Research On Operation Uniformity Control Of High Pressure Common Rail Diesel Engine

Because of stringent emission regulations and the energy demand contradictions increasingly prominent, diesel engine high pressure common rail fuel injection system was created. With the rapid development of electronic technology, internal combustion engine electronic control technology progress unceasingly, which makes better engine control, improve engine performance.Due to the high pressure common rail diesel engine each cylinder fuel injection imbalances and each cylinder combustion system differences in other factors, engine cylinder-to-cylinder uneven work is caused. Thus deteriorate the engine emissions and reduce the economic performance, increased the mechanical stress and wear, reduce the comfort of the vehicle. Aiming to improve the engine running characteristics under the steady state condition, the cylinder-to-cylinder work uniformity control of high pressure common rail diesel engine is one of the key technologies of electronic control system. To better play to the advantage of high pressure common rail system on the flexible control, on the basis of full research at home and abroad a large number of literature and data, combined with the research of high pressure common rail diesel engine electronic control unit (ECU), around cylinder-to-cylinder work uniformity control problem of high pressure common rail diesel engine electronic control system, a deep and systemic theory and experiment research was carried out. Research works mainly focus on four aspects:(1) In consideration of characterization parameters about cylinder-to-cylinder work uniformity, the feature of the crankshaft angular segment period signal (CASPS) was studied. Based on the characteristics of the crankshaft instantaneous angular velocity, real-time demand for ECU data processing, a kind of new characterization parameters about cylinder-to-cylinder work uniformity is developed, namely the crankshaft angular segment period signal (CASPS). The cylinder pressure signal and the CASPS were tested. By discrete Fourier transform for data analysis, combined with multi-cylinder torque vector superposition theory to order time component, the variation law of CASPS under different working condition was studied, and the relationship of CASPS to each cylinder crankshaft torque was analyzed. Research shows that in engine working uniform state, the CASPS spectrum characteristics are different in high, medium and low speed range. In low speed range, the main order (order 2k (k= 1,2,3,...)) spectrum amplitude is significantly greater than the adjacent subordinate order (order (2k±)) spectrum amplitude, its significant degree gradually reduced, with the increase of engine average speed and also with the increase of harmonic order k. Under uneven engine working condition, the spectrum amplitude of low and non-main order harmonics (order 0.5, order 1 and order 1.5) below the firing frequency increase obviously. The spectrum amplitude size of low-order non-primary harmonic component associates with the degree of uneven engine working and the uneven status of each cylinder. In each cylinder pressure action range, the variation of CASPS can be divided into two sections:rising and the falling range of interval, namely acceleration and deceleration interval of the crankshaft instantaneous angular velocity. Regardless of engine in the working condition of uniform or non-uniform conditions, the starting point of CASPS falling range basically corresponds to each cylinder top dead center of compression stroke.(2) In consideration of the accuracy of CASPS reflecting the engine work non-uniformity, the influence of the torsion vibration upon CASPS was investigated. A multi-quality and double quality elastic torsion vibration characteristic of crankshaft system was investigated through theoretic analysis. Torsion vibration testing and analysis was carried upon crankshaft free-end and the flywheel end of a four cylinder high pressure common rail diesel engine. Research shows that low order non-main order torsion vibration completely belongs to the rigid crankshaft torsion vibration; this has the advantage for using transient speed and CASPS to detect engine work uniformity. Under the condition of elastic shaft, the low order harmonic components below the firing frequency are no longer able to correctly reflect the internal combustion engine work non-uniformity.(3) In consideration of fuel control problem upon the internal combustion engine work non-uniformity, fuel offset control was researched based on CASPS. Based on CASPS characteristics, quantitative method of engine work uneven degree and individual cylinder fuel offset control (FOC) algorithm was built, and the work uniformity control strategy of high pressure common rail diesel engine was putted forward. According to the principle of FOC control, based on automotive electronics development ASCET software platform, FOC control software module of ECU was designed, and the simulation experiment was carried out. Research shows that for Z cylinder engine, just the first Z/2 harmonic components below fire frequency can fully reflect the state of the engine uneven work. The control target to individual cylinder FOC is that synthetic waveform amplitude of the first Z/2 harmonic components is zero. Based on this target, proportional integral (PI) control algorithm is proposed to quantify engine individual cylinder unevenness degree, and the fuel amount offset value was got. Based on CASPS characteristics under engine different working condition, the reasonable working condition of detecting engine individual cylinder unevenness degree was put forward, and the open loop and closed loop control mode based on the condition was set up. In view of the high pressure common rail diesel engine electronic control system functional requirements, using a powerful 32-bit processor TC1796, through modular concept, the ECU board was designed. Bench test shows, it can meet the design index, satisfy the requirement of precise control for common rail diesel engine. In the design of ECU board, the crankshaft sensor signal conditioning circuit required by FOC was optimized.(5) In view of the high pressure common rail fuel injection control and engine crankshaft phase management strictly depended on by FOC control, the engine position determination sensors signal configuration, the control strategy for engine position determination and the backup mode of engine position determination was studied. Research shows that requirements of the installation phase of sensor fluted disc can be reduced, and engine position determination time can be reduced through high pressure common rail diesel engine position determination sensors signal configuration method based on the software control identification word. The high pressure common rail diesel engine position determination software based on software control identification word has good portability and can be flexible to adapt to the different number of cylinders of the engine and sensor fluted disc. Through the state machine control mode, the high pressure common rail diesel engine position determination control strategy to meet the requirements of accuracy, rapidity, security, usability. Backup mode is divided into individual crankshaft signal backup mode and individual camshaft signal backup mode. Backup mode can ensure the safety and availability of the system. Normal mode can ensure the accuracy and rapidity of the system.