A potência em um motor de combustão interna depende, dentre outros parâmetros, da proporção da reação da mistura oxidante/combustível. Esses reagentes são oriundos de hidrocarbonetos e do oxigênio disponível no ar atmosférico. Para cada tipo de combustível utilizado, a mistura apresenta diferentes curvas de desempenho do motor, cuja máxima potência disponibilizada está diretamente relacionada ao valor e à posição da pressão desenvolvida no cilindro em cada ciclo. A posição da máxima pressão deve ser ajustada na melhor condição de aproveitamento do mecanismo biela/manivela a partir da variação do ponto de ignição. O valor da pressão varia, fundamentalmente, com a eficiência de conversão de combustível, com a variação do número de mols proveniente da combustão, com a entalpia de vaporização, com a temperatura de funcionamento do motor, e com a relação entre o carbono, o hidrogênio e o oxigênio existente na molécula. Com a finalidade de verificar o ponto de máxima potência desenvolvida no motor em relação à mistura ar/combustível, foram levantadas curvas de potência para cinco combustíveis, quais sejam: gasolina montadora e condensado, etanol (álcool hidratado 98%), tolueno e mtbe. O fator que estabelece a proporção da mistura ar/combustível real na combustão com a mistura quimicamente balanceada (estequiométrica) é designado por λ. Utilizou-se valores de λ >1, caracterizando a mistura pobre, até os valores de λ <1, os quais permitem o funcionamento do motor em condição de mistura rica. Os experimentos foram realizados em um motor ciclo Otto quatro cilindros, montado em um dinamômetro elétrico e monitorado por uma injeção eletrônica programável. O objetivo deste trabalho foi o de estudar, a partir de dados experimentais, a influência de λ na potência efetiva do motor. Os valores de λ de maior potência obtidos ficaram entre 0,85 e 0,90 podendo servir de parâmetro para o mapeamento da injeção de combustível na condição de aceleração do veículo quando se fizer necessário imprimir a máxima potência. A aquisição de tais valores pode auxiliar ainda no desenvolvimento de novas misturas de combustíveis, em que se procura maior desempenho do motor para competições automobilísticas. / The power developed in an internal combustion engine depends, amongst other parameters, on the ratio oxidizer/combustible. These reagents are deriving of hydrocarbons and atmospheric air. For each type of used fuel, the mixture presents different types of performance curves for the same engine, whose maximum available power is directly related to the value and the crank position of the maximum pressure developed in the cylinder, in each cycle. The crank position of the maximum pressure must be rightly placed, with ignition timing changes, in order to get the best exploitation of the rod/crankshaft mechanism. The value of the pressure varies, basically, with the fuel conversion efficiency, with the mole number variation due to combustion, with the enthalpy of formation, the engine’s operating temperature and with the relation between carbon, hydrogen and the existing oxygen in the fuel’s molecule. With the purpose of verifying the point of highest engine power with relation to the air/fuel ratio, curves of power for five different fuels had been raised. These fuels are: condensed gasoline, OEM gasoline, ethanol, toluen and mtbe. The factor that establishes the air/fuel ratio with the stoichiometric mixture is assigned by λ . Values of λ > 1 characterize lean mixture until the values of λ <1 characterize a rich mixture condition. The experiments had been carried with a four cylinders Otto cycle engine, with programmable electronic fuel injection and ignition control, assembled in an eddy current dynamometer. The objective of this work was to verify, from experimental data, the influence of λ in the engine’s output. The λ values for highest power lie between 0.85 and 0.91, being able to act as an input for tuning the fuel injection system for getting better throttle response and maximum power. The acquisition of such values can still assist in new fuel mixtures development, where increase in power and torque are expected.

Visando uma opção de substituição, onde for possível e aplicável, do motor de indução monofásico, este trabalho relata o estudo teórico, a construção, o acionamento e os ensaios de um motor bifásico com ímã permanente no rotor, de baixa potência, utilizando imãs de ferrita na confecção do rotor. / This work shows the theoretical studies, building, driving systems and tests of a small-power double-phase motor with ferrite permanent-magnet in the rotor, based on the original structure of a single-phase induction motor. The objective is to create an option to replace the single-phase induction motor where it is possible and applicable.

A driving simulator reproduces the essential features of a vehicle and provides an interface for direct human operation. It provides a safe and less expensive way of training people how to drive. Against the backdrop of a comprehensive literature survey on driving simulators and their applications, this thesis endeavours to make five unique contributions. Many of the military armoured vehicles have eight wheels, are able to cross trenches of approximately two meters, and can climb steps of as high as one meter. Available research, however, focuses primarily on the vehicle dynamics modelling of commercial four wheel vehicles. In this thesis, a mathematical model is given for simulating the vehicle dynamics of an eight wheel vehicle over rough terrain, taking into account the limitations of real-time driving simulation. A discussion of the model by Janse van Rensburg et al. is contained in a paper which is currently under review by the International Journal of Modern Physics C (IJMPC). To prove the validity of a vehicle model, it is necessary to provide a method of testing the model. Detail about the vehicle dynamics model used is not always available when developed by a third party. This thesis describes a “black box” testing method for the verification of a vehicle dynamics model. An article regarding this matter by Janse van Rensburg et al. has been submitted to the IJMPC and is currently under review. Normally, the focus on driving simulators is on the modelling of realistic vehicle dynamics models. However, the design of a realistic simulation environment is of equal importance. A human driver usually steers one vehicle, but the rest of the vehicles used in the simulation should be managed by a computer program. An automatic driver model is described to be used within the simulation environment. The current presentation is based on the published paper [86] by Janse van Rensburg et al. (IJMPC, 16(6):895-908, 2005). An understanding of three-dimensional coordinate system transformations is one of the most important parts of a flight or driving simulator. Although the procedure of using Euler angles for coordinate system transformations is nothing new, almost no literature is available of how it can be applied on more complex situations. This thesis supplies more information on how a program language such as C++ could be used to apply more complex coordinate transformations in real-life situations. Results appeared in the published paper by Janse van Rensburg et al. (IJMPC, 16(6):909-920, 2005). Finally the use of vocoders is proposed for the modelling of engine sound. For a driving simulator which should be an exact replica of a certain vehicle, an accurate sound model is of extreme importance. By using vocoders, a technique used for the manipulation of voice, a higher level of accuracy and realism can be obtained than with the methods currently discussed in literature. A paper on this matter, compiled by Janse van Rensburg et al. is currently under review by the IJMPC. / Prof. M. A. van Wyk

<p>Stability is the ability of a system to reject noise and maintain or return to the desired movement pattern and is an important feature of a motor system. In contrast, maneuverability is the ability of a system to transition between different motor states. A system that prioritizes stability inhibits its ability to transition between different motor states in a dexterous fashion. Since stability and maneuverability are opposing characteristics of a system, stability could be traded off to increase maneuverability. This study focuses on isometric finger force production, and its goals were to identify whether (1) the amount of information available about an upcoming motor transition influences the reduction in stability of total isometric force produced by the fingers, (2) stability reduction was correlated with greater maneuverability, i.e., less time for initiating a change in the total force, (3) the amount of stability reduction is correlated across tasks with different amount of information regarding the upcoming force changes, and (4) the times required to change force correlated across tasks with different informational content. </p> <p>Twenty-nine young adults (17 women; age, 23.3 ± 4.3 years) participated in this study and completed three different finger force tasks. For each task, the participants modulated the total pressing force produced by the four fingers of their right hand to track a target presented on a computer screen. In each task, participants began by producing a consistent (10% of their maximum voluntary contraction, MVC) background force with their fingers. In the Steady task, the target remained stationary and participants knew the target would not move. In the Reaction Time (RT) task, the target moved randomly in the vertical direction and participants knew that this could happen at any point in time. In the Self-paced task, participants started producing a background force and then produced a quick increase in total force using a predefined target that was displayed at the beginning of the trial, and visible throughout the trial. </p> <p>The uncontrolled manifold analysis was used to assess the stability of the total force during each task. This assessment was performed when the participants produced the same force (10% MVC), but expected different upcoming force changes, and had different amount of information about these upcoming force changes. This analysis yielded a stability index, and measures of the variance structure in the finger forces, computed across multiple repetitions. The reaction time and the movement time in the RT and the Self-paced tasks, respectively, was computed to quantify maneuverability. </p> <p>In contrast to previous findings and our expectations, the stability index was not statistically different for the Steady, RT, and Self-paced tasks, meaning that stability of the total force was not reduced in response to the mere expectation of an upcoming change in total force. However, the stability index reduced immediately before individuals changed their total force in the Self-paced tasks, which supports findings from previous studies. The stability modulation between the Steady and RT tasks did not correlate with the RT, and the stability modulation between the Steady and Self-paced tasks did not correlate with the movement time. Therefore, this study did not reveal a stability-maneuverability trade-off in isometric finger force production tasks. The movement time for the RT and Self-paced tasks were also not correlated. However, the novel finding of this study was that participants changed stability similarly for the RT and Self-paced tasks.</p> <p>Finally, the variance components obtained from the uncontrolled manifold analysis were higher in the RT task compared to the Steady task, consistent with previous reports. In fact, the increase in the performance error (greater variability in total force) while expecting to change total force in uncertain conditions (RT tasks) is the most striking and consistent result across multiple similar studies. This result indicates that despite the inconsistent results regarding the stability index, the performance of the current task (producing a constant total force) is hampered by the uncertainty and the expectation of upcoming changes in total force.</p> <p>It is likely that the stability-maneuverability trade-off is not essential for young, healthy adults in manual force production tasks. Investigations that include participants across the lifespan will shed light on this relation and help identify whether it plays a salient role in understanding loss of manual dexterity with healthy aging. </p>

Past research has indicated that motor imagery, or imagined movement, follows Fitts' law similarly to physical movement. Additionally, motor imagery has been shown to improve real motor performance in multiple contexts, showcasing a remarkable connection with real motion. The current study examines how the subject of motor imagery, imagining oneself, another person, or an object, impacts this faithfulness to real movement, specifically in following Fitts' law. Participants viewed 2D photos of a virtual environment with an "X", a humanoid, or a disc facing a gate at 6 distances and 4 widths for 24 combinations. Each combination was repeated twice randomly for 48 trials per condition, and conditions were presented in random order for a total of 144 trials. Results indicate that object-imagery does trigger motor imagery and follow Fitts' law, in contrast to prior research. However, further analysis showed that the function produced in the object condition was significantly different from both self and other, while self and other were not significantly different from one another. This was due to a higher index of performance value in the object condition, implying that participants assigned the object different abilities than the two human-centered conditions. These results indicate a difference related to biological, or perhaps human, motion, and future studies should further explore the impact of the subject and characteristics of the subject on motor imagery. Understanding these intricacies is crucial to refine and understand the benefits of motor imagery seen in multiple motor performance contexts.

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