Ball Bearing Turbo Reference
07-18-2008, 04:15 PM
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Ball Bearing Turbo Reference
There has been a lot of discussion on this board about ball bearing turbos. "Street Turbocharging" by Mark Warner, HPBooks, ISBN 1-55788-488-9 is an excellent resource.
Below is a quote from page 52. CHRA = Center Housing and Rotating Assemblies.
"As mentioned earlier, ball bearing-equipped CHRAs are somewhat superior to journal-style bearings from a performance point of view. They're also more costly, however.
Ball-bearing turbochargers were originally developed for diesel engines used in long-haul trucking and certain marine applications. The technology was needed to help shorten spool-up times and create boost earlier in a diesel's relatively limited RPM range. Shortly thereafter, the word got out to rest of the automotive world: ball bearings could offer a performance advantage for gasoline engine enthusiasts.
The biggest advantage of ball bearing-equipped CHRAs in gasoline applications is their ability to create boost sooner in the engine's RPM range - sometimes 500-700 rpm sooner. This is due almost solely to their lower rotating friction. It's been shown that reducing friction in a CHRA is functionally equivalent to improving turbine effeciency.
Ball bearing CHRAs also work well wiht lower oil flow rates. They're also assembled to very high tolerances, which means a closer fit between the rotating wheels and housing is possible. In addition, angular-contact ball bearings offer an inherent axial, or thrust load capacity, that can eliminate a separate thrust bearing altogether. Depending on the application and mounting configuration, a ball bearing CHRA can withstand 2 to 50 times the thrust loads that a conventional washer-type journal thrust bearing can tolerate. This in turn means greater resistance to compressor surge and other transient backpressure events in the intake and exhuast tracks."
The section goes on discusses different strategies for Garrett and Turbonetics and introduces ceremic ball bearings that will improve the design further.
For those who are interested, I would recommend the book. It has a lot of great content.
Below is a quote from page 52. CHRA = Center Housing and Rotating Assemblies.
"As mentioned earlier, ball bearing-equipped CHRAs are somewhat superior to journal-style bearings from a performance point of view. They're also more costly, however.
Ball-bearing turbochargers were originally developed for diesel engines used in long-haul trucking and certain marine applications. The technology was needed to help shorten spool-up times and create boost earlier in a diesel's relatively limited RPM range. Shortly thereafter, the word got out to rest of the automotive world: ball bearings could offer a performance advantage for gasoline engine enthusiasts.
The biggest advantage of ball bearing-equipped CHRAs in gasoline applications is their ability to create boost sooner in the engine's RPM range - sometimes 500-700 rpm sooner. This is due almost solely to their lower rotating friction. It's been shown that reducing friction in a CHRA is functionally equivalent to improving turbine effeciency.
Ball bearing CHRAs also work well wiht lower oil flow rates. They're also assembled to very high tolerances, which means a closer fit between the rotating wheels and housing is possible. In addition, angular-contact ball bearings offer an inherent axial, or thrust load capacity, that can eliminate a separate thrust bearing altogether. Depending on the application and mounting configuration, a ball bearing CHRA can withstand 2 to 50 times the thrust loads that a conventional washer-type journal thrust bearing can tolerate. This in turn means greater resistance to compressor surge and other transient backpressure events in the intake and exhuast tracks."
The section goes on discusses different strategies for Garrett and Turbonetics and introduces ceremic ball bearings that will improve the design further.
For those who are interested, I would recommend the book. It has a lot of great content.
