Volkswagen’s not saying it directly, but the company’s unique new twist on its well-established EA888 gasoline 4-cylinder engine family looks to be a potentially effective high-efficiency surrogate for the diesel engines it no longer will sell in North America.
The company calls the new third-generation variant of the AE888 engine architecture “B-Cycle,” so named for its developer, VW group advanced-powertrain engineer Ralf Budack, who for years envisioned this melding of the increasingly popular Atkinson- and Miller-cycle combustion processes that seek to use a truncated compression ratio—via late closing of the intake valves—to achieve an effectively longer expansion ratio.
Resulting is a 2.0-L engine that VW said has the power of the 1.8-L TSI it replaces, but roughly 8% better fuel economy—generating efficiency one might expect from a smaller 1.4-L engine. So in effect, buyers who get the new B-Cycle engine—first in the all-new 2018 Tiguan compact crossover and then the Passat, Jetta and Golf and Beetle—will enjoy 2.0-L displacement in place of today’s 1.8-L, with the added bonus of 1.4-L-like efficiency.
New cylinder head, fancy cam
Although the EA888’s iron cylinder block remains, the new B-Cycle variant has what amounts to an almost entirely new cylinder head design, said Marcel Zirwes, a VW powertrain engineer who detailed the engine’s development during a recent media program.
The central technology for the B-Cycle variant is a two-step intake camshaft that employs a sliding cog to locate the cam on one of two discrete timing regimes: a normal intake-valve opening setup when maximum power is required, or the partial-load setting that angles the cam lobes for the early intake-valve closing that delivers the B-Cycle effects. Zirwes said the B-Cycle intake-valve regime brings not only more-brief initial valve-opening duration, but also a smaller opening.
A new alloy piston has a unique crown and bowl shape that enables the higher 11.7:1 compression ratio (the standard third-generation EA888 4-cylinder engines have just a 9.6:1 compression ratio)—but the B-Cycle engine’s optimized interplay of engine operation, along with a new, faster-responding turbocharger, means the engine can develop full power and torque on regular-grade gasoline. The direct-injection system has relocated injectors compared with the standard 2.0-L engine and enables up to three injection events per combustion cycle.
The new engine’s friction is reduced by some 8% with lower-tension piston rings; the design’s lower full-load brake mean effective pressure (BMEP) also means that the crankshaft main-bearing diameter could be reduced and the size of the chain driving the twin balance shafts is smaller.
The B-Cycle is the only engine offering in the new Tiguan and develops 184 hp at 4,400 rpm, the power peak coming slightly sooner than with the previous 2.0-L engine. Maximum torque is 221 lb·ft (300 N·m), arriving at a low, almost diesel-like 1,600 rpm and holding to almost 4000 rpm. The hp figure does represent a reduction from the 200 hp available from the outgoing Tiguan’s 2.0-L TSI engine, but the more-economical B-Cycle engine surprisingly makes 14 lb·ft (19 N·m) more torque.
For the 2018 Tiguan, the B-Cycle engine is available exclusively with VW’s 8-speed automatic transmission. Although the new Tiguan is based on the company’s widespread MQB vehicle architecture that sees most engines coupled with the direct-shift gearbox (DSG) automated-manual transmission, VW said the conventional torque-converter automatic was specified for the Tiguan in the U.S. because of its smoother driving characteristics.