Overrun Mode, Basic Function - GF08.00-P-1004B
Hybrid vehicles
Overview
This document contains information on:
- General
- Function requirements
- Function
- Regenerative braking levels
- Limits of regenerative braking
- Deceleration mode
- Regenerative braking in deceleration mode
- Cruising mode without use of the accelerator pedal
General
If the brake and accelerator pedals are not actuated for a rolling vehicle, the following can occur:
- Where the high-voltage battery is not fully charged, kinetic energy is absorbed via the electric machine and converted into electrical energy (recuperation).
- An overrun mode fuel shutoff of the combustion engine can also take place.
Function requirements
- Hybrid drive system operational
- Accelerator not operated
- Service brakes not operated
- Vehicle rolling.
- Gear range "D"
Function
Regenerative braking levels
Additional function requirements:
- EL (Electric) drive program active
- B (Battery Hold) or H (Hybrid) drive program active (depends on the model)
The driver has the option to increase or reduce the recuperation in overrun mode via the "Upshift" steering wheel shift button and the "Downshift" steering wheel shift button. Alternatively, the driver can select automatic regulation of regenerative braking.
After an engine start or after the engagement of the drive range "D", the recuperation level D or the recuperation level DAUTO is automatically active.
| Stage | Recuperation | 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. In order to brake, the driver must press the brake pedal more frequently than in stage D-. |
| D- | reinforced | Increased braking effect in deceleration mode. |
| D- - | high | Maximum braking effect in deceleration mode. In this stage, most kinetic energy is recovered. (depends on the model) |
| DAUTO | Automatic | The level of the regenerative braking and the braking effect are automatically adapted to the current traffic situation. Map data can also be used for this purpose. |
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.
Deceleration mode
If the brake pedal is actuated regenerative braking occurs. The powertrain control unit directly reads in the following signals in overrun mode:
- Accelerator pedal position
- Gear range status
- Engine clutch, status
- Transmission oil temperature signal
- Status of electric auxiliary oil pump
- Wheel speed
- Service brake, status
- High-voltage battery voltage
- Temperature of high-voltage battery
- Status of electric machine
- Torque of electric machine
- Engine speed of electric machine
- Tolerable charging voltage/current signal
Depending on the state of charge of the high-voltage battery and the selected drive program, the powertrain control unit calculates a specified overrun torque that the combustion engine control unit implements with overrun mode fuel shutoff and/or recuperation.
Regenerative braking in deceleration mode
Kinetic energy is taken up over the electric machine and converted into electrical energy (regenerative braking) for a low charge level of the high-voltage battery. To do this, the powertrain control unit requests a generative torque from the power electronics control unit.
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.
In overrun mode > 180 km/h and/or in the drive program S (Sport), the engine separator clutch remains closed and the combustion engine goes into overrun mode fuel shutoff and thus generates an overrun torque. The electric machine supports this deceleration torque if necessary by a generative torque.
In deceleration mode and active deceleration fuel shutoff the internal combustion engine generates a boost torque which can be greater together with the recuperative boost torque than the calculated specified boost torque. In this case the deceleration fuel shutoff is not activated and the internal combustion engine generates a minimum actuatable torque. This concept ensures that the drive always remains the same for the driver as much as possible, with and without deceleration fuel shutoff.
The decel mode with deceleration fuel shutoff is more effective from an energy usage point of view. At a low charge level for the high-voltage battery and a low nominal deceleration torque the regenerative braking in deceleration mode without deceleration fuel shutoff is actually more meaningful.
Cruising mode without use of the accelerator pedal
Additional function requirements:
- Drive program E (Eco) active (depends on the model)
If the brake and accelerator pedals are not actuated for a rolling vehicle and recuperation can take place, the combustion engine is disconnected from the drive up to a speed < 180 km/h by opening the engine separator clutch and switched off. If it is not possible for regenerative braking to take then the deceleration fuel shutoff of the internal combustion engine can also be activated.
For a slightly actuated accelerator pedal, the electric machine supports the drive for an adequately high charge level of the high-voltage battery in order to counteract the falling vehicle speed.
| Function schematics | |||
| Function schematic for overrun mode | Model 167, 213 as of model year 2021 | PE08.00-P-2502-97B | |
| Model 177, 247 | PE08.00-P-2502-97C | ||
| Model 206, 223 with engine 256 | PE08.00-P-2502-97E | ||
| Model 290 | PE08.00-P-2502-97H | ||
| Additional basic functions | |||
| Power electronics control unit, basic function | GF08.20-P-9891A | ||
| Electric machine, basic function | GF08.10-P-2000A | ||
| Accelerator pedal sensor, basic function | GF30.20-P-2000A |