Directional control valves are commonly used in position control systems for hydraulic cylinders. The valves direct the oil flow either in or out of a cylinder chamber, thus changing the cylinder length. It is state of the art to have two valve actuation systems (usually solenoids) per operated cylinder: one for extending and one for retracting it.

At ARGO-HYTOS it was found that it is possible to fulfil these requirements with a specially designed 4/3-proportional spool layout and to use only one solenoid for its actuation. This way the valve size can be reduced significantly. Furthermore the system is expected to be cost-competitive even compared to regular systems with two on/off valves. Thus it is possible to provide a proportional valve function and reduce necessary design space.

Compared to regular proportional valves, the here mentioned valve has a lower resolution which is due to the limited spool stroke with only one actuator – this is acceptable in many applications. One of these is suspension systems with their cylinder position and pressure control. Here, the typically used on/off-valves with constant orifices have already proven their function in many suspension control systems. However, the setting of constant orifices is always a compromise within many external boundary conditions.

Therefore an adjustable valve opening area is beneficial for suspension systems. This can be due to oil viscosity/temperature, as well as extreme load changes or varying pressure supply from the central hydraulic system. With a proportional valve, the cylinder position and the rodside preload pressure can be brought to the desired level quicker, yet without overshoot. This particularly improves comfort and reduces undesired overloads on suspension components.

The mentioned valve is already used in the ARGO-HYTOS Modular Hydro Pneumatic Suspension MHPS, which is currently under development. The valve has successfully passed lab tests, system and field tests are planned for summer 2013.

Gear volumetric pumps produce high level of vibrations and fluidic pressure fluctuations even in normal operating conditions owing to periodic meshing of the gear teeth. In general, conventional spectral analysis of vibration signals may neither help to analyse the signals nor to reveal the presence of this periodicity. Cyclostationary models have proven their usefulness for understanding experimental data, for predicting trends and for machines diagnosis where faults in rotating components will typically produce a repetitive release of energy. These models are based on statistical descriptors rather than partial differential equations. In addition, when the cyclostationary framework is used with the angular variable of the machine rather than the time variable, it makes it possible to localise precisely the fault within the angular reference thus simplifying extremely its detection. The presence of a fault in gear pumps such as tooth defect, tooth crack or wear usually affects the pressure and the vibration signals by imposing strong periodic modulation, which a cyclostationary approach is well suited to detect.
In this paper, many condition monitoring indicators are calculated using cyclostationarity analysis of the down stream pressure signal. This signal is measured using ICP sensor installed on the outlet of the pump. An accelerated life time test is used in order to check the evolution of these indicators during the gear degradation. The historical trends of these calculated parameters reveals that they are relevant for detecting the pump efficiency degradation and can be used as relevant features for condition monitoring of gear volumetric pumps.
Finally, it is proved that cyclostationarity improves wear detection in gear pumps and the extracted diagnostic information can be used for condition-Based Maintenance system.

A thin pressure sensor finds many areas of interesting challenges where the application of standard pressure transducers takes high design effort or simply is not possible.
The basis of the sensor is a thin Polyvinylidene fluoride film (PVDF). As the film solidified under electrical potential, it has piezoelectric qualities. When the film is subjected to pressure, electrical charges can be measured on the film’s surface and serve as a measure for the pressure.
The main advantages of the described sensor are its thickness, flexibility and the possibilities to realize both a spatially and temporally resolved measurement. The fluid flows are hardly influenced by the low thickness of the sensor and due to its flexibility, it can be mounted on curved surfaces as well. The spatial resolution is defined by the width of the electrode (currently 150 μm). The temporal resolution can be set from the cutoff frequency of the charge-amplifiers (0.01 Hz) up to the natural frequency of the sensor (in the range of GHz).
One challenge in the realization of this measurement system is the affixing of electrodes on the PVDF-film’s surface. The material has a very low adhesive force on the surface. Methods such as sputtering or electroplating have failed to affix the electrodes on the film’s surface properly.
Hence, the first sensor prototypes produced were manufactured using Flex-PCB technology. An example of this sensor design is shown in
Figure 1. This sensor is used to measure cavitation implosions, where pressures in the range of 5-50 MPa arise. The sample rates necessary to resolve these implosions go up to the range of several MHz.
Another interesting method for the manufacture of the sensors is the screen printing technology. At the time, this printing technique is increasingly used for the realization of organic and inorganic electronics. The method allows a low cost production of different electric parts and a relatively high resolution of the structures.
The new printed sensor has a small total thickness in comparison to Flex-PCB- technology. The printing process takes place on a semi-automatic screen printing machine Kammann K15Q-SL with a printing speed of 0.5 m/s. The electrodes are printed on a PVDF-film with a thickness of 28μm wet on wet two times to ensure a better reproducibility of the printed structures. All in all, a layer thickness of about 6µm could be achieved for both sides of the sensor.
The width of the smallest printable electrodes is currently about 150μm. As fluid is a silver acrylic-based adhesive used.
The printed electrodes are connected to a board via FFC connectors. On the current board 32 charge amplifiers are installed whose analog outputs can be connected to a data acquisition card (PC). The analog channels are multiplexed, so that currently a sensor resolution of 1024 pixels is feasible. Alternatively the analog signals can be routed to the on board analog-digital-converters (ADC). ADC modulates the analog voltage into a TTL signal with a voltage-dependent pulse width with frequencies of up to 10 MHz for all 32 channels. Depending on the application, the digital data from the ADCs is processed with a FPGA device and stored in a PC.
The sensor design is used for measurement of cavitation impacts in a nozzle. In this test rig a maximum pressure in the range of 5 MPa and frequencies up to 500 kHz are expected.

Oil condition monitoring is a vital part of integrated asset health management. With an increasing impetus towards real-time decision making, delays incurred in offline laboratory oil analysis are becoming less acceptable. At present, several oil quality parameters can be monitored by commercially available sensors, and active research and development programmes are being pursued by both academic and industrial researchers to develop robust, cost effective sensors for the remaining key parameters.
State of the art are optical particle sensors, dielectric relative water sensors and to a certain degree dielectric and conductive oil quality sensors.
This paper presents an overview of currently available oil condition sensors, their advantages and limitations and looks at some recent developments, particularly in the following three areas: Contamination by metallic wear debris, measurement of total water content and determination of in-service oil viscosity. In each case, quite different technological solutions have been adopted.
Metallic Wear Debris: Recent improvements in the sensitivity of inductive particle counters have enabled the detection of individual ferrous particles down to the sub-100μm diameter regime and close to the 100μm diameter mark for non-ferrous metals. Experiences of particle counters in wind turbine applications have shown the potential for enormous benefits in failure prevention.
Total Water Sensor: Online sensors for total water content measurement utilising infrared transmission measurements have also been recently developed. The advantage is, that this type of sensor, in comparison to the state of the art dielectric relative water sensors, can measure the absolute water content over a wide range.
Viscosity Measurement: Commercially available viscosity sensors include both the oscillating piston type and high frequency oscillating crystal designs (SAW/TSM). However a cost effective device employing a low amplitude, mid-frequency vibrating sensor element has been recently developed. Key features include accurate measurements over a very wide viscosity range and an operating range which covers high temperature and pressure applications.

Within the scope of the proposed paper the functional principles of these new measuring technologies will be presented theoretically enriched by measured data from application examples.