A method for on-line measurement of thermal deformation and second-order motion posture of a piston

Abstract

The present application relates to a kind of piston thermal deformation and second-order motion posture online measurement method, comprising: obtaining the cylinder liner cold-state geometric profile radius of internal combustion engine, cylinder liner thickness and the cold-state geometric profile parameter of piston;Dynamic signal under combustion state is collected and processed, form cylinder liner outer wall dynamic strain matrix and piston-cylinder dynamic oil film thickness matrix;Based on cylinder liner outer wall dynamic strain matrix, calculate the coupling deformation data of cylinder liner under thermal stress and piston dynamic knock, combine cylinder liner outer wall dynamic strain matrix, calculate the cylinder liner inner wall thermal geometric radius matrix under combustion state;Based on piston-cylinder dynamic oil film thickness matrix and cylinder liner inner wall thermal geometric radius matrix, calculate the thermal profile matrix of piston, obtain the dynamic thermal deformation of piston and export the second-order motion posture of piston.The present application can obtain the thermal deformation and second-order motion state of piston in real time, provide important reference for the reliability design of piston second-order motion theory and engine operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the internal combustion engine control technology field, in particular to a kind of piston thermal deformation and second-order motion posture online measurement method. BACKGROUND

[0002] When internal combustion engine works, piston skirt is in direct contact with cylinder wall and slides at high speed, and simultaneously plays a guiding role for piston itself and bears side thrust. The movement of piston skirt is composed of reciprocating axial movement along the center line of cylinder sleeve and second-order movement perpendicular to the center line of cylinder sleeve. The second-order movement of piston, although small, has an important influence on the performance of internal combustion engine. Existing researches have shown that the thermal deformation of piston is directly related to the second-order movement of piston, and the conditions such as piston knock, skirt lubrication, friction and wear, and cylinder sleeve cavitation.

[0003] Due to the combined action of factors such as gas pressure, piston group inertia force, cylinder gap, piston pin offset, connecting rod force, skirt side thrust, piston-cylinder sleeve system thermal deformation and mechanical deformation, the movement condition of piston skirt second-order movement is relatively complex. Most of the current researches on piston second-order movement are carried out by numerical method, and the results obtained are not accurate and lack effective verification, so it is difficult to obtain the actual movement state of piston under combustion state. Therefore, it is extremely important to develop a reliable, practical and easy-to-implement online measurement method for the thermal deformation and second-order movement posture of piston. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide an online measurement method for the thermal deformation and second-order movement posture of piston. Through online measurement of oil film thickness and dynamic deformation of cylinder sleeve, the thermal deformation and second-order movement state of piston can be extracted synchronously, which is of great significance for the theoretical promotion of piston second-order movement, optimization design of piston, improvement of piston friction and wear, and monitoring of engine vibration and lubrication state.

[0005] To achieve the above-mentioned purpose, the present application provides the following scheme:

[0006] An online measurement method for the thermal deformation and second-order movement posture of piston, comprising:

[0007] obtaining the cold-state geometric radius of the outer wall of cylinder sleeve, the thickness of cylinder sleeve and the cold-state geometric profile parameters of piston;

[0008] collecting dynamic signals under the combustion state of the internal combustion engine, and processing the dynamic signals to form a cylinder sleeve outer wall dynamic strain matrix and a piston-cylinder sleeve dynamic oil film thickness matrix based on the crank position signal;

[0009] Based on the cylinder liner outer wall dynamic strain matrix, cylinder liner coupling deformation data is calculated, and the coupling deformation data is combined with the cold state geometric radius of the cylinder liner outer wall and the cylinder liner thickness to calculate the hot state geometric radius matrix of the cylinder liner inner wall in the combustion state, wherein the coupling deformation data is generated under thermal stress and piston dynamic knocking;

[0010] Based on the piston-cylinder liner dynamic oil film thickness matrix and the cylinder liner inner wall hot state geometric radius matrix, a hot state profile matrix of the piston is calculated.

[0011] Based on the hot state profile matrix of the piston and in combination with the cold state geometric profile parameters of the piston, the dynamic thermal deformation of the piston is obtained and the second-order motion posture of the piston is derived.

[0012] Preferably, the dynamic signals of the internal combustion engine in the combustion state include: crankshaft position signals, cylinder liner axial and circumferential dynamic strain signals, and piston axial and circumferential dynamic oil film thickness signals.

[0013] Preferably, the method for calculating the cylinder liner outer wall dynamic strain matrix is:

[0014]

[0015] Wherein, L m×n is the cylinder liner outer wall dynamic strain matrix; m is the number of rows of strain sensors and film thickness sensors, and n is the number of columns of strain sensors and film thickness sensors; l is the original length of the strain gage; ε mn is the dynamic strain of the strain gage; t is the time variable of the strain sensor.

[0016] Preferably, the hot state geometric radius matrix of the cylinder liner inner wall in the combustion state is calculated based on the cold state geometric radius of the cylinder liner outer wall and the cylinder liner thickness.

[0017]

[0018] Wherein, R m×n is the hot state geometric radius matrix of the cylinder liner inner wall, K m×n is the cold state geometric radius matrix of the cylinder liner outer wall, and T m×n is the cylinder liner thickness matrix.

[0019] Preferably, the hot state profile matrix of the piston is calculated, including:

[0020] The hot state geometric profile matrix of the piston is derived by combining the hot state geometric radius matrix of the cylinder liner inner wall and the piston-cylinder liner dynamic oil film thickness matrix, and determining the specific position of the piston through the crankshaft position signal.

[0021] Preferably, the method for calculating the hot state geometric profile matrix of the piston is:

[0022] P a×n (t)=R a×n (t)-H a×n (t)

[0023] wherein, R a×n is a hot-state geometric profile matrix of the piston, a is the number of sensor rows in the area where the piston is located; H a×n is a piston-cylinder liner dynamic oil film thickness matrix, R a×n is a hot-state geometric radius matrix of the inner wall of the cylinder liner.

[0024] Preferably, the second-order motion posture of the piston comprises: a rotation angle of the piston around the piston pin and a lateral displacement of the piston.

[0025] wherein, the method for calculating the rotation angle of the piston around the piston pin is as follows:

[0026]

[0027] wherein, a is the rotation angle of the piston around the piston pin; h Top is an oil film thickness at a top measuring point of the piston; h Bottom is an oil film thickness at a bottom measuring point of the piston; and d is an axial spacing of the two film thickness sensors.

[0028] Preferably, the method for calculating the lateral displacement of the piston is as follows:

[0029]

[0030] wherein, u x is a lateral motion displacement of the piston; h ATS is an oil film thickness parameter of the piston mass center position at the secondary thrust side; and h TS is an oil film thickness parameter of the piston mass center position at the primary thrust side.

[0031] The present application has the following beneficial effects:

[0032] The present application can acquire the thermal deformation and the second-order motion state of the piston in real time, realize the evaluation of the lubrication state and the vibration characteristics of the engine, and provide an important reference for the piston second-order motion theory and the reliability design of the engine. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0034] Figure 1A method flow chart in the embodiment of the present application;

[0035] Figure 2 A sensor annular arrangement layout schematic diagram in the embodiment of the present application;

[0036] Figure 3 A sensor annular cross arrangement layout schematic diagram in the embodiment of the present application;

[0037] Figure 4 A test system schematic diagram in the embodiment of the present application;

[0038] Figure 5 A piston main and auxiliary thrust side oil film distribution schematic diagram in the embodiment of the present application;

[0039] Wherein, 1, piston, 2, cylinder liner, 3, dynamic strain sensor, 4, film thickness measurement sensor, 5, crankshaft phase sensor. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0041] In order to make the above objectives, characteristics and advantages of the present application more apparent, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0042] The present application discloses a kind of piston thermal deformation and second-order motion posture on-line measurement method under combustion operating condition, this method is measured and calculated the thermal profile of piston under combustion state, and combine cold profile to achieve the purpose of piston thermal deformation and second-order motion posture on-line measurement, including two parts of cylinder liner thermal geometry parameter measurement and piston thermal profile measurement under combustion operating condition.

[0043] As shown in Figure 1 The present application relates to a kind of piston thermal deformation and second-order motion posture on-line measurement method, specifically including the following steps:

[0044] 1) measure the cold geometry radius of cylinder liner outer wall, cylinder liner thickness and cold geometry profile of piston, and arrange dynamic strain measurement sensor matrix and oil film thickness measurement sensor matrix on the surface of cylinder liner;

[0045] Sensor layout mode is: annular arrangement layout and annular cross arrangement layout, two kinds of sensor layout schematic diagram as shown in Figure 2 And Figure 3 .

[0046] 2) Collecting crankshaft position signal, cylinder liner dynamic strain signal and oil film thickness signal under combustion condition synchronously;

[0047] Selecting a suitable method to measure the oil film thickness between the engine piston and the cylinder liner, the measuring method is: ultrasonic method, capacitance method, resistance method, eddy current method, optical interference method, optical fiber sensor method or laser-induced fluorescence method.

[0048] In this embodiment, the ultrasonic film thickness measurement is taken as an example, and its test system is shown in Figure 4 The crankshaft position signal and the cylinder liner dynamic strain signal are acquired by the acquisition instrument and input to the control computer; the oscilloscope is controlled based on the crankshaft position signal to acquire the axial and circumferential film thickness signals of the piston. The signals are synchronously processed to form the cylinder liner outer wall dynamic strain matrix and the piston-cylinder liner dynamic oil film thickness matrix based on the crankshaft position signal.

[0049] 3) Calculating the dynamic strain matrix of the cylinder liner outer wall based on the coupling strain data of the cylinder liner under thermal stress and the dynamic knocking of the piston, and combining the cold-state geometric radius of the cylinder liner outer wall and the cylinder liner thickness to calculate the hot-state geometric radius of the cylinder liner inner wall under combustion condition;

[0050] The geometric radius matrix of the cylinder liner inner wall is calculated by the following formulas (1) and (2):

[0051]

[0052] Wherein, L m×n is the dynamic strain matrix of the cylinder liner outer wall; m is the number of rows of the strain sensor and the film thickness sensor, and n is the number of columns of the strain sensor and the film thickness sensor; l is the original length of the strain gage; ε mn is the dynamic strain of the strain gage; t is the time variable of the strain sensor.

[0053]

[0054] Wherein, R m×n is the hot-state geometric radius matrix of the cylinder liner inner wall, K m×n is the cold-state geometric radius matrix of the cylinder liner outer wall, and T m×n is the thickness matrix of the cylinder liner.

[0055] 4) Calculating the hot-state geometric profile matrix of the piston based on the piston-cylinder liner dynamic oil film thickness matrix and the hot-state geometric radius matrix of the cylinder liner inner wall;

[0056] The cylinder liner inner wall thermal state geometry radius matrix is combined with the piston-cylinder dynamic oil film thickness matrix, and the piston specific position is determined through the crankshaft phase signal, and then the piston thermal state geometry profile is derived. The piston thermal state geometry profile matrix is calculated by the following formula (3):

[0057] P a×n (t)=R a×n (t)-H a×n (t) (3)

[0058] Wherein, P a×n is the piston thermal state geometry profile matrix, a is the number of sensor rows in the area where the piston is located; H a×n is the piston-cylinder dynamic oil film thickness matrix, and R a×n is the a*n thermal state geometry radius matrix of the cylinder liner inner wall.

[0059] 5) Based on the thermal profile matrix of the piston, and combined with the cold state geometry profile parameters of the piston, the dynamic thermal deformation of the piston is obtained, and the second-order motion posture of the piston is derived.

[0060] The piston second-order motion posture measurement includes the swing of the piston around the piston pin and the lateral movement of the piston. The oil film distribution of the main and auxiliary thrust sides of the piston is shown in Figure 5 . The swing of the piston around the piston pin is derived from the oil film thickness parameters of the bottom and top of the main and auxiliary thrust sides of the piston region, and the lateral movement is derived from the piston mass center position film thickness parameters of the main and auxiliary thrust sides.

[0061] The swing angle of the piston around the piston pin is calculated by the following formula (4):

[0062]

[0063] Wherein, α is the swing angle of the piston around the piston pin; h Top is the oil film thickness of the piston top measuring point; h Bottom is the oil film thickness of the piston bottom measuring point; d is the axial spacing of the two film thickness sensors;

[0064] The lateral displacement of the piston is calculated by the following formula (5):

[0065]

[0066] Wherein, u x is the lateral movement displacement of the piston; h ATS is the oil film thickness parameter of the piston mass center position at the auxiliary thrust side; h TS is the oil film thickness parameter of the piston mass center position at the main thrust side.

[0067] The measurement method can accurately reflect the piston thermal deformation and second-order motion posture information of the engine during operation, has high measurement precision, is easy to implement in engineering, and has high reference value for the research on the lubrication between the engine and the piston-cylinder sleeve.

[0068] The above-described embodiments are merely descriptions of the preferred modes of the present application and are not intended to limit the scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A method for on-line measurement of thermal deformation and second-order motion posture of a piston, characterized in that, The method comprises the following steps: acquiring the cold geometric radius of the outer wall of the cylinder liner, the thickness of the cylinder liner and the cold geometric profile parameters of the piston; collecting dynamic signals in the combustion state of the internal combustion engine, processing the dynamic signals, and forming a dynamic strain matrix of the outer wall of the cylinder liner and a dynamic oil film thickness matrix of the piston-cylinder liner based on the crankshaft position signal; calculating the coupling deformation data of the cylinder liner based on the dynamic strain matrix of the outer wall of the cylinder liner, combining the coupling deformation data with the cold geometric radius of the outer wall of the cylinder liner and the thickness of the cylinder liner, and calculating the hot geometric radius matrix of the inner wall of the cylinder liner in the combustion state, wherein the coupling deformation data is generated under thermal stress and dynamic knocking of the piston; calculating the hot profile matrix of the piston based on the dynamic oil film thickness matrix of the piston-cylinder liner and the hot geometric radius matrix of the inner wall of the cylinder liner; acquiring the dynamic thermal deformation of the piston and deriving the second-order motion posture of the piston based on the hot profile matrix of the piston and combining the cold geometric profile parameters of the piston; wherein the calculation of the hot profile matrix of the piston comprises: combining the hot geometric radius matrix of the inner wall of the cylinder liner and the dynamic oil film thickness matrix of the piston-cylinder liner, determining the specific position of the piston through the crankshaft position signal, and then deriving the hot geometric profile matrix of the piston; the calculation method of the hot geometric profile matrix of the piston is as follows: wherein, is the matrix of the hot geometry profile of the piston, a is the number of sensor rows in the area where the piston is located; is the matrix of the dynamic oil film thickness of the piston-cylinder liner, is the matrix of the hot geometry radius of the inner wall of the cylinder liner; the second-order motion posture of the piston comprises the rotation angle of the piston around the piston pin and the lateral displacement of the piston; the calculation method of the rotation angle of the piston around the piston pin is as follows: wherein a is the angle of rotation of the piston around the piston pin; h Top is the oil film thickness at the top of the piston; h Bottom is the oil film thickness at the bottom of the piston; d is the axial distance between the two film thickness sensors; the calculation method of the lateral displacement of the piston is as follows: where u x is the lateral displacement of the piston; h ATS is the oil film thickness parameter at the piston centroid position at the secondary thrust side; h TS is the oil film thickness parameter at the piston centroid position at the primary thrust side.

2. The method of claim 1, wherein, the dynamic signals in the combustion state of the internal combustion engine include the crankshaft position signal, the dynamic strain signals of the cylinder liner in the axial and circumferential directions, and the dynamic oil film thickness signals of the piston in the axial and circumferential directions.

3. The method of claim 1, wherein, the calculation method of the dynamic strain matrix of the outer wall of the cylinder liner is as follows: wherein, is the dynamic strain matrix of the cylinder liner outer wall; m is the number of rows of strain sensors and film thickness sensors, and n is the number of columns of strain sensors and film thickness sensors; l is the original length of the strain gauge; is the dynamic strain of the strain gauge; t is the time variable of the strain sensor.

4. The method of claim 3, wherein, the calculation method of the hot geometric radius matrix of the inner wall of the cylinder liner in the combustion state is as follows: wherein, Rhot is a matrix of hot state geometric radii of the inner wall of the cylinder liner, Rcold is a matrix of cold state geometric radii of the outer wall of the cylinder liner, Rthick is a matrix of thicknesses of the cylinder liner.

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