Study On The Influence Of The Roundness Of Connecting Rod On Elastic Hydrodynamic Lubrication Of Connecting Rod Bearing

With the improvement of degree of the engine, The explosion pressure in cylinder is higher, and the reliability of the parts is higher. As the main part of the transmission power, Conrod bearing is required to have a higher structural strength and lubrication performance to withstand alternating compression and tensile loading. The lubrication state of conrod bearing are greatly influenced by the machining precision and assembly precision. However there are such factors as dimensional tolerance, machining error and assembly error in the manufacturing process of the conrod, which leads to the positioning deviation in the assembly process of the conrod body and the conrod cap, makes the big hole to produce different type of roundness, So that the connecting rod bearing presents the non circle condition, resulting in bearing lubrication performance degradation. Therefore, the influence of the non circular degree of the conrod bearing on elastohydrodynamic lubrication is studied, which provides a reference for the conrod bearing to improve the design and optimization of the conrod bearing assembly process.Combined with the conrod bearing manufacturing company to test data, summarizes the conrod bearing round degree of different forms and causes to the crank and connecting rod mechanism of a high pressure common rail inline four cylinder diesel engine; On the basis of this, the finite element model and the finite element model of elastic dynamic lubrication are established. Studied the effect deformation of different assembly load on the conrod bigend and the effect of different forms of roundness to elastic dynamic lubrication of conrod; It was tested with roundness measuring instrument that deformation of conrod bigend hole before and after assembly and deformation of conrod bigend under different bolt pre tightening force. The main research contents are as follows:(1) Simulation research on influence of conrod bearing bolt pretightening force and bearing force interference on deformation of conrod bigend.In a simple bolt pretightening force, conrod bearing bigend hole stress is the largest region appeared in bearing the 90°and 270°position (0°direction is direction of between smallend to bigend); conrod bigend has a shrink deformation, conrod cap deformation was significantly greater than the conrod bigend deformation, it has the maximum deformation at 120°and 240°.In the simple bearing interference force, the conrod bearing bigend hole stress is the largest region appeared in bearing the 90°position and 270°location area; Conrod bearing bigend hole appeared to expand deformation, conrod bearing cap deformation was significantly greater than that of the conrod bearing shaft deformation, deformation maximum area of the bearing degree of 120 and 240°position.When the bolt pretightening force and bearing force interference common loading, due to the bolt pretightening force and bearing a surplus force should force in the opposite direction, deformation direction is opposite, stress and deformation were counteracted partially, areas of maximum stress and deformation area and the maximum appeared in the 90°and 270°position of conrod bigend hole. When the conrod bearing bolt pre tightening force is increased, the connecting rod big end hole between 55 degrees to 130 degrees and 230 degrees to 305 degrees between the position of the stress will increase, deformation of between 125°to 135°position becomes small, other regions are not affected by the preload of the connecting rod bolts..(2) The conrod bearing bigend hole test showed that: ① Conrod complex roundness is diversity when the conrod cap and the conrod body assembled and disassembled at different times, there are different forms of the same conrod with different assembled and disassembly; ② The influence of pre tightening force of connecting rod bolt on the side deformation of the connecting rod is larger than that of the rod body side, with increase of the bolt pre tightening force; With the increase of the bolt pre tightening force, the large deformation of the conrod bigend hole 120°and 240°position. The simulation results of the simulation bolt preload are verified. ③ With the increase of the bolt pre tightening force, conrod bearing circle shape and elliptical deformation round degree increases, conrod bearing dislocation deformation roundness decreases.(3) Effects of different degrees of bearing roundness to elastic hydrodynamic lubrication.When the conrod bigend bearing has a circular deformation and the relative roundness is less than-0.051, with relative roundness decreases, conrod bearing lubrication performance variation; when the relative roundness is greater than-0.051, conrod bearing lubrication performance with relative roundness increases becomes worse.When the conrod bearing occurs in the transverse elliptical deformation, the lubrication performance of the conrod bearing becomes poor with the increase of the absolute value of the relative roundness.When the conrod has a longitudinal elliptical deformation and the relative roundness less than-0.051, with relative roundness decreases, conrod bearing lubrication performance variation; when the relative roundness is greater than-0.051 and less than 0, lubrication performance of conrod bearing with relative roundness decreases and changed for the better; when the relative roundness is greater than 0, the performance of bearing lubricating rod with relative roundness increases relatively good.When the connecting rod occurs horizontal displacement, with the increase of the absolute value of the relative degree of round rod, conrod bearing lubrication performance variation. It is appears asperity contact on the conrod bearing bearing edge, asperity contact pressure and friction loss are increased sharply.