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Optimization and weight reduction analysis of diesel engine connecting box

with the increase of railway transportation volume, the requirements for the speed of diesel locomotives are further improved, and the weight of locomotives should be as light as possible. Therefore, the design department of our factory has put forward weight reduction requirements for many parts in locomotives. In order to ensure that the weight reduction is based on a reasonable theory, we use the finite element method to minimize the size of the structure by using the internal optimization analysis function of the software. In this paper, the connecting box of diesel engine is selected as the object of weight reduction to optimize the weight reduction analysis

Figure 1 finite element model of diesel engine connecting box

1. Establish the finite element model

the connecting box of diesel engine is a thin-walled casting, and its shape is relatively complex, as shown in Figure 1. When building a solid model, if the shape of a thin wall is complex, its thickness cannot be displayed as a size, so it cannot be used as a design variable to drive the change of solid shape. If the shell element is used to model, its element thickness can be easily set as the design variable. Therefore, the shell element is used to simulate the structure of the connecting box. Because the connection box is a symmetrical structure, a 1/2 structure model can be established, and then the whole model can be formed by turning the model. Then properly constrain the model, and apply the force and torque transmitted by the diesel engine and the main generator at the bolt hole position of the front and rear flange plates (because the load is not evenly distributed, the force and torque should be first converted to the node of each bolt hole by the finite element method, and then applied to the bolt hole position of the connection box). And apply supercharger load on the upper part of the connection box. The finite element model is shown in Figure 1. In this paper, I-DEAS software will be used for analysis

the result of static strength analysis is: the v o n m i s e s stress is 185 m PA, bit 2.2 automatic shift: automatically switch to the appropriate range and shift to 1.59mm according to the load. At this time, the mass of the model is 294.7kg. The stress diagram is shown in Figure 2

Figure 2 stress diagram of the model

II. Establishment of the optimization model

next, the optimization method of mathematical programming redesign is selected in the optimization analysis module of I-DEAS software to optimize the model, and the parameters of the optimization model are as follows

1. Optimization variable

◎ T25 - flange edge thickness connected with the main generator. The initial value is 25mm, the upper limit is 30mm, and the lower limit is 20mm. The unit is shown in Figure 3

◎ T30 - thickness of flange edge connected with diesel engine. The initial value is 30mm, the upper limit value is 33mm, and the lower limit value is 20mm. The unit is shown in Figure 4

◎ T18 - wall thickness of the box. The initial value is 18mm, the upper limit is 20mm, and the lower limit is 15mm. The unit is shown in Figure 5

◎ T16 - thickness of stiffener. The initial value is 16mm, the upper limit value is 20mm, and the lower limit value is 10mm. The unit is shown in Figure 6

◎ T17 - thickness of flange connected with main generator. The initial value is 17mm, the upper limit value is 20mm, and the lower limit value is 10mm. The unit is shown in Figure 3

Figure 3 optimization model

2 The material of the stress constraint

connection box is ZG, and its yield strength is 230MPa. Taking the safety factor as 1.3, the allowable stress is 177mpa. Set this value as the constraint function

since the displacement value is very small from the static strength analysis results, only the stress value can be constrained here

3. The objective function

model has the lightest weight

III. solution of optimization model

1 The first optimization solution

set the iterative control according to the following values: the maximum number of iterations is 50, the redesign factor is 5%, and the convergence limit is 0.005

after 50 iterations, the actual weight (red line) does not converge with its upper limit (green line) and lower limit (blue line), indicating that it does not converge, that is, it does not reach the optimal goal. The optimization results are shown in Figure 4

Figure 4. The results of 50 iterations

stress history curve and weight history curve are shown in Figure 5. The historical curve of each design variable is shown in Figure 6

Figure 5 stress history curve and weight history curve

Figure 6 historical curve of each design variable

through analysis, it is concluded that the maximum von Mises stress after optimization is reduced to 178mpa, and the model mass is reduced to 289kg. At this time, the values of the optimization variables are: t25=25.19mm, t30=27.99mm, t18=17.82mm, t16=17.54mm, t17=14.8mm. These optimization variables are rounded appropriately: t25=25.2mm, t30=28mm, t18=17.8mm, t16=17mm, t17=15mm, and then a new model optimal-1 is established. After static strength calculation, the following results are obtained: the maximum von Mises stress is 176mpa. At this time, the mass of the model is 288.3kg

2. The second optimization solution

because the first solution does not reach the optimal range selection principle: 0~50kg is selected for measuring the tensile strength of garment leather; 0~100kg upper leather; The 0 250kg target is selected for the sole leather, so the results should be optimized again

when optimizing again, we set the iterative control as: the maximum number of iterations is 10, the redesign factor is 1%, and the convergence limit is 0.005

Figure 7 the result of 10 iterations

the historical curve of the objective function after solution is shown in Figure 7, and it is close to convergence after 13 iterations. At this time, the historical curves of stress, mass and each optimization variable are shown in Figures 8 and 9

Fig. 8 historical curve of stress and variables

Fig. 9 historical curve of optimized variables

after optimization, the von Mises stress is 177 MPa, and the model quality is 281 at this time (3) Pour 3 kg of concrete with strength grade not less than C20 in the pit. The values of each optimization variable are: t25=25.25mm, t30=26.63mm, t18=17.38mm, t16=17.04mm, t17=13.77mm

since the dimension of wall thickness cannot be decimal, the above variable values must be rounded for many times. The first rounding result is as follows:

t 25 = 25 mm, T 30 = 27 mm, t 18 = 17 mm, t 16 = 17 m, t17=14mm

at this time, the static strength analysis result is that the V O nmises stress is 180MPa, and the model mass is 279.3kg. The stress is out of tolerance

the second rounding result is:

the thermal conductivity is superior to the others, t 25 = 26 m m, T 30 = 27 m, t 18 = 17 m, t 16 = 17 m, t17=14mm

at this time, the static strength analysis result is still vonmises stress 180MPa, and the stress is out of tolerance. The mass of the model is 280.8kg

the results of the third rounding are:

t 25 = 26 m m, T 30 = 27 m, t 18 = 18 m, t 16 = 17 m, t17=14mm

at this time, the static strength analysis result becomes the von Mises stress 177mpa, and the model mass is 287.5kg

IV. conclusion

after the above optimization analysis, the von Mises stress of the connecting box model is reduced from 185mpa to 177 MPa, and the 1/2 mass of the connecting box is reduced from 294 7 kg down to 287 5 kg, reducing 7.2kg, reducing the mass of the whole connecting box by 14.4kg. Since the design of the connection box itself is more refined, the weight reduction is limited. However, through finite element analysis, the stress distribution of the redesigned structure tends to be more reasonable, and further analysis can be carried out on this basis to constantly seek better results. (end)

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