The new EQE: electric drive

Sep 5, 2021
Stuttgart

The models available on launch are the EQE 350 (power consumption acc. to WLTP: 19.3-15.7 kWh/100 km; CO2 emissions: 0 g/km)[1] with 215 kW, and a second model. Further versions will follow. The battery has ten modules with a usable energy content of around 90 kWh, and the range of up to 660 km2 acc. to WLTP is absolutely suitable for long distance touring.

All EQE models have an electric drivetrain (eATS) on the rear axle. The later versions with 4MATIC also have an eATS on the front axle. In the 4MATIC models, the Torque Shift function ensures intelligent, continuously variable distribution of drive torque between the rear and front electric motors and thus the use of the most efficient eATS in each case. The modular powertrain concept ensures high overall performance and long range.

The electric motors on the front and rear axles are permanently excited synchronous motors (PSM). With the PSM, the rotor of the AC motor is fitted with permanent magnets and therefore does not need to be supplied with power. The magnets – and thus the rotor – follow the rotating alternating current field in the stator windings. In the EQE, Mercedes-Benz uses what is known as a pull-in winding for a particularly strong magnetic field. The engine is referred to as synchronous because the rotor turns at the same rate as the magnetic field of the stator. The frequency is adjusted in the power electronics converters to the speed requirements of the driver. The advantages of this design include high power density, high efficiency and high power constancy. The motor on the rear axle is particularly powerful due to its six-phase design: it has two windings with three phases each.

Cooling: sophisticated thermal concept for high load capacity

Consistently high performance and multiple accelerations without a drop in power characterise the EQE's drive philosophy. This includes a sophisticated thermal concept with some special features. What is known as a water lance in the shaft of the rotor cools it from the inside. Other cooling elements in the cooling circuit are fins on the stator, a needle-shaped pin-fin structure on the inverter and a transmission oil cooler. This also brings more efficiency during cold driving, because the heat exchanger then serves to heat the transmission oil and thus reduces friction in the transmission.

Intelligent recuperation: one-pedal driving to a standstill

The EQE offers several variants of energy recovery by means of recuperation: in this process, the high-voltage battery is charged by converting the mechanical rotary motion into electrical energy during overrun or braking mode. The driver can manually select the deceleration in three stages (D+, D, D-) as well as the gliding function via shift paddles behind the steering wheel. Also available: DAuto.

ECO Assist also offers situation-optimised recuperation - deceleration is so strong or weak that it ultimately results in the most efficient driving style. Recuperative deceleration is also used as far as possible for vehicles detected ahead until they come to a standstill, for example at traffic lights. The driver does not need to press the brake pedal for this - literally one-pedal driving.

Noise and vibration comfort: conceptual advantage plus extensive measures

As a saloon with a boot lid, the EQE's concept is well equipped to offer a high level of NVH comfort. Numerous measures contribute to this:

Even the design of the electric powertrains (eATS) takes noise and vibration comfort (NVH - Noise, Vibration, Harshness) into account. The magnets are arranged inside the rotors in an NVH-optimised way (known as 'sheet metal cut'). This also reduces the use of rare earths. The shape of the winding, what is known as the stator tilt, also supports vibration comfort, especially at low speeds. In relation to the permanent magnets of the rotor, the coils of the stator are obliquely wound. Otherwise, what is known as cogging torque could occur. This would lead to slight but unpleasant vibrations when driving very slowly.

In addition, the eATS have a special foam mat all around as an NVH cover. The inverter cover has a sandwich construction of three metal and plastic layers. The eATS are doubly decoupled from the body via elastomeric bearings: at the front axle opposite a supporting frame and this against the body, at the rear axle with a subframe.

Highly effective spring/mass components provide continuous sound insulation from the crossmember under the windscreen to the floor of the boot. Acoustic foams are inserted into many carriers during body-in-white construction.

The electric refrigerant compressor has an NVH cover as encapsulation. In the rear-wheel-drive EQE, it is also soft-suspended, while in the 4MATIC models it is bolted directly to the front eATS. The operating strategy of the refrigerant compressor was designed for the highest possible noise and vibration comfort. Certain rpm ranges at which disturbing resonances may be audible when stationary or in a traffic jam are avoided or quickly passed through.

[1] Data on power consumption and range are provisional and were determined internally in accordance with the "WLTP test procedure" certification method. Confirmed TÜV figures, EC type approval and certificate of conformity with official figures are not yet available. Differences between the stated figures and the official figures are possible.

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