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The new EQS: Electric drive[1]

Jul 24, 2021

Non-stop from Munich to Berlin or from Oslo to Stockholm: with an operating range of up to 780 kilometres (WLTP) and an output of up to 385 kW, the powertrain of the EQS also meets every expectation of a progressive saloon in the S-Class segment. All EQS models have an electric powertrain (eATS) at the rear axle, while the versions with 4MATIC also have an eATS at 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 modular drive concept allows a wide range of maximum total drive powers from 245 to 385 kW. A performance version with up to 560 kW is being planned. Depending on the size of the battery and the vehicle equipment and also configuration, WLTP ranges of up to 780 kilometres are possible.

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 EQS, Mercedes-Benz uses a so-called pull-in winding for a particularly strong magnetic field. The engine is said to be 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 drive philosophy of the EQS. This includes a sophisticated thermal concept with some special features. A so-called 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 EQS 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 push or braking operation. 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. On top of this there is DAuto: here deceleration of up to 5 m/s² is achieved, 3 m/s² of which is due to recuperation (2 m/s² via the service brakes). The recuperation power of the all-wheel drive versions is up to 290 kW[1], and for rear-wheel drive vehicles, traction (and thus driving stability) is the limiting factor.

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 - pure one-pedal driving.

4MATIC models: infinitely variable distribution of the drive torques
In the models with 4MATIC, the Torque Shift function intelligently and continuously distributes the drive torques between the front and rear axles. It thus ensures the use of the most efficient eATS in each case, as these can be regulated independently of each other. The required drive torque at the wheels is checked 10,000 times per minute and set if necessary: The reaction is thus much faster than would ever be possible with a mechanical all-wheel drive.

Extensive testing: special test benches at Mercedes-Benz
On its way to series production, the EQS covered around five million test kilometres, including at the Test and Technology Centre (PTZ) in Immendingen. The systematic validation of the overall vehicle serves to guarantee the high quality standards and is one of the extensive measures in the development process of every Mercedes-Benz model series. Stations included tough winter tests in Scandinavia, chassis and powertrain tests on proving grounds, public roads and on the high-speed test track in Nardò, as well as integrated complete vehicle heat testing in Southern Europe and South Africa. The EQS was also on the road for test drives in China, Japan, Dubai and the USA.

In the process, it completed the same demanding testing program as any other vehicle that can proudly wear a star. In addition, a number of tests were carried out specifically for electric cars, covering important development priorities such as range, charging and efficiency. Of course, special attention was paid to the e-drive and the battery.

In addition, there were several million test kilometres on a total of more than two dozen test benches in Stuttgart-Untertürkheim and at the development site in Nabern. Testing takes place on pure eATS test benches, where the current comes from a special direct current source, a so-called battery simulation, and on eDrive test benches: Here, the testing also includes the battery and the complete charging components of the vehicle. The track profile/test bench profile was modified compared to the combustion engines, for example to take into account the torque load on the transmissions in both directions - a special load case determined by the high recuperation power. In addition, there is the special hot/cold testing of the power electronics.

[1] This value refers to the electrical power fed into the electric battery due to recuperation. Deviations are possible