It’s the question that’s been asked for years. If diesels give such good fuel economy, and petrol hybrids give such good fuel economy, why not produce a diesel hybrid? Amongst the first is the coming Mercedes-Benz E 300 BlueTec Hybrid.

The E 300 BlueTEC Hybrid pairs a 2.2-litre four-cylinder diesel engine developing 150 kW (204 hp) with a powerful hybrid module. Its 15kW electric motor, positioned between the internal combustion engine and the 7-speed automatic transmission, assists the diesel engine when the car is accelerating. It is also used to capture braking energy (regeneration). Finally, the vehicle can also drive on electric power alone.

The E 300 BlueTEC Hybrid consumes 4.1 litres of fuel per 100 kilometres (CO2 109 g/km). It will be launched at the end of 2011.
Engineering
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The technical basis for the E 300 BlueTEC Hybrid is the E 250 CDI with a four cylinder diesel engine developing 150 kW (204 hp).

For the new hybrid model, the Mercedes-Benz engineers have used the fuel-efficient 4-cylinder diesel engine in combination with a compact electric motor developing 15 kW. The electric motor draws its energy from a high-voltage, lithium-ion battery, which has already proven itself in the S 400 Hybrid.

Despite the high overall output of up to 165 kW (224 hp) and a torque of over 580 Nm, the E 300 BlueTEC HYBRID consumes no more than 4.1 litres of fuel per 100 km (NEDC), equivalent to CO2 emissions of 109 g/km. Fuel consumption is therefore on a par with extremely efficient small cars, while the hybrid drive system outperforms current six cylinder diesel engines.

Operational strategy

The operational strategy incorporates the following principal features:

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Even at low revs, the electric motor assists the diesel engine with high torque. The result is excitingly high, clearly noticeable agility.

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When driving for longer distances or on the motorway, the intelligent electronics recognise the driving situation and automatically adjust the load point of the internal combustion engine to achieve a lower specific fuel consumption, thereby helping to save fuel and reduce emissions.

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Thanks to a clutch between the engine and the electric motor, the E 300 BlueTEC Hybrid can cover short distances at speeds of up to 35 km/h using electric drive alone. Consequently, the internal combustion engine does not even need to be started in most cases when driving in stop-and-go urban traffic or manoeuvring in parking spaces.

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The internal combustion engine in the new diesel hybrid is switched off as soon as the vehicle starts to coast down from 80 km/h; in this case, the electric motor just keeps the road speed constant. [Maybe they mean the rate of coast down is reduced? – Ed]

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The diesel engine is started smoothly as soon as the driver releases the brake pedal, presses the accelerator pedal or reaches a defined limit speed during acceleration.

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Regeneration starts as soon as the driver releases the accelerator pedal –in this case, the electric motor functions as an alternator and converts the kinetic energy into electrical energy, which is stored in the high-voltage battery. Even when braking, part of the energy is converted into electrical energy.

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The air conditioning compressor and the steering are powered electrically, meaning that both systems operate even when the internal combustion engine is not running. What's more, none of these measures restrict boot space and variability in the slightest, as all of the hybrid technology, including the high-voltage battery, is housed in the engine compartment.