| With increasingly stringent emissions standards, a variety of emissions saving technology become an important research topic to improve diesel engine level. The electronically controlled technology, which makes a variety of other technology flexible, accurate, efficient and feature-rich, has been widely used in domestic and foreign automotive diesel engine.In order to adapt to the requirement of above national sate IV emissions regulatory, not only the diesel injection pressure, fuel injection quantity and injection timing should be controlled accurately, but also air-fuel ratio and exhaust gas of diesel engine should be controlled like gasoline engine.The content of this article is researching and software optimization on control strategy of rail pressure based on multi-stage closed-loop, control strategy of multi-injection based on coordination, control strategy of air charge management based on coupling, control strategie of DPF regeneration based on inner machine, as well as diesel and vehicle test. The detail contents are as follows:1. By analysis of “EGR + DPF " and " SCR " technology, system precept of target diesel engine was designed. Depending on inner purification, more accurate and flexible fuel injection system and VGT+EGR-based electronic air charge management system have been designed to achieve precise control of fuel injecting and air charge. Depending on outside purification, the DOC + DPF after-treatment system is designed to filter the exhaust, achieving ultra-low emissions.2. In aspect of improving control precision of rail pressure, multi-level closed-loop control strategy based on the actual rail pressure and Inlet Metering Unit(IMU) current has been designed. According to complex operating conditions of diesel passenger cars, a reasonable division of the rail pressure control status was devoloped, in order to control the driving signal of each actuator timely and accuratly; in transient operating conditions, self-learning of closed-loop current initial value, transient pre-control of rail pressure, relief control of fuel injector have been researched and designed. Simulation and experimental results show that the control strategy has the desired control effect, with rail pressure deviation within ± 5bar in stable conditions and within ± 20 bar in transient operating conditions, meeting requirements of the actual use.3. Multi-injection control strategy has been designed, in order to make diesel combustion law close to the ideal combustion model. According to large number of experiments, diesel injection curve under different operating conditions has been abtained by analysis of the multiple injection combination affecting emissions. Based on the injection curve and physical characteristics of injectors and pump, coordination control arithmetic has been designed, accessing to multiple combinations and solve the problems of coordination between the multi-injection. Furter, based on engine operating conditions and multiple combinations, multiple injection activation, injecting quantity and timing model was built.4. As a goal to improve the PM and NOx emissions, control strategy of VGT+EGR-based coupling air charge management has been proposed, which determines the technical direction of reducing PM and NOx emissions. Air charge management control model, based on the inlet air flow rate and inlet air pressure, has been designed to achieve the precise control of the inlet air. Combined with the fuel injection control, air-fuel ratio could be closed loop controlled. In aspect of improving control results of air charge management, multi-level closed-loop control model based on the inlet air flow rate, inlet air pressure and position sensors, the stable and transient air flow and boost pressure prediction model have been built. Experiments show that the control strategy provides an ideal control to meet the actual application requirements.5. Regeneration of DPF based on inner machine has been first proposed, which increase exhaust gas temperature of diesel to realize regenerating by coordinating multi-injection and air charge management. Soot loading model based on the pressure error, engine speed and load, as well as exhaust back limited pressure model based on speed and exhaust temperature, has been built to determine the timing of regeneration, ensuring the regeneration is accurate and reliable. Map model of regeneration measures containing the diesel engine speed and load factor, as well as the regeneration temperature control model, has been built to determine regeneration measures in different condition, achieving safety and effective regeneration process for DPF.6. The above control strategy has been tested on the hardware in loop and pump test stand, diesel engine bench and vehicle. The test results show that the control strategy was implemented with good performance and high reliability. Meanwhile, the emissions of diesel meet the Natioal IV emissions standard with a larger margin, which of NOx and PM emissions, achieves more than 20% and 50% margin respectively. |
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