CN107291967B - Hydraulic pump performance degradation dual-stress index model modeling method - Google Patents
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Abstract
The invention discloses a hydraulic pump performance degradation dual-stress index model modeling method which is mainly used for fault prediction and development of on-demand maintenance of a missile weapon equipment hydraulic system. A double-stress index model is provided as a hydraulic pump performance degradation theoretical model, an acceleration coefficient is set according to the characteristics of an accelerated degradation test, and a determination method of key parameters of the model is provided; and by designing accelerated degradation tests under different stresses, estimating the parameter values of the model by utilizing the distribution obeyed by the volumetric efficiency at each moment, respectively establishing a basic model of the performance degradation of the hydraulic pump and a performance degradation model under the accelerated test condition, improving the prediction capability of the model on the residual life of the hydraulic pump under different working conditions, improving the applicability of the model, relatively objectively reflecting the performance degradation rule of the hydraulic pump, and having important significance for developing maintenance according to situations.
Description
Technical Field
The invention relates to a performance degradation modeling technology in the technical field of fault prediction of typical hydraulic pump equipment.
Background
The hydraulic pump is one of the key components of the hydraulic system, and the performance of the hydraulic pump directly affects the reliability of the whole hydraulic system. The degradation of the performance of a hydraulic pump is a very complex process due to the compressibility of the fluid, the fluid-solid coupling of the pump source and the servo system, and the large inherent mechanical vibrations that it has. An effective performance degradation model is established, potential early failure behaviors can be captured as early as possible, and the state evolution trend and the approximate failure time of the hydraulic pump are estimated, so that a proper preventive maintenance strategy is adopted, and accidents can be effectively avoided. Therefore, the construction of the hydraulic pump performance degradation model has great significance for the development of hydraulic pump fault prediction technology and the implementation of state-based maintenance.
The performance degradation modeling provides a method for representing the system degradation evolution process as a mathematical function, and a certain performance parameter is used as a reference to evaluate the failure time point and the residual service life of the system. At present, most performance degradation modeling is based on the traditional reliability theory, failure time is used as an analysis object, failure data of a tested system is obtained through a large number of tests, and then a statistical distribution model is deduced. However, the modeling method based on statistical distribution needs to obtain the full life cycle data of the performance index in each test, which consumes a lot of time, manpower and material resources, and the established model has a large deviation from the actual one, so that it is difficult to effectively characterize the general rule of performance degradation.
The inside of the hydraulic pump is provided with a plurality of typical friction pairs, mainly comprising a slipper boot cap and a plunger ball head, a slipper and a swash plate, a port plate and a swash plate and the like. In the hydraulic pump working process, because the effect of internal stress, can produce wearing and tearing of different degrees because of the friction between the friction pair, lead to the increase of moment coefficient between the friction pair component, the oil film attenuation, the fit clearance grow, and then cause the leakage of hydraulic oil, the performance of hydraulic pump descends. Therefore, the wear of the key friction pair is the main reason for accelerating the performance degradation of the pump and limiting the service life of the pump, and the most critical factors influencing the wear are the pressure and the rotating speed. Therefore, a method of accelerated degradation test can be adopted, and a proper performance degradation model is established by utilizing the relation between the sample standard deviation of the product performance degradation quantity distribution and the time and the stress.
In summary, the main content of the present invention is to establish a hydraulic pump performance degradation model more conforming to the general rule by using an accelerated degradation test method.
Disclosure of Invention
The invention aims to provide an effective hydraulic pump performance degradation modeling method by designing a dual-stress accelerated degradation test and acquiring data of performance indexes. The method can avoid the problems of long time consumption and large error of the traditional statistical distribution modeling method, is easy to realize, and can better reflect the general rule of performance degradation.
According to the performance degradation principle of the hydraulic pump and the early-stage related test conclusion, the performance degradation model of the hydraulic pump is mainly related to the initial value of the performance index, the pressure and the rotating speed and is approximately an exponential function of time. Volumetric efficiency was chosen as a performance parameter. The basic model of hydraulic pump performance degradation can be expressed as:
η＝η0-αv0P0eβt (1)
wherein eta is the volumetric efficiency, eta0Is the initial value of the volume efficiency; v. of0At a rated speed, P0Is a rated pressure; alpha and beta are parameters. Under the condition of an accelerated degradation test, the performance degradation model of the hydraulic pump has some changes, and the dual-stress index degradation model is as follows:
wherein v is the rotation speed of the accelerated degradation test, P is the pressure of the accelerated degradation test, alpha, beta, eta0K is an acceleration coefficient, as in the case of the formula (1).
The basic schematic block diagram of the present invention is shown in fig. 1. Let the number of extracted samples be n, and respectively perform different accelerated test conditions (v > v)0，P＞P0) According to vP/v0P0Carrying out accelerated degradation test in sequence from big to small, wherein the monitoring quantity is volume efficiency, the measuring time is 0, and t is1，...，tmAnd recording the corresponding numerical value. In the first accelerated degradation test, i.e. vP/v0P0Performing normal distribution hypothesis test on the volume efficiency values of n samples at the time of 0 under the highest condition, and obtaining the mean value and standard deviation obeying normal distribution, namely eta0The value of (d); for each accelerated test condition, 0-tmCarrying out normal distribution hypothesis test on the volume efficiency numerical values of all samples at each measurement moment, and estimating the mean value and the standard deviation of normal distribution obeyed by the volume efficiency at each moment; respectively fitting the mean value of normal distribution at each moment under each accelerated degradation test condition by using a dual-stress exponential degradation model (formula (2)) to obtain a performance degradation model under the accelerated test condition, further estimating alpha and beta parameter values, wherein the standard deviation can be the mean value of the standard deviation of the normal distribution at each moment; the alpha and beta parameter values obtained under all accelerated test conditions are averaged to obtain the estimated values of alpha and beta
And
finally utilize
And
establishingA basic model of performance degradation and a model of performance degradation under accelerated degradation conditions.
The invention is characterized in that:
(1) the modeling method is easy to realize
The method based on the accelerated degradation test only needs to collect volumetric efficiency data for a period of time under several different stress conditions, avoids the dependence of the traditional modeling method based on statistical distribution on the life data, greatly reduces the test time and is easy to realize;
(2) the model has more applicability
The method is based on the dual-stress index degradation model, utilizes the accelerated degradation test distribution to establish a basic hydraulic pump performance degradation model and a performance degradation model under the accelerated degradation condition, can be suitable for hydraulic pumps of various models, expands the application conditions of the model and ensures that the model has higher applicability;
(3) higher prediction accuracy
The method is based on the consideration of the working principle and the performance degradation rule of the hydraulic pump, adopts the dual-stress index degradation model as the performance degradation model, and fits the model by utilizing the distribution condition of volume efficiency average values under different stress conditions, so that the diversity of the sample is effectively improved, the model is closer to the actual degradation process, and the prediction precision of the model is improved.
Drawings
FIG. 1 is a functional block diagram of the present invention;
FIG. 2 is a view of an accelerated degradation test rig of the present invention;
FIG. 3 is a view of the test hydraulic pump of the present invention;
FIG. 4 is an accelerated degradation test operator interface view of the present invention;
FIG. 5 is a degradation plot fitted to the basic model of performance degradation of the present invention.
Detailed Description
The invention is further described with reference to the following figures and examples.
Fig. 2 shows an accelerated degradation test bench for a hydraulic pump. The model of the driving motor is YPT-280M-2, and the rotating speed can be set to be 0-3000 r/min. The model of the hydraulic pump is L10VSO28DFR (shown in figure 3), the rated pressure is 26Mpa, the rated rotating speed is 2200r/min, and the volumetric efficiency eta is judged to be less than or equal to 80% after failure. According to the relevant data provided by the manufacturer, the acceleration coefficient of the hydraulic pump under the accelerated degradation test condition is as follows:
randomly extracting 10 hydraulic pumps from 15L 10VSO28DFR hydraulic pumps in the same brand new batch as test samples, wherein v is 2860r/min, and P is 30 MPa; v is 2800r/min, P is 29.5 MPa; the accelerated degradation test is carried out under three double-stress accelerated test conditions of v 2700r/min and P28 MPa, and the operation interface is shown in figure 4. The volumetric efficiency values were monitored at 10 hour acquisition intervals and at 100 hour test time.
Under the acceleration test conditions of v 2860r/min and P30 MPa, the volume efficiency monitoring values of 10 hydraulic pumps at the time of 0 are subjected to normal distribution hypothesis test, and the probability is 0.9921 under the significance level of 0.05, so that the volume efficiency monitoring values are subjected to normal distribution with the mean value of 0.9682 and the standard deviation of 0.0042, and eta is subjected to normal distribution with the standard deviation of 0.96820＝0.9682；
Carrying out normal distribution hypothesis test on the volume efficiency monitoring values of 10 hydraulic pumps 10h-100h under the acceleration test conditions of v-2860 r/min and P-30 MPa, and fitting the average value of 0h-100h normal distribution by using a dual-stress index accelerated degradation model (formula (2)) to obtain a hydraulic pump performance degradation model under the conditions of v-2860 r/min and P-30 MPa, wherein the hydraulic pump performance degradation model is as follows:
y＝0.9682-0.0001632*e0.0159t (4)
obtaining an acceleration coefficient k according to the formula (2)1Estimating the values of model parameters alpha and beta under the conditions that v is 2800r/min and P is 29.5MPa, 2.5;
for the second accelerated degradation test condition (v 2800r/min, P29.5 MPa), as in the previous step, it is noted that: the dual-stress exponential accelerated degradation model (equation (2)) used for fitting needs to be added at the independent variable tInitial value t0The expression is:
wherein k is2The acceleration factor under the second accelerated degradation condition. The performance degradation model under the conditions that v is 2800r/min and P is 29.5MPa is obtained as follows:
y＝0.9682-0.0001718*e0.0138(t+113.64) (6)
for the third accelerated degradation test condition (v is 2700r/min, P is 28MPa), fitting the initial value t in the adopted dual-stress index accelerated degradation model0Two approximate conversions are needed, and the expression is as follows:
wherein k is3The acceleration factor under the second accelerated degradation condition. The performance degradation model under the conditions that v is 2800r/min and P is 29.5MPa is obtained as follows:
y＝0.9682-0.0002202*e0.0092(t+293.75) (8)
and sixthly, respectively calculating the estimated values of alpha and beta under three accelerated degradation test conditions to obtain a basic hydraulic pump performance degradation model corresponding to the formula (1):
the performance degradation model under the accelerated degradation condition corresponding to the formula (2) is obtained as follows:
according to the obtained basic model of the performance degradation of the hydraulic pump, a performance degradation curve of the L10VSO28DFR type hydraulic pump under the rated condition is fitted, as shown in FIG. 5, the predicted total life time (eta is more than 80%) is 1656.1h, the theoretical total life time is 1700h, and the relative error is 2.58%.
Claims (5)
1. The hydraulic pump performance degradation dual-stress index model modeling method is characterized by comprising the following steps:
respectively carrying out accelerated degradation tests on at least one test sample under different accelerated test conditions; monitoring the volumetric efficiency of each test sample under different accelerated test conditions; the acceleration test conditions comprise the rotating speed of the hydraulic pump and the pressure of the hydraulic pump;
calculating corresponding acceleration coefficients under various acceleration test conditions;
establishing a dual stress index degradation model and a degradation basic model;
calculating key parameters of the model according to the volumetric efficiency and the acceleration coefficient of each test sample under different acceleration test conditions; the model key parameters comprise a volume efficiency initial value, alpha and beta;
substituting the model key parameters into the degradation basic model to obtain a performance degradation basic model of the hydraulic pump;
substituting the model key parameters and the acceleration coefficients into the dual stress index degradation model to obtain a hydraulic pump performance degradation model under an accelerated degradation test condition;
the dual stress index degradation model includes:
wherein v is the rotation speed of the hydraulic pump, P is the pressure of the hydraulic pump, k is the acceleration coefficient, v0The rated speed is P0 is rated pressure; alpha and beta are parameters;
the degradation base model includes:
η＝η0-αv0P0eβt
wherein eta is the volumetric efficiency, eta0Is the initial value of the volume efficiency; v. of0At a rated speed, P0Is a rated pressure; alpha and beta are parameters.
2. The modeling method of the hydraulic pump performance degradation dual stress index model according to claim 1, wherein the calculating the corresponding acceleration coefficient under various acceleration test conditions comprises:
and (3) calculating:
obtaining corresponding acceleration coefficients under various acceleration test conditions;
wherein k represents an acceleration coefficient, v represents a hydraulic pump rotation speed, p represents a hydraulic pump pressure, v represents0Indicating rated speed, p0Indicating the nominal pressure.
3. The hydraulic pump performance degradation dual stress index model modeling method of claim 1, wherein the calculating model key parameters according to volumetric efficiency and acceleration coefficient of each test sample under different acceleration test conditions comprises:
carrying out normal distribution hypothesis test on the corresponding volumetric efficiency of each test sample under the first accelerated test condition at each moment, and estimating the mean value and standard deviation of overall distribution obeyed by the volumetric efficiency at each moment; obtaining a volume efficiency initial value corresponding to the first acceleration test condition; the first accelerated test condition is any accelerated test condition;
and calculating alpha and beta corresponding to the first acceleration test condition according to the dual stress index degradation model, the acceleration coefficient corresponding to the first acceleration test condition and the initial value of the volume efficiency.
4. The hydraulic pump performance degradation dual-stress index model modeling method according to claim 1, wherein the step of substituting the model key parameters into the degradation basic model to obtain the hydraulic pump performance degradation basic model comprises the steps of:
averaging alpha under each accelerated test condition to obtain an alpha estimation value;
averaging beta under each accelerated test condition to obtain a beta estimated value;
and substituting the initial value of the volumetric efficiency, the alpha estimated value and the beta estimated value into the basic degradation model to obtain the basic degradation model of the performance of the hydraulic pump.
5. The hydraulic pump performance degradation dual-stress index model modeling method according to claim 1, wherein the step of substituting the model key parameters and the acceleration coefficients into the dual-stress index degradation model to obtain the hydraulic pump performance degradation model under an accelerated degradation test condition comprises the steps of:
averaging alpha under each accelerated test condition to obtain an alpha estimation value;
averaging beta under each accelerated test condition to obtain a beta estimated value;
and substituting the initial value of the volumetric efficiency, the acceleration coefficient, the alpha estimated value and the beta estimated value into the dual-stress index degradation model to obtain a hydraulic pump performance degradation model under the accelerated degradation test condition.
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| Accelerated testing in hydraulic component operational life test;Congmin Niu;《Proceedings of the JFPS international symposium on fluid power》;20020131;第5卷(第1期);125-130 * |
| 基于性能退化数据的航空液压泵可靠性分析;袁亚芹;《中国优秀硕士学位论文全文数据库工程科技Ⅱ辑》;20100115;C031-3 * |
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