Atualmente, a utilização de suspensão traseira do tipo twist beam é muito difundida em veículos de pequeno porte e alto volume de produção, por apresentar um bom compromisso entre custo e desempenho. No entanto este conceito possui limitações no que diz respeito à absorção de vibrações de ride (conforto) secundário e impactos, e possui um compromisso com as características de handling (estabilidade) do veículo. Este trabalho apresenta um estudo de influência da rigidez das buchas da suspensão twist beam nos eventos de impacto singular para ride e no regime permanente do handling. É utilizado no estudo um modelo de multicorpos com veículo completo construído no software ADAMS. Para o estudo de ride é utilizada uma abordagem semi-analítica, através dos dados de medição em pista utilizando transdutores de força nas rodas (WFT). A partir do uso de tais carregamentos é possível simular os fenômenos de ride sem necessitar de um modelo específico de pneu. Para o estudo de handling é utilizado modelo pneu correlacionado com medição de curva em uma bancada chamada Flat-Trac. Utilizando os modelos construídos para ride e handling, são apresentados os dados de correlação dos modelos com veículo protótipo e um estudo da influência da rigidez de bucha nas métricas de impacto singular para ride e gradiente de esterçamento para handling. / Currently, the use of rear suspension twist beam is widespread in small vehicles and high-volume production, because it presents a good compromise between cost and performance. However, this concept has limitations regards the absorption of secondary ride vibrations and impacts, and has a commitment with handling characteristics of the vehicle. This dissertation presents a study of the stiffness influence of the twist beam suspension bushings in impact singular events to the ride and the steady state handling behavior. A multibody model of vehicle complete built in ADAMS software has been used for the study. For the ride study is using a semi-analytical approach, through the track measurement data using wheel force transducers (WFT). From the use of such road loads is possible to simulate the ride phenomena without needing a specific model of tire. For the handling study a tire model used is correlated with measurement curve on a workbench called Flat-Trac. Using models built for ride and handling are shown the correlation data models with prototype vehicle and a study of the influence of the bushing stiffness for the singular impact event metrics for ride and the steering gradient metric for handling.

The Variable Displacement Engine (VDE) is a new generation of engines that are designed to decrease the fuel consumption at the cruise speed of a vehicle. The isolation of the VDE's new vibration pattern is beyond the capabilities of conventional mounts and bushings. Consequently, in this thesis, novel active and semi-active solutions are proposed to develop various semi-active and active hydraulic bushing proof-of-concept systems that may solve the isolation problem in a VDE system. <br /><br /> The dynamic stiffness response, which is the transfer function that relates the engine displacement to the transmitted force, is normally used as the key design criterion for engine mounts and bushings. In this thesis, a linear mathematical model of a conventional hydraulic bushing is purposed. The validity of the mathematical model is confirmed by an experimental analysis, and the various parameters in the dynamic stiffness equation are evaluated. The experimental results indicate that the dynamic stiffness frequency response of the conventional hydraulic bushing has both soft and stiff regions. The soft region is limited to low frequencies. For the VDE isolation, the goal is to provide a soft bushing for a wider range of frequencies than a conventional bushing can accommodate. Addition of a short inertia track, similar to a decoupler used in conventional hydraulic engine mounts, may be used to extend the soft region of a conventional hydraulic bushing, and the experimental results validate it. <br /><br /> Since the short inertia track provides no additional damping, a supplementary Magnetorheological (MR) valve is also devised. The MR valve has the advantage to minimize the amount of MR fluid used, which significantly reduces the cost of the overall system. The novel valve allows the damping coefficient of the bushing assembly to be controlled by varying the electrical current input to a solenoid coil. A mathematical model is derived for the MR bushing, and is validated experimentally. <br /><br /> In addition, an active bushing to solve the VDE isolation problem is purposed in this thesis. In this bushing, a magnetic actuator, composed of a permanent magnet and a solenoid coil, is included in the active bushing. This active chamber affects the dynamic stiffness response of the bushing by altering the bushing's internal pressure. The nonlinear equation of motion of the permanent magnet is linearized and is incorporated into the new mathematical model of the system. The new purposed model for the active bushing is in good agreement with the experimental results. This active chamber is also proved capable of producing complex dynamic stiffness frequency response. <br /><br /> The conclusion is that the proposals in this thesis can contribute to the isolation of the vibration pattern, imposed by the application of a VDE system.

The Variable Displacement Engine (VDE) is a new generation of engines that are designed to decrease the fuel consumption at the cruise speed of a vehicle. The isolation of the VDE's new vibration pattern is beyond the capabilities of conventional mounts and bushings. Consequently, in this thesis, novel active and semi-active solutions are proposed to develop various semi-active and active hydraulic bushing proof-of-concept systems that may solve the isolation problem in a VDE system. <br /><br /> The dynamic stiffness response, which is the transfer function that relates the engine displacement to the transmitted force, is normally used as the key design criterion for engine mounts and bushings. In this thesis, a linear mathematical model of a conventional hydraulic bushing is purposed. The validity of the mathematical model is confirmed by an experimental analysis, and the various parameters in the dynamic stiffness equation are evaluated. The experimental results indicate that the dynamic stiffness frequency response of the conventional hydraulic bushing has both soft and stiff regions. The soft region is limited to low frequencies. For the VDE isolation, the goal is to provide a soft bushing for a wider range of frequencies than a conventional bushing can accommodate. Addition of a short inertia track, similar to a decoupler used in conventional hydraulic engine mounts, may be used to extend the soft region of a conventional hydraulic bushing, and the experimental results validate it. <br /><br /> Since the short inertia track provides no additional damping, a supplementary Magnetorheological (MR) valve is also devised. The MR valve has the advantage to minimize the amount of MR fluid used, which significantly reduces the cost of the overall system. The novel valve allows the damping coefficient of the bushing assembly to be controlled by varying the electrical current input to a solenoid coil. A mathematical model is derived for the MR bushing, and is validated experimentally. <br /><br /> In addition, an active bushing to solve the VDE isolation problem is purposed in this thesis. In this bushing, a magnetic actuator, composed of a permanent magnet and a solenoid coil, is included in the active bushing. This active chamber affects the dynamic stiffness response of the bushing by altering the bushing's internal pressure. The nonlinear equation of motion of the permanent magnet is linearized and is incorporated into the new mathematical model of the system. The new purposed model for the active bushing is in good agreement with the experimental results. This active chamber is also proved capable of producing complex dynamic stiffness frequency response. <br /><br /> The conclusion is that the proposals in this thesis can contribute to the isolation of the vibration pattern, imposed by the application of a VDE system.

The purpose of this work is to design a semi-active magnetorheological (MR) hydraulic bushing. The semi-active bushing is intended to be used to isolate a cylinder deactivating engine. Cylinder deactivation causes high transient torsional loading in addition to changing the magnitude and mode of engine vibrations requiring an adaptive or controllable isolator. <br /><br /> Practical and simple semi-active control strategies are inspired by investigating the optimization of linear and slightly cubic nonlinear single degree of freedom isolators. Experimental verification of the optimization technique, which minimizes the root mean square (RMS) of engine acceleration frequency response and RMS of the force transmitted frequency response, shows that this method can be implemented on real linear systems to isolate the engine from harmonic inputs. This optimization technique is also applied to tune selected model parameters of existing two degree of freedom hydraulic bushings. <br /><br /> This thesis also details the development of a MR hydraulic bushing. The MR bushing design retrofits an existing bushing with a pressure driven flow mode valve on the inertia track. A new efficient valve design is selected and developed for the application. The MR hydraulic bushing is designed, mathematically modeled, and numerically simulated. The simulation results show that the MR bushing tends to increase the low frequency dynamic stiffness magnitude while simultaneously decreasing the phase. The next stage of the project is fabrication and testing of the semi-active bushing. The performance of the manufactured MR bushing is tested on a base excitation apparatus. Varying the current input to the MR valve was found to have a small effect on the response of the suspended mass. The results are in agreement with the effects demonstrated by the dynamic stiffness numerical simulation.

The purpose of this work is to design a semi-active magnetorheological (MR) hydraulic bushing. The semi-active bushing is intended to be used to isolate a cylinder deactivating engine. Cylinder deactivation causes high transient torsional loading in addition to changing the magnitude and mode of engine vibrations requiring an adaptive or controllable isolator. <br /><br /> Practical and simple semi-active control strategies are inspired by investigating the optimization of linear and slightly cubic nonlinear single degree of freedom isolators. Experimental verification of the optimization technique, which minimizes the root mean square (RMS) of engine acceleration frequency response and RMS of the force transmitted frequency response, shows that this method can be implemented on real linear systems to isolate the engine from harmonic inputs. This optimization technique is also applied to tune selected model parameters of existing two degree of freedom hydraulic bushings. <br /><br /> This thesis also details the development of a MR hydraulic bushing. The MR bushing design retrofits an existing bushing with a pressure driven flow mode valve on the inertia track. A new efficient valve design is selected and developed for the application. The MR hydraulic bushing is designed, mathematically modeled, and numerically simulated. The simulation results show that the MR bushing tends to increase the low frequency dynamic stiffness magnitude while simultaneously decreasing the phase. The next stage of the project is fabrication and testing of the semi-active bushing. The performance of the manufactured MR bushing is tested on a base excitation apparatus. Varying the current input to the MR valve was found to have a small effect on the response of the suspended mass. The results are in agreement with the effects demonstrated by the dynamic stiffness numerical simulation.

The manufacturing process for the core of an RIP bushing was studied. Simulations of a test model was performed, due to the non-linear nature of the fluid filling process. Varying of governing parameters in the model, that could realistically be varied, was carried out and their affect was observed. The model was then compared to real measurements to view its practical reliability. Proposals to optimize the filling speed of the process in order to avoid the creation of bubbles was discussed and conducting it would be the next step for further research of the subject.

No description available.

This report focuses on the practicality and results of using the COMSOL 6.0 Optimization Module on a HVDC bushing corona shield model provided by Hitachi Energy to minimize electric field. The Optimization Module has several functions and parameters for altering the geometry of a model. Parameter Optimization, Polynomial Boundary and Free Shape Boundary was the primary methods used. The best results in minimizing the electric field was found with the Polynomial Boundary. The optimized shape decreased the maximum electric field by about 15% and when run with constraints to the change in volume the optimization showed similar results. Tests with Parameter Optimization did decrease the electric field but lacked the ability to fine-tune the shape like Polynomial Boundary can. Free Shape Boundaryseemed to have great potential in the documentation but we did not finda successful way of implementing the method. Through testing of different setups for methods and solvers we have concluded that the Optimization Module is both useful and practical for the given model and a clear improvement in electric field was observed in the new shape. Polynomial Boundary is the best option for the given model but more research is needed about Free Shape Boundary.

No description available.

The overall reliability of a power transformer depends to a great extent on the sound operation of the bushings thereof. In view of its overwhelming advantages, resin impregnated paper (RIP) is acquiring prominence over conventional oil impregnated paper (OIP) in transformer bushings. The main advantages of RIP bushings are low dielectric loss and capability of positioning them at any desired angle over the transformer. The RIP structure, being an all-solid system, is completely free from oil phase. The temperature rise in RIP bushings under normal operating conditions is seen to be a difficult parameter to control in view of the limited options for effective cooling. The degradation of dry-type insulation such as RIP is often due to thermal and electrical stresses. The long time performance thereof, depends strongly, on the maximum operating temperature. In order to be able to predict the regional temperature, it is necessary to consider the thermal and electrical parameters of insulation in question; and to identify and solve the governing equations under the relevant boundary conditions. Electrical failure of insulation is known to be an extremal random process wherein nominally identical specimens of equipment insulation, at constant stress fails at inordinately different times. In order to be able to estimate the life of power equipment like transformer bushing, it is necessary to run long duration ageing experiments under accelerated stresses, to acquire and analyze insulation specific failure data. The present work is an attempt to provide reliability and life estimation of High Voltage RIP bushing insulation. The literature survey carried out in this view indicate that investigation on thermal and electric field distribution and the models for failure under combined stress and analysis of the data so as to be able to estimate the possible life of RIP bushing is scanty. Having these aspects in focus, the scope of the present work is defined as: (i) Mapping of the temperature and electric field distribution in the body of 400kV RIP bushing (ii) Deduction of parameters of the probabilistic models for the failure under electrical and thermal ageing (iii) Estimation of life based on diagnostic testing using PD With this in view, the temperature distribution in the body of a 400kV RIP bushing is studied considering the heat generation both in central conductor and that in the insulation. Presence of multiple materials with non-confirming interfaces makes analytical solution rather difficult and hence numerical approach is adopted. In the present work, vertex-centered Finite Volume Method (FVM) is employed for both thermal and electrical analysis. The electric stress distribution is accurately evaluated considering both the non-zero conductivity of the RIP material and the presence of capacitive grading foils. These analysis has clearly shown that Stress grading foils uniforms the stress across the major portion of the bushing insulation Enhancement of the electric conductivity by the temperature is not found to be affective in changing the electric field distribution The temperature distribution is shown to have a maxima near the flange due to the influence of top oil temperature of the transformer Heat generated in the dielectric due to the prevailing electric stress is shown to be insignificant. This ruled out the possibility of thermal runaway and hence the dielectric temperature is within the safe working limits for the bushing considered. The deduction of physical models governing insulation failure depends on the nature of stress. In this work, the insulation failure at constant accelerated stress has been considered and the estimation of life is computed based on inverse power law coupled with Arrhenius law. A high degree of scatter is generic to the experimental data forming the ingredients to develop the models. In view of this, the concept of a random process is invoked. Probabilistic models for the failure of RIP bushing under synergy are adopted and an attempt is made to estimate the life. The well known Weibull distribution and probability plotting of life data is used in this endeavor. The maximum likelihood estimation is used to determine the scale and shape parameters of the Weibull distribution. In the diagnosis of the extent of degradation of insulation due to PD, under long duration electric stress, a non-conventional voltage application method called the classical stepped stress method is adopted. In this technique, the voltage is applied in pre-determined steps over predetermined duration of time. The magnitude of voltage steps is carefully computed based on Miners law and the end-of-life is computed using inverse power law. In summary, this thesis work has contributed to the thermal and electrical degradation of resin impregnated paper insulation for high voltage transformer bushing. The thermal and electrical field distributions computed in the body of bushing clearly shown that these stresses are well within the limit, thereby ruling out the possibility of a thermal runaway. Comparing the estimates of the most probable life of RIP, based on several methods appears to show that any of the method can be adopted. However, as matter of caution and safety, the lowest among them can be taken as a reasonable estimate.