Innovative Drive Technology for Enhanced Driving Pleasure and Efficiency

Power Units of the new MINI Cooper and the new MINI Cooper S

More power, greater economy, more driving pleasure, less emissions - the introduction of innovative petrol engines brand-new from the ground up is not only the key to enhanced driving dynamics in the MINI, but also an important step in the process of implementing the pledge made by the European automotive industry to cut CO2 emissions to a fleet average of 140 g/km by the year 2008. "Introducing the new range of engines, we have succeeded in carrying over the most demanding and technically sophisticated engine technology to the segment of small and compact cars", states Erich Sonntag, the Drivetrain Project Manager in the development of the new MINI. "Our fundamental philosophy is that of Efficient Dynamics. In other words: enhanced performance on less fuel."

The first representatives of the new engine family are a normal-aspiration and a turbocharged power unit each with four cylinders and built at the BMW Group Engine Plant in Hams Hall, Great Britain. Compared with the previous power units, both of the new engines have been turned around by 180 degrees, with the exhaust side now facing to the front.

The engine block as such is highly similar on both the normal-aspiration and turbocharged petrol engines: Both power units share the same distance between cylinders of 84 millimetres or 3.31'', the same bore of 77 millimetres or 3.03'', stroke of 85.5 millimetres or 3.37'', and, accordingly, engine displacement of 1,598 cubic centimetres. The two-piece bedplate structure of the crankcase is a technology carried over from motorsport, with the cylinder block and bearing cast out of an aluminium alloy. Integration of the chainbox into the crankcase helps to save weight, improve engine acoustics, and reduce the number of components and design features required.

Yet a further innovation in the MINI segment is the introduction of a volume flow-controlled oil pump on the engines. Driven by a chain, the pump delivers only as much oil at any time as is actually required by the engine, thus reducing the drive power required by the ancillary units by approximately 160 Watt, saving approximately 1.25 kW at 6,000 rpm, and reducing fuel consumption by roughly 1 per cent.

The on-demand water pump featured in the coolant circuit offers a similar effect, only being switched on when the engine has reached its regular operating temperature. This helps to save fuel in the warming-up phase, with the catalyst reaching the temperature required for optimum efficiency more quickly and efficiently than before. 

Both engines come with composite-structure camshafts. And contrary to conventional castings, the cam rings are made of high-strength stainless steel and are shrunk-fit on to the camshaft as such, after which the cams are fine-polished down to an accuracy of 1∕1,000 th millimetre. The eccentric shaft for phase adjustment is also made in this process, helping once again to save weight.

The lightweight concept consistently applied in developing the new MINI's power units also serves to reduce frictional losses. The crankshafts on both drive units, for example, are weight-optimised in their construction and come with special bearing shells as well as relatively small bearing journals measuring just 45 millimetres or 1.77'' in diameter.

The alternator and air conditioning compressor, in turn, are each driven by one single poly-V-belt, while the water pump is driven by a friction wheel. Both of these features help to make the power units featured in the new MINI particularly compact, the new engines thus ranking among the shortest four-cylinders in their class.


Normal-aspiration power unit with fully variable valve control

Notwithstanding all their similarities and, indeed, common features in their overall design and configuration, the two power units in the new MINI differ significantly in terms of their cylinder heads: The 1.6-litre normal-aspiration engine featured in the MINI Cooper comes with fully variable valve control developed on the basis of the BMW Group's VALVETRONIC technology.

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