The temperature distribution of the lubricating interfaces is an important aspect of the functioning of positive displacement machines. It can determine the efficiency and the life time of the unit. In particular, it directly affects the fluid properties and the thermal induced deformations of the solid bodies. A simulation tool capable of predicting the fluid temperature in such gaps thus becomes very useful in the design process of these machines. The temperature distribution in a film comprises of many physical phenomena including convection and conduction along and across the film. Past numerical approaches solved this multi-directional conduction-convection problem using a threedimensional(3D) grid, making the tool computationally expensive and unsuitable for fast simulations. This paper proposes a hybrid fluid temperature solver, based on, a low computational cost twodimensional(2D) grid, to reduce the simulation time with reasonable accuracy. The piston/cylinder interface of an axial piston machine is selected as reference case to demonstrate the proposed approach. The hybrid approach was found to speedup the simulation times by 36%.

In the present paper the preliminary results of the potentialities that surface texturing has in improving the coupling of lubricated surfaces in relative motion is presented. This kind surface engineering requires careful design of the geometry to obtain relevant improvements; therefore, it is useful to study in detail the behavior of the fluid confined between the coupled surfaces by means of CFD analysis. The purpose of this research is to study the effect of dimples created on one of the two coupled surfaces and to observe the variation of tribological properties as their principal design parameters vary, such as dimple shape, size and spatial distribution. Furthermore, simulations have been carried out with different sliding velocities and fluid temperatures to analyze the effects that these variables have on the tribological performance of the textured surface. The simulations also consider the presence of cavitation and the influence of this phenomenon on the overall behavior of the textured surface is evaluated.

The piston/cylinder pair is the key lubricating interface of axial piston pumps. It suffers from excessive wear due to the huge lateral force, especially under high output pressure. In order to achieve predictive maintenance, it is significant to detect the performance degradation of the piston/cylinder pair. In this paper, a method to predict the wear of the piston/cylinder pair is proposed. The wear regions and corresponding wear depths under different conditions are investigated. The distributive characteristic parameters of the oil film are obtained, which can reflect the load-bearing and lubrication conditions at each region of the friction pair. Based on the oil film characteristic parameters, the most suitable wear model is chosen to calculate the wear depth, and then the entire wear profile of the piston/cylinder pair is obtained. The experimental investigation is carried out, and the results show that the accuracy of the wear regions and corresponding wear depth prediction is high. This method can be used to pump healthy management and choose the suitable working conditions of the axial piston pump.

In hydraulic-mechanically controlled variable displacement pumps, the actual pump controller produces additional power losses. Due to the low damping coefficients of all pump controller’s components, hydraulic-mechanically pressure controlled pumps use to oscillate while adjusting the pressure level in the hydraulic system. In several state-of-the-art variable pump controllers, a damping orifice connects the control actuator’s displacement chamber with the reservoir. This bypass dampens the movement of the control actuator but also leads to bypass losses during steady-state operation of the pump. A new concept for damping via feedback loops avoiding bypass losses is presented in t his paper.

This paper presents a numerical model for the evaluation of the actual torque in Gerotor units. The model consists of two major modules: the pre-processor module and the HYGESim module. The preprocessor module consists of the geometric and the mechanical module. The geometric pre-processor module considers the CAD geometry of Gerotor with tolerances as input and it provides as output the geometric features needed to evaluate the rotor loading and the flow features. The mechanical preprocessor module evaluates the forces of interaction at the contact points between the rotors. The flow displaced by the unit is evaluated using a lumped parameter model whereas the lubricating gaps are evaluated by solving the Reynolds Equation. The main novel aspects consist of the evaluation of the frictional losses at various interfaces. An Elasto-Hydrodynamic Lubrication (EHL) approach is used to evaluate the frictional losses at the contact points between the rotors. Tests on a prototype Gerotor unit are performed for the model validation, particularly as pertains to the features of the shaft torque. Additionally, the paper comments on the distribution of the different torque loss contributions associated with the operation of the unit taken as reference.

This paper provides an overview of the challenges and possibilities of the integration of electric drives into diesel-hydraulic excavators. Due to the drivers of emission reduction, the use of renewable energies and more energy efficient systems, a global push leads to the integration of electric drives in excavators. In mobile machinery such as excavators, new possibilities and challenges of the adaptation of the drive train and energy storage arise. Rotational actuators can be powered by direct electric drives to avoid losses of the hydraulic system. Adapted hydraulic system topologies enable recuperation and reduce throttling losses in hydraulic systems. Variable and overall higher electric motor speeds reduce the size of the electric and hydraulic components and enable operation in more efficient operating points. To evaluate possible changes to the traditional hydraulic excavator systems, a simulation model is built and the proposed adaptations are implemented. The paper concludes with the evaluation of the proposed system changes and an outlook for further possibilities of hydraulic system adaptions in relation to the electric drive.

The boom systems of mobile cranes and aerial platform vehicles are driven by hydraulic systems, to be specified, valve-controlled hydraulic cylinders. This hydraulic actuated boom system can accomplish the tasks such as lifting heavy loads or carrying personal to high position, by the design of a long boom structure. In practice, the boom structure is designed as light and slender as possible to control the structure self-weight. However, such structure is quite flexible and can be easily stimulated by the loads, including the driving force or torque from the hydraulic system. Our research focuses on trajectory planning for hydraulic actuated boom where both hydraulic driven system and boom structure deformation are considered. In this paper, the hydraulic actuated boom system is formulated as a port-Hamiltonian system which is a proper modelling method for multi-domain system. The problems of trajectory optimization and vibration control are formulated as optimal control problem based on port-Hamiltonian model and this procedure is tested on a model of hydraulic cylinder. A reasonable result is solved with the selected cost function and inputs.

In the field of fluid power, accurate knowledge of fluid properties is vital for reasonable prediction of component behaviour and system performance. In general, these properties depend on the pressure and temperature levels that the respective medium is exposed to. The properties and their respective dependencies are not publicly accessible for many fluids commonly used in fluid power. If measured values – typically published in the form of mathematical fluid property models – are available at all, their quality is typically unknown. The paper aims to provide tools to objectively ascertain the quality of measured fluid properties. For this purpose, an equation is derived which establishes a relationship between the thermodynamic parameters of density, bulk modulus, heat capacity and thermal expansion coefficient. The presented equation is always satisfied by liquids as well as gases as long as they can be treated as a continuum. Based on this relationship, the degree of thermodynamic consistency of measured properties is evaluated: The less the equation is fulfilled by experimentally determined fluid properties, the more the measured values violate physical laws. The procedure of assessing the thermodynamic consistency is demonstrated by evaluating published fluid property models with the method outlined above. To aid engineers in judging which degree of thermodynamic inconsistency is acceptable, a cut-off value is suggested.

Thermo-elastic errors are one of the main drivers for reduced quality of workpieces in machining. Cooling systems can prevent these errors and improve quality. The paper describes a simulation method that takes into account both the temperature field of a machine tool frame and the fluid cooling system. Such simulations can help to improve the thermal stability of the machine tool frame.

Mass flow models for gaseous media describe the relationship between gas flow through throttle elements depending on pressure, temperature and type of medium. These models are used to calculate pneumatic components, to simulate pneumatic systems or to plan facilities. The known flow models are verified for ideal gases, such those as according to ISO 6358-1 (International Standard ISO 6358- 1: pneumatic fluid power – Determination of flow-rate characteristics of components using compressible fluids: General rules and test methods for steady-state flow, 2013). But they fail with real gases, especially at higher pressures. The objective of this contribution is to recommend a simple-touse model for the mass flow calculation of real gases. The advantage of the C and b model is the use of only two parameters. A testbench for high pressure up to 300 bar was used for model verification with air and hydrogen. The Library for standard dry air and hydrogen up to 1000 bar was used for the state variables of the real gases. The parameters C and b are obtained, applied and verified in the state space of real gas. With the C and b parameter it is possible to simulate not only the single component (valve, throttle, nozzle and so on) but also the whole system with a complete system simulation, like such as hydrogen filling stations.