Special Coverage

Management Briefing Seminars

TRAVERSE CITY, MI – Powertrain-expert BorgWarner Inc. expects greater demand for its turbocharging technologies as North American auto makers downsize engines to meet a consumer shift from gas-guzzling trucks to more fuel-efficient passenger cars.

However, Joel Wiegert, director-manufacturing, BorgWarner Turbo & Emissions Systems, says the supplier faces a number of production and environmental challenges with its sophisticated variable turbine geometry (VGT) turbochargers and regulated 2-stage systems.

By providing extra punch to smaller displacement engines, turbochargers allow auto makers to provide passenger vehicles with greater fuel efficiency without sacrificing performance.

“Because of these advantages, naturally aspirated engines continue to move to turbocharging through both ‘dieselization’ and gasoline direct injection,” says Wiegert, whose company built 7 million turbochargers last year and 56 million since 1970.

“Turbodiesel engines have grown dramatically over the past six years and will continue to have good growth, (but) more dramatic growth will be seen with turbo-gasoline engines.”

However, BorgWarner’s growth aspirations face a number of hurdles, Wiegert tells the Management Briefing Seminars here.

In addition to manufacturing puzzles, the supplier must meet demands for even greater fuel efficiency; improved transient behavior of its product to meet mandated vehicle emissions and drivability requirements; and higher boost pressure to achieve greater power density.

There also is the need for improved reliability, which faces a threat from higher temperatures caused during the exhaust recirculation phase to purge diesel particulate filters. Finally, the company must reduce the potential for oil leaks from its products, as well as the consumption of oil used for lubrication.

“Those final two are the ones that continue to challenge us in terms of maintaining strong durability requirements at the lowest cost possible,” Wiegert says.

Outside influences also impact turbocharger plans. Geographic location, for example, influences performance and durability due to altitude and ambient temperatures.

Variability in an auto maker’s engine oil quality and pressure affects turbocharger bearings, which can reduce the product’s life, as can vibrations from the powertrain and the cleanliness of the intake/exhaust air.

BorgWarner also must account for the growing number of applications, which today can range from a commuter bus in Mexico City to a European minicar.

“The application and how that product is going to be utilized is obviously very critical, as is balancing all that vs. the life of the product and the ultimate cost of the product,” Wiegert says.

One product BorgWarner expects to grow is its VTG turbocharger. Previously restricted to commercial-vehicle diesel engines, the technology now appears in many diesel passenger cars and is finding its way into direct-gasoline injection engines.

With the ability to regulate the turbine, BorgWarner can control flow rates and optimize efficiency. That means better performance at lower engine speeds, Wiegert says, as well as improved turbo response, which reduces turbo lag.

VTGs also achieve rated power faster than a fixed or waste-gated turbo, and the technology reduces nitrogen-oxide emissions, a key factor in growing diesel penetration in Europe to its current levels.

“This product has been key in making that happen, improving the durability and in meeting emissions,” Wiegert says.

But in a gasoline engine, where exhaust temperatures are greater, the many moving parts of VTG are subjected to a much hotter, non-lubricated environment. That leads to challenges of dimensional stability, as the heat can distort the product, and represents a key hurdle to its proliferation in gasoline engines.

“Robust design analysis and rigorous testing is required,” Wiegert says of VTG application development.

Manufacturing challenges unique to VTGs also exist, he says. The technology requires the development of production processes capable of holding critical tolerances to ensure the product’s reliability without impacting efficiency, as well as the use of high-grade materials, such as high-temperature nickel and chrome superalloys.

VTGs additionally demand sophisticated raw-materials processing, Wiegert adds, such as centrifugal casting and metal-injection molding. Complex component machining also is required.

“To pull all these components together, advanced assembly automation is necessary, utilizing modular assembly stations with robotic positioning,” he says. “Along the way, there are multiple quality checks to ensure the product meets the design specifications, as well as a final quality inspection.”

Wiegert sees an opportunity in the next five years for turbocharger suppliers and auto makers to partner in upcoming technologies, such as VTGs.

BorgWarner also builds a market-leading, regulated 2-stage turbocharger, he says, which utilizes a small turbo and a larger one to provide a boost at lower and higher engine speeds to enhance drivability and fuel efficiency.

An engine module and turbo-control unit communicate back-and-forth to optimize performance.

Temperatures and turbine-shaft speeds on the 2-stage turbocharger exceed 1,832º F (1,000º C) and 110,000 rpm, respectively, which also are demands the manufacturing process must take into consideration to provide a balanced product.

Many of the same production processes, material use, raw-material processing and quality checks for the VTG are required for the 2-stage product.

Says Wiegert: “This application is being used in a lot of European (vehicles), and there are many new launches that will be coming into the (U.S.), as well.”