Critical speed

About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.

Fuel feeding device for two-cycle internal combustion engine

Abstract: PURPOSE:To prevent overspeed without hindering the cooling ability and the lubricating ability of an engine when a detected result of the engine speed exceeds the predetermined value by controlling the fuel injection quantity from a fuel injection device provided in an intake passage so as to be increased CONSTITUTION:A solenoid type fuel injection valve 46 for injecting the lubricating oil mixed fuel is provided in an intake pipe 26 connected to an intake port 30 provided in a cylinder 12 The pressure-raised fuel is fed to the fuel injection valve 46 with a fuel pump 44, and while the pressure of the force-fed fuel is maintained at a certain value by a pressure controlling unit 48 The injection quantity of the fuel injection valve 46 is controlled by a control unit 58 for taking the speed signal N therein Namely, the detected speed N this time exceeds a preset critical speed N0 or not is judged, and when the detected speed N is less than the critical speed N0, the ordinary control operation is carried out, and when the detected speed N is more than the critical speed N0, the increase control operation is carried out

The Vibration Isolating Properties of Uncentralized Squeeze-Film Damper Bearings Supporting a Flexible Rotor

Abstract: The ability of an uncentralized squeeze-film damper bearing to inhibit the effects of vibration in a flexible rotor-bearing system, has been assessed in terms of non-dimensional system parameters. This analytical approach has shown that a correctly designed squeeze-film damper bearing is a very effective means of reducing both the amplitude of motion of the rotor and the force transmitted to the bearing support structure. However, the analysis has also indicated that a poorly designed squeeze-film damper bearing can produce amplitudes and forces greater than those which would arise if the bearing support remained rigid. An experimental programme has supported the validity of the above analytical technique by showing that the measured motion orbits of the journal and disk centers as the rotor passes through the critical speed, are very similar to those predicted theoretically. Also, the response curves for specific groups of system parameters show very similar trends in practice, to those which result from the analytical approach. Some indication of the ability of a squeeze-film damper bearing to reduce the effect of much greater unbalance than normal is also reported.

Analysis of Transient Response of Cracked Flexible Rotor

Abstract: The transient vibration response of a cracked flexible rotor passing through its critical speed is analyzed for crack detection and monitoring. The effects of different factors such as various crack depths, acceleration, damping, torque, unbalance eccentricity, and rotor weight on the rotor vibrational response are studied. The breathing types of cracks are analyzed using simple hinge model in a case of shallow cracks, and the cosine function is employed in the case of deep cracks. The developed strategy enables the analysis of cracked rotor vibrational response with and without weight dominance, taking into account also the nonsynchronous rotor whirl. In addition, the local cross-flexibility for deep cracks is taken into account. Lastly, the effect of the crack depth on "stalling" of the rotor due to the limited driving torque is investigated.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Hybrid Gas Bearings With Controlled Supply Pressure to Eliminate Rotor Vibrations While Crossing System Critical Speeds

Abstract: Micro-turbomachinery (MTM) implements gas bearings in compact units of enhanced mechanical reliability. Gas bearings, however, have little damping and wear quickly during transient rub events. Flexure pivot tilting pad bearings offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability; and when modified for hydrostatic pressurization, demonstrate superior rotordynamic performance over other bearing types. External pressurization stiffens gas bearings thus increasing system critical speeds, albeit reducing system damping. Most importantly, measurements demonstrate that external pressurization is not needed for rotor super critical speed operation. In practice, the supply pressure could be shut off at high rotor speeds with substantial gains in efficiency. The paper introduces a simple strategy, employing an inexpensive air pressure regulator to control the supply pressure into the hybrid bearings, to reduce or even eliminate high amplitudes of rotor motion while crossing the system critical speeds. Rotor speed coast-down tests with the pressure controller demonstrate the effectiveness of the proposed approach. A simple on-off supply pressure control, i.e. a sudden increase in pressure while approaching a critical speed, is the best since it changes abruptly the bearing stiffness coefficients and moves the system critical speed to a higher speed. A rotordynamic analysis integrating predicted bearing force coefficients forwards critical speeds in agreement with the test results. Predicted rotor responses for the controlled supply conditions show an excellent correlation with measured data. The experiments validate the predictive tools and demonstrate the controllable rotordynamic characteristics of flexure pivot hybrid gas bearings.Copyright © 2008 by ASME

Stability of a flexible wheelset for high speed rail vehicles with constant and varying parameters

Abstract: The stability of an elastic wheelset coupled with torsional spring and damper is studied in this paper. With flexible elements between two wheels, the advantages of both rigid and independently rotating wheel systems may be obtained. Previous investigations indicated that axle flexibility will affect the vehicle dynamic behavior and an optimal design may improve the system performance. Those studies were limited to constant wheel/rail geometry as the wheelset rolls along the track. In this paper, it is intended to determine the critical speed regions for both constant and time-varying models. The variation in conicity is assumed to be periodic thus the Floquet stability concept may be employed. The computation of the state-transition matrix is based on a Runge-Kutta algorithm.