Tractor load spectrum resampling method based on extreme load retention

Abstract

The invention provides a tractor load spectrum resampling method based on extreme load retention, and belongs to the technical field of tractor load spectrum resampling. The technical problem to be solved is to provide the improvement of the tractor load spectrum resampling method based on extreme load retention. According to the technical scheme, the method comprises the steps that a load spectrum needing weight reduction sampling is input, the sampling time and the corresponding sampling frequency are determined, and sampling points of the load spectrum are input; determining a loading frequency of a target load spectrum, calculating a resampling proportion, and determining an expression of an input load spectrum resampling process; calculating an average value of the input load spectrum, sequentially extracting load data in the input load spectrum as a candidate sequence according to a resampling proportion, finding an extreme load in the candidate sequence, and repeating the steps until the load data in the input load spectrum is extracted completely; the method is applied to tractor load spectrum resampling.

Description

Technical Field

[0001] The invention provides a tractor load spectrum resampling method based on extreme value load retention, belonging to the technical field of tractor load spectrum resampling. Background Art

[0002] Tractors are the main power machinery used in agricultural production. The reliability level of the whole machine or its parts during use will directly affect the safety and efficiency of agricultural production. At present, the reliability verification of tractors mainly includes two methods: field tests and bench tests. The former requires testers to track various operating processes of the tractor for up to 1,500 hours, which greatly consumes manpower and material resources and has low test efficiency. The bench test is stable and controllable, and is not affected by natural conditions. It is the main way to conduct tractor reliability tests at this stage.

[0003] The reliability test of the tractor bench is mainly based on the measured load spectrum. The measured load spectrum represents the actual load time history of the tractor during field operation, including the load changes and fatigue damage actually borne by the components. The currently used load spectrum downsampling technology cannot reduce the load spectrum loading frequency while retaining the consistency of the original load damage. In order to make the compiled load spectrum able to comprehensively and accurately characterize the field operation load characteristics, a higher sampling frequency (>1000Hz) is usually used to collect the measured load, which will result in a high loading frequency of the compiled load spectrum. If the high-frequency load spectrum is directly used for the bench reliability test, the bench loading equipment also needs to have a sufficiently high dynamic response characteristic, otherwise it will not be able to accurately reproduce the actual field conditions, which will lead to errors in the test results and the tractor fatigue reliability test effect is not in line with reality.

[0004] At present, most of the technical solutions for using load spectrum for bench tests do not mention the relationship between the load spectrum frequency and the dynamic response characteristics of the bench equipment. That is, most bench tests do not load according to the frequency required by the load spectrum, but only conduct research on loading control methods to achieve waveform reproduction of the load spectrum. However, from the current technical point of view, there are two main solutions to solve the mismatch between the load spectrum frequency and the bench loading capacity: one is to improve the bench loading equipment and improve its dynamic response characteristics to match the loading frequency required by the load spectrum; the other is to resample the load signal to reduce the load frequency;

[0005] For method 1, in order to achieve high dynamic characteristics, a higher performance loading device is required. The high-frequency load spectrum has very high requirements on the dynamic response characteristics of the test bench, which will lead to the high cost of the test bench, greatly increase the research and development cost of the system, and cause a waste of economic resources. In addition, it is sometimes difficult to achieve the reproduction of ultra-high frequency load spectrum at the technical level.

[0006] For method 2, the conventional resampling method only extracts the load at a predetermined interval. The commonly used tractor loading test bench cannot realize dynamic loading based on the high-frequency load spectrum, which will cause the extreme loads in the load to be missed, making it difficult to reproduce the actual field operation conditions. In the application of the load spectrum, its damage is the focus of attention, and the extreme load is the main manifestation of load damage. If it is ignored in the resampling process, it will cause the loss of damage information, and the damage characteristics of the load spectrum cannot be guaranteed, resulting in errors in the reliability load spectrum loading test results and poor test results. Summary of the invention

[0007] In order to overcome the deficiencies in the prior art, the present invention aims to solve the technical problem of providing an improved tractor load spectrum resampling method based on extreme load retention.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a tractor load spectrum resampling method based on extreme load retention, comprising the following sampling steps:

[0009] Step 1: Input the load spectrum x(n1T1) to be downsampled, the sampling time is T1, and the corresponding sampling frequency is F1=1 / T1, where n1 is the sampling point of the input load spectrum;

[0010] Step 2: Determine the target load spectrum y(n2T2), whose sampling time is T2 and the corresponding loading frequency is F2, where n2 is the sampling point of the target load spectrum, and calculate the resampling ratio M. The calculation formula is:

[0011]

[0012] It can be obtained that T2 = MT1. According to the resampling theorem, the expression for the resampling process of the input load spectrum x(n1T1) is:

[0013] y(n2T2)=λ(n1T1)·x(n1T1);

[0014] Where λ(n1T1) is the resampling sequence, which satisfies:

[0015]

[0016] Step 3: Calculate the average value A of the input load spectrum using the following formula:

[0017]

[0018] Where n is the total number of sampling points; ∑x(n1T1) is the sum of all sampling points of the input load spectrum x(n1T1);

[0019] Step 4: According to the resampling ratio M, sequentially extract the M load data x((n1-M)T1), x((n1-M+1)T1), …, x(n1T1) in the input load spectrum x(n1T1) as candidate sequences, where n1=Mn2 is the sequence number and n2 is the sampling point of the target load spectrum λ(n1T1);

[0020] Step 5: Find the extreme value load in the candidate sequence, the expression is:

[0021]

[0022] Where k = n1-M, n1-M+1,…, n1;

[0023] Step 6: Repeat steps 4 and 5 until all load data in the input load spectrum are extracted;

[0024] Step 7: The final value y(n2T2) is the resampled load spectrum sequence.

[0025] The beneficial effects of the present invention compared to the prior art are as follows: when the reliability test of the tractor is carried out, the present invention makes the dynamic response characteristics of the bench loading equipment match the loading frequency of the load spectrum. There is no need to improve or reduce the dynamic response characteristics of the bench loading equipment. Instead, on the basis of retaining the damage consistency of the load spectrum, the loading frequency of the load spectrum is reduced, thereby matching the dynamic response characteristics of the bench loading equipment and realizing dynamic loading and reproduction of the load spectrum. On the basis of ensuring the reliability test effect, the upgrade and modification of the bench loading equipment is avoided, the utilization rate of the bench loading test is improved, and the reliability test and evaluation of the tractor are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below in conjunction with the accompanying drawings:

[0027] Figure 1 is a flow chart of the steps of resampling of the present invention;

[0028] Figure 2 A schematic diagram of a load spectrum input in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of load resampling in an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of the load spectrum after resampling in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention specifically provides a tractor load spectrum resampling method based on extreme load retention, which is mainly used for tractor dynamic loading test; in order to enable the compiled load spectrum to comprehensively and accurately characterize the field operation load characteristics, a higher sampling frequency is usually used to collect the measured load, which results in the frequency of the compiled load spectrum being also very high; if the high-frequency load spectrum is directly used for bench test loading, then the bench loading equipment is required to have sufficiently high dynamic response characteristics, otherwise it will not be able to accurately reproduce the actual working conditions in the field, which will lead to errors in the test results. In response to the above problems, the present invention proposes a torque load spectrum loading method for a tractor power output shaft PTO based on extreme load retention resampling, which can balance the contradiction between the load spectrum data frequency and the dynamic response characteristics of the loading platform, and provide a reference for the tractor power output shaft PTO bench test.

[0032] like Figure 1 As shown, the load spectrum resampling method for retaining extreme loads adopted by the present invention has the following specific sampling operation steps:

[0033] Step 1: Input the load spectrum x(n1T1) to be downsampled, the sampling time is T1, and the corresponding sampling frequency is F1=1 / T1, where n1 is the sampling point of the input load spectrum;

[0034] Step 2: Determine the target load spectrum y(n2T2), whose sampling time is T2 and the corresponding loading frequency is F2, where n2 is the sampling point of the target load spectrum, and calculate the resampling ratio M. The calculation formula is:

[0035]

[0036] It can be obtained that T2 = MT1. According to the resampling theorem, the expression for the resampling process of the input load spectrum x(n1T1) is:

[0037] y(n2T2)=λ(n1T1)·x(n1T1);

[0038] Where λ(n1T1) is the resampling sequence, which satisfies:

[0039]

[0040] Step 3: Calculate the average value A of the input load spectrum using the following formula:

[0041]

[0042] Where n is the total number of sampling points; ∑x(n1T1) is the sum of all sampling points of the input load spectrum x(n1T1);

[0043] Step 4: According to the resampling ratio M, sequentially extract the M load data x((n1-M)T1), x((n1-M+1)T1), …, x(n1T1) in the input load spectrum x(n1T1) as candidate sequences, where n1=Mn2 is the sequence number and n2 is the sampling point of the target load spectrum λ(n1T1);

[0044] Step 5: Find the extreme value load in the candidate sequence, the expression is:

[0045]

[0046] Where k = n1-M, n1-M+1,…, n1;

[0047] Step 6: Repeat steps 4 and 5 until all load data in the input load spectrum are extracted;

[0048] Step 7: The final value y(n2T2) is the resampled load spectrum sequence.

[0049] In the embodiment of the present invention, the down-sampling of a tractor PTO torque reliability load spectrum is taken as an example to illustrate the implementation effect of the present invention.

[0050] The PTO torque load spectrum obtained by time domain extrapolation before resampling is as follows: Figure 2 As shown, its loading frequency is 62.93Hz; resampling ratios of 2, 3, 4, and 5 are performed on it respectively. The resampling ratio of 3 is shown as follows Figure 3 The resampling results are shown in Figure 4 As shown in the figure, compared with the load points (green points) obtained by traditional resampling, the extreme load resampling method can extract the extreme loads in the resampling process and retain the damage characteristics in the original signal.

[0051] Then the damage retention ratio after resampling is calculated to verify its feasibility, and the results are shown in Table 1;

[0052]

[0053] Table 1 Damage retention ratio of load spectrum after resampling

[0054] According to the data in Table 1, if traditional resampling is used, the damage retention ratio is seriously reduced, while the sampling method proposed in the present invention can effectively retain the fatigue damage. It is generally believed that when the damage retention is above 90%, its fatigue characteristics can be considered consistent.

[0055] The present invention provides a tractor load spectrum resampling method based on extreme value load retention. The key lies in changing the traditional resampling method of sampling at fixed intervals, and instead extracting extreme values ​​(maximum values ​​or minimum values) within a certain interval as new resampling points. The extreme value load is a concentrated reflection of fatigue damage in the load spectrum. Therefore, during the resampling process, the fatigue damage of the load spectrum can be effectively retained by retaining the extreme value load, thereby ensuring that the resampled load spectrum is consistent with the fatigue damage characteristics of components.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tractor load spectrum resampling method based on extreme load retention, characterized in that: The sampling steps include the following: Step 1: Input the load spectrum x(n1T1) to be downsampled, the sampling time is T1, and the corresponding sampling frequency is F1=1 / T1, where n1 is the sampling point of the input load spectrum; Step 2: Determine the target load spectrum y(n2T2), whose sampling time is T2 and the corresponding loading frequency is F2, where n2 is the sampling point of the target load spectrum, and calculate the resampling ratio M. The calculation formula is: It can be obtained that T2 = MT1. According to the resampling theorem, the expression for the resampling process of the input load spectrum x(n1T1) is: y(n2T2)=λ(n1T1)·x(n1T1); Where λ(n1T1) is the resampling sequence, which satisfies: Step 3: Calculate the average value A of the input load spectrum using the following formula: Where n is the total number of sampling points; x(n1T1) is the sum of all sampling points of the input load spectrum x(n1T1); Step 4: According to the resampling ratio M, extract the M load data x((n1-M)T1), x((n1-M+1)T1), …, x(n1T1) in the input load spectrum x(n1T1) as the candidate sequence, where n1=Mn2 is the sequence number and n2 is the sampling point of the target load spectrum λ(n1T1); Step 5: Find the extreme value load in the candidate sequence, the expression is: Where k = n1-M, n1-M+1,…, n1; Step 6: Repeat steps 4 and 5 until all load data in the input load spectrum are extracted; Step 7: The final value y(n2T2) is the resampled load spectrum sequence.

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