No description available.

Because of the highly complex structure of the load-sensing pump, its compensators and controlling elements, simulation of load-sensing pump system pose many challenges to researchers. One way to overcome some of the difficulties with creating complex computer model is the use of black box approach to create an approximation of the system behaviour by analyzing input/output relationships. That means the details of the physical phenomena are not so much of concern in the black box approach. Neural network can be used to implement the black box concept for system identification and it is proven that the neural network have the ability to model very complex behaviour and there is a well defined set of neural and neural network structures. Previous studies have shown the problems and limitations in dynamic system modeling using static neuron based neural networks. Some new neuron structures, Dynamic Neural Units (DNUs), have been developed which open a new area to the research associated with the system modelling.<p>The overall objective of this research was to investigate the feasibility of using a dynamic neural unit (DNU) based dynamic neural network (DNN) in modeling a hydraulic component (specifically a load-sensing pump), and the model could be used in a simulation with any other required component model to aid in hydraulic system design. To be truly representative of the component, the neural network model must be valid for both the steady state and the transient response. Due to three components (compensator, pump and control valve) in a load sensing pump system, there were three different pump model structures (the pump, compensator and valve model, the compensator and pump model, and the pump only model) from the practical point of view, and they were analysed thoroughly in this study. In this study, the DNU based DNN was used to model a pump only model which was a portion of a complete load sensing pump. After the trained DNN was tested with a wide variety of system inputs and due to the steady state error illustrated by the trained DNN, compensation equation approach and DNN and SNN combination approach were then adopted to overcome the steady state deviation. <p>It was verified, through this work, that the DNU based DNN can capture the dynamics of a nonlinear system, and the DNN and SNN combination can eliminate the steady state error which was generated by the trained DNN. <p>The first major contribution of this research was in investigating the feasibility of using the DNN to model a nonlinear system and eliminating the error accumulation problem encountered in the previous work. The second major contribution is exploring the combination of DNN and SNN to make the neural network model valid for both steady state and the transient response.

Because of the highly complex structure of the load-sensing pump, its compensators and controlling elements, simulation of load-sensing pump system pose many challenges to researchers. One way to overcome some of the difficulties with creating complex computer model is the use of black box approach to create an approximation of the system behaviour by analyzing input/output relationships. That means the details of the physical phenomena are not so much of concern in the black box approach. Neural network can be used to implement the black box concept for system identification and it is proven that the neural network have the ability to model very complex behaviour and there is a well defined set of neural and neural network structures. Previous studies have shown the problems and limitations in dynamic system modeling using static neuron based neural networks. Some new neuron structures, Dynamic Neural Units (DNUs), have been developed which open a new area to the research associated with the system modelling.<p>The overall objective of this research was to investigate the feasibility of using a dynamic neural unit (DNU) based dynamic neural network (DNN) in modeling a hydraulic component (specifically a load-sensing pump), and the model could be used in a simulation with any other required component model to aid in hydraulic system design. To be truly representative of the component, the neural network model must be valid for both the steady state and the transient response. Due to three components (compensator, pump and control valve) in a load sensing pump system, there were three different pump model structures (the pump, compensator and valve model, the compensator and pump model, and the pump only model) from the practical point of view, and they were analysed thoroughly in this study. In this study, the DNU based DNN was used to model a pump only model which was a portion of a complete load sensing pump. After the trained DNN was tested with a wide variety of system inputs and due to the steady state error illustrated by the trained DNN, compensation equation approach and DNN and SNN combination approach were then adopted to overcome the steady state deviation. <p>It was verified, through this work, that the DNU based DNN can capture the dynamics of a nonlinear system, and the DNN and SNN combination can eliminate the steady state error which was generated by the trained DNN. <p>The first major contribution of this research was in investigating the feasibility of using the DNN to model a nonlinear system and eliminating the error accumulation problem encountered in the previous work. The second major contribution is exploring the combination of DNN and SNN to make the neural network model valid for both steady state and the transient response.

In this thesis, dual-frequency optoelectronic oscillators (OEOs) and their applications to transverse load sensing are studied. Two configurations of dual-frequency OEOs are proposed and investigated. In the first configuration, a polarization-maintaining phase-shifted fiber Bragg grating (PM-PSFBG) is employed in the OEO loop to the generation of two oscillating frequencies. The beat between the two oscillating frequencies is a function of the load applied to the PM-PSFBG, which is used in transverse load sensing. To avoid the frequency measurement ambiguity, a second configuration is proposed by coupling a dual-wavelength fiber laser to the dual-frequency OEO. A single tone microwave signal with the frequency determined by the birefringence of the grating is generated in the OEO and is fed into the fiber ring laser to injection lock the dual wavelengths. The sensitivity and the resolution are measured to be 9.73 GHz/(N/mm) and 2.06×10-4 N/mm, respectively. The high stability of the single-tone microwave signal permits accurate measurement, while the frequency interrogation allows an ultra-high speed demodulation.

In spite of their high technical maturity, load sensing systems (LS) have system-inherent energy losses that are largely due to the operation of parallel actuators with different loads at the same pressure level. Hereby, the pressure compensators of the system are crucial. So far, excessive hydraulic energy has been throttled at these compensators and been discharged as heat via the oil. The research project “Reduction of System Inherent Pressure Losses at Pressure Compensators of Hydraulic Load Sensing Systems” aims to investigate a novel solution of reducing such energy losses. The pressure of particular sections can be increased by means of a novel hydraulic circuit. Therefore, a recovery unit is connected in series with a hydraulic accumulator via a special valve in the reflux of the actuators. The artificially increased pressure level of the section reduces the amount of hydraulic power to be throttled at the pressure compensators. As long as a section fulfills the switching condition of the valve, pressure losses at the respectiv pressure compensator can be reduced. Thus, via a suitable recovery unit excessive energy can be regenerated and can be directed to other process steps eventually.

Load sensing pumps in hydraulic system of wheel loaders helps in increasing the energy efficiency of wheel loaders. Present day machines have hydro mechanical load sensing system. After the advent of hydro mechanical load sensing concept, over the years, lots of research has been carried out relevant to electro hydraulic load sensing, trying to control the pump electronically. Currently, Volvo Construction Equipments (VCE) is interested in investigating the possibility of implementing electro hydraulic load sensing system in the wheel loaders. Research works has shown existence of several configurations of electro hydraulic load sensing pumps. Successful simulation results of an electro hydraulic load sensing pump configuration would provide a backing for the proposal of building and testing that configuration of electro hydraulic load sensing pump prototype. Also, the thesis work aims in benchmarking hydraulic system simulation capabilities of AMESim and GT- Suite by simulating the existing hydro mechanical load sensing system in both in both the simulation packages. / The thesis work has been carried out at Virtual Product Development (VPD) division of Volvo Construction Equipments (VCE), Eskilstuna, Sweden.

No description available.

In spite of their high technical maturity, load sensing systems (LS) have system-inherent energy losses that are largely due to the operation of parallel actuators with different loads at the same pressure level. Hereby, the pressure compensators of the system are crucial. So far, excessive hydraulic energy has been throttled at these compensators and been discharged as heat via the oil. The research project “Reduction of System Inherent Pressure Losses at Pressure Compensators of Hydraulic Load Sensing Systems” aims to investigate a novel solution of reducing such energy losses. The pressure of particular sections can be increased by means of a novel hydraulic circuit. Therefore, a recovery unit is connected in series with a hydraulic accumulator via a special valve in the reflux of the actuators. The artificially increased pressure level of the section reduces the amount of hydraulic power to be throttled at the pressure compensators. As long as a section fulfills the switching condition of the valve, pressure losses at the respectiv pressure compensator can be reduced. Thus, via a suitable recovery unit excessive energy can be regenerated and can be directed to other process steps eventually.

Heavy load equipment, such as tractors, shovels, cranes, airplanes, etc, often employ fluid power (i.e. hydraulic) systems to control their loads by way of valve adjustment in a pump-valve control configuration. Most of these systems have low energy efficiency as a consequence of pressure losses across throttle valves. Much of the energy is converted into heat energy which can have determinantal effects on component life and the surrounding environment. From an energy efficiency point of view, an ideal hydraulic system is one that does not include any throttling valve. One such circuit is made of a variable pump and motor load (pump/motor configuration). The velocity of the load is controlled by manipulating the pump displacement or by changing the rotary speed of the pump shaft. In such a system, the transient response of the load is often unsatisfactory because it is difficult to quickly and accurately manipulate the pump displacement or change shaft speed. Thus circuit design must be a compromise between the energy efficiency of the pump/motor system and the controllability of a pump/valve/motor combination. One possible compromise is to use a pump-valve configuration which reduces energy losses across the valve. One way to achieve this is by controlling the pressure drop across the valve and limiting it to a small value, independent of load pressure. Based on this idea, a type of hydraulic control system, usually called load-sensing (LS), has recently been used in the flow power area. This type of system, however, is complex and under certain operating conditions exhibits instability problems. Methods for compensating these instabilities are usually based on a trial-and-error approach. Although some research has resulted in the definition of some instability criterion, a comprehensive and verifiable approach is still lacking. This research concentrates on identifying the relationship between system parameters and instability in one particular type of LS system. Due to the high degree of non-linearity in LS systems, the instabilities are dependent on the steady state operating point. The study therefore concentrates first on identifying all of the steady state operating points and then classifying them into three steady state operating regions. A dynamic model for each operating region is developed to predict the presence of instabilities. Each model is then validated experimentally. This procedure, used in the study of the LS system, is also applied to a pressure compensated (PC) valve. A PC valve is one in which the flow rate is independent in variations to load pressure. A system which combines a LS pump and a PC valve (for the controlling orifice) is called a load sensing pressure compensated (LSPC) system. This research, then, examines the dynamic performance of the LSPC system using the operating points and steady state operating regions identified in the first part of the research. The original contributions of this research include: (a) establishment of three steady state operating conditions defined as Condition I, II & III, which are based on the solution of steady state non-linear equations; (b) the provision of an empirical model of the orifice discharge coefficient suitable for laminar and turbulent flow, and the transition region between them; (c) and the development of an analytical expression for orifice flow which makes it possible to accurately model and simulate a hydraulic system with pilot stage valve or pump/motor compensator. These contributions result in a practical and reliable method to determine the stability of a LS or LSPC system at any operating point and to optimize the design of the LS or LSPC system.

Heavy load equipment, such as tractors, shovels, cranes, airplanes, etc, often employ fluid power (i.e. hydraulic) systems to control their loads by way of valve adjustment in a pump-valve control configuration. Most of these systems have low energy efficiency as a consequence of pressure losses across throttle valves. Much of the energy is converted into heat energy which can have determinantal effects on component life and the surrounding environment. From an energy efficiency point of view, an ideal hydraulic system is one that does not include any throttling valve. One such circuit is made of a variable pump and motor load (pump/motor configuration). The velocity of the load is controlled by manipulating the pump displacement or by changing the rotary speed of the pump shaft. In such a system, the transient response of the load is often unsatisfactory because it is difficult to quickly and accurately manipulate the pump displacement or change shaft speed. Thus circuit design must be a compromise between the energy efficiency of the pump/motor system and the controllability of a pump/valve/motor combination. One possible compromise is to use a pump-valve configuration which reduces energy losses across the valve. One way to achieve this is by controlling the pressure drop across the valve and limiting it to a small value, independent of load pressure. Based on this idea, a type of hydraulic control system, usually called load-sensing (LS), has recently been used in the flow power area. This type of system, however, is complex and under certain operating conditions exhibits instability problems. Methods for compensating these instabilities are usually based on a trial-and-error approach. Although some research has resulted in the definition of some instability criterion, a comprehensive and verifiable approach is still lacking. This research concentrates on identifying the relationship between system parameters and instability in one particular type of LS system. Due to the high degree of non-linearity in LS systems, the instabilities are dependent on the steady state operating point. The study therefore concentrates first on identifying all of the steady state operating points and then classifying them into three steady state operating regions. A dynamic model for each operating region is developed to predict the presence of instabilities. Each model is then validated experimentally. This procedure, used in the study of the LS system, is also applied to a pressure compensated (PC) valve. A PC valve is one in which the flow rate is independent in variations to load pressure. A system which combines a LS pump and a PC valve (for the controlling orifice) is called a load sensing pressure compensated (LSPC) system. This research, then, examines the dynamic performance of the LSPC system using the operating points and steady state operating regions identified in the first part of the research. The original contributions of this research include: (a) establishment of three steady state operating conditions defined as Condition I, II & III, which are based on the solution of steady state non-linear equations; (b) the provision of an empirical model of the orifice discharge coefficient suitable for laminar and turbulent flow, and the transition region between them; (c) and the development of an analytical expression for orifice flow which makes it possible to accurately model and simulate a hydraulic system with pilot stage valve or pump/motor compensator. These contributions result in a practical and reliable method to determine the stability of a LS or LSPC system at any operating point and to optimize the design of the LS or LSPC system.