Analytical and experimental studies of rear axle efficiency

Die vorliegende Arbeit ist ein Beitrag zur Wirkungsgradberechnung von Achsgetrieben im Betriebsbereich. Die Optimierung des Achsgetriebes kann bei Fahrzeugen mit längseingebautem Motor bzw. Allradantrieb einen signifikanten Beitrag zur Verbesserung des Wirkungsgrades und damit zur Reduktion der CO2-Emission leisten. Daher besteht der Wunsch den Einfluss der maßgeblichen Parameter auf den Wirkungsgrad bzw. die Verlustleistung bei der Auslegung der Komponenten darzustellen und bewerten zu können. Die Entwicklung entsprechender Methoden ist Gegenstand der Arbeit. Der Fokus liegt hierbei auf dem Einfluss konstruktiver Parameter auf Reibwert und Wirkungsgrad bei der Auslegung der Radsätze. Es wird ein thermo-elasto-hydrodynamisches Mischreibmodell für elliptische Kontakte entwickelt und auf Hypoidradsätze angewandt. Das Verzahnungsverlustmodell wird mit Methoden zur Berechnung der Lager-, Plansch- und Dichtungsverluste zu einem Achsgetriebeverlustmodell erweitert. Der verwendete Prüfstandsaufbau zur Wirkungsgradmessung wird beschrieben und Vergleiche mit experimentellen Ergebnissen werden gezogen. Einen Schwerpunkt der Arbeit bildet die Parameterstudie zum Einfluss makro- und mikrogeometrischer Verzahnungsparameter auf Reibwert und Wirkungsgrad. Anhand der Parametervariation werden qualitative und quantitative Aussagen zum Einfluss der konstruktiven Parameter auf den Wirkungsgrad erarbeitet. Weiterhin wird am Beispiel eines Achsgetriebes aufgezeigt welchen Einfluss die verwendeten Fahrzyklen auf die Zusammensetzung der Verluste besitzen. Die ganzheitliche Betrachtung der Wirkungsgradproblematik schließt mit einer kennfeldbasierten Bewertung von Optimierungsmaßnahmen im Betriebsbereich.The present thesis is a contribution to the efficiency calculation of axles in the operating range. The optimization of the axles can make a significant contribution to improve the efficiency of drive trains and therefore reduce the CO2 emissions of vehicles with inline engines or all-wheel drives. Thus, there is a desire to investigate and evaluate the effect of the relevant parameters on the efficiency and the power dissipation in the design process. The development of appropriate methods is the objective of the thesis. The main focus is to model the effect of the design parameters of hypoid gears on friction and efficiency. A thermo-elasto-hydrodynamic mixed lubrication model for elliptic contacts is developed and applied to hypoid gear sets. This gear mesh loss model is combined with methods to calculate the bearing, churning and seal losses into an axle loss model. The test setup used for axle efficiency measurement is described and comparisons with experimental results are drawn. One major focus of the work is the parametric study of the effect of macro- and micro-geometry design parameters on hypoid gear friction and efficiency. Based on the parametric study the influence of design parameters on the efficiency is derived in both quality and quantity. Furthermore the effect of drive cycles on rear axle efficiency is identified and a break down of losses for different drive cycles is facilitated. The holistic approach to efficiency analysis in the operating range concludes with a map-based assessment of optimization measures

Design of an aircraft generator with radial force control.

With the increasing electrical energy demands in aviation propulsion systems, the increase in the onboard generators’ power density is inevitable. During the flight, forces coming from the gearbox or gyroscopic forces generated by flight manoeuvres like take-off and landing can act on the generators’ bearings, which can lead to wear and fatigue in the bearings. Utilizing the radial force control concept in the electrical machine can relieve loads from the bearings that not only minimize the bearing losses but also increase bearing life. The objective of the MAGLEV project (Measurement and Analysis of Generator bearing Loads and Efficiency with Validation) is to study, demonstrate, and test a new class of high-speed generators with radial force control. In this paper, design steps of this type of generator and its test rig are presented and the measurement methodology used for radial force control is explained. The concept is developed in an electrical machine and is validated on a test rig by measuring required parameters like shaft displacement, vibrations and bearing temperature. Additionally, the friction moment of each generator’s bearings is measured and validated in a separate test rig under comparable conditions to the bearing loads in the generator. Therefore, a novel approach to determine precisely the bearing friction in a radial load unit, rotatably supported by an additional needle bearing is used, which shows a good agreement with the calculated friction. Furthermore, new calculation methods for the operating behavior of cylindrical roller bearings with clearance are presented, which are utilized in the generator test rig

The Friction of Radially Loaded Hybrid Spindle Bearings under High Speeds

Friction losses are an important parameter for evaluating the operational behaviour of high-speed rolling bearings. Specifically, in machine tool applications, the bearings are subjected to high radial loads and high speeds, which lead to increased forces in the rolling contact and, as a result, increased bearing friction. In this high-speed application, hybrid spindle bearings, typically made of ceramic balls and steel raceways, show better frictional behaviour compared to full steel-made bearings. Therefore, precise knowledge of the friction characteristics of high-speed hybrid bearings can improve friction models and generalise them to spindle bearings with different types, geometries, and operating conditions. In this article, a new straightforward and cost-efficient method for measuring the frictional torque in spindle bearings is presented. A rigidly arranged 7008 hybrid spindle bearing pair was tested up to rotational speeds of 24,000 rpm and high radial loads of 3 kN. The effects of oil–air and grease lubrication are discussed in characteristic diagrams of the tested bearings. Then, based on the test results, a friction calculation model is presented and validated for the outer race control and minimised power dissipation regarding the influence of radial forces

The Friction of Radially Loaded Hybrid Spindle Bearings under High Speeds

Friction losses are an important parameter for evaluating the operational behaviour of high-speed rolling bearings. Specifically, in machine tool applications, the bearings are subjected to high radial loads and high speeds, which lead to increased forces in the rolling contact and, as a result, increased bearing friction. In this high-speed application, hybrid spindle bearings, typically made of ceramic balls and steel raceways, show better frictional behaviour compared to full steel-made bearings. Therefore, precise knowledge of the friction characteristics of high-speed hybrid bearings can improve friction models and generalise them to spindle bearings with different types, geometries, and operating conditions. In this article, a new straightforward and cost-efficient method for measuring the frictional torque in spindle bearings is presented. A rigidly arranged 7008 hybrid spindle bearing pair was tested up to rotational speeds of 24,000 rpm and high radial loads of 3 kN. The effects of oil–air and grease lubrication are discussed in characteristic diagrams of the tested bearings. Then, based on the test results, a friction calculation model is presented and validated for the outer race control and minimised power dissipation regarding the influence of radial forces