CN106777661B - Method for determining acceleration factor interval of diesel engine electric control oil injector based on life theoretical calculation - Google Patents
Method for determining acceleration factor interval of diesel engine electric control oil injector based on life theoretical calculation Download PDFInfo
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Abstract
The invention provides a method for determining an acceleration factor interval of an electric control oil injector of a diesel engine based on life theoretical calculation, which comprises the following steps: and step one, analyzing a mechanism, and determining loss-type failure mechanisms and sensitive stress of all the lowest appointed hierarchical units of the diesel engine electric fuel injector in the whole life cycle. And step two, weak link determination. And step three, analyzing the acceleration of the failure mechanism. And step four, calculating damage. And step five, carrying out equivalent analysis on the load spectrum. And step six, determining an acceleration test load spectrum. And seventhly, determining a unit acceleration factor interval. And step eight, determining a product comprehensive acceleration factor interval. The method is based on the service life calculation model, provides a solution for determining the acceleration factor interval of the diesel engine electric control fuel injector considering the uncertainty influence of model parameters and the synergistic effect of a multi-stress multi-failure mechanism, and provides a method support for the reliability verification of products with long service life indexes.
Description
Technical Field
The invention belongs to the field of accelerated life test design, and particularly relates to a method for determining an acceleration factor interval of an electrically controlled diesel injector based on life theoretical calculation.
Background
The electric control oil injector of the diesel engine is the most key and complex part in a common rail type fuel oil system, and the electric control oil injector of the diesel engine is used for injecting fuel oil in a high-pressure oil rail into a combustion chamber of the diesel engine at the best oil injection timing, oil injection quantity and oil injection rate by controlling the opening and closing of an electromagnetic valve according to a control signal sent by an ECU. Each set of diesel engine electric control oil injector consists of seven subsystems, namely a needle valve coupling part, a control plunger piston component, a ball valve component, an armature component, a coil component, an oil injector body component and an oil inlet pipe connecting component.
The diesel engine electric control oil injector belongs to a product with long service life indexes, and due to high price, the test time is difficult to reduce by increasing the sample volume, and the test time can only be reduced by improving the test stress level, so that the cost is reduced; however, the operating environment of the diesel engine electric control fuel injector is complex, and the failure of the diesel engine electric control fuel injector is the result of the combined action of a plurality of failure mechanisms, so that the acceleration factor is difficult to determine. At present, a multi-stress accelerated life test is established on the basis of statistics, an acceleration factor of the product accelerated life test is determined by using a method of assuming product life distribution, the specific information requirement of a product is less, a large number of samples are required for testing, and the diesel engine electric control oil injector which is expensive and small in number is difficult to develop. The method for determining the acceleration factor based on the mechanism model is only suitable for single-mechanism single-stress conditions at present, and does not provide a complete acceleration factor determination method based on forward design under the condition of considering multiple stresses and multiple mechanisms.
Based on the current situation, the invention provides a method for determining an acceleration factor interval of an electrically controlled diesel injector based on life theory calculation, which considers the uncertainty influence of model parameters and the synergistic effect of a multi-stress and multi-failure mechanism, can verify the acceleration performance of the existing acceleration test load spectrum based on experience and guide designers to correct, and provides the acceleration test load spectrum to guide the implementation of an acceleration life test, thereby finally determining the comprehensive acceleration factor interval of the electrically controlled diesel injector.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a method for determining an acceleration factor interval of an electrically controlled diesel injector based on life theory calculation.
Specifically, the invention provides a method for determining an acceleration factor interval of an electrically controlled diesel injector based on life theory calculation, which comprises the following specific steps:
the method comprises the following steps: and (3) mechanism analysis: determining potential loss-type failure mechanisms and sensitive stress thereof of all lowest appointed hierarchical units of the diesel engine electric control oil injector in the whole life cycle;
step two: weak link determination: selecting a corresponding life calculation model according to the loss type failure mechanism determined in the step one, and calculating the damage and the theoretical life of each loss type failure mechanism under a conventional test load spectrum, so as to determine a weak link and a main mechanism;
step three: failure mechanism accelerated analysis: analyzing the acceleration of the corresponding main mechanism by using a life calculation model on the basis of the weak link and the main mechanism determined in the step two;
step four: and (3) damage calculation: on the premise of considering the dispersity of model parameters, performing damage calculation on the load spectrum of the existing acceleration test based on experience;
step five: load spectrum equivalent analysis: on the basis of the third step, the damage ratio of each main mechanism to the conventional test load spectrum under the existing accelerated test load spectrum under different model parameter dispersivity is calculated through comparison, and the equivalence of the existing accelerated test load spectrum based on experience and the conventional test load spectrum is analyzed;
step six: determination of acceleration test load spectrum: determining an acceleration test load spectrum based on a conventional test load spectrum and an existing acceleration test profile based on experience;
step seven: unit acceleration factor interval determination: on the basis of considering the parameter dispersity of the life calculation model, calculating the acceleration factor interval of each main mechanism under the acceleration test load spectrum by using the life calculation model so as to determine the acceleration factor interval of each unit;
step eight: determining a product comprehensive acceleration factor: and determining a comprehensive acceleration factor interval of the diesel engine electric control fuel injector according to the unit acceleration factor interval determined in the step seven.
Preferably, the mechanistic analysis described in step one specifically includes the following steps:
a. determining the lowest agreed hierarchical unit of the product by carrying out structural decomposition according to a given load spectrum or a task profile and combining the composition, structure and principle of the diesel engine electric control fuel injector;
b. determining the local load borne by each lowest appointed hierarchical unit according to the load spectrum, and analyzing all corresponding possible loss-type failure mechanisms;
c. the stress sensitivity of each loss-type failure mechanism is determined.
Preferably, the weak link in the second step is a lowest agreed level unit with the theoretically calculated life being less than 100 times of the life index;
preferably, the main mechanism in the second step is a wear-out failure mechanism corresponding to the weak link and playing a key role in the product life.
Preferably, the method for determining the master authority specifically includes:
aiming at the fatigue mechanism, the allowable fatigue times are selected to be less than 1010A secondary corresponding loss-type failure mechanism;
aiming at the wear mechanism, selecting a wear-out failure mechanism corresponding to the wear loss larger than 0.02 mm;
aiming at the aging mechanism, selecting a loss-type failure mechanism corresponding to the aging life of less than 10000 h.
Preferably, the specific steps of the failure mechanism accelerated analysis described in step three are as follows:
a. determining the limit allowable stress born by the unit corresponding to the failure mechanism;
b. substituting the determined limit allowable stress into a life calculation model to obtain the theoretical life under the stress level;
c. and calculating the ratio of the theoretical life under the ultimate stress level to the theoretical life under the conventional test load spectrum, and judging whether the failure mechanism has acceleration. If the lifetime ratio is greater than 2, the mechanism is considered to be accelerated.
Preferably, the specific steps of the damage calculation in step four are as follows:
a. aiming at the host computer with acceleration determined in the third step, calculating the damage under the load spectrum of the existing acceleration test by using a corresponding service life calculation model;
b. considering the dispersibility of the selected model parameters, setting the dispersion coefficient to be 20%, and respectively calculating the damage intervals corresponding to the main mechanisms under different model parameter dispersibility.
Preferably, the load spectrum equivalent analysis specific method in the step five is as follows:
if the damage ratio of the main mechanism is more than 1, the existing acceleration test load spectrum has acceleration performance on the main mechanism;
if the damage ratio of the main mechanism is less than 1, the existing acceleration test load spectrum has no acceleration for the main mechanism.
Preferably, the specific method for determining the loading spectrum of the accelerated test in the sixth step is as follows: under the condition that the acceleration test working condition is not changed, the test time of the conventional acceleration test load spectrum under each working condition is adjusted according to the ratio of the conventional test load spectrum to the total test time of the acceleration test load spectrum, so that the adjusted total test time is consistent with the total test time of the conventional test load spectrum.
Preferably, the specific method for determining the unit acceleration factor interval in step seven is to select the smallest acceleration factor in all the main physical acceleration factor intervals corresponding to the unit as the acceleration factor interval of the unit on the basis of the determination of each main physical acceleration factor interval.
Preferably, the specific method for determining the product comprehensive acceleration factor interval in the step eight is to select the acceleration factor interval corresponding to the lowest agreed hierarchical unit with the shortest theoretical life as the comprehensive acceleration factor interval of the diesel engine electrically-controlled fuel injector according to the theoretical life ranking results of the lowest agreed hierarchical units determined in the step two.
The invention relates to a method for determining an acceleration factor interval of an electric control oil injector of a diesel engine based on life theoretical calculation, which has the following advantages:
the invention provides a method for determining an acceleration factor interval of an electrically controlled diesel injector based on life theoretical calculation, which comprehensively considers the model parameter uncertainty and the synergistic effect of a multi-stress and multi-failure mechanism, and has more accurate and credible evaluation result.
The invention provides a method for determining a mechanism-unit-product bottom-up acceleration factor interval based on a life calculation model, which can comprehensively recognize the fault rule of a product and ensure that an accelerated life test scheme is more in line with the actual condition of the product.
The method overcomes the defect that the traditional acceleration test based on statistics needs a method of determining the acceleration factor by a large number of samples, reduces the test samples and the test cost, and provides method support for the test verification of the product with the long service life index.
Drawings
FIG. 1 is a flow chart of a determination method of the present invention; and
fig. 2 is an exploded level diagram of an electric control injector structure of a diesel engine.
Detailed Description
The invention will be further explained in detail with reference to the following figures and examples:
specifically, the invention provides a method for determining an acceleration factor interval of an electrically controlled diesel injector based on life theory calculation, which comprises the following specific steps:
the method comprises the following steps: and (3) mechanism analysis:
and determining potential loss-type failure mechanisms and sensitive stress of the diesel engine electric control fuel injector in the whole life cycle of all the lowest appointed hierarchical units.
The mechanism analysis comprises three steps: 1) determining the lowest agreed hierarchical unit of the product by carrying out structural decomposition according to a given load spectrum or a task profile and combining the composition, structure and principle of the diesel engine electric control fuel injector; 2) and determining the local load borne by each lowest appointed hierarchical unit according to the load spectrum, thereby analyzing all corresponding possible loss-type failure mechanisms. 3) The stress sensitivity of each loss-type failure mechanism is determined.
Step two: weak link determination:
and (4) selecting a corresponding life index calculation model according to the loss type failure mechanism determined in the step one, and calculating the damage and the theoretical life of each failure mechanism under a conventional test load spectrum, so as to determine weak links and main mechanisms.
The weak link refers to the lowest agreed level unit with the theoretical calculation life being less than 100 times of the life index.
The main mechanism refers to a loss-type failure mechanism which is corresponding to the weak link and plays a key role in the service life of the product. 1) Aiming at the fatigue mechanism, the allowable fatigue times are selected to be less than 1010A secondary corresponding loss-type failure mechanism; 2) aiming at the wear mechanism, selecting a wear-out failure mechanism corresponding to the wear loss larger than 0.02 mm; 3) aiming at the aging mechanism, selecting a loss-type failure mechanism corresponding to the aging life of less than 10000 h.
Step three: failure mechanism accelerated analysis:
and analyzing the acceleration of the corresponding main mechanism by using a life index calculation model on the basis of the weak link determined in the step two.
The concrete steps of the failure mechanism acceleration analysis are as follows:
a. determining the limit allowable stress born by the unit corresponding to the failure mechanism;
b. substituting the determined limit allowable stress into a life calculation model to obtain the theoretical life under the stress level;
c. and calculating the ratio of the theoretical life under the ultimate stress level to the theoretical life under the conventional test load spectrum, and judging whether the failure mechanism has acceleration. If the lifetime ratio is greater than 2, the mechanism is considered to be accelerated.
Step four: and (3) damage calculation:
and on the premise of considering the dispersity of the model parameters, performing damage calculation on the load spectrum of the existing acceleration test based on experience.
The specific steps of the damage calculation are as follows: 1) aiming at the host computer with acceleration determined in the third step, calculating the damage under the load spectrum of the existing acceleration test by using a corresponding service life calculation model; 2) considering the dispersibility of the selected model parameters, setting the dispersion coefficient to be 20%, and respectively calculating the damage intervals corresponding to the main mechanisms under different model parameter dispersibility.
Step five: load spectrum equivalent analysis:
and on the basis of the third step, the damage ratio of each main mechanism to the conventional test load spectrum under the existing accelerated test load spectrum under different model parameter dispersivity is calculated through comparison, and the equivalence of the existing accelerated test load spectrum based on experience and the conventional test load spectrum is analyzed.
The load spectrum equivalent analysis principle is as follows: if the damage ratio of the main mechanism is more than 1, the existing acceleration test load spectrum has acceleration performance on the main mechanism; if the damage ratio of the main mechanism is less than 1, the existing acceleration test load spectrum has no acceleration for the main mechanism.
Step six: determination of acceleration test load spectrum:
an accelerated test load spectrum is determined based on the conventional test load spectrum and an existing empirically based accelerated test profile.
The criterion of the acceleration test load spectrum determination is as follows: under the condition that the acceleration test working condition is not changed, the test time of the conventional acceleration test load spectrum under each working condition is adjusted according to the ratio of the conventional test load spectrum to the total test time of the acceleration test load spectrum, so that the adjusted total test time is consistent with the total test time of the conventional test load spectrum.
Step seven: unit acceleration factor interval determination:
on the basis of considering the parameter dispersity of the life calculation model, the life calculation model is used for calculating the acceleration factor interval of each main mechanism under the acceleration test load spectrum, and therefore the acceleration factor interval of each unit is determined.
The unit acceleration factor interval determination is to select the minimum acceleration factor in all the main physical acceleration factor intervals corresponding to the unit as the acceleration factor interval of the unit on the basis of the determination of each main physical acceleration factor interval.
Step eight: determining a product comprehensive acceleration factor interval:
and determining a comprehensive acceleration factor interval of the diesel engine electric control fuel injector according to the unit acceleration factor interval determined in the step seven.
The specific method for determining the product comprehensive acceleration factor interval comprises the step of selecting the acceleration factor interval corresponding to the lowest agreed hierarchical unit with the shortest theoretical life as the comprehensive acceleration factor interval of the diesel engine electric control fuel injector according to the theoretical life sequencing result of each lowest agreed hierarchical unit determined in the step two.
Examples
The invention will be further described in detail with reference to a specific process for determining an acceleration factor interval of an electrically controlled diesel injector, which is shown in fig. 1, and the invention is a method for determining an acceleration factor interval of an electrically controlled diesel injector based on a life theory calculation, and the method comprises the following specific implementation steps:
the method comprises the following steps: and performing mechanism analysis to determine potential loss-type failure mechanisms and sensitive stress of the diesel engine electric fuel injector in all the lowest agreed hierarchical unit whole life cycles. The level diagram of the disassembled structure of the electric control fuel injector of a certain diesel engine is shown in figure 2. The workload types of the lowest appointed hierarchical unit are determined as follows: stroke, fuel pressure, load force, working medium temperature, the environmental load type is: ambient temperature, vibration load. The final wear-out failure mechanism is summarized in Table 1.
TABLE 1 summary of failure mechanism of electrically controlled fuel injector of diesel engine
Step two: and (4) determining a weak link. And (3) selecting a corresponding life calculation model according to the loss type failure mechanism determined in the step one, and calculating the damage and the theoretical life of each failure mechanism under a conventional test load spectrum (shown in table 2), so as to determine a weak link and a main mechanism.
TABLE 2 load spectrum of conventional test of electrically controlled fuel injector of certain diesel engine
Common life calculation models required for the development of index calculations include:
a. fatigue-like mechanisms:
the life calculation model of the fatigue-like failure mechanism is shown as follows:
wherein σmax,σmin-maximum and minimum stress in one motion cycle, MPa, of a certain lowest agreed level unit;
σm,σa-the corresponding mean stress and stress amplitude, MPa, of a certain lowest agreed level unit within one motion cycle;
σe-equivalent mean stress, MPa;
σb-material tensile strength limit, MPa;
σ-1A-allowable fatigue limit, MPa;
b-fatigue coefficient of the material;
Ni,Difatigue life and damage at each stage load;
N0-the number of cycles when the maximum principal stress is the fatigue limit;
ni,Niactual cycle number and fatigue life under each level of loading;
l-fatigue life under comprehensive conditions;
b. wear-type mechanism:
the life calculation model of the wear-type failure mechanism is shown as follows:
A＝2πrLj
wherein: r is the inner diameter of the friction pair, mm;
Ljthe length of the contact part of the friction pair, mm;
a-nominal contact area, mm2；
hs-maximum allowable wear of the friction pair, mm;
h-hardness of material, MPa;
k-wear coefficient;
Lm-the length of the full stroke of the friction pair, mm;
Wa-microprotrusion loading, N;
n-wear life;
c. aging-like mechanism:
the life calculation model for the aging-like failure mechanism is shown as follows:
wherein: e-activation energy of the material, J mol-1；
R-gas constant, 8314/(J mol)-1)；
T-aging reaction time, K;
t-aging life, h;
and calculating the theoretical life of each lowest agreed hierarchical unit by using a life calculation model, wherein the theoretical life is shown in a table 3.
TABLE 3 theoretical Life summary Table corresponding to wear-out failure mechanism
Aiming at the fatigue mechanism, the allowable fatigue times are selected to be less than 1010A secondary wear-out failure mechanism; aiming at the abrasion mechanism, selecting a wear-out failure mechanism with the abrasion loss larger than 0.02 mm; aiming at the aging mechanism, a wear-out failure mechanism with the aging life less than 10000h is selected. The final selected weak link and the host mechanism are shown in table 4.
TABLE 4 summary table of weak links and host computer of electric control fuel injector of diesel engine
Step three: accelerated analysis of failure mechanism. And analyzing the acceleration of the corresponding main mechanism by using a life calculation model on the basis of the weak link determined in the step two. Finally, all failure mechanisms with acceleration are shown in table 5.
TABLE 5 failure mechanism summary table with acceleration
Step four: and (4) calculating damage. The damage calculation was performed on the existing empirically based accelerated test loading spectra (see table 6) taking into account the model parameter dispersion.
TABLE 6 load spectrum of electric controlled injector of diesel engine in current acceleration test
The dispersity of the model parameters is set to be 20%, so that the theoretical service life and damage distribution condition of the failure mechanism corresponding to each unit under different dispersity can be obtained. The specific steps of the method are explained by taking the impact fatigue of the needle valve and the welded needle valve body as an example:
a. needle valve impact fatigue
The theoretical life and damage of the needle valve under different model parameter dispersivity corresponding to the impact fatigue are shown in tables 7 and 8.
TABLE 7 theoretical life of needle valve impact fatigue
TABLE 8 damage of needle valve impact fatigue
| Divergence degree | b | Routine test load spectrum | Existing acceleration test load spectrum |
| -20％ | 2.528 | 1.11 | 0.65 |
| -10％ | 2.844 | 0.79 | 0.48 |
| 0 | 3.16 | 0.56 | 0.35 |
| 10％ | 3.476 | 0.39 | 0.25 |
| 20％ | 3.792 | 0.28 | 0.18 |
b. Impact fatigue of welded needle valve body
The theoretical life and damage of the welded needle valve body under different model parameter dispersivity corresponding to the impact fatigue are shown in tables 9 and 10.
TABLE 9 theoretical life of welded needle valve impact fatigue
| Divergence degree | b | Routine test load spectrum | Existing acceleration test load spectrum |
| -20％ | 3.91472 | 2.06E+06 | 1.47E+06 |
| -10％ | 4.40406 | 1.68E+06 | 1.16E+06 |
| 0 | 4.8934 | 1.38E+06 | 9.08E+05 |
| 10％ | 5.38274 | 1.13E+06 | 7.12E+05 |
| 20％ | 5.87208 | 9.21E+05 | 5.58E+05 |
TABLE 10 damage of welded needle valve body from impact fatigue
| Divergence degree | b | Routine test load spectrum | Existing acceleration test load spectrum |
| -20％ | 3.91472 | 87.58 | 56.18 |
| -10％ | 4.40406 | 106.95 | 71.56 |
| 0 | 4.8934 | 130.66 | 91.20 |
| 10％ | 5.38274 | 159.71 | 116.29 |
| 20％ | 5.87208 | 195.34 | 148.34 |
Step five: and (5) carrying out equivalent analysis on the load spectrum. And on the basis of the third step, the damage ratio of each main mechanism to the conventional test load spectrum under the existing accelerated test load spectrum under different model parameter dispersivity is calculated through comparison, and the equivalence of the existing accelerated test load spectrum based on experience and the conventional test load spectrum is analyzed.
And (3) comparing and analyzing the damage of each mechanism under the conventional life load spectrum and the conventional accelerated test load spectrum, and obtaining the damage ratio under different values of b, which is shown in table 11.
TABLE 11 Damage ratio of various failure mechanisms at different model parameter scatter
If the damage ratio of the main mechanism is more than 1, the existing acceleration test load spectrum has acceleration performance on the main mechanism; if the damage ratio of the main mechanism is less than 1, the existing acceleration test load spectrum has no acceleration for the main mechanism. Therefore, the existing acceleration test load spectrum only has acceleration performance for the control plunger, the armature and the guide body, and the conventional test load spectrum cannot be equivalent for other units.
Step six: and (4) determining an accelerated test load spectrum. Based on the conventional trial load spectrum and the existing empirically based acceleration test profile, an acceleration trial load spectrum was determined, as shown in table 12.
TABLE 12 adjusted accelerated test load Spectrum
Step seven: and determining the unit acceleration factor interval. On the basis of considering the parameter dispersion of the life calculation model, the life calculation model is used to calculate the acceleration factor interval of each main mechanism under the accelerated test load spectrum, so as to determine the acceleration factor interval of each unit, which is shown in table 12.
TABLE 12 acceleration factor for each failure mechanism at different parameter spread
| Ratio of | Needle valve | Welding needle valve body | Control plunger | Metering orifice plate | … | Guide body |
| 0.8 | 1.4038 | 1.5875 | 2.3746 | 1.5177 | … | 2.1488 |
| 0.9 | 1.4349 | 1.6552 | 2.5769 | 1.5685 | … | 2.3241 |
| 1 | 1.4658 | 1.7254 | 2.7873 | 1.6202 | … | 2.5086 |
| 1.1 | 1.4966 | 1.7982 | 3.0043 | 1.6727 | … | 2.7015 |
| 1.2 | 1.5273 | 1.8735 | 3.2264 | 1.7261 | … | 2.9015 |
Step eight: and determining a product comprehensive acceleration factor interval. And determining the lowest agreed hierarchical unit with the shortest theoretical life as a welding needle valve body according to the theoretical life sequencing result of each lowest agreed hierarchical unit determined in the step two, wherein the corresponding acceleration factor interval is [1.5875,1.8735], and therefore the lowest agreed hierarchical unit is used as the comprehensive acceleration factor interval of the diesel engine electric control fuel injector.
Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for determining an acceleration factor interval of an electric control oil injector of a diesel engine based on life theoretical calculation is characterized by comprising the following steps: the method comprises the following specific steps:
the method comprises the following steps: and (3) mechanism analysis: determining potential loss-type failure mechanisms and sensitive stress thereof of all lowest appointed hierarchical units of the diesel engine electric control oil injector in the whole life cycle; the workload types of the lowest agreed hierarchical unit are as follows: stroke, fuel pressure, load force, working medium temperature, the environmental load type is: ambient temperature, vibration load;
step two: weak link determination: selecting a corresponding life calculation model according to the loss type failure mechanism determined in the step one, and calculating the damage and the theoretical life of each loss type failure mechanism under a conventional test load spectrum, so as to determine a weak link and a main mechanism;
step three: failure mechanism accelerated analysis: analyzing the acceleration of the corresponding main mechanism by using a life calculation model on the basis of the weak link and the main mechanism determined in the step two; the service life calculation model specifically comprises the following steps:
a. fatigue-like mechanisms:
the life calculation model of the fatigue-like failure mechanism is shown as follows:
wherein σmax,σminMaximum stress and minimum stress in one motion cycle of a certain lowest appointed hierarchical unit, namely MPa; sigmam,σaThe corresponding average stress and stress amplitude in one motion cycle of a certain lowest appointed hierarchical unit are MPa; sigmaeEquivalent mean stress, MPa; sigmabIs the tensile strength limit of the material, MPa; sigma-1AAllowable fatigue limit, MPa; b is the fatigue coefficient of the material; n is a radical ofi,DiFatigue life and damage under various levels of loading; n is a radical of0The number of cycles when the maximum principal stress is the fatigue limit; n isiThe actual cycle times under the loads of all levels are obtained; l is fatigue life under comprehensive conditions;
b. wear-type mechanism:
the life calculation model of the wear-type failure mechanism is shown as follows:
A＝2πrLj
wherein: r is the inner diameter of the friction pair, mm; l isjThe length of the contact part of the friction pair is mm; a is the nominal contact area, mm2；hsThe maximum allowable abrasion loss of the friction pair is mm; h is the material hardness, MPa; k is the wear coefficient; l ismThe length of the full stroke of the friction pair is mm; waIs the microprotrusion load, N; n is wear life;
c. aging-like mechanism:
the life calculation model for the aging-like failure mechanism is shown as follows:
wherein: e is the activation energy of the material, J mol-1(ii) a R is a gas constant, 8314/(J mol)-1) (ii) a T is the aging reaction time, K; t is the aging life, h;
step four: and (3) damage calculation: on the premise of considering the dispersity of model parameters, performing damage calculation on the load spectrum of the existing acceleration test based on experience;
step five: load spectrum equivalent analysis: on the basis of the third step, the damage ratio of each main mechanism to the conventional test load spectrum under the existing accelerated test load spectrum under different model parameter dispersivity is calculated through comparison, and the equivalence of the existing accelerated test load spectrum based on experience and the conventional test load spectrum is analyzed;
when the host mechanism damage ratio is larger than 1, the existing acceleration test load spectrum has acceleration to the host mechanism; when the host mechanism damage ratio is less than 1, the existing acceleration test load spectrum has no acceleration to the host mechanism; therefore, the acceleration test load spectrum only has acceleration performance for the control plunger, the armature and the guide body, and the conventional test load spectrum cannot be equivalent for other units;
step six: determination of acceleration test load spectrum: determining an acceleration test load spectrum based on a conventional test load spectrum and an existing acceleration test profile based on experience;
step seven: unit acceleration factor interval determination: on the basis of considering the parameter dispersity of the life calculation model, calculating the acceleration factor interval of each main mechanism under the acceleration test load spectrum by using the life calculation model so as to determine the acceleration factor interval of each unit;
step eight: determining a product comprehensive acceleration factor interval: and determining a comprehensive acceleration factor interval of the diesel engine electric control fuel injector according to the unit acceleration factor interval determined in the step seven.
2. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: step one the mechanistic analysis specifically comprises the following steps:
a. determining the lowest agreed hierarchical unit of the product by carrying out structural decomposition according to a given load spectrum or a task profile and combining the composition, structure and principle of the diesel engine electric control fuel injector;
b. determining the local load borne by each lowest appointed hierarchical unit according to the load spectrum, and analyzing all corresponding possible loss-type failure mechanisms;
c. the stress sensitivity of each loss-type failure mechanism is determined.
3. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation as claimed in claim 2, is characterized in that: step two, the weak link is a lowest appointed hierarchical unit with the theoretical calculation life being less than 100 times of the life index;
and the main mechanism in the second step is a loss-type failure mechanism which is corresponding to the weak link and plays a key role in the service life of the product.
4. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation as claimed in claim 3, is characterized in that: the method for determining the master authority specifically comprises the following steps:
aiming at the fatigue mechanism, the allowable fatigue times are selected to be less than 1010A secondary corresponding loss-type failure mechanism;
aiming at the wear mechanism, selecting a wear-out failure mechanism corresponding to the wear loss larger than 0.02 mm;
aiming at the aging mechanism, selecting a loss-type failure mechanism corresponding to the aging life of less than 10000 h.
5. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: step three the concrete steps of the failure mechanism acceleration analysis are as follows:
a. determining the limit allowable stress born by the unit corresponding to the failure mechanism;
b. substituting the determined limit allowable stress into a life calculation model to obtain the theoretical life under the stress level;
c. and calculating the ratio of the theoretical life under the ultimate stress level to the theoretical life under the conventional test load spectrum, judging whether the failure mechanism has acceleration, and if the ratio of the lives is more than 2, determining that the failure mechanism has acceleration.
6. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: step four the specific steps of the damage calculation are as follows:
a. aiming at the host computer with acceleration determined in the third step, calculating the damage under the load spectrum of the existing acceleration test by using a corresponding service life calculation model;
b. considering the dispersibility of the selected model parameters, setting the dispersion coefficient to be 20%, and respectively calculating the damage intervals corresponding to the main mechanisms under different model parameter dispersibility.
7. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: the concrete method for equivalent analysis of the load spectrum in the step five comprises the following steps:
if the host mechanism damage ratio is larger than 1, the existing acceleration test load spectrum has acceleration to the host mechanism;
if the damage ratio of the main mechanism is less than 1, the existing acceleration test load spectrum has no acceleration for the main mechanism.
8. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: the specific method for determining the accelerated test load spectrum in the sixth step comprises the following steps: under the condition that the acceleration test working condition is not changed, the test time of the conventional acceleration test load spectrum under each working condition is adjusted according to the ratio of the conventional test load spectrum to the total test time of the acceleration test load spectrum, so that the adjusted total test time is consistent with the total test time of the conventional test load spectrum.
9. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: the specific method for determining the unit acceleration factor interval in the seventh step is to select the smallest acceleration factor in all the main physical acceleration factor intervals corresponding to the unit as the acceleration factor interval of the unit on the basis of determining each main physical acceleration factor interval.
10. The method for determining the acceleration factor interval of the electrically controlled diesel injector based on the theoretical life calculation of claim 1 is characterized in that: and step eight, the specific method for determining the product comprehensive acceleration factor interval is to select the acceleration factor interval corresponding to the lowest agreed hierarchical unit with the shortest theoretical life as the comprehensive acceleration factor interval of the diesel engine electric control fuel injector according to the theoretical life sequencing result of each lowest agreed hierarchical unit determined in the step two.
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