CVT steel ring friction pair safety margin calculation method and device, and CVT steel ring friction pair safety margin evaluation method and device

Abstract

The invention discloses a CVT steel ring friction pair safety margin calculation and evaluation method and device. According to the safety margin calculation method, the safety margin of the CVT steel ring friction pair is obtained by comparing the abrasion depth of the steel ring local position x of the CVT steel ring friction pair with the thickness of the oil film between the first-layer steel ring and the second-layer steel ring of the CVT steel ring friction pair, and therefore the reliability and the service life of the CVT can be evaluated through the safety margin.

Description

[0001] This application is a divisional application based on the following original application, the application date of which is December 16, 2021; application number: 2021115454384; invention: calculation and evaluation method and device for wear depth and safety margin of CVT steel ring friction pair. Technical Field

[0002] The invention relates to the technical field of CVT (Continuously Variable Transmission, metal belt type continuously variable transmission), and in particular to a method and device for calculating and evaluating the safety margin of a CVT steel ring friction pair. Background Art

[0003] As the core component of the automobile transmission device, CVT can keep the power transmission of the transmission at the optimal operating point and has been widely used in various types of automobiles. However, the transmission working conditions of the transmission are complex and changeable, and the losses generated during the period cannot be ignored, which directly affects the transmission efficiency of CVT and its own life. Under the action of multi-field coupling such as heat-force-hydraulic, the contact characteristics and lubrication state of each layer of steel rings under the relative movement of the friction plate will gradually form surface damage with stress, strain and temperature distribution. With the change of load, micro-slip and wear will occur between the mating surfaces of the steel rings. The contact characteristics and relative movement between the belt and the pulley will also change through the transmission of the friction plate, causing the metal belt to slip, the pulley to deflect, the bearing to creep, and generate noise. Therefore, it is essential to fully understand the micro-motion phenomenon of the steel ring under the action of multi-field coupling and the lubrication state between the mating surfaces of the steel rings, which will affect the overall application performance of the transmission and its service life.

[0004] In recent years, the research on improving the application efficiency of automobiles has become increasingly mature, but few people have paid attention to the influence of micro-motion frequency and macro parameters on the application efficiency and service life of mechanical systems. Some scholars have studied the micro-motion corrosion of 690TT alloy tubes and 405 stainless steel plates in high temperature and high pressure water, and finally concluded that with the increase of micro-vibration frequency, the wear volume of 690TT tubes first increased and then decreased, while the wear volume and of 405 stainless steel plates gradually increased, and proposed a corresponding life prediction model. The type of debris also has a certain influence on micro-motion wear. AM Kirk et al. proposed new insights into the frequency effect by studying the influence of displacement amplitude on micro-motion wear within the frequency range. It was finally concluded that the increase in vibration frequency will cause the oxidation-based wear mechanism to transform into a mechanism that cannot form an oxidized debris layer, and the oxidized debris will isolate the direct contact of the contact surface, resulting in serious underground damage. L. Xin et al. studied the influence of frequency on the micro-motion corrosion behavior of 690TT alloy on 304 stainless steel in high temperature and high pressure water and its mechanism. The results show that the main causes of wear are delamination wear, material transfer wear and oxidation wear. The increase in frequency accelerates the escape of wear debris, which is not only due to the damage of the TTS layer, but also due to the crushing of oxide particles between the contact surfaces. The effect of temperature on fretting wear cannot be ignored. Temperature not only affects the geometric shape change of the friction pair, but also affects the contact characteristics between the friction surfaces. N Srivastava et al. proposed a finite element-based prediction method for fretting wear and fretting fatigue of the press-fit shaft. This method combines the wear model with fretting fatigue analysis to quantitatively predict the stress redistribution caused by fretting wear. The results show that the stress at the contact edge is the most significant. Aiming at the problem of low transmission efficiency of existing CVT, Fu Bing et al. constructed a calculation model for steel ring friction loss by deriving the corresponding steel ring pressure model and steel ring kinematic model, analyzed the influence of torque, speed and speed ratio on steel ring friction loss, and verified its conclusion through bench test. Finally, by improving the metal belt structure, a design idea for optimizing transmission efficiency is provided. In summary, the torque, speed and fretting frequency of the steel ring part of CVT input have a great influence on fretting wear. It is very necessary to explore the relationship between them and improve the application efficiency and service life of CVT.

[0005] The lubrication state of mechanical systems in service has attracted widespread attention in the scientific research field, and scholars have been conducting more and more in-depth research on the characteristics of lubricating oil films. Wang et al. conducted a comprehensive study on the lubrication dynamic contact oil film stiffness of point-contact spiral bevel gears (SBG) under periodic fluctuating loads and speeds, and concluded that there is a competitive relationship between dynamic load and contact area. Under a certain fluctuation amplitude, the phenomenon of positive and negative stiffness reversal will occur, which will lead to extremely low stiffness or extremely high stiffness. WHB is based on the crowned double helical gears in point-contact mixed EHL. The Archard theory is extended to the lubrication situation to evaluate the wear rate of point-contact mixed EHL, and finally the effect of surface roughness on wear life is obtained. A wear life prediction model is proposed to improve the wear life of crowned double helical gears by reasonably matching lubrication, dressing and working parameters. Some scholars have studied the influence of factors such as torque, speed, and roughness on the transient mixed lubrication state of the friction pair surface, and obtained the intrinsic connection between them. The stability and service life of the mechanical system are improved by optimizing and improving methods. CHUN et al. proposed a thermal mixed lubrication model to study the influence of temperature on the mechanical properties and tribological properties of the coating. In summary, scholars have used many methods to study the lubrication characteristics of different mechanical systems. Summary of the invention

[0006] The object of the present invention is to provide a method and device for calculating and evaluating the wear depth and safety margin of a CVT steel ring friction pair to overcome or at least alleviate at least one of the above-mentioned defects of the prior art.

[0007] To achieve the above object, the present invention provides a method for calculating the wear depth of a CVT steel ring friction pair, which comprises:

[0008] The wear depth of the CVT steel ring friction pair is calculated using the steel ring wear depth model expressed in formula (15);

[0009]

[0010] Where h(x) is the wear depth of the local position x of the steel ring of the CVT steel ring friction pair, the x-axis is the axial direction of the steel ring, ΔK is the preset fretting wear cycle acceleration number, K is the preset steel ring friction pair wear cycle number, i is the fretting wear number, K is the int is the incremental step in the continuous fretting friction process of the preset fretting wear cycle, j is the number of wear increments, S f is the safety factor of the preset clamping force, σ s is the yield limit of the metal material used for the preset steel ring, υ s is the preset local wear coefficient of the steel ring friction pair, ε is the preset CVT input torque amplitude fluctuation coefficient, α is the preset CVT steel ring friction pair pulley cone angle, R p is the working radius of the driving wheel of the CVT steel ring friction pair, kv is the dynamic load coefficient of the CVT motion process, T m is the average input torque of the CVT driven pulley, ω is the fretting frequency of the steel ring friction pair, t is the time variable of the fretting wear process, ds is the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair, i,j (x) is the relative slip distance of the jth wear increment under the i-th fretting friction, T p is the input torque of the driven wheel of the CVT steel ring friction pair, f is the friction coefficient of the steel ring contact surface of the CVT steel ring friction pair, F si is the clamping force applied to the steel ring of the CVT steel ring friction pair by the i-th micro-friction, which is described as formula (12);

[0011]

[0012] The present invention also provides a method for calculating the safety margin of a CVT steel ring friction pair, which comprises:

[0013] By comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer of steel ring and the second layer of steel ring of the CVT steel ring friction pair, the safety margin of the CVT steel ring friction pair is obtained, wherein the x-axis is the axial direction of the steel ring.

[0014] Furthermore, the safety margin of the CVT steel ring friction pair is calculated by formula (26):

[0015]

[0016] Where h(x) is the wear depth of the steel ring at the local position x of the CVT steel ring friction pair as described above, and h l It is the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair.

[0017] The present invention also provides a CVT steel ring friction pair evaluation method, which comprises:

[0018] Step 1: Collect the working radius R of the driving wheel of the CVT steel ring friction pair p , the average input torque T of the CVT driven pulley m , the micro-vibration frequency of the steel ring friction pair ω, the dynamic load coefficient k of the CVT motion process v , and the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair

[0019] Step 2, obtaining the safety margin of the CVT steel ring friction pair by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer steel ring and the second layer steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring;

[0020] Step 3, determine whether the safety margin is less than 0, if so, determine that the safety state of the CVT is good; otherwise, determine that the reliability of the CVT is poor.

[0021] Furthermore, the safety margin of the CVT steel ring friction pair is calculated by formula (26):

[0022]

[0023] Wherein, h(x) is the wear depth of the steel ring at the local position x of the CVT steel ring friction pair in claim 1, and h l It is the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair.

[0024] The present invention also provides a CVT steel ring friction pair wear depth calculation device, which comprises:

[0025] The steel ring wear depth model, which is described as Equation (15), calculates the wear depth of the CVT steel ring friction pair;

[0026]

[0027] Where h(x) is the wear depth of the local position x of the steel ring of the CVT steel ring friction pair, the x-axis is the axial direction of the steel ring, ΔK is the preset fretting wear cycle acceleration number, K is the preset steel ring friction pair wear cycle number, i is the fretting wear number, K is the int is the incremental step in the continuous fretting friction process of the preset fretting wear cycle, j is the number of wear increments, S f is the safety factor of the preset clamping force, σ s is the yield limit of the metal material used for the preset steel ring, υ s is the preset local wear coefficient of the steel ring friction pair, ε is the preset CVT input torque amplitude fluctuation coefficient, α is the preset CVT steel ring friction pair pulley cone angle, R p is the working radius of the driving wheel of the CVT steel ring friction pair, k v is the dynamic load coefficient of the CVT motion process, T m is the average input torque of the CVT driven pulley, ω is the fretting frequency of the steel ring friction pair, t is the time variable of the fretting wear process, ds is the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair, i,j(x) is the relative slip distance of the jth wear increment under the i-th fretting friction, T p is the input torque of the driven wheel of the CVT steel ring friction pair, f is the friction coefficient of the steel ring contact surface of the CVT steel ring friction pair, F si is the clamping force applied to the steel ring of the CVT steel ring friction pair by the i-th micro-friction, which is described as formula (12);

[0028]

[0029] The present invention also provides a CVT steel ring friction pair safety margin calculation device, which comprises:

[0030] A safety margin model is used to obtain the safety margin of the CVT steel ring friction pair by comparing the wear depth of the steel ring at a local position x of the CVT steel ring friction pair with the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring.

[0031] Furthermore, the safety margin of the CVT steel ring friction pair is calculated by formula (26):

[0032]

[0033] Where h(x) is the wear depth of the steel ring at the local position x of the CVT steel ring friction pair as described above, and h l It is the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair.

[0034] The present invention also provides a CVT steel ring friction pair evaluation device, which comprises:

[0035] The collection unit is used to collect the working radius R of the driving wheel of the CVT steel ring friction pair p , the average input torque T of the CVT driven pulley m , the micro-vibration frequency of the steel ring friction pair ω, the dynamic load coefficient k of the CVT motion process v , and the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair

[0036] A safety margin model, which is used to obtain the safety margin of the CVT steel ring friction pair by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer steel ring and the second layer steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring;

[0037] The judging unit is used to judge whether the safety margin is less than 0. If so, it is judged that the safety state of the CVT is good; otherwise, it is judged that the reliability of the CVT is poor.

[0038] Furthermore, the safety margin of the CVT steel ring friction pair is calculated by formula (26):

[0039]

[0040] Where h(x) is the wear depth of the steel ring at the local position x of the CVT steel ring friction pair as described above, and h l It is the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair.

[0041] The present invention adopts the above technical solution, which has the following advantages:

[0042] The present invention establishes a steel ring wear depth model that associates wear depth with macro and micro factors, and obtains the wear depth and oil film thickness results of the CVT steel ring friction pair to obtain the safety margin of the steel ring friction pair within the working range of the CVT, thereby using the safety margin to evaluate the reliability and service life of the CVT.

[0043] Instruction Manual

[0044] Figure 1 This is a schematic diagram of CVT transmission and structure.

[0045] Figure 2 This is the observation diagram of the CVT steel ring surface wear.

[0046] Figure 3 This is the microstructure and contact model diagram of the CVT steel ring.

[0047] Figure 4 This is the temperature simulation diagram of the CVT steel ring structure.

[0048] Figure 5 This is the simulation result of the CVT steel ring mating surface profile.

[0049] Figure 6 The wear depths at different positions of the CVT steel ring under different torques, where: (a) is the wear depth of the first outer layer of the CVT steel ring friction pair, (b) is the wear depth of the first inner layer of the CVT steel ring friction pair, and (c) is the wear depth of the second outer layer of the CVT steel ring friction pair.

[0050] Figure 7 The wear depths at different positions of the CVT steel ring under different rotational speeds, where: (a) is the wear depth of the first outer layer of the CVT steel ring friction pair, (b) is the wear depth of the first inner layer of the CVT steel ring friction pair, and (c) is the wear depth of the second outer layer of the CVT steel ring friction pair.

[0051] Figure 8 Observation diagram of CVT steel ring surface roughness at different frequencies

[0052] Fig. 9 The wear depths at different positions of the CVT steel ring under different micro-vibration frequencies, where: (a) is the wear depth of the outer side of the first layer of the CVT steel ring friction pair, (b) is the wear depth of the inner side of the first layer of the CVT steel ring friction pair, and (c) is the wear depth of the outer side of the second layer of the CVT steel ring friction pair.

[0053] Fig.10 The three-dimensional roughness surface of the CVT steel ring.

[0054] Fig.11 The simulation diagram of CVT oil film characteristics, where: (a) is the CVT oil film pressure change diagram, (b) is the CVT oil film thickness change diagram, and (c) is the CVT oil film temperature rise change diagram. DETAILED DESCRIPTION

[0055] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0056] The CVT metal belt is composed of hundreds of metal friction plates and 6 to 12 layers of steel rings. Its transmission and structure diagram is as follows: Figure 1 As shown. The steel ring group is tensioned under the clamping force of the metal pulley to prop up the friction plate for torque transmission. During CVT operation, the relative sliding and vibration between the steel rings and between the steel rings and the saddle surface of the friction plate cause wear between the steel rings. Since the loss of the first layer of steel rings accounts for 70% of the total friction power loss of the steel rings, and the loss of the second to ninth layers of steel rings is only 6% to 0.008%, the loss proportion of the first layer of steel rings is much greater than the loss proportion of other steel rings. Therefore, the research object of the embodiment of the present invention selects the first layer of steel rings and the second layer of steel rings. Figure 2 This is the observation diagram of steel ring surface wear.

[0057] There are about 100 models for calculating wear in the prior art, and they are applicable to different ranges of conditions. Currently, the most widely used wear model in engineering is the Archard-related adhesive wear model.

[0058]

[0059] Where k is the wear coefficient; P is the contact normal load; S is the sliding distance; and H is the material hardness.

[0060] When calculating wear, the Archard model can only be applied to the case where the friction coefficient is constant. Considering the complexity and variability of the wear process of the CVT steel ring friction pair surface material, it is necessary to model the friction and wear under variable load conditions. From the energy point of view, this process can be regarded as the result of energy consumption and conversion, that is, the friction pair produces wear on the material surface due to energy consumption during the friction process.

[0061] In the dissipation theory, it is assumed that there is a linear relationship between the amount of fretting wear and the dissipated energy, namely:

[0062]

[0063] Where, v is the energy wear coefficient; E di is the dissipated energy of a single fretting cycle under a given slip amplitude; K is the number of wear cycles.

[0064] The dissipated energy is the friction work done by the shear force and is described by equation (3):

[0065]

[0066] In the formula, is the total force on the metal belt during the ith micro-friction; s i is the relative sliding distance between the two steel ring friction pairs in the i-th micro-friction.

[0067] During the research process, the contact area is set as a limit contact area dA, and the fretting wear depth dh is expressed as:

[0068]

[0069] In the formula, υ s is the local wear coefficient.

[0070] From formula (3), the i-th local wear dissipation energy at any x point in the steel ring arc segment can be obtained: for:

[0071]

[0072] In the formula, ds is the total force at the local position of the first steel ring and the second steel ring in the i-th micro-friction; i (x) is the relative sliding distance between the local position x of the i-th micro-friction first-layer steel ring and the second-layer steel ring.

[0073] From equations (4) and (5), the wear depth of the contact position between the first steel ring and the second steel ring in the i-th micro-dynamic friction is:

[0074]

[0075] In the formula, τ i (x) is the friction shear stress at the local contact position x between the first steel ring and the second steel ring in the i-th micro-friction.

[0076] From the above formula, the fretting wear depth here can be expressed as:

[0077] Δh i (x) = v s ∫τi (x)ds i (x) (7)

[0078] Assume that in the continuous micro-friction process, there is K int Incremental step, the jth (j = 1, 2..., K int The wear depths of the first steel ring and the second steel ring are linearly superimposed, and the wear depth of the local contact position of the i-th micro-friction is obtained as follows:

[0079]

[0080] In the formula, τ i,j (x) is the shear stress of the jth wear increment under the i-th fretting friction; ds i,j (x) is the relative slip distance of the jth wear increment under the i-th fretting friction.

[0081] Therefore, the wear depth at the local contact position x of the steel ring under the Kth micro-friction is:

[0082]

[0083] In the actual micro-friction process, the number of frictions is quite large. If the amount of friction is calculated in sequence during the calculation process, the calculation cost will increase and the time will be longer. Considering that the amount of wear caused by each micro-friction is very small and has a slight impact on the next wear result, the energy wear coefficient can be appropriately increased through the similarity principle, and at the same time, one micro-friction process can be replaced by ΔK friction processes, thereby greatly shortening the calculation time.

[0084] It can be obtained that when the acceleration number is ΔK, the wear depth of the local position x of the steel ring during the entire micro-friction process is:

[0085]

[0086] The metal surfaces in the air have a naturally polluted surface film. Friction and sliding will shear the film. Let the shear strength of the film be τ i,j (x). If the shear strength of the metal is τ b The unit is τ i,j (x), can be written as τ i,j (x) = Cτ b , C is a constant.

[0087]

[0088] Formula (11) summarizes the universality of various surface states, including both adhesive friction and friction of oxide films and other reaction films.

[0089] The clamping force applied to the steel ring in the above formula is:

[0090]

[0091] In the formula, S f is the safety factor; T p is the input torque of the driven wheel; α is the pulley cone angle; f is the friction factor; R p is the working radius of the driving wheel.

[0092] Considering that the working conditions of the transmission are variable and have multiple excitation characteristics, the transmission load is variable during the transmission process. Assuming that the transmission load changes in the form of a simple harmonic wave, the torque transmitted by the steel ring friction pair is:

[0093]

[0094] In the formula, k v is the dynamic load coefficient, which is related to the speed; T m is the average input torque; ε is the input torque amplitude fluctuation coefficient; ω is the micro-vibration frequency; It is the angle between the common tangent line of the working circle of the master and driven wheels and the centerline.

[0095] From the above formula, the shear stress can be obtained as:

[0096]

[0097] Therefore, the method for calculating the wear depth of the CVT steel ring friction pair provided by the embodiment of the present invention includes:

[0098] The wear depth of the CVT steel ring friction pair is calculated using the steel ring wear depth model expressed in formula (15);

[0099]

[0100] The metal belt transmits torque through thrust and friction, and the lubrication between the friction pairs conforms to the form of thermoelastic point contact, where the Reynolds equation is shown in the formula:

[0101]

[0102] In the formula, x and y are the directions of the coordinate system, y is the direction of movement of the steel ring; h is the oil film thickness; ρ and η are the density and viscosity of the lubricating oil respectively considering the influence of temperature, which can be obtained according to the density-temperature-density-pressure equation and the viscosity-temperature-viscosity-pressure equation.

[0103] When the pressures in the outlet and inlet areas are both 0 and the pressure change rate in the outlet area is 0, the boundary conditions of the equation are:

[0104] At the entrance: p(x1,y)=0;

[0105] At the exit: p(x2,y)=0,

[0106] Where x1 is the x-coordinate of the entrance, and x2 is the x-coordinate of the exit.

[0107] The point contact film thickness equation considering roughness is:

[0108]

[0109] Where h0 is the center film thickness; R x , R y are the equivalent radius of curvature along the x and y directions respectively; h(x,y) is the elastic deformation displacement caused by pressure; r(x,y) is the surface roughness function; E is the comprehensive elastic modulus; s and g are the coordinates of the pressure point in the x and y directions respectively. E1 and v1 represent the elastic modulus and Poisson's ratio of the metal sheet respectively; E2 and v2 represent the elastic modulus and Poisson's ratio of the pulley respectively.

[0110] The roughness peaks between the steel rings are randomly distributed according to the probability density function. Therefore, the number of contact peaks between them should also be calculated according to the probability density function. The root mean square values ​​of the surface roughness of the two friction pairs are σ1 and σ2 respectively. The contact situation between them can be converted into the contact between a smooth rigid surface and a rough elastic surface. The root mean square value of the rough elastic surface is

[0111] When the distance between the center lines of the friction pair is l, the steel ring surfaces will only come into contact when the profile height z is greater than the center line distance l. In the probability density distribution curve, the area where the two surfaces come into contact is the surface contact probability:

[0112] P(z>x)=∫ l ∞ ψ(z)dz (20)

[0113] If the number of peaks on the rough surface is n, then the number of peaks in the contact part is m:

[0114] m=n∫ l ∞ ψ(z)dz (21)

[0115] The normal deformation of the contact peak is zl, and the actual contact area A is:

[0116] A=mπR∫ l ∞ (zl)=nπR(zl)ψ(z)dz (22)

[0117] The total load W supported by the contact peak is:

[0118]

[0119] Usually, the actual surface profile height follows the Gauss distribution. In the Gauss distribution, the part close to the larger z value is similar to the exponential distribution. If ψ(z) = exp(-z / σ), the calculation can be obtained:

[0120]

[0121] The heat transfer mode of the lubricating oil film is mainly convection heat dissipation, and the heat conduction along the film thickness direction can be ignored. The required energy equation is:

[0122]

[0123] In the formula, c p is the isobaric specific heat of lubricating oil; T is the temperature of lubricating oil; J is the thermal work equivalent.

[0124] The temperature solution is along the direction of oil film movement from the inlet to the outlet. The x direction is set as the flow direction of the lubricating oil. T0 is the dimensionless initial temperature. The boundary conditions are set as follows:

[0125] In the x direction: T(x1,y) = T0;

[0126] In the y direction:

[0127] The CVT used in this embodiment is a nine-layer steel ring. The first layer steel ring and the second layer steel ring are conceptually separated to facilitate the meshing and simulation of the subsequent finite element calculation. ANSYS software is used for simulation calculation. When meshing, in order to make the calculation process more accurate, the multi-zone meshing method (MultiZone) is used. The minimum mesh length is 1mm, and the element size is limited to 1mm. The surface morphology of the first layer steel ring and the second layer steel ring are respectively Figure 3 As shown in (a) and (b), Figure 3 (c) in the figure is the contact form diagram of the friction pair, which consists of two martensitic steel rings with a length of 20.0 mm and a thickness of 0.18 mm.

[0128] After setting the boundary conditions using the established model, the temperature distribution of the entire steel ring under 3000 cycles was obtained by numerical method. Figure 4The temperature distribution result is shown in Figure 2. The temperature rise is mainly concentrated in the area near the contact surface between the friction plate and the steel ring. During the operation of the transmission, the inner side of the friction plate contacts the side of the steel ring and produces relative sliding, and the friction work causes a significant change in temperature. There is lubricating oil between the saddle surface and the steel ring contact surface, and the heat dissipation form between them is usually conduction heat dissipation, so the temperature is more obviously conducted to the edge of the steel ring. The temperature in the middle part drops faster due to the weak friction and the cooling effect of the lubricating oil, and the temperature rise is not obvious.

[0129] This embodiment takes CVT as the research object, and calculates the relationship between the micro-motion wear and micro-motion parameters between the first layer steel ring and the second layer steel ring according to the above-constructed model. When simulating and analyzing the interference section of the steel ring, the micro-motion cycle number K is first determined.

[0130] Figure 5 The simulation results of the steel ring matching surface contour for different cycles are shown in Figure 2. The horizontal axis is the distance between any position of the steel ring and the center of the steel ring. Since the profile of the steel ring matching surface changes the most at the edge, the profile within the range of 0 to 1.0 mm from the center of the steel ring is selected for research. The 0.9 mm point is the edge of the interference fit, and the left side is the interference fit position. Figure 5 It can be seen that within the same cycle, the wear depth of the mating surface reaches the maximum at the edge of the interference fit and gradually decreases toward the center line of the steel ring; Figure 5 In the figure, along the longitudinal axis, from top to bottom, the corresponding cycle number of the curve increases continuously, the wear depth from the edge of the steel ring to the center line direction increases continuously, and the wear width also increases continuously. Since the roughness amplitude between the first layer of steel ring and the second layer of steel ring is kept at about 1, and the oscillation amplitude does not exceed 1, in order to ensure the accuracy of the results, the minimum cycle number of 3000 is selected to ensure the accuracy of the wear degree of the matching surface profile.

[0131] In order to explore the effect of transmitted torque on the wear depth between the first steel ring and the second steel ring, different input torque values ​​were selected for simulation analysis of the wear depth. Figure 6 The wear depth change of the steel ring surface along the axial direction of the CVT after 3000 load cycles of the two friction pairs under the three conditions of torque of 30N·m, 90N·m and 150N·m. Figure 6 (a) shows the wear depth distribution of the outer side of the first layer of the steel ring friction pair. From the inner side of the steel ring (X / L=0) to the outer side (X / L=1), the wear depth first decreases and then increases. The wear depth increases rapidly at X / L=0.83 and reaches the maximum at X / L=1.0. When the torque T m =150N·m, the maximum wear depth is 1.54μm. Figure 6 (b) in the figure is the wear depth distribution of the first layer of the steel ring friction pair. The change trend is roughly the same as that of the tight side of the steel ring, but the change trend is slower. Figure 6(c) is the wear depth distribution of the second outer layer of the steel ring friction pair. From the inner side of the steel ring (X / L=0) to the outer side (X / L=1), the wear depth first decreases and then increases. The wear depth increases rapidly at X / L=0.86 and reaches the maximum at X / L=1.0. When the torque T m =150N·m, the maximum wear depth can reach 3.1μm. This is because when the metal sheet transmits torque through the extrusion force at the interference of the friction pair, the pressure on the steel ring increases, resulting in an increase in the contact pressure and shear force of the micro-motion surface, which leads to an increase in the wear depth here. Due to the pressure accumulation here, the contact pressure and shear force have stress concentration, resulting in a sharp increase in the wear depth at the interference.

[0132] CVT speed is an important factor affecting the wear depth of the steel ring. During the simulation process, the highest and lowest speeds of the transmission input were avoided, and the input speed values ​​were set to 1400, 2100, and 2800 r / min respectively. Figure 7 The graphs are respectively the variation of the wear depth of the first layer outer side, the first layer inner side and the second layer outer side steel ring surface with the input speed. Figure 7 In (a), it can be seen that the wear depth of the steel ring in the axial direction first decreases and then increases, and the greater the speed, the greater the wear depth. The wear depth increases rapidly at X / L=0.9, because this is the wear edge, and the extrusion force of the transmission metal sheet on the steel ring is relatively large, resulting in a change in the wear depth. The change in the wear depth of the first layer of the steel ring is similar to the change trend of the tight edge, but because the extrusion force of the metal sheet on the steel ring is smaller than that of the tight edge, the wear depth is relatively small and the amplitude change is small. Figure 7 (c) in the figure shows the wear depth change of the outer side of the second layer of the steel ring. Its change trend first decreases, then increases rapidly around X / L=0.5, and then increases rapidly around X / L=0.9. This is because the above two places are the positions where the metal sheet enters and leaves the metal pulley. Under the extrusion and thrust of the metal sheet, the steel ring moves with the metal sheet, and a relatively high pressure is generated at the position where it enters and leaves the metal pulley. Therefore, the wear frequency here is relatively fast, resulting in a relatively rapid increase in the wear depth of the steel ring.

[0133] The material of the transmission steel ring friction pair used in the embodiment of the present invention is 18% Ni with a yield limit of 175 grade martensitic aged steel, and various alloy elements for age hardening are added to the composition. Table 1 shows the chemical composition of the martensitic steel ring. Its elastic modulus is 192GPa, Poisson's ratio is 0.30, and density is 7800kg / m 3 Before the test, the specimens were cleaned in ethanol and processed in a dryer.

[0134] Table 1 Composition of martensitic steel

[0135]

[0136] When CVT is in service, the metal belt and steel ring tight fit structure will cause micro-vibration and micro-wear. The micro-vibration frequency will affect the change of surface roughness between the steel ring friction pairs. When considering the effect of surface roughness on wear depth, it is necessary to first explore the effect of micro-vibration frequency on surface roughness. The electron microscope scanning test is used to observe the effect of micro-vibration frequency on surface roughness. This embodiment uses the HITACHI Regulus8100 cold field emission scanning electron microscope, which retains the advantages of SU8100 such as easy maintenance and easy operation, and further improves performance.

[0137] With the help of the vibration test bench, the micro-vibration frequencies were gradually set to 30, 60, 90, and 120 Hz, respectively, and the steel ring samples under 3000 cycles were obtained. The first layer steel ring and the second layer steel ring were sampled respectively, and the steel ring samples were placed in the electron microscope for observation in turn, and the result graph with good surface condition was selected. Figure 8 It can be seen that with the increase of micro-vibration frequency, the surface roughness of the friction pair also increases. Micro-vibration frequency not only increases the amount of wear, but also accelerates the mechanical crushing of the friction surface, promotes the removal of surface debris, and reduces the wear protection effect. When the micro-vibration frequency increases from 30Hz to 90Hz, the roughness increases sharply, and the wear amount also increases. When the frequency exceeds 90Hz, the surface roughness and wear amount decrease instead. This is because excessive frequency will have a greater impact on the crack propagation rate on the steel ring surface. The depth of crack initiation is shallow, and the rate of its generation is slow, resulting in a decrease in the stratification efficiency between the friction pairs, and the surface roughness decreases with the increase of frequency.

[0138] As the frequency of micro-vibration changes, the wear depth between the steel ring friction pairs also changes significantly. Fig. 9 The graphs are respectively showing the variation of wear depth of the first outer layer, first inner layer and second outer layer of the steel ring friction pair with micro-vibration frequency. The wear depth in the axial direction generally increases first and then decreases. This is because the increase in micro-vibration frequency and the increase in wear volume lead to an increase in the mechanical crushing rate of the friction surface and an increase in the removal rate of surface crushed objects, thus increasing the wear depth. When the frequency exceeds 90Hz, the stratification efficiency between the friction pairs decreases, and the wear depth decreases with the increase in frequency. Fig. 9 (a) shows that when the frequency increases from 30Hz to 90Hz, the maximum wear depth of the steel ring friction pair increases from 0.72μm to 1.44μm; when the frequency of the first layer of the steel ring increases from 30Hz to 90Hz, the maximum wear depth of the friction pair increases from 0.78μm to 1.18μm; Fig. 9From (c), it can be seen that when the frequency is 30, 60, 90, and 120 Hz, the wear depth increases rapidly at X / L = 0.80, X / L = 0.72, X / L = 0.52, and X / L = 0.56. At the interference point, when the frequency increases from 30 Hz to 90 Hz, the maximum wear depth of the steel ring friction pair increases from 1.24 μm to 1.73 μm.

[0139] According to the above modeling of the lubrication between the first and second steel rings, the lubrication characteristics between the two friction pairs are analyzed. The commonly used solution for point contact mixed lubrication is the Newton-Raphson algorithm, which has a fast convergence speed and more accurate calculation results. However, this solution process requires decomposing the Jacobian matrix of the solution equation for one-dimensional linear analysis, and the calculation process is more complicated. Therefore, the Newton iteration algorithm is the best choice for this simulation process.

[0140] In the calculation process, the array ROU space is first provided, and the number of arrays is consistent with the number of nodes. Secondly, in order to facilitate the calculation, the roughness is calculated in advance in the program directory and saved in the corresponding subroutine. The roughness function is added to the film thickness equation to calculate the change of oil film thickness under the influence of roughness. Finally, since the random roughness is asymmetric, the calculation process in the Y direction is fully executed during the calculation process without symmetric processing.

[0141] Solve for the input torque T p =150N·m, driving wheel speed n p =5500r / min, slip rate ε=3%, speed ratio i=1 CVT working condition, the dimensionalized results of the film thickness, pressure, and temperature rise distribution between the steel ring friction pairs. Fig.10 This is a three-dimensional surface roughness surface generated according to the established model. It can be seen from the figure that the roughness peak of the generated surface does not exceed 1.0 μm, and the roughness peak distribution is random.

[0142] like Fig.11 As shown, X is the moving direction of the friction plate, and Y is the dimensionless coordinate in the normal direction of the steel ring.

[0143] Under the influence of random roughness peaks, the oil film distribution between the friction pairs is also random. When a sharper roughness peak appears, a pressure peak will be generated at the top of the peak, such as Fig.11 The peak pressure generated during the period shown in (a) can reach up to 1.77GPa. As the torque and speed increase, the pressure at the peak rises sharply, and the lubrication method around it changes to mixed lubrication, which will cause the risk of oil film rupture.

[0144] Fig.11(b) is the oil film thickness variation diagram between the steel ring friction pair. Due to the influence of surface roughness, the surface of the oil film thickness result is also rough. When the wear between the friction pairs gradually increases, the lubricating oil will penetrate into the two surfaces of the steel ring. At this time, the comprehensive performance of various lubricating film composition characteristics is formed between the two friction pairs. The oil film pressure rises rapidly at the top of the rough peak. Due to the pressure applied by the friction pair on both sides of the oil film, it undergoes elastic deformation, and the oil film has the first extreme pressure. At this time, the film thickness will also drop sharply. At this time, the oil film thickness is 0.3μm. The oil film pressure drops when the lubricating oil passes through the rough peak. When the lubricating oil reaches the adjacent rough peak, a necking phenomenon occurs. The oil film pressure will reach a pressure extreme again. At this time, the oil film thickness will also reach an extreme value, and the film thickness is 0.37μm.

[0145] Fig.11 (c) in the figure is a graph showing the change in oil film temperature under the influence of surface roughness. The temperature change is similar to the pressure change. The oil film temperature rises rapidly at the sharper roughness peak. Macroscopically, the friction at the peak causes the mechanical energy to be converted into heat energy, which increases the temperature. Microscopically, the shear strain rate inside the oil film at the top of the roughness peak increases, causing the shear force to increase. The oil film obtains more shear work, causing the temperature to rise. Under the influence of factors such as torque, speed, and micro-vibration frequency, the oil film temperature rise at the top of the roughness peak can reach up to about 48°C.

[0146] During the operation of CVT, the random roughness and random oil film distribution between the steel ring friction pairs will change under the influence of factors such as torque, speed, and micro-vibration frequency. The lubrication state between the friction pairs gradually shifts to mixed lubrication. The overall characteristics of mixed lubrication are the comprehensive performance of the composition characteristics of various lubricating films. The proportion of the lubricating film on the contact surface of the friction pair is related to the friction interface morphology and working conditions. During the friction process, the thickness, proportion and distribution of the lubricating film are changing. When the height of the roughness peak is greater than the thickness of the maximum lubricating film, a dry friction state will be formed, resulting in surface damage. As the load fluctuates, the mating surface produces micro-slip and wear, which is transmitted through the friction plate, causing the contact characteristics and relative movement between the belt and the pulley to change, resulting in metal belt slip, pulley deflection, and bearing creep.

[0147] Therefore, the method for calculating the safety margin of the CVT steel ring friction pair provided in the embodiment of the present invention includes:

[0148] By comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer of steel ring and the second layer of steel ring of the CVT steel ring friction pair, the safety margin of the CVT steel ring friction pair is obtained, wherein the x-axis is the axial direction of the steel ring.

[0149] In a specific embodiment, in order to ensure the reliability of transmission and extend the service life of the transmission, the safety margin of the CVT steel ring friction pair is calculated by formula (26):

[0150]

[0151] When the wear depth is greater than the thickness of the oil film between the first and second steel rings of the CVT steel ring friction pair, that is, the safety margin is greater than 0, the steel ring wear is aggravated, the failure probability and the life reduction probability increase, which is worse at this time, otherwise it is considered to be in a good safety state. The RD150 CVT is selected as the research object to solve the safety margin. Table 2 shows the structure and working parameters of the selected CVT:

[0152] Table 2 Structure and working parameters of CVT

[0153]

[0154] The minimum value of the CVT working parameter range is set as the initial value, the step size of the driving wheel speed is selected as 100r / min, the step size of the slip rate is selected as 0.1%, the step size of the speed ratio is selected as 0.2, and the step size of the torque is selected as 10N·m; secondly, combined with the temperature change of the metal belt transmission process, the safety margin value of each working point is calculated and interpolated; finally, the corresponding safety margin surface diagram when the working conditions change is obtained.

[0155] This paper mainly focuses on the application performance and safety issues of CVT. Based on the dissipative wear model that conforms to the steel ring friction pair, a wear depth model that associates the wear depth with its influencing variables is established, and a lubrication model that conforms to the steel ring friction pair is constructed. Based on the constructed model, simulation experiments are carried out under specific working conditions to obtain the corresponding wear depth and oil film characteristics. Finally, the application performance and safety issues are analyzed in depth by combining macro parameters and micro lubrication. The main conclusions are summarized as follows:

[0156] 1) The wear depth of the steel ring friction pair will gradually increase with the increase of torque and speed, and in the axial direction, the wear depth will increase rapidly near X / L=0.8, and reach the maximum at X / L=1.0. The wear depth changes with the change of micro-vibration frequency in the axial direction, and generally increases first and then decreases. The increase in micro-vibration frequency is because the increase in wear leads to an increase in the mechanical crushing rate of the friction surface and an increase in the removal rate of surface crushed objects. When the frequency exceeds 90Hz, the stratification efficiency between the friction pairs decreases, and the wear depth decreases with the increase of frequency.

[0157] 2) When CVT is running, the heat generated by friction of the metal belt will be dissipated by heat conduction. Since the inner side of the friction plate contacts one side of the steel ring and produces relative sliding, the friction work causes the temperature of the contact part to rise significantly. In addition, there is lubricating oil between the saddle surface and the contact surface of the steel ring, which causes the middle part of the steel ring to cool relatively quickly, so the temperature is more obviously conducted to the edge of the steel ring. Due to the influence of the roughness peak, the oil film temperature will be randomly distributed in a peak shape, and a higher temperature peak will be generated at the surface roughness peak, with the highest temperature rise reaching 48°C.

[0158] 3) Under the influence of random roughness peaks, the oil film distribution between the friction pairs is also random. When a sharper roughness peak appears, a pressure peak will be generated at the top of the peak, and the peak pressure generated during the period can reach up to 1.77GPa. Under the influence of the roughness peak, the oil film pressure rises rapidly at the top of the roughness peak. Due to the pressure applied by the friction pair on both sides of the oil film, it undergoes elastic deformation, and the film thickness drops sharply for the first time, with a film thickness of 0.3μm. When the lubricating oil reaches the adjacent roughness peak, a necking effect occurs, and the oil film thickness drops sharply for the second time, with a film thickness of 0.37μm.

[0159] 4) With the increase of torque and speed, the micro-vibration frequency also gradually increases. Under the comprehensive consideration of application performance and safety, the safety margin gradually decreases with the decrease of macro parameters. When the transmission torque is greater than 130N·m, that is, the safety margin drops below 0, the safety margin is in the non-safe area, the transmission efficiency is low, and the probability of safety failure increases significantly.

[0160] The embodiment of the present invention also provides a CVT steel ring friction pair evaluation method comprising:

[0161] Step 1: Collect the working radius R of the driving wheel of the CVT steel ring friction pair p , the average input torque T of the CVT driven pulley m , the micro-vibration frequency of the steel ring friction pair ω, the dynamic load coefficient k of the CVT motion process v , and the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair

[0162] Step 2, by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer of steel ring and the second layer of steel ring of the CVT steel ring friction pair, obtain the safety margin of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring.

[0163] Step 3, determine whether the safety margin is less than 0, if so, determine that the safety state of the CVT is good; otherwise, determine that the reliability of the CVT is poor.

[0164] The CVT steel ring friction pair wear depth calculation device provided in an embodiment of the present invention includes a steel ring wear depth model. The steel ring wear depth model is described as formula (15) and is used to calculate the wear depth of the CVT steel ring friction pair.

[0165] The CVT steel ring friction pair safety margin calculation device further provided in an embodiment of the present invention includes a safety margin model, which is used to obtain the safety margin of the CVT steel ring friction pair by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer of steel ring and the second layer of steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring.

[0166] In one embodiment, the safety margin of the CVT steel ring friction pair is calculated by formula (26).

[0167] The CVT steel ring friction pair evaluation device provided in the embodiment of the present invention includes a collection unit, a safety margin model and a judgment unit, wherein:

[0168] The acquisition unit is used to acquire the working radius R of the driving wheel of the CVT steel ring friction pair p , the average input torque T of the CVT driven pulley m , the micro-vibration frequency of the steel ring friction pair ω, the dynamic load coefficient k of the CVT motion process v , and the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair

[0169] The safety margin model is used to obtain the safety margin of the CVT steel ring friction pair by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring.

[0170] The judging unit is used to judge whether the safety margin is less than 0. If so, it is judged that the safety state of the CVT is good; otherwise, it is judged that the reliability of the CVT is poor.

[0171] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some of the technical features thereof may be replaced by equivalents; 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 calculating the safety margin of a CVT steel ring friction pair, characterized in that: include: By comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer steel ring and the second layer steel ring of the CVT steel ring friction pair, the safety margin of the CVT steel ring friction pair is obtained, wherein the x-axis is the axial direction of the steel ring, The safety margin of the CVT steel ring friction pair is calculated by formula (26): Wherein, h(x) is the wear depth of the steel ring at the local position x of the CVT steel ring friction pair as claimed in claim 1, and h l is the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair, The wear depth of the CVT steel ring friction pair is calculated using the steel ring wear depth model expressed in formula (15); Where h(x) is the wear depth of the local position x of the steel ring of the CVT steel ring friction pair, the x-axis is the axial direction of the steel ring, ΔK is the preset fretting wear cycle acceleration number, K is the preset steel ring friction pair wear cycle number, and K int is the incremental step in the continuous fretting friction process of the preset fretting wear cycle, S f is the safety factor of the clamping force, σ s is the yield limit of the metal material used for the steel ring, v s is the local wear coefficient of the steel ring friction pair, ε is the input torque amplitude fluctuation coefficient of the CVT, α is the pulley cone angle of the CVT steel ring friction pair, R p is the working radius of the driving wheel of the CVT steel ring friction pair, k v is the dynamic load coefficient of the CVT motion process, T m is the average input torque of the CVT driven pulley, ω is the fretting frequency of the steel ring friction pair, t is the time variable of the fretting wear process, ds is the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair, i,j (x) is the relative slip distance of the jth wear increment under the i-th fretting friction, T p is the input torque of the driven wheel of the CVT steel ring friction pair, f is the friction coefficient of the steel ring contact surface of the CVT steel ring friction pair, F si is the clamping force applied to the steel ring of the CVT steel ring friction pair by the i-th micro-friction, which is described as formula (12); 2. A CVT steel ring friction pair evaluation method, characterized in that: include: Step 1: Collect the working radius R of the driving wheel of the CVT steel ring friction pair p , the average input torque T of the CVT driven pulley m , the micro-vibration frequency of the steel ring friction pair ω, the dynamic load coefficient k of the CVT motion process v , and the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair Step 2, by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair, the safety margin of the CVT steel ring friction pair is obtained, wherein the x-axis is the axial direction of the steel ring; specifically, the safety margin is determined by the method according to claim 1; Step 3, determine whether the safety margin is less than 0, if so, determine that the safety state of the CVT is good; otherwise, determine that the reliability of the CVT is poor.

3. A CVT steel ring friction pair safety margin calculation device, characterized in that: include: The safety margin model is used to obtain the safety margin of the CVT steel ring friction pair by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer steel ring and the second layer steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring, The safety margin of the CVT steel ring friction pair is calculated by formula (26): Wherein, h(x) is the wear depth of the steel ring at the local position x of the CVT steel ring friction pair as described in claim 7, and h l is the thickness of the oil film between the first steel ring and the second steel ring of the CVT steel ring friction pair, The wear depth of the CVT steel ring friction pair is calculated using the steel ring wear depth model expressed in formula (15); Where h(x) is the wear depth of the local position x of the steel ring of the CVT steel ring friction pair, the x-axis is the axial direction of the steel ring, ΔK is the preset fretting wear cycle acceleration number, K is the preset steel ring friction pair wear cycle number, and K int is the incremental step in the continuous fretting friction process of the preset fretting wear cycle, S f is the safety factor of the clamping force, σ s is the yield limit of the metal material used for the steel ring, υ s is the local wear coefficient of the steel ring friction pair, ε is the input torque amplitude fluctuation coefficient of the CVT, α is the pulley cone angle of the CVT steel ring friction pair, R p is the working radius of the driving wheel of the CVT steel ring friction pair, k v is the dynamic load coefficient of the CVT motion process, T m is the average input torque of the CVT driven pulley, ω is the fretting frequency of the steel ring friction pair, t is the time variable of the fretting wear process, ds is the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair, i,j (x) is the relative slip distance of the jth wear increment under the i-th fretting friction, T p is the input torque of the driven wheel of the CVT steel ring friction pair, f is the friction coefficient of the steel ring contact surface of the CVT steel ring friction pair, F si is the clamping force applied to the steel ring of the CVT steel ring friction pair by the i-th micro-friction, which is described as formula (12); 4. A CVT steel ring friction pair evaluation device, characterized in that: include: The collection unit is used to collect the working radius R of the driving wheel of the CVT steel ring friction pair p , the average input torque T of the CVT driven pulley m , the micro-vibration frequency of the steel ring friction pair ω, the dynamic load coefficient k of the CVT motion process v , and the angle between the common tangent line and the connecting center line of the working circle of the driving wheel and the driven wheel of the CVT steel ring friction pair A safety margin model, which is used to obtain the safety margin of the CVT steel ring friction pair by comparing the wear depth of the local position x of the steel ring of the CVT steel ring friction pair with the thickness of the oil film between the first layer of steel ring and the second layer of steel ring of the CVT steel ring friction pair, wherein the x-axis is the axial direction of the steel ring; specifically, the safety margin model uses the CVT steel ring friction pair safety margin calculation device according to claim 3 to determine the safety margin; The judging unit is used to judge whether the safety margin is less than 0. If so, it is judged that the safety state of the CVT is good; otherwise, it is judged that the reliability of the CVT is poor.

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