RU2184360C1 - Method of diagnosing condition of cylinder-piston group of internal combustion engine - Google Patents

Abstract

FIELD: mechanical engineering; engine testing. SUBSTANCE: engine crankshaft is crankshaft is cranked using external source and communicating above-piston space in cylinder with atmosphere at compression stroke and isolating above-piston space from atmosphere at expansion stroke, and maximum first depression P_1m in above-piston space is measured at expansion stroke and technical condition of valve mechanism is judged by comparing P_1m with preliminarily set maximum depression P_{V max} for valve mechanism. At P_1m>P_{V max} technical condition of cylinder sleeve is determined by comparing P_1m with preliminarily set maximum depression for sleeve P_{S max} and with nominal depression for sleeve P_{S max}. At P_1m>P_{S max} crankshaft is cranked additionally isolating above-piston space from atmosphere at expansion and compression strokes, maximum second depression is above-piston space is measured at expansion stroke and technical condition of compression rings is determined by comparing measured second depression P_2m with preliminarily set maximum depression for rings P_{R max} and nominal depression for rings P_{R nom} At number of cylinders in engine more than one and at condition that in all cylinders P_1m>P_{S max} and neither replacement nor repair of separate sleeves have been carried out in all cylinders, difference between two maximum measured values of P_1m in two different cylinders is determined, and by value of found difference, condition of oil control rings of cylinder having maximum value P_1m is determined. EFFECT: reduced labour input and provision of accurate determination of technical condition of valve mechanism, cylinder sleeves and piston rings. 2 cl, 1 dwg

Description

 The invention relates to the field of technical diagnostics and can be used to determine the technical condition of individual cylinders (cylinder-piston group) in an internal combustion engine by measuring rarefaction in the above-piston space.

 Among the various methods used to diagnose a cylinder-piston group (CPG) of an internal combustion engine (ICE), the pneumatic method based on measuring rarefaction in the above-piston space of a CPG is quite widespread.

Thus, there is a known method for diagnosing an internal combustion engine CPG, which consists in turning the crankshaft of the engine by an external source, communicating the over-piston space with the atmosphere on the compression stroke and isolating the over-piston space from the atmosphere on the expansion stroke, and measuring the maximum depression (P ₁ ) in the over-piston on the expansion stroke space, additionally crank the crankshaft, isolating the over-piston space from the atmosphere on the expansion and compression strokes, while measuring the new rarefaction (P ₂ ) in the over-stroke on the expansion stroke Piston space and determine the technical condition of the compression rings by two measured rarefactions, namely by their ratio (ed. St. USSR 1467423, IPC G 01 M 15/00, 1989).

The specified known method allows to assess the condition of the compression rings, provided that the condition of the cylinder liner and oil scraper rings is satisfactory. However, firstly, the known method does not disclose what should be understood as a satisfactory condition of the liner and oil scraper rings and by what method this condition is determined. Secondly, the use of the ratio of the two indicated measured vacuum to determine the state of the compression rings in this method has the disadvantage associated with the following. According to the results of numerous studies, it was found that the value of P ₁ practically does not depend on the state of the compression rings, but mainly depends on the condition of the sleeve and, as will be shown below, the valve mechanism, and with increasing wear of the sleeve P ₁ decreases. On the other hand, the value of P ₂ depends on the condition of both the liner and the compression rings, and also increases with wear. Imagine the case when the wear of the sleeve is close to the limit, and the compression rings are not worn. In this case, the value of P ₁ due to wear of the sleeve will be reduced, and the value of P ₂ will increase slightly for the same reason. Then the ratio P ₁ / P ₂ will decrease significantly (in comparison with the case when both the sleeve and the compression rings are not worn) and formally, in accordance with the known method, it will erroneously indicate some kind of malfunction of the compression rings. Thus, the assessment of the state of compression rings in relation to P ₁ / P ₂ does not always give reliable results.

Diagnostics of the general condition of the CPG with an estimate of the total amount of leaks in the above-piston space is described in another source of information, from which there is a known method for diagnosing the CPG of a diesel engine, which consists in scrolling the crankshaft of the engine with an external source, reporting the cylinder’s over-piston space with the atmosphere and isolating it on the expansion stroke, the over-piston space from the atmosphere, measure the maximum depression in the over-piston space on the expansion stroke and determine they reveal the technical condition of the cylinder-piston group according to the measured vacuum, comparing it with a pre-set limit (permissible) vacuum (see Belsky V.I. Tractors maintenance and diagnostic manual, M., Selkhozizdat, 1986, p. 123- 125). This method is adopted as a prototype of the claimed method. In accordance with this known method, when the measured vacuum is less than the permissible (0.78 kg / cm ² ), the leaks of the valves are checked and, if the valves do not require grinding (that is, their technical condition is satisfactory), then they decide to repair the cylinder liner and rings.

This method makes it possible to assess the overall condition of the cylinder liner and compression rings and, to some extent, the state of the valves. This method does not allow, without disassembly, to evaluate the state of the valve mechanism separately from the condition of the sleeve, since, as further studies have shown, a comparison of the measured vacuum with the above allowable value, which for diesels is 0.78 kg / cm ² , cannot actually be used for characterization of the state of the valves. To clarify their condition after diagnosis by the specified method, disassembly of the engine is required. This method also does not allow to individually determine the technical condition of the sleeve and compression rings, namely to detect a malfunction of the compression rings with a satisfactory condition of the sleeve.

 In addition, none of these known methods can not determine the state of the oil scraper rings.

 The objective of the present invention is to create a diagnostic technology for CPG ICE, which provides the least time-consuming and completely reliable determination separately of the technical condition of, first of all, the valve mechanism, as well as the cylinder liner, compression and oil scraper rings.

This problem is achieved by the fact that in the method for diagnosing an internal combustion engine CPG, which consists in scrolling the crankshaft of the engine with an external source, reporting the over-piston space of the cylinder to the atmosphere on the compression stroke and isolating the over-piston space from the atmosphere on the expansion stroke, measure the maximum first depression on the expansion stroke P _{1 and} in the above-piston space and determine the technical condition of the valve mechanism, according to the claimed method, the technical condition of the valve mechanism is determined by We compare the measured first vacuum (P _1i ) with the pre-set limit vacuum for the valve mechanism (P _Vп ).

Comparison in the proposed method of the value of P _1and with the limit value of P _Vп , which characterizes the limiting state of the valve mechanism itself, makes it possible to evaluate the state of the valves with a certain degree of reliability, regardless of the state of other CPG elements.

Further, when P _{1 and>} P _vn determine the technical condition of the cylinder liner by comparing P _{1 and} with the preset limiting vacuum to the liner (P _Sn) and a nominal underpressure of the sleeve (P _SH) Further, when P _{1 and>} P _Sn additionally scroll crankshaft isolating the over-piston space from the atmosphere on the expansion and compression strokes, the maximum second depression in the over-piston space is measured on the expansion stroke and the technical condition of the compression rings is determined by comparing the measured second zheniya (P _2i) with a predetermined limiting underpressure for compression rings (P _Rp) and a nominal underpressure of compression rings (P _RL).

If the number of cylinders in the engine is more than one, and under the conditions that no separate sleeves have been replaced or repaired in all cylinders P _1i > P _Sп , the difference between the two largest measured values of P _1i in two different cylinders is determined and the value of the specified difference is determined the state of the oil scraper rings of the cylinder having a maximum value of P _1i .

 Extensive statistics collected by the authors of the present invention have shown the following.

The failure of the valve mechanism of the CPG is manifested practically in the form of a sudden failure (chip, crack, burnout, carbon deposits), leading to the loss of operability of a particular cylinder. The associated formation of a conditional hole in the combustion chamber leads to a sharp decrease in the measured value of the first vacuum P _1i , since no source of additional pneumatic density (excess oil, unburned fuel) is not able to seal this formed hole. Therefore, the technical state of the valve mechanism can be determined by comparing the value of P _1i with a predetermined value of P ₁ , which corresponds to the state of the valve mechanism immediately preceding the moment of sudden failure in it, characterizes the maximum permissible state of the valve mechanism and is designated here as the ultimate vacuum for the valve mechanism ( P _Vп ). Thus, if P _1i <P _Vп , then a conclusion follows about a malfunction of the valve mechanism in this cylinder, while one cannot say anything definite about the condition of the sleeve and compression rings, since in this case the malfunction of the valves "overlaps" other possible malfunctions characterizing leaks in the CPG. Any leaks associated with wear of the sleeve (including the limit) and the failure of the compression rings, and even the sum of these leaks, will not show a decrease in P _{1 and} below P _Vп . Thus, when R _{1 and} ≤P _vn has no sense to conduct subsequent measurement P ₂ to determine the state of compression rings.

It should be noted in this case that the case when P _{1 and} <P _Vп can also occur during burnout of the piston. However, firstly, according to the statistical data on the number of ICE failures, burnout of the piston occurs significantly (about 5 times) less often than valve valve leaks, and secondly, burnout of the piston is easily determined by the external sign - the release of oil from the breather, while time as the proposed method is intended to determine primarily those malfunctions that, by external signs, cannot be unambiguously determined.

In the normal state of the valve mechanism, i.e. at Р _1и > P _{Vп the} state of the sleeve can be estimated by comparing Р _1и with the vacuum values characterizing the maximum permissible and nominal state of the sleeve, which are designated here respectively as the maximum vacuum for the sleeve (P _Sп ) and nominal vacuum for the sleeve (Р _Sн ). _Vn at P <P _{1 and Sn} ≤P must conclude Inappropriate (limiting) the wear sleeve, which can be characterized by its roundness, taper, the presence of burrs, grooves. The case where _Sn P <P _{1 and} ≤R _SH, corresponds to the allowable wear sleeve or its nominal state (at P _{1 and} P = _SH).

It should be noted that the determination of the states of the valves and the sleeve separately became possible in the claimed method due to the fact that the maximum vacuum for the sleeve P _{Sп is} much larger than the maximum vacuum for the valve mechanism P _Vп (see table 1 below).

According to the measurement result P ₁ , i.e. rarefaction in the space above the piston when it communicates with the atmosphere on the compression stroke, it is impossible to determine the state of the compression rings, since with the nominal or acceptable condition of the sleeve and the normal state of the valve mechanism, the presence of an oil wedge in the gaps between the sleeve and the rings will always provide a sufficiently high value of P ₁ . Therefore, the failure of the compression rings is determined by the magnitude of the second vacuum P ₂ , measured by isolating the over-piston space from the atmosphere at the compression stroke. In this case, the pressure in the above-piston space at the compression stroke rises to the maximum value (compression), while part of the compressed air penetrates through the rings into the engine crankcase. At the expansion stroke in the above-piston space, a rarefaction Р _{2 is formed} , the value of which at the end of the expansion stroke will be obviously less than р ₁ due to the presence of compression at the beginning of this stroke (in contrast to the above measurement conditions P ₁ ) and will be directly proportional to that part of the pressure (compression) , which was "lost" as a result of the penetration of compressible air through the rings. The worse the condition of the rings (wear, breakage, coking), the greater the volume of air erupted between the piston and the sleeve, the less compression is achieved at the end of the compression stroke and, therefore, a larger vacuum P _{2 is} formed in the over-piston space at the end of the expansion stroke, and, on the contrary, with the best condition of the rings, the rarefaction of P ₂ is smaller. Therefore, given the measured value of P ₂ , it is possible to determine the state of the compression rings. For this, according to the proposed method, the measured value of P _{2i is} compared with predetermined rarefaction values of P ₂ , which, similarly to the condition of the sleeve, characterize the maximum permissible and nominal state of the compression rings and which are designated respectively as the maximum vacuum for rings (P _Rp ) and nominal vacuum for rings (P _Rn ).

A reliable determination of the technical condition of the compression rings from the second vacuum P _{2 is} possible only with an acceptable or nominal condition of the sleeve, i.e. provided that P _Sп <Р _{1 and} ≤Р _sн . This is due to the fact that in the case of severe wear of the liner, the presence of a gap between the cylinder mirror and the compression ring causes air leakage from the crankcase at the rarefaction stroke and this suction cannot be eliminated by any oil wedge. Therefore, the measured value of the second rarefaction P ₂ will be low primarily due to the unsatisfactory condition of the sleeve and will not characterize the state of the rings, which in this case can be either extremely worn or broken, or in a nominal or permissible worn state.

 The stage of the claimed method related to the assessment of the technical condition of the compression rings is in many respects similar to the above method according to the author. St. USSR 1467423. However, in the claimed method, this stage is carried out only after it is established that the valve mechanism is in a normal state and the sleeve is in a nominal or permissible state. The presence of these conditions increases the reliability of determining the state of compression rings.

In addition, in the claimed method, the state of the compression rings is determined not by the value of the ratio P ₁ / P ₂ (as in the method known from the author of the USSR USSR 1467423), but by comparing the measured P ₂ with the normalized values of P _Rп and Р _Rн , which is significantly reduces the influence of the condition of the sleeve (in the range from nominal to limit) on the assessment of the state of compression rings.

If there are several cylinders in the engine and under the conditions that in all cylinders Р _1и > P _Sп and no individual sleeves were replaced or repaired, it is possible to determine the condition of the oil scraper rings in the cylinder having the maximum value of Р _1и . To do this, determine the difference ΔP ₁ between the two largest measured values of P _{1 and} in two different cylinders and compare the specified difference with the allowable difference ΔP _1e . The case when ΔP ₁ <ΔP _1d , informs about the failure of the oil scraper rings of the cylinder having the maximum value of P _1i .

The ability to determine the state of oil scraper rings is based on the fact that for normal operating conditions and subject to maintenance and repair standards (when no individual sleeves are replaced or repaired), the difference ΔP ₁ is due to the condition of the sleeves in the permissible limit (when P _1and > P _Sп ), cannot be greater than a certain allowable value ΔP _1d . The case where ΔP _1> ΔP _1d, informs about the presence of a cylinder having the maximum in comparison with the other cylinders _{1 and} P value, pnevmoplotnosti additional sources which are not related to the state of the sleeve. Studies have shown that the most likely source of such pneumatic density is a failure in the oil scraper rings.

The values of the maximum vacuum for the valve mechanism (P _Vп ), the maximum vacuum for the sleeve (P _Sп ), the nominal vacuum for the sleeve (P _Sн ), the maximum vacuum for the rings (P _Rп ), the nominal vacuum for the rings (P _Rн ), as well as the permissible the differences ΔP _1e used to determine the state of oil scraper rings are established in advance by known methods using a statistically sufficient amount of experimental data and taking into account the nature and magnitude of wear of the corresponding CPG elements. The specific values of these values depend, in particular, on the degree of compression of the fuel used in the engine (its brand), the temperature (viscosity) of the oil used and the speed of the crankshaft of the engine. Most often, the indicated normative values of rarefactions are established in relation to the starting frequency of rotation of the engine crankshaft. For domestic and a significant number of foreign engines, the values of these values (kgf / cm ² ) can be within the limits indicated in table 1.

 Thus, the method of the present invention proposes a certain sequence of actions, which, with minimal laboriousness, quite unambiguously provides a phased assessment of the valve mechanism, sleeve and compression rings in the ICG ICE, as well as the condition of the oil scraper rings under certain conditions.

The proposed method is as follows. For measurements of P ₁ and P _2, you can use the KI-5315 GOSNITI vacuum analyzer known from the prototype, which provides a measurement of P ₁ when the over-piston space communicates with the atmosphere and allows you to isolate this space from the atmosphere for measuring P ₂ . When scrolling the engine crankshaft at the starting frequency using a bench drive or starting device, the tip of the vacuum analyzer is tightly inserted into the nozzle (candle) hole of the CPG of any cylinder. In the mode of communication of the over-piston space with the atmosphere, the steady-state maximum vacuum P _{1 is} determined by the vacuum meter on the compression stroke. To determine P _{2, the} measurements are repeated in the isolation mode of the over-piston space from the atmosphere at the compression stroke, for which the exhaust valve of the vacuum analyzer is locked in its closed position. Then, these measurements are carried out for other engine cylinders. According to the measurement results, the technical condition of the elements of the cylinder-piston group is determined as described above in the following order.

The state of the valve mechanism is determined by comparing P _1and with P _Vп . When Р _1и > P _Vп determine the condition of the sleeve by comparing P _1и with P _Sп and Р _Sн . When all the cylinders _{1 and} P> P _SH, the difference ΔP ₁ determine the state of the scraper rings for the cylinder having the maximum value P _{1 and.} Further, if Р _1и > P _Sп , then the state of the compression rings is determined by comparing Р _2и with Р _Rп and Р _Rн . For clarity, the attached drawing shows a diagram of the implementation (algorithm) of the claimed method.

Table 2 presents examples of some experimental results of measurements of P ₁ and P ₂ carried out by the authors of the present invention on various diesel and carburetor engines to justify the claimed method. The presence in the example of several values of P ₁ and P ₂ means the corresponding amount of vacuum in the engine cylinders, starting from the first. The actual state of the CPG elements (sixth column of the table) was established after disassembling the engine.

 The following are additional comments on some of the examples shown in table. 2.

Example 1
The measurement of P ₁ showed the presence of a source of additional pneumatic density in the 5th cylinder (ΔP ₁ = 0.94-0.87 = 0.07> ΔP _1e ). Such a source of pneumatic density was the wear of the oil scraper rings of the 5th cylinder.

Example 2
Values P ₁ show the nominal condition of the liners of all cylinders. The value of P ₂ for the second cylinder is much greater than P _Rp , which is explained by damage to the compression rings.

Example 3
When the wear of the liners is greater than the limit (cylinders 3 and 4), the value of P ₂ does not characterize the actual state of the compression rings. Although the P ₂ value is much larger than P R _p in both cylinders 3 and 4, the compression ring turned out to be faulty only in cylinder 3.

Example 4
In the cylinder 5, P _{1 is} less than P _Vп as a result of a valve malfunction, while P ₂ does not characterize the state of the compression rings in this cylinder.

Example 5
The value of P ₂ in the cylinder 5 is much greater than P _Rp as a result of a failure of the compression rings.

Example 6
The wear of the sleeve in the cylinder 3 is greater than the limit, the value of P ₂ in this cylinder does not characterize the state of the compression rings.

Example 7
The maximum wear of the piston groups of cylinders 1 and 2. The wear of the liners and compression rings in the cylinders 3 and 4 is close to the maximum.

Example 8
In the almost nominal condition of the liners, an increased value of P ₂ in the cylinder confirms the malfunction associated with the state of the compression rings (the absence of such a ring). In addition, ΔP ₁ > ΔP _1e (ΔP ₁ = 0.94-0.89 = 0.05) and a value of P _{1 of} cylinder 4, which exceeds P _{1 of} other cylinders by more than 0.04 kg / cm ² , does not indicate the best condition of cylinder 4 in comparison with other cylinders, and the presence of a source of additional pneumatic density in it in the form of a defective oil scraper ring.

Example 10
The condition of the cartridges as a whole is close to the limit. The wear of the compression rings is greater than the limit.

Example 11
Permissible liner wear on all cylinders. Depreciation of compression rings in cylinders 1 and 2 within the permissible limits, failure of compression rings in cylinders 3 and 4.

Example 12
P ₁ in cylinder 3 is less than P _Vн as a result of a valve malfunction, and P ₂ in this cylinder does not characterize the state of the compression rings, all of them were in a nominal state.

Example 13
The wear of the cylinder liners within the tolerance, the values of P ₂ in all cylinders confirm the nominal condition of the new compression rings.

Example 15
In the cylinder 1 at the nominal condition of the sleeve, an increase in P ₂ confirmed the failure of the compression ring. Moreover, ΔP ₁ = 0.84-0.79 = 0.05> ΔP _1e , the oil scraper is faulty in the third cylinder.

Claims (2)

1. A method for diagnosing a cylinder-piston group of an internal combustion engine, which consists in scrolling the crankshaft of the engine with an external source, reporting the piston space of the cylinder with the atmosphere on the compression stroke and isolating the piston space from the atmosphere on the expansion stroke, measuring the maximum first negative pressure on the expansion stroke P _{1 and} in the overpiston space and determine the technical condition of the valve mechanism, characterized in that the technical state of the valve mechanism defining by comparing the measured first negative pressure P _{1 and} a preset limiting vacuum to valve mechanism P _vn, when R _{1 and>} P _vn determine the technical condition of the cylinder liner by comparing P _{1 and} with a preset limiting vacuum thermowell P _Sn and a nominal underpressure thermowell P _SH, further, at Р _1и > P _{Sп, the} crankshaft is additionally scrolled, isolating the over-piston space from the atmosphere on the expansion and compression strokes, and the maximum second rarefaction is measured on the expansion stroke e Р _2и in the over-piston space and determine the technical condition of the compression rings by comparing the measured second rarefaction Р _2и with the pre-set limit vacuum for rings P _Rп and nominal vacuum for rings P _Rн . 2. The method according to p. 1, characterized in that when the number of cylinders in the engine is more than one and under the conditions that no replacement or repair of any individual liners was performed in all cylinders P _1i > P _Sп , the difference between the two largest the values of P _1i in two different cylinders and the magnitude of the specified difference determines the state of the oil scraper rings of the cylinder having a maximum value of P _1i .

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