Overview
This document contains information on:
General
Function requirements
Function
General
During regenerative braking, a portion of the braking energy is generated solely through alternator operation of the electric machine. The vehicle's kinetic energy is converted to electrical energy and then used to charge the high-voltage battery. Once the high-voltage battery is charged, braking is then through hydraulic operation only. The regenerative brake system (RBS) supports the driver in situations of sudden danger and so actively promotes safety.
Function requirements
Drive train operational
Vehicle speed > 15 km/h
Function
The driver's brake command is registered by the accelerator pedal sensor and a brake vacuum sensor. 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. When the brake pedal is operated lightly, the electric motor acts as an alternator and minimally brakes the vehicle by means of power generation. The braking torque is only generated at the rear axle during light brake application. 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 is dependent, among other things, on the charge level of the high-voltage 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 direct voltage and supplies the high-voltage battery with it. The ESP® control unit divides the overall braking torque requested by the driver into a regenerative and hydraulic braking torque part. In the regenerative portion, the brake force is converted by the drivetrain. In the hydraulic portion, deceleration is generated by means of the disk brakes.
In the event of emergency braking or a fault message, braking torque is only generated hydraulically.
Radar-based regenerative braking system
The following components register the distance and speed differential to the vehicle driving in front:
With code 258 (COLLISION PREVENTION ASSIST): Active Brake Assist controller unit
With code 23 P (Driving Assistance Package): Mercedes Intelligent Drive control unit
A specified deceleration (negative acceleration) is calculated from the relative speed and the distance to the vehicle in front. This results in a desired force which is provided as the engine drag torque.
Deceleration by an increase in regenerative torque occurs 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.