Method and device for determining critical condition of boundary lubrication failure of wheel-rail contact interface

Abstract

The invention provides a method and a device for determining critical conditions of boundary lubrication failure of a wheel-rail contact interface, and relates to the technical field of rail transit, the method comprises the following steps: determining relative oil film loss of the wheel-rail contact interface in a mixed lubrication state; based on the relative oil film loss, determining association information among the friction coefficient of the wheel-rail contact interface, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface in the mixed lubrication state; based on the associated information, determining the change information of the proportion of the lubricating oil boundary lubricating film of the wheel-rail contact interface along with the adsorption heat; and determining the boundary lubrication failure critical temperature of the wheel-rail contact interface based on the change information of the proportion of the lubricating oil boundary lubrication film along with the adsorption heat. According to the method, rapid calculation of the boundary lubrication critical failure condition of the wheel-rail contact interface under the condition of the lubricating oil medium is realized, and the accuracy of determining the low-adhesion critical failure condition under the condition of the lubricating oil medium is improved.

Description

Technical Field

[0001] The present invention relates to the field of rail transportation technology, and in particular to a method and a device for determining critical conditions of boundary lubrication failure at a wheel-rail contact interface. Background Art

[0002] At present, in the current field of wheel-rail adhesion of rail vehicles, there is a lack of direct calculation and solution methods for the critical failure conditions of boundary lubrication of the wheel-rail contact interface under the condition of the third medium on the rail surface. The elastic flow lubrication theory method in the indirect calculation method needs to be solved through multiple iterations. The complex model leads to slow calculation speed and cannot be applied to the real-time calculation of wheel-rail adhesion and critical failure conditions. The empirical formula method based on test data fitting depends to a large extent on the test accuracy of the test equipment, and there are many accidental uncertain factors in the test process. The lack of clear physical meaning of the undetermined parameters leads to low calculation accuracy of this method. Based on this, improving the accuracy of determining the critical failure conditions of low adhesion under lubricating oil medium has become an urgent problem to be solved. Summary of the invention

[0003] The present invention provides a method and device for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface, which are used to solve the defect in the prior art of how to improve the accuracy of determining low-adhesion critical failure conditions under a lubricating oil medium, realize rapid calculation of critical failure conditions for boundary lubrication at a wheel-rail contact interface under lubricating oil medium conditions, and improve the accuracy of determining low-adhesion critical failure conditions under a lubricating oil medium.

[0004] The present invention provides a method for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface, comprising the following steps: Determine the relative oil film deficit at the wheel-rail contact interface under mixed lubrication conditions; Based on the relative oil film deficit, determining correlation information among the friction coefficient of the wheel-rail contact interface under a mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface, and the boundary film friction coefficient of the wheel-rail contact interface; Based on the correlation information, determining information on the change of the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface with adsorption heat; Based on the information of the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat, the critical temperature of the boundary lubrication failure of the wheel-rail contact interface is determined.

[0005] According to a critical condition determination method for boundary lubrication failure of a wheel-rail contact interface provided by the present invention, the determination of the variation information of the proportion of the lubricating oil boundary lubrication film at the wheel-rail contact interface with the adsorption heat based on the correlation information includes: Based on the thermal vibration period of polar molecules perpendicular to the wheel-rail contact interface, adsorption heat, gas constant and wheel-rail surface contact temperature, the average time that the lubricating oil medium adsorbed molecules occupy the wheel-rail contact interface is determined; the adsorption heat is the heat generated between the components in the lubricating oil and the wheel-rail contact interface during the adsorption process; Determine the duration of the interaction between the wheel and rail friction surfaces based on the sliding velocity and contact length of the wheel and rail friction surfaces; Determining the proportion of boundary film at the wheel-rail contact interface based on the average time and the duration of the interaction between the wheel-rail friction surfaces; Based on the boundary film proportion and the associated information, information on changes in the lubricating oil boundary lubrication film proportion at the wheel-rail contact interface as a function of adsorption heat is determined.

[0006] According to a method for determining a critical condition for boundary lubrication failure at a wheel-rail contact interface provided by the present invention, the critical temperature for boundary lubrication failure at the wheel-rail contact interface is determined based on information on changes in the proportion of the lubricating oil boundary lubrication film with adsorption heat, including: Determining adsorption heat information based on information on changes in the proportion of the lubricating oil boundary lubricating film as a function of adsorption heat; Based on the adsorption heat information, determining a curve of the relative oil film deficit and the critical temperature of the lubricating oil; The critical temperature of boundary lubrication failure at the wheel-rail contact interface is determined according to the maximum value of the curvature change of the curve.

[0007] According to a method for determining a critical condition for boundary lubrication failure at a wheel-rail contact interface provided by the present invention, after determining the critical temperature for boundary lubrication failure at the wheel-rail contact interface based on information on the change in the proportion of the boundary lubrication film of the lubricating oil with adsorption heat, the method further comprises: Based on the critical temperature of boundary lubrication failure, the thermal conductivity of the wheel-rail material, the Hertzian contact radius of the wheel-rail contact spot in the sliding direction, the wheel-rail contact interface friction coefficient, the Hertzian average pressure of the wheel-rail contact spot, the relative sliding speed between the wheel and rail, and the Peclet number of the wheel-rail material, the variation information of the wheel-rail contact interface friction coefficient with the relative sliding speed between the wheel and rail is determined.

[0008] According to a critical condition determination method for boundary lubrication failure of a wheel-rail contact interface provided by the present invention, the method determines, based on the relative oil film deficit, the correlation information between the wheel-rail contact interface friction coefficient, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface under a mixed lubrication state, including: Determining weight coefficients of the dry friction coefficient and the boundary film friction coefficient based on the relative oil film deficit; Based on the weight coefficient, a weighted sum operation is performed on the dry friction coefficient and the boundary film friction coefficient to determine correlation information among the wheel-rail contact interface friction coefficient, the dry friction coefficient and the boundary film friction coefficient under the mixed lubrication state.

[0009] According to a method for determining critical conditions of boundary lubrication failure at a wheel-rail contact interface provided by the present invention, the method for determining the relative oil film deficit at the wheel-rail contact interface under a mixed lubrication state comprises: Obtaining a direct contact area and a boundary film area of ​​the micro-asperities at the wheel-rail contact interface; The relative oil film deficit of the mixed lubrication is determined according to the direct contact area of ​​the micro-protrusion and the boundary film area.

[0010] The present invention also provides a device for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface, comprising the following modules: A relative oil film deficit determination module is used to determine the relative oil film deficit at the wheel-rail contact interface under mixed lubrication conditions; A correlation information determination module, for determining, based on the relative oil film deficit, correlation information between the friction coefficient of the wheel-rail contact interface under a mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface, and the boundary film friction coefficient of the wheel-rail contact interface; A change information determination module, used to determine the change information of the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface as a function of the adsorption heat based on the correlation information; The critical condition determination module is used to determine the critical temperature of boundary lubrication failure of the wheel-rail contact interface based on the variation information of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat.

[0011] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method for determining the critical condition of boundary lubrication failure at the wheel-rail contact interface as described in any one of the above is implemented.

[0012] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements any of the above-mentioned methods for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface.

[0013] The present invention also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the critical condition determination method for boundary lubrication failure of the wheel-rail contact interface as described in any one of the above is implemented.

[0014] The critical condition determination method and device for boundary lubrication failure of wheel-rail contact interface provided by the present invention are as follows: by determining the relative oil film deficiency of the wheel-rail contact interface under mixed lubrication; based on the relative oil film deficiency, determining the correlation information between the friction coefficient of the wheel-rail contact interface, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface under mixed lubrication; based on the correlation information, determining the variation information of the proportion of the lubricating oil boundary lubrication film of the wheel-rail contact interface with the adsorption heat; based on the variation information of the proportion of the lubricating oil boundary lubrication film with the adsorption heat, determining the critical temperature of boundary lubrication failure of the wheel-rail contact interface. The present invention realizes the rapid calculation of the critical failure condition of boundary lubrication of the wheel-rail contact interface under lubricating oil medium conditions, and improves the accuracy of determining the critical failure condition of low adhesion under lubricating oil medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a flow chart of a method for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface provided by the present invention.

[0017] Figure 2 It is a numerical calculation result diagram of the rapid calculation model of critical failure conditions of boundary lubrication at the wheel-rail contact interface provided by the present invention.

[0018] Figure 3 It is a comparison diagram between the friction coefficient-slip rate simulation calculation curve and the experimental measured curve of the wheel-rail contact interface boundary lubrication critical failure condition rapid calculation model provided by the present invention.

[0019] Figure 4 It is a schematic diagram of boundary lubrication failure at the wheel-rail contact interface caused by temperature increase under the lubricating oil medium condition provided by the present invention.

[0020] Figure 5 It is a flow chart of a method for constructing a rapid calculation model of critical failure conditions of boundary lubrication at a wheel-rail contact interface provided by the present invention.

[0021] Figure 6 It is a structural schematic diagram of a device for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface provided by the present invention.

[0022] Figure 7 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the relevant technology, rail train braking methods are mainly divided into two categories: adhesion braking and non-adhesion braking. Adhesion braking is the main braking method currently used by trains because it is applicable to all speed ranges, does not require changes to the track and vehicle structure, and is safe and reliable. The braking deceleration required for adhesion braking is provided by the adhesion generated by the interaction between the wheel and the rail. The reduction of wheel-rail adhesion can easily cause the wheelset to slide or even lock during braking, resulting in an increase in the braking distance of the train, damage to the wheel tread and rail surface, and greatly increase the maintenance cost. In severe cases, major safety accidents such as parking and derailment may occur, causing great harm to the safety of train operation. Lubricating oil, as the most common third medium on the rail surface, is usually distributed in the train gearbox and bearings for lubrication, but when it falls on the track surface, it will cause a significant reduction in the wheel-rail adhesion coefficient, resulting in low wheel-rail adhesion. Compared with the water medium on the rail surface, the adhesion coefficient caused by lubricating oil is lower, and the adhesion force that can be provided to the wheelset is smaller. Therefore, the presence of lubricating oil on the rail surface will more seriously endanger the safety of train operation. The lubricating oil medium is distributed on the rough peak surface of the wheel-rail contact interface in the form of boundary lubrication. When the boundary lubrication reaches certain conditions, lubrication failure will occur, which can destroy the low adhesion of the wheel and rail caused by the lubricating oil medium, thereby improving the wheel-rail adhesion conditions. If the critical conditions for the failure of boundary lubrication at the wheel-rail contact interface under the condition of lubricating oil medium can be captured and utilized, it can provide a certain reference for the destruction and viscosity increase of the low adhesion interface of the wheel and rail in the third medium, which is of great significance for improving the adhesion conditions of the rail surface and ensuring the safety of train operation. Therefore, a fast calculation model for the critical failure conditions of boundary lubrication at the wheel-rail contact interface under the condition of lubricating oil medium is constructed, which can capture the critical failure conditions of boundary lubrication at the wheel-rail contact interface, and propose corresponding adhesion improvement measures based on this, thereby ensuring the safety of rail vehicle operation.

[0025] In the related art, the wheel-rail adhesion coefficient and low adhesion critical failure conditions under lubricating oil medium conditions are mainly obtained through two means: wheel-rail adhesion test and numerical simulation. By testing actual trains or scaled test benches under different working conditions under oil medium conditions, and using measuring equipment such as torque meters to record test data, the wheel-rail adhesion coefficient values ​​at different times can be calculated, thereby capturing the critical conditions for improving the wheel-rail adhesion coefficient, that is, the low adhesion critical failure conditions of the lubricating oil medium. However, the accuracy of the adhesion coefficient and the low adhesion critical failure conditions depends to a large extent on the accuracy of the measuring equipment, and it is difficult to accurately control the amount of lubricating oil medium in the test. Therefore, the adhesion coefficient and the low adhesion critical failure conditions obtained from the test are of low accuracy. In terms of the numerical simulation of wheel-rail adhesion with the third medium, the related art mainly studies the wheel-rail contact tribological process, establishes a fluid bearing model based on the elastohydrodynamic lubrication theory, and establishes a solid bearing model based on the microscopic solid contact theory, thereby constructing a wheel-rail adhesion model that comprehensively considers surface conditions such as roughness, fluid third medium, and boundary lubrication, and inputs relevant actual parameters to calculate the low adhesion critical failure conditions of the lubricating oil medium wheel-rail. The physical meaning of this method is clear, but it requires complex iterative calculations of solid and liquid loads. The complex model leads to slow solution speed and cannot perform real-time calculation of the wheel-rail adhesion coefficient and the critical failure condition of wheel-rail contact boundary lubrication under lubricating oil medium conditions. Therefore, the critical damage condition of wheel-rail low adhesion can only be used for theoretical research, and cannot be applied to the simulation platform related to the train braking anti-skid process to perform real-time calculation of the adhesion coefficient and provide real-time adhesion force for the wheelset. Therefore, it cannot be used as a basis for proposing new train braking anti-skid control strategies to destroy the wheel-rail low adhesion interface and improve the track surface adhesion conditions. In addition to the wheel-rail adhesion model based on the elastohydrodynamic lubrication theory, the numerical calculation methods of the wheel-rail adhesion coefficient in the relevant technology also include some empirical formula models based on test data fitting. This type of method can calculate the wheel-rail adhesion coefficient value in real time, but due to many uncertain factors in the test process, its calculation accuracy is questionable, and the physical meaning of the undetermined coefficients is unclear, and the influence of accidental factors on the model cannot be ruled out. Most of the empirical formula models in the relevant technology can only calculate the wheel-rail adhesion coefficient of the third medium, and cannot calculate the critical failure conditions of low adhesion of the third medium wheel-rail. Therefore, this method still has major defects.

[0026] In view of the above-mentioned technical problems, the present invention proposes a method for determining the critical conditions for boundary lubrication failure of the wheel-rail contact interface, specifically a method for constructing a rapid calculation model for the critical failure conditions of boundary lubrication of the wheel-rail contact interface under lubricating oil medium conditions. This method is based on the boundary film adsorption heat theory of tribology principles, and focuses on the influence of temperature on the boundary lubrication failure of the wheel-rail contact interface. The physical meaning of the undetermined parameters in the model is clear, and the analytical solution of the critical failure condition can be calculated in real time without a complex iterative process. The accuracy of the model can be further improved while ensuring the calculation speed, and the critical failure condition of low adhesion of the third medium is supplemented to the existing wheel-rail adhesion theory. It can be applied to wheel-rail adhesion enhancement and train braking anti-skid control processes, providing a certain theoretical reference for proposing new adhesion improvement measures and ensuring train braking performance and operation safety.

[0027] Combine the following Figure 1-Figure 7 The present invention describes a method and device for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface.

[0028] Figure 1 : is a flow chart of a method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface provided by the present invention, such as Figure 1 As shown, the method includes the following: Step 101, determining the relative oil film deficit at the wheel-rail contact interface under the mixed lubrication state.

[0029] Relative oil film deficit is an indicator used to measure the state of the oil film at the wheel-rail contact interface. Under mixed lubrication conditions, the ideal situation is that there is a thick enough oil film to completely separate the wheel and rail, achieving a state similar to fluid lubrication, at which time the oil film thickness reaches a theoretical maximum value. However, the actual situation is that due to the combined influence of factors such as the roughness of the wheel and rail surface, load, speed, etc., the actual oil film thickness is less than this ideal oil film thickness. Relative oil film deficit is a quantity used to express the relative gap between the actual oil film thickness and the ideal oil film thickness.

[0030] Specifically, the direct contact area and boundary film area of ​​the micro-convex body at the wheel-rail contact interface are obtained, and then the relative oil film deficit of mixed lubrication is determined based on the direct contact area and boundary film area of ​​the micro-convex body. It can be understood that according to the boundary lubrication theory, under the mixed lubrication state, the actual contact area of ​​the friction pair at the wheel-rail contact interface is the direct contact area of ​​the micro-convex body. and boundary membrane area It consists of two parts, and the relative oil film loss is: ; (1) In formula (1), is the relative oil film deficit, is the direct contact area of ​​the micro-convex body, Boundary film area. Among them, micro-convex bodies refer to the tiny raised parts formed on the wheel rail surface due to processing technology, wear or material characteristics. From a microscopic perspective, the wheel rail surface is not absolutely smooth, but there are many uneven structures, and these tiny protrusions are micro-convex bodies.

[0031] Step 102: determining, based on the relative oil film deficit, correlation information among the friction coefficient of the wheel-rail contact interface under a mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface, and the boundary film friction coefficient of the wheel-rail contact interface.

[0032] It can be understood that the friction coefficient of the wheel-rail contact interface under mixed lubrication is a coefficient that comprehensively reflects the friction characteristics between the wheel and the rail. The dry friction coefficient refers to the friction coefficient between the wheel and the rail contact interface in the absence of any lubricating medium. The boundary film friction coefficient refers to the friction coefficient under boundary lubrication (i.e., the lubricating oil is distributed on the wheel-rail contact interface in a boundary lubrication manner to form a layer of boundary film).

[0033] After calculating the relative oil film deficiency of mixed lubrication, the correlation information between the friction coefficient of the wheel-rail contact interface and the two friction coefficients (dry friction coefficient and boundary film friction coefficient) under the mixed lubrication state is determined based on the relative oil film deficiency.

[0034] For example, the relationship between the wheel-rail contact interface friction coefficient, dry friction coefficient and boundary film friction coefficient under mixed lubrication state is established as follows: ; (2) In formula (2), is the friction coefficient of the wheel-rail contact interface under mixed lubrication, is the dry friction coefficient, is the boundary film friction coefficient.

[0035] This expression can be transformed into: ; (3) Step 103: Based on the correlation information, determine the variation information of the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface with the adsorption heat.

[0036] Adsorption heat is the heat generated during the adsorption process between the components in the lubricating oil and the wheel-rail contact interface. It can be understood that when the components in the lubricating oil (mainly additives) are adsorbed to the wheel-rail surface, a certain amount of heat will be released or absorbed, and this heat is the adsorption heat. Specifically, the additives in the lubricating oil carry polar groups or active ingredients, which have an adsorption effect on the wheel-rail surface. When the additives are adsorbed to the wheel-rail surface, the molecules change from the original relatively free state to the adsorbed state. In this process, the energy of the system changes, thereby generating adsorption heat. This adsorption heat originates from the interaction between the components in the lubricating oil and the wheel-rail surface.

[0037] The boundary lubrication film of lubricating oil at the wheel-rail contact interface refers to a thin lubricating film formed by the components in the lubricating oil adsorbed on the micro-convexities (rough peaks) on the wheel-rail surface and part of the contact area. This film is in a boundary lubrication state, that is, it cannot completely separate the wheel-rail surface like fluid lubrication, but it can reduce the direct contact between the wheel-rail surface to a certain extent, thereby reducing friction and wear.

[0038] Specifically, based on the thermal vibration period of polar molecules perpendicular to the wheel-rail contact interface, adsorption heat, gas constant and wheel-rail surface contact temperature, the average time that the adsorbed molecules of the lubricating oil medium occupy the wheel-rail contact interface is determined; based on the sliding velocity and contact length of the wheel-rail friction surface, the duration of the interaction between the wheel-rail friction surface is determined; based on the average time and the duration of the interaction between the wheel-rail friction surface, the proportion of the boundary film at the wheel-rail contact interface is determined; based on the proportion of the boundary film and related information, the change information of the proportion of the lubricating oil boundary lubrication film at the wheel-rail contact interface as a function of the adsorption heat is determined.

[0039] The proportion of boundary membrane can be calculated by the following formula: ; (4) In formula (4), The wheel-rail friction surface is at sliding speed Through contact length The time of the wheel-rail friction surface interaction. Among them, the sliding speed It refers to the relative sliding speed of the wheel-rail friction surface, which describes the relative movement speed between the wheel and rail. It refers to the contact length of the wheel-rail friction surface, that is, the length range of the wheel and rail on the wheel-rail contact interface where the wheel and rail actually come into contact and interact (such as friction, load transfer, etc.). From a microscopic perspective, the wheel-rail surface is not smooth, and there are various microscopic protrusions (micro-protrusions). When the wheel and rail contact each other, the actual contact area between these micro-protrusions extends along the wheel-rail contact line. The length is the contact length. The calculation method is: ; (5) is the average time that the adsorbed molecules of the lubricating oil medium occupy the wheel-rail contact interface, which is calculated as: ; (6) In formula (6), is the thermal vibration period of the polar molecules perpendicular to the wheel-rail contact interface; It is the heat of adsorption, i.e. the heat of desorption, which is the basic property of lubricating oil; is the gas constant; is the wheel-rail surface contact temperature.

[0040] Combining the above formulas (3)-(6), we can establish the function of the proportion of the lubricating oil boundary lubrication film changing with the adsorption heat: ; (7) The proportion of the boundary lubrication film of the lubricating oil refers to the proportion of the boundary lubrication area or the degree of boundary lubrication in the entire wheel-rail contact area or lubrication process. According to formula (7), the greater the adsorption heat, the greater the proportion of the boundary lubrication film of the lubricating oil, and therefore the better the boundary lubrication effect. The function of formula (7) is used to describe the relationship between the proportion of the boundary lubrication film of the lubricating oil and the adsorption heat. Based on this, the information on the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat can be determined.

[0041] Step 104 : determining a critical temperature of boundary lubrication failure at the wheel-rail contact interface based on information on changes in the proportion of the lubricating oil boundary lubrication film as a function of adsorption heat.

[0042] It is understandable that during the wheel-rail contact process, when the temperature rises to a certain value, the boundary lubrication film (formed by the additives in the lubricating oil adsorbed on the wheel-rail surface) can no longer effectively reduce the friction and wear between the wheel and rail, resulting in a sharp drop in lubrication performance. This temperature is the critical temperature for boundary lubrication failure.

[0043] Specifically, based on the information on the change in the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat, the adsorption heat information is determined; based on the adsorption heat information, the curve of relative oil film deficiency and critical temperature of the lubricating oil is determined; and according to the maximum value of the curvature change of the curve, the critical temperature of boundary lubrication failure at the wheel-rail contact interface is determined.

[0044] In formulas (6)-(7): ; (8) ; (9) In formulas (8)-(9), is the molar mass of the lubricating oil; is the molar volume of lubricating oil; is the melting point of the base lubricant, , is the critical temperature value of lubricating oil.

[0045] The above variables and Substitute the function of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat to construct the adsorption (desorption) heat equation, which is expressed as follows: ; (10) According to the above adsorption (desorption) heat equation, the relative oil film deficit-lubricating oil critical temperature curve can be drawn ( - Curve). In actual wheel-rail contact interface boundary lubrication application, usually - The point where the curvature of the curve changes the most, that is, the inflection point of the curve, is used as the boundary lubrication failure criterion. This point should satisfy According to this condition, the critical temperature of the wheel-rail contact interface boundary lubrication failure can be derived: : ; (11) Optionally, As the failure criterion, a simplified calculation formula for the critical temperature can be obtained, which can greatly improve the calculation speed and perform real-time calculation: ; (12) When the contact temperature of the friction pair surface of the wheel-rail contact interface Exceeding critical temperature When the boundary lubrication film breaks and fails, the wheel-rail adhesion coefficient increases.

[0046] The critical condition determination method for boundary lubrication failure of the wheel-rail contact interface provided by the embodiment of the present invention is based on the boundary film adsorption heat theory of the tribological principle, and the relationship between the wheel-rail contact interface friction coefficient and the dry friction coefficient, the boundary lubrication film friction coefficient and the boundary film area ratio under the mixed lubrication state is established. By studying the adsorption and desorption process of molecules at the wheel-rail contact interface, a function of the boundary lubrication film ratio changing with the adsorption heat is established. Based on the material properties such as the melting point and critical temperature value of the lubricating oil, an adsorption heat equation is constructed, and a functional relationship between the relative oil film deficit and the critical temperature of the lubricating oil is established. By calculating the inflection point of the function, the critical temperature of the boundary film failure is derived. By defining the failure criterion for the critical temperature expression, the rapid calculation of the critical failure condition of the boundary lubrication of the wheel-rail contact interface under the lubricating oil medium condition is realized, thereby serving as a theoretical reference for proposing new adhesion improvement related measures and ensuring the braking performance and operation safety of the train.

[0047] Based on the above embodiment, after determining the critical temperature of boundary lubrication failure of the wheel-rail contact interface based on the information of the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat, the method further includes: Step 201, based on the critical temperature of boundary lubrication failure, the thermal conductivity of the wheel-rail material, the Hertzian contact radius of the wheel-rail contact spot in the sliding direction, the wheel-rail contact interface friction coefficient, the Hertzian mean pressure of the wheel-rail contact spot, the relative sliding speed between the wheel and rail, and the Peclet number of the wheel-rail material, determine the variation information of the wheel-rail contact interface friction coefficient with the relative sliding speed between the wheel and rail.

[0048] It is understandable that the wheel-rail adhesion characteristics are the basis and key factor for optimizing the train adhesion braking and anti-skid control technology, and the essence of wheel-rail adhesion is the friction behavior of the wheel-rail contact interface. Therefore, the curve of adhesion coefficient or friction coefficient with slip rate is the theoretical basis for the current upgrade and optimization of train braking anti-skid control technology. The curve obtained through simulation or experiment has practical engineering significance and value for ensuring the safety of train operation. The slip rate of rail vehicle wheelsets can be calculated by the following formula: ; (13) In formula (13), is the relative sliding speed between wheel and rail, is the train running speed.

[0049] Substituting the calculated critical temperature of boundary lubrication failure into the following formula, we can obtain the relationship between the friction coefficient of the wheel-rail contact interface and the relative sliding speed between the wheel and rail: ; (14) In formula (14), , is the thermal conductivity of the wheel / rail material, is the Hertzian contact radius of the wheel-rail contact patch in the sliding direction, is the friction coefficient of the wheel-rail contact interface, is the Hertzian mean pressure at the wheel-rail contact patch, is the relative sliding speed between wheel and rail, , is the Péclet number for different wheel-rail materials.

[0050] According to formula (14), the relationship between the friction coefficient and the critical failure temperature can be calculated, as follows: Figure 2 As shown. Figure 2It can be seen from the figure that when the interface temperature is lower than a certain numerical condition, the friction coefficient of the wheel-rail contact interface is low, less than 0.1; when the interface temperature is higher than this numerical condition, the friction coefficient of the wheel-rail contact interface increases suddenly, up to about 0.2. At this time, the boundary lubrication characteristics of the lubricating oil film on the wheel-rail contact interface are destroyed. The numerical condition of the interface temperature is the critical failure condition of the boundary lubrication of the wheel-rail contact interface under the lubricating oil medium.

[0051] According to formula (13) and formula (14), the relationship between the friction coefficient of the wheel-rail contact interface and the slip rate can be calculated. Based on the friction coefficient and slip rate curve actually measured in the wheel-rail adhesion test, we can get Figure 3 The comparison between theoretical and experimental results is shown in Figure 3 The friction coefficient obtained by simulation and the friction coefficient measured in the experiment have the same trend of variation with the slip rate and are relatively close in value, which verifies the accuracy and practicality of the method of the present invention.

[0052] By determining the variation information of the friction coefficient of the wheel-rail contact interface with the relative sliding speed between the wheel and the rail, the embodiment of the present invention can understand the variation of the friction coefficient under different slip rates, thereby finding the optimal slip rate range during braking, so that the train can fully utilize the adhesion conditions between the wheel and the rail during braking, maximize the braking force, shorten the braking distance, and ensure the safe and efficient operation of the train.

[0053] In order to further analyze and illustrate the method for determining the critical conditions for boundary lubrication failure at the wheel-rail contact interface proposed in the present invention, reference is made to the following examples.

[0054] The purpose of the embodiment of the present invention is to provide a method for constructing a rapid calculation model of critical failure conditions of boundary lubrication of the wheel-rail contact interface under lubricating oil medium conditions. The modeling process is based on the boundary film adsorption heat theory of the tribology principle with clear physical meanings of the undetermined parameters and fast calculation speed. The influence of temperature on the boundary lubrication failure of the wheel-rail contact interface is focused on. The accuracy of the model can be further improved under the premise of ensuring the calculation speed, and the real-time calculation of the critical failure conditions of boundary lubrication of the wheel-rail contact interface under lubricating oil medium conditions can be achieved. The embodiment of the present invention supplements the critical failure conditions of low adhesion of the third medium to the existing wheel-rail adhesion theory, and can be applied to wheel-rail viscosity enhancement and train braking anti-skid control processes, providing a certain theoretical reference for proposing new measures to improve wheel-rail adhesion under lubricating oil medium conditions and ensuring train braking performance and operation safety.

[0055] refer to Figure 4 , Figure 4It is a schematic diagram of the failure of boundary lubrication at the wheel-rail contact interface caused by temperature rise under the lubricating oil medium condition provided by the present invention. When the lubricating oil medium exists on the rail surface due to partial leakage of lubricating oil in train components, the third medium and the microscopic rough peaks at the contact interface between the wheel and the rail constitute boundary lubrication, resulting in a decrease in the friction coefficient and adhesion coefficient between the wheel and the rail, forming low adhesion between the wheel and the rail. When the temperature of the wheel-rail contact interface is low, the lubricating oil medium molecules between the wheel and the rail will be adsorbed on the contact surface, and their movement is relatively slow, causing the lubricating oil medium to gather into oil droplets. The medium viscosity is high, so the friction coefficient is low; and when the relative speed between the wheel and the rail increases or the relative sliding increases, the temperature of the wheel-rail contact interface will rise rapidly, causing the lubricating oil medium molecules between the wheel and the rail to move more violently, and then desorb from the wheel-rail contact interface and detach from the contact surface, forming a more dispersed flow state, resulting in a significant decrease in viscosity. At this time, the boundary lubrication characteristics of the wheel-rail contact interface are destroyed, and effective boundary lubrication cannot be formed, resulting in a sharp increase in the friction coefficient, and then a sudden increase in the wheel-rail adhesion coefficient. This phenomenon is the failure of boundary lubrication. Boundary lubrication failure will greatly increase the friction coefficient of the wheel-rail contact interface, thereby improving wheel-rail adhesion, greatly improving the adhesion braking performance of rail trains, and helping to ensure the safety of train operation. When the temperature of the wheel-rail contact interface is higher than a certain critical condition, its boundary lubrication film will be destroyed and fail. When this critical condition is reached, the wheel-rail adhesion coefficient increases suddenly. Therefore, the critical failure condition rapid calculation model of the boundary lubrication of the wheel-rail contact interface is based on the idea that the oil medium boundary lubrication film is destroyed. By studying the influence of interface temperature on the properties of lubricating oil and interface friction characteristics, a critical failure condition rapid calculation model can be constructed.

[0056] refer to Figure 5 , Figure 5 The flowchart of the method for constructing a rapid calculation model of critical failure conditions of boundary lubrication at the wheel-rail contact interface provided by the present invention includes: Step 1, calculating the relative oil film deficit of mixed lubrication; Step 2: Establish the relationship between the friction coefficient of the wheel-rail contact interface under mixed lubrication state and the dry friction coefficient and boundary film friction coefficient; Step 3, establishing a function of the proportion of the lubricating oil boundary lubrication film and the adsorption heat; Step 4: Construct the adsorption (desorption) heat equation; Step 5: Draw the relative oil film loss-lubricating oil critical temperature curve ( - curve); Step 6: Calculate the critical temperature for boundary lubrication failure.

[0057] The embodiment of the present invention realizes the rapid calculation of the critical failure condition of boundary lubrication of the wheel-rail contact interface under the condition of lubricating oil medium, and improves the accuracy of determining the critical failure condition of low adhesion under the condition of lubricating oil medium.

[0058] The critical condition determination device for boundary lubrication failure of wheel-rail contact interface provided by the present invention is described below. The critical condition determination device for boundary lubrication failure of wheel-rail contact interface described below and the critical condition determination method for boundary lubrication failure of wheel-rail contact interface described above can be referenced to each other.

[0059] refer to Figure 6 The critical condition determination device for boundary lubrication failure of wheel-rail contact interface provided by the present invention comprises: A relative oil film deficit determination module 601 is used to determine the relative oil film deficit of the wheel-rail contact interface under the mixed lubrication state; A correlation information determination module 602 is used to determine the correlation information between the friction coefficient of the wheel-rail contact interface under the mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface based on the relative oil film deficit; A change information determination module 603 is used to determine the change information of the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface as a function of the adsorption heat based on the correlation information; The critical condition determination module 604 is used to determine the critical temperature of the boundary lubrication failure of the wheel-rail contact interface based on the information of the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat.

[0060] The critical condition determination device for boundary lubrication failure of the wheel-rail contact interface provided by the embodiment of the present invention establishes the relationship between the friction coefficient of the wheel-rail contact interface and the dry friction coefficient, the boundary lubrication film friction coefficient and the boundary film area ratio under the mixed lubrication state based on the boundary film adsorption heat theory of the tribological principle, and further establishes the function of the boundary lubrication film ratio changing with the adsorption heat by studying the adsorption and desorption process of molecules at the wheel-rail contact interface, and constructs the adsorption heat equation based on the material properties such as the melting point and critical temperature value of the lubricating oil, and establishes the functional relationship between the relative oil film deficit and the critical temperature of the lubricating oil, and derives the critical temperature of the boundary film failure by calculating the inflection point of the function, and defines the failure criterion for the critical temperature expression, so as to realize the rapid calculation of the critical failure condition of the boundary lubrication of the wheel-rail contact interface under the lubricating oil medium condition, thereby serving as a theoretical reference for proposing new adhesion improvement related measures and ensuring the braking performance and operation safety of the train.

[0061] In one embodiment, the change information determination module 603 is specifically configured to: Based on the thermal vibration period of polar molecules perpendicular to the wheel-rail contact interface, adsorption heat, gas constant and wheel-rail surface contact temperature, the average time that the lubricating oil medium adsorbed molecules occupy the wheel-rail contact interface is determined; the adsorption heat is the heat generated between the components in the lubricating oil and the wheel-rail contact interface during the adsorption process; Determine the duration of the interaction between the wheel and rail friction surfaces based on the sliding velocity and contact length of the wheel and rail friction surfaces; Determining the proportion of boundary film at the wheel-rail contact interface based on the average time and the duration of the interaction between the wheel-rail friction surfaces; Based on the boundary film proportion and the associated information, information on changes in the lubricating oil boundary lubrication film proportion at the wheel-rail contact interface as a function of adsorption heat is determined.

[0062] In one embodiment, the critical condition determination module 604 is specifically configured to: Determining adsorption heat information based on information on changes in the proportion of the lubricating oil boundary lubricating film as a function of adsorption heat; Based on the adsorption heat information, determining a curve of the relative oil film deficit and the critical temperature of the lubricating oil; The critical temperature of boundary lubrication failure at the wheel-rail contact interface is determined according to the maximum value of the curvature change of the curve.

[0063] In one embodiment, the critical condition determination module 604 is further configured to: Based on the critical temperature of boundary lubrication failure, the thermal conductivity of the wheel-rail material, the Hertzian contact radius of the wheel-rail contact spot in the sliding direction, the wheel-rail contact interface friction coefficient, the Hertzian average pressure of the wheel-rail contact spot, the relative sliding speed between the wheel and rail, and the Peclet number of the wheel-rail material, the variation information of the wheel-rail contact interface friction coefficient with the relative sliding speed between the wheel and rail is determined.

[0064] In one embodiment, the association information determination module 602 is specifically configured to: Determining weight coefficients of the dry friction coefficient and the boundary film friction coefficient based on the relative oil film deficit; Based on the weight coefficient, a weighted sum operation is performed on the dry friction coefficient and the boundary film friction coefficient to determine correlation information among the wheel-rail contact interface friction coefficient, the dry friction coefficient and the boundary film friction coefficient under the mixed lubrication state.

[0065] In one embodiment, the relative oil film deficit determination module 601 is specifically used to: Obtaining a direct contact area and a boundary film area of ​​the micro-asperities at the wheel-rail contact interface; The relative oil film deficit of the mixed lubrication is determined according to the direct contact area of ​​the micro-protrusion and the boundary film area.

[0066] Figure 7 An example of a physical structure diagram of an electronic device is shown in FIG. Figure 7As shown, the electronic device may include: a processor 710, a communication interface 720, a memory 730 and a communication bus 740, wherein the processor 710, the communication interface 720 and the memory 730 communicate with each other through the communication bus 740. The processor 710 may call the logic instructions in the memory 730 to execute a critical condition determination method for boundary lubrication failure of the wheel-rail contact interface, the method comprising: determining the relative oil film deficit of the wheel-rail contact interface under the mixed lubrication state; determining the association information between the wheel-rail contact interface friction coefficient, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface under the mixed lubrication state based on the relative oil film deficit; determining the change information of the proportion of the lubricating oil boundary lubrication film of the wheel-rail contact interface with the adsorption heat based on the association information; determining the critical temperature of the boundary lubrication failure of the wheel-rail contact interface based on the change information of the proportion of the lubricating oil boundary lubrication film with the adsorption heat.

[0067] In addition, the logic instructions in the above-mentioned memory 730 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when it is sold or used as an independent product. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or the part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0068] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the critical condition determination method for boundary lubrication failure of the wheel-rail contact interface provided by the above methods, the method including: determining the relative oil film deficiency of the wheel-rail contact interface under the mixed lubrication state; based on the relative oil film deficiency, determining the correlation information between the friction coefficient of the wheel-rail contact interface under the mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface; based on the correlation information, determining the change information of the proportion of the lubricating oil boundary lubrication film of the wheel-rail contact interface with the adsorption heat; based on the change information of the proportion of the lubricating oil boundary lubrication film with the adsorption heat, determining the critical temperature of the boundary lubrication failure of the wheel-rail contact interface.

[0069] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to execute the critical condition determination method for boundary lubrication failure of the wheel-rail contact interface provided by the above-mentioned methods, the method comprising: determining the relative oil film deficiency of the wheel-rail contact interface under the mixed lubrication state; based on the relative oil film deficiency, determining the correlation information between the friction coefficient of the wheel-rail contact interface, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface under the mixed lubrication state; based on the correlation information, determining the change information of the proportion of the lubricating oil boundary lubrication film of the wheel-rail contact interface with adsorption heat; based on the change information of the proportion of the lubricating oil boundary lubrication film with adsorption heat, determining the critical temperature of the boundary lubrication failure of the wheel-rail contact interface.

[0070] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, i.e., they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Those of ordinary skill in the art may understand and implement it without creative effort.

[0071] Through the description of the above implementation modes, those skilled in the art can clearly understand that each implementation mode can be implemented by means of software plus a necessary general hardware platform, or of course by hardware. Based on such an understanding, the above technical solution can essentially or in other words be embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods of each embodiment or some parts of the embodiment.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface, characterized in that: include: Determine the relative oil film deficit at the wheel-rail contact interface under mixed lubrication conditions; Based on the relative oil film deficit, determining correlation information among the friction coefficient of the wheel-rail contact interface under a mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface, and the boundary film friction coefficient of the wheel-rail contact interface; Based on the correlation information, determining information on the change of the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface with adsorption heat; Based on the information of the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat, the critical temperature of the boundary lubrication failure of the wheel-rail contact interface is determined.

2. The method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface according to claim 1, characterized in that: The determining, based on the correlation information, information on the change in the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface as a function of the adsorption heat includes: Based on the thermal vibration period of polar molecules perpendicular to the wheel-rail contact interface, adsorption heat, gas constant and wheel-rail surface contact temperature, the average time that the lubricating oil medium adsorbed molecules occupy the wheel-rail contact interface is determined; the adsorption heat is the heat generated between the components in the lubricating oil and the wheel-rail contact interface during the adsorption process; Determine the duration of the interaction between the wheel and rail friction surfaces based on the sliding velocity and contact length of the wheel and rail friction surfaces; Determining the proportion of boundary film at the wheel-rail contact interface based on the average time and the duration of the interaction between the wheel-rail friction surfaces; Based on the boundary film proportion and the associated information, information on changes in the lubricating oil boundary lubrication film proportion at the wheel-rail contact interface as a function of adsorption heat is determined.

3. The method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface according to claim 1, characterized in that: The determining of the critical temperature of boundary lubrication failure at the wheel-rail contact interface based on the information of the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat includes: Determining adsorption heat information based on information on changes in the proportion of the lubricating oil boundary lubricating film as a function of adsorption heat; Based on the adsorption heat information, determining a curve of the relative oil film deficit and the critical temperature of the lubricating oil; The critical temperature of boundary lubrication failure at the wheel-rail contact interface is determined according to the maximum value of the curvature change of the curve.

4. The method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface according to claim 1, characterized in that: After determining the critical temperature of boundary lubrication failure of the wheel-rail contact interface based on the information of the change of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat, the method further includes: Based on the critical temperature of boundary lubrication failure, the thermal conductivity of the wheel-rail material, the Hertzian contact radius of the wheel-rail contact spot in the sliding direction, the wheel-rail contact interface friction coefficient, the Hertzian average pressure of the wheel-rail contact spot, the relative sliding speed between the wheel and rail, and the Peclet number of the wheel-rail material, the variation information of the wheel-rail contact interface friction coefficient with the relative sliding speed between the wheel and rail is determined.

5. The method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface according to claim 1, characterized in that: Determining the correlation information between the friction coefficient of the wheel-rail contact interface, the dry friction coefficient of the wheel-rail contact interface and the boundary film friction coefficient of the wheel-rail contact interface under the mixed lubrication state based on the relative oil film deficit includes: Determining weight coefficients of the dry friction coefficient and the boundary film friction coefficient based on the relative oil film deficit; Based on the weight coefficient, a weighted sum operation is performed on the dry friction coefficient and the boundary film friction coefficient to determine correlation information among the wheel-rail contact interface friction coefficient, the dry friction coefficient and the boundary film friction coefficient under the mixed lubrication state.

6. The method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface according to claim 1, characterized in that: Determining the relative oil film deficit at the wheel-rail contact interface under the mixed lubrication state includes: Obtaining a direct contact area and a boundary film area of ​​the micro-asperity at the wheel-rail contact interface; The relative oil film deficit of the mixed lubrication is determined according to the direct contact area of ​​the micro-protrusions and the boundary film area.

7. A device for determining critical conditions for boundary lubrication failure at a wheel-rail contact interface, characterized in that: include: A relative oil film deficit determination module is used to determine the relative oil film deficit at the wheel-rail contact interface under mixed lubrication conditions; A correlation information determination module, for determining, based on the relative oil film deficit, correlation information between the friction coefficient of the wheel-rail contact interface under a mixed lubrication state, the dry friction coefficient of the wheel-rail contact interface, and the boundary film friction coefficient of the wheel-rail contact interface; A change information determination module, used to determine the change information of the proportion of the lubricating oil boundary lubricating film at the wheel-rail contact interface as a function of the adsorption heat based on the correlation information; The critical condition determination module is used to determine the critical temperature of boundary lubrication failure of the wheel-rail contact interface based on the variation information of the proportion of the boundary lubrication film of the lubricating oil with the adsorption heat.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the method for determining the critical condition of boundary lubrication failure at the wheel-rail contact interface as claimed in any one of claims 1 to 6 is implemented.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface as claimed in any one of claims 1 to 6 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for determining critical conditions for boundary lubrication failure at the wheel-rail contact interface as claimed in any one of claims 1 to 6 is implemented.

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