The Study And Design On Camshaft Wearing Based On Exhaust Braking

The vehical brake systerm is the main quarantee of high speed and safety driving.As a car,the brake systerm includes driving brake,parking brake and so on.The driving brake can not brake continuously.The practical driving experience shows long and frequent using driving brake will make brake too hot to brake effectively,even arises danger.So it is necessary to introduce un-declining accessorial brake. The exhaust brake make vehical speed keep steady declining by using the declining of engine speed.It don't use driving brake. As a contious brake device,the exhaust brake has much benefit.1.simple and low cost;2. reliable work and convenient use;3.high efficiency and long life;4.saving much fuel;5.making brake smooth and comfort. In this paper, the necessity and benefit of exhaust braking of engine have been discussed. Also some wearing problems between cam and tappet of valve train are set forth because of applying exhaust braking.And the author proposes that these problems can be soluted by the optimizing design of cam profile Using exhaust braking bring some questions for engine.The most serious question is that valve train is so different that it arose rebound of valve. The phenomena can be eliminated by improving the sping stiffness.But thus will lead to the wearing between cam and tappet of valve train,the reliability of valve train and the life of engine.The paper intend to reduce the wearing of valve train and improve the reliability of engine. The method of optimizing design of cam profile can improve performance of valve train and reduce the wearing between cam and tappet.It's a effective method. Some correlative research show optimizing design of cam profile can reduce the wearing.And another method is to improve material character of important parts of valve train.The paper discuss the concept, category, research and application of optimizing design of valve train,especially stress the definition, research status and application of cam valve train According to the characteristics of the cam valve train, the paper thoroughly analyzed the kinematics and dynamics of cam valve train. The results illuminate the influence of valve-timing, ample factor and the contact stress between cam and tappet on the design of cam profile. According to the category of valve train, the paper design three cam profile by polydyne method. The paper thoroughly analyz the kinematics and dynamics of valve train cam profile, checkample factor and the contact stress between cam and tappet and pick out the optimized cam profile. Finally,the reliability experiment prove the new cam profile can solute the problem about the contact stress between cam and tappet.and reduce the wearing.between cam and tappet. The main study work: (1) Ensure that exhaust brake brings serious problems for cam valve train,and propose the method to solve wearing problem; (2) According to the requirement of valve train,design several cam profile,make dynamic calculation to verify them; (3) Obtain the optimizing cam profile by performance test and reliable test; (4) Ensure corresponding engine exhaust brake using optimizing cam profile,improve the reliablity of engine.