B. Sauer

An Alternative Slicing Technique to Consider Pressure Concentrations in Non-Hertzian Line Contacts

A new, fast method is presented for the analysis of roller-race contact in roller bearings. Based on a theoretical and implicit load-deflection relationship, an improved slicing technique is developed which accounts for a more accurate representation of the pressure distribution along the line of contact. For validation, the method is compared to literature data and results obtained by FEM analysis. In the course of this, roller profiling and misalignment are considered. Due to its fastness and accuracy, the method has its particular advantages when many contacts have to be evaluated several times, e.g., in static load distribution calculations and dynamic simulations.

Calculation and validation of a bearing impedance model for ball bearings and the influence on EDM-currents

This paper deals with the electric bearing impedance model for a ball bearing, based on a detailed mechanical bearing calculation. Based on the model, it is shown, how electrical parameters as well as mechanical parameters have an effect. The influences of the electrical and mechanical parameters are presented for EDM-currents Electrical Discharge Machining currents (EDM) at PWM voltage source inverter operation. For the calculation of the bearing impedance and description of EDM currents the electric properties of the lubricant, like dielectric constant, specific resistance and dielectric strength are discussed. The mechanical parameters such as bearing load, Hertzian area and lubrication thickness are necessary to be calculated. Calculated and measured bearing impedance are presented. A method to predict the speed range with EDM-current occurrence is discussed for the bearing type 6205 C3 and a mineral oil based lubricant.

Detaillierte Mehrkörpersystem-Simulationen des hochbelasteten Nocken-Rollen-Kontakts

Zur Einhaltung aktueller und zukunftiger Anforderungen an den Kraftstoffverbrauch, sowohl aus Kunden- als auch aus Gesetzgebersicht, steht neben der Optimierung der Brennverfahren auch die Reduzierung der auftretenden Reibungsverluste im Fokus der aktuellen Motorenentwicklungsprojekte. Hauptstellgrose der Reibungsreduzierung ist dabei die Verwendung von Schmierolen mit niedrigeren Viskositaten, durch die vor allem Reibung im Triebwerk reduziert werden kann. Im Gegensatz dazu steht die Ventilsteuerung, bei der die Reduzierung der Olviskositat eine Zunahme der Reibung hervorruft. Dabei steigt aufgrund der hohen spezifischen Belastungen und geringen Schergeschwindigkeiten der Anteil der Festkorperreibung, was sich neben dem Anstieg der Reibung auch in einer erhohten Verschleisanfalligkeit bemerkbar macht.

Optimized Cage Design for Increasing the Life of Solid Lubricated Roller Bearings

Roller bearings rank among the most used machine elements. Depending on the applications a lifetime of thousands of hours (e.g. machine tools: 15000h) can be realized as long as standard lubrications can be used. Nevertheless some applications only provide special environments, like high temperatures or vacuum, where oil or grease cannot be used. In these areas solid lubrication might be a choice. However solid lubricated roller bearing cannot offer similar lifetimes nor is a universally valid lifetime prediction available for such systems. Currently the friction work of a tribologically stressed surface offers a possibility for estimating the life. For doing so the paper gives an introduction. Further a test rig designed to examine roller bearings under high temperatures up to 300°C and high vacuum will be presented. In various experiments the influence of roller bearing cage design on its possible lifetime could be proven, especially if the cage has been used as a lubricant depot. On this basis a multibody simulation (mbs) model was built to get an understanding of the inner dynamics of roller bearings and its parts, e.g. rolling bodies and cage. While the geometry was built in commercial software the calculation of contacts, e.g. rolling body to raceway, and loads as well as friction is done in user written subroutines developed at the Institute of Machine Elements, Gears, and Transmissions at the University of Kaiserslautern. This model allows for an investigation of the effects resulting due to a parameter study of the geometry of the different parts a common roller bearing consists of: inner race, outer race, rolling bodies and cage. By using this tool the weak points in cage design could be determined as well as options for increasing the functionality of a cage as lubricant depot were shown. Combining experimental with simulated results, a new cage design for solid lubricated roller bearings could be developed. This new cage design increases the lifetime of the used test bearings from 2.5 million revolutions to more than 40 million revolutions. A further benefit of the new cage design is the ability to run at much higher rotational speeds than bearing systems that are available on the market nowadays.Copyright