This paper investigates the effect of hydraulic oil on the efficiency of an electro-hydraulic forklift with lithium-titanate battery. The control of the system is implemented directly with a motor drive without conventional control valves. The measurements with two oils, a conventional multigrade hydraulic oil and a high performance hydraulic oil were carried out using the two lifting zones of the forklift. The paper provides accurate evaluation of the hydraulic system and a detailed analysis of the properties of the hydraulic oils before and after use in the mobile working machine. Finally, efficiency improvements in the suggested system are observed.

Within the cluster of excellence “Tailor-made Fuels from Biomass” at RWTH Aachen University new biofuels are developed and investigated. To ensure safe and reliable functioning of the new fuels in combination with state of the art fuel injection equipment, every fuel has to fulfill minimum requirements regarding lubricity. Hence, one focus of the cluster lies on the tribology of the fuel candidates.
Compared to diesel fuel the so far investigated biofuels differ strongly in their rheological characteristics. To investigate the impact of the fuel candidates on the tribological contact in standard common rail pumps a single-piston-test-rig was set up. The rig allows the measurement of friction forces in a piston/bushing-contact under realistic operating conditions. In the test rig all components of the relevant fuel lubricated contacts are original parts from the common injection pumps. In this paper results of measurements for different fuel candidates and pump operating points are presented and compared to the result of laboratory scale lubricity test methods like the well established HFRR-test.
In parallel to the experiment an elastohydrodynamic simulation model for the single-piston-test-rig is presented. The simulative outcome is compared to measurement results from the test rig.
The paper ends with a critical discussion based on experimental and simulative results regarding the validity of the simple pass/fail criterion defined in several norms for evaluating diesel fuel lubricity for the investigated low viscosity fuel candidates.

Environmental protection regulations are becoming increasingly strict. However, by using water instead of a hydraulic mineral oil in power-control hydraulic systems we can make a very positive step towards complying with these regulations. Nevertheless, using water instead of oil in power-control hydraulics is a novel and difficult task. Moreover, due to some specific characteristics of water, several requirements need to be fulfilled in every test rig and test specimen. On the other hand, the storage and regeneration of energy is also very important.

In this paper we present a newly developed water hydraulic accumulator. This piston-type of water hydraulic accumulator was designed to match the requirements mentioned above using water as the hydraulic liquid. The new water hydraulic accumulator has a volume of 4 litres and an allowed maximum pressure of 390 bar. A prototype was manufactured and a certificate was acquired from the European pressure directive PED 97/23/EC.

The new water hydraulic accumulator was designed, manufactured and tested by the Laboratory for Power-Control Hydraulics. This water accumulator was constructed so that we could simply exchange its sealings and/or guiding to investigate the tribological and hydraulic behaviour of the sliding contacts.

The results based on the hydraulic dynamics and thermodynamic changes of the gas in the hydraulic accumulator using two different hydraulic liquids (distilled water and mineral hydraulic oil) are presented and compared for three different pressures of nitrogen (30, 60 and 90 bar) and four different thermodynamic processes. The results show significant differences in the tested hydraulic accumulator efficiency between the slow thermodynamic transformation (isothermal process) and the fast adiabatic process.

The results indicate we should be optimistic about the use of the new water hydraulic accumulator in the field of water hydraulics in general.

Under low-speed high-torque conditions, hydraulic motors operate in the boundary lubrication regime. As a result, lubricating oil additives can affect friction and efficiency. This paper presents an investigation of boundary additive film formation, friction, and surface topography in benchtop tribometers and hydraulic motors. The mechanical efficiencies of geroler, axial piston, bent axis, and radial piston motors were measured under low-speed, high-torque conditions. The addition of a friction modifier to an ashless hydraulic fluid increased the efficiency of the motors at low speed. EDX analysis of motor surfaces after testing revealed the presence of tribochemical films from the hydraulic fluid additives. The ratio of additive elements to base metal was higher for the ZDDP fluid than the fluid formulated with ashless additives. AFM and 3-D surface mapping of tribometer surfaces revealed that the friction modifier reduced the surface roughness variation of the wear scar. The friction modifier also increased wear and reduced the concentration of phosphorus on the surface. These findings are significant because they provide insights to the development of fluids that can enhance motor efficiency.