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Through the use of a supercharger strategy, Audi is able to tune the performance of various vehicles while using a common base engine.
While some people might think “supercharger” and, say, “Corvette,” there is also applicability in small cars, such as the European Nissan Micra city car, which is available with a 1.2-liter, three-cylinder engine that features gasoline direct injection and a supercharger. The engine produces 98 hp, which is what would be expected of an engine with an additional cylinder, and the supercharging helps with the throttle response of the car.
Here we are in the 21st century, and Grant S. Terry of the Eaton Corp. (eaton.com) Vehicle Group thinks that more OEMs should become familiar with the benefits that can be provided today for performance and fuel efficiency by an invention that was made in the 19th century.
In 1860, two brothers, Philander and Francis Roots, patented a positive-displacement rotary piston machine. Think of it as a highly efficient air pump. In time, this has become the Roots-type supercharger, which Eaton has been manufacturing since the 1980s, with the first application of its Gen V supercharger going into the 1989 Ford Thunderbird Supercoupe.
(Terry, not surprisingly, is the Business Development Manager handling Superchargers at Eaton.)
And here’s the thing that may not be recognized about superchargers. While there have been many vehicles since then that have been supercharged, vehicles like that early Thunderbird have been focused on performance, it is not just a go-fast addition to an engine, although it does increase performance. As Terry points out, in that Thunderbird application, what would have been a V8 was a V6 because the supercharger provided the sort of performance that they were looking for. So while fuel efficiency may have been way down the list of concerns of those Ford powertrain engineers, the supercharger did provide the performance they were looking for.
Today, the latest technology in super-charging from Eaton—the 2300 Series Twin Vortice Series—can be found under the hood of the 2012 Corvette ZR1, which has a top speed of 205 mph. This super-charger, a sixth-generation Eaton design, provides toque at lower rpm and then carries that power up in a linear manner up to 6,000 rpm. Again, fuel efficiency isn’t the reason why someone would opt for the ‘Vette.
But there is a growing number of examples of places where OEMs are opting for supercharging for reasons that are oriented toward efficiency—but efficiency without sacrificing performance.
As in the case of the Nissan HR12DDR, a three-cylinder, 1.2-liter, three-cylinder, direct-injected engine that it is offering in its European Micra. This engine is designed to be highly efficient in order to minimize CO2 emissions. It runs on the Miller Cycle, which essentially has the intake valves open longer, which has the consequence of reducing power, which is where the supercharger comes in. So while the amount of CO2 produced is just 95 g/km on the New European Driving Cycle (NEDC), when it comes to the need for performance the supercharger is engaged so that, according to Nissan, the 1.2-liter engine provides “power on a par with a 1.5-liter engine.” The otherwise 79-hp engine produces 98-hp. The supercharger is disengaged when the engine is running at a steady-state, which helps with the emissions performance, as does the use of start-stop technology and variable valve timing on the engine.
Stop-start systems are becoming more prevalent as OEMs are working to improve their fuel efficiency. And according to Terry, “Turbos”—and let’s face it, the phrase “downsized and turbocharged” is becoming the norm as people talk about a prevailing trend when it comes to powertrains—“don’t like stop-start.” He explains that turbochargers, unlike superchargers, need heat for efficiency. And when the engine is shut off, there is cooling. Which is not good for turbo performance. So here’s a place where superchargers can be a greater consideration because after the car stops it needs to get going again, and, according to Terry, “When the driver applies the accelerator, we can get full manifold pressure in 300 msec or less. This is our big advantage.”
The issue is one of “transient response.” Superchargers, he says, are good at it. Turbochargers aren’t. (Think: “turbo-lag.”) So possibly that “downsized and turbocharged” may have to be amended, especially as start-stop systems proliferate. That said, he admits that one of the benchmark engines, the Volkswagen TSI engine actually combines a supercharger and a turbocharger such that the supercharger operates until about 3,500 rpm and then it is clutched out and the turbocharger takes over. This setup is known as a “compound boost system,” and Terry suggests that this is where there is likely to be a considerable amount of growth.
Audi is using superchargers in an interesting way. By using a 3.0-liter engine and a supercharger, through calibrations it is able to adjust the output of the engine in order to match particular vehicles. So, for example, the 3.0 TFSI in the Audi S4 produces 333 hp, and the 3.0 TFSI in the A6, 310 hp. And the 3.0-liter TFSI engine in the Q5 produces 272 hp. Audi uses the Eaton TVS supercharger. This consists of two four-vane rotary pistons that counter-rotate at up to 23,000 rpm, providing a boost pressure of up to 0.8 bar. It is belt-driven and can provide full boost pressure from idle.
Because this is a compact system, Audi fits it right between the cylinder banks. Eaton provides Audi with the top end of the engine, the integrated supercharger, intake manifold, intercoolers, throttle body, and bypass valve. It is a single part number for a variety of applications.
Clearly, a clever way to rationalize engine manufacture.
There are a variety of activities at Eaton to improve the supercharger. Like finding the ways to reduce the weight of the rotors to reduce inertia. To integrate a clutch. To develop continuously variable drives. To use an electric motor to drive the supercharger (“You’d need more than a 12-volt system to make it worthwhile,” Terry notes.).
They’ve come a long way since 1860. With the demands for fuel efficiency, performance, and reduced manufacturing costs all drivers today, chances are the developments in the supercharger space are going to come at a pace that will make changes in the last 150 years seem incredibly incremental.