slk55er

Here is my take of a comparison of the technology of the Mercedes Formula 1 hybrid engine and the technology transfer carried over to the mild-hybrid vehicles with the M256 engine. This includes some “450” series vehicles with the EQ Boost engine (CLS450, GLE450) and the AMG “53” series vehicles with the EQ Boost+ engine (including my CLS53, the E53 Cabriolet, Coupe and Sedan, and the GT53.) This technology and design will likely appear in most Mercedes model lines. I expect that I have missed or misrepresented some important items — corrections, clarifications and additions are welcome, please.

FORMULA 1

The 2019 F1 1.6 Liter engines use an ERS (Energy Recovery System) which includes an MGU-K (Motor Generator Unit - Kinetic) and MGU-H (Motor Generator Unit - Heat.) Note: the MGU -H will be eliminated in the 2026 engines.

The MGU-K uses a motor/generator in conjunction with a Li-ion battery pack to convert kinetic energy of the vehicle during deceleration and braking into chemical energy stored in the battery. The MGU-K unit is connected to the crankshaft of the engine via a gear set. Maximum rpm of the MGU-K is 50,000 rpm and it can supply an additional 161hp when acting as a motor to augment the turbocharged gasoline engine. Mercedes states that “Each F1 major braking generates enough energy to boil four household kettles (of water.)”

The MGU-H can also charge the LI-ion battery via a motor/generator which is spun by the exhaust and can act in motor mode to spin the turbocharger to eliminate turbo lag. The MGU-H motor/generator is installed between the intake compressor and exhaust turbine sides of the turbocharger. Mercedes calls this an “Electric Turbocharger.” It has a maximum speed of 125,000rpm!

M256 ENGINE with EQ Boost and EQ Boost+

The new 3-Liter straight-6 M256 engines in the mild-hybrid vehicles employ much of the technology and experience from Formula 1 — not necessarily directly, but similar approaches used to yield similar benefits.

Kinetic energy recovery is provided by the flywheel/motor/generator/starter which Mercedes calls an Integrated Starter Generator (ISG). This unit is built by Mitsubishi and is installed between the engine and transmission, the traditional location of the flywheel. It can provide 21hp and 180lb-ft of torque when acting as a motor powered by a 48volt Li-ion battery which is charged by the ISG during deceleration and braking. This hybrid system using the ISG is called “EQ Boost” by Mercedes.

The kinetic energy of the vehicle is converted to stored chemical energy in the 48volt Li-ion battery for later use by the ISG acting as a motor. (See the Footnote on “Regenerative Braking.”

On the AMG version of the M256 “53” series engines there is no “heat recovery” system per se like the MGU-H on the Formula 1 cars. However, in addition to the ISG, there is a unit made by BorgWarner which they call “eBoost.” The hybrid engine with the ISG and this unit is called “EQ Boost+” by Mercedes.

There is an excellent description of the BorgWarner unit at

https://www.youtube.com/watch?v=Asxi...ature=youtu.be

The Formula 1 MGU-H motor/generator is installed between the two sides of the turbocharger as described above. However, the eBoost unit is a separate, electrically-driven (48volt) compressor/supercharger that forces air into the intake side of the turbocharger to spin it up quickly and to provide additional pressure-boosted air into the intake manifold, primarily at low engine rpm. A bypass valve opens and closes depending on engine speed and throttle position to provide optimal benefits. I have not seen it mentioned in any descriptions, but it seems that this unit would also provide a beneficial vacuum effect on the exhaust turbine side of the turbocharger when it is spun up by the eBoost forced air on the compressor side.

There is an excellent description by AutoWeek of the M256 engine and with its hybrid components at

https://autoweek.com/article/technol...en-well-see-it

SUMMARY

I hope this is a reasonably accurate description of these amazing engines and the similarities and differences. Here is a quote from one of Mercedes’ F1 pages:

“While it's difficult to envisage the advanced Hybrid technology of these monstrous F1 beasts trickling down to cars on the road, they are very much helping test and develop the technology of the future - what we'll see in the Hybrid Mercedes-Benz cars and AMG models being driven in years to come.

“After all, it's the perfect training ground, right? Putting this Hybrid technology through its paces at some of the toughest race tracks in the world, at ridiculously-high speeds and in intense conditions. So, while it isn't always obvious, the influence F1 has on the automotive industry is significant and as relevant as it has ever been.”

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Footnote on “Regenerative Braking”:

There has been some discussion on whether the kinetic energy recovery by the ISG qualifies as “regenerative braking.” A Mercedes Customer Help page states: “For regenerative braking, the kinetic energy of the decelerating vehicle is absorbed by the electric motor to generate a brake torque. The generated electrical energy is then fed to the high voltage battery for storage…If the required total braking torque can be achieved using regenerative means alone, then none of the braking is done hydraulically. In this case deceleration is achieved solely by using the electric motors to generate electricity.”

Perhaps on our street vehicles there is not enough electric-motor brake torque provided to qualify as “regenerative braking” — perhaps in the Mercedes vernacular we have “Electric Drive Recuperation” as identified in the B-class descriptions.

I do know that the “POWER/CHARGE” display on my CLS53 shows half-charging during deceleration and then instantly shows full-charging when the brakes are applied. It seems that some software is programmed to increase the charging level when the brake pedal is depressed. In my perspective, this constitutes “regenerative braking” which Wikipedia defines this way: “Regenerative braking is an energy recovery mechanism which slows a vehicle or object by converting its kinetic energy into a form which can be either used immediately or stored until needed….The most common form of regenerative brake involves an electric motor as an electric generator.” At least for now in discussion with my motorhead and racing friends, the ISG function is close enough to be called “regenerative braking.”

slk55er

Note that the MGU-H has been removed from the 2021 Formula 1 engines. Autosport magazine says this about eliminating the MGU-H...

"(this) is a "backwards step" for Formula 1's 2021 engine regulations, according to Mercedes' powertrain boss Andy Cowell."

Note: The MGU-H may not have been removed in 2021 but is due to be eliminated for the 2026 season along with increase output from the MGU-K.

Louka 11

Hi SLK55er, I am new to the forum and came across your post.
Thank you very much for the detailed explanation. I have been looking for ages to find an article about the technical differences between the CLS 450 and 53 but couldn't find any. This is perfect

Do you think it's possible to add a "BorgWarner's eBooster" to the 450 in order to improve its low rpm lag?

Cheers

slk55er

Hmm. I think this would be very difficult. Not only would there be physical equipment to locate and ducting to install, there would likely be some software changes and perhaps some additional circuitry involved. I'd encourage you to enjoy your 450 as is and use Sport Mode whenever you need additional performance.

Louka 11

Thank you very much