Research On Electronic Control Unit Of A Multi-Variable Control Diesel Engine

Based on the characteristics of "low temperature combustion controlled by combustion boundary conditions",the new generation combustion technology was an effective way to achieve high efficiency and clean combustion of diesel engine.After years of research,our group had proposed a multi-variable control diesel combustion system using a mixing strategy of low temperature combustion and high-density low temperature combustion.The combustion system was coupling intake charge,intake valve closing timing,EGR rate and injection strategy to achieve the full range of operating conditions of low temperature combustion path control and efficient clean combustion process,yet the electronic control technology was the most effective way to control combustion process.Therefore,the problem of multi-variable collaborative control as the guide,the scientific and systematic research as the core,the high efficiency clean combustion with multi variables as the purpose,MPC5554 microprocessor of Freescale company adopted,the cooperative control of multiple control variables,the expansion of the hardware and software functions of electronic control unit,and the improvement of the control accuracy requirements were studied systematically in this thesis.The main conclusions were as follows:The new generation of combustion technology demanded electronic control unit could flexibly adjust fuel injection mode,and accurately control injection quantity,injection timing and so on.This put forward higher requirements for injector drive circuit and injection timing algorithm.In order to improve the control precision of fuel injection quantity and reduce combustion cyclic variations,injector drive circuit,structure parameters,and driving parameters were studied,also the performance Comparison between variable freewheeling and RD freewheeling was carried out.It can be seen that of variable freewheeling,the current cutting off process was 30 us shorter,and the control accuracy of cycle fuel injection quantity was improved 0.36%at least and 2.86%especially at small fuel injection quantity.Moreover,Variable freewheeling showed low electric consumption due to the driving energy recovery realized through a feedback from the solenoid to the Boost power,and the temperature rise of the drive circuitry was only 37?,which was 127? lower than RD freewheeling due to decrease of electric consumption of drive circuitry.Finally,a multi-cylinder engine combined type double power supply variable freewheeling drive circuit and optimized scheme of reducing circuit noise were produced.The combustion cycle-to-cycle validation by using it was reduced 0.5%,and the biggest reductions of NOx and soot emission were 3.5%and 4%,which compared to last generation of electronic control unit by experimental test.Aiming at increasing the transient condition injection timing control precision and reducing CPU logical load,the reason why a great injection timing deviation in fast acceleration coursed by injection timing algorithm based on CPU interrupt mode was analyzed,and further develop of injection timing algorithm based on angle clock was designed.Without using CPU interrupts,the new injection timing algorithm could determine engine phase,and flexibly modulate multi-pulse fuel injection strategy,and ensure The maximum injection timing deviation is not more than 0.02?A under transient conditions.Moreover,the exhaust gas recirculation(EGR)control system,the intake valve delay closing(RIVCT)control system,the variable geometry turbocharger(VGT)control system and engine stability and transient control strategy were designed.In order to improve the reliability and stability of software system,the multitask real time operating system was grafting on it,and the combination partition and priority assignment of tasks were carried out according to the task characteristics.Multi variable control technology was not a simple superposition relationship,but mutual promotion and mutual restriction.In order to study the strategy of multi-variable control diesel engine combustion system,the test was carried out using the new electronic control unit.The effect of high pressure,RIVCT,EGR and two-pulse injection on combustion was studied under steady state conditions.It was found that after high pressure turbocharged diesel engine adopting RIVCT at high speed and medium load,the compromise emissions between NOx and soot were substantially reduced,the effective thermal efficiency was improved due to the decrease of pumping loss.soot emission was more sensitive to EGR,which meant the optimal compromise emission between NOx and soot could be found by appropriately reducing the EGR rate.soot emission was greatly reduced when post injection ratio and timing were appropriate,also NOx emissions declined slightly.Compared with 1600rpm,the best post injection radio is smaller and the best post injection timing is earlier at 1900rpm,which meant decreasing post injection radio and advancing injection timing were helpful to obtain better emission from medium to high speed under middle load.VGT opening strategy adopting constant first then increasing gradually and RIVCT keeping opened,an experimental test of how double injection strategy and EGR valve retarded opening timing affect the performance of adding load process at 1600rpm indicated that single injection had a satisfactory torch response performance but double injection could reduce emission.The main injection timing of double injection mainly affected torch response performance and post injection timing mainly affected emissions.The EGR opening timing come too early would course torch response and peak value of soot deteriorated,but torch response and NOx emission deteriorated when it was too late.Finally,the feasibility of transient control strategy was verified by the National IV standards:under ELR test condition,torch response of each speed were within Is,and peak value of soot were less than 0.4m"1;Under ETC test condition,correlation coefficient R2 of torch response was 0.99,the weighted average value of PM and NOx were 0.023 5g/kWh and 3.46g/kWh,which could meet the requirements of the regulation test.