The components of the S 500 PLUG-IN HYBRID. Click to enlarge.

The S 500 PLUG-IN HYBRID is the first luxury saloon with the performance of a V8 and the fuel consumption of a compact model. The greatest challenge in this is to translate efficiency into superior performance. In this respect there is a highly interesting parallel with our successful Formula 1 racing car, which likewise has a turbocharged V6 engine and a high-tech hybrid drive.

—Prof. Dr. Thomas Weber, member of the Daimler Board of Management responsible for Group Research and Mercedes-Benz Cars Development

All three hybrid S-Class models have environmental certificates documenting the models’ environmental performance from development through to recycling, across the entire lifecycle; the performance is certified to internationally recognized standards by independent experts. Regarding CO₂ emissions, the certificate of the S 500 PLUG-IN HYBRID states:

Over the entire lifecycle, comprising manufacture, use over 300,000 kilometers [186,411 miles] and recycling, clear advantages result compared with the S 500. External charging with the European electricity mix can cut CO₂ emissions by some 43 percent (35 tonnes). Through the use of renewably generated hydroelectricity a 56 percent reduction (46 tonnes) is possible.

Battery and charging. The 8.7 kWh Lithium iron phosphate battery pack is water-cooled, weighs 114 kg (251 lbs) and occupies a volume of 96 liters (3.4 ft³). The pack uses a modular design with 120 serially connected VDA single cells (22 Ah/cell) and supplies rated voltage of 396 V, which can vary between 270 V and 430 V depending on the operating point.

To ensure highest levels of crash safety and dynamic handling and also maximum trunk space, the housing is made of die-cast aluminium and the high-voltage battery is located in the rear of the vehicle above the rear axle. The S 500 PLUG-IN HYBRID thus takes first place among the plug-in hybrids in terms of trunk capacity (395 liters, 14 ft³) and luggage compartment accessibility.

The high-voltage battery can be charged using a 3.6 kW on-board charger. The unit is permanently installed in the vehicle and charges single-phase up to 16 A. The connection for the charging cable is located under a flap in the rear bumper underneath the tail light on the right-hand side. An automatic lock ensures that the cable cannot be separated from the vehicle by unauthorized persons. The new S-Class can be charged in two hours anywhere in the world, e.g. at a wallbox or a charging pole (400 V, 16 A). Alternatively, charging via house connection is also possible. Depending on the connection a charge time e.g. of two hours and 45 minutes can be attained (with 230 V and 13 A).

Mercedes-Benz has also announced it will test inductive charging with the S 500 PLUG-IN HYBRID in order to develop a genuine S-Class solution, in terms of comfort and ease of operation. (Earlier post.)

Electric motor. The electric motor has been further developed from the previous hybrid vehicles. The modular design enabled longitudinal scaling from 6 to 9 rotor plate packs. Despite its compact design the electric motor delivers an output of up to 85 kW and torque of up to 340 N·m. The permanently excited synchronous motor is fully integrated into the hybrid transmission. Stator and rotor of the internal rotor motor are cooled by transmission oil.

Transmission. The hybrid transmission is based on the 7G-TRONIC PLUS 7-speed automatic transmission. The plug-in-hybrid system in the S-Class is based on the Mercedes-Benz parallel hybrid modular system. The common system-specific feature is the additional clutch integrated between combustion engine and electric motor.

On the one hand, it decouples the combustion engine during purely electric operation; on the other hand, if the combustion engine is employed it affords the possibility to move off drawing on the performance of a wet start-up clutch. The clutch then substitutes for the torque converter and requires no additional space owing to its complete integration in the torque converter housing.

Power electronics and voltage transformer. The high-voltage battery feeds the electric motor through a water-cooled DC/AC converter, the power electronics. This too is a component from the Mercedes-Benz modular system and was first developed for the technology platform SLS AMG E-CELL, which went into production as the SLS AMG Coupé Electric Drive. The integration of the power electronics with an electric motor optimized for plug-in operation enables top performance in terms of comfort and output over the entire operating range.

The power electronics operate with a rated voltage of 325 V and supply 350 A maximum current, at the same time determining the position and status of the electric motor by means of a rotor position sensor as well as various component temperatures. Depending on operating situation, actuation of the electric motor is guided by the rotational speed or the torque, within the permissible limits. To optimise the effort for wiring, packaging and cooling, the DC/AC converter has been integrated into the engine space. A separate DC/DC converter at the rear of the vehicle supports the 12 V on-board power supply with an output of up to 3 kW.

Engine. For inherent design reasons, electric motors and combustion engines have different torque curves, which can complement each other. An electric motor makes its peak torque available as soon as it starts and can therefore compensate an internal combustion engine’s weak torque in the low rev range.

The 3.0-liter V6 biturbo comes from the M276 engine family and features the BlueDIRECT injection and combustion system. Cylinder heads and block are made of aluminium. To reduce friction, the cylinder barrels are coated with the aid of the innovative NANOSLIDE process. Other engine characteristics include four valves per cylinder, a particularly quiet chain drive system with silent chains and two camshaft adjusters each for the intake and exhaust sides.

The third-generation direct injection system has a fuel pressure of 200 bar and spray-guided multiple injection with piezo injection nozzles. The on-demand vane-type oil pump cools and lubricates the engine depending on engine load and engine speed. The volume control distinguishes between a low and a high pressure level and adjusts the volume flow as required. The weight of the components of the water circuit could be reduced through the systematic use of plastic. In an extended temperature range the heating supply for the interior is preferentially served. The desired temperature is thus very quickly reached during the warm-up phase. An electric heater element ensures rapid warming of the car interior also during electric driving.

Depending on the power requirement and battery charge status, the S 500 PLUG-IN HYBRID drives in purely electric mode. Moving off from stationary also takes place in electric mode. This “silent start” is part of the driving experience and perfects the start/stop procedure, e.g. with noiseless starting at traffic lights. In transmission mode “S” electric driving can be excluded.

If more power is required, the internal combustion engine is started by means of a process developed specifically for hybrid drives with direct-injection gasoline engines, and then is quickly and conveniently engaged by actuating the clutch, depending on operating conditions. The Mercedes-Benz starting procedure combines appropriate actuation of the starter with the ECO start/stop function of direct-injection gasoline engines, in which starting is optimized by well-targeted injections and ignitions.

This and the simultaneous actuation of the clutch, with its additional accelerating effect on the starting engine, make an extremely rapid start possible compared with a conventional starting procedure, ensuring a good transition from electric driving.

The internal combustion engine is shut off as often as possible for purely electric driving. But even so, in combination with the electric motor it delivers a total torque on the level of an eight-cylinder drive when such power is required.

2nd generation recuperative braking system. The largest potential for lowering the energy consumption of hybrid drive systems lies in maximizing energy recovery during coasting and braking. Upon depressing the brake pedal the deceleration is initially effected by the electric motor and not by the disc brakes. The hybrid models of the new S-Class are the first to use a second-generation recuperative braking system, which is designed to ensure an unnoticeable overlapping of the conventional mechanical brakes and the electric braking performance of the electric motor in generator mode.

The driver’s desired braking power is recorded by a pedal-travel sensor. The deceleration is dependent on the driving condition and is split into a recuperative brake-force portion and a portion to be supplied by the wheel brakes. The brake pressure on the rear axle is controlled dependent on the current recuperation potential of the drive system.

In addition, the combustion engine is switched off any time the vehicle is coasting, and its drag torque when rolling is used by the electric motor as recuperation torque. However, without depressing the brake pedal no additional deceleration torque is provided for charging the battery, and the vehicle can “sail”.

Radar-based recuperation. Via a noticeable double impulse in the haptic accelerator pad, the driver receives a recommendation to take the foot off the accelerator pedal. In this way, the combustion engine can be switched off and disconnected from the drive train, with the vehicle switching to sailing mode or radar-based recuperation mode. The double impulse is deployed based on the speed of the vehicle and the distance from and relative speed to a vehicle in front. Radar-based recuperation adjusts the recuperation based on the traffic conditions detected via the DISTRONIC PLUS/CPA sensor. If no vehicle is detected in front, or a distant or accelerating vehicle is detected, automatic sailing mode is implemented. When the system detects that a slower moving vehicle is being approached, a target vehicle is slowing down, or the distance to the target vehicle is reducing on a downhill stretch, stronger deceleration is implemented by increasing recuperation. Thanks to a targeted choice of either stronger or longer recuperation or sailing mode, depending on traffic condition, fuel consumption is improved and electric range is increased. In actual traffic, this results in fuel savings of around 3% - 5%. This has comfort benefits for the driver, who is relieved of the strong due to support in deceleration mode during distance and speed control tasks. In sailing mode, the vehicle also feels lighter and more agile. Click to enlarge.

Haptic accelerator pedal. The plug-in hybrid features a haptic accelerator pedal. In the background, depending on the chosen operating mode, the intelligent operating strategy automatically selects the ideal combination of internal combustion engine and electric motor and in so doing not only adapts its strategy according to the charge status of the battery, but also adjusts it according to the traffic or route. The driver can also intervene manually and with the aid of four operating modes and three transmission modes regulate the hybrid interplay themselves.

The haptic accelerator pedal can signal via a double impulse when drivers should take their foot off the accelerator for sailing and recuperating. During electric operation it can supply the driver with feedback on the switch-on point of the combustion engine. The energy flow is shown in all operating states in the instrument cluster and in the central display, if this is selected by the customer.

Extended pre-entry climate control. The standard equipment in the S 500 PLUG-IN HYBRID is extensive and includes a world premiere: the extended pre-entry climate control. This is target-value controlled, meaning that at the start of the journey the S-Class is air conditioned to the preset temperature if the driver has entered the departure time, via Mercedes connect me, for example.

This is possible due to the electrically driven refrigerant compressor and electric heating elements for the heated air. In addition to this, when preheating it is not just the interior air but also the seats, steering wheel and armrests in the doors and centre console which are heated, and when cooling the seat ventilation is also activated if the respective optional extra is on board.

Intelligent operating strategy. The intelligent operating strategy supports the driver to achieve the most efficient driving style. The control strategy, for example, seeks to ensure that the battery, if at all possible, is flat at the end of an uphill stretch so that it can be recharged going downhill. Another key point is the requirement that urban areas be reached with a fully charged battery, if possible, so that the vehicle can be operated in stop-and-go traffic electrically.

In the S 500 PLUG-IN HYBRID the energy management system basically covers these three areas:

• Route-based operating strategy. The route-based operating strategy takes the decision for the optimum sequence of operating modes for a route off the driver’s hands. If the exact destination is known because the relevant data has been entered into the navigation system, charge and discharge of the high-voltage battery are controlled to ensure the optimal use of energy on the overall route, for as much as 1,000 kilometers (621 miles). One objective is to use the battery’s energy content to drive uphill while recharging the battery through recuperation on the downhill stretch. The system uses data from the COMAND Online navigation system to calculate the recuperation potential of the road ahead. For example, the data provides information about the route profile and speed limits ahead in a one-meter grid for up to seven kilometres in advance.

  If on the other hand the destination is not known, an assumed route is taken as a basis using likely turn-offs. In this case the system computes the probability depending on the road category. If, for example, the hybrid vehicle is travelling on a motorway, the system assumes that it will remain on the motorway for the next seven kilometers (4.3 miles).

• Traffic-based operating strategy. In transmission mode E+, during electric operation the overrun torque is reduced to a minimum to enable sailing as often and as long as possible. However, heavy braking after a long sailing phase, or premature sailing resulting in the need to restart the engine, are counterproductive. Consequently, the system makes use of radar information in bumper-to-bumper traffic in order to get its bearings from the vehicle travelling ahead.

  The distance from the vehicle ahead and the speed difference are recognized with the aid of radar sensors. At exactly the moment when releasing the accelerator pedal would lead to optimally fuel-efficient “docking” onto the vehicle ahead, the driver receives a recommendation, in the form of a noticeable double impulse in the haptic accelerator pedal, to back off the accelerator. If the driver accepts the recommendation and electric operation is available, the combustion engine is switched off and disconnected from the drive system. The vehicle then sails. If the vehicle ahead reduces its speed or the gap becomes smaller for some other reason, radar-based overrun torque control sets in. Increased recuperation by the electric motor correspondingly changes the gap to the vehicle ahead – and recovers energy.

• Driver based: by way of three transmission modes

Four operating modes and three transmission modes. By means of operating mode and transmission mode switches next to the Controller on the center console it is possible to switch between four operating modes. A display in the middle of the instrument cluster tells which mode is currently selected. The four operating modes are:

• Hybrid: This standard mode offers hybrid driving. The extent to which the electric motor is used to optimize consumption, or with boost function for especially dynamic acceleration, depends—apart from the driving style—on the battery charge status and the chosen transmission mode. Three transmission modes are available in this operating mode and can be activated using the transmission mode switch:

  Transmission mode E (Economy) is standard; the electric motor is used for both the benefit of efficiency and for driving pleasure. A power reserve is retained for the electric motor so that maximum additional thrust can be provided.

  In transmission mode E+ (Economy +) the objective is maximum fuel economy; all features of the intelligent operating strategy are active in E+. The greatest possible advantage is taken of the hybrid’s energy efficiency. For example, the vehicle sails as much as possible during coasting, while energy is increasingly recuperated only upon approaching another vehicle travelling ahead. Transmission mode E+ additionally makes use of radar technology.

  In transmission mode S (Sport) the sporty features of the drive system dominate. The transmission selects the shift points to benefit agility. This mode does without purely electric driving. The larger amount of electrical energy available because of this is used for the electrically supported boost function.

• E-mode: In this operating mode the S 500 PLUG-IN HYBRID runs purely electrically as much as possible. To ensure that the driver does not inadvertently engage the combustion engine by stepping on the accelerator, the haptic accelerator pedal with pressure point is automatically activated in this mode. The combustion engine engages only when the driver overcomes the pedal’s distinct pressure point.

• E-save: Here the charge status of the battery is preserved as it was when this operating mode was activated. For example, a fully charged battery can be held available if purely electric driving in a big city is on the agenda later. Electric driving in especially favorable situations, for instance after brief stops, is still permitted, but is metered so that the charge status does not fall below the value set by pressing the button.

• Charge: Here the high-voltage battery is charged during vehicle operation with the aid of the internal combustion engine. Electric driving and boost operation are completely dispensed with. Under optimal conditions a run-down high-voltage battery can be fully charged in just about half an hour. As soon as the high-voltage battery is fully charged, the system automatically switches to E-save mode.

Warranty. In order to strengthen the customers’ trust in the new, innovative plug-in drive technology, for the S 500 PLUG-IN HYBRID Mercedes-Benz is for the first time issuing a warranty for the high-voltage battery and plug-in components (i.e., power electronics and electric motor, PEEM). This ensures that every technical malfunction within a period of six years after initial delivery or registration, or up to a mileage of 100,000 kilometers (62,137 miles), is corrected by Mercedes-Benz.