Study On Mechanical Properties Of Connecting Rod-Bearing Bush Contact And Shot Peening On Hole Surface Of A Diesel Engine

Large high power Marine diesel engine is always working under high speed and heavy load conditions.Connecting rod and bearing bush are the key parts of power output.The correct coordination of the contact surface is an important guarantee for the transmission system to maintain reliable working state under complex and changeable working conditions.At present,the contact of connecting rod-performance requirements rise ceaselessly,the matching characteristic has received extensive attention of scholars both at home and abroad,this subject focused on a certain type of ship diesel engine connecting rod-the interface between the contact behavior,the contact surface before and after the long running circumferential relative slipping phenomenon(skid)study,in order to avoid the occurrence of busbar skid.In view of the above problems,this paper firstly analyzed the causes of circumferential slip between connecting rod and bearing bush from the dynamic characteristics,then carried out numerical analysis on the contact performance between connecting rod and bearing bush,and finally optimized the mating parameters of connecting rod and bearing bush by using the orthogonal test method,the specific contents are as follows:(1)The friction between connecting rod and bearing bush and between bearing and journal is introduced.The rotation speed of the crankshaft when the bearing slips is obtained through torsional vibration test,and the scratches on the inner surface of the bearing are found through disassembly,and the dry friction between the crankshaft and bearing bush is determined.Then,the thick-wall cylinder theory of interference assembly of connecting rod and bearing bush was introduced and the maximum and minimum binding pressures of interference assembly of bearing bush were calculated to be 9.7MPa and 17 MPa respectively.Interference range is0.14mm-0.26 mm.(2)Motion analysis was carried out on the crank connecting rod mechanism,the dynamic calculation into connecting rod statics calculation,after connecting rod-bearing shell finite element model is established,and numerical calculation under different axle bush interference quantity under the condition of assembly cylindrical surface contact friction force and the maximum compression condition bearing internal and external round surface contact with the shaft friction,through comparing the findings: Under the maximum compression condition,the contact friction of the outer circular surface of the bearing bush is smaller than that of the assembly condition.When the interference is 0.18-0.22 mm,the friction of the inner circular surface of the bearing bush is greater than that of the outer circular surface of the bearing bush.Finally,the single factor analysis of the connecting rod and bearing bush’s matching parameters(bolt preload and interference)shows that the influence of bolt preload on the contact friction of the outer circular surface of bearing bush is increasing,and the influence of interference is basically positive linear.It is proposed to change the friction coefficient between the contact surface of bearing bush to avoid the slip of bearing bush.(3)By analyzing roughness and friction coefficient,it can be obtained that the recommended range of friction coefficient between connecting rod and bearing bush of Ra3.2-6.3 is 0.18-0.3,and that of Ra6.3-12.5 is 0.3-0.5.By analyzing roughness and contact force,it can be obtained as follows: The contact force between connecting rod and bearing bush decreases with the increase of roughness,and the roughness of the connecting rod’s big hole reaches 21.88μm,and the contact friction of the outer circular surface of bearing bush is 226249 N,which effectively increases the friction between connecting rod and bearing bush to resist the sliding friction of bearing and journal.A single shot peening finite element model was established to analyze the surface roughness of the connecting rod hole holder.The single factor method was used to study the influence of shot peening parameters(projectile size,projectile velocity,incident Angle)on the surface roughness,and it was concluded that the projectile size and projectile velocity had a linear relationship with the workpiece surface roughness.The incidence Angle from 75° to 90° decreases first and then increases with the increase of Angle.Combined with orthogonal test analysis of shot peening parameters on the hole inner surface roughness of the influence degree of projectile respectively from big to small sizes,projectile velocity,Angle,when the projectile dimension is 0.25 mm,the projectile velocity of 85m/s,the incident Angle is90°,get the target value of surface roughness,connecting rod hole by using BP neural network to predict workpiece surface roughness after shot peening,It provides reference for shot peening treatment.