BMW introduces turbo I4, develops electrics

  • 26-Apr-2011 08:56 EDT
aei-bmw-2.0w-int.JPG

Turbo-side view of the new BMW 2.0-L four-cylinder with intercooler rated at 240 hp (179 kW) at 5000 rpm. The engine’s complete package is about 10 kg (22 lb) lighter than the inline six-cylinder, which it will replace on the Z4 this year and on other models thereafter.

BMW faces a major challenge in augmenting its “ultimate driving machine” image with fuel economy numbers that meet the 2017 U.S. regulations, but it showed a key element in its plans at the 2011 New York Auto Show introduction with a 2.0-liter twin-scroll intercooled turbo.

The engine will replace most applications of the 3.0-L inline six-cylinder in gradual steps, starting with the Z4 coupe later this year. The company also will introduce a test fleet of its Active-E, an all-electric model based on the 1 Series sedan but admitted that even by 2020 it expects that 85-90% of its U.S. sales will be gasoline/diesel-engine powered.

The company is very confident about bringing back a four-cylinder gasoline engine, which it has not offered in the U.S. for 10 years. Each of the turbo engine’s two scrolls is fed by an exhaust stream from a separate cylinder pair for minimum back pressure. The engine is rated at 240 hp (179 kW) at 5000 rpm, which is an approximate match for the two versions of the 3.0-L I6, one rated at 230 hp (172 kW) and the other at 255 hp (190 kW).

The four-cylinder delivers 20% better fuel economy (about 29.8 mpg) than the I6 on the European Driving Cycle Combined, the company stated. Unsurprisingly, the performance of the 2.0-L turbo is much greater than the naturally aspirated four-cylinder of a decade ago. That powerplant, at 1.9 L, was rated at just 138 hp (103 kW).

The new 2.0-L turbo is direct injected with fuel at up to 200 bar (2900 psi). It is a slightly long-stroke unit at 84 x 90 mm (3.31 x 3.54 in), which along with the Valvetronic fully variable lift/timing system, produces a torque curve that is virtually flat from 1250 to 4800 rpm, explained Dr. Harald Unger, Head of BMW Petrol In-Line Engines. Peak torque is 260 lb·ft (354 N·m).

The manual transmission version has a plastic oil pan and dual-mass flywheel. The automatic requires a more robust structure and uses an aluminum oil pan, he said.

Although the A/C compressor and alternator are driven by a serpentine belt, the 2.0 L's water pump, mounted at the lower right side of the engine, is electric-motor-driven, with a peak output of 7000 L/h (1850 gal/h). The engine oil pump is engine driven, but the output is map-controlled by the engine computer regulation of a solenoid valve. The oil filter is a cartridge type in a top-of-engine housing combined with an oil cooler. The engine control module is mounted atop the intake manifold, which includes air passages that align with ones in the module for cooling.

Instead of pressed-in cylinder liners, BMW is using a German twin-wire steel alloy spray process identified as LDS by Unger. Although other engines have used spray liners in some high-performance applications over the years, this is the company’s first application of a spray process, and the choice for a high-volume application indicates the company’s confidence in it.

Unger noted that eliminating the liners in favor of the thin spray increases the engine block wall thickness between cylinders, permitting BMW to drill cooling passages through them vs. the slits that normally would be the maximum possible. The spray coating also provides more uniform heat transfer than actual liners. Further, as long done by Toyota, the crankshaft is offset—by 14 mm (0.55 in) for the 2.0 L, so peak cylinder pressures occur with the pistons at top dead center, which minimizes friction from piston side forces during compression.

The engine has twin counter-rotating balance shafts, chain-driven off the crankshaft, in the oil pan. Although total engine weight was not announced, Unger said the four-cylinder including turbocharger and intercooler would be lighter than the I6, saving about 10 kg (22 lb).

BMW’s approach to fully electric vehicles has been cautious, with the 600 vehicle Mini-E test fleet (450 leased in the U.S.) having been the first step, and the Active-E test fleet, scheduled for a 24-month public lease this fall, set as the next stage. Some 700 Active-E vehicles will be available in the U.S. for a projected $499/month lease price with a $2250 down payment.

The electric powertrain, rated at 170 hp (127 kW) and 184 lb·ft (250 N·m), will use a 32 kW·h capacity battery pack consisting of 192 large-format laminar lithium-ion cells supplied by a Samsung-Bosch joint venture. This compares with 582 small cylindrical cells in the Mini-E.

BMW’s Rich Steinberg, Manager of Electric Vehicle Operations and Strategy, said the Active-E will deliver 0-60 mph (0-96 km/h) acceleration in under 9 s and have a range of 100 mi (160 km). BMW learned many lessons from the Mini test fleet, most important that consistent battery range is what gives drivers the needed confidence, explained Steinberg. As a result, engineering of these next-generation models is aimed at providing that, in part, from a sophisticated system for heating or cooling of the pack for the ambient conditions while the vehicle is plugged into the grid.

A specifically sized version of the laminar cell powertrain also will be used in the “city” vehicle, the i3 series proposed for 2013 production.

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