Design Of Fully Hydraulic Variable Valve System For Diesel Engine And Research On Exhaust Heat Management Performance

Aiming at the problem of low working environment temperature of the aftertreatment system under certain working conditions of diesel engine,fully hydraulic variable valve system(FHVVS)suitable for single overhead camshaft drive was developed to achieve exhaust heat management performance.By matching and designing different cam profiles and oil control valve components,it can realize the functions of early intake valve closing(EIVC),secondary/single opening of intake and exhaust valves,early exhaust valve opening(EEVO)and closing of intake and exhaust valves.Based on this,the appropriate valve opening method is selected as the heating control strategy for exhaust heat management.At the same time,the simulation calculation results of different opening strategies in terms of exhaust temperature increase and fuel economy are used as measurement standards,and the best control strategy is selected and the structure matching design is carried out.Based on the above research ideas,this article mainly carried out the following work:(1)The 1D thermodynamic simulation calculation software GT-Power was used to build the simulation calculation model of the target diesel engine.In the process of building the simulation model,subsystems are first divided according to the actual structure of the diesel engine.Then use the component module to complete the function and mathematical description of different subsystems,and establish the corresponding mathematical model.The initial parameter values of each module are set by using the existing reference materials.Finally,the experimental data are used to compare the simulation results under the same working conditions,and the error between the two is less than 5%,which ensures the accuracy of the established model.(2)Innovatively proposed a "one core two valves" oil control valve and a variable independent control system for the intake and exhaust valves.The new design scheme can effectively expand the variable control range of FHVVS,and realize a richer combination of valve opening.Based on the reference to the structural composition of FHVVS and the working principle of the core component oil control valve,modular analysis and paired design methods are used to complete the overall structural design of the FHVVS matching six-cylinder diesel engine.(3)The diesel engine gas distribution mechanism reverse towing test bench was built.The variable frequency motor is used to drive and simulate the engine’s different speed working conditions,the hydraulic pump station is used to replace the original machine lubrication system to realize the parts lubrication and transmission medium supply,and the laser displacement sensor and other equipment are used to complete the valve lift signal collection and analysis.(4)The exhaust heat management performance of diesel engine based on variable intake valve opening strategy was studied.The simulation model is used to calculate the exhaust heating effect of EIVC and IVRO strategy.The results show that the exhaust temperature can be increased to 185℃ when the intake valve early closing time is 486℃A,and the charge coefficient is reduced to 0.6,which is the limit position where the diesel engine can achieve stable compression ignition.The IVRO strategy adopts the method of only changing the reopening time and fixing the maximum opening lift and duration.When the reopening time is adjusted to 183℃A,the maximum exhaust temperature rise of 15.3℃ can be achieved.(5)The exhaust heat management performance of DI engines based on variable intake and exhaust valve opening strategy was studied.Early exhaust valve opening can slightly increase the exhaust temperature,but it is detrimental to fuel economy;the normally closed cylinder deactivation to increase the exhaust temperature gradually increases with the decrease in the number of working cylinders.Innovatively proposed a combination of early intake valve closing and exhaust valve reopening strategy.The simulation results show that the exhaust temperature can be increased to more than 250℃ under idling conditions to meet the requirements of the aftertreatment system.