No description available.

No description available.

No description available.

O motor de combustão interna, embreagem, transmissão, diferencial, eixo Cardan, semi-eixos e rodas motrizes compõem o trem de potência de um veículo que, por diversas razões de refinamento e peso, oferecem baixa “resistência" aos ruídos decorrentes da irregularidade de rotação do motor. O presente trabalho reúne elementos para analisar os efeitos das flutuações de rotação (vibrações torcionais) presentes nos volantes de motores de quatro tempos, medidas em dinamômetro, no desenvolvimento de sistemas de embreagem. O uso de simulação matemática computacional permite amenizar ou eliminar os ruídos provenientes da transmissão no veículo protótipo, possibilitando assim ganhos significativos no tempo de desenvolvimento de discos de embreagem e/ou volantes de dupla massa. / The internal combustion engine, clutch, transmission, differential, propeller shaft, half shafts and driven wheels compose the powerline of a vehicle which, due to several reasons of refinement and weight, offer low noise "counter resistance" to engine irregularity. This report is a collection of elements to analyze the effects of the engine revolution irregularity (torsional vibration) present on flywheels of 4-stroke engines, as measured in dynamometer, in the development of clutch systems. The use of computer simulation allows to soften or to eliminate the noise deriving from the transmission of prototype vehicles with new powertrain combination (clutch discs and/or dual-mass-flywheels), bringing considerable development time gains.

Kinetic energy storage via flywheels is an emerging avenue for hybrid vehicle research, offering both high energy and power density compared to more established electric and hydraulic alternatives. However, connecting the high speed flywheel to the relatively low speed drivetrain of the vehicle is a persistent challenge, requiring a transmission with high variability and efficiency. A proposed solution drawing inspiration from the electrical domain is the Switch-Mode Continuously Variable Transmission (SM CVT), which uses a high speed clutch to transfer energy to a torsion spring in discrete pulses with a variable duty cycle. The greatest limitation to the performance of this system is the speed and efficiency of commercial clutch technology. It is the goal of this thesis to develop a novel clutch which meets the actuation speed, controllability, and efficiency requirements of the SM CVT, with potential for reapplication in other rotary mechanical systems with switching functionality. The performance demands of the clutch were derived via a theoretical design case based on the performance requirements of a typical passenger vehicle, indicating the need for a sub-millisecond engagement and disengagement cycle. This is not met by any conventional clutch. Several concepts were considered across the fluid, electromagnetic and mechanical energy domains. A final concept was chosen which employs a friction disk style architecture, with normal force produced by compressing springs via an axial cam mounted to the flywheel. To control duty cycle, the cam was designed with a radially varying profile such that increasing radial position results in proportionally increasing ratio of high dwell to low dwell. Three synchronized followers are then translated radially on the cam by a control linkage. Analysis of the follower train dynamics and system stiffness were carried out to inform the design of a scaled benchtop prototype. Experimental testing was carried out to characterize the performance of the prototype. It was found that the intended functionality of the design was achieved, with discrete energy transfer accomplished via pulsing of the clutch. However, maximum efficiency was only 33% and torque capacity was only 65% of the intended 70Nm. Significant opportunity exists for improvement of the clutch performance in future research.

HiGtech är en projektgrupp på Högskolan i Gävle vilka konstruerar och bygger energisnåla tävlingsfordon. Ett av fordonen tävlar i Shell Eco Marathons prototypklass för bensindrivna förbränningsmotorer och drivs av en på högskolan konstruerad motor. Motorns effekt överförs till en kedjetransmission via en inköpt och modifierad centrifugalkoppling. Den nuvarande centrifugalkopplingen väger cirka 1,5 kg. Då en stor faktor för tävlingsresultatet är fordonets rullmotstånd, vilken beror av fordonets vikt, har målet med detta arbete varit att konstruera en specialanpassad centrifugalkoppling, vars vikt endast är hälften så stor som motorns nuvarande koppling. Experiment på motorn, en undersökning av befintliga centrifugalkopplingar samt en litteraturstudie har utförts vilket gav indata för konstruktionsarbetet. Centrifugalkopplingens diameter har optimerats med avseende på låg vikt, där massan av kopplingens nav, trumma och backar tagits fram och jämförts för olika diametrar. Backarnas massa har beräknats med en framtagen beräkningsmodell och navets samt trummans massor har tagits fram genom 3D-modellkoncept. Vidare har en centrifugalkoppling konstruerats av stål, anpassad för tävlingsfordonets motor med individuell justering av ingreppsvarvtalet för dess backar. Centrifugalkopplingens optimala diameter beräknades till 110 millimeter, vilket har resulterat i en totalvikt på den utvecklade kopplingen på cirka 730 g. En specifikationslista har tagits fram på lämpligt friktionsmaterial, dock krävs vidare tester för att säkerställa att önskad funktion uppnås på grund av vibrationer som kan uppstå, något som avgränsats bort i detta arbete. / HiGtech is a project group at the University of Gävle, in which students design and build energy efficient vehicles to compete with around the world. One of the vehicles is competing in the Shell Eco Marathon prototype class for gasoline-powered internal combustion engines and is driven by an on campus designed engine. The engine's power is transmitted to a chain transmission via a purchased and modified centrifugal clutch. The current centrifugal clutch weighs about 1.5 kg. An important factor for the outcome in the competition is the rolling resistance of the vehicle, which depends on its weight, the aim of this work has been to design a customized centrifugal clutch, whose weight is only half as large as the engine’s current clutch. Experiments on the engine, a survey of centrifugal clutches and a literature study has been performed which gave input for the design work. The diameter of the centrifugal clutch has been optimized for low weight, where the mass of the clutch hub, drum and shoes has been compared for the different diameters. The shoe mass has been calculated using a developed model and the hub and drum masses have been developed through a 3D model concept. Furthermore, a centrifugal clutch out of steel, adapted for the engine of the competing vehicle, has been developed, with individual adjustments of the engagement speed of its shoes. The optimal diameter of the centrifugal clutch was calculated to 110 millimeters, resulting in a total weight of the developed clutch of about 730 g. A list of specification has been developed for an appropriate choice of friction material, however, further testing is required to ensure that the desired functionality is achieved due to vibrations that may occur, this was however demarcated in this work.

O motor de combustão interna, embreagem, transmissão, diferencial, eixo Cardan, semi-eixos e rodas motrizes compõem o trem de potência de um veículo que, por diversas razões de refinamento e peso, oferecem baixa “resistência” aos ruídos decorrentes da irregularidade de rotação do motor. O presente trabalho reúne elementos para analisar os efeitos das flutuações de rotação (vibrações torcionais) presentes nos volantes de motores de quatro tempos, medidas em dinamômetro, no desenvolvimento de sistemas de embreagem. O uso de simulação matemática computacional permite amenizar ou eliminar os ruídos provenientes da transmissão no veículo protótipo, possibilitando assim ganhos significativos no tempo de desenvolvimento de discos de embreagem e/ou volantes de dupla massa. / The internal combustion engine, clutch, transmission, differential, propeller shaft, half shafts and driven wheels compose the powerline of a vehicle which, due to several reasons of refinement and weight, offer low noise "counter resistance" to engine irregularity. This report is a collection of elements to analyze the effects of the engine revolution irregularity (torsional vibration) present on flywheels of 4-stroke engines, as measured in dynamometer, in the development of clutch systems. The use of computer simulation allows to soften or to eliminate the noise deriving from the transmission of prototype vehicles with new powertrain combination (clutch discs and/or dual-mass-flywheels), bringing considerable development time gains.

This thesis deals with the design of the magnetorheological (MR) clutch. The extensive literature research with particular conclusions to each design variant of MR clutches or brakes has been done in the first part of the thesis. The second part of the thesis describes the design of the actual MR clutch based on the results of the analytical calculation of the magnetic circuit. Finally, the experiments verifying the function of the key segments of the clutch, and the whole clutch are summarized in the third part of the thesis.

No description available.

This study attempted to explore the phenomenon of free throw shooting under pressure. The participants in the study were 10, Division III college basketball players who agreed to take part in an interview centered around free throw shooting. The data were gathered from the responses of the players, using a semi-structured interview, developed by the researcher with the suggestions and approval of an expert basketball panel, comprised of sport psychology professors, NBA sport psychologists, basketball coaches, and former players. Four of the interviews were done in person, while the other six were done over the phone. The interviews were transcribed and coded using a constant comparative method described by Boeije (2002). This entailed a process of open coding, which resulted in 65 codes. Of these 65 codes, 57 codes were assigned into eight categories during a process of axial coding. These categories were as follows; routine, practice, focus, pressure, pressure management skills, confidence, clutch factors, and non-clutch factors. Confidence was technically a sub-category of clutch factors, but was deemed large and separate enough to be its own category. The coding of interviews went through a process of inter-rater reliability via an independent coder. The independent coder and the researcher agreed on over 86% of the coded responses. The disagreements were discussed and a mutual understanding was established. Players emphasized the importance of a pre-shot routine, especially under high-pressure circumstances. Players discussed the importance of practice in preparation for high-pressure free throws. Players gave their level of focus on task-relevant and task-irrelevant stimuli when attempting free throws, both under normal circumstances and under pressure circumstances. Players revealed pressure management strategies that they used to aid in the performance of attempting high pressure free throws. Possible links to clutch performance were explored by the researcher. / Kinesiology