The increasingly stringent emission legislation and requirements related to fuel consumption reduction not only influence the powertrain but also their testing processes and methods. These become increasingly complex and must be specifically designed for the targeted optimization of internal combustion engines. FEV offers customized test benches for the development process and end-of-line inspection to meet these challenging targets. “These special test benches are the result of years of research and extensive experience in powertrain development as well as development and use of the corresponding testing tools,” explains Dr.-Ing. Alexander Tolga Uhlmann, Department Manager Thermodynamic Simulation & TC Development at FEV. “Each test bench is precisely adapted to the customer’s requirements and delivered as a turn-key product.”
FEV’s turbocharger friction loss test bench
Turbocharger bearing friction losses impact the overall turbocharger performance. Therefore, an in-depth understanding of bearing systems and their characteristics is essential in order to drive future improvements. One important tool for these investigations is FEV’s turbocharger friction loss test bench. In contrast to more typical turbocharger test procedures, in which performance maps are measured on a hot gas test bench, the compressor and turbine wheels are removed from the Turbocharger shaft on the friction loss test bench in order to measure only the mechanical losses. “Turbine efficiencies measured on a hot gas test bench do not reflect the pure aerodynamic values because they are superimposed by adiabatic effects and mechanical losses”, explains Uhlmann regarding the disadvantages of such testing.
The testing setup
An electrical drive with active magnetic bearings is connected with a torque sensor to the compressor side of the turbocharger shaft. Data transfer is performed telemetrically. The velocity and shaft raceway are monitored with optical sensors. As a special feature the axial force on the shaft may also be monitored and varied via a linear motor as may the oil temperature and, optionally, the cooling water.
Results for a passenger car turbocharger present a speed sweep at standard oil condition of TOil=90 °C. A quadratic dependency of friction loss vs. turbocharger speed was detected. Furthermore, the dependency of the friction power on oil temperature is shown for three discrete turbocharger speeds. This outcome also illustrates the challenge of this test device: i.e. high speeds (n>120,000 1/min) with very low friction power below 300 W. For lower speeds in passenger car applications extremely low friction torque below 0.005 Nm has to be resolved.
>> AN IN-DEPTH UNDERSTANDING OF BEARING SYSTEMS AND THEIR CHARACTERISTICS IS ESSENTIAL FOR FUTURE IMPROVEMENTS