Research On Fretting Wear And Contact Fatigue Characteristics For Underneath Type Valve Train Of Engine

Underneath type valve train is one of the most important valve mechanisms for engines.It completes intaking and exhausting gas for engine by closing and opening engine valve.Its property has an important influence on the performance of engine.When underneath type valve train performs regularly,the fiction action appears between transmission friction pairs.Wear is generated on the components.Which leads to the failure of valve mechanisms,which has a bad effect on gas exchanging process of engine.So research on the friction and wear properties of transmission friction pairs for underneath type valve train has very important significance and applied value.In the work,the fretting friction and wear characteristics of transmission friction pairs for underneath type valve train were studied.The friction transmission pairs contains the pair of tappet and beam,the pair of beam and rocker arm,and the pair of rocker arm and boot.Besides,considering the performing condition of the critical component,the contact fatigue property of boot was studied too.The main contents are as follows:(1)The fretting wear properties of the friction pair of tappet and beam were investigated under different working conditions.The results show that under the condition of dry friction,with the increase of load or frequency,the average coefficient increases prior and decreases then Meanwhile the wear loss of tappet always increases,when load and frequency are certain,the friction coefficient under oil lubrication is far less than which under dry fiction.Compared with the condition of dry friction,the wear loss of tappet decreases 98.2%under oil lubrication,under the condition of dry friction,the wear mechanism is mixed with slight abrasive wear,adhesive wear and fatigue wear.By contrast,under the condition of oil lubrication,the wear mechanism of tappet is mainly abrasive wear.(2)Effect of rolling on fretting wear properties of beam material were investigated.The results show that Treated by rolling process,the Friction coefficient and wear loss of the friction pair decrease significantly.It generated a harden layer which is high hardness and contains residual compressive stress.It can improve wear resistance of material.The wear mechanism of untreated samples is mixed with intense adhesive wear and fatigue wear.By contrast,the wear mechanism of treated samples is slight abrasive wear mainly.(3)The fretting wear properties of the friction pair of rocker arm and boot and the contact fatigue properties of boot were investigated.The boot material was treated by surface carburization.The results show that it generates a carburized layer on surface of boot material by carburization treatment.It enhances the wear resistance of material.The wear mechanism of untreated samples is mixed with abrasive wear and fatigue wear.By contrast,the wear mechanism of treated samples is slight adhesive wear mainly.With the increase of load,the average coefficient decreases.But with the increase of frequency,the average coefficient increases prior and decreases then.Meanwhile the wear loss of boot always increases.Besides,the wear mechanism of contact fatigue are mainly pitting corrosion and peeling corrosion.