thereby providing greater heat dissipation at the 48 V onboard electrical system battery. Inversely, a lower pump output dissipates less heat.
The waste heat in low-temperature circuit 2 is dissipated to the surrounding air through the cooler of the low-temperature circuit 2.
Integrated into the 48 V on-board electrical system battery is a cooling and heating element, which is actuated by the DC/DC converter control unit. Additional heat can also be dissipated in this manner. At low temperatures, the cooling and heating element is also used for heating, so that the 48 V on-board electrical system battery reaches its optimum operating temperature faster.
The drivetrain control unit sends the "Water cooling active" signal over the suspension FlexRay, electronic ignition lock control unit and the interior CAN to the DC/DC converter control unit.
| Electrical function schematic for 48 V on-board electrical system | PE54.10-P-2078-97FBA | ||
| Overview of energy management system components | GF54.10-P-9990RF |