The ECO Assistant will not only conserve fuel and electricity but also give drivers valuable information about how to make their driving style more environmentally friendly. In an interview, Carmen Gander, the main developer of the ECO Assistant, explains the background of the new assistance system.
Ms. Gander, how did the idea for this assistance function come about?
One question always arises in the course of developing electrified drive systems: How strongly should the vehicle decelerate when the driver releases all the pedals? In the systems that exist today, the drivers usually have two modes to choose from. First, there’s the “one-pedal feeling,” which means the vehicle rolls freely when the driver is pressing the gas pedal halfway down, for example. If he then gives more gas, the vehicle accelerates; if he gives less gas, the vehicle is slowed down or braked. The battery is charged through this electrical deceleration, which causes energy to be recovered. The brake pedal itself is actually needed only to stop the vehicle or for emergency braking.
The second mode is similar to the overrun in a combustion engine. If the vehicle is a hybrid, it can go into overrun — with or without a fuel shutoff function — to roll freely, or coast. It can even do that with the motor switched off or when recovering energy. The most appropriate mode in terms of environmental benefits and convenience depends on the given traffic and driving situation.
And that’s exactly where our function — the ECO Assistant — comes in. The distance and speed of the vehicle ahead are known from the standard-fitted radar sensor. The camera in the windshield supplies the current maximum permissible speed, and information about the speed limits, traffic circles, curves, intersections and gradient data is available from the navigation system's map data.
Exactly what does the ECO Assistant do?
The ECO Assistant combines all of these data and then sets the optimal deceleration mode. Coasting makes sense when the aim is to avoid losing any speed, for example on slight downward gradients and on clear stretches of road. By contrast, energy recovery is activated and set to the optimal level in case of steeper gradients, slower vehicles ahead, an approaching speed limit, or intersections and curves on the road ahead.
The core of the ECO Assistant is known as the coast-down simulation function. On the basis of the gradient and curve profile ahead, this function calculates how far the vehicle will roll in coasting mode and how far it will roll at maximum energy recovery. The ECO Assistant control range lies within this distance range. When the vehicle enters this control range, a small green "foot off the gas" symbol appears in the instrument cluster.
This shows the driver that if he takes his foot off the gas pedal the vehicle will reach a speed-related event up ahead — a downward gradient, vehicle, traffic sign, curve etc. — in an energy-efficient way without any braking. We have configured the ECO Assistant in a way that will avoid a row of honking cars forming behind the vehicle.
The driver can find out at any time why the ECO Assistant is displaying the "foot off the gas" recommendation and why the current deceleration setting has been selected. But only if he wishes to do so. He can call up an assistance graphic in the instrument cluster which provides information about events on the road ahead. For example, the gradient is displayed ahead of a hilltop to explain the reason for coasting, or the beginning of a built-up area is indicated by “km/h” to explain why the coasting mode has been switched to energy recovery.
Can the driver still intervene and decide on his driving style himself?
The driver remains in control. In contrast to the DISTRONIC mode, the ECO Assistant does not accelerate or brake the vehicle. It merely gives the driver tips and adjusts the deceleration according to the given situation. If you consider even this to be too much interference, you can simply switch the ECO Assistant off. At the moment, the ECO Assistant is fully active only in the e-drive program, and the gas and brake pedals can override the ECO Assistant at any time.
When will the ECO Assistant be available?
The ECO Assistant was introduced in the new S500 model [fuel consumption combined (gasoline): 6.9-6.6 l/100 km; CO₂ emissions (combined): 157 g/km*] . The motor has a 48V electric power system as standard and is able to use it to recover energy. The ECO Assistant will be successively introduced in all of the upcoming hybrids — both plug-ins and 48V motors — and electric vehicles, initially in Europe. It will then be launched in more and more countries for which map data is available. On the subject of map data, in addition to electrification, an additional precondition is the installation of the COMAND navigation system and the traffic sign recognition system.
And what about driving pleasure?
Customer surveys in Germany and the USA both confirm that a new form of driving pleasure exists today: ecological driving. The respondents had especially high praise for the option of cruising with the engine turned off and for the brilliant restarting function of the 48V ISG electric motor’s stop/start system. The ECO Assistant is the logical continuation of this course of development. And fans are already talking about the addictive nature of the preview function.