Technical Research And Equipment Development For Crankshaft Fillet Impact Strengthening Of Internal Combustion Engine

To meet the increasingly stringent requirements of emission regulations and fuel consumption standards,internal combustion engines will continue to adopt technologies such as supercharging and high-pressure fuel injecting to improve the efficient of combustion,thus the maximum explosive pressure will be increased dramatically accordingly.For heavy duty commercial vehicles,the maximum cylinder explosion pressure has increased from 170-190bar in the current national V standards to 200-250bar in next generation VI.To meet the requirements of GB20891,which stated that off road diesel engines below 560KW must meet the emission standard released in fourth stage,the medium and large capacity internal combustion engines will be required to improve emissions standard and decrease fuel consumption through new techniques subsequently.For the goal of "higher mobility,greater load capacity,and greater power output" within the limited space,the expectation of internal combustion engine power density is increased higher and higher.Not only the structure optimized,the explosive maximum pressure in the cylinder will be increased to 250-300bar.Thus,the requirement for the higher strength and more fatigue cycles of the crankshaft in proposed accordingly.For the limitation of separated measures available to improve the strength of crankshaft under higher explosive maximum pressure（≥220bar）and density of power performance,compound strengthening approaches are highly needed.Advanced numerical computations algorithms and newly invented experimental testing techniques provide good approaches and equipment for solving the urgent problems.Based on the above techniques,this work proposes the solution measures of crankshaft fillet strengthening.The main works are listed as follows:The main existing compound strengthening methods are classified into two categories,one is nitrogen hardening combined with fillet rolling,and the other is induction hardening with fillet rolling.Corner rolling is important and applied in both strategies of manufacturing processing for crankshaft.But for better results,extremely large rolling pressure is required to strengthen crankshafts mounted on off-road medium and large internal combustion engine.It is difficult that the current rolling equipment,no matter that manufactured at home or abroad,are capable to satisfy the requirements mentioned above.Deep rolling equipment is monopolized by Hegenscheidt,a German company.It needs 10 million Rmb to import a rolling equipment for automobile crankshaft,a larger one is more expensive.This work researched the mechanism of mechanical shock strengthening for crankshaft fillet on internal combustion engine,The conclusion could be stated as follows.The exterior surface material plastic deformation can be obtained through mechanical impacting,this processing result in the distortion of lattice.With the appearance of the distortion.compressive residual stress will be created.It can be expected to enhance the fatigue cycles of crankshaft through reducing the maximum tensional stress in working conditions.then a mechanical platform is established for shock testing,with which the feasibility of shock strengthening technology was validated.Using finite element method,this work established a new parameterized model of crankshaft to simulate strengthening procedure and proposed computational schemes under different working conditions.Through the simulation of the fillet impact strengthening,the response under different boundary conditions and loading parameters are solved,then resultant stress and displacement distribution analyzed.Different computational schemes,such as impacting angle,impacting speed,and crankshaft rotation angle,affect the deformation and stress distribution of the impact the local region.The optimal processing parameters holding best impact effect are obtained according to numerical results,which lays the foundation for the structure layout and parameters selections of subsequent impact strengthening equipment.According to the parameters obtained through experiment and numerical simulation,this work proposes the scheme of mechanical impact strengthening equipment for the crankshaft fillet.From numerical computation and analysis,the influence of crankshaft fillet impact on the residual stress distribution was obtained,which laid the theoretical foundation for the mechanical impact strengthening.Then the structure and processing parameters of the crankshaft fillet impact strengthening equipment can be determined.Using the equipment,the objective strength parameters can be satisfied for manufacturing crankshaft of heavy-duty internal combustion engine.Experiment was designed and conducted to get the parameters of impact strengthening,including the crankshaft fillet deformation,surface hardness,surface and subsurface residual stress distribution,metallography structure,crankshaft fatigue strength.The mathematical model was constructed between processing parameters and procedure,residue stress and fatigue cycles accordingly.Test results show that for the crankshaft with a fillet radius of 5.5±0.25mm,after surface induction quenching and surface grinding,the impact hammerhead with a radius of 5.25mm is applied according to the process parameters of 45° included angle between the impact hammer axis and the crankshaft axis,the impact speed of the impact hammer is 3m/s,and the crankshaft angle between two adjacent impacts is 2°.The crankshaft fillet is mechanically impacted,and the residual compressive stress of the crankshaft fillet can cover the circle.The residual compressive stress of the crankshaft fillet is 60%higher than that of the crankshaft without mechanical shock strengthening,and the fatigue strength of the crankshaft is 31.7%higher than that without mechanical shock strengthening.The resultant comparisons show general objective parameters are satisfied through the proposed mechanical shock strengthening.In conclusion,this work proposes compound measures,integrating theoretical development and simulation analysis,with experimental verification systematically.It proposes a solution to the key techniques of crankshaft fillet impact strengthening,and develops an automated crankshaft fillet mechanical impact strengthening equipment successfully.The impact strengthening of medium and large internal combustion engine crankshaft is implemented for specified type,in which the processing procedure is streamlined and the processing parameters are optimized.Results show that the fatigue strength of the crankshaft is increased.The equipment is manufactured for the strengthening of crankshaft in medium and large internal combustion engine,getting rid of the dependence on expensive imported equipment.The application and test of the compound measures has proved the effectiveness and reliability of the proposed solutions.