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The cluster of excellence “Tailor-Made Fuels from Biomass” (TMFB) at RWTH Aachen University seeks to identify and investigate new potential biofuels and their production routes. To ensure a safe handling in common-rail systems the lubricity of future biofuels is part of the investigations. To further deepen the understanding of the behaviour of such fluids in the regime of boundary lubrication a group of twelve potential biofuels and systematically derived fluids was investigated by a modified version of the standardised High Frequency Reciprocating Rig test procedure for Diesel lubricity. Insufficient lubricity is observed for most biofuels whereas linear molecules with polar head groups provide good or very good lubrication. For all studied groups longer molecules provide better lubricities. The position of the functional group significantly influences the overall lubricity and impact of the carbon chain length.

In this paper compatibility studies of biofuel candidates and similar liquids with the elastomeric materials nitrile butadiene rubber and fluoroelastomer are presented. The results gained with defined reference elastomers are compared to results gained with the materials used in the technical application. For this purpose test specimens are prepared from fuel hoses and the material used for shaft seals of fuel pumps. The experimental results are subsequently used to evaluate prediction approaches based on the HSP- and QSPR-method. Finally a comparison of these two approaches is given.

This paper analyzes different concepts for storage and recuperation of kinetic energy during braking operation in a forklift truck application. The reduction of fuel consumption is one of the challenges for on and off-road vehicles. Starting from a conventional hydrostatic transmission, secondary hydraulic control and a hybrid solution are investigated. Wasting kinetic energy during braking operation of mobile working machines in cyclic applications and converting it into heat energy instead of reusable energy is a very inefficient principle still used in industry. Rising energy costs, enhanced government guidelines and increased environmental awareness require more efficient drive concepts for the next decades. Recuperation of kinetic energy during braking operation provides the opportunity of increasing the efficiency of mobile working machines. Efficient recuperation of kinetic energy requires a proper application and a low-loss system design.

A new hydraulic brake utilizing a self-energizing effect is developed at the Institute for Fluid Power Drives and Controls (IFAS). In addition to a conventional hydraulic braking actuator, it features a supporting cylinder conducting the braking forces into the vehicle undercarriage. The braking force pressurizes the fluid in the supporting cylinder and is the power source for pressure control of the actuator. The new brake needs no external hydraulic power supply. The only input is an electrical braking force reference signal from a superior control unit. One major advantage of the SEHB concept is the direct control of the actual braking torque despite friction coefficient changes. The prototype design, presented in this paper, is done in two phases. The first prototype is based on an automotive brake caliper. It is set up to gain practical experience about the hydraulic self-energisation and to prepare the laboratory automation environment.

The floating cup principle is a new axial piston concept for hydrostatic machines. It features a high number of pistons, arranged in a double ring, back-to-back configuration. Furthermore the pistons are locked onto a central rotor and each piston has its own cuplike cylinder. These ‘cups’ are floating on and supported by a barrel plate. The pistons have a ball shaped crown, which is sealing directly on the cylinder without a piston ring. A first prototype of the new pump has been built and tested. For comparison a state-of-the-art slipper type pump and a bent axis pump (both constant displacement, 28 cc/rev) have been tested as well. The steady-state performance tests have proven the high efficiency of the floating cup principle. The low speed tests, during which the pumps are tested as a motor, have confirmed the low friction losses and high starting torque of the floating cup principle. Furthermore the high number of pistons strongly reduces the torque variations.

Proportional valves for hydraulic and pneumatic applications are well developed and the technology behind it can be considered mature. The paper focuses on valves that are already on the market as well as on developments which can be observed at universities and their institutes or departments. For both fields - meaning hydraulics and pneumatics - the trend of integrating digital electronics into the components is treated and discussed. Developments accompanying these innovations include miniature, micro and low power valves as well as standards to drive these valves directly from a field bus. However, also innovations on the mechanic, electric or fluidic side on valves are remarkable and will be introduced to the reader.

A special clamping cell developed in the framework of the collaborative research center 368 at the Technical University of Aachen (RWTH) is able to clamp different workpieces in an absolutely autonomous way. In this paper an autonomous hydraulic clamping system for milling processes as well as a clamping system for 3-dimensional laser welding are presented. In particular a proportional throttle valve for several hydraulic cylinder developed for this clamping cell is introduced. The clamping system for the milling process is a completely autonomous hydraulic clamping system. All of the hydraulic as well as the electric components are integrated into this device. Further more a micro controller and a power supply are integrated into the clamping system as well. For the welding process the clamping system has to hold two sheet metal.

The simple, compact design and the high power and force density of linear-motion hydraulic actuators make them suitable for a wide range of applications in the machine building and systems engineering sectors. Linear hydraulic actuators do, however, demonstrate more elasticity with respect to the desired position than their electric counterparts by dynamically changing loads. The time response for maintenance of the desired position when subjected to dynamic load changes is referred to below as dynamic load stiffness. This article begins by considering the elementary principles of a cylinder's stiffness. Afterwards it then goes on to describe various approaches in an attempt to increase dynamic load stiffness and to present the simulation results for the different systems. Then it concludes by discussing these results and using them as the basis for an assessment of the potential of each approach.

Tribological systems in hydraulic pumps, motors and cylinders are considerably stressed by friction and wear. Working life of components in hydraulic circuits might be extended by the use of wear resistant materials. Modern processes like Thermal Spray Technology, Physical Vapour Deposition and Plasma Nitration enable the application of wear resistant coatings with excellent friction characteristics. A wide variety of diffe-rent coating materials is available with various proper-ties concerning surface hardness, surface structure and coefficient of friction. Thus, an adaptation of surface properties and loads can be achieved. This paper presents results from investigations of coated simplified specimen and from tests with coated fluid power components.

While the oxidation stability of environmentally friendly hydraulic fluids has been markedly improved, the controllability of hydrolysis is still poor. A research project IFAS has taken up this problem. The aim was to prevent the water entry and to diminish the water content of hydraulic fluids by changes in reservoir design and separation devices. An essential point of interest was the development of low-cost solutions suitable for the refit of existing mobile machines. The ability to separate water is primarily determined by its degree of solubility in the respective fluid. The only method that will keep the water content in a hydraulic fluid far below its saturation point is vaporization into the surrounding atmosphere. An attractive application of this principle is the separation within the reservoir. The heat of the oil vaporizes the water, transporting it into the gas phase which may then be removed by exchange with the outside air.

Environmental aspects will have a major influence on the application of hydraulics in mobile systems in the near future. With the use of environmentally friendly fluids, these aspects can be fulfilled in a convenient way. Nevertheless there are differences between the well known mineral based oils and environmentally friendly fluids based on synthetic esters which represent a new mainly unknown fluid type. For a trouble free usage of these fluids in hydraulic systems, a founded knowledge of the fluid's properties and its interaction with hydraulic components is a basic requirment. For this purpose an application based testing of these fluids is essential.