Bearing Thermal Performance and Cage Slip Measurement for All-Steel and Ceramic Hybrid Compressor Thrust Bearings

Honeywell Aerospace is developing a 700 hp class turboshaft engine for the U.S. Army’s Small Heavy Fuel Engine (SHFE) program to meet the engine needs of future manned and unmanned rotorcraft. These engines will demand high performance, robust, reliable, efficient and affordable mechanical systems. The SHFE engine program is targeted to provide 700 SHP at Intermediate Rated Power (IRP) with a 20% reduction in Specific Fuel Consumption (SFC) while operating at 50% IRP. Furthermore, the engine design goal is to provide a 50% improvement in power to weight ratio. This paper focuses on rig tests to generate data for the gas generator hybrid ceramic thrust bearing and front bearing compartment. The bearing is a split-inner ring ball bearing that runs at 2.4 million dN at maximum HP shaft speed. This speed approaches the condition where a ceramic hybrid bearing may offer a higher-life design over a conventional all-steel thrust bearing. A hybrid configuration may also be more thermally stable, generate less heat, and be capable of operating at higher temperatures. For this reason the SHFE program performed a series of rig tests on both an all-steel and a ceramic hybrid version of the compressor thrust bearing. With the exception of the ball material, both bearings were identical, providing a unique opportunity to obtain a true “back-to-back” performance comparison. Data was collected on bearing heat generation and ring temperatures at these advanced operating conditions. Cage rotating speed was also measured to assess rolling element slip.