Tiguan Takes on the B Cycle for Improved Fuel Efficiency

If you’re a powertrain engineer (or someone who has a particular interest in efficient engines), you undoubtedly know about the Atkinson cycle. After all, that was developed back in 1882.
And then there’s the Miller cycle, which was patented by Ralph Miller in 1957.

But there’s a cycle that is being used by the Volkswagen Group—first Audi, in a longitudinal application for the current generation A4, now VW for the all-new Tiguan SUV in a transverse setting—that’s comparatively fresh and efficient.

It’s called the “B cycle,” named after VW Group’s Dr. Ralf Budack, who is with the Advance Development Charge Cycle/Thermodynamics group.

This system in the 2018 Tiguan application, explains Marcel Zirwes, manager, Powertrain Product Management, Volkswagen of America, is based on the company’s EA888 four-cylinder engine architecture, which debuted in the 2009 VW CC. But the engine is been modified, so that this third-generation version, a 2.0-liter engine, is designated with “EA888 Generation 3B,” with the “B” standing for Dr. Budack.

In the Budack cycle, the intake valves are closed much earlier than is ordinarily the case, thereby resulting in a case where the cylinder is not filled 100 percent. But this is highly compressed—11.7:1—thanks, in part, to a modified piston crown, so that there is improved mixing of the fuel and the air in the cylinder. Then there is a longer expansion phase (which led to a redesign of the intake ports, valves, and combustion chamber, as well as the pistons).

The objective is to gain greater efficiency and power for the turbocharged engine. The engine is rated at 184 hp and 221 lb-ft of torque.

While the EPA estimates are not, at the time of this writing, available, Zirwes says that the engine will provide “1.8-liter power with 1.4- to 1.5-liter efficiency.”

Wait a minute, you might think. This is a 2.0-liter engine and he says that it provides the power of a 1.8-liter engine?

That’s right. But Zirwes goes on to explain that the objective was to create an engine that has better fuel efficiency but still high levels of torque, which is the kind of thing that people are looking for in crossover vehicles like the Tiguan. Zirwes says that there is a reduction of friction on the order of 8 percent in the engine, which can be thought of in the context of improved fuel efficiency.        

However, there are situations where there is not just regular street driving, which is where the B cycle is most effective, but a need for more performance. So the engine also features a variable valve timing system on the intake camshaft so that when there is greater load, there is 30 degrees more camshaft angle than is the case when in the fuel optimization mode (170 degrees vs. 140 degrees).

According to Zirwes, the approach they’re now taking at VW in terms of powertrains is what they’re calling a “rightsizing” strategy versus the “downsizing” that has long held sway in the industry. The company is using turbochargers, which has been part of the commonly used phrase: “downsized, turbocharged engines.” But, he says, this combo has “reached the optimized level,” explaining, “A further tradeoff without cycle optimization would be less power at one point or more ‘peaky’ power where you have more turbo-lag if you reduce the displacement more and more. The Volkswagen philosophy is to optimize the current engine with further fuel reduction technology like this B cycle.”

Given that the Tiguan is a reasonable large (though compact) crossover, measuring 185.2 inches long, 72.4 inches wide and 65.3 inches high, given that it is available with an all-wheel-drive system and a third row, there is a non-trivial amount of mass to be moved. So with the “rightsizing” strategy, it isn’t just about reducing the size of the engine in order to achieve better fuel efficiency, because with that comes less power, which would not necessarily be appealing in situations like merging onto a freeway.
That’s one of the key reasons why the B cycle is being put in play. And when asked why not simply take the 1.8-liter engine that’s available (for now) in the Passat, Jetta, Beetle and Golf vehicles and apply Budack’s approach to it, Zirwes says that there would comparatively small savings in fuel, but a concomitant reduction in power. Which wouldn’t necessarily be a good thing for the Tiguan.—GSV