Mercedes-Benz S 400 HYBRID

Driving on the Road to the Future

The year 2009 proved like a turning point in the history of the automobile. This year we have witnessed more hybrid models than ever, either being released on the market or announced as in development phase. The cars of tomorrow will be more efficient than we could expect. Mercedes, as always, is writing its own page of history with its S Class exponent of efficiency, the S 400 HYBRID model.

Mercedes-Benz S 400 HYBRID is the first passenger car model with hybrid drive introduced by Mercedes.  At the basis of the new S 400 HYBRID has stood the Mercedes S 350 model. But the Mercedes S 400 HYBRID is not just another version of S 350 since there were a lot of modifications that turned it into a totally new car like: an extensively modified drive train, a further development of the 3.5 V6 petrol engine plus some extras: an additional magneto-electric motor, the 7G-TRONIC seven speed automatic transmission designed and configured for the hybrid module, all the necessary operating and control electronics, the transformer and a high voltage lithium-ion battery. As you can see the Mercedes engineers have been quite busy. But the best part of this is the result which deserves a closer look. The reason can be found in the way they combined all the extras not only to achieve a more efficient car but also a more enjoyable one. This is the most amazing part of all. But how did they do it?

Mercedes engineers have designed a compact hybrid module in the form of a disc shaped electric motor that acts both as starter and a generator. This system offers a double benefit saving fuel and increasing the driving enjoyment at the same time, as the electric motor of the S 400 HYBRID backs up the petro engine with an additional torque of up to 160 Nm during the high consumption acceleration phase providing a booster effect. This means that the electric motor helps at achieving a better acceleration while using less fuel. This is the kind of feature that any driver would love.

If you would expect to find a start/stop function as a complementary way to increase this model’s efficiency, well, you are right. The Mercedes S 400 HYBRID does have a convenient start/stop function which turn off the engine while is the car is standing still. So no more fuel consumption at traffic lights. Green light? No problem! As soon as you want to set the car on the move again, the electric motor restarts smoothly the main power unit. By using this approach Mercedes succeeded to contribute to the fuel economy of the S 400 HYBRID and also minimizing emissions during the start phase.

When the brakes are used the electric motor of the S 400 HYBRID acts as a generator and recovers braking energy through a process of recuperation. Practically braking is smooth and progressive due to the way in which the electric motor supplements the braking effect of the combustion engine and the wheel brakes. Mercedes used a highly efficient lithium-ion battery to store the recuperated energy. This complex system is managed by a high-performance control unit, which just like the lithium-ion battery is located in the engine compartment.

At the heart of the Mercedes-Benz S 400 HYBRID system: The lithium-ion battery

Mercedes-Benz S 400 HYBRID has a very compact and highly efficient hybrid drive system which is powered by a new high voltage lithium-ion battery specially developed for automotive use, and it is also the first such unit worldwide to be introduced in a series production vehicle. This unit has several major advantages over conventional nickel/metal hybrid batteries such as: a higher energy density, a better electrical efficiency, more compact dimensions and a reduced weight. Since Mercedes engineers have found a way to install it in a space saving manner in the engine compartment where it takes the place of the conventional starter battery the interior space and boot capacity remain unchanged.

This lithium-ion battery that Mercedes used for the S 400 HYBRID has many tasks to support: it stores energy for the electric motor and the electrical refrigerant compressor and at the same time it is connected to the 12 Volt onboard network via a DC transformer to supply power to other consumers such as headlamps and various comfort features. The battery system developed for the Mercedes S 400 HYBRID is more than just a cell block packing lithium-ion cells. It has an electronic cell monitoring system, a baterry management function, a high strength housing, a cooling system that consists of a cooling gel, a cooling plate together with a coolant feed and a high voltage connection.

The Engine of the Mercedes-Benz S 400 HYBRID

The 3.5 litre V6 petrol engine with variable valve control has been reengineered and improved. Mercedes engineers took into account the advantages offered by the Atkinson principle where the expansion phase is longer than the compression phase. Therefore in the case of the S 400 HYBRID the intake valve of the engine is kept open slightly longer between the intake and the compression phases, which improves the engine’s thermal efficiency  and also reduces the specific fuel consumption and untreated emissions. There are many new elements regarding the engine that equips the S 400 HYBRID like a new cylinder head, different pistons and a modified camshaft with different camshaft control which lead to obtaining an increase in output power of 7 hp up to 279 hp while reducing fuel consumption at the same time. Impressive, isn’t it?

The electric motor of the Mercedes-Benz S 400 HYBRID

The overall efficiency of the Mercedes S 400 HYBRID model is further improved by the compact disc shaped electric motor installed cleverly between the combustion engine and the 7G-TRONIC 7 speed automatic transmission. The 3 phase AC external rotor magneto motor develops a peak output of 20 hp and a starting torque of up to 160 Nm. While the power might not be impressive, the maximum torque surely is and do not forget that this compact motor operating at voltage of 120 Volts acts both as a starter and generator practically carrying out both functions of these conventional units.

The most impressive of all things Mercedes has done on their S 400 HYBRID is the way in which they finely tuned the contribution of the electric motor not only to fuel efficiency but also to a lot of other aspects of driving this car which brings in more comfort and a special driving experience. The interaction of the electric unit with the combustion engine became so sophisticated because Mercedes did not aim only to put an electric motor next to the classical propulsion solution but also to make a positive experience in terms of the S 400 HYBRID agility. They found a solution for the disc shaped motor to effectively dampen torsional vibrations in the drive train reducing the level of noise and vibrations in the interior of the car.

More agility and more comfort together with improved efficiency, is what builds up the essence of the Mercedes-Benz S 400 HYBRID.

Mercedes-Benz S 400 HYBRID benefits from a boost effect for even more driving pleasure

The electric motor of the S 400 HYBRID has a great feature that contributes significantly to the driving pleasure and overall car dynamics. Since it is capable of delivering its maximum torque of 160 Nm right from the beginning of the acceleration phase, it successfully backs up the main engine giving a boost effect right at the point where the combustion engine needs it most and that is at low engine revs. But the extra torque of the hybrid module can also be felt during subsequent acceleration phases, which means that the driver can take full advantage from the interaction between the two units in the form of a more powerful acceleration response.  Usually for a better acceleration in a normal car you would need a more powerful engine which generally is translated into higher fuel consumption. In the case of the Mercedes-Benz S 400 HYBRID, however, it’s exactly the opposite: you get better acceleration but without an increase in fuel consumption.

When it comes to performance figures, the S 400 HYBRID accelerates from 0 to 100 km/h in just 7.3 seconds and reaches a top speed of 250 km/h (electronically limited). If it would come to a little car compare between the S 400 HYBRID and the S 350, you probably would be amazed to find out that S 400 HYBRID has a fuel consumption which is better than that of its brother by 2.2 litres while the CO2 emissions are reduced by 21 percent.

Why the Mercedes-Benz S 400 HYBRID ECO start/stop system is an intelligent electronic partner?

Since it is an S Class model this goes without saying that such a must like a start/stop system for the S 400 HYBRID could only be extremely comfortable and efficient. But it is smart too. This one already switches the engine off when the vehicle is coming to a stop and rolling with less than 15 km/h. Either by releasing the brakes or by touching the acceleration pedal the engine wakes up again and it does it in a smooth way with minimum vibrations and jolts for the maximum comfort of its occupants.

Being electrically powered, both steering and climatic comfort remain unchanged during the time the main engine is switched off automatically.  The intelligent control unit is able to detect whether the driver is executing a turning or parking manoeuvre. In this case the automatic start/stop function is temporarily deactivated.

When braking the Mercedes-Benz S 400 HYBRID recovers energy

Braking generates electric power for the battery. When the Mercedes-Benz S 400 HYBRID decelerates the kinetic energy of the car is converted into electrical energy which is stored in order to be made available when required.

The electric motor assists the engine braking effect in two smooth stages:

1. On the overrun with no braking action the electric motor acts as a generator and begins to recuperate energy
2. As soon as the driver lightly operates the brake pedal the generator output is increased proportionally and perceived as heavier deceleration by the driver.

The wheel brakes are activated only in the case of a heavier deceleration and when more brake pedal pressure is applied. In this way the S 400 HYBRID achieves two things at once: first, it generates more electrical energy, and secondly it saves wear and tear on the hydraulic braking system. For best results a new braking system with a new brake module has been made for the S 400 BlueHYBRID.

Monitoring the status of the hybrid system of the Mercedes-Benz S 400 HYBRID

The instrument cluster of the Mercedes Benz S 400 HYBRID has also a separate, centrally positioned display showing the energy flow during boost and recuperation phases as well as the battery charge status allowing the driver to monitor the current status of the hybrid system functionality at all times.

Mercedes-Benz S 400 HYBRID special safety and reliability features

It is a common thing for Mercedes to show a special attention when it comes to the safety their cars provide. And the S 400 HYBRID makes no exception from this rule. The car does not only comply with all crash test requirements but it is also built to ensure the best possible safety for the electrical components.

The hybrid technology of the S 400 HYBRID features an extensive 7 stage safety concept:

1. In order to eliminate confusion all the wiring is color coded
2. The entire system benefits from comprehensive contact protection by means of generous insulation and special designed new dedicated connectors
3. The innovative lithium-ion battery of the S 400 HYBRID has a high strength steel housing. Besides that feature the battery cells are placed in a special gel to dampen  any jolts or knocks while an internal electronic controller monitors continuously safety of the battery and also signals any possible malfunctions.
4. All high voltage components are connected by an electric loop. In the event of a malfunction the high voltage system is automatically switched off.
5. In this case all the high voltage components are de-energized while the battery remains charged so that the engine can be restarted at any time.
6. In case of an accident the entire high voltage system is completely switched off in just fractions of a second.
7. The functioning of the system is continuously monitored for short circuits.

All of the above safety features of the Mercedes Benz S 400 HYBRID are packed in a compact and modular design which both saves space and mass the overall system weighing only 75 kilograms.

Prior to entering the production phase the Mercedes specialists subjected 200 pre-series units of the S 400 HYBRID to extended trials around the globe. You could gain a lot more confidence in this model if you would know that these test versions of the S 400 HYBRID covered almost ten million kilometers in extreme weather conditions like extreme cold and extreme heat, in all possible driving conditions like full acceleration and in stop and go traffic as well as in daily driving conditions.

After all these intensive tests the drive system of the S 400 HYBRID proved to be robust, reliable, efficient and suitable for a daily use with no reserves. Only after this extreme tests the S 400 HYBRID entered production, which makes it a wise choice not only in terms of efficiency and comfort but in terms of reliability as well.

Mercedes Benz has definitely made a further step on the Road to the Future with this S 400 HYBRID model. Packing together ultimate elegance, comfort, driving dynamics and fuel efficiency with a reliable hybrid system makes the S 400 HYBRID a combination hard to resist and also builds up the image of the complete car of the future.