The contact parts of the connecting rod are: connecting rod body and connecting rod cover, connecting rod body and connecting rod body bearing bush, connecting rod cover and connecting rod cover bearing bush, connecting rod body and bolt, connecting rod cover and nut, connecting rod body bearing bush and A total of 11 contact pairs are provided for the connecting rod cover bushings, bolts and nuts, connecting rod cover bushings and crankshafts, connecting rod bushings and crankshafts, connecting rod bodies and bushings, bushings and piston pins.
The connecting rod bearing is not a true circle in the free state, and the indication and measurement of the interference is performed on a special measuring tool as shown. The interference of the bearing bush is h=u+v. If u is the part above the platform, it is given by the tolerance, which is 0.06mm; v is the shortening deformation caused by the pressure of 8740N, calculated as 0.048mm, so The interference of the bearing bush is 0.108mm. This interference is the interference between the connecting rod bearing bush and the connecting rod cover bushing, which is different from the traditional way of adding radial interference.
In the numerical analysis and calculation of the bolt pre-tightening force, the analysis is mainly carried out under the two calculation conditions of the maximum pulling condition and the maximum pressing condition. During the working process, the maximum torque condition has a low rotation speed and the pressure working condition is relatively bad, but the pulling condition has no bad working condition; the overspeed condition has a high rotation speed and the pulling condition is bad, but the pressure working condition is not rated. Poor working conditions. Therefore, the rated operating conditions are selected as the calculation conditions. In order to determine the appropriate bolt pre-tightening force, 13 different bolt pre-tightening forces were selected from 28kN to 60kN for calculation, and the response of each part of the connecting rod with the bolt pre-tightening force was observed.
According to the actual situation and experience analysis, the influence of the bolt pre-tightening force on the stress and strain value of the contact surfaces of the connecting rod mainly has the following aspects: 1) The combination of the connecting rod body and the connecting rod cover, mainly considering them Is it possible to maintain a certain amount of contact pressure? 2) The combination of the connecting rod cover bush and the connecting rod bearing bush also sees whether a certain contact pressure can be maintained between them. 3) Deformation of the connecting rod cover bush. 4) The strength of the bolt itself.
The calculation results analyze the combination of the connecting rod body and the connecting rod cover. The sufficient contact pressure between the connecting rod body and the connecting rod cover is the key to the normal operation of the connecting rod. Therefore, many links numerical analysis also regard this part as the analysis focus.
The combination of the connecting rod cover bush and the connecting rod bearing bushing is an interference fit between the connecting rod bearing bush and the connecting rod. This interference fit relies on the bolt preloading force to compress the connecting rod upper and lower bushings. Therefore, the pressure on the contact surface between the connecting rod cover bush and the connecting rod bearing bush is an important index for evaluating whether the bolt pre-tightening force is suitable.
The strain condition of the connecting rod cover bushing is more susceptible to damage due to the connecting rod cover bushing than the connecting rod bearing bushing. Therefore, the strain on the connecting rod cover bushing is mainly analyzed.
The main analysis of the four parts: 1) the average strain on the contact surface of the bearing bush and the connecting rod cover. 2) The contact surface is the area No. 1 shown as 0, which is in contact with the link body bush. 3) The contact area is the area No. 2 as indicated by 0. 4) The area 3 on the contact surface as indicated by 0. Since the area is far from the bolt and is on the split plane, a symmetry constraint is imposed in the analysis.
It can be seen from 1 that the average strain decreases with the increase of the bolt pre-tightening force during the pulling condition; the change under the pressure working condition is not obvious. The strain change amplitude of the two kinds of working conditions has a significant decreasing trend with the increase of the bolt pre-tightening force. The smaller the variation, the better the contact between the connecting rod cover and the connecting rod cover bushing, and the less wear between the contact surfaces, which is very beneficial to improve the life of the connecting rod.
Summary Through the above analysis, the following conclusions can be drawn: 1) The bolt pre-tightening force has a great influence on the joint state of the connecting rod cover and the connecting rod body. In order to ensure a good contact pressure, for this type of diesel engine connecting rod, the bolt pre- The tightening force should be at least greater than 44kN. The bolt pre-tightening force also has a great influence on the joint state of the connecting rod cover bush and the connecting rod bearing bush. In order to ensure the normal operation of the bearing bush, the pre-tightening force of the bolt is greater than 44kN.2) The pre-tightening force of the bolt is mainly concentrated on the bolt hole of the connecting rod cover. The larger the pre-tightening force of the bolt, the connecting rod cover and the connecting rod cover bearing bush The better the contact state.
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