Garrett Motion Ball Bearing Turbochargers
Production turbos have traditionally used a Hydrodynamic Bearing system to control the motion of the rotating assembly; the turbine wheel, shaft and compressor wheel. It is a simple system employing just a few parts, typically either 1 or 2 journal bearings, a thrust bearing thrust collar and spacer(s). It is also extremely reliable and needs only two factors to operate efficiently for the lifetime of the turbo:
- 1. A supply of good quality clean oil of the correct grade.
- 2. Operating within its designed performance envelope.
However, when looking at turbos for high performance applications, condition 1 is usually easy to meet, but by the nature of high performance applications, it means that condition 2 will be often exceeded. For this reason, we launched our range of ball bearing turbos for performance applications. Our first ball bearing wastegated turbo was launched for a gasoline engine production vehicle in 1993, so we already had a lot of positive experience with these.
The ball bearing cartridge offers a number of benefits over hydrodynamic bearings; firstly it absorbs much less power – all bearing systems are “parasitic” because they use some of the power generated by the turbine wheel to “drive” the bearing system. This then leads to a second major benefit; the “time to boost” is dramatically reduced, to give exceptional response to driver demands when needed.
There are also a number of other additional benefits, which all added together have now led to their adoption on mainstream, volume production turbos too and Garrett Motion took the lead by introducing the world’s first Ball Bearing VNT turbo for a production vehicle in 2010. But it is no ordinary ball bearing – it uses Ceramic Hybrid balls, as used in the aircraft industry and also in the latest version of Garrett’s LeMans 24 Hours winning turbos.
The Ceramic Hybrid ball bearing cartridges are now being rolled out retrospectively throughout our range of Performance Turbos and by the end of this year, most of the turbos currently using the extremely reliable Ball Bearing cartridges with steel balls, will be available using the latest Ceramic Hybrid ball bearings. All of the larger BB turbos with our 10 and 16mm cartridges – so anything from GT37R right up to GT55R (and of course the much improved GTX models) already use them!
The Silicon Nitride balls running on high grade bearing tracks elimates one of the possible natural wear characteristics of steel balls in steel tracks; adhesive wear. This is when wear takes place at microscopic levels between the two steel surfaces, due to “cold welding” (sticking together) between the components – and this can happen even under normal load and lubrication conditions. This inevitably creates wear particles, which will be carried by the oil and may lead to more wear. Ceramic balls cannot “cold weld” to the steel bearing tracks and this type of contamination of the oil is avoided.
The ceramic balls are also around 60% lighter than steel balls and lighter weight = lower inertia = centrifugal forces reduced = lower vibration levels = less heat build-up.
In addition, reduced ball skidding means that wear rates are improved when compared to conventional steel balls.
One fact about our Performance Turbos is that they will often be applied onto the highest tuned, most highly stressed applications and despite the advice offered on our Performance turbo website.
We know that our turbos may sometimes be subjected to mis-matching installations.
But even on well matched and well designed installations, they still work pretty hard and sometimes the extreme temperatures encountered during heat soak-back conditions can lead to a ball bearing cartridge becoming damaged as the oil oxidises on the bearings and shaft. Also, the temperature limit of the Polyamide (Engineering Plastic) retainers may be exceeded.
To help to combat this, we have also introduced some special treated steel cages to retain the balls. These have much higher tolerance of high temperatures (although oil temperature limits should still not be exceeded!), reduced wear rates and improved durability.
A lot of benefits from something that cannot be seen!