1,721,023 research outputs found
Effect of an inter-ring crevice on unburned hydrocarbon emissions in a spark-ignition engine
No full textThe effect of the inter-ring crevice, the volume between the top and the second piston rings, on unburned hydrocarbon (UHC) emission was experimentally investigated. The ultimate goal of this study was to reduce the level of UHC emission by minimizing the effect of the inter-ring crevice. For this purpose, the unburned mixture trapped in the inter-ring crevice was extracted to the crankcase during the late period of expansion and the early period of the exhaust stroke through the engraved grooves on the lower part of the cylinder wall. The extraction of the mixture resulted in significant reductions in UHC emission by 23 per cent at maximum over a range of speeds (1250-3500 r/min) and loads (185-556 kPa, b.m.e.p.), without any losses of efficiency and power. This experimental study has confirmed the importance of the inter-ring crevice on UHC emission in a spark-ignition (SI) engine.The authors thank Professor Kyoung Doug Min of Seoul National University for his valuable advice
A dead-beat type digital controller for the direct torque control of an induction motor
No full textIn this paper, a dead-beat type digital controller has, been introduced to overcome the problems of a conventional direct torque controller. The proposed induction motor drive with a digital dead-beat controller shows the good transient response and negligible steady-state error even at a low switching frequency, which is needed for high power machines used for transportation. Including the rotor dynamics, the stability condition and steady-state error of the proposed control system have been examined in the z-plane. In addition, the good performance has been verified through the simulation and experiment. The flux and torque controllers have been designed with only stator voltage equations in the stator flux reference frame in order to take advantages of the direct torque control. Therefore, the proposed flux and torque controllers have simple forms and can be easily designed and implemented
Characterization of magnetic properties in Co/Pd multilayers by Hall effect measurement
No full textA Hall voltage measurement has been carried out by adopting four-probe technique to characterize the magnetization reversal characteristics in ultra-thin ferromagnetic films of (2-Angstrom Co/11-Angstrom Pd)(n) multilayer having different number of repeats it, where the anisotropy constant and saturation magnetization increased with increasing the number of repeats n. The Hall voltage exhibited a clear hysteresis behavior of Co/Pd multilayer films with sweeping the external magnetic field, and the field angle dependence and the temperature dependence of the magnetization reversal characteristics have been investigated using the Hall voltage hysteresis. (C) 2002 Elsevier Science B.V. All rights reserved.This work was supported by the Korean Ministry of
Science and Technology through the Creative Research
Initiatives Project
Detection of Three-Phase Currents in Space-Vector PWM Inverter with Only One DC Link Current Sensor
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Study on maximum torque generation for sensorless controlled brushless DC motor with trapezoidal back EMF
No full textThe sensorless controlled brushless DC motor with trapezoidal back EMF has been studied. Since the detected position information on the sensorless rotor has some uncertainty, the brushless DC motor cannot be driven with a maximum torque. To investigate the nature of torque in the sensorless controlled brushless DC motor, the torque characteristics as a function of commutation delay (or commutation timing error) have been analysed. It shows that the generation torque is influenced by the commutation delay and has a single maximum point. This maximum point is changed by the rotating speed and load conditions. Therefore, it needs to be adjusted at every operating point. However, if the operating condition is varied continuously, the sensorless controlled brushless DC motor cannot be driven with a maximum torque at every operating point. In the paper, an iterative learning algorithm and a fuzzy logic controller are employed to drive the brushless DC motor with maximum torque. To show the effectiveness of the proposed control scheme, the change of the torque-current ratio is shown in various operating points through computer simulations and real experiments. It is well demonstrated from these results that the proposed drive method provides desirable performance by the sensorless controlled brushless DC motor with trapezoidal back EMF
Dissolved oxygen concentration and growth rate control in fed-batch fermentation process
No full textA New Instantaneous Torque Control of PM Synchrounous Motor for High Performance Direct Drive Applications
No full textNew instantaneous torque control of PM synchronous motor for high performance direct drive applications
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