|The S 400 BlueHYBRID with Li-ion battery pack. Click to enlarge.|
Daimler will launch its first hybrid-drive passenger car model—the Mercedes-Benz S400 BlueHYBRID (earlier post)—in the summer of 2009. The S 400 hybrid is one of seven hybrid models Daimler announced in September 2007 that will be rolled out over the next few years.
The S400 BlueHYBRID combines a modified 3.5-liter V6 gasoline engine that delivers 205 kW (279 hp) of power with a 120V, 15 kW electric motor and a starting torque of 160 Nm (118 lb-ft) of torque. The combined system delivers power of 220 kW (299 hp) and a combined maximum torque of 385 Nm (284 lb-ft), with fuel consumption of 7.9 L/100km (30 mpg US) and CO2 emissions of 190 g/km.
The S 400 BlueHYBRID accelerates from zero to 100 kph in 7.2 seconds, and has an electronically governed top speed of 250 kph (155 mph). The fuel consumption betters that of the conventionally powered S 350 by up to 2.2 liters per 100 kilometers. CO2 emissions are reduced by 21%.
The S 400 BlueHYBRID is the first series-production model to be equipped with a Li-ion battery. Continental and Johnson Controls-Saft (JCS) are teaming on the pack, with JCS is providing the cells. Continental is the pack integrator and will also supply power electronics: the inverter and the DC/DC converter. (Earlier post.)
The new Mercedes-Benz S 400 BlueHYBRID is based on the S 350, and features an extensively modified drive train. This encompasses a further development of the 3.5-liter V6 gasoline engine, the additional magneto-electric motor, a 7G-TRONIC seven-speed automatic transmission specially configured for the hybrid module, the necessary operating and control electronics, the transformer and a high-voltage lithium-ion battery.
The compact hybrid module is a disc-shaped electric motor that also acts as a starter and generator. The hybrid module also has a start/stop function, and supports regenerative braking.
The lithium-ion battery not only stores energy for the electric motor, but is also connected to the 12-Volt onboard network via the transformer to supply power to other standard consumers such as the headlamps and comfort features. The newly designed battery system consists of the cell block with its lithium-ion cells and the cell monitoring system, the battery management function, the high-strength housing, the cooling gel, the cooling plate, the coolant feed and the high-voltage connector.
The 3.5-liter V6 gasoline engine with variable valve control makes use of the advantages offered by the Atkinson principle, where the expansion phase is longer than the compression phase. The intake valve is kept open slightly longer between the intake and compression phases, which improves the engine’s thermal efficiency while reducing the specific fuel consumption and untreated emissions. A new cylinder head, different pistons and a modified camshaft with different camshaft control increase the output by 5 kW (7 hp) to 205 kW (279 hp) while reducing fuel consumption at the same time.
On rural journeys and on highways, the S 400 BlueHYBRID achieves a further efficiency improvement by moving the operating point of the gasoline engine to produce a lower specific fuel consumption. The extremely high start-off torque made possible by the boost effect of the electric motor gives the driver a strong feeling of powerful acceleration, while fuel consumption and emissions are reduced.
The current converter is located in the space formerly occupied by the starter. As the control electronics heat up as a result of electric currents measuring up to 150 amps, the system is equipped with its own, additional low-temperature cooling circuit.
Mercedes-Benz engineers placed the transformer in the right front wheel arch, where it facilitates the exchange of energy between the 120-Volt high-voltage network and the 12-Volt onboard network, and also allows the option of emergency starting with jump leads if the standard battery should lose its charge. To ensure a consistently high level of electrical efficiency, the transformer is likewise cooled by a low-temperature circuit.
The 12-Volt lead/acid battery is installed in the trunk, and not only supplies the standard consumers but also the monitoring system for the high-voltage components with energy. Because of its interaction with the lithium-ion battery, it is smaller in size and lighter than usual.
Mercedes-Benz developers also adapted the 7G-TRONIC automatic transmission to suit the hybrid drive, with newly programmed software for the transmission management system. A newly developed auxiliary oil pump ensures reliable lubrication of the transmission even during phases when the internal combustion engine is switched off.
This system is managed by the modified high-performance engine control unit. This unit distinguishes between operating conditions such as city traffic, rural journeys, highway driving or slow manoeuvring.
The driver is also able to monitor the status of the hybrid drive system visually. The instrument cluster has a separate, centrally positioned, display showing the energy flow during boost and recuperation phases, as well as the battery charge status.
The hybrid technology of the S 400 BlueHYBRID is equipped with an extensive 7-stage safety concept:
All the wiring is color-coded to eliminate confusion, and marked with safety instructions. This prevents assembly errors in production, and makes the regular quality checks easier to carry out.
Contact protection for the entire system by means of generous insulation and newly developed, dedicated connectors.
A package of safety measures for the Li-ion battery. This battery is accommodated in a high-strength steel housing, and also secured in place. Bedding the battery cells in a special gel effectively dampens any jolts and knocks. There is also a blow-off vent with a rupture disc and a separate cooling circuit. An internal electronic controller continuously monitors the safety requirements and immediately signals any malfunctions.
Separation of the battery terminals, individual safety-wiring for all high-voltage components and continuous monitoring by multiple interlock switches. This means that all high-voltage components are connected by an electric loop. In the event of a malfunction the high-voltage system is automatically switched off.
Active discharging of the high-voltage system as soon as the ignition is switched to “Off”, or in the event of a malfunction.
During an accident, the high-voltage system is completely switched off within fractions of a second.
The system is continuously monitored for short circuits.
The additional weight of the overall system is only 75 kilograms (165 pounds), including the comprehensive safety systems. Payload remains unchanged at 595 kilograms (1,312 pounds).
The S 400 BlueHYBRID is produced at the Sindelfingen plant, together with the other S-Class models. The gasoline engine, 7G-TRONIC automatic transmission and electric motor are first put together to form a hybrid module, then delivered to the production line as a unit. The market launch in western Europe is planned for June 2009; China is expected to follow in August 2009 and the USA in September 2009.