Can't Beat 'Em? Join 'Em

A truce may be in the works in the battle for forced-induction supremacy.

Turbochargers and superchargers have been slugging it out for a generation, and neither wants to yield any ground in the automotive high-performance landscape.

Each technology has its pros and cons, but one automotive supplier has a potentially radical idea that could compensate for the inherent weaknesses of each device.

Eaton Corp., a leading producer of superchargers, proposes marrying the two in a concept it calls SuperTurbo Compounding.

A supercharger is most effective at low engine speed, providing immediate power and compensating for the “lag” generally associated with turbochargers at low rpm. Above 2,000 rpm, however, turbochargers typically spring to life, driven by increasing engine exhaust velocity and providing considerable kick in a power band where the supercharger becomes less effective.

Combining the two technologies is more than a concept, as the strategy debuted recently on a 1.4L direct-injection gasoline (DIG) 4-cyl. in the '06 Volkswagen Golf GT at the Frankfurt auto show.

VW is marketing the unique approach as “Twincharging,” or TSI, in the new Golf GT, which goes on sale in Europe this year, followed later by other VW models employing the technology. There are no immediate plans to sell the Golf GT in the U.S., VW says.

The 1.4L I-4 is technically advanced not only because of its air-induction strategy but because it employs Volkswagen's celebrated new FSI (Fuel Straight Injection) DIG system, which is appearing on a growing number of VW and Audi AG models.

VW is drawn to Twincharging for several reasons. The 1.4L's torque rating of 177 lb.-ft. (240 Nm) between 1,750 and 4,500 rpm corresponds to that of a much larger 2.3L powerplant, VW says.

The Twincharged 1.4L produces 20% more torque than VW's excellent new normally aspirated 2L FSI 4-cyl. in the Golf. The powerplant also churns out 167 hp at 6,000 rpm, compared with 147 hp from the 2L.

VW clocks the TSI-powered Golf GT from 0 to 62 mph (100 km/h) in 7.9 seconds, significantly better than the 8.8-second time for the Golf with the 2L FSI.

Remarkably, VW also claims fuel consumption is enhanced. On the highway, the 2L FSI and the Twincharged 1.4L achieve the same rating of 40 mpg (5.9L/100 km). But the combined city/highway fuel economy for the 1.4L is 33 mpg (7.2L/100 km), compared with 31 mpg (7.6L/100 km) for the 2L FSI, based on the European driving cycle. The improved fuel economy translates into reductions in carbon dioxide emissions, which is a key environmental goal in Europe.

Pairing a supercharger with a turbocharger allows VW to use a smaller engine, which reduces weight, simplifies underhood packaging and can generate material cost savings.

“You can downsize the engine and still achieve at least the same power,” Jeff Romig, Eaton's vice president and general manager-air induction, says during a recent media event in suburban Detroit.

For the Golf GT program, Eaton supplies a conventional Roots-style supercharger, while the turbocharger comes from BorgWarner Inc.

“It doesn't matter whose turbocharger it is,” says Grant Terry, customer manager-new business development for Eaton's engine air-management operations. “This is a breakthrough in system integration. We think customers will love it.”

Eaton has supplied more than 3 million superchargers as original equipment for new vehicles for more than 15 years. Its biggest customers have been General Motors Corp. and Mercedes-Benz AG.

Romig uses a computer-generated model to demonstrate how Eaton's system works at varying engine speeds.

At initial acceleration, about 1,500 rpm, a clutch closes a bypass valve, allowing the supercharger to boost low-end torque by pumping fresh air directly to the engine, while turning the compressor wheel of the turbocharger.

At 2,500 rpm, the valve gradually closes to begin the transition from the supercharger to the turbocharger, which begins to pump on its own. By 3,500 rpm, all of the additional boost is coming directly from the turbocharger.

The throttle and bypass valve work in concert, coordinated by a sophisticated electronic control unit to maximize the operating ranges and thus the efficiency of both the turbocharger and the supercharger.

“The idea for this isn't new, but the technology wasn't there before to control it in this way,” Terry says.

For the VW program, Eaton is ramping up supercharger production at a new plant in Tczew, Poland, Romig says. VW assembles the Twincharged 1.4L engines at its plant in Chemnitz, Germany.

In its evaluation of the technology, Eaton says SuperTurbo Compounding can produce up to 20% better fuel economy and more horsepower in a 1.5L gasoline engine vs. a 2.0L turbodiesel engine.

“You get lower cost, more power and better fuel economy; and consumers will feel it (the benefit) immediately when they put their foot down,” Romig says.

Eaton says the approach works best with smaller 4-cyl. powerplants, and the supplier is banking that the popularity of diesels in Europe will soften as diesel fuel becomes more expensive, opening the door to advanced-technology gasoline engines.

“The (fuel) price advantage for diesel is gone, so that's a reason for people to switch to gasoline engines,” Terry says.

SuperTurbo Compounding is effective for diesels, too, but Eaton is focusing primarily on gasoline engines for now. Romig says the supplier has demonstrated that diesels employing SuperTurbo Compounding can meet strict new U.S. emissions requirements that take effect in 2007.

One barrier for widespread market acceptance, however, could be cost. In the current tightfisted product-development climate, auto makers on virtually any continent may not want to spend money for both a supercharger and a turbocharger.

However, if consumers express a willingness to pay for the technology, auto makers may be more inclined to try SuperTurbo Compounding, Eaton says.