Predictive driving for economy: the ECO Assist assistance system comprehensively supports drivers in implementing this effective efficiency strategy: the driver is prompted when it is appropriate to release the accelerator, e.g. because the vehicle is approaching a speed limit, and assisted by innovative functions such as coasting and recuperation. For this purpose, navigation data, traffic sign recognition and information from the intelligent safety assistants (radar and stereo camera) are linked and processed. The current ECO Assistant version premiered in the new S-Class variants featuring EQ Boost (integrated starter alternator).
ECO Assist takes the following traffic situations and information into account in its driving recommendations and efficiency strategy:
- Route profile (bends, junctions, roundabouts)
- Speed limits
- Distance from vehicles ahead.
ECO Assist continuously generates coasting simulations in the background: depending on the charge level of the battery and the traffic situation, it computes whether the vehicle should ideally be allowed to coast freely ("sail") with the lowest possible driving resistance when releasing the accelerator, or whether it should be decelerated so that the battery can be efficiently charged (recuperation).
Within the limits of the system, ECO Assist regulates the impetus according to the situation as soon as the driver's foot is lifted off the accelerator. The driver is given a discreet 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").
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 is driven with the engine switched off, and shows this in the central display. Rewards not only materialise in the shape of reduced fuel consumption, but also of increased (fully electric) range.
ECO Assist predictively computes the driving situation when deciding whether to drive with the lowest resistance or whether to recuperate. Some examples:
- Dip: the vehicle recognises that a downhill gradient is followed by a climb, and that a speed limit is shown. When approaching the downhill gradient, the driver is already prompted to "Release accelerator". As soon as the driver acts on this, the vehicle continues with the combustion engine switched off. Recuperation takes place on the downhill stretch (the battery is charged), but only enough to ensure that the maximum permitted speed is maintained if possible. 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 70 km/h before the brow of a hill for example, and afterwards the limit increases to 100 km/h. Once again the prompt to drivers is to "Release accelerator" before the brow is reached, followed by coasting when the driver complies. On the downhill stretch, the new target speed of 100 km/h can be reached by coasting, without assistance from the combustion engine.
- Speed limit: when the system recognises an impending speed limit using the navigation data or the camera, the driver is prompted to "Release accelerator". The vehicle is then gently decelerated (while recuperating) to the new speed using electric power, 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.
In the interests of operating comfort, too many driver prompts are avoided if possible. For this purpose, ECO Assist analyses speed limits that occur in rapid succession, and for instance in the case of an impending limit of 70 km/h shortly followed by a built-up area, it gently regulates the speed directly down to 50 km/h when the driver responds to the "Release accelerator" prompt.
Coasting mode: driving without the combustion engine
To keep energy consumption as low as possible when coasting, not only is the powertrain disengaged, but the combustion engine is also switched off. In drive systems with EQ Boost (integrated starter alternator) the transmission is shifted to the neutral position. Disengaging the powertrain reduces its drag loss and allows energy-efficient coasting for as long as possible.