First test run of the MAHLE Range Extender

The 900 cm³ two-cylinder 4-stroke engine with a 0° / 180° firing order makes 30 kW with a maximum torque of 72 Nm at 2000 to 4000 rpm. The synchronous electrical machine delivers 55 kW (100 kW peak). The torque is via a two-speed reduction gearbox with a maximum of 120 km / h on the road. With dimensions comparable to those of a hand luggage, the entire unit is much more compact than the 1.2-litre, in-line, four-cylinder engine from the base vehicle Audi A1. This leads to a significant reduction in NVH levels in the interior, as all major drive components, apart from the high-voltage battery, could be placed in the front of the car. The battery has a 350 V nominal voltage and over 14 kWh storage capacity and is located under the boot floor in the spare wheel well, although built-in the centre tunnel and behind the rear seats would also be conceivable. An integrated management system has been used to ensure optimized thermal management.

The small battery package reduces cost and weight, so that the total vehicle only weighs about 200 kg more than the donor car. The range extender engine from MAHLE starts in response to both the applied load and the state of charge, but the battery in the prototype uses an impressive 80 percent of its capacity. Naturally, the range extender starts earlier on, especially at low temperatures, for example, the vehicle must be heated, but even in winter - provided sufficient battery charge is available - a pure electric drive away is possible. Cold starts should be largely avoided by catalyst pre-heating before the engine starts.

But how does it feel to drive? To put it succinctly: Surprisingly good. As you would expect from an electric drive, the car accelerates strongly. The claimed 12 seconds from 0 to 100 km / h seems to be a realistic value. Steering and brakes are to be expected in an Audi A1, so all focus can be directed to the drive train, which plays the lead role in this test drive. The sticking point in series hybrids is the insertion of the internal combustion engine and here the MAHLE Range Extender scores significantly compared to other well known vehicles. The small two-cylinder unit starts almost imperceptibly and provides instant power to the battery. At speeds above 50 km / h, the engine is barely heard or noticed - in any case the wind and tyre noise is more dominant at these speeds. Even at slower speeds under 30km / h, the range extender creates no distracting background noise, but works unobtrusively in the background. Although, to be honest, a customer might not realise this, since the range extender is basically designed so that it only starts above 45 km / h. But, for the test drive of this prototype, that speed was lowered to 25 km / h to allow the NVH levels to be experienced. The first impression was of an efficient, quiet and low vibration drive, but a longer test drive would be necessary for a conclusive assessment. In the driving seat there were no dazzling, colorful graphics, just clear and factual dials with information about charge status, energy consumption and the range extender operation.

MAHLE set the operating strategy at minimum fuel consumption in compliance with the limits for emissions, noise and vibration levels. The fuel tank has been reduced by almost half to 25 liters. In real traffic, a battery-only range of 70 km should be possible with an additional 430 km available using the range extender, with emissions of less than 45 g CO2/km. Fuel consumption would thus be around 2.0 litres/100 km when starting with a fully charged battery. This is achieved by the high efficiency of the MAHLE-drive, which at its best point is 31 percent. Although this figure is below those of conventional drives, it is still quite remarkable for a series hybrid. Of course, the fuel consumption (unfortunately) is measured on the NEDC, whereas in this vehicle, the real world usage would further benefit from the regenerative braking to potentially achieve better values. But in order to be as close as possible to reality, the MAHLE engineers have optimised the vehicle for best results on the Artemis cycle. This is based on real world driving profiles which are currently being verified during the vehicle development. First results show that even emissions of about 40 g CO2/km are in the range of possibility.

In addition to the driving range, the market acceptance will also depend on the NVH levels. There is still potential for big improvements in this area - especially through optimisation of the exhaust system. However, the reduced speed of the prototype in the test drive had a very positive impact on NVH reduction.

Of course, the cost of the range extender depends on the production volume, and the cost of the electric motor in particular is more critical than that of the internal combustion engine. MAHLE, however, could build and supply the range extender for several customers so higher volume would be possible, which would have a positive effect on the costs. The price for a vehicle with a range extender could therefore be more competitive than a series hybrid and thus become commercially viable. Plus a series hybrid is probably already more attractive than a pure BEV.