1,720,970 research outputs found
One-Dimensional Fluid Dynamic Modeling of a Gas Bladder Hydraulic Damper for Pump Flow Pulsation
No full textSimulation approaches for the study of the oil flow rate distribution in lubricating systems with rotating shafts
No full textThis study addresses the issue of predicting the distribution of lubricant flow through the outlets of a rotating
shaft used in vehicle power transmission. A typical geometry with closely spaced rows of holes, suitable for the
lubrication of multi-disk clutches, was considered. Both lumped parameter and computational fluid dynamics
approaches were applied and compared. The test rig for model validation was designed with a variable speed shaft
featuring an axial oil inlet and three equally spaced pairs of radial outlet holes. The main characteristic of the
experimental facility is the possibility to selectively measure the flow rates through each outlet. It was found that the
three-dimensional model based on the multiple reference frame approach provides a reliable prediction of how the
flow rate is distributed. Generally, the flow rate is lower through the outlet closest to the inlet and is maximum at the
farthest exit. The flow distribution is minimally affected by the shaft speed. The influence of geometric parameters
on making the flow distribution more uniform was studied. It was found that a better flow balance is obtained with
a low ratio between the diameter of the radial holes and that of the axial channel. The results obtained offer bestpractice
guidelines for accurately simulating comparable systems, in order to optimize reliability of the mechanical
transmission and energy efficiency of the flow generation uni
Experimental methods for measuring the viscous friction coefficient in hydraulic spool valves
Full text linkIn hydraulic components, nonlinearities are responsible for critical behaviors that make it difficult to realize a reliable mathematical model for numerical simulation. With particular reference to hydraulic spool valves, the viscous friction coefficient between the sliding and the fixed body is an unknown parameter that is normally set a posteriori in order to obtain a good agreement with the experimental data. In this paper, two different methodologies to characterize experimentally the viscous friction coefficient in a hydraulic component with spool are presented. The two approaches are significantly different and are both based on experimental tests; they were developed in two distinct laboratories in different periods of time and applied to the same flow compensator of a pump displacement control. One of the procedures was carried out at the Fluid Power Research Laboratory of the Politecnico di Torino, while the other approach was developed at the University of Parma. Both the proposed methods reached similar outcomes; moreover, neither method requires the installation of a spool displacement transducer that can significantly affect the results
Modelling and validation of cavitating orifice flow in hydraulic systems
No full textCavitation can occur at the inlet of hydraulic pumps or in hydraulic valves; this phenomenon should be always avoided because it can generate abnormal wear and noise in fluid power components. Numerical modeling of the cavitation is widely used in research, and it allows the regions where it occurs more to be predicted. For this reason, two different approaches to the study of gas and vapor cavitation were presented in this paper. In particular, a model was developed using the computational fluid dynamics (CFD) method with particular attention to the dynamic modeling of both gaseous and vapor cavitation. A further lumped parameter model was made, where the fluid density varies as the pressure decreases due to the release of air and the formation of vapor. Furthermore, the lumped parameter model highlights the need to also know the speed of sound in the vena contracta, since it is essential for the correct calculation of the mass flow during vaporization. A test bench for the study of cavitation with an orifice was set up; cavitation was induced by increasing the speed of the fluid on the restricted section thanks to a pump located downstream of the orifice. The experimental data were compared with those predicted by CFD and lumped parameter models
Energy Comparison between a Load Sensing System and Electro-Hydraulic Solutions Applied to a 9-Ton Excavator
Full text linkWith the increasingly stringent regulations on air quality and the consequent emission limits for internal combustion engines, researchers are concentrating on studying new solutions for improving efficiency and energy saving even in off-road mobile machines. To achieve this task, pump-controlled or displacement-controlled systems have inspired interest for applications in offroad working machines. Generally, these systems are derived from the union of a hydraulic machine coupled to an electric one to create compact components that could be installed near the actuator. The object of study of this work is a 9-ton excavator, whose hydraulic circuit is grounded on load sensing logic. The validated mathematical model, created previously in the Simcenter Amesim© environment, represents the starting point for developing electro-hydraulic solutions. Electric components have been inserted to create different architectures, both with open-and closed-circuit layouts, in order to compare the energy efficiency of the different configurations with respect to the traditional load sensing system. The simulations of a typical working cycle show the energy benefits of electrohydraulic solutions that allow for drastically reducing the mechanical energy required by the diesel engine and, consequently, the fuel consumption. This is mainly possible because of the elimination of directional valves and pressure compensators, which are necessary in a load sensing circuit, but are also a source of great energy dissipations. The results show that closed-circuit solutions produce the greatest benefits, with higher energy efficiencies than the open-circuit solution. Furthermore, closed-circuit configurations require fewer components, allowing for more compact and lighter solutions, as well as being cheaper
Combined speed control and centralized power supply for hybrid energy-efficient mobile hydraulics
Full text linkImproving energy efficiency in mobile hydraulics is paramount and feasible via machine electrification, but all actuators' power in standard systems must flow through the electric motors, which is unfeasible for medium-to-high power applications. Therefore, this paper leverages the idea of splitting the transferred power between the hydraulic and electric domains to save energy while downsizing the electric motors. A novel layout of a hybrid excavator is presented, validated using high-fidelity simulations, and compared to the state-of-the-art, load-sensing machine. The results show the expected system's functioning and efficiency benefits (fuel savings close to 28% compared to the original excavator). Almost 60% of the energy is transferred to the actuators hydraulically minimizing the power rating of the electric machines in favor of the system's cost and compactness. Future research will focus on controlling the hybrid system to maximize energy savings and make it easily applicable to different fluid power machines
Evaluation of tooth space pressure and incomplete filling in external gear pumps by means of three-dimensional cfd simulations
No full textThe paper presents the computational fluid dynamics simulation of an external gear pump for fluid power applications. The aim of the study is to test the capability of the model to evaluate the pressure in a tooth space for the entire shaft revolution and the minimum inlet pressure for the complete filling. The model takes into account the internal fluid leakages and two different configurations of the thrust plates have been considered. The simulations in different operating conditions have been validated with proper high dynamics transducers measuring the internal pressure in a tooth space for the entire shaft revolution. Steady-state simulations have been also performed in order to detect the fall of the flow rate due to the incomplete filling of the tooth spaces when the inlet pressure is reduced. It has been demonstrated that, despite the need of a compromise for overcoming the limitation of considering fixed positions of the gears' axes and of the thrust plates, significant results can be obtained, making the CFD approach very suitable for such analyses
Downsizing the electric machines of energy-efficient electro-hydraulic drives for mobile hydraulics
Full text linkThe poor energy efficiency of state-of-the-art mobile hydraulics affects the carbon dioxide released into the atmosphere and the operating costs. These crucial factors require urgent improvements that can be addressed by the electrification of fluid power. This approach has already generated electro-hydraulic drives that remove flow throttling and enable energy recovery. However, the entire power managed by the actuators of conventional systems must pass through the electric machines. This characteristic is unfeasible for medium-to-high power applications since they need electric motors and electronics with high power ratings and large onboard generation of electricity. Thus, this paper applies to a hydraulic excavator’s boom the idea of splitting the power being transferred to/from the actuator between the hydraulic and electric domains (i.e., a centralized hydraulic power supply is involved). The objective is downsizing the power rating of the boom’s electric components while maintaining the highpower output of the hydraulic actuator. The results show the expected behavior of the hybrid excavator in terms of motion control, but only 57% of the boom’s peak power is now exchanged electrically. The resulting electric machine with 61% downsizing favors the system’s cost and compactness supporting the electrification process that is aligned with the low-carbon economy
Energy analysis of a hybrid electro-hydraulic system for efficient mobile hydraulics
Full text linkEnergy efficiency plays a significant role in mobile hydraulics due to the high amount of carbon dioxide and pollutants being released into the atmosphere. Efficiency improvements are urgently needed, so the electrification of mobile hydraulics represents a fantastic opportunity in this regard. This approach leads to electro-hydraulic systems that remove functional flow throttling in control valves and enable energy recovery. Fuels savings were already demonstrated in simulation, but the literature does not offer entire energy analyses of these electro-hydraulic solutions. This limitation prevents complete system-level comprehension and does not give enough insight to pinpoint areas for further efficiency improvements. Thus, this paper focuses on a hybrid system for excavators based on electro-hydraulic drives that is compared against the original valve-controlled layout. The objective is to quantify the energy flows insight the excavator during relevant operations and highlight the resulting energy losses. The outcomes confirm that electro-hydraulic solutions are suitable for a low-carbon economy. They indicate hydraulic actuators, speed-controlled pumps, and electric motors as the critical components for further energy efficiency enhancement excluding the combustion engine
Instantaneous flowrate measurements in high-pressure liquid flows
Full text linkA new flowmeter suitable for high-pressure flows and with a prompt dynamic response is presented. It is constituted by two pressure transducers installed on the monitored high-pressure pipe at a fixed distance one from the other, together with a low-pressure flowmeter that provides a time-averaged flowrate. The measurement algorithm consists of an ordinary differential equation obtained by combining the mass conservation partial differential equation and the momentum balance one applied to the considered piece of pipe comprised between the two pressure transducers. Due to the absence of a master instrument that can be employed as reference to verify the consistency of the measured flowrate, the flowmeter accuracy has been demonstrated by means of numerical models of various hydraulic components, rigorously validated through pressure measurements. The flow ripple of gear pumps has been measured, as well as the flowrate entering a Common Rail injector. For all these cases, the measured flowrate and the one obtained by means of the numerical model are in very good agreement, leading to a robust validation of the presented measurement device
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