The term ‘supercharger’ may currently be drawing media attention as Tesla rolls out its electric vehicle (EV) charging network, but those outside the EV world will have a different understanding of the term.
Eaton, a leading global supercharger supplier, describes a supercharger as “a device used to force more air into an engine”. Force air into an engine, and combine it with increased fuel delivery, and greater power can be derived from the engine. The difference with turbocharging is key: while turbochargers are driven by hot exhaust, superchargers are mechanically-driven.
Although it sounds like an advanced technology, supercharging is not restricted to super cars. Eaton offers a broad range of supercharger applications, from 1.2-litre engines and small vehicles through to 6.2-litre engine applications and performance vehicles, explains Jeff Schick, Vice President and General Manager for Eaton’s Supercharger Division, which sits within Eaton’s Vehicle Group. “The device is used to improve transient response and acceleration, especially in high power density applications. High horsepower or kilowatt-per-litre engines require supercharger boosting technology. As the downsizing of engines occurs and the average displacement of engines continues to be reduced, and those engines are still needed in heavier vehicles, the initial transient response or acceleration is achieved through supercharging.”
Supercharging is not used exclusively – there are numerous cases of supercharging and turbocharging being used in combination, usually where downsized engines require higher output, or when they are used across additional vehicle platforms. “We’re seeing compound boosting as a trend in the marketplace, and here the supercharger technology is very applicable,” says Schick, who has responsibility for managing the business unit globally, including engineering, marketing, sales, and the advanced manufacturing-related process technology for the production of the product as well.
“In terms of fuel economy and downsizing, many engine manufacturers think about alternative combustion processes. They’re reverting to things like the Miller cycle technology versus the auto cycle, and the Miller cycle uses late intake valve closing, which helps eliminate pumping losses in the engine. When you do that, you lose some power performance. In order to overcome that loss of power, boosting, specifically supercharging, is very applicable.” Eaton has recently highlighted the Nissan Note as an application where Miller cycle technology, using its supercharger in a 1.2-litre engine, has enjoyed considerable success.
Most superchargers are used in vehicles with 2.0-litre engines and above. Eaton’s first supercharger application was used in the 1988 Ford Super Coupe, “and it has evolved significantly since then,” says Schick. “We’re now on our TVS-style rotor technology, which has increased efficiency in our device to around 74% – 75%, enabling us to target an increasing number of supercharging applications.” Schick cites as an example the 3.0-litre technology used by Audi, which came into production in 2008; that, he says, was used for both downsizing and fuel economy. “The current trend is to reduce engine sizes, and to be able to use engines across a multitude of vehicle platforms. That requires engine architectures that have a wider range of horsepower and torque requirements.”
Schick’s reference to the first supercharger being offered in 1988 is an interesting one: this is not a new technology, but the rate of installation and penetration is increasing. “Even last year, we saw 30% year-on-year growth in terms of unit fitment of superchargers,” says Schick, and that growth is being driven by the need to downsize because of fuel economy and emissions regulations. “Generally speaking, all global vehicle regions are migrating towards 95g CO2/km. In the US, the EPA is shooting for 54.5 mpg by 2025. Regulations are driving engine performance and design.”
With 2025 being such a significant year for powertrain technology in the US, is Eaton expecting an increase in penetration specifically in the US market to meet the 54.5 mpg target?
“Yes,” says Schick. “Right now, the industry is really searching for the right combination of technologies, from combustion techniques to valve train technologies. Eaton has variable valve train technology as well, which is right in the sweet spot of engine air management, along with boosting technology. The jury is still out on which technologies will be the most widely adopted. I’m convinced it will be a variety of technologies tailored to customer applications and market expectations, for not only fuel economy and emissions reduction, but also driveability.”
However, Schick acknowledges the need to balance great fuel economy and reduced emissions with performance. “If it takes 60 seconds to accelerate from 0 to 60, that’s not going to be accepted by most drivers in most vehicles! Some form of boosting or boosting system is required to get that power back when it’s needed.”
Superchargers may have their benefits, but they are up against a range of technologies that can also help increase performance, reduce fuel consumption and lower emissions. What are the main alternative technologies against which superchargers compete? It depends on the application, explains Schick. “Turbocharger and twin turbocharging technology could be viable technologies. It depends on the engine and the engine performance specification. If you’re looking at the fuel economy version and the eco version of an engine and an engine family, you might pick a combustion technique like Miller cycle, for which supercharging is required to achieve the low end torque factor that is lost in the Miller cycle. But you still can achieve fuel economy benefits in the range of 3-5% or more.
“If that’s what you’re looking for in your engine, supercharging is the answer. If you’re looking for a mid-specification, mid-power engine in a mid to small vehicle, turbocharging might be the appropriate boosting application. If you’re looking for a high output version of that engine, then compound boosting is the trend. A supercharger at the low end, plus a turbocharger at the high end, is a very palatable boosting solution for engine performance.”
As with any technology, cost is a major consideration. Schick explains the trade-offs to consider when deciding whether superchargers are viable: “It’s a case of examining the target vehicle, the required engine specification, and how the mix of engine combustion technology and boosting architecture can achieve those requirements.”
At present, the 1.2-litre engine application on the Nissan Note is at the smaller end of the scale. Eaton shows 1.0-litre applications on its website, but below that, the technology enters the realms of diminishing returns. “It depends what you want to do with your engine,” says Schick. “The 1.2-litre engines are going down to 1.0-litre, and there are even considerations for 0.8-litre engines.”
The adoption of superchargers to date has been somewhat region-specific, with adoption in the BRIC markets slower than in other parts of the world. This Schick attributes to where most engine design decisions are made, namely Japan, Europe, and the US. As those countries prove the benefits of superchargers, vehicle manufacturers in markets like China and India will examine the applicability of those engines and engine architectures, to see how they can help them meet fuel economy and emissions reduction requirements in their countries. “They may be a little further behind in terms of the emissions requirements, but we see a convergence in the range 95g to 120g CO2/km across the globe, in the 2020 to 2025 timeframe,” says Schick. “This technology will also be applicable in those regions, where the drive cycles don’t involve much high speed, but here’s a lot of starting and stopping, or transient type responses. In those applications, the supercharger, along with a Miller cycle or some more alternative combustion process, is very applicable. Over the next five to ten years, supercharging technology will also be required to meet emissions targets in those regions.”
Supercharger technology is adaptable, not just for different geographic applications, but also for different engine geographies. There is no engine layout for which they cannot be used, says Schick, when asked whether they could be used in opposed cylinder engines, or the three and even two-cylinder engines which are gaining popularity Europe. “Superchargers are not exhaust gas driven, so they can be used on any engine architecture. There really isn’t any [engine architecture] that I would classify as most suitable.” Indeed, in an application where exhaust gas energy is lacking, like a 2-cylinder engine, a supercharger would have an advantage over a turbocharger, he adds.
There’s considerable room for further development in supercharger technology, believes Schick, who says he expects further improvements in performance and efficiency. “I also see the drive technology moving forward, with technologies like clutch deactivation and boost on demand delighting engine designers, enabling them to really tailor and tune an engine to the drive cycle and driving performance of any vehicle.” A combination of how the supercharger is driven, as well as improvements in the device, concludes Schick, will make superchargers “even more desirable” as engine technologies evolve over the next decade.