The inner bearing of a turbocharger decides many factors – efficiency, reliability, and longevity of the turbocharging system, as well as fuel consumption, emissions, and NVH properties of the entire vehicle. The development of the new bearing for turbochargers would encompass the use of state-of-the-art design tools and methods and also combine all the experience and best practices that BorgWarner had gathered in development and production over the past decades.
Standardized construction program for all requirements
The aim of the developers was to replace generations 1 and 2 of the existing B0, K, and S-Hundred friction bearing systems with a single product family. The new bearing system family would be named B10 through B30 for PC applications – depending on the size. The range for the CV market was originally to be named B50H through B70H, however the B80H and B90H frame sizes are recent additions to the plan due to the increased customer requests in these frame sizes.
Comprehensive marketing and application data were used to ensure optimal gradation across the size range and to better target customer needs. In addition, global applications groups were surveyed to provide information on expected future customer requirements. Critical characteristics such as rotor speeds, oil types, temperatures, pressures, leakage and blow-by requirements, NVH limits, etc. were explored and defined. Based on these market needs, the development team set itself aggressive goals for friction, rotor dynamic stability, size, weight, thermal isolation, oil draining, and sealing. Two of the key requirements were use of oil grades down to 0W20 at 150°C and operation to 800°C turbine inlet temperature without water cooling (with a stretch goal of 850°C).
The goal: a leap in innovation
The current B-Series Gen2 bearing system was really more of an evolution of the K and S-Hundred Series. For the Gen3 project, the team faced the challenge of taking a revolutionary step in design and performance. The Gen3 design team utilized multiple simulation tools to model rotor dynamics, fluid flow, heat transfer, and stress on the new bearing. The extremes of geometry and operating conditions, and not just nominal conditions, were a core part of the analysis plan. They used a multi-variable optimization technique to find and optimize all of the key characteristics simultaneously. These modeling and optimization techniques allowed the team to quickly and efficiently explore a far larger solution space than previously possible.
The oil flow visualization shows significant improvements over the previous generation in terms of sealing and oil flow.
The Gen3 team.
Development of the new B-Series Gen3 bearing system family has been
a fun and rewarding challenge for the team of developers from BorgWarner.
A number of parameters were optimized for the rotor design in order to improve the rotor stability, reduce the length, and minimize manufacturing tolerances.
As the thermal simulation shows, the heat from the turbine side is effectively kept away from the bearing and compressor side of the turbocharger.
Photos: © BorgWarner
B70H was the first frame size that the team worked on. Within a few months, they had analyzed hundreds of rotor designs and quickly converged on a solution space that met all the requirements, including increased rotor stability, reduced length, and minimized manufacturing tolerances. They also worked on optimizing the mechanical design to reduce mass and improve thermal isolation, keeping the turbine heat away from the bearings and compressor side of the turbocharger. The team also chose to utilize a bolted compressor backplate design in order to significantly improve weight and manufacturability. It also significantly improves accessibility for installation of the actuator pivot shaft in VTG applications.
Significant improvements achieved
The resulting B70H design was completed within 9 months. The experts at BorgWarner then procured development hardware and started testing the new turbo to verify that they hit all the design targets. As the results came in, they verified the methodology that the team used.
The BorgWarner team was able to achieve the rotor stability targets, although they did need to do an iteration on the thrust bearing to achieve the load capacity requirement. Oil flow visualization was done to confirm improvements in the compressor seal area, and measurements were made showing up to 50% reduction in oil flow without compromising thrust capacity or rotor stability. At the same time, measurements showed a 30 to 50% improvement in seal blow-by, and a 75% improvement in oil leakage – even at extreme pitch and roll angles required for some off-highway applications. The Gen3 bearing system also significantly reduces bearing friction, resulting in 1 to 2% improvement in combined turbinemechanical efficiency.
The thermal survey and hot shut down testing demonstrated that the new Gen3 bearing housing and thermal isolation design were able to maintain temperatures at the turbine seal and bearing area well below the oil coking limit, even at the stretch goal of 850°C turbine inlet temperature. This enables the Gen3 bearing system to be used on more demanding natural gas applications without water cooling.
Gen3 test samples already available
The team has made continuous improvements throughout this process, incorporating lessons learned from the B70H simulation and testing. As they started design work on the B50H and B60H frame sizes, they were able to reduce the overall time, effort and cost to develop and validate the smaller center sections. As of March 2019, the B70H and B60H center sections were released for application and are being used by a number of customers as test samples. The B50H is currently undergoing validation, which is set to be complete by Q3 of 2019.
Development of the new B-Series Gen3 bearing system family has been a fun and rewarding challenge for the team of developers from BorgWarner. The success of this large-scale project can be attributed to the motivation of everyone involved, as well as to clear inputs and strict, efficient program management. Automotive manufacturers are already showing a lot of interest in turbocharging systems with the new bearing, and BorgWarner is now focusing on supporting applications teams and industrialization activities to continue the success of the innovative new Gen3 product line.
Photos: © BorgWarner