RU2240529C1 - Method of evaluation of condition of mated parts - Google Patents

Abstract

FIELD: mechanical engineering; engines.

SUBSTANCE: invention relates to acoustic diagnostic methods and it can be used for checking condition of parts of internal combustion engine valve actuating mechanism. According to proposed method air leakage past mated surfaces of parts is measured and diagram is plotted representing changes of microirregularities and area of contact at different air leakages, then harmonic oscillations at natural frequencies are excited whose form is determined by equation φ(x)=A[S(B_m/l^.x)-V(B_m)/U(B_m)^.T(B_m/l^.x)] where S, V, U, T are Krilov functions; B_m is root of characteristic equation; x are coordinates along longitudinal axis of part, m; A is constant coefficient found from boundary conditions; 1 is length of part, m. _m - are 1, 2, 3 … . Shifting of frequency of natural oscillations and intensity of wave at natural oscillation frequency at propagation of elastic waves through layer formed by microirregularities in mated surfaces. If shifting of natural oscillations frequency and intensity of wave at natural oscillations frequency lies out of zone of tolerable values, mated parts do not provide required degree of sealing.

EFFECT: improved accuracy and provision of reliable evaluation of condition of mated parts of piston machine, reduced labor input at diagnosing.

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Description

The invention relates to technical diagnostics by the acoustic method and can be used to control valve parts of an internal combustion engine.

A known method for assessing the technical condition of the mating parts of a piston machine (RF patent No. 2166743, IPC G 01 M 15/00, 2001), which consists in the fact that on an idle engine harmonic oscillations are excited in the base part at natural frequencies, the shape of which is given by the equation

where S, V, U, T are the Krylov functions;

In _m is the root of the characteristic equation;

x - coordinates along the longitudinal axis of the part, m;

A is a constant coefficient determined from the boundary conditions;

l is the length of the part, m;

m - 1, 2, 3, ...

and the amplitude of the shock pulses is determined.

The disadvantage of this method is the low accuracy and reliability of the control, as well as the high complexity of its implementation, since it is necessary to use a special device to create an alternating load. The task of the claimed invention is aimed at improving the accuracy and reliability of monitoring the assessment of the technical condition of the mating parts of the piston machine, reducing the complexity of diagnosis. The objective of the claimed invention is achieved by the fact that in the method for assessing the technical condition of the mating parts of a piston machine, which consists in determining the air leakage through the mating parts and constructing a diagram of changes in microroughness and contact area with different air leakage, then harmonic oscillations are excited at natural frequencies, shape which is given by the equation

where S, V, U, T are the Krylov functions;

In _m is the root of the characteristic equation;

x - coordinates along the longitudinal axis of the part, m;

A is a constant coefficient determined from the boundary conditions;

l is the length of the part, m;

m - 1, 2, 3, ...

in this case, in order to improve the accuracy of diagnosis of mating surfaces, the frequency offset of the natural oscillations and the wave intensity at the natural frequency are determined.

Figure 1 shows the wave propagation pattern.

Figure 2 shows a diagram of the change in the contact area b from the height of the microroughness of the surface h of the sealing surface with air leakage Q = 2 cm ³ / min and Q = 4 cm ³ / min.

Figure 3 shows a graph of the increment of the frequency of natural oscillations from the height of the surface roughness.

Figure 4 shows a graph of changes in the intensity of the wave I at the frequency of natural oscillations from the contact area b.

Figure 5 shows a diagram of changes in the parameters of the acoustic signal at an air leakage of 2 cm ³ / min and 4 cm ³ / min.

Figure 6 presents a device for diagnosing mating parts.

Figure 7 presents a graph of diagnostic parameters (natural frequency Δf and wave intensity I).

The essence of the method lies in the fact that during the passage of elastic waves through the contact layer formed by the microroughnesses of the mating surfaces, their parameters change, which leads to a frequency shift of individual resonances. In this case, the waves propagate only through the contact contact zones, outside the contact zones they are almost completely reflected. The wave propagation pattern is shown in FIG. The protrusions of the contacting surfaces are a set of N oscillators. The wave intensity emitted by one oscillator is proportional to the square of the frequency f and the square of the amplitude A of the oscillations

Ii ~ A ² f ²

and is determined by the expression [1]:

where A is the oscillation amplitude, dB;

f is the oscillation frequency, Hz:

ρ is the density of the medium, kg / m ³ ;

s - wave propagation velocity in the medium, m / s.

The intensity of wave I passing through the contact zone is equal to the sum of the intensities of the waves emitted by all oscillators:

and is proportional to the interface contact area S:

I ~ S.

The larger the contact area of the mating surfaces, the greater the energy of the waves propagating through the contact zone. It is known that air leakage through mating surfaces depends on the microgeometry of the contacting surfaces and is determined by the height of the microroughness and the actual contact area [2]. To implement the method, first, on several samples of the mating parts, the air leakage Q is determined through coupling at a pressure of 0.15 MPa depending on the height of the roughness h and the contact area b, and a diagram of the change in the roughness h and the contact area b for different air leakage Q is constructed. FIG. 2 shows a diagram of the change in the contact area b from the height of the microroughnesses of the surface h of the sealing surface with air leakage Q = 2 cm ³ / min and Q = 4 cm ³ / min.

Then, vibrations with a natural vibration frequency are excited in the valve and the frequency shift of the natural oscillations and the wave intensity at the natural oscillation frequency are determined during the propagation of elastic waves through a layer formed by microroughnesses of the mating surfaces. Figure 3 shows a graph of the increment of the frequency of natural oscillations from the height of the surface roughness; figure 4 is a graph of changes in the intensity of the wave I at the frequency of natural oscillations from the contact area b.

The values of the microroughness h and contact area b for various air leakages Q are compared with the values of the acoustic signal parameters. Figure 5 shows a diagram of changes in the parameters of the acoustic signal at an air leakage of 2 cm ³ / min and 4 cm ³ / min.

As an implementation of the proposed method, we consider the determination of the technical condition of the saddle - valve coupling of the KamAZ 740 engine, the air leakage through which should not exceed 3.6 cm ³ / min [3].

The method is as follows. In the valve 2, pressed against the cylinder head by a spring 5, elastic vibrations are excited by the vibrator 1 at the natural frequency of the valve. The vibrator’s oscillation frequency is set using a sound generator 7. An elastic wave is sensed by sensors 3, 4, caused by fluctuations of the particles of the medium only in the contact areas of the valve and cylinder head 6. The signal from the sensors enters the spectrum analyzer 8. During the measurement, the vibration intensity perceived by the sensor is determined , and the shift of the resonant maximum at the natural frequency of the valve, then the technical state of the pairing is determined from the diagram. A device for diagnosing mating parts is shown in Fig.6.

Figure 7 presents a graph of diagnostic parameters (natural frequency Δf and wave intensity I). In Fig. 7 it is seen that when the values of the diagnostic parameters — the shift in the frequency of the natural oscillations Δf and the intensity of the wave I at the natural frequency are outside the range of permissible values (this region is shaded in Fig. 7), the interface does not provide a given degree of tightness.

Sources of information

1. Lependin L.F. Acoustics. - M .: Higher school, 1978, p. 132-171.

2. Khrushchev M.M. Classification of conditions and types of wear of machine parts. Sat Theory, friction and wear in machines. T.8. - M., 1963, p. 78-93.

3. Titunin B. A., Starostin N. G., Mushnichenko V. M. Car repair KamAZ. - L .: Agropromizdat, Leningrad Branch, 1987, p. 147-148.

Claims (1)

A method for assessing the technical condition of mating parts of a piston machine, which consists in determining the air leakage through mating parts and constructing a diagram of changes in microroughness and contact area with various air leaks, then they generate harmonic oscillations at natural frequencies, the shape of which is given by the equation

where S, V, U T are the Krylov functions; In _m is the root of the characteristic equation; x - coordinates along the longitudinal axis of the part, m; A is a constant coefficient determined from the boundary conditions; l is the length of the part, m; m- 1, 2, 3, ..., determine the shift in the frequency of natural oscillations and the intensity of the wave at the frequency of natural oscillations during the propagation of elastic waves through the layer formed by the microroughness of the mating surfaces, and if the shift in the frequency of natural oscillations and the intensity of the wave at the frequency of natural oscillations lies outside the range of permissible values, the conjugation does not provide a given degree of tightness .

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