Overview
This document contains information on:
General
Function requirements
Regenerative braking levels
Limits of regenerative braking
Automatic braking effect during map-based events
Automatic braking effect during distance control
Gesamte Bremswirkung auf Vorder- und Hinterachse verteilen
General
In vehicles with two electric machines, the following explanations apply per machine.
In deceleration mode, the vehicle activates the electric machine. Since no clutch is available, the frictional connection in the powertrain is always present. If the accelerator pedal is not pressed while the vehicle is rolling, either the glide mode is activated or the electric machine absorbs kinetic energy and converts it into electrical energy (regenerative braking). The electric machine generate a braking effect during regenerative braking. This braking effect can be set in several regenerative braking levels or automatically controlled.
The multifunction display shows the currently set regenerative braking level.
If the driver presses the brake pedal, the braking effect is initially generated by regenerative braking before the service brake comes into play. This type of regenerative braking has been described in another document.
The energy gained in deceleration mode is fed into the high-voltage on-board electrical system via the power inverter integrated in the power electronics control unit.
Function requirements
Circuit 15 ON
Regenerative braking levels
The driver can raise or lower regenerative braking in deceleration mode by upshifting the steering wheel gearshift button and downshifting the steering wheel downshift button. Alternatively, the driver can select automatic regulation of regenerative braking.
Nach erneutem Setzen der Klemme 15 oder nach einem Einlegen der Fahrstufe D ist automatisch die Rekuperationsstufe D aktiv.
Regenerative braking levels |
Stage | Regenerative braking | Properties |
D+ | None | The vehicle rolls freely (glide mode), no regenerative braking takes place. |
D | NORMAL | Medium settings as compromise from braking via accelerator pedal and braking via brake pedal. |
D- | reinforced | Increased braking effect in deceleration mode. |
D- - | high | Maximum braking effect in deceleration mode. |
DAUTO | Automatic | The level of the regenerative braking and the braking effect are automatically adapted to the current traffic situation. |
Limits of regenerative braking
The regenerative braking in deceleration mode is only reduced or not even present at all in the following situation:
as the charge level of the high-voltage battery increases
if the high-voltage battery is not yet at operating temperature
when driving close to vehicle standstill
during and after an intervention by the vehicle dynamics control
In these cases, the required braking effect is set via the service brake.
Automatic braking effect during map-based events
Additional function requirements:
Drive program EL active and level DAUTO selected
Drive program C, BL or E active
Depending on map-based events, regenerative braking is increased as required. The following events influence regenerative braking:
Speed limit
Inclines and gradients
Intersections and roundabouts
Corners
The multimedia system control unit generates data about the vehicle's probable route.
Das Steuergerät Antriebsstrang wertet diese Daten aus, mit dem Ziel, die Fahrweise optimal an die vorausliegende Strecke anzupassen und somit den Energieverbrauch zu reduzieren. This is achieved through an intelligent combination of coasting mode and higher and longer regenerative braking phases. The working area of regenerative braking covers all manually selectable regenerative braking levels.
The driver receives feedback about the optimum accelerator pedal position via the multimedia display and the haptic accelerator pedal.
The powertrain control unit calculates the appropriate specified deceleration and sends the request for the braking torque to the power electronics control unit. The power electronics control unit actuates the electric machine accordingly.
Automatic braking effect during distance control
Additional function requirements:
Level DAUTO selected
When approaching a slower or a decelerating vehicle, or during follow-up trips downhill, regenerative braking is increased as necessary. A target deceleration is calculated on the basis of the relative speed and the distance to the vehicle in front, and the electric machine is activated accordingly.
Gesamte Bremswirkung auf Vorder- und Hinterachse verteilen
Bei Fahrzeugen mit zwei elektrischen Maschinen teilt die Antriebsregelung das gesamte Bremsmoment auf ein Bremsmoment für die Vorderachse und ein Bremsmoment für die Hinterachse auf. Die Aufteilung erfolgt unter anderem nach Kriterien der Achslastverteilung und der Antriebsschlupfregelung. Das maximale Bremsmoment wird mit einer Aufteilung von 70 % an der Vorderachse und 30 % an der Hinterachse erreicht.
The powertrain control unit requests the partial torques from the power electronics control unit.