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The fluid borne-vibration generated from a hydraulic pump is known to be one of drawbacks in hydraulic systems. In order to decrease the noise and vibration effectively, the simulation tool to predict the pressure ripple at an arbitrary point in the hydraulic circuit must be used at a design stage. Therefore, accurate mathematical models for hydraulic components is required for such simulation. In this research, the target is set to develop a precise mathematical model for the source impedance characteristics of an axial piston pump. In the past research, the simple approximation models have been already developed to be able to express the source impedance characteristics. These models need the parameter identification for the dimension of discharge passageway by the experimental acquired source impedance. Hence, the models can not be used as a design purpose. In this report, the theoretical investigations which consider shapes and dimensions of a discharge passageway inside the pump, as well as the pump chambers with discharge process, are conducted and compared with the experimental results. It was found that the source impedance of axial piston pump can be modeled by the distributed parameter pipe model which takes into account all pump chambers connecting the discharge port.

Generally, industrial vehicles such as agricultural machines and construction machinery use hydraulic systems for heavy-load work. Also the work often continues for a long time in a certain area. Consequently, noise exposure of the surrounding environment is increased. Thus noise regulations are established in several countries. The noise emitted from the hydraulic system has a significant contribution to the over-all of the noise in an industrial vehicle. Recently, the choice of power sources in industrial vehicles has tended to shift from internal combustion engines to electric motors. Consequently, the contribution of noise emitted from the internal combustion engine will decrease and the contribution of noise emitted from a hydraulic system will become relatively prominent in the future. It is, therefore, more than ever important to take care of the noise generated by the hydraulic system of the industrial vehicles. It is known that speed of sound in hydraulic oil has an effect on pressure ripples which can be source of noise. Therefore, it is important to understand behavior of the speed of sound reasonably in design of quiet hydraulic systems. However, relationship between operating conditions and the speed of sound has not been revealed up to now. In this study, the speed of sound has been investigated at the operating conditions that are oil temperature, loading pressure, volume ratio of entrained air to the hydraulic oil and type of the oil for typical agricultural machines and construction machinery.

It is known that fluid-borne noise emitted from a hydraulic system often causes severe discomfort of the operator. It is also known that the noise can change as the system warms up. The temporal change in steady operation can be a factor for misperception of mechanical failure, because noise can play an important role as a signal that indicates abnormal operation. It is therefore important to understand the behavior of hydraulic pressure ripples that are a source of hydraulic noise in steady operation, and how they change in relation to the operating time. This study has investigated the influence of oil temperature changing over time on pressure ripples in a hydraulic line in steady operation. Variables that can change in steady operation have been considered using mathematical models of the pressure ripples. The consideration has shown that, when there is no air-entrainment from an outer system, the change over time is caused solely by the change of the hydraulic oil temperature. Physical properties of the oil and speed of sound in the oil have been defined as temperature-related variables in the mathematical models. The physical properties that are used in the mathematical models have been obtained directly from the manufacturer. In contrast, the speed of sound in the oil has to be obtained using theoretical approaches. The behaviors of the hydraulic pressure ripples in three simple hydraulic systems have been investigated using mathematical models that took into account the thermal properties. Each hydraulic system consists of a hydraulic pump, a straight pipe and a termination condition that is one of the following typical three types: non-reflection, valve and volume. The mathematical models have shown distinct behaviors resulting from the change in the oil temperature. The behaviors have been verified experimentally.

In fluid power systems, a Helmholtz type hydraulic silencer is often utilized in order to attenuate pressure pulsations, which are detrimental to the system because of the vibration and noise that they generate. The silencer has the important feature that it is effective within a narrow band range around the resonance frequency. Therefore, it is very useful to be able to predict the attenuation characteristics by means of a mathematical model. Previous research has shown that there are noticeable discrepancies between the experimental values and calculated results when the ratio of the volume length L to diameter D is comparatively small. In this paper, a novel distributed parameter model was proposed in order to examine these discrepancies. The mathematical model was derived by taking into account the elastic deformation on the upper and lower vessel walls of a Helmholtz silencer with a flat volume. The analysis revealed that the resonance frequency of the silencer is reduced by a reduction in the volume length or by a reduction in the cover thickness. The reason for this is the reduction of the effective bulk modulus. In addition, experimental work was conducted to examine the attenuation characteristics under various conditions. The experimental results were found to correspond to the mathematical model qualitatively.

Recently, highly efficient small heat transport devices have been required. In particular, pulsating heat pipes (PHP) have come to draw a lot of attention. The contribution of sensible heat transport and latent heat transport in oscillating working fluid, which plays an important role in heat transport performance of PHP, has not been clarified enough experimentally yet. The purpose of this study is to evaluate the contribution of sensible heat transport and latent heat transport experimentally by making liquid column oscillate sinusoidally in the channel. The channel was initially evacuated, and ethanol was charged to form a liquid column, which is called single component system. In addition, the ethanol was charged in the channel with air in the gas phase at atmospheric pressure, which is called two components system. The effective thermal conductivity of latent heat transport is determined by the difference between the effective thermal conductivity in single component system and that in two component system. In two components system, that is sensible heat transport, the effective thermal conductivity decreases monotonically as oscillation center moves to cooling section under the same amplitude, because residence time of liquid column at heating section decreases. On the other hand, in latent heat transport, the effective thermal conductivity increases as oscillation center moves to cooling section under the same amplitude, because liquid film at cooling section becomes longer. In addition, numerical analysis was conducted for sensible heat transport in oscillating working fluid. The comparison of the numerical results with the experimental results indicates that liquid film at the tip of liquid column would enhance sensible heat transport.

Pressure pulsation is caused by the flow ripples from a positive displacement hydraulic pump. It transmits throughout fluid power equipment and causes unwanted excitation of the mechanical parts. In many practical applications, a Helmholtz type hydraulic silencer may be used to attenuate such pulsation. It is the preferred solution on account of its simple structure and high attenuation performance. However the distinctive drawback of this silencer is that it is effective only within a narrow range of the attenuating frequency. Therefore, the silencer is only suitable for use in the hydraulic systems running at constant pump rotational speeds. The purpose of this research is to develop a novel silencer for hydraulic systems that have a fixed displacement pump driven under variable speed. Firstly, a mechanism for adjusting the resonant frequency has been pro-posed. This works by changing the volume of the silencer. Secondly, a prototype of the novel silencer was designed using a new distributed parameter system model, in which the vessel volume was modelled as an annular fluid line. Finally, the at-tenuation characteristics of the prototype silencer were verified by measuring the transmission loss and insertion loss under various conditions, and comparing them with the calculated results.

The noise and vibration caused by pressure pulsation are one of detrimental problems in hydraulic systems. A Helmholtz type hydraulic silencer, which is based on the resonant phenomena of a mass-spring-damper system for its attenuate principle, is known as one of the most practical silencers in the hydraulic systems. In the previous researches, the transmission loss characteristics of the Helmholtz type hydraulic silencer were modeled by a distributed parameter model. However, in the design case that the ratio of the length and diameter L/D of the cylindrical volume is smaller, the resonance frequency of the existing model begins to deviate from the experimental results and the disparity increases with decreasing the ratio of L/D. The purpose of this research is to clarify the influence of a neck and volume geometry on the attenuation characteristics. In particular, a mathematical model that considers the flow for the radial direction of the cylindrical volume is newly proposed for the design case that L/D is smaller. The transmission loss characteristics of the Helmholtz type hydraulic silencer are investigated theoretically for both the proposed model and existing models. In addition, the experimental examination of the influence of volume geometry on the attenuation characteristics is carried out in order to verify the theoretical investigations.

This paper presents a real-time simulation for coupled system with rigid body system and hydraulic system. The equations of motion for the rigid body are derived by transforming the rigid body motion to the linear element motion. The system equations can be presented as the ordinary differential equations of motion for the coupled system of the rigid body system and the hydraulic system without introducing the constraint conditions, describing the motions of the rigid body system using the linear element motion. Then, this modeling is useful for the real time simulation for the coupled system, as numerical stability is improved by carrying out coupled system simulation in one software package. Firstly, rigid body system driven by the linear element is formulated, coupled analysis theory with the hydraulic system is derived, and electric motor drive system is formulated. Finally, the actual digging simulations of a hydraulic excavator are implemented using the present technique. It is clarified that the real time simulation is successfully conducted.