RU2239803C2 - Method of diagnostics of shafts for rotor machines transmitting torque loading - Google Patents

Abstract

FIELD: measuring engineering.

SUBSTANCE: two pulse pickups of angular position are mounted on the shaft. In rotation of unloaded shaft the signals from the pickups are synchronized in phase of torsional oscillations to be measured. When the shaft is loaded, the shifts of signal pulses of torsional oscillations are determined in two spaced sections of the shaft. The difference between the shifts determine the angular deformations caused by the oscillations of the torque in the drive of machine.

EFFECT: enhanced accuracy and reliability of measurements.

4 cl, 5 dwg

Description

The invention relates to the technical diagnosis of rotary machines and is intended for measuring torques and their vibrations on rotating shafts, mainly gas turbine engines, drilling machines, rolling mills and internal combustion engines transmitting torque loads, which are necessary, for example, to assess the maximum permissible operating modes, as well as the characteristics of low- and multi-cycle fatigue of the material.

In particular, the invention can be used to diagnose the technical condition and regulate the process of transferring loads when drilling wells, the operation of ship propulsion systems, metal rolling and for other objects.

A device for controlling torsional vibrations (see RF patent No. 2044285, class G 01 H 9/00 from 09/20/95, bull. No. 26), comprising a housing fixed to the object, made in the form of two communicating vessels, is placed inertial an element, a light source, a light guide installed in the housing and optically coupled to an inertial element, which is used as mercury, and a light source, a measuring unit with a photoconverter.

This device has disadvantages in that it is impossible to measure torsional vibrations with a frequency of more than 1 Hz and, in addition, it uses harmful material - mercury.

There is a method of determining the torque, which consists in converting the torsion strain of the shaft into an electrical signal using strain gauges mounted on it, recording and comparing electrical signals at operating and idle modes (see RF patent No. 2017097, class G 01 L 1/22. Method determination of axial force and torque. Publish. July 30, 94, bull. No. 14), which allows to specify the measurement of axial loads arising in the shafts.

The disadvantage of this method is the low accuracy and inaccuracy of measuring torsional power loads and their vibrations due to angular errors in the orientation of the strain gauges when they are mounted on the shafts, the presence of interference when transmitting signals through slip rings and brushes, as well as the limited frequency range of the transmitted signals (see, for example, [1] p. 231). Although proposed by US Pat. No. 20177097, the method makes it possible to clarify the value of the measured axial force by introducing an experimentally determined correction; in principle, it does not solve the problem of increasing the accuracy of measuring torques and their oscillations.

A known torsiograph (see RF patent No. 2059208, class G 01 H 1/10, publ. 04/27/96, bull. No. 12) for measuring torsional vibrations of shaft lines of power plants, containing a seismic mass, a housing with an elastic connection between them bearings, a recording unit for the mutual angular position of the seismic mass and the housing, consisting of a reflector, polaroids, stator, light source, photodetector, power supply and recorder, which eliminates the influence of electromagnetic fields on the information transfer channel and improves the accuracy of measurements of torsional oscillations.

However, the known torsiograph is structurally complex and cannot be installed in any place of the shaft, but is fixed only on its end part, which limits the conditions for its use, and in this case the possibility of recording angular vibrations associated with the action of vibrational torsional loads (on the free end of the shaft only free own torsional vibrations of the shaft can be registered).

A device is known (see RF patent No. 2177145, class G 01 H 1/08. Pre-emergency signaling device for deformation of turbomachine blades. Publish. December 20, 2001, bull. No. 35), designed to measure the heterogeneity of the blade of a turbomachine caused by dynamic deformations blades, which is achieved by measuring the current time intervals between the blades in dynamic mode and comparing them with the average time interval between the blades on each revolution of the turbomachine rotor using a pulse sensor, shaper, code adder, Ithel total code difference calculation unit, a control unit and a comparison circuit.

The known device allows you to register torsional vibrations of the shaft, however, it does not provide the possibility of measuring torque and the allocation of torsional vibrations due to the action of these moments, which does not allow its use in assessing the likelihood of fatigue failure of the shaft, as well as the turbine blade apparatus under the action of variable torsional loads.

The aim of the present invention is to improve the accuracy and reliability of diagnosing the technical condition of rotary-type machines by determining moment loads and their vibrations on rotating shafts.

To achieve this, two impulse sensors of the angular position of the shaft are installed on the drive shaft of the machine, fixing its torsional vibrations. During rotation of the unloaded shaft, the signals from these sensors are synchronized in the phase of the measured torsional vibrations. During the operation of the loaded shaft, the torsional vibration signal pulses are fixed in two shaft sections located at a distance from each other, and the angular deformations caused by the fluctuations in the torque in the machine drive line are determined by the difference in the values of these shifts.

The determination of the magnitude of the torque depending on the magnitude of the angular deformations is carried out using the coefficients obtained by experimental calibration or by well-known formulas of the theory of elasticity (see, for example, [2] p. 160), according to which the magnitude of the torque is directly proportional to the angular strain of twisting of the shaft, which, in turn, is directly proportional to the ratio of the instantaneous values of the time interval between pulses of electrical signals from two sensors the global position of the shaft to the time interval between adjacent pulses from one of these sensors.

To clarify the measurements of momentary idle loads, the pulse shift is first measured by two sensors when the shaft rotates in one or the other direction, after which half the previously measured shift is added to the measured pulse shift when the shaft is under load.

In order to identify and localize the source of energy of the torsional vibration of the shaft for each of the expressed frequency components of the vibration spectrum of the measured torque in accordance with the Umov-Poynting criterion (see, for example, [3] p. 63), the cosine of the angle equal to the phase angle is additionally determined the shift between the selected corresponding frequency components in two time sequences - the current values of the time interval between pulses from one and the other sensors of the angular position of the shaft and the reverse the value of the current values of the time interval between adjacent pulses of any of the sensors. The cosine sign of the specified angle allows you to set the direction of the wave of vibrational pulses and thereby reveal the localization of their source along the length of the shaft.

Figure 1 shows a block diagram of a device that implements the proposed method; figure 2 - waveform of the pulses of the electrical signal from the eddy current sensor of the angular position of the shaft; figure 3 - typical waveforms and spectrograms.

The device (figure 1) consists of identical gear rings-inductors 1-2, rigidly fixed around the perimeter of the shaft 3, sensors (sensors), for example, eddy currents 4-5, mounted on a fixed base near the gear rings 1-2, amplifiers 6, 7 signals from sensors 4, 5 of blocks 8, 9 of generating standard pulses from amplified signals introduced to eliminate interfering factors in pulse signals, in addition to informative time shifts, block 10 for estimating the values of time intervals τ ₁ between adjacent pulses from the sensor 4 of the angular position in ala in the forms depending on the current time and the current phase position of the shaft, unit 11 for evaluating the values of time intervals τ ₁₂ between pulses from the sensor 4 and the sensor 5 for the angular position of the shaft in forms depending on the current time and the current phase position of the shaft, unit 12 for evaluating the working torque and its vibrations, the computer 13 characteristics (for example, spectra) of the vibrational component of the torque.

A device that implements the proposed method works as follows. When the unloaded shaft 3 is rotated mechanically by adjusting the installation of the gear rings 1, 2 on the shaft 3, either by electrically introducing a time delay in the unit for generating standard pulses 9, or phasing the pulses mechanically and electrically together so that the time intervals τ ₁₂ between the pulses from the sensors 4 and 5 of the angular position of the shaft 3 were equal to 0 (τ ₁₂ = 0). Then, when the loaded shaft 3 and the associated gear rings 1 and 2 are rotated, electric pulses i ₁ and i ₂ are induced in eddy current sensors 4 and 5, the instantaneous repetition rate of which is proportional to the instantaneous rotational speed of the shaft 3. Next, the pulses are sent to the current value estimation unit 10 time intervals τ ₁ between adjacent pulses i ₁ from sensor 4 and a block 11 for evaluating the current values of time intervals τ ₁₂ between pulses from sensors 4 and 5. In block 12, the working circle is evaluated based on the current values of time intervals τ ₁ and τ ₁₂ torque and its oscillations according to the formula

M = Ct ₁₂ / τ ₁ ,

where C is a constant coefficient determined by experimental calibration or by calculation by the formula

C = 2πG / ZL,

where G is the modulus of elasticity during torsion of the shaft;

Z is the number of generated pulses per revolution of the shaft,

L is the distance between the gear rings 4 and 5 on the shaft.

Figure 2 shows the oscillograms of the amplified pulsed electrical signal from the eddy current sensor of the rotor angular position of the turbopump unit of one of the designs of the marching liquid rocket engine in the initial part of the starting mode (rapidly increasing rotor speed from 140.6 rpm to 178.5 rpm per 17.8 μs). The number of pulses per revolution of the rotor is 128.

On figa and 3b presents fragments of the waveforms of standardized pulses i ₁ and i ₂ at the output of blocks 8, 9 at a steady state engine operation at a rotor speed of 2200 rpm. The number of pulses per rotor revolution for both sensors is Z = 128, the distance between the sensors installed in two sections of the rotor, L = 0.5 m, the rotor diameter is 0.15 m, the rotor material is steel. The average values of the time intervals between adjacent pulses in the signal i ₁ and pulses in the signals i ₁ and i ₂ in the fragments shown in Fig. 3 are τ ₁ = 213.0 μs, τ ₁₂ = 40.0 μs. In this case, the average value of the twist angle of the rotor in the measured section was

φ = 360 · τ ₁₂ / Zτ ₁ = 9.21 · 10 ^-3 rad.

The value of the working torque at a known angle of rotation of the rotor φ in the measuring section of length L is determined by the formula

M = GJφ / L,

where G is the modulus of elasticity of the rotor material under shear (G = 81 · 10 ³ MPa);

J is the polar moment of inertia of the rotor section (J = πr / 2 ⁹ = 0.194 · 10 ^-6 m ⁴ );

r is the radius of the rotor shaft (r = 0.075 m).

Substituting the values of these quantities in the formula for determining the torque, which is calculated in block 12 (figure 1), we obtain

M = 0.142 tm.

As for the vibrational component of the torque, it is determined according to a similar scheme in block 12 from the fluctuation component of the time interval τ ₁₂ , determined with an accuracy of at least 10 ns (nanoseconds).

Fig.3c shows a graph of the total torque (constant and vibrational components) in the frequency range up to 1000 Hz, and Fig.3d is a spectrogram of the vibrational component of the torque, determined in block 13. This spectrogram is informative from the point of view of diagnosing the technical state of the kinematic rotor-stator pairs of the motor, in particular, the fragments correspond to the moment of development of powerful torsional self-oscillations due to the closure of the parasitic positive feedback loop ru of the engine: torsional tangential vibrations of the turbine blade apparatus - torsional rotor vibrations - vibrational flow rate of the oxidizer through the turbocharger to the gas generator - torsional vibrations of the turbine blade apparatus.

When the shaft rotates without load, a static idle moment acts on it, causing a pulse shift from one and the other sensors, which is measured when the shaft is idling and taken into account when determining the total effective torque when working under load.

When the shaft rotates under load, torsional shear deformations occur, caused by the action of torque and its oscillations. As a result, pulses excited by the sensors shift in time relative to each other.

At the same time, the parameters of the measured time shifts of these pulses make it possible to fix the instantaneous values of angular deformations with an accuracy of fractions of angular minutes and higher. In addition, measurement errors associated with inaccuracies in sensor fastening and violation of switching conditions in the measurement lines of electrical signals are eliminated.

Thus, the measurement of torsional vibration pulses in two sections of the shaft and a comparison of their time shifts can improve the accuracy of determining the magnitude of the torques and their vibrations and, thereby, increase the accuracy of fatigue strength assessment and diagnosing the technical condition of the machine, which was the purpose of the present invention.

Sources of information

1. Vibration in technology. T. 5. M .: Mechanical engineering, 1981, p.231.

2. Odinets SS, Topilin G.E. Torque measuring tools. M .: Mechanical Engineering, 1977, p. 160.

3. Gulo D. D., Umov N. A. M .: Education, 1977, p. 63.

Claims (5)

1. A method for determining the operating torque transmitted by the shaft and its oscillations, which consists in converting the angular rotations of the shaft into electrical signals using the sensors of the angular position of the shaft and recording these electrical signals when the shaft is under load, characterized in that, in order to improve accuracy and reliability diagnosing the technical condition of the machine, measuring the torques and their vibrations on the shaft of the machine is carried out by sensors located in its two sections, synchronized by the phase of the pulses The systems from both sensors are idling, after which they measure and compare the pulses received from the sensors during shaft operation under load, determine the current values of the time intervals between adjacent pulses from one of the sensors and between pairs of matched pulses from one and the other sensors, and then the instantaneous torque values are determined as the quotient of dividing the time shift between pulses from one and the other sensors by the time shift between pulses from one of the sensors, multiplied by a constant determined by the formula C = 2 · 7π · G / Z · L, where G is the torsion modulus; Z is the number of pulses generated per revolution of the shaft; L is the distance between the gear rings on the shaft. 2. The method according to claim 1, characterized in that, in order to improve accuracy, first measure the angular vibration pulses from both sensors at idle of the shaft in one direction of rotation, and then in the other direction, after which the time shift of the pulses from both sensors is determined relative to each other and set the initial position of the sensors themselves so that the pulse shift is equal to half the shift obtained by rotating the shaft at idle in the forward and reverse directions. 3. The method according to claim 1, characterized in that two adjacent pulses from the sensing elements of each of the two sensors are associated with the same angular rotations of the shaft so that their number for one revolution of the shaft is equal to or greater than twice the upper frequency the range of measurement of fluctuations in torque divided by the value of the lower frequency of the operating range of shaft rotation frequencies, and the distance between the sensors is selected empirically based on the minimum angular defect required to measure the absolute value shaft shaft. 4. The method according to claim 1, characterized in that, for the purpose of identifying and localizing the source of excitation energy of torsional vibration of the shaft, for each of the expressed frequency components of the vibration spectrum of the measured torque in accordance with the Umov-Poynting criterion, the sign of the cosine of the angle equal to phase shift between the selected corresponding frequency components in two time sequences - the current values of the time interval between pulses from two sensors of the angular position of the shaft and the reverse the value of the current values of the time interval between adjacent pulses of one (any) of the sensors. 5. The method according to claim 1, characterized in that the sensor-pulse recorder is installed perpendicular to the axis of the shaft and maintain its position and a constant gap between its surface and the surface of the gear wheels of the pulse inductors.

Images