Future BMW 3-series to lead EV revolution

Autocar understands that BMW has adopted similar technology to that being used by Audi. It involves building future architectures from a mixture of high-strength steels, aluminium in cast and extruded forms and some types of carbonfibre composites. These materials are variously bonded, glued, screwed and riveted together.

Using composites in strategic structural areas, such as the roof pillars and sills, allows thinner-skinned steel pressings to be used, saving weight and improving rigidity.

Using a combination of adhesives and spot welds can also allow relatively thin-skinned steel pressings to be formed into immensely light and rigid structures.

It is expected to take another generation of the 3-series, expected in 2018, before BMW is ready to switch its mainstream car to this kind of carbonfibre-intensive construction. That’s partly because it will take some years to reduce the cost of this kind of construction.

The next stage of the reinvention is BMW’s rethink of the hybrid powertrain. The surprise is that the final concept — demonstrated a few weeks ago under a 5-series Gran Turismo — is not so far in basic principle from the system that propels the Chevrolet Volt. It also means that on-demand four-wheel drive will be available on all future BMWs.

This new hybrid powertrain is described by BMW as being “scalable from the 3-series to a V12 Rolls-Royce”. It uses two electric motors, one on the rear axle and one mounted directly behind the engine.  

A large battery occupies the centre tunnel and some of the space usually occupied by the fuel tank. The front-mounted engine acts as a generator in most driving situations, creating electricity to help drive the electric motors. The front electric motor is key to the new powertrain.

In normal use, it drives the front wheels via a still-secret new type of transmission. At speeds above 50mph or so, the engine ‘assists’ the electric motor by attaching itself to the new transmission and helping to drive the front wheels at motorway speeds.

BMW won’t reveal the details of this new combined electric motor and transmission system, but company engineers told Autocar that the combustion engine would probably be driving the front wheels only about 10 per cent of the time in a typical journey.

This, they said, allowed them to run the engine at ‘Lambda 1’ for 90 per cent of the time. This means that the engine is run very lean, with no need for any kind of enrichment by the fuel injection system, resulting in reduced fuel use.

Indeed, because the engine works mostly as a generator, it can be totally rethought in its design and operation. And because the engine is only working mechanically at limited times and with substantial assistance from electric motors, it can potentially be much simpler and less expensive to build than today’s complex turbo engines.

Reducing the cost and complexity compared with today’s engines should help offset the cost of the batteries and power electronics.

These fundamental changes to the make-up of future models also play into BMW’s promise of being the ‘ultimate driving machine’. The heavy battery is placed low down and in the centre of the car and the new generator/motor will often be lighter and mounted farther back in the car’s nose. The upshot will be generation of BMWs even better balanced than today’s rear-drive models.

When BMW switches to the new range-extender electric powertrains, traditional badging will become redundant. With performance dictated mainly by the electric motors, BMW could switch badging to reflect torque output, so ‘345’ would be a 3-series with 450Nm.

Coming first - the 2016 BMW 3-series plug-in hybrid 

The first step in the process of introducing electrification to BMW’s whole range is to make a relatively conventional plug-in hybrid version of the facelifted 3-series, because it “offers the largest economies of scale” for the company’s fleet-wide fuel economy.

Engine

The car uses a conventional 180bhp turbocharged 2.0-litre four-cylinder petrol engine. It drives an eight-speed auto gearbox.

Battery Pack 

A 7.6kWh battery has been packaged over the rear axle, reducing boot space only marginally. The electric-only range is 22 miles.

3D Sat-nav

The 3D GPS system works out the topography of the route and selects the most appropriate drive mode: Comfort, Sport or Eco Pro.

Coasting Function

The car can ‘sail’ at speeds of up to 99mph, disengaging the transmission and idling the engine to reduce fuel use to zero.

Electric Motor

The conventional torque converter has been replaced by an electric motor, which is good for about 95bhp and 185lb ft.

Coming later - the 2022 BMW 3-series hybrid

Because the new-generation engine runs as a lean-burn generator for 90 per cent of the time and the twin electric motors provide significant torque, demands on the engine are much reduced. So it probably doesn’t need a turbocharger, the accompanying intercooler system or the Valvetronic system.

The emissions control system should also be less complex and expensive, all of which greatly reduces the cost of the unit. The engine is likely to be significantly lighter, too.

The new transmission is unlikely to have more than three ratios and could be a mechanical planetary system. It’s likely to be less expensive than today’s eight and nine-speed autos and dual-clutch transmissions.

The battery pack can be larger. It will fit neatly in space freed up by the removal of the propshaft and the use of a smaller fuel tank. A rear differential is also not needed. Braking assistance from electric motors means the mechanical brakes can be smaller, lighter and cheaper.