Interest in the control of variable fluid power pumps/motors has increased in recent years. The actuators used are inefficient and expensive and this reduces the variable units' usability. This paper introduces displacement control of pumps/motors by means of a rotating valve plate. By changing the angle of the valve plate, the effective use of the stroke is changed. The rotating valve plate is experimentally verified by a modified in-line pump. In the prototype, the valve plate is controlled with a worm gear connected to an electric motor. The results show potential for this kind of displacement control. However, the rotating valve plate creates pressure pulsations at part-displacement due to the commutation being performed at high piston speeds. If the piston speed and hence the flow from each piston is low, the pressure pulsation is acceptable.
A major concern in the forest industry is impact on the soil caused by forest machines during harvesting. A six-wheel pendulum arm forwarder is being developed. The new forwarder aims at reducing soil damage by an even pressure distribution and smooth torque control and thereby also improving the working environment. The suspension contains pendulum arms on each wheel controlled by a hydraulic load sensing system in combination with accumulator. A natural approach is to model each part of a system in the best-suited software. In this case, the hydraulic system is modelled in the Hopsan simulation tool, while the vehicle mechanics is modelled in Adams. To understand the whole system it is necessary to simulate all subsystems together. An open standard for this is the Functional Mock-up Interface. This makes it possible to investigate the interaction between the hydraulic system and the multi-body mechanic model. This paper describes how different simulation tools can be combined to support the development process. The technique is applied to the forwarder’s pendulum suspension. Controllers for height and soil force are optimized to minimize soil damage and maximize comfort for the operator.
This paper presents the first prototype of a novel axial piston pump/motor of slipper type. The pistons are floating in the cylinders and hence the name floating piston pump. The novel pump design fills a gap in the traditional pump design. The pump is made to fit the automobile requirements to use fluid power in a more prominent manner. One of the expected benefits of this design is its simplicity and therefore the machine does not require high manufacturing capabilities. The production cost is expected to be low. The machine is designed with high number of pistons, which leads to a pump/motor with low noise level. The displacement angle is small, 8 degrees, which leads to low piston speeds with its benefits. The main challenge in the design is the piston seal configuration. The seals will both, deform (ovality) and move in a circle relative to the pistons. The paper discusses design considerations and proposes a design. The efficiency measurement of the first prototype is in level of a series produced slipper type machine at its sweet spot.
Noise is a well-known challenge in hydraulic systems and hydrostatic pumps are one of the largest noise contributors in a hydraulic system. The existing noise reduction features, such as pressure relief groove and pre-compression filter volume, are more or less dependent on the working condition. It is essential to know the amount of free air when designing a quiet pump; however, it is not evident how much free air the oil contains. The free air content is different if the suction port is boost pressured or self-priming. The amount of free air in a well-designed system can be as low as 0.5% while in others up to 10%. This paper uses the three-transducer method to measure the amount of free air in the oil. The oil's compressibility can be measured for different working conditions and the free air content can then be calculated. The pre-study is performed with an extensive simulation model. Various noise reduction features' sensitivity to free air content is considered.
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