(Regenerative Brake System, Basic Function - GF42.22-P-1008A)
Electric vehicles and hybrid vehicles
Overview
This document contains information on:
- General
- Function requirements
- Function
- Radar-assisted regenerative brake system
General
In recuperative braking, part of the braking energy is generated solely by the generator mode of the electric machine. The kinetic energy of the vehicle is converted into electric energy and used to charge the high-voltage battery or the 48V battery.
If the high-voltage battery or the 48V battery is charged, only hydraulic braking is used. The regenerative brake system (RBS) supports the driver in situations of sudden danger and so actively promotes safety.
Function requirements
- Drivetrain operational
- Vehicle speed > 15 km/h
Function
The driver's brake command is registered by the accelerator pedal sensor as well as the sensor system at the brake booster. The signal is registered in the traction system hydraulic unit and transmitted to the ESP® control unit.
If the brake pedal is operated lightly, the vehicle only brakes by means of the electric motor. The mechanical brakes are not operated in this case. If the brake pedal is operated lightly, the electric motor acts as an alternator and brakes the vehicle minimally as a result of the energy generation.
On all-wheel drive vehicles, the braking torque is only generated in the event of light brake applications on the rear axle. In order to receive the current values of the available regenerative braking torque, the ESP® control unit is in constant communication with the powertrain control unit. The value also depends on the state of charge of the high-voltage battery or the 48V battery.
A 3-phase alternating voltage is generated by the electric machine during recuperation. The power electronics control unit converts the alternating voltage into high voltage or 48V direct voltage and thus supplies the high-voltage battery or the 48V battery.
The ESP® control unit divides the overall braking torque requested by the driver into a regenerative and hydraulic braking torque portion. In the regenerative portion, the brake force is converted by the drivetrain. In the hydraulic portion, the deceleration is generated by the disk brakes.
In the event of emergency braking or a fault message, the braking torque is generated hydraulically only.
Radar-assisted regenerative brake system
The following components register the distance and speed differential to the vehicle driving in front:
- With code 258 (Active Brake Assist): Active Brake Assist control unit
- With code 23P (Drive package): Mercedes control unit for Mercedes-Benz Intelligent Drive
Code 23P (Drive package) only valid for all passenger cars
A specified deceleration (negative acceleration) is calculated from the speed differential and the distance to the vehicle in front. This results in a desired force, which is provided as the engine drag torque.
Deceleration by increasing the recuperation torque takes place under the following conditions:
- Pulling up towards a slow-moving vehicle
- Pulling up towards a braking vehicle
- Following a vehicle downhill
The power electronics control unit actuates the electric motor accordingly.
| Additional basic functions | |||
| Electric drive powertrain control unit, basic function | Electric vehicles | GF08.20-P-9892A | |
| Electronic Stability Program, basic function | GF42.45-P-1002A | ||
| Powertrain control unit, basic function | GF54.21-P-9894A |