Drive requirements of tractors and communal vehicles are demanding and varied. Energy efficiency and the different requirements in off-road and on-road operation are the basis for a powerful drive. Combinations with the so-called hydrostatic wide angle technology are often used. The article deals with a hydraulic drive with wide angle technology (45°) and an integrated, quick-shift, single stage transmission. A particularly large conversion range can be realized with this. Special shift elements, sensors and an adjustment developed for this purpose enable a fast, quiet and low-wear gear change. This new gearbox development will in future be implemented at RIGITRAC in cooperation with SAUER BIBUS.

The dynamic of cavitation in hydraulic components cannot be computed accurately yet and therefore cavitation is hard to predict. The cavitation phenomenon can be divided in three sub-phenomenona: Pseudo-cavitation, Gas-cavitation and Vapour-cavitation. Pseudo-cavitation discribes the enlargement of an air bubble due to a pressure drop. Gas-cavitation refers to bubble growth which is driven by diffusion of dissolved air from the surrounding fluid into the bubble, when the solubility of air in the fluid is lowered by a pressure drop. Vapor-cavitation is the evaporation of the liquid phase on the bubble surface. Usually all three sub-phenomenona occur simultaneously when the pressure decreases and are summarised as cavitation in general. To implement the physics of gas-cavitation in a dynamic mathematical model it is necessary to know the diffusion coefficient of air in the hydraulic liquid and the maximum amount of air which can be dissolved in the liquid. The calculation can be accomplished by using the Bunsen coefficient. In this paper both coefficients for three different hydraulic oils are calculated based on experimental results.

The cylinder block/valve plate interface is a critical design element of axial piston machines. In the past, extensive work has been done at Maha Fluid Power Research center to model this interface were a novel fluid structure thermal interaction model was developed which accounts for thermal and elasto-hydrodynamic effects and has been proven to give an accurate prediction of the fluid film thickness. This paper presents an in-depth investigation of the impact of the elastic deformation due to pressure and thermal loadings of the end case/housing on the performance of the cylinder block/valve plate interface. This research seeks to understand in a systematic manner the sensitivity of the cylinder block/valve plate interface to the structural design and material properties. A comparison between simulations results is done by utilizing different end case designs and material compositions, both in the valveplate and end case solids.

Markets show a clear trend towards an ever more extensive electronic networking in mobile and stationary applications. This requires a certain degree of electronic integration of hydraulic components such as axial piston pumps. Beside some wellknow approaches, the transmission of axial piston units still is relatively unexplored regarding electronification. Nonetheless there is a quite high potential to be optimized by electronic. In view of this fact, the present paper deals with the tribological contacts of pumps based on a demand driven hydrostatic relief. The contact areas at cylinder - distributor plate, cradle bearing and slipper - swash plate will be investigated in detail and it will be shown how the pump behavior can be improved considerably through a higher level of relief and a central remaining force ratio. The potential of optimization is to improve the efficiency, especially in partial loaded operation, power range, also for multi quadrant operation, precision and stability. A stable lubricating film for slow-speed running and for very high speeds at different pressures is ensured as well.

Avoiding cavitation and especially cavitation erosion are tasks, which have to be considered when working with hydraulics. State of the art is the assessment of the risk of erosion by component testing or to completely avoid cavitation by means of CFD. Another reliable method to assess the risk of cavitation erosion is until now not available. This paper deals with this problem and delivers comparative values for a later method development. In a first step the cavitation of a poppet valve, which controls a methanol flow, is visualized. The resulting three cavitation appearances are deeply examined. After that the results of long-term tests at different operation conditions are presented. A poppet surface analysis following each experiment has shown different types of surface attacks. As a result of this work it is shown that both cavitation appearance and surface attack are strongly influenced by the temperature dependent air solubility of the liquid.

The aim of this paper is to evaluate the effects of the dissolution time – time for the liquid to absorb the gas till the saturation state - on the behaviour of positivedisplacement vane pumps, in terms of pressure peaks within internal chambers and forces applied to the stator ring. The chamber pressurization depends on the volume variation and fluid Bulk modulus in the pre-compression phase during which the volume is trapped between the suction and the delivery port rims. If the dissolution time is short, then the entrained air is quickly absorbed and the fluid Bulk modulus sharply increases just before opening the connection to the outlet; as a consequence, pressure peaks may appear thus degrading the NVH characteristics of the pump. Moreover the pressure within internal chambers generate i) a torque demand to the driver (the combustion engine or an electrical motor) and ii) a total force applied to the stator ring. In case of fixed displacement designs, the resultant pressure force simply represents a load for support bearings; while in case of variable designs, it contributes to the displacement regulation. Simulation results show that the pump behaviour is very sensitive to the dissolution time when it is quite close to the duration of the trapped period.

Hydrostatic steering systems are used in construction and agricultural machines alike. Because of their high power density, hydraulic drives are qualified for the use in vehicles with high steering loads. Conventional hydrostatic steering systems are limited in terms of steering comfort and driver assistance. For realisation of appropriate steering functions, electro-hydraulic solutions are necessary. This paper provides an overview on existing implementations and introduces a novel steering system. The presented active steering system with independent meter-in and meter-out valves fills the gap between existing active steering systems and steer-by-wire solutions. An appropriate control and safety concept provides advanced steering functions for on-road usage without the fully redundant structure of steer-by-wire systems.

This paper presents an approach for an automated calibration process for electronic control units (ECU) of power split transmissions in agricultural tractors. Today the calibration process is done manually on a prototype tractor by experts. In order to reduce development costs the calibration process is shifted from prototype testing to software modelling. Simultaneous optimization methods are used within the software modelling to calculate new parameters. The simultaneous optimization includes objective evaluation methods to evaluate the tractor behaviour. With the combination of both methods inside the software modelling, the calibration process can be automated. The success of this approach depends on the quality of the software modelling. Therefore the identification of the initial prototype behaviour and the fitting of the tractor software model is done at the beginning. At the end of the automated calibration the validation and fine-tuning of the calculated parameters are done on the real tractor. These steps are condensed to a five step automated calibration process which includes simultaneous optimization and objective evaluation methods in several applications. After the detailed discussion of this automated calibration process one function of the ECU (one transmission component) will be calibrated through this process as example.

The paper describes the design of a prototype vehicle used by Dana Holding Corporation as a mobile laboratory for the development of Spicer® PowerBoost® hydraulic-hybrid powertrain technology. A telehandler vehicle was selected due to its versatility. Starting from the high-level requirements, design choices from the powertrain layout to the control architecture are discussed. The hydraulic-hybrid powertrain system is described, and its performance is analyzed based on representative driving cycles.

Along with the general requirement of continuously increasing efficiency of hydrostatic drivetrains, variable displacement machines are of major concern in research and development. To this effect, the whole machine performance is mainly dependent of the displacement variation system (DVS) performance. A lot of work to this topic focusses on the controller and actuator level. The aim of this paper is to offer a more fundamental view on DVS by giving a focus to the basic hydro-mechanical principles.