Under the microscope: intelligent operating strategy and recuperation: Copilot for efficient motoring
Predictive driving for economy: In implementing this effective efficiency strategy, the assistance system ECO Assist comprehensively supports the driver by giving prompts when it is appropriate to come off the accelerator, e.g. because the vehicle is approaching a speed limit, and by functions such as 'gliding' and specific control of recuperation. For this purpose, navigation data, traffic sign recognition and information from the intelligent safety assistants (radar and stereo camera) are linked and processed.
ECO Assist takes the following traffic situations and information into account in its driving recommendations and efficiency strategy:
- Route profile (bends, junctions, roundabouts, gradients)
- Speed limits
- Distance from vehicles ahead.
ECO Assist continuously generates coasting simulations in the background: depending on the state of charge of the battery and the traffic situation, it computes whether the vehicle should ideally be allowed to coast with the lowest possible driving resistance with the driver's foot off the pedals, or whether it should be decelerated so that the battery can be efficiently charged (recuperation).
The haptic accelerator helps the driver to achieve an economical and comfortable driving style. A pressure point in the pedal, for example, tells the driver that the maximum electric power is being delivered. If the driver continues to press the pedal beyond the pressure point, the combustion engine kicks in. A perceptible resistance in the haptic accelerator advises the driver to take their foot off the accelerator. If the driver follows this recommendation, the combustion engine is switched off and decoupled from the powertrain.
Within the limits of the system, ECO Assist controls the overrun mode according to the situation as soon as the driver takes their foot off the accelerator. The driver is also given a visual prompt to do this: by the appearance of a "release accelerator" symbol in the central display (or if installed, in the Head-up Display). At the same time, a diagram gives the driver the reason for the recommendation (e.g. "Junction ahead" or "Gradient ahead").
ECO Assist predictively computes the driving situation when deciding whether to drive with the lowest resistance or whether to recuperate. Examples include dips, brows or speed limits ahead, which the system recognises from the map data.
- Dip: The vehicle recognises that a downhill gradient is followed by a climb, and that a speed limit is shown. The driver receives the prompt "Foot off accelerator" in good time. As soon as the driver acts on this, the vehicle continues with the drive switched off. Recuperation takes place on the downhill stretch, but only enough to ensure that the maximum permitted speed is maintained. Recuperation ends just before the lowest point in the dip, and coasting commences to maintain as much impetus as possible for the uphill stretch in the interests of energy efficiency.
- Brow: There is a speed limit of 90 km/h before the brow of a hill, and afterwards 100 km/h. Once again the driver is prompted with "Foot off accelerator" before the brow is reached, followed by coasting when the driver complies. On the following downhill stretch, the new target speed of 100 km/h can be reached by coasting and maintained by recuperation.
- Speed limit: When the system recognises a speed limit from the navigation data or via Traffic Sign Assist, the driver is once again prompted with "Foot off accelerator pedal". The vehicle is then gently decelerated (while recuperating) to the new speed, followed by coasting. In this way suitable speeds for junctions, roundabouts and bends are also supported.
- Slow-moving traffic: When the radar sensors of the system recognise slow-moving vehicles ahead while coasting, coasting is automatically interrupted if necessary. Deceleration with recuperation takes place to the extent that braking action by the driver is often unnecessary. If the vehicle ahead accelerates, coasting is reactivated automatically so as to cease deceleration and maintain the current speed as much as possible. The driver operates the accelerator if needed.
To increase the driver's motivation to follow the recommendations of ECO Assist, the on-board computer records how many kilometres/for how much time during a journey the car was driven with the engine off, and shows this in the central display. The reward not only takes the form of reduced fuel consumption, but also an increased electric range.