Ellison says that fuel economy is not completely due to the turbocharger, but from a combination of the electronic controls and fuel injection.
"It's pretty much a trouble-free system," Ellison says. "For people that are familiar with the medium duty engines, the only thing that will catch them a little bit by surprise is the electronic VG actuator."
USING 'ELECTRONIC DISCIPLINE'
If the technician is observing fault codes, there are troubleshooting trees to follow. Of the two or three turbochargers that Ellison knows that needed to be escalated beyond the technician, he found out that the service request was because the technician incorrectly followed the 'troubleshooting tree,' or a consecutive order of steps to follow for turbocharger repair.
Technicians and dealers are also able to access the troubleshooting trees in an electronic manual called QuickServe Online. This is a Web-based program designed for communicating online troubleshooting techniques.
"Working with this new generation turbocharger is a bit different," Ellison says, "it takes a little more electronic discipline, but it's a quantum leap in turbocharger technology."
The 2007 BorgWarner Turbocharger has been developed with variable turbine geometry (VTG) technology to provide boost control at all engine speeds, according to application engineer Adam Reinke with BorgWarner Turbo Systems. Using a traditional turbocharger package, Reinke says, this technology includes moveable guide vanes in the turbine housing to direct the speed and flow where the exhaust gases hit the turbine wheel.
He adds that the vanes are controlled by an electronic actuator mounted on the turbocharger. The vanes are moved from a fully open position, which makes the size of the turbine larger and allows more flow through it, to a fully closed position.
When fully closed, Reinke says, the flow is decreased and causes exhaust gas to accelerate through the turbine.
"There are two conditions you can look at for why a VTG is used," says Reinke. "At low engine speed and low load, there's not a lot of exhaust energy produced by the engine. If you close the vanes, you're maximizing the energy that's available because it accelerates the exhaust gas across the turbine wheel, which allows you to increase the boost pressure at those lower speeds. This reduces turbo lag, a common component of turbocharged engines."
An additional benefit, according to Reinke, is that there's an increase in exhaust back pressure by closing the vanes. "This helps drive exhaust gas recirculation, which lowers emissions output of the engines," he says.
Reinke also adds that under high-engine speed and high-load conditions there is a large amount of exhaust energy. During that time, the vanes can be opened to limit the boost and speed of the turbocharger. In turn, this will limit the boost that the turbocharger is delivering to the engine, which helps overall durability of the engine and turbocharger.
A combination of the vane mechanism is factored in to how the turbocharger helps meet emission targets.
"It can act like a small turbo, or it can act like a large turbo; it can accomplish both of those tasks in one package," Reinke says. "This allows for the flexibility to control it with electronic adjustment based on the driver's needs."
CHANGES IN 2007
For 2007, Reinke says that there are various improvements which increase the "robustness" of the turbocharger. The rotating components of the turbocharger are high-speed balanced, a process that spins the turbocharger at real-world turbo speeds, and records and corrects the balance level.
Reinke adds that the balancing process reduces the occurrence of instability at high turbo speeds.
"The bearing system has also been redesigned for increased durability," he says.
The VTG has also been updated to a new 'rollerless' design as well, according to Reinke, which features less moving parts and reduces the chance of binding or sticking in the mechanism.
"From an applications standpoint, you've got a lot of small-moving parts and a high-temperature environment. Reducing friction and increasing the corrosion-resistance is going to make a more durable part," says Reinke.
More on troubleshooting '02 EGR and ACERT engines from the Technology & Maintenance Council.