During the past three years the Institute for Fluid Power Drives and Controls in Aachen has developed a new hydraulic system for mobile machinery called STEAM. The system represents a new step in excavator hydraulics, as it aims to reduce both the hydraulic system losses as well as those of the internal combustion engine by using a hybrid hydraulic architecture with accumulators. Starting with initial simulation studies the development has been followed by scaled test bench measurements and has progressed to a full scale validation using an 18 t excavator. The following publication aims to summarise the results obtained thus far with the aim of making them available to industry and encouraging their implementation in future applications.

/pdf/steam-a-hydraulic-hybrid-architecture-for-excavators-1apllrseva.pdf

STEAM – a hydraulic hybrid architecture for excavators

How to determine subsystem’s reliability and evaluate the whole machine’s reliability of the CNC (computer numerical control) grinding machine tool is important for reliability design and promotion. Each subsystem was modeled by a different distribution based on collected data and the models were optimized by the modified gray correlation degree, which was called the similar slope and close median gray correlation method. Methods of generating random data were proposed for different models. The reliability evaluation algorithm based on Monte Carlo simulation was studied and the whole machine’s reliability of the CNC grinder was evaluated by the algorithm. The evaluation result by the Monte Carlo algorithm was compared using the observed value and the evaluation value by the whole fitting method. The results show that the point estimation value evaluated by the algorithm based on Monte Carlo has high accuracy. The interval estimation by the Monte Carlo method was 20.2% and 38.1% by the observed value and the whole fitting value, respectively, which has more practical engineering significance. The reliability evaluation method can be used to assess the whole CNC grinding machine’s reliability in reliability design, and is also one reference for reliability evaluation of other electromechanical equipment.

/pdf/reliability-modeling-and-evaluation-method-of-cnc-grinding-2aj8ccpr2m.pdf

Reliability Modeling and Evaluation Method of CNC Grinding Machine Tool

The fatigue lifetime calculation of rolling bearings has been intensively researched in the past and has been well documented in standards. The majority of the conducted research in the field of bearing life expectancy only applies to bearings under continuously rotating conditions as can be found in many technical systems, such as vehicle transmissions. However, there are many other technical applications in which bearings perform oscillating motions, for which the fatigue life calculation is currently not standardized. For such oscillatory behaviour, there exist several modifications for the standardized lifetime calculation. The available modification approaches, however, assume purely sinusoidal oscillations. Thus, irregular non-sinusoidal oscillations require approximation with a simple sinusoidal oscillation to comply with the available approaches, which can lead to a loss of information. In this paper, a numerical calculation approach to modify the lifetime calculation for oscillating bearings underlying irregularly reversing speeds and varying loads is presented. The lifetime calculation results of this approach are compared to results of existing calculation approaches for fatigue life calculation of oscillating bearings. For this, the approaches are applied on simple sinusoidal speeds and loads. Subsequently, results of all calculation approaches are shown for irregularly varying speeds and loads, using the example of the drivetrain of an offshore crane winch with Active Heave Compensation (AHC). The calculation results indicate, that available lifetime modification approaches for oscillating bearings seem to overestimate the lifetime for irregularly oscillating conditions.

/pdf/lifetime-calculation-of-irregularly-oscillating-bearings-in-wchz87km6f.pdf

Lifetime Calculation of Irregularly Oscillating Bearings in Offshore Winches

To match the high expectations and demands of customers for long-lasting machines, the development of reliable products is crucial. Furthermore, for reasons of competitiveness, it is necessary to know the future product lifetime as accurately as possible to avoid over-dimensioning. Additionally, a more detailed system understanding enables the designer to influence the life expectancy of the product without performing an extensive amount of expensive and time-consuming tests. In early development stages of new equipment only very basic information about the future system design, like the ratio or the system structure, is available. Nevertheless, a reliable lifetime prediction of the system components and subsequently of the system itself is necessary to evaluate possible design alternatives and to identify critical components beforehand. Lifetime predictions, however, require many parameters, which are often not known in these early stages. Therefore, this paper performs a sensitivity analysis on the drivetrain of an offshore winch with active heave compensation for two typical load cases. The influences of the parameters gear center distance and ambient temperature are investigated by varying the parameters within typical ranges and evaluating the quantitative effect on the lifetime.

/pdf/sensitivity-analysis-on-the-reliability-of-an-offshore-winch-237w71c2c2.pdf

Sensitivity Analysis on the Reliability of an Offshore Winch Regarding Selected Gearbox Parameters

By defined structuring of sliding surfaces at dynamic contact seals friction and leakage can be reduced. Compared to macro-structures, micro-structures have the advantage of a quasi-homogeneous influence on the fluid behavior in the sealing gap. The development of suitable microstructures based on prototypes, whose properties are studied on the test bench, is very expensive and time-consuming due to the challenging manufacturing process and measuring technologies, which are necessary to investigate the complex rheological behavior within the sealing gap. A simulation-based development of microstructured sealing surfaces offers a costand time-saving alternative. This paper presents a method for simulative design and optimization of microstructured sealing surfaces at the example of a microstructured mechanical face seal.

Reducing Friction and Leakage by Means of Microstructured Sealing Surfaces – Example Mechanical Face Seal

In modern times, it is necessary to oer reliable products to match the statutory directives concerning product liability and the high expectations of customers for durable devices. Furthermore, to maintain a high competitiveness, engineers need to know as accurately as possible how long their product will last and how to inuence the life expectancy without expensive and time-consuming testing. As the components of a system are responsible for the system reliability, this paper introduces and evaluates calculation methods for life expectancy of common machine elements in technical systems. Subsequently, a method for the quantitative evaluation of the reliability of technical systems is proposed and applied to a heavy-duty power shift transmission.

/pdf/modular-system-modeling-for-quantitative-reliability-2n3iy49x8o.pdf

Modular System Modeling for Quantitative Reliability Evaluation of Technical Systems

Simulation einer mikrostrukturierten Laufwerkdichtung als flexibles Mehrkörpersystem mit Kopplung zur Elastohydrodynamik

Automatisierte Synthese leistungsverzweigender Antriebe

Automatisierte Parametrierung der Getriebesteuerung eines leistungsverzweigten Getriebes

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