| The full-floating piston pin connection pair is a common mechanism with gaps in internal combustion engines.Because there is a certain gap between the parts,periodic collisions between the piston pin and the small end of the connecting rod are easy to form.When the impact is excessively excited,it may even cause the internal combustion engine Abnormal noise occurs during the work process,causing abnormal damage to parts.Due to the continuous improvement of the degree of strengthening of diesel engines,the mechanical load of the sliding bearing formed by the piston pin and the small connecting rod bushing will not only increase,but the lubrication performance is also likely to decrease,thereby strengthening the impact between the piston pin and the small connecting rod head As well as friction and wear,and form a larger knocking noise.Therefore,in view of the noise generated by the collision between the full-floating piston pin and the small end of the connecting rod,the mechanism and influencing factors are studied,and the collision noise between the piston pin and the small end of the connecting rod is controlled.NVH performance is of great significance.This paper takes an in-line four-cylinder engine as the research object,uses Hypermesh software to perform finite element pre-processing on the piston,connecting rod and piston pin models,and verifies the correctness of the reduced model through the combination of modal test and modal simulation.Based on AVL EXCITE POWER UNIT,a flexible multi-body dynamics model of the piston connecting rod group was built.The main research contents and results are as follows:1)In the intake stroke stage,the crankshaft rotation angle 764°CA—802°CA piston pin quickly moves from the upper end of the connecting rod small end bushing to the bearing area under the bushing.This stroke displacement is-45.8?m;in the exhaust stroke stage,the crankshaft The rotation angle is 1376°CA—1413°CA.The piston pin moves from the bearing area under the connecting rod small head bushing to the upper surface of the bushing quickly,and the displacement stroke is-42.5?m.2)The vertical force of the piston pin relative to the small end of the connecting rod and the vertical velocity have dynamic changes during the intake and exhaust strokes.The vertical force of the piston pin relative to the small end of the connecting rod fluctuates around the crankshaft angles of 798°CA and 1394°CA.The former has a maximum value of 3207.9N,and the latter has a minimum value of-3041N;the piston pin is relative to the connecting rod.The vertical speed of the small head fluctuates greatly around the crank angle of 796°CA and 1389°CA,respectively.The peak speed of the former is 9.4mm/s,and the peak speed of the latter is-7.96 mm/s.3)The longitudinal acceleration of the piston fluctuates greatly around the crankshaft angles of 798°CA and 1393°CA respectively.The peak acceleration of the former is 881.2m/s2,and the peak acceleration of the latter is-266 m/s2;The impact between the small ends of the rods causes the vertical component of force to reverse,and drives the piston to form a longitudinal knock on the cylinder liner to produce noise.By controlling the gap between the piston pin and the piston pin seat,it shows that the impact between the piston pin and the small end of the connecting rod is the main factor for the noise of the piston pin.4)There are extreme values corresponding to the minimum oil film thickness curve and the maximum oil film pressure curve near the noise of the piston pin,and when the crankshaft angle is 798°CA(the minimum oil film thickness point of the intake stroke),the minimum oil film thickness appears in the circumferential direction of the bearing bush.At the position of 174°,and at the crankshaft angle of 797°CA(maximum point of maximum oil film pressure in the intake stroke),the maximum oil film pressure is also located at 174° in the circumferential direction of the bearing bush.The impact position is not near the ideal 180° position,but near the extreme point of the maximum oil film pressure position;similarly,when the crankshaft angle is 1394°CA,the maximum oil film pressure extreme value appears at 21° in the circumferential direction,as explained above The appearance of piston pin noise has a mutual influence with lubrication.5)Three schemes of parabolic,superelliptical and triangular are designed,and the radial gradient of each scheme is 4?m,8?m and 12?m respectively.The lubrication performance of the parabolic line is significantly improved compared to the lubrication performance of the non-profiled line,while the lubrication performance of the superelliptic and triangular-shaped line is lower than that of the non-profiled line,and the roughness between the journal and the bearing is increased.Probability of contact.Among them,the parabola with a radial gradient of 4?m can improve the lubrication performance of the small end bearing of the connecting rod;the parabola with a maximum radial deformation of 12?m not only affects the vertical displacement of the piston pin relative to the small end of the connecting rod in the early stage of the intake stroke.The peak velocity in the vertical direction is significantly reduced,and the vertical peak velocity of the piston pin relative to the small end of the connecting rod at the end of the exhaust stroke is also reduced.6)It can be seen from the matching clearance between different connecting rod bushes and piston pin that within the radius clearance range of 16-28?m,increasing the matching clearance can effectively increase the lubrication performance of the bearing,but it will also strengthen the piston pin.The degree of impact with the small end of the connecting rod indicates that the noise of the piston pin is sensitive to the clearance.7)The increase in roughness will improve the lubrication,and has a significant impact on the vertical speed peak of the piston pin relative to the small end of the connecting rod at the beginning of the intake stroke,and the vertical speed peak of the piston pin relative to the small end of the connecting rod at the end of the exhaust stroke.Has little effect. |
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