By Csaba Csere
We drove the three-banger in a European-market 1-series similar to this one.
We’ve barely digested the notion of four-banger BMWs being available here again when the company invites us to try a car with even one fewer cylinder. The engine is called the B38 and it’s a turbocharged three-cylinder, with an 82.0-mm bore and a 94.6-mm stroke, displacing 1499 cc. This engine represents a new family for BMW that also will be produced in four- and six-cylinder form, all with the same half-liter per cylinder. There will also be closely related diesels in the three configurations—the 1.5-liter triple, a 2.0-liter four, and a 3.0-liter inline-six.
The new engine family employs BMW’s Valvetronic system, which controls intake valve limit to efficiently regulate engine power, as well as direct fuel injection to provide the coolest possible combustion conditions to limit knock. While direct fuel injection has been in widespread use for more than 10 years, manufacturers are still experimenting with ways to optimize the injectors. For example, BMW’s first DI turbo engine was the twin-turbo N54 introduced in the 2007 335i. That engine had its fuel injectors nestled next to the spark plugs in the apex of the combustion chamber. The current N20 four-cylinder turbo positions its injectors horizontally between the outer edges of the two intake valves.
With this new B38 engine, BMW has gone back to the centrally placed vertical injectors. Heidelinde Holzer, BMW’s powertrain integration manager, explained that the vertical injectors better mix fuel and air, leading to reduced soot formation. This in turn decreases the deposits on the backs of the intake valves, and largely eliminates the sooty exhaust-pipe residue that plagues many cars with DI engines.
The new engine uses a conventional aluminum block and head. Holzer explained that the magnesium block used on BMW’s older 3.0-liter naturally aspirated six-cylinder posed some production problems, as the scrap magnesium was difficult to recycle. To reduce the natural imbalance in three-cylinder engines, which causes the engine to rock longitudinally like a teeter-totter, there is a single balance shaft located in the oil pan.
The B38 is about 20 pounds lighter than the current four-cylinder N20 and a few inches shorter. More important, it is expected to deliver up to 15 percent better fuel efficiency, thanks to its reduced friction, more-efficient combustion, and more highly loaded operation.
Including the shared half-liter cylinders, the gasoline members of this family are expected to share up to 60 percent of their parts, although that commonality drops considerably with the diesel version. However, both types of engines will be manufactured on the same production lines, allowing BMW flexibility to quickly alter engines types and sizes to match market demand.
A prototype of the three-cylinder was installed in a European 1-series five-door hatchback for a limited test drive around the BMW USA grounds. Coupled to an eight-speed automatic, the little triple in …read more
Source: FULL ARTICLE at Car & Driver
