A method for calculating fatigue life of steel belt ring of belt-type CVT under high speed conditions

Abstract

The present invention relates to a method for calculating the fatigue life of a steel belt ring of a belt-type CVT under high-speed conditions, including: performing transient dynamic analysis of the belt-type CVT; using an equivalent method to obtain a load spectrum of a steel belt ring micro-element segment running for one cycle, and then calculating the fatigue life of the belt ring under this specified condition; considering two types of situations, speed, torque change and speed ratio change under a fixed speed ratio, respectively, using the same life calculation method as the first two steps and combining the data interpolation method to obtain a theoretical life image of the CVT belt ring; considering general working conditions, first using a statistical method to obtain the probability distribution of the speed ratio, input torque and input speed under general working conditions; then considering the probability of the CVT theoretical life image and the input conditions to calculate the belt ring life at a fixed speed ratio; finally using the life of the belt rings with different speed ratios and the probability distribution of the speed ratio to obtain the actual life of the belt ring under general working conditions. The present invention provides a method for calculating the fatigue life of the steel belt ring from a theoretical perspective, which can accurately estimate the fatigue life of the steel belt ring.

Description

Technical Field

[0001] The invention relates to a research field of metal belt CVT technology under high speed conditions, and specifically to a method for calculating the fatigue life of a metal steel belt ring under high speed conditions. Background Art

[0002] With the continuous development of society, cars have become an essential means of transportation for people to travel, but with it comes the increasingly serious thorny problem of environmental pollution caused by a large amount of automobile exhaust. Countries around the world attach great importance to environmental issues. Electric vehicles use batteries as a power source and are a kind of emission-free means of transportation. As the country continues to strictly control automobile emission index parameters, electric vehicles are expected to replace traditional cars and become the main means of transportation for people to travel in the future. Studies have shown that equipping electric vehicles with transmissions can greatly improve the power and economy of electric vehicles and increase their endurance. Among all types of transmissions, the continuously variable transmission CVT equipped with electric vehicles has a nearly ideal performance. In addition to greatly improving the power and economy of electric vehicles, it also has unique advantages such as simple structure, small size, and good shifting smoothness compared to traditional transmissions. With the widespread use of electric vehicles, CVT continuously variable transmissions are expected to become the most widely used transmissions in the future.

[0003] However, experiments show that the reliability of CVT will be greatly reduced under high speed conditions. The outermost steel belt ring of the metal steel belt is very likely to break, causing CVT failure. The failure time is much earlier than normal damage, which is very likely due to fatigue failure of the belt ring. However, due to the specific experimental conditions and the special structure of CVT, it is impossible to obtain the actual load condition of the belt ring under high speed through experiments, and the entire ring of the CVT steel belt ring is subjected to load, and the number of loads at the same time is large. Due to the continuous rotation of the belt ring, the position of the load application point is also constantly changing, which makes it difficult to calculate the fatigue life of the belt ring. In order to improve the reliability of the metal belt under high speed conditions and avoid fatigue fracture, it is of great engineering value to propose a feasible solution to accurately calculate the fatigue life of the metal steel belt ring under high speed conditions. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for calculating the fatigue life of a CVT steel belt ring under high speed conditions, so as to facilitate enterprise personnel to develop and design a transmission with better performance, improve the service life of the CVT and expand the application field of the CVT.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for calculating the fatigue life of a CVT steel belt ring under high speed conditions comprises the following steps:

[0007] Step 1: Perform transient dynamic analysis of belt-type CVT;

[0008] Step 2: Use the equivalent method to extract the load spectrum of the steel belt ring micro-element segment during one cycle of operation, and then calculate the fatigue life of the steel belt ring under this specified condition;

[0009] Step 3: Consider the two situations of speed and torque change and speed ratio change under fixed speed ratio respectively, use the same life calculation method as the previous two steps and combine the data interpolation method to obtain the theoretical life image of CVT belt ring;

[0010] Step 4: Considering the general working condition, first use the statistical method to obtain the probability distribution of the speed ratio, input torque, and input speed under the general working condition;

[0011] Step 5: Calculate the belt ring life at a constant speed ratio by combining the CVT theoretical life image with the probability of the input conditions;

[0012] Step 6: Finally, the actual life of the belt ring under general working conditions is obtained by using the probability distribution of the life of the belt ring with different speed ratios and the speed ratio;

[0013] Preferably, in step 1, a three-dimensional model of a CVT assembly at a certain speed ratio is established using solid works modeling software, and is imported into ANSYS WORKBENCH for transient dynamic analysis of the CVT assembly;

[0014] Preferably, in step 2, the step of obtaining the load spectrum of the belt ring micro-element segment during one cycle of operation by the equivalent method, and calculating the fatigue life of the belt ring under the specified conditions comprises:

[0015] Step 2.1: Extract the contact load values ​​of all metal sheet saddle surfaces in the entire CVT from the transient dynamics analysis results, and regard the CVT steel belt ring as a belt ring microelement segment with the same number of metal sheets as the flexible connection. Take the belt ring microelement segment corresponding to the first metal sheet at the entrance of the driving wheel as the research object, and regard the next metal sheet rotating clockwise adjacent to it as the motion state of the first metal sheet at the next moment. After one cycle, arrange the metal sheet saddle surface load values ​​in order and regard them as the force change of the belt ring microelement segment during one cycle. Obtain the load spectrum of the belt ring microelement segment and record it as the saddle surface load matrix;

[0016] Step 2.2: Divide the total time of one stable movement of the belt ring into a time series equal to the number of metal sheets, convert the load matrix of the saddle surface of the belt ring microelement into the relationship between time and stress, and obtain the time series load spectrum;

[0017] Step 2.3: Use the rain flow counting method to convert the time series load spectrum into the stress load spectrum used for calculation, and obtain the actual number of cycles A under stress of different levels of amplitude i ;

[0018] Step 2.4: According to the SN fatigue life curve of the material, the theoretical life number N of the steel belt ring corresponding to the stress of different levels of amplitude is obtained. i ;

[0019] Step 2.5: According to Miner's linear cumulative damage theory, under stresses of different levels and amplitudes, the sum of the damage degrees should be: Therefore, the life T of the belt ring under this working condition can be calculated, and the calculation formula is:

[0020] Preferably, in step 3, the two situations of speed change, torque change and speed ratio change when the speed ratio is fixed are considered respectively, and the steps of obtaining the theoretical life image of the CVT belt ring by using the life calculation method in step 2 and combining the data interpolation method include:

[0021] Step 3.1: First, under a fixed speed ratio, determine the vehicle speed range under this speed ratio, reverse the transmission speed range, and then obtain the transmission input torque range based on the relationship between engine speed and torque;

[0022] Step 3.2: Under the condition of constant speed ratio and constant speed, take the two end points of the torque range and select several representative input torques within the torque range. The calculation method remains unchanged, and the fatigue life of the steel belt ring under the corresponding input conditions of the life is calculated respectively. The several data points are obtained, and then the relationship image between torque and life is obtained by fitting using Newton interpolation formula;

[0023] Step 3.3: Keep the speed ratio unchanged, change the speed once, select the same input torque points as in step 3.2, and use the same calculation method to calculate the fatigue life of the steel belt ring under the corresponding input conditions. Use the Newton interpolation formula to fit the obtained set of data points to obtain the relationship diagram between torque and life;

[0024] Step 3.4: Repeat the above process several times to obtain some data points. Use these data points to plot the relationship between input speed, input torque and life under a constant speed ratio;

[0025] Step 3.4: Consider different speed ratios again, reselect a speed ratio within the speed ratio range, rebuild the assembly model, and perform transient dynamic analysis in ANSYS WORKBENCH. After the simulation, use the same extraction method to extract the saddle surface load matrix, and calculate the speed-torque-life relationship graph under the corresponding speed ratio according to the above steps. Similarly, by using the Newton interpolation formula, you can get a series of fatigue life values ​​at consecutive points. Change the speed ratio several times, rebuild the assembly, repeat the above work, and finally plot the points to get the theoretical relationship image of speed ratio-speed-torque-life.

[0026] Preferably, in step 4, considering the general working condition, the step of first using a statistical method to obtain the probability distribution of the speed ratio, input torque, and input speed under the general working condition includes:

[0027] Step 4.1: Under normal working conditions, collect the change of speed ratio over time during the entire cycle; extract the change of input torque over time and input speed over time under different speed ratios;

[0028] Step 4.2: Based on this data, convert the input torque time history diagram, input speed time history diagram, and speed ratio time history diagram into a frequency histogram;

[0029] Step 4.3: According to the central limit theorem in statistics, when the amount of data is large enough, the distribution of any variable will approximately obey the normal distribution. For the working conditions of the transmission, the middle gear is undoubtedly the most used, and the low-speed gear and the high-speed gear are the gears that are used less frequently. Similarly, the frequency of cars maintaining high and low speeds is generally low, and the accelerator is generally pressed at a moderate position. Therefore, it is also determined that the speed ratio, input speed, and input torque variables obey the normal distribution. The normal distribution function is used to fit the histogram, and the mean and standard deviation of the three normal distribution function variables are calculated to obtain the normal probability distribution function expression. Then, the probability of using a specified speed ratio in actual driving conditions and the probability of using a certain input torque and input speed under a specified speed ratio are obtained. The obtained probability distribution is the mathematical function used to characterize the service condition of the metal belt at this time.

[0030] Preferably, in step 5, the step of calculating the belt ring life at a constant speed ratio by combining the CVT theoretical life image with the probability of the input conditions comprises:

[0031] Step 5.1: After the probability distribution of the three variables is obtained in step 4, the service conditions of the metal strip under general working conditions are clarified. In order to make the calculation operation simple, practical operability strong and the settlement result maintain high accuracy, the continuous function is approximated by multiple small intervals for actual calculation. First, the median of the interval corresponding to the small interval divided when the three variables are counted is calculated, and then the range of this small interval is substituted into the distribution function to calculate the probability. The median of this interval represents the probability of the corresponding small interval. The finer the interval, the better the fitting effect.

[0032] Step 5.2: After obtaining the above probability data, the input torque and input speed corresponding to the median of the divided small intervals are checked in the theoretical life image of the steel belt ring established in step 3 to obtain the theoretical life value, and then multiplied by the probability of the corresponding median of the interval being used under this service condition, to calculate the actual life value of the metal belt at a certain speed ratio.

[0033] Preferably, in step 6, the actual life values ​​of the steel belt ring under multiple speed ratios obtained in step 5 are combined with the speed ratio probability distribution function to obtain the probability value of the corresponding speed ratio. Then, the actual life of the belt ring under general working conditions is equal to the actual life of the corresponding speed ratio multiplied by the probability of the corresponding speed ratio and added together. The actual value calculation formula of the CVT steel belt ring life used is:

[0034]

[0035] Where: is the fatigue life of the belt CVT at each constant speed ratio; η 1 is the probability of using the corresponding constant speed ratio; T is the fatigue life of the belt CVT under normal working conditions.

[0036] Preferably, in step 4, the method for establishing the frequency histogram is:

[0037] The three histograms are respectively based on input torque M, input speed n, and speed ratio i as horizontal coordinates, and torque frequency H as horizontal coordinates. Mi Ratio to input torque interval ΔM Speed ​​frequency H ni Ratio to input speed interval Δn Speed ​​ratio frequency H ii Ratio to speed ratio interval Δi is the vertical axis, frequency H Mi , H ni , H ii It reflects the percentage of the target value occurrence in each level of the interval, so the histogram reflects the proportion of the number of occurrences of the corresponding indicator.

[0038]

[0039] Q Mi , Q ni , Q ii is the number of occurrences of each level parameter.

[0040] Preferably, in step 4, the normal distribution function used to fit the frequency histogram is obtained in the following manner, and the relationship between the ordinate and the abscissa of the histogram can be expressed by the normal distribution function:

[0041]

[0042]

[0043]

[0044] Where: x 1 , x 2 , x 3is a certain input torque, a certain input speed, and a certain speed ratio value in the collected data; P 1 (x 1 ), P 2 (x 2 ), P 3 (x 3 ) are the probability value of using a certain input torque under a certain speed ratio, the probability value of using a certain speed, and the probability value of using a certain speed ratio; H Mi , H ni , H ii : torque frequency, speed frequency, speed ratio frequency; ΔM, Δn, Δi: torque interval, speed interval, speed ratio interval; M i 、n j 、i k : Input torque, input speed and speed ratio of each stage; The mean torque, The average speed, The average speed ratio, Standard deviation, σ x2 : standard deviation, σ x3 : standard deviation, e: base of natural logarithms.

[0045] Preferably, in step 5, the fatigue life of the steel belt ring under a constant speed ratio is calculated by the following formula:

[0046]

[0047] Where: i is the probability that the corresponding input torque and speed conditions are used simultaneously, and its size is the product of the two probabilities; T i To find the fatigue life of the steel belt ring under the corresponding input torque and speed obtained by searching the theoretical image; Fatigue life of steel belt ring of belt-type CVT at a certain constant speed ratio.

[0048] The present invention has the following beneficial effects:

[0049] The present invention provides a method for calculating the fatigue life of CVT belt under high speed conditions, which can calculate the fatigue life of CVT under general working conditions as accurately as possible. It provides a research method for relevant practitioners to design high-reliability belt-type CVT. In the past, the fatigue life of steel belt rings could only be studied through experiments. With the rise of electric vehicles, when the speed conditions become higher and higher, it is often difficult to achieve experimental conditions. This theory can accurately calculate the fatigue life of steel belt rings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1Calculation method of fatigue life of steel belt ring under high speed conditions;

[0051] Figure 2 The calculation method of theoretical fatigue life of steel belt ring under constant speed ratio;

[0052] Figure 3 The calculation method of theoretical fatigue life of steel belt ring at different speed ratios. DETAILED DESCRIPTION

[0053] The present invention is further described in detail below with reference to the accompanying drawings. The present invention adopts a calculation scheme such as Figure 1 As shown, the specific steps are as follows:

[0054] Step 1: Perform transient dynamic analysis of belt-type CVT;

[0055] Step 2: Use the equivalent method to extract the load spectrum of the steel belt ring micro-element segment during one cycle of operation, and then calculate the fatigue life of the steel belt ring under this specified condition;

[0056] Step 3: Consider the two situations of speed and torque change and speed ratio change under fixed speed ratio respectively, use the same life calculation method as the previous step and combine the data interpolation method to obtain the theoretical life image of CVT belt ring;

[0057] Step 4: Considering the general working condition, first use the statistical method to obtain the probability distribution of the speed ratio, input torque, and input speed under the general working condition;

[0058] Step 5: Calculate the belt ring life at a constant speed ratio by combining the CVT theoretical life image with the probability of the input conditions;

[0059] Step 6: Finally, the actual life of the belt ring under general working conditions is obtained by using the probability distribution of the life of the belt ring with different speed ratios and the speed ratio.

[0060] In the present invention, in order to accurately calculate the fatigue life of the steel belt ring, the overall scheme can be summarized as follows: first, the theoretical working life value of the steel belt ring is considered, then the random factors of the steel belt ring working under general working conditions are considered, and finally the data of the two are combined to give the calculation method of the fatigue life of the steel belt ring under general working conditions. Specifically: First, in the theoretical fatigue life analysis stage, it means solving the fatigue life of the steel belt ring under fixed input conditions until failure. For example, given a speed ratio, an input torque and an input speed, this condition is regarded as the working condition of the steel belt ring, and the fatigue life calculation method mentioned in the present invention is used to obtain the theoretical life value of the steel belt ring under this fixed condition. Then, under the fixed speed ratio, different points are selected to calculate the theoretical life of multiple steel belt rings under the corresponding fixed conditions in two cases of changing the input speed, input torque and changing the speed ratio. Finally, the data interpolation method is combined to obtain the theoretical life image of the speed ratio, input torque, input speed and life of the steel belt ring. The above is the task of the theoretical life analysis stage. Second, in the general working condition stage, the fatigue life of the belt ring working under general working conditions is considered. The present invention characterizes the service conditions of the belt ring under general working conditions with a distribution function in statistics, and proposes how to calculate the fatigue life value of the steel belt ring under more general conditions. In order to improve the practical feasibility of the present invention, it is also proposed to approximate the distribution function characterizing the service conditions of the steel belt ring by dividing it into small intervals, calculate the fatigue life of the steel belt ring in a discrete manner, and provide a formula for calculating the fatigue life of the steel belt ring under a constant speed ratio and a formula for the fatigue life of the steel belt ring under general working conditions, a total of two new formulas. This method has high accuracy in calculating the fatigue life of the steel belt ring and is highly operable, which is of great help to the design and research of the steel belt ring.

[0061] In the specific implementation process, in step 1, the transient dynamic analysis of the belt CVT is performed by the following method: SolidWorks 3D modeling software is used to establish a speed ratio of i L1 CVT model (L represents the symbol used to establish the theoretical life of the belt ring; i L1 Symbol meaning: refers to a speed ratio used in establishing the theoretical life. In actual operation, you can select any speed ratio within the speed ratio range to build a model. This symbol is used to compare with the speed ratio i used in calculating the actual life later. S1 Distinguish. L and S mentioned later are the abbreviations of theory and practice), then save it in x_t format, import it into ANSYS WORKBENCH to set materials, contact, kinematic pairs, mesh, boundary conditions, analysis, and finally solve for transient dynamics analysis of belt CVT;

[0062] In the specific implementation process, in step 2, the steps of obtaining the load spectrum of the belt ring micro-element segment during one cycle of operation by the equivalent method and calculating the fatigue life of the belt ring under the specified conditions include:

[0063] Step 2.1: Given input speed n Lb1 (L represents the speed used when establishing the theoretical life of the belt ring; b represents the speed ratio at this time; 1 represents the first time the speed takes a point, and the symbols below all have this meaning), input torque M Lbk (b represents the speed ratio at this time; k represents the position of a certain point of speed and torque, and the symbols below all have this meaning). After the transient dynamics simulation is completed, the saddle surface contact stress value of all metal sheets in the entire metal belt is extracted as σ 1 , σ 2 , σ 3 ....σ n . Where n is the number of metal sheets. The belt ring microelement segment corresponding to the first metal sheet at the entrance of the driving wheel is taken as the research object (the same applies to other belt ring microelement segments). Since the metal sheets distributed on the entire belt ring are almost exactly the same, the next metal sheet rotating clockwise adjacent to it is equivalent to the motion state of the first metal sheet at the next moment. Then, we regard the contact load on the saddle surface of the second metal sheet as the load condition of the first metal sheet at the next moment. This cycle continues clockwise until it returns to the first sheet of the driving wheel and stops. For the belt ring, the only direct force application object is the metal sheet. Therefore, the extracted metal sheet saddle surface load can be regarded as the force change of the belt ring microelement segment during one cycle, and the obtained metal sheet saddle surface stress value is organized into the saddle surface load matrix B 1 , as shown in Table 1:

[0064] Table 1 Saddle surface load matrix B 1

[0065] Sheet metal saddle load <![CDATA[σ 1 ]]> <![CDATA[σ 2 ]]> <![CDATA[σ 3 ]]> ……… <![CDATA[σ n ]]>

[0066] Step 2.2: Divide the total time t of the belt ring's stable movement into a number of metal slice time series t 1 -t n . The saddle surface load matrix B 1 Converted into a time-stress relationship diagram, the time series load spectrum is obtained, as shown in Table 2:

[0067] Table 2 Time series load spectrum

[0068] time <![CDATA[t 1 ]]> <![CDATA[t 2 ]]> <![CDATA[t 3 ]]> ……… <![CDATA[t n ]]> Sheet metal saddle load <![CDATA[σ 1 ]]> <![CDATA[σ 2 ]]> <![CDATA[σ 3 ]]> ……… <![CDATA[σ n ]]>

[0069] Step 2.3: After obtaining the time series load spectrum, use the rain flow counting method to count the amplitude of the obtained random alternating stress. The stress load spectrum used in the calculation is obtained as follows:

[0070] Let Smax 1 =σ max1 ,Smax 2 =σmax2 ,.......,Smax n =σ maxn

[0071] Where: maxi With Smax 1 The maximum stress of stress cycles of different amplitudes after the rain flow counting method is used. The rain flow counting method does not consider the order in which stress side effects affect parts, so there is no time sequence here. i During the process of running one circle with the ring, the parts are under stress Smax i The actual number of cycles under action:

[0072] Table 3 Stress s of different levels of amplitude maxi The number of actual actions under action

[0073]

[0074] Step 2.4: Then, the stress s is obtained according to the SN fatigue life curve of the material. maxi The theoretical life times under action are shown in Table 4:

[0075] Table 4 Stress s of different levels of amplitude maxi The limiting number of cycles of the material under action

[0076]

[0077] In Table 4: N i is the stress σ at a certain amplitude maxi The limiting number of cycles of the material under action can be easily obtained from the SN curve of the material. i From this, we can calculate that during one cycle of the belt ring, its damage degree should be

[0078] Step 2.5: According to Miner's linear cumulative damage theory, under the stress of different levels of amplitude, the sum of the damage degree during the belt ring operation is Thus, the life of the belt ring under this condition can be calculated

[0079] For the indicator T Lbk1 Meaning: The letter L represents the code for establishing the theoretical life of the belt ring, the letter code b represents the specified speed ratio, the third number k represents the change of the point (randomly selected from 1 to n) within the input torque range, and the fourth number 1 represents the number of changes of the speed point (randomly selected from 1 to n).

[0080] In the specific implementation process, in step 3, if Figure 2 , Figure 3 The calculation principle shown in the figure considers two types of situations: speed, torque change and speed ratio change under fixed speed ratio. The same life calculation method as the previous two steps is used and combined with data interpolation method to obtain the theoretical life image of CVT belt ring. The steps include:

[0081] Step 3.1: First consider the constant speed ratio i L1 When determining the speed range V under this speed ratio 1 -V n , reverse thrust transmission speed range n Lb1 -n Lbn , and then according to the relationship between engine speed and torque, the input torque variation range M is obtained Lb1 -M Lbn ;

[0082] Step 3.2: Under constant speed ratio and constant speed, take the two end points M of the torque range Lb1 and M Lbn And select another representative input torque point M within the torque range Lbj , the calculation method remains unchanged, and the life span T can be calculated Lb11 , T Lbj1 , T Lbn1 (For the indicator T Lb11 Meaning, the letter code b indicates the specified speed ratio, the second number 1 represents the change of the point (from the range of 1-n) in the input torque range, and the third number 1 represents the number of changes in the speed point (from the range of 1-n). In addition to the initial torque point, a total of four input torque points are taken within the torque range under this speed ratio, and finally four coordinate points are obtained (M Lb1 , T Lb11 ), (M Lbk , T Lbk1 ), (M Lbj , T Lbj1 ), (M Lbn , T Lbn1 ), and then use Newton's interpolation formula to obtain the relationship between torque and life at the four coordinate points;

[0083] Step 3.3: Still keep the speed ratio unchanged, change the speed n Lb2 , then select the same four input torque points in step 3.2, and the calculation method remains unchanged to calculate the life T Lb12 , T Lbk2 , T Lbj2 , T Lbn2 . The four coordinate points (M Lb1 , T Lb12 ), (M Lbk , TLbk2 ), (M Lbj , T Lbj2 ), (M Lbn , T Lbn2 ), use Newton interpolation formula to get the relationship between torque and life;

[0084] Step 3.4: Repeat the above process four times, that is, take four more speeds, a total of five speeds, and calculate the life values. In this way, some data points can be finally obtained. The obtained data are shown in Table 5 (b in the table represents the speed ratio i L1 Parameters used below):

[0085] Table 5 Speed ​​ratio is i L1 When the steel belt ring runs stably under the corresponding input conditions until failure, the fatigue life

[0086] Input speed n Input torque M The fatigue life of this condition is stable. <![CDATA[n Lb1 ]]> <![CDATA[M Lb1 ]]> <![CDATA[T Lb11 ]]> <![CDATA[n Lb1 ]]> <![CDATA[M Lbk ]]> <![CDATA[T Lbk1 ]]> <![CDATA[n Lb1 ]]> <![CDATA[M Lbj ]]> <![CDATA[T Lbj1 ]]> <![CDATA[n Lb1 ]]> <![CDATA[M Lbn ]]> <![CDATA[T Lbn1 ]]> <![CDATA[n Lb2 ]]> <![CDATA[M Lb1 ]]> <![CDATA[T Lb12 ]]> <![CDATA[n Lb2 ]]> <![CDATA[M Lbk ]]> <![CDATA[T Lbk2 ]]> <![CDATA[n Lb2 ]]> <![CDATA[M Lbj ]]> <![CDATA[T Lbj2 ]]> <![CDATA[n Lb2 ]]> <![CDATA[M Lbn ]]> <![CDATA[T Lbn2 ]]> <![CDATA[n Lb3 ]]> <![CDATA[M Lb1 ]]> <![CDATA[T Lb13 ]]> <![CDATA[n Lb3 ]]> <![CDATA[M Lbk ]]> <![CDATA[T Lbk3 ]]> ……… ……… ………… <![CDATA[n Lb5 ]]> <![CDATA[M Lbn ]]> <![CDATA[T Lbn5 ]]>

[0087] Then, by using the plotting point diagram, we can get the relationship between input speed, input torque and life under a constant speed ratio.

[0088] Step 3.5: If Figure 3 The calculation process shown in the figure is to reselect a speed ratio i within the speed ratio range. L2 , re-establish the assembly model, perform transient dynamic analysis in ANSYS WORKBENCH, and after the simulation, use the same extraction method to extract the saddle surface load matrix B 2 According to the steps of calculating the life of the previous speed ratio, the relationship between the speed, torque and life under the corresponding speed ratio can be obtained. The calculated data is shown in Table 6 ((c in the table represents the life of the corresponding speed ratio i L2 Parameters used below):

[0089] Table 6 Speed ​​ratio is i L2 When the steel belt ring is in stable operation under the corresponding input conditions, the fatigue life

[0090] Input speed n Input torque M The fatigue life of this condition is stable. <![CDATA[n Lc1 ]]> <![CDATA[M Lc1 ]]> <![CDATA[T Lc11 ]]> <![CDATA[n Lc1 ]]> <![CDATA[M Lck ]]> <![CDATA[T Lck1 ]]> <![CDATA[n Lc1 ]]> <![CDATA[M Lcj ]]> <![CDATA[T Lcj1 ]]> <![CDATA[n Lc1 ]]> <![CDATA[M Lcn ]]> <![CDATA[T Lcn1 ]]> <![CDATA[n Lc2 ]]> <![CDATA[M Lc1 ]]> <![CDATA[T Lc12 ]]> ……… ……… ……… <![CDATA[n Lc5 ]]> <![CDATA[M Lcn ]]> <![CDATA[T Lcn5 ]]>

[0091] Similarly, by using the Newton interpolation formula, the fatigue life values ​​of a series of consecutive points can be obtained. L3 、i L4 、i L5 , re-establish the assembly, repeat the above work, and then draw a graph by plotting points, and finally you can get the theoretical relationship image of speed ratio-speed-torque-life. The Newton interpolation formula used in the above steps is as follows:

[0092] P(x)=f(x 0 )+f[x 0 ,x 1 ](xx0 )+f[x 0 ,…,x n ](xx 0 )…(xx n )

[0093]

[0094]

[0095] Where: P(x) is the interpolation function obtained using known data points; f[x i ,x j ] is the first-order difference quotient, x i ,x j is the horizontal coordinate of the known data point; f[x 0 ,x 1 ,…,x n ] is the n-order difference quotient value.

[0096] In this embodiment, after we have mastered the theoretical life image data, as long as we know the input torque and input speed of a transmission under a certain speed ratio, we can find out the theoretical fatigue life of the transmission under stable operation under this working condition through the established theoretical life image. 0 When the speed is n 0 , torque is M 0 , we can find out from the image that the life span at this time is T 0 .

[0097] In the specific implementation process, in step 4, considering the general working condition, the step of first using a statistical method to obtain the probability distribution of the speed ratio, input torque, and input speed under the general working condition includes:

[0098] Step 4.1: Under normal working conditions, collect the change of speed ratio over time during the entire cycle; extract the change of input torque over time and input speed over time under different speed ratios;

[0099] Step 4.2: Based on the collected data, convert the input torque time history diagram, input speed time history diagram, and speed ratio time history diagram into frequency histograms. The three histograms use input torque M, input speed n, and speed ratio i as horizontal coordinates, and divide the input torque M, input speed n, and speed ratio i into equal parts, such as 0-5, 5-10, etc. Then let the torque frequency H Mi Ratio to input torque interval ΔM Speed ​​frequency H ni Ratio to input speed interval Δn Speed ​​ratio frequency H ii Ratio to speed ratio interval Δi As the vertical axis, make a graph. Frequency H Mi , H ni , H ii It reflects the percentage of the number of times the value occurs within the target range set at each level, so the histogram reflects the proportion of the number of times the corresponding indicator occurs.

[0100]

[0101] Q Mi , Q ni , Q ii is the number of occurrences of each level parameter;

[0102] Step 4.3: According to the central limit theorem in statistics, when the amount of data is large enough, the distribution of any variable will approximately obey the normal distribution. For the working conditions of the transmission, the middle gear is undoubtedly the most used, and the low-speed gear and high-speed gear are both less frequently used gears. Similarly, the frequency of cars maintaining high and low speeds is generally low, and the accelerator is generally stepped on at a moderate position. Therefore, it is also determined that the speed ratio, input speed, and input torque variables obey the normal distribution. The normal distribution function is used to fit the histogram, and the relationship between the ordinate and the abscissa can be expressed by the normal distribution function:

[0103]

[0104]

[0105]

[0106] Where: x 1 , x 2 , x 3 is the value of a certain input torque, a certain input speed, and a certain speed ratio in the collected data; P 1 (x 1 ), P 2 (x 2 ), P 3 (x 3 ) are the probability value of using a certain input torque under a certain speed ratio, the probability value of using a certain speed, and the probability value of using a certain speed ratio; H Mi , H ni , H ii : torque frequency, speed frequency, speed ratio frequency; ΔM, Δn, Δi: torque interval, speed interval, speed ratio interval; M i 、n j 、i k : Input torque, input speed and speed ratio of each stage; The mean torque, The average speed, The average speed ratio, Standard deviation, σ x2 : standard deviation, σ x3 : standard deviation, e: base of natural logarithms.

[0107] In this embodiment, the mean and standard deviation are calculated according to the calculation formula of the mean and standard deviation of the above variables, and are substituted into the distribution function expression to obtain the probability distribution function, which is used to replace the histogram, and then the probability of using the specified speed ratio and the probability of using a certain input torque and input speed under the specified speed ratio are obtained when the car is in actual driving conditions. The obtained probability distribution is a mathematical function that characterizes the service condition of the metal belt at this time.

[0108] In a specific implementation, in step 5, the step of calculating the belt ring life at a constant speed ratio by combining the CVT theoretical life image with the probability of the input conditions includes:

[0109] Step 5.1: After obtaining the probability distribution of the above three variables in step 4, the service conditions of the metal strip under general working conditions are clarified. In order to make the calculation operation simple, practical operability strong and the settlement results maintain high accuracy, the continuous function is approximated by multiple small intervals for actual calculation. First, the median of the interval corresponding to the small interval divided when the three variables are counted is calculated, and then the range of this small interval is substituted into the distribution function to calculate the probability, and the median of this interval is used to represent the probability of the corresponding small interval. The finer the interval, the better the fitting effect. Each speed ratio value used in the table mentioned below (for example, i s1 ) and the input speed (e.g. n sb1 ), input torque (e.g. M sb1 ) are the median values ​​of the divided small intervals. First, the probability values ​​of input torque and input speed under different speed ratios are calculated respectively;

[0110] The specific data calculation results are shown in Table 7 (probability is represented by the symbol P; i s1 represents the speed ratio used when calculating the actual life):

[0111] Table 7 Speed ​​Ratio i s1 (b is used in the table to represent the probability value obtained under this speed ratio)

[0112] Speed ​​small interval median Probability Torque small range median Probability <![CDATA[n sb1 ]]> <![CDATA[P sbn1 ]]> <![CDATA[M sb1 ]]> <![CDATA[P sbM1 ]]> <![CDATA[n sb1 ]]> <![CDATA[P sbn1 ]]> <![CDATA[M sb2 ]]> <![CDATA[P sbM2 ]]> <![CDATA[n sb1 ]]> <![CDATA[P sbn1 ]]> <![CDATA[M sb3 ]]> <![CDATA[P sbM3 ]]> <![CDATA[n sb1 ]]> <![CDATA[P sbn1 ]]> <![CDATA[M sb4 ]]> <![CDATA[P sbM4 ]]> <![CDATA[n sb2 ]]> <![CDATA[P sbn2 ]]> <![CDATA[M sb1 ]]> <![CDATA[P sbM1 ]]> <![CDATA[n sb2 ]]> <![CDATA[P sbn2 ]]> <![CDATA[M sb2 ]]> <![CDATA[P sbM2 ]]> <![CDATA[n sb2 ]]> <![CDATA[P sbn2 ]]> <![CDATA[M sb3 ]]> <![CDATA[P sbM3 ]]> …… …… …… …… <![CDATA[n sb5 ]]> <![CDATA[P sbn5 ]]> <![CDATA[M sb4 ]]> <![CDATA[P sbM4 ]]>

[0113] Table 7 sbi ,M sbi for i s1 The median of the small interval divided under the speed ratio, where the following must be satisfied under this speed ratio:

[0114] P sbn1 +P sbn2+P sbn3 +P sbn4 +P sbn5 =1

[0115] P sbM1 +P sbM2 +P sbM3 +P sbM4 =1

[0116] When the speed ratio i s2 The specific data calculation results are shown in Table 8:

[0117] Table 8 Speed ​​Ratio i s2 (In the table, c refers to the probability value obtained under this speed ratio)

[0118] Speed ​​small interval median Probability Torque small range median Probability <![CDATA[n sc1 ]]> <![CDATA[P scn1 ]]> <![CDATA[M sc1 ]]> <![CDATA[P scM1 ]]> <![CDATA[n sc1 ]]> <![CDATA[P scn1 ]]> <![CDATA[M sc2 ]]> <![CDATA[P scM2 ]]> <![CDATA[n sc1 ]]> <![CDATA[P scn1 ]]> <![CDATA[M sc3 ]]> <![CDATA[P scM3 ]]> <![CDATA[n sc1 ]]> <![CDATA[P scn1 ]]> <![CDATA[M sc4 ]]> <![CDATA[P scM4 ]]> <![CDATA[n sc2 ]]> <![CDATA[P scn2 ]]> <![CDATA[M sc1 ]]> <![CDATA[P scM1 ]]> <![CDATA[n sc2 ]]> <![CDATA[P scn2 ]]> <![CDATA[M sc2 ]]> <![CDATA[P scM2 ]]> …… …… …… …… <![CDATA[n sc5 ]]> <![CDATA[P scn5 ]]> <![CDATA[M sc4 ]]> <![CDATA[P scM4 ]]>

[0119] Table 8 n sci ,M sci for i s2 The median of the small interval divided under the speed ratio, where the following must be satisfied under this speed ratio:

[0120] P scn1 +P scn2 +P scn3 +P scn4 +P scn5 =1

[0121] P scM1 +P scM2 +P scM3 +P scM4 =1

[0122] Similarly, we can find i s3 、i s4 、i s5 The probability value of input torque and input speed being used under the speed ratio;

[0123] Step 5.2: With the above probability data, the input torque and input speed of the median of the divided small intervals are looked up in the established theoretical life image of the steel belt ring to obtain the theoretical life value, and then multiplied by the probability of the corresponding median of the interval being used under this vehicle condition, the actual life value of the metal belt under a certain speed ratio can be calculated by using the following calculation formula:

[0124]

[0125] The number of accumulations in the formula depends on the number of divided cells; P sbni , P scni ...is the probability of a certain speed under a certain speed ratio; P sbMi , P scMi...is the probability of a certain torque at a certain speed ratio; T sb11 , T sb21 ...to find the fatigue life under a certain input torque and speed obtained by searching the theoretical image; Fatigue life of belt-type CVT at a constant speed ratio;

[0126] In this embodiment, in step 5.2, the specific operation is as follows: through the theoretical image established in step 3, the speed ratio is obtained by checking the image. s1 、i s2 、i s3 、i s4 、i s5 First, when the speed ratio is i s1 When the input speed and input torque are in the small interval median, the theoretical fatigue life of the belt ring is obtained by checking the chart as shown in Table 9.

[0127] Table 9 Speed ​​ratio is i s1 When the input speed and input torque are in a small interval, the fatigue life value of the belt ring is obtained by looking up the graph.

[0128]

[0129]

[0130] Combined with the input probability value of the corresponding small interval median obtained in step 5.1, we can calculate:

[0131]

[0132] The same calculation method as above is used to calculate Complete the fatigue life calculation of the steel belt ring under a constant speed ratio.

[0133] In the specific implementation process, in step 6, the actual life values ​​of the steel belt ring under multiple speed ratios obtained in step 5 are combined with the speed ratio probability distribution function to obtain the probability value of the corresponding speed ratio. The actual life of the belt ring under general working conditions is equal to the actual life of the corresponding speed ratio multiplied by the probability of the corresponding speed ratio and added together. The actual value calculation formula of the CVT steel belt ring life used is:

[0134]

[0135] Where: is the fatigue life of the belt CVT at each constant speed ratio; η 1 is the probability of using the corresponding constant speed ratio, and its size is calculated by the speed ratio distribution function; T is the fatigue life of the belt CVT under normal working conditions.

[0136] In this embodiment, in step 6, the specific operation is as follows: according to the fatigue life at five speed ratio points obtained in step 5, the probability value of the median of the speed ratio small interval is obtained in combination with the speed ratio distribution function, as shown in Table 10:

[0137] Table 10 Probability of speed ratio itself complying

[0138]

[0139]

[0140] The speed ratio probability satisfies

[0141] P 1 +P 2 +P 3 +P 4 +P 5 =1

[0142] Finally, the calculated life of the belt ring under the assumed working conditions is:

[0143]

[0144] The present invention calculates the fatigue life of a steel belt ring under high-speed conditions. Due to the particularity of the loading form and movement mode of the steel belt ring, there are many loading points on the metal steel belt at the same time, and due to the continuous rotation of the belt ring, the force application point is also constantly changing. Therefore, it is very difficult to use theory to calculate the fatigue life of the steel belt ring. This is also the first theoretical analysis method proposed for the fatigue life of the steel belt ring, which has a certain novelty. In previous studies, the fatigue life of steel belt rings is usually studied experimentally, but this is only limited to lower experimental requirements, and the calculated life is still the fatigue life under specified working conditions, which is not general. The present invention proposes a method for calculating the fatigue life of the belt ring when it works under general working conditions, which is more in line with actual conditions and can estimate the fatigue life of the steel belt ring as accurately as possible.

[0145] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for calculating fatigue life of steel belt ring of belt-type CVT under high speed conditions, characterized in that: The following steps are involved: Step 1: Perform transient dynamic analysis of belt-type CVT; Step 2: Use the equivalent method to extract the load spectrum of the steel belt ring micro-element segment during one cycle, and then calculate the fatigue life of the steel belt ring under this specified condition, including: Step 2.1: Extract the contact stress values ​​of all metal sheet saddle surfaces in the entire CVT from the transient dynamic analysis results, and regard the CVT steel belt ring as a belt ring microelement segment with the same number of metal sheets as the flexible connection. Take the belt ring microelement segment corresponding to the first metal sheet at the entrance of the driving wheel as the research object, and regard the next metal sheet rotating clockwise adjacent to it as the motion state of the first metal sheet at the next moment. After one cycle, arrange the metal sheet saddle surface load values ​​in order and regard them as the force change of the belt ring microelement segment during one cycle. Obtain the load spectrum of the belt ring microelement segment and record it as the saddle surface load matrix; Step 2.2: Divide the total time of one stable movement of the belt ring into a time series equal to the number of metal sheets, convert the load matrix of the saddle surface of the belt ring microelement into the relationship between time and stress, and obtain the time series load spectrum; Step 2.3: Use the rain flow counting method to convert the time series load spectrum into the stress load spectrum used for calculation, and obtain the actual number of cycles A under stress of different levels of amplitude i ; Step 2.4: According to the SN fatigue life curve of the material, the theoretical life number N of the steel belt ring corresponding to the stress of different levels of amplitude is obtained. i ; Step 2.5: According to Miner's linear cumulative damage theory, under stresses of different levels of amplitude, the sum of the damage degrees should be Thus, the life T of the belt ring under this working condition can be calculated, and the calculation formula is: Step 3: Consider the two situations of speed, torque change and speed ratio change under fixed speed ratio respectively, use the same life calculation method as the previous two steps and combine the data interpolation method to obtain the theoretical life image of CVT belt ring; Step 4: Considering the general working condition, firstly use the statistical method to obtain the probability distribution of the speed ratio, input torque and input speed under the general working condition; Step 5: Calculate the belt ring life at a constant speed ratio by combining the CVT theoretical life image with the probability of the input conditions; Step 6: Finally, the actual life of the belt ring under general working conditions is obtained by using the probability distribution of the life of the belt ring with different speed ratios and the speed ratio.

2. The method for calculating fatigue life of a belt-type CVT steel belt ring under high speed conditions according to claim 1 is characterized in that: For step 1, the three-dimensional model of the CVT assembly at a certain speed ratio is established using the Solid Works modeling software, and then imported into ANSYS for transient dynamic analysis of the CVT assembly.

3. The method for calculating fatigue life of a belt-type CVT steel belt ring under high speed conditions according to claim 1 is characterized in that: In step 3, the two situations of speed, torque change and speed ratio change under fixed speed ratio are considered respectively. The life calculation method in the previous step is used in combination with the data interpolation method to obtain the theoretical life image of the CVT belt ring. The steps include: Step 3.1: First, under a fixed speed ratio, determine the vehicle speed range under this speed ratio, reverse the transmission speed range, and then obtain the transmission input torque range based on the relationship between engine speed and torque; Step 3.2: Under the condition of constant speed ratio and constant speed, take the two end points of the torque range and select several representative input torques within the torque range. The calculation method remains unchanged, and the fatigue life of the steel belt ring under the corresponding input conditions is calculated respectively. Then, some data points are obtained, and the relationship image between torque and life is obtained by fitting using Newton interpolation formula; Step 3.3: Keep the speed ratio unchanged, change the speed once, select the same input torque points as in step 3.2, and use the same calculation method to calculate the fatigue life of the steel belt ring under the corresponding input conditions. Use the Newton interpolation formula to fit the obtained set of data points to obtain the relationship diagram between torque and life; Step 3.4: Repeat the above process several times to obtain some data points. Use these data points to plot the relationship between input speed, input torque and life under a constant speed ratio; Step 3.5: Consider different speed ratios again, reselect a speed ratio within the speed ratio range, rebuild the assembly model, and perform transient dynamic analysis in ANSYS WORKBENCH. After the simulation, use the same extraction method to extract the saddle surface load matrix, and calculate the speed-torque-life relationship graph under the corresponding speed ratio according to the above steps. Similarly, use the Newton interpolation formula to obtain the fatigue life values ​​of a series of continuous points, change the speed ratio several times, rebuild the assembly, repeat the above work, and finally obtain the theoretical relationship image of speed ratio-speed-torque-life by tracing points.

4. The method for calculating fatigue life of a belt-type CVT steel belt ring under high speed conditions according to claim 1 is characterized in that: In step 4, considering the general working condition, the steps of first using a statistical method to obtain the probability distribution of the speed ratio, input torque, and input speed under the general working condition include: Step 4.1: Under normal working conditions, collect the change of speed ratio over time in a random cycle, extract the change of input torque over time under different speed ratios, and the change of input speed over time; Step 4.2: Based on the collected data, convert the input torque time history diagram, input speed time history diagram, and speed ratio time history diagram into a frequency histogram; Step 4.3: According to the central limit theorem in statistics, when the amount of data is large enough, the distribution of any variable will approximately obey the normal distribution. For the working conditions of the transmission, the middle gear is undoubtedly the most used, and the low-speed gear and high-speed gear are both less frequently used gears. Similarly, the frequency of cars maintaining high and low speeds is generally low, and the accelerator is generally pressed at a moderate position. Therefore, it is also determined that the speed ratio, input speed, and input torque variables obey the normal distribution. Use the normal distribution function to fit the histogram, first calculate the mean and standard deviation of the three normal distribution function variables, and then get the normal probability distribution function expression, and then find the probability of using a specified speed ratio in the actual driving condition of the car and the probability of using a certain input torque and input speed under the specified speed ratio. The obtained probability distribution is understood as a mathematical function that characterizes the service condition of the metal belt at this time.

5. The method for calculating fatigue life of a belt-type CVT steel belt ring under high speed conditions according to claim 1 is characterized in that: In step 5, the steps of calculating the belt ring life at a constant speed ratio by combining the CVT theoretical life image with the probability of the input conditions include: Step 5.1: After the probability distribution of the three variables is obtained in step 4, the service conditions of the metal strip under general working conditions are clarified. In order to make the calculation operation simple, practical operability strong and the settlement result maintain high accuracy, the continuous function is approximated by multiple small intervals for actual calculation. First, the median of the interval corresponding to the small interval divided when the three variables are counted is calculated, and then the range of this small interval is substituted into the distribution function to calculate the probability. The median of this small interval is used to represent the probability of the corresponding small interval. The finer the interval, the better the fitting effect; Step 5.2: After obtaining the above probability data, the input torque and input speed corresponding to the median of the divided small intervals are used in the theoretical life image of the steel belt ring established in step 3 to obtain the theoretical life value, and then multiplied by the probability of the corresponding median of the interval being used under this service condition, to calculate the actual life value of the metal belt at a certain speed ratio.

6. The method for calculating fatigue life of a steel belt ring of a belt-type CVT under high speed conditions according to claim 1 is characterized in that: For step 6, the actual life of the belt ring under general working conditions is finally obtained by using the probability distribution of the life of the belt ring with different speed ratios and the speed ratio. The calculation formula used is: Where: The fatigue life of the belt CVT at each constant speed ratio; η1 is the probability of using the corresponding constant speed ratio; T is the fatigue life of the belt CVT under normal working conditions.

7. The method for calculating fatigue life of a steel belt ring of a belt-type CVT under high speed conditions according to claim 4 is characterized in that: In step 4, the frequency histogram is established as follows: The three histograms are respectively based on input torque M, input speed n, and speed ratio i as horizontal coordinates, and torque frequency H as horizontal coordinates. Mi Ratio to input torque interval ΔM Speed ​​frequency H ni Ratio to input speed interval Δn Speed ​​ratio frequency H ii Ratio to speed ratio interval Δi is the vertical axis, frequency H Mi , H ni , H ii It reflects the percentage of the target value occurrence in each level of the interval, so the histogram reflects the proportion of the number of occurrences of the corresponding indicator; Q Mi , Q ni , Q ii is the number of occurrences of each level parameter.

8. The method for calculating fatigue life of a steel belt ring of a belt-type CVT under high speed conditions according to claim 4 is characterized in that: In step 4, the normal distribution function used to fit the frequency histogram is obtained in the following way: The relationship between the ordinate and the abscissa of the histogram is expressed by the normal distribution function: Where: x1, x2, x3 are input torque, input speed, and speed ratio values ​​in the collected data; P1(x1), P2(x2), and P3(x3) are the probability values ​​of using a certain input torque, a certain speed, and a certain speed ratio under a certain speed ratio, respectively; H Mi , H ni , H ii : torque frequency, speed frequency, speed ratio frequency; ΔM, Δn, Δi: torque interval, speed interval, speed ratio interval; M i 、n j 、i k : Input torque, input speed and speed ratio of each stage; The mean torque, The average speed, The average speed ratio, σ x1 : standard deviation, σ x2 : standard deviation, σ x3 : standard deviation, e: base of natural logarithms.

9. The method for calculating fatigue life of a belt-type CVT steel belt ring under high speed conditions according to claim 5, characterized in that: In step 5, the fatigue life of the steel belt ring under a constant speed ratio is calculated by the following formula: Where: i is the probability that the corresponding input torque and speed conditions are used simultaneously, which is the product of the two probabilities; T i To find the fatigue life of the steel belt ring under the corresponding input torque and speed obtained by searching the theoretical image; It is the fatigue life of the steel belt ring of the belt-type CVT at a certain constant speed ratio.

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