Mercedes-Benz has introduced the EQA, the new entry-level model to the all-electric world of Mercedes-EQ vehicles. The EQA is the first all-electric member of the compact car vehicle from Mercedes-Benz. A close relation of the GLA, it delivers all the characteristics of that vehicle, combined in this case with an efficient electric power train.
The EQA is being launched as the EQA 250 (combined electrical consumption: 15.7 kWh/100 km) with 140 kW and a range according to WLTP of 426 kilometers (265 miles). The EQA 250 will be available in Germany at prices from €47,540.50. Based on the net list price of €39,950, customers can avail themselves of the environmental bonus of €6000 offered by the federal government and €3000 from Mercedes-Benz as the manufacturer.
Further variants to meet specific customer requirements will follow. These will include on the one hand a series of even more athletic all-wheel-drive models with an additional electric powertrain (eATS) and an output of 200 kW or more, and on the other hand a version with a range of more than 500 kilometers (311 miles) (WLTP). Mercedes-EQ sees the key to a bigger range not in ever-larger batteries, but in systematic improvement in the efficiency of all vehicle components.
The “double-decker” lithium-ion battery, which sits as a structural element within the underbody of the vehicle, has an energy content of 66.5 kWh. In order to meet the high standard of noise and vibration comfort that is such a hallmark of the brand, complex measures have been taken to isolate the electric powertrain from the chassis and body. Numerous damping measures enhance this effect.
An asynchronous motor is used at the front axle. The electric motor, a fixed-ratio transmission with a differential, the cooling system and the power electronics form a highly integrated, very compact unit: the electric powertrain (eATS). The transmission ratio and gear wheels have been configured for the requirements of the front-wheel drive system.
The more powerful models include a further electric powertrain (eATS) at the rear axle featuring a redesigned, permanently excited synchronous motor. This is extremely compact in design.
In a permanently excited synchronous motor, the rotor of the AC motor is studded with permanent magnets. The magnets—and thus the rotor—follow the rotating alternating current field in the winding of the stator. The engine is said to be synchronous, because the rotor turns at the same rate as the magnetic field of the stator. The rate is adjusted to the speed requirements of the driver in the frequency converters of the power electronics. The advantages of this design include the high power-to-size ratio, high level of efficiency and high output consistency.
The balance of performance between the front and rear axles in the 4MATIC versions is intelligently adjusted up to 100 times per second, depending on the driving situation. The Mercedes-EQ philosophy is to optimize consumption by using the rear electric motor as often as possible, while the asynchronous motor at the front axle generates only minimal drag losses in partial-load operation.
In overrun mode or during braking, the electric motors become alternators: their mechanical rotation is converted into electrical energy and used to charge the high-voltage battery (recuperation)999. The driver can select the recuperation function manually using paddles behind the steering wheel.
The paddle on the left increases the level of recuperation, the paddle on the right reduces it. The driver can see the selected setting in the instrument cluster. The following recuperation stages are available: DAuto (recuperation via ECO Assist to suit the particular situation, see next section), D+ (coasting), D (low recuperation), D- (medium recuperation) and D- -(high recuperation). New with the EQA is that, if the function DAuto is selected, this mode remains the setting when the car is restarted. To stop, the driver must activate the brake as normal, whatever the recuperation stage.
The EQA is fitted with a lithium-ion battery with a high energy density. The battery is made up of five modules and is located underneath the passenger compartment in the middle of the vehicle. The lowest point of the vehicle, however, is the lower edge of the side skirts, giving the EQA more than 200 mm of ground clearance.
The battery features a double-decker design, making it another example of the intelligent use of space: The “nose” of the battery, which accommodates the battery management system, is situated towards the front, behind the center console. An aluminum housing as well as the body structure of the vehicle itself protect the component from potentially touching the ground and against loose chippings. The battery housing is part of the vehicle structure and thus an integral part of the crash concept.
The high-voltage battery has a maximum voltage of 420 V and a nominal capacity of 190 Ah, giving it an energy content of 66.5 kWh. The battery is part of the intelligent thermal management system of the EQA. To ensure that it is always kept within the optimum temperature range, it can be cooled or heated as required via a coolant-fed plate underneath the battery.
If Navigation with Electric Intelligence is activated, the battery may also be pre-heated or cooled while driving in order to ensure that it is within the ideal temperature window for a rapid charging station. On the other hand, if the battery is cold when the car reaches the rapid charging station, a considerable proportion of the charging capacity will initially be used simply to warm it up. The net effect is to optimize the charging time as a means of significantly shortening the charging stop.
As for all other high-voltage batteries, Mercedes-Benz issues a battery certificate, thus providing a performance warranty. This is valid for eight years or a distance covered of 160,000 kilometers and guarantees a properly functioning high-voltage battery: the certificate also covers capacity loss in the battery.
Charging management: CCS charging socket for alternating current as well as direct current. At home or at public charging points, the on-board charger provides a convenient way of charging the EQA with up to 11 kW using alternating current (AC). The charging time required for a full charge depends on the available infrastructure and the country-specific vehicle equipment. Charging at a Mercedes-Benz Wallbox is considerably faster than at a domestic power socket.
Depending on the SoC (state of charge) and the temperature of the high-voltage battery, the EQA can also be fast-charged with a maximum output of up to 100 kW at an appropriate charging station. The battery can be charged in this case from 10 - 80% SoC in around 30 minutes. For AC and DC charging, the EQA is equipped as standard in Europe and the US with a CCS connector (Combined Charging System) in the right-hand side wall. In Japan or China the corresponding country-specific charging sockets are used. The charging times may also vary compared with those for the European model.
ECO Assist recuperation. ECO Assist offers a recuperation process optimized to the particular situation. It takes into account navigation data, traffic sign recognition and information from the vehicle sensors in its efficiency strategy. Anticipatory driving saves power, thereby extending the range.
ECO Assist coaches the driver with messages when the accelerator can be released, for instance because a speed limit is approaching, and with 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 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 (glide) 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).
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 travelling ahead
Within the limits of the system, ECO Assist controls the overrun according to the situation as soon as the driver’s foot leaves the accelerator. The driver is also given a visual prompt to do this: by showing a “foot off the accelerator” symbol in the media display (or if available, 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 in the road, 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, in order to maintain as much impetus as possible for the uphill stretch.
Brow: If ECO Assist recognizes that gliding makes sense because of the individual driving situation, the topography and the speed limits, the driver is told to “Remove foot from accelerator” even before reaching the brow. The vehicle then drives over the brow in gliding mode, and subsequently uses the downhill stretch to reach the target speed.
Speed limit: When the system recognizes 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 recognize slow-moving vehicles ahead while coasting, gliding 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.
Automatic anticipatory driving. Navigation with Electric Intelligence calculates as a matter of course the route that will get you to your destination fastest, taking into account charging times, thus taking the stress out of route planning for the driver. On the basis of continual range simulations, the system makes allowance for any necessary charging stops as well as for numerous other factors, such as the topography and the weather. It is also able to react dynamically to changes, for instance in the traffic situation or personal driving style.
Aerodynamics. The EQA is the first model from Mercedes-EQ the aerodynamic development of which has been undertaken entirely digitally. The ensuing measurements undertaken in the wind tunnel revealed a Cd value of 0.28, thereby confirming the high quality of the numerical simulation. The frontal area A totals 2.47 m2.
Among the most important aerodynamic measures are the completely closed cooling air control system in the upper section, the aerodynamically efficient front and rear aprons, a very smooth, almost completely enclosed underbody, specially optimized Aero wheels and specifically adapted front and rear wheel spoilers.