Improving the Atmosphere
One of the dominant suppliers of superchargers for both the retail automotive industry and the racing market, Eaton Corp. (Beachwood, OH) specializes in Roots-style design. While other manufacturers provide centrifugal and screw-type superchargers, Eaton is practically alone in delivering production quantities of Roots-style devices. The company has been building such superchargers since 1949. The oil shocks of the 1970s spurred development of the devices for increased fuel economy for production vehicles, culminating in the use of superchargers on the 1988 Ford Thunderbird Super Coupe. Eaton superchargers are now on a variety of production and aftermarket vehicles worldwide. “We have delivered over four-million superchargers since 1988,” said Lorry Jackson, plant manager for Eaton’s Athens, GA, plant. These are in more than 70 OEM applications, wearing brands ranging from GM, Ford, BMW, Nissan, Mercedes, to even Kawasaki Jet Skis.
Fuel Economy Means Mass Production
Supplying more air to an engine, also called boosting or forced induction, is a quick way to get more horsepower from an engine. While turbochargers scavenge energy from an engine’s exhaust to provide power to a boost system, the engine itself powers superchargers. Paradoxically, even though boosting is a way to increase performance, automakers are increasingly looking to boosting to improve fuel economy. Jeff Jowett, manager–Americas Powertrain Forecasting for IHS Automotive concurred that boosting in general contributes to better fuel economy, in the right application. “Some people look at those stringent CAFE regulations coming up and immediately think electrification,” he said. “There are a whole host of technologies that will be important, and supercharging is certainly one of the pieces of the puzzle as OEMs assemble the right technologies to meet their needs.”
To improve fuel economy, turbochargers seem to have the upper hand over superchargers. The engineers at Eaton, however, are quick to point out that supercharging offers many of the same advantages. “There was a time when people thought of superchargers as protruding from the hoods of race cars, like dragsters, where they gave more horsepower and enhanced performance [while using more gas],” said Tim Cavanagh, product line manager. “Eaton is in the process of changing that thought process, to thinking fuel economy. How? Through downsizing the engine same as [is done with] turbocharging. A V6 with a supercharger can provide better fuel economy than a naturally-aspirated V8.”
Downspeeding is the key. Supercharging allows an engine to deliver the same torque as a normally-aspirated engine but at lower rpm—burning less fuel—to maintain horsepower. By downspeeding, a supercharger can improve fuel economy 15%, according to Eaton. “They are useful on hybrids, too, because with the supercharger you can tune the engines for maximum fuel economy,” he explained. The Roots-style supercharger also offers these advantages at low engine rpm, where turbochargers and even other styles of superchargers lag behind in generating torque at those engine speeds. This is important in everyday use by real-life drivers. Future improvements may include a clutched supercharger that disengages the device when not in use, which can be up to 90% of the time for typical driving.
OEMs Select Superchargers
As proof, Cavanagh said efficiency was the main attraction for automakers choosing Eaton’s Twin Vortex Series supercharger. First introduced in 2007, it is now on vehicles like the Audi A7 3.0L V6, VW BlueMotion Hybrid with 1.4L I4, Golf GT, and the Nissan Micra with 1.2L I3.
There are other practical advantages superchargers have over turbochargers. Packaging and cost for assembly in the vehicle is competitive with turbochargers, according to Cavanagh, when the cost for all of the tubing and exhaust pipes included with turbocharger installs is taken into account. As a self-contained package, the Twin Vortex usually fits neatly into existing engine compartments. Another advantage is long-term maintenance. “Our superchargers are sealed packages, requiring no service or maintenance for the life of the vehicle,” said Cavanagh. He pointed out they use no special oil or air filters, either.
Eaton is optimistic for the future. “We are in a transitional phase, with business picking up in Europe, primarily,” he explained. Eaton believes the available market for boosting gasoline engines will grow from four-million boosted gasoline engines in 2010 to 17.5 million in 2017. Boosting in this context means either supercharging or turbocharging of any sort, for light vehicles. Light-duty diesel remains an untapped market for supercharging, with a potential size of 16.8 million by 2017, according to figures supplied by Eaton.
Better Design through Manufacturing
The Eaton Twin Vortex Series supercharger represents the state of the art in a Roots-style system. The essence of the Roots-style is two counter-rotating lobed rotors that trap and push air as they rotate. Eaton’s Twin Vortex Series replaced an earlier three-lobe design with a four-lobe blower turned by a class 13 gear.
The blowers are solid components made from a special-purpose aluminum alloy. The tolerance in the interface fit between the two rotors is vital to making an efficient and quiet supercharger. “We used to use an epoxy paint that was baked hard on each rotor,” said Doug Brouillard, assistant engineering manager. “What we found was that very small differences in the tolerance and fit made a profound difference in the overall performance and efficiency.” To solve this problem, Eaton switched to a patented abradable powder coating in 2002. This abradable coating is applied electrostatically, and then “worked in” or “broken in” during operation. What this essentially does is provide a zero-gap fit between the rotors. “It creates a custom fit for each pair of rotors in each supercharger,” said Brouillard.
While ingenious, there is more to the design than creating a custom tight fit with a gap of about 0.0001" (0.0025 mm). “The essential part of the Eaton intellectual property is the profile of the rotor itself. It is the profile that provides the durability, NVH, and other performance,” explained Brouillard. Designing it is one thing, making it is another.
Concentration Is the Key to Success
According to Jackson, the Athens plant has established a number of competencies they believe are necessary in order to produce a finished product that maintains a competitive advantage. Starting around 2004, Eaton chose to concentrate on just three core competencies: rotor machining, assembly, and end-of-line testing. To this end, other on-site functions needed to manufacture the devices—operations such as metrology, maintenance, and MRO—are outsourced: Their partner company, Advanced Technology Services (ATS), is reponsible for maintenance, while Bruckner handles MRO-related indirect materials replenishment, and Gage performs metrology functions within the plants.
Another factor is empowerment. “This is an ‘Eaton Philosophy’ plant, where every employee is a salaried worker,” Jackson explained, with the same benefits as professionals and engineers. It is a philosophy that allows a relatively small team to produce hundreds of thousands of precision-built superchargers each year at the facility.
Certainly a unique design is critical to Eaton’s competitive advantage. So is the design of the tooling and programming of milling machines and assembly automation—especially for milling the critical rotors—according to Brouillard. In fact, profile designs are a joint effort between the design engineering staff in Eaton’s Marshall (MI) facility and the Athens plant. Why? Because manufacturability is just as essential as an efficient design to give Eaton a competitive advantage.
Precision, Automation, Skill and Advantage
It was also obvious during an exclusive visit to Eaton’s manufacturing facility, that certain aspects of the manufacturing process require a high level of operator skill. This is especially true when precisely machining and milling the rotors.
After precision milling, the abradable coating is electrostatically applied and then heat-treated and bonded onto each rotor. “The coating is an inexpensive way to make a high-tolerance device. This is in the never-ending fight to balance tolerance against cost,” explained Brouillard.
In line with concentrating competency in assembly, Eaton outsources other parts of the final product (such as housings, gears, and shafts) that are assembled by Eaton in purpose-designed automation cells. Each cell uses advanced levels of machine vision, servo-processes, and load-measuring cells right in the assembly process itself. Each part is marked with a unique bar-code identifier and as the part is assembled, all of the key process information data is measured. This is stored and tagged to that unique bar-code identifier. “That provides part traceability for individual parts and allows us to perform trending analysis for manufacturing,” said Brouillard. For such precision equipment, they target a process capability index (Cpk) in excess of typical automotive requirements.
The last element of the assembly process is setting the timing of the rotors—the relationship of how they are geared to turn relative to one another. Again, this is another process that requires operator expertise. “The difference in rotor fit can make the difference between a good rotor and a ‘do-over’, even scrap,” explained Brouillard. An automatic machine sets the timing, but loading the machine and post-process checking is done manually. The fit between rotors for each pair is checked to ensure the critical gap is within tolerance.
The final assembly into each sealed end-item is followed by a final test inside a sound-isolated cabinet. Each supercharger is acoustically and NVH tested before shipping.
“We are essentially a build-to-order facility, with low inventories. We build them and ship them basically the same day,” said Brouillard.
For manufacturers attempting to sustain competitive advantages over time, attention to detail is just as important as big decisions like concentrating on key core competencies. “We are looking to continue developing technologies for real-time process control and monitoring,” said Steve Poulter, engineering manager for the Athens plant. Continued application of machine vision, RFID tagging, laser marking, and data management are all such details that he thinks will find their way into making the superchargers of the future.
This article was first published in the 2013 edition of the Motorized Vehicle Manufacturing Yearbook.
Published Date : 11/13/2013