Takayoshi Ichiyanagi

A Consideration on the Behavior of Hydraulic Pressure Ripples in Relation to Hydraulic Oil Temperature

It is well known that hydraulic noise can change as a system warms up. That change 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 operating conditions, and how they change in relation to the temperature of the hydraulic oil.This study has investigated the ripple behavior that results from temperature change in simple hydraulic systems, using mathematical models that took thermal properties into account. Physical properties of the oil and the speed of sound in the oil have been defined as temperature-related variables in the mathematical models. The physical properties that should be used in the mathematical models have been obtained directly from the oil manufacturer. In contrast, the speed of sound in the oil has to be obtained from the isentropic tangent bulk modulus of the oil in an actual operating condition. That has been determined from the specific volume ratio of entrained air to the oil and the isentropic tangent bulk modulus of the only oil. The thermal properties of the speed of sound in the oil have been determined from the thermal characteristics of these variables, and it has been found that the speed of sound in the oil decreases with a rise in the oil temperature.The mathematical models of pressure ripples have shown that there were three distinct phenomena resulting from the temperature change of the oil. The first is the change of wavelength. The second is the spatial dependence of the thermal characteristics of the pressure ripples. The third is the difference of the thermal characteristics of the pressure amplitude at the peak in spatial modes. These changes that result from the temperature variation tend to be large at higher frequency.Copyright

Development of a novel Helmholtz hydraulic silencer for attenuating the pressure ripple from a fixed displacement pump with variable rotational speed

The Helmholtz type hydraulic silencer is basically composed of a vibration system based on mass and spring. In the lumped model, the mass and spring correspond with hydraulic oil in the neck and compressibility of the vessel volume respectively. If this resonance frequency is designed to match the fundamental frequency of the pressure ripple from the displacement pump, it can be effectively attenuated. The fundamental frequency ff is defined as a product using the pump element number z and rotational speed N.

Experimental Investigation on Effective Bulk Modulus and Effective Volume in an External Gear Pump

Pressure ripples generated by a positive displacement pump in a hydraulic system can lead to severe noise and vibration problems. The source impedance of a positive displacement pump has a considerable impact on the generation of pressure ripples. It is, therefore, important to be able to predict the source impedance in order to design quiet hydraulic systems.The source impedance of a positive displacement pump depends, amongst other things, on bulk modulus and volume. However, it is known that the mathematical model that takes into account the bulk modulus of hydraulic oil and the volume of a discharge room in the pump results in an estimated value of the source impedance that is greater than the measured value.In this study, the factors which affect the source impedance of an external gear pump for an agricultural tractor have been investigated. In particular, the effect of the following factors has been investigated experimentally: the effective bulk modulus as determined by the components of the pump: leakage in the pump: the specific volume ratio of entrained air to hydraulic oil: and the volume of the tooth space of the pump. In addition, the effect of volumetric change of the discharge room by pumping action has been investigated using CFD with moving mesh technique.Copyright

Experimental Investigation on the Helmholtz Hydraulic Silencer With Flat Cylindrical Vessel Configuration

The Helmholtz type of hydraulic silencer is known as one of the most practical silencers. The silencer consists of a neck and a cylindrical vessel. A distinctive characteristic of the Helmholtz of hydraulic silencer is that the effective range of attenuation frequency is very limited. The maximum attenuation performance can be obtained at the resonant frequency because the Helmholtz resonance phenomenon is utilized. Therefore, it is very important to estimate the resonant frequency precisely at the design stage. In the design case that the length of cylindrical vessel becomes close to the diameter, i.e. the ratio of the length and diameter is nearly equal to 1.0, the resonant frequency of the existing model begins to deviate from the experimental results and this disparity increases with a decrease in the ratio of length and diameter. The purpose of this research is to clarify the influence of geometry on the attenuation characteristics of a Helmholtz type hydraulic silencer. In particular, a new mathematical model is proposed, that considers the flow for the radial direction of cylindrical vessel in the design case where the ratio is small. The transmission loss characteristics of the Helmholtz type hydraulic silencer are investigated theoretically for both the proposed model and existing model. These models are evaluated by experimental examinations in which the ratio is varied.© 2014 ASME

CFD Analysis and Improvement of Torque Detected Type Flow Meter

Abstract We propose a unique flow meter that uses a lateral flow force generated on a pressure sensing bar in a rectangular flow channel. The mathematical model, based on laminar viscous flow analysis, has been previously described and the design criterion was established from the fundamental characteristics. The test flow meter has also been investigated experimentally to clarify the torque versus flow characteristics. Although the meter performed well in terms of linearity and repeatability in the low flow rate region, the results deviated from the analytical results at high flow rates. This paper presents a theoretical analysis of the flow meter based on CFD (computational fluid dynamics). The aim is to examine the flow behavior and the pressure distribution inside the meter. CFD analysis is conducted over a range of dimensional configurations and boundary conditions. The flow versus torque characteristics are derived from pressure distribution results and compared with the analytical model. On the basis of CFD analysis, we propose a revised configuration of the flow meter, and verify its performance experimentally.

Online System Identification of Hydraulic Servo Actuators by the Self-Excited Oscillation Method (Application to Angular Velocity Control System)

Abstract It has been well known that hydraulic servo actuators can often be approximated with a standard second order transfer function when the controller is designed for these systems. Earlier research developed a simple method utilizing the self-excited oscillation caused from the hydraulic servo actuators to directly estimate the dynamic parameters such as the damping ratio and undamped natural frequency. The advantage of this method is an online identification ability that is able to identify these parameters while the operation conditions are continually changing. Although this method was confirmed to be very useful, it is available only when the spool valve is close to the neutral position, which corresponds to the operation of position control systems. In the practical situations, the spool valve sometimes operates at displaced position from the neutral center position such that a hydraulic motor speed is controlled. This paper proposes a revised self-excited oscillation method for this system. The experimental works are conducted by giving the various system pressures and angular velocities so as to validate the method. The resulting frequency characteristics of these identified transfer functions are then compared with those of the measured data by the frequency characteristics method. In addition, in order to demonstrate the effectiveness of the self-excited oscillation method, the dynamic parameters of two practical devices such as a motion seat and aircraft tail surface control simulator are identified and compared with the results from the frequency response method.

An Optimum Design of Side Branch Considering Pulsation Characteristics of Hydraulic Circuits

It is well known that all positive displacement pumps generate a flow pulsation which interacts with the system to produce a pressure pulsation. This pressure pulsation is a periodic function of time with a fundamental frequency and higher harmonics. Therefore, if the change of pump rotational speed in the operation cycle is not large such as in a hydraulic excavator, folk lift, an injection molding machine, etc., the harmonic frequencies of pressure pulsation would be almost fixed. For these kinds of hydraulic systems, a quarter wavelength side branch has been widely used for attenuating the pressure pulsation. In this paper, an effective design method for the insertion of the quarter wavelength side branch is described. An optimum design calculation used in this study searches the design parameters such as lengths and an insertion position of the side branch by taking account of wave propagation characteristics of the all circuit elements. The design results were examined by both the theoretical calculation and the experimental results, and the designed side branch showed good attenuation performance in the certain hydraulic circuit.

Evaluation and Improvement of Basic Characteristics on the Flowmeter Utilizing Lateral Flow Force Acted on the Stationary Plate with Minute Slope in a Rectangular Fluid Line

In the previous research, the authors have been proposed a unique flowmeter, which utilizes a lateral flow force generated on the plate with minute slope in a rectangular flow line. In the previous works, the test flowmeter was investigated experimentally to confirm the torque versus flow characteristics. Although the results showed expected performance in terms of linearity and repeatability, the deviation between the experimental and analytical results occurred on the high flow rate condition. Then the theoretical analysis using the CFD approach was conducted to obtain the detailed information of the flow behavior inside the flowmeter. It was found that one of the reasons for this deviation was caused by the remarkable pressure drop and flow disturbance at the inlet region of the flowmeter. In this paper, in order to improve the performance of the present flowmeter, the revised configuration of the flowmeter is proposed. Basic static characteristics are studied experimentally including the measurement of pressure distribution inside the flowmeter to verify the performance of the revised configuration. In addition, the dynamic characteristics are also investigated and compared with commercial flowmeters.

An Application of the Self-Excited Oscillation Method to a Hydraulic Motor Angular Velocity System

It has been known that a hydraulic servo system can be generally dealt with a second order delay element for designing an adequate controller. In the previous work, our research group developed a simple method utilizing the self-excited oscillation of a hydraulic servo system to directly estimate the dynamic parameters such as the damping ratio and undamped natural frequency. The advantage of this method is the “on-line” ability that is able to identify these parameters instantaneously with changing the operating conditions. Although this method was found to be very useful, it is available only when the spool valve is close to the neutral position. This paper proposes an online parameter estimation method for the hydraulic motor angular velocity system. In this method, the self-excited oscillation around the displaced position from the neutral spool position is utilized. In order to demonstrate the effectiveness, the experimental work is conducted by giving the various input voltages, system pressures and angular velocities. The resulting frequency characteristics of these identified transfer functions are then compared with those of the measured data by the frequency characteristics method in order to confirm coincidence.Copyright