A Design Method for a Marine Cam-Roller Pair

Abstract

The present invention discloses a design method for a marine cam-roller pair, which comprises the following steps: S1, obtaining the initial parameters of the cam-roller pair; S2, constructing a parametric model of the cam-roller pair; S3, inputting the obtained initial parameters of the cam-roller pair into the constructed parametric model, importing it into a dynamics analysis software, and calculating the maximum load acting on the roller and the corresponding cam rotation angle at a certain rotation speed of the cam; S4, importing the parametric model into ANSYS workbench, reassembling the cam and the roller according to the cam rotation angle corresponding to the obtained maximum load, constructing a finite element simulation analysis model of the cam-roller pair, and analyzing and calculating the equivalent stress, contact stress, deflection and fatigue life of the cam-roller pair corresponding to the initial parameters; S5, optimizing and iterating the parameters of the cam-roller pair by using a multi-island genetic algorithm. It can shorten the design and development time of the marine cam-roller pair and reduce the design cost caused by multiple trial productions and tests.

Description

Technical Field

[0001] The present invention relates to a high-pressure fuel pump for marine diesel engines, and particularly to a design method for a marine cam-roller pair. Background Art

[0002] As a key component in marine diesel engines, the cam roller directly affects the fuel supply amount and fuel supply law of the high-pressure fuel pump. Especially in the current context, various classification societies have imposed more stringent restrictions on ship emissions. In order to reduce fuel consumption and emissions, one common measure is to increase the injection pressure of the fuel system. The increase in pressure further raises the performance requirements for the high-pressure fuel pump. Among them, the design of parameters such as the profile curve design of the cam roller, the base circle radius, the cam thickness, the roller radius, and the roller thickness becomes particularly important. The existing technology generally selects multiple parameter values based on similar models and design experience, and repeatedly verifies the dynamics, structural strength, contact strength, fatigue life, etc. of the cam roller, and then selects a relatively optimal structure from them. However, due to the lack of interactivity between multiple disciplines, each time the model is changed, a three-dimensional model and related finite element models need to be rebuilt, resulting in a long design cycle. And currently, most scholars only study the profile curve optimization of the cam alone and fail to consider the comprehensive performance of the cam roller. Summary of the Invention

[0003] The purpose of the present invention is to provide a design method for a marine cam-roller pair, which can shorten the design and development time of the marine cam-roller pair and reduce the design cost caused by multiple trial productions and tests.

[0004] The design method for the marine cam-roller pair described in the present invention includes the following steps:

[0005] S1, obtaining the initial parameters of the cam-roller pair;

[0006] S2, using NX software to construct a parametric model of the cam-roller pair;

[0007] S3, inputting the initial parameters of the cam-roller pair obtained in S1 into the parametric model constructed in S2, importing the parametric model into Recurdyn dynamic analysis software, and calculating the maximum load acting on the roller and the corresponding cam rotation angle at a certain rotation speed of the cam;

[0008] S4, importing the parametric model into ANSYS workbench, reassembling the cam and the roller according to the cam rotation angle corresponding to the maximum load analyzed in S3, constructing a finite element simulation analysis model of the cam-roller pair, and analyzing and calculating the equivalent stress, contact stress, deflection, and fatigue life of the cam-roller pair corresponding to the initial parameters;

[0009] S5. Use the multi-island genetic algorithm to optimize and iterate the parameters of the cam-roller pair. Input the width of the cam, the width of the roller, the inner diameter of the roller, and the outer diameter of the roller as optimization variables, and output the contact stress value of the cam roller as the optimization objective. Use the multi-island genetic algorithm to optimize and iterate to obtain the minimum contact stress value of the cam roller and its corresponding optimization variables. Analyze and calculate the equivalent stress, contact stress, deflection, and fatigue life of the cam-roller pair corresponding to the optimization variables, and compare and analyze them with the equivalent stress, contact stress, deflection, and fatigue life of the cam-roller pair corresponding to the initial parameters obtained in S4 to determine whether the optimization variables meet the design requirements.

[0010] Further, the specific content of S2 is as follows: Construct an initial two-dimensional contour sketch in the NX software according to the initial parameters of the cam-roller pair obtained in S1, mark the linear dimensions of each parameter in the two-dimensional contour sketch, and obtain the initial three-dimensional model of the cam-roller pair through stretching and rotation.

[0011] Use the expression function module in the NX software to establish expressions for the characteristic dimensions and positioning dimensions representing the cam-roller pair, and establish all expressions as a characteristic expression set. Use the secondary development function to develop a UI interface for the characteristic expression set to realize the parametric modeling of the cam roller of the marine diesel engine high-pressure oil pump. The three-dimensional model of the cam-roller pair can be updated by directly modifying the parameters through the UI interface.

[0012] Further, when using the multi-island genetic algorithm for optimization and iteration in S5, the number of subgroups is not less than 10, the number of island groups is not less than 10, the number of generations of evolution is not less than 10, the migration interval algebra between islands is 5, and the number of optimization and iteration times is not less than 1000 times.

[0013] Further, in S4, import the equivalent stress, contact stress, and deflection of the calculated cam-roller pair into ncode, analyze and calculate the number of cycles of the cam-roller pair, and convert to obtain the fatigue life of the cam-roller pair.

[0014] Further, after reassembling the cam and the roller according to the cam rotation angle corresponding to the maximum load analyzed in S3 in S4, geometrically divide the theoretical contact position of the cam and the roller. The division standard is that the width on the left and right of the contact line between the cam and the roller is 20% of the cam base circle radius, and the height above and below is 15% of the cam base circle radius; establish a reference point at the center of the roller, and make an MPC constraint between this reference point and the inner ring surface of the roller to limit the left and right degrees of freedom of the roller, so that the roller can only roll up and down around the cam. At the same time, apply the maximum load at the reference point; define the property of the entire contact surface during the working process of the cam and the roller as a hard contact, and the friction coefficient is 0.02 to obtain the finite element simulation analysis model of the cam-roller pair.

[0015] The present invention establishes a rapid design template for the cam-roller pair of a marine diesel engine high-pressure oil pump, facilitating designers to analyze parameters such as the roller, main shaft, 3D modeling of the assembly, maximum pressure, rotation angle, maximum stress value, etc. in the camshaft during the process of developing new products, evaluate whether the camshaft meets the design requirements, standardizes the design process and method of the cam roller of the marine diesel engine high-pressure oil pump, improves the design optimization efficiency of the high-pressure oil pump in the marine diesel engine fuel system, and reduces the design cost. Description of the Drawings

[0016] Figure 1 It is a schematic flow chart of the design method for the marine cam-roller pair described in the present invention;

[0017] Figure 2 It is a schematic UI interface diagram of the feature expression set;

[0018] Figure 3 It is an assembly model of the cam-roller pair established according to the obtained initial parameters of the cam-roller pair;

[0019] Figure 4 It is a schematic diagram of the Recurdyn dynamic analysis result;

[0020] Figure 5 It is the cross-sectional shape of the contact position of the cam-roller pair after segmentation;

[0021] Figure 6 It is a schematic diagram of the finite element mesh model of the cam-roller pair;

[0022] Figure 7 It is an equivalent stress distribution nephogram of the cam-roller pair obtained by finite element analysis;

[0023] Figure 8 It is a contact stress distribution nephogram of the cam-roller pair obtained by finite element analysis;

[0024] Figure 9 It is a schematic diagram of the path from the first point to the second point established on the cam axis and the deflection distribution on the path;

[0025] Figure 10 For Figure 9 It is a schematic diagram of the camshaft deflection curve on the established 1-2 path;

[0026] Figure 11 It is a schematic diagram of the fatigue life analysis result of the cam roller;

[0027] Figure 12 It is an optimized contact stress distribution nephogram of the cam-roller pair;

[0028] Figure 13 It is an optimized equivalent stress distribution nephogram of the cam-roller pair;

[0029] Figure 14 Schematic diagram of the path from the first point to the second point established for the optimized camshaft and the deflection distribution on the path. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] See Figure 1 , the design method of the marine cam-roller pair shown, which comprises the following steps:

[0032] S1. Obtain the initial parameters of the cam-roller pair, and the cam-roller pair is applied to the high-pressure oil pump of a marine diesel engine. In this embodiment, according to the main application scenario of the embodiment, the camshaft adopts an integral structure, the cam profile of the cam is a functional cam, which is composed of five polynomial functions, and its calculation uses a sixth-order polynomial function expression as:

[0033] y(x) = c6x 6 + c5x 5 + c4x 4 + c3x 3 + c2x 2 + c1x + c,

[0034] In the formula, y(x) is the cam displacement; x = θ / β, θ is the angle rotated by the cam, β is the angle of rotation of the cam movement cycle; c, c1, c2, c3, c4, c5, c6 are determined by the parameters of the designed high-pressure oil pump.

[0035] Determine the base circle diameter of the cam according to the mechanical load of the diesel engine. Generally, the base circle diameter D is 3 - 5 times the cam lift h, and the cam lift is determined by the parameters of the designed high-pressure oil pump. The value of the base circle diameter D in this embodiment is 76 mm.

[0036] Calculate the eccentricity of the cam according to the pressure angle calculation formula, and its expression is: In the formula, α is the pressure angle, v is the speed of the plunger in the high-pressure oil pump, ε is the eccentricity, R D is the base circle radius;

[0037] Calculate the curvature radius of the theoretical contour line of the cam, and the calculation expression is: Where ρ is the curvature and a is the acceleration of the plunger in the high-pressure fuel pump;

[0038] Based on the calculated radius of curvature, the maximum radius of the roller can be directly obtained, and the relationship satisfies that the maximum roller radius is less than the minimum radius of curvature of the theoretical profile. According to the relevant design parameters, the maximum roller radius in this embodiment is 20 mm.

[0039] According to the material selection of the cam roller, the maximum allowable contact stress value can be determined, and then the minimum width of the cam can be calculated by the Hertz contact formula, and its expression is: In the formula, σ H is the allowable contact stress, F is the normal cam pressure, b is the contact width between the roller and the cam, is the roller radius.

[0040] The material selected for the cam roller is 18CrNiMo7-6, and the contact width between the roller and the cam is 7 mm.

[0041] Other detailed parameters obtained by calculation, such as the total length of the camshaft, the geometric parameters of the spline, the spacing between cams, and the cam thickness, are as Figure 2 shown.

[0042] S2. Use NX software to build a parametric model of the cam-roller pair; construct an initial 2D profile sketch in NX software according to the initial parameters of the cam-roller pair obtained in S1, mark the linear dimensions of each parameter in the 2D profile sketch, and obtain the initial 3D model of the cam-roller pair through stretching and rotation.

[0043] Using the expression function module in NX software, establish the characteristic dimensions and positioning dimensions representing the cam-roller pair as expressions, and establish all expressions as a set of characteristic expressions. Use the secondary development function to develop a UI interface for the set of characteristic expressions. The UI interface is shown in Figure 2 shown, to realize the parametric modeling of the cam-roller pair of the high-pressure fuel pump of the marine diesel engine. By directly modifying the parameters through the UI interface, the 3D model of the cam-roller pair can be updated. The 3D model is as Figure 3 shown.

[0044] S3. Input the initial parameters of the cam-roller pair obtained in S1 into the parametric model constructed in S2 to obtain the initial parametric model, and import the initial parametric model into Recurdyn dynamic analysis software. Apply the plunger spring force and oil pressure load on the roller, apply a "bushing" constraint at the installation position of the camshaft bearing, and give a certain rotational speed of the camshaft around the axis. Through calculation, the maximum load acting on the roller and the corresponding cam rotation angle at this speed can be obtained. The calculation results are as Figure 4As shown, the maximum load acting on the roller is 22062.4 N, and the corresponding cam rotation angle is 11.072°.

[0045] S4. Import the initial parameterized model in S3 into ANSYS workbench, and rotate the cam rotation angle to 11.072°. Then, geometric segmentation is performed at the theoretical contact position of the cam and the roller. The segmentation criterion is that the width on the left and right of the contact line between the cam and the roller is 20% of the cam base circle radius, and the height above and below is 15% of the cam base circle radius. As Figure 5 shown, the cross-sectional shape of the segmented area is approximately an isosceles trapezoid; the basic mesh size of the contact part area after segmentation is defined as 0.3 mm, the mesh type is a second-order hexahedral element, and the basic mesh size of the remaining parts is 5 mm, and the mesh type is a second-order tetrahedral element. The meshed model after division is as Figure 6 shown; the mesh sizes of the contact surface between the cam and the roller, the roller mesh size, the overall mesh size, and the load parameters are parameterized, which can be used to study the mesh independence of different cam-roller structures.

[0046] A reference point is established at the center of the roller, and an MPC constraint is made between this reference point and the inner ring surface of the roller, and the degrees of freedom of the roller left and right are restricted, so that the roller can only roll up and down around the cam. At the same time, a spring pre-tightening force and the pump end pressure of the high-pressure oil pump, that is, the calculated maximum load of 22062.4 N, are applied at the reference point. The property of the entire contact surface during the operation of the cam and the roller is defined as hard contact, and the friction coefficient is 0.02. The finite element model of the cam-roller pair under the initial parameters is obtained.

[0047] According to the established finite element model, the equivalent stress, contact stress and deflection of the cam-roller pair are analyzed and calculated. In order to intuitively obtain the deflection of the camshaft, a path from 1 to 2 is established on the camshaft axis, and the calculation results are respectively as Figure 7 、 8 、9, 10 shown. It can be seen from the figure that the maximum equivalent stress of the cam-roller pair is 1388 MPa, which is located near the contact surface of the cam and the roller; the maximum contact stress is 1940.1 MPa. Ignoring the influence of the marginal effect, the contact stress value at the middle part of the contact zone is about 1700 MPa; the maximum deflection of the camshaft is 0.005 mm, which is located at the middle position between the two cams.

[0048] The result containing the equivalent stress of the cam-roller pair obtained from the ANSYS finite element analysis is imported into ncode. According to the oil pump operation frequency and the cam-roller material properties, the cycle times of the cam-roller pair are analyzed and calculated, and further converted to obtain the fatigue life of the cam-roller pair. The calculation results are as shown in 11. The minimum stress cycle times is 6.25E+07, which is located at the contact position of the cam and the roller.

[0049] S5. Use the multi-island genetic algorithm to optimize and iterate the parameters of the cam-roller pair. Input the width of the cam, the width of the roller, the inner diameter of the roller, and the outer diameter of the roller as the optimization variables, and output the contact stress value of the cam-roller pair as the optimization objective. Use the multi-island genetic algorithm to optimize and iterate to obtain the minimum contact stress value of the cam-roller pair and its corresponding optimization variables.

[0050] When using the multi-island genetic algorithm for optimization and iteration, the value of the subgroup scale is 10, the number of island groups is 10, the number of generations of evolution is 10, the migration interval algebra between islands is 5, and the number of optimization and iteration times is 1000 times.

[0051] To verify whether the optimization variables meet the design requirements, further input the optimization variables corresponding to the minimum contact stress value of the cam-roller pair into the parametric model constructed in S2, import the parametric model into the Recurdyn dynamic analysis software, and calculate the maximum load acting on the roller and the corresponding cam rotation angle at a certain rotational speed of the cam;

[0052] Similarly, according to S3 and S4, the equivalent stress distribution cloud diagram, contact stress distribution cloud diagram, and deflection distribution schematic diagram of the cam-roller pair corresponding to the parameter optimization can be obtained, and a horizontal comparison is made with the performance of the cam-roller pair corresponding to the initial parameters to quickly judge the optimization effect, which is convenient and fast.

[0053] The optimized calculation obtains the contact stress distribution of the optimized cam-roller pair as Figure 12 , It can be seen from the figure that the maximum contact stress value of the cam-roller pair is 1492.6 MPa. Ignoring the marginal effect, the contact stress in the middle section of the contact zone is about 1280 MPa. Compared with the contact stress value before optimization, it is optimized by about 24.7%; the equivalent stress distribution of the optimized cam-roller pair is as Figure 13 shown. Compared with the maximum equivalent stress of 1388 MPa before optimization, the maximum equivalent stress after optimization is 979.39 MPa, and the optimization percentage is 29.87%; the deflection of the optimized cam-roller pair is as Figure 14 shown. Its optimized deflection is 0.0027 mm, which is 0.0023 mm less than the deflection of 0.005 mm before optimization. Further analysis shows that the stress cycle times of the cam-roller pair are much greater than 6.25E+07, and the optimized cam-roller pair meets the life design requirement value. At the same time, output the parameter values and three-dimensional geometric structure of the cam-roller pair.

[0054] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

[0055] The above embodiments are only the preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention.

Claims

1. A design method for a marine cam-roller pair, characterized in that, It includes the following steps: S1. Obtain the initial parameters of the cam-roller pair; S2. Use NX software to build a parametric model of the cam-roller pair; S3. Input the initial parameters of the cam-roller pair obtained in S1 into the parametric model built in S2, import the parametric model into Recurdyn dynamic analysis software, and calculate the maximum load acting on the roller and the corresponding cam rotation angle at a certain rotation speed of the cam; S4. Import the parametric model into ANSYS workbench, reassemble the cam and the roller according to the cam rotation angle corresponding to the maximum load obtained in S3, build a finite element simulation analysis model of the cam-roller pair, and analyze and calculate the equivalent stress, contact stress, deflection and fatigue life of the cam-roller pair corresponding to the initial parameters; S5. Use the multi-island genetic algorithm to optimize and iterate the parameters of the cam-roller pair. Input the width of the cam, the width of the roller, the inner diameter of the roller, and the outer diameter of the roller as optimization variables, and output the contact stress value of the cam roller as the optimization target. Use the multi-island genetic algorithm to optimize and iterate to obtain the minimum contact stress value of the cam roller and its corresponding optimization variables. Analyze and calculate the equivalent stress, contact stress, deflection and fatigue life of the cam-roller pair corresponding to the optimization variables, and compare and analyze them with the equivalent stress, contact stress, deflection and fatigue life of the cam-roller pair corresponding to the initial parameters obtained in S4 to judge whether the optimization variables meet the design requirements.

2. The design method of the marine cam-roller pair according to claim 1, characterized in that, The specific content of S2 is as follows: Build an initial two-dimensional contour sketch in NX software according to the initial parameters of the cam-roller pair obtained in S1, mark the linear dimensions of each parameter in the two-dimensional contour sketch, and obtain the initial three-dimensional model of the cam-roller pair through stretching and rotation; Use the expression function module in NX software to establish expressions for the characteristic dimensions and positioning dimensions between the cam and the roller, and establish all expressions as a set of characteristic expressions. Use the secondary development function to develop a UI interface for the set of characteristic expressions to realize the parametric modeling of the cam roller of the marine diesel engine high-pressure oil pump. The three-dimensional model of the cam-roller pair can be updated by directly modifying the parameters through the UI interface.

3. The design method of the marine cam-roller pair according to claim 1 or 2, characterized in that: When using the multi-island genetic algorithm for optimization and iteration in S5, the number of subgroup scales is not less than 10, the number of island group scales is not less than 10, the number of evolutionary generations is not less than 10, the migration interval algebra between islands is 5, and the number of optimization and iteration times is not less than 1000 times.

4. The design method of the marine cam-roller pair according to claim 1 or 2, characterized in that, In S4, import the calculated equivalent stress, contact stress and deflection of the cam-roller pair into ncode, analyze and calculate the number of cycles of the cam-roller pair, and convert to obtain the fatigue life of the cam-roller pair.

5. The design method of the marine cam-roller pair according to claim 1 or 2, characterized in that: After reassembling the cam and the roller according to the cam rotation angle corresponding to the maximum load obtained by the analysis in S3 in S4, geometric segmentation is performed at the theoretical contact position of the cam and the roller. The segmentation standard is that the width on the left and right of the contact line between the cam and the roller is 20% of the cam base circle radius, and the height above and below is 15% of the cam base circle radius; a reference point is established at the center of the roller, and an MPC constraint is applied between this reference point and the inner ring surface of the roller to restrict the left and right degrees of freedom of the roller, so that the roller can only roll up and down around the cam. At the same time, the maximum load is applied at the reference point; the property of the entire contact surface during the working process of the cam and the roller is defined as hard contact, and the friction coefficient is 0.02, obtaining a finite element simulation analysis model of the cam-roller pair.

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