| The crankshaft connecting rod system plays a transmission role in the crankshaft operation,and there is great friction between the journal and the connecting rod surface,especially in the area of incomplete liquid lubrication,which increases the temperature of the friction interface and intensifies the wear,resulting in the journal and bearing bush sintering and locking,affecting the vehicle operation safety.Research and development of high performance ductile cast iron instead of forged steel crankshaft,providing important support for the development of lightweight engine technology and high strength,high wear resistance crankshaft technology development.During the research of ductile cast iron crankshaft,it was found that the in-situ pits formed after the surface graphite ball fell off played a positive role in enhancing the tribological properties.The reasonable application of surface in-situ texture technology on surface can improve the problem of burnt bush during the working process of crankshaft.Using a new polishing technology to accelerate the falling off of graphite balls on the surface of ductile cast iron,in-situ textures with different diameters,depths and area densities were prepared.Through friction and wear experiments and fluid simulation analysis,the effect of in-situ texture parameters on surface tribological behavior is analyzed from the perspective of wear mechanism.Combining hydrodynamic lubrication theory,the mechanism of in-situ texture improving crankshaft operating performance and surface lubrication is explored,and the optimal texture parameters are searched.The effect of in-situ textured ductile iron parts and polished forged steel parts on tribological performance is compared,providing theoretical reference for the processing of high-performance ductile iron crankshafts.In structural simulation,use SOLIDWORKS to establish a structural model of an in-line six-cylinder crankshaft and import it into ANSYS simulation software.Add QT700-2 material parameters for static,dynamic,fatigue strength,and modal analysis.Simulate the working process of the crankshaft by applying a load to the journal.The stress distribution on the journal surface of the single crank and integral crankshaft models in the static and dynamic simulation results provides a reference basis for the range of bearing capacity required for the oil film,and verify that the QT700 strength meets the use conditions.The fatigue strength results show that the fatigue life under rated load exceeds one million revolutions,meeting the design requirements.In the modal analysis,the vibration frequency of the crankshaft at a rotational speed of 3000 rpm is 150 Hz,which is smaller than the first order natural frequency with constraints.Therefore,the fracture failure of the crankshaft is not caused by the vibration of the engine itself.In the field of fluid simulation,the in-situ texture was prepared by using the graphite ball shedding characteristics,through heating,heat preservation,rapid cooling pretreatment,and then vibration polishing to accelerate the graphite ball shedding.A planar unidirectional sliding friction convergent wedge shaped micro texture geometric array model was established by observing in-situ texture.Combining the N-S equation,a numerical solution is used to solve the lubrication model and perform dimensionless transformation.The dimensionless tribological performance parameters of the oil film are calculated,thereby judging the hydrodynamic lubrication performance.Five texture elements and four area density textured oil film fluid simulations were conducted using FLUENT simulation software to simulate the effects of texture diameter,depth,and area density parameters on hydrodynamic lubrication.The results show that as the texture diameter increases,the dimensionless bearing capacity of the oil film first increases and then decreases,with a maximum increase of 18%.The dimensionless friction force and friction coefficient at the friction interface gradually decreased,with the maximum friction force decreasing by 42%.When the graphite ball completely falls off and has a complete hemispherical pit depth,the best pressure supply effect for the oil film is achieved.When the area density is 9%,the dynamic pressure effect of the oil film is the most obvious.In terms of friction and wear,RTECMFT-50 friction and wear testing machine was used to conduct friction and wear experiments on in-situ textured QT700 ductile iron and polished40 Cr forged steel under different loads,frequencies,and lubrication conditions.Analyze the tribological behaviors such as friction coefficient,wear rate,and wear morphology of the surfaces,and analyze the wear mechanism and lubrication mechanism of the in-situ textured specimen surface,and provide reference for the manufacturing and processing of iron instead of steel crankshafts. |
