阅读说明：本技术 实现预控废气再循环系统的控制方法 (Control method for realizing pre-control exhaust gas recirculation system ) 是由 尹丛勃 张振东 崔兴龙 何明宇 朱海兵 于 2019-10-21 设计创作，主要内容包括：本发明涉及一种实现预控废气再循环系统的控制方法,根据所采集的发动机转速和负荷的变化率信号,来确定下一周期预控EGR阀开度的调整量,在实际EGR阀开度的基础上增加EGR阀开度预调整量,完成对EGR阀预开度计算；当前信号采样周期内,控制器根据发动机转速、负荷以及各种修正信号确定EGR阀理想的目标开度,然后和确定的EGR阀预控制开度进行比较,基于两者的误差和误差率通过MAP查表的方式,确定PID调整参数,而非通过多次计算进行PID参数整定的方式完成对EGR开度误差的调节。通过上述预控制EGR系统可以有效解决系统瞬态响应慢的问题,有效的降低了系统的震荡和超调,提高了EGR系统的瞬态响应性。(The invention relates to a control method for realizing a pre-control exhaust gas recirculation system, which determines the adjustment quantity of the pre-control EGR valve opening in the next period according to the collected change rate signals of the engine rotating speed and the load, increases the pre-adjustment quantity of the EGR valve opening on the basis of the actual EGR valve opening, and completes the calculation of the pre-opening of the EGR valve; in the current signal sampling period, the controller determines the ideal target opening degree of the EGR valve according to the rotating speed, the load and various correction signals of the engine, then compares the target opening degree with the determined pre-control opening degree of the EGR valve, determines PID adjusting parameters in a MAP table look-up mode based on the error and the error rate of the target opening degree and the error rate of the EGR valve, and does not complete the adjustment of the EGR opening degree error in a PID parameter setting mode through multiple times of calculation. The problem of slow transient response of the system can be effectively solved by the pre-control EGR system, the oscillation and overshoot of the system are effectively reduced, and the transient response of the EGR system is improved.)

1. A control method for realizing a pre-control exhaust gas recirculation system is characterized by comprising the following steps:

1) the control unit collects a current throttle position signal and an engine rotating speed signal in each sampling period to perform conversion calculation, and two groups of signals corresponding to the sampling periods are obtained: the first group of signals are engine speed signals and load signals; the second group of signals are an engine speed change rate signal and a load change rate signal;

2) obtaining the opening of a basic exhaust gas recirculation valve according to the current first group of signals, correcting the opening of the basic exhaust gas recirculation valve by combining the temperature of cooling liquid at the current acquisition moment and the temperature of inlet air, and determining the target opening of the exhaust gas recirculation valve under the current engine working condition by looking up a calibrated exhaust gas recirculation valve opening map;

3) predicting the pre-control change value of the opening of the exhaust gas recirculation valve in the current period according to the second group of signals in the previous period, and obtaining the pre-opening of the exhaust gas recirculation valve in the current period together with the actual opening of the exhaust gas recirculation valve in the previous period;

4) calculating the error and the error rate of the current target opening of the exhaust gas recirculation valve obtained in the step 2) and the preset opening of the exhaust gas recirculation valve obtained in the step 3), wherein if the error does not exist between the current target opening of the exhaust gas recirculation valve and the preset opening of the exhaust gas recirculation valve, the preset opening of the exhaust gas recirculation valve is the opening of the exhaust gas recirculation valve in the current engine running state, and the PID (proportion integration differentiation) parameters do not need to be adjusted to control the opening of the exhaust; and if the error exists, adjusting the opening degree of the exhaust gas recirculation valve by looking up a table to adjust the PID parameters according to the error and the error rate.

Technical Field

The invention relates to an energy recycling technology, in particular to a control method for realizing a pre-control exhaust gas recirculation system.

Background

EGR (exhaust Gas recirculation) is to introduce a part of exhaust Gas in an exhaust pipe of an engine into an intake manifold through an EGR system, mix the exhaust Gas with fresh air again and then enter a cylinder, and because the exhaust Gas has the characteristics of higher specific heat and capability of reducing combustion temperature, the introduction of the EGR system can effectively reduce the emission amount of NOx in the emission of the engine. However, if the actual EGR rate is not properly controlled, the effect of reducing engine emissions is not achieved, but the engine dynamics and fuel economy are affected, so that it is very important to accurately control the EGR rate. In order to solve the problem, the market mostly adopts an electric control EGR system to control the flow of the exhaust gas.

The existing mature electric control EGR system is generally composed of an ECU (electronic control unit), an EGR valve position sensor, a stepping motor actuator, an oxygen sensor, an EGR valve with a return spring and the like. And the ECU completes the functions of data acquisition, working condition judgment, coordination of various subprograms, control signal output and the like. The sensors include sensors of rotational speed, accelerator pedal position, coolant temperature, and intake air pressure. The rotary motion of the stepping motor is changed into linear motion through the screw mechanism to push the EGR valve to be balanced with the return spring, and the position of the EGR valve is determined. And obtaining an EGR valve position MAP graph under each working condition through experiments and storing the EGR valve position MAP graph into the ECU. When the engine runs, the ECU calculates the position of the EGR valve according with the working condition at that time according to the correction signals of the engine speed, the load basic signal, the temperature and the like, the ECU converts the determined target EGR valve opening degree into an EGR solenoid valve Pulse Width Modulation (PWM) signal, and the duty ratio of the solenoid valve control signal is adjusted, so that the opening and closing time of the EGR solenoid valve is changed, and the exhaust gas flows to an air inlet pipe through an EGR system. The control logic is shown in the flow chart of the electrically controlled EGR valve driving execution in FIG. 1. The actual opening degree of the EGR valve is fed back to the ECU through the displacement sensor, and for the error existing between the actual EGR opening degree and the target EGR opening degree, PID is generally adopted for adjusting to eliminate the error, namely, the feedback signal of the displacement sensor is utilized for carrying out closed-loop control on the EGR valve, so that the control progress is improved, and the schematic diagram of the closed-loop control is shown in FIG. 2.

The exhaust gas of the control process needs to pass through an exhaust pipe, an EGR cooler, an EGR valve and a compressor and then enters an intake manifold, the structure that the exhaust gas passes through is large, meanwhile, the calculation amount of a setting parameter is complex due to the fact that the traditional PID control is used for the error existing between the actual EGR valve opening and the target EGR valve opening, and the overshoot and oscillation phenomena can occur in the adjustment process system.

Disclosure of Invention

The invention provides a control method for realizing a pre-control exhaust gas recirculation system, aiming at the problem that the response of an EGR system is slow and the actual EGR rate is inaccurate due to the fact that overshoot and oscillation phenomena are easy to occur in the process of adjusting the time-varying nonlinear EGR system by a traditional PID control method, and the pre-control of the EGR valve opening of the next signal sampling period of an engine is completed based on the current EGR valve opening by combining the change rate of the load and the rotating speed of the engine and the adjustment of a time sequence; and adopting a MAP look-up table PID control to control the error of the opening of the EGR valve determined by pre-control and the ideal EGR valve opening corresponding to the engine working condition in the next signal sampling period.

The technical scheme of the invention is as follows: a control method for realizing a pre-control exhaust gas recirculation system specifically comprises the following steps:

1) the control unit collects a current throttle position signal and an engine rotating speed signal in each sampling period to perform conversion calculation, and two groups of signals corresponding to the sampling periods are obtained: the first group of signals are engine speed signals and load signals; the second group of signals are an engine speed change rate signal and a load change rate signal;

2) obtaining the opening of a basic exhaust gas recirculation valve according to the current first group of signals, correcting the opening of the basic exhaust gas recirculation valve by combining the temperature of cooling liquid at the current acquisition moment and the temperature of inlet air, and determining the target opening of the exhaust gas recirculation valve under the current engine working condition by looking up a calibrated exhaust gas recirculation valve opening map;

3) predicting the pre-control change value of the opening of the exhaust gas recirculation valve in the current period according to the second group of signals in the previous period, and obtaining the pre-opening of the exhaust gas recirculation valve in the current period together with the actual opening of the exhaust gas recirculation valve in the previous period;

4) calculating the error and the error rate of the current target opening of the exhaust gas recirculation valve obtained in the step 2) and the preset opening of the exhaust gas recirculation valve obtained in the step 3), wherein if the error does not exist between the current target opening of the exhaust gas recirculation valve and the preset opening of the exhaust gas recirculation valve, the preset opening of the exhaust gas recirculation valve is the opening of the exhaust gas recirculation valve in the current engine running state, and the PID (proportion integration differentiation) parameters do not need to be adjusted to control the opening of the exhaust; and if the error exists, adjusting the opening degree of the exhaust gas recirculation valve by looking up a table to adjust the PID parameters according to the error and the error rate.

The invention has the beneficial effects that: the control method for realizing the pre-control exhaust gas recirculation system determines the adjustment coefficients of proportion, integral and differential parts of PID (proportion integration differentiation) regulation by means of MAP (MAP) table look-up according to the error existing between the pre-control EGR valve opening and the target EGR valve opening instead of eliminating the error by performing PID setting through traditional repeated calculation, thereby effectively reducing the oscillation and overshoot of the system and improving the transient response of the EGR system.

Drawings

FIG. 1 is a flow chart of an electronically controlled EGR valve actuation implementation;

FIG. 2 is a schematic diagram of closed-loop control of an EGR electronic control system;

FIG. 3 is a flowchart illustrating the operation of a control method for implementing a pre-controlled EGR system in accordance with the present invention;

FIG. 4 is a schematic diagram of a prior art EGR system control method;

FIG. 5 is a schematic diagram of a control method for implementing a pre-controlled EGR system in accordance with the present invention;

FIG. 6 is a diagram of an electronically controlled EGR system of the present invention.

Detailed Description

The operation flow chart of the control method for realizing the pre-control exhaust gas recirculation system of the invention as shown in FIG. 3 comprises the following steps:

the ECU converts and processes the acquired throttle position signal and the acquired engine speed signal into two signals: the first signal is an engine speed and load signal; the second signal is an engine speed and load rate of change signal. A time sequence exists when the two signals are sent, and 5ms delay exists between the rotating speed and load change rate signals and the sending of the rotating speed and load signals;

the method comprises the following steps that a first signal engine speed and a first signal load signal are used for judging the basic state of an engine, meanwhile, the correction effect of the temperature of cooling liquid and the temperature of inlet air on the basic EGR valve opening degree is considered, the calibrated EGR valve opening degree map is looked up, the ideal EGR valve opening degree of the current engine working condition is determined, and the method has the following effects: comparing the pre-opening degree of the EGR valve determined by the previous signal sampling period; the engine speed and load change rate signals are used for determining the change trend and the adjustment quantity of the opening of the pre-control EGR valve, and the ideal opening adjustment quantity of the pre-control EGR valve is determined by a calibrated MAP (MAP look-up table);

after the opening of the EGR valve in the current signal acquisition period is adjusted, the adjustment quantity of the opening of the pre-controlled EGR valve is determined based on the load change rate and the rotating speed change rate, and the pre-control of the opening of the EGR valve corresponding to the working condition of the engine in the next signal acquisition period is completed on the basis of the opening of the EGR valve in the current period and the adjustment quantity of the opening of the pre-controlled EGR valve;

and fourthly, judging the current basic running state of the engine according to the load and rotating speed signals acquired in the current signal sampling period (the action finished in the previous signal sampling period at the moment in the third step), considering the correction effect of the coolant temperature and the intake air temperature on the opening degree of the EGR valve, and determining the target opening degree of the EGR valve in an ideal state by looking up the calibrated ideal MAP value of the opening degree of the EGR valve.

And fifthly, determining the error rate and the error rate between the target EGR valve opening degree of the current signal acquisition period (step four) and the pre-control EGR valve opening degree of the previous signal acquisition period (step three). If the two have no error, the pre-control EGR opening degree of the previous sampling period is the EGR valve opening degree of the current engine running state, and the PID parameter does not need to be adjusted to control the EGR valve opening degree; and if the error exists, adjusting the opening degree of the EGR valve by looking up a table to adjust the PID parameter according to the error and the error rate.

The MAP lookup table PID used in the step five is specifically: and determining the magnitude of the adjusting coefficients of the proportional, integral and differential parts in a MAP table look-up mode according to the error and the error rate of the target EGR opening degree and the opening degree of the pre-control EGR rate. The P, I, D three-part coefficients are determined by bench test and real vehicle calibration in the early stage, and then a parameter MAP is determined by taking error and error rate as dependent variables. The mode of determining the PID adjustment parameters by the MAP table lookup can well overcome the problems of large calculation amount, easy occurrence of delay, overshoot and oscillation of the traditional PID setting. The operation flow chart is shown in fig. 3.

According to the flow chart of FIG. 3, the implementation steps of the technical scheme are detailed as follows, namely, on the basis that the EGR valve opening degree is adjusted in the last signal sampling period, the EGR valve pre-control opening degree in the current period is determined according to the engine speed and the load change rate. Determining a target EGR valve opening corresponding to the current engine state according to signals such as the engine speed, the load and the like of the current signal sampling period, if the pre-controlled opening of the EGR valve and the ideal EGR valve opening do not have errors, the pre-controlled EGR valve opening of the previous signal sampling period is the actual EGR valve opening corresponding to the current engine state, if the pre-controlled opening of the EGR valve and the ideal EGR valve opening do not have errors, performing PID pulse spectrum table lookup according to the errors and the error rates of the pre-controlled EGR valve opening and the ideal EGR valve opening, directly determining adjustment parameters of the proportion, the integral and the differential, and determining the actual EGR valve opening after PID adjustment. On the basis that the EGR valve opening adjustment is completed in the current signal sampling period, the EGR valve opening variation is determined in a MAP table look-up mode based on the current rotating speed and the load variation rate, and the pre-control of the EGR valve opening in the next signal sampling period is completed according to the actual EGR valve opening and the pre-control EGR valve opening adjustment.

The method is characterized in that the pre-control amount of the EGR valve opening is determined by calculating the change rate of the current engine speed and load, and the pre-control EGR valve opening adjustment amount is added on the basis of the current finished EGR valve opening before the sampling of a next sampling signal is not started to pre-adjust the EGR valve opening of the next sampling period. Calculating the error of the pre-control opening of the EGR valve and the target opening of the EGR valve corresponding to the engine state in the current signal sampling period, wherein if the error does not exist, the pre-control opening of the EGR valve at the moment is the opening of the EGR valve in the current sampling period; if an error exists, the PID adjustment coefficient map is looked up according to the error and the error rate, the optimal adjustment parameter is determined, the adjustment is not performed through calculation, the response speed is greatly improved, and the system oscillation is effectively avoided. The problem of slow transient response of the system can be effectively solved through the pre-control EGR system, the required target EGR rate can be quickly and accurately achieved, and further the fuel economy and the dynamic performance of the gasoline engine are improved.

In the aspect of control software, a pre-control EGR valve opening degree calculation module based on the engine speed and the load change rate is adopted; for error adjustment, the invention is improved relative to the traditional PID control, and parameters of the PID are directly determined by a MAP table look-up mode based on the error and the error change rate instead of repeated error calculation and setting, thereby greatly reducing the calculated amount and avoiding the problems of system oscillation, overshoot and the like caused by the traditional PID adjustment. The control scheme of the EGR regulation system is shown in the figures 4 and 5, wherein the figure 4 is the scheme of the existing EGR control system, and the figure 5 is the scheme of the EGR control system of the invention.

By comparing the two EGR control schemes of fig. 4 and 5, the present invention is advantageous in that: (1) and predicting the running condition of the engine in the current signal acquisition period according to the engine speed and the load change rate in the previous signal sampling period, and increasing the opening adjustment amount of the pre-control EGR valve on the basis of the actual opening of the EGR valve in the previous signal sampling period to complete the pre-control of the opening of the EGR valve in the current signal period. The purpose of quickly responding to the opening degree of the ideal target EGR valve corresponding to the current engine can be achieved; (2) and for the error between the pre-control EGR valve opening and the ideal target EGR valve opening corresponding to the current engine, performing the following processing: and calculating the error and the error rate of the two parts, and completing the PID regulation of the error and the error rate by using ideal control coefficients corresponding to proportion, integral and differential parts in the PID control corresponding to the previous calibration error and error rate. Through the calibration of the early parameter MAP, the problems of large calculated amount, overshoot, system oscillation and the like in the parameter setting process in the traditional PID adjustment can be effectively solved. Through a mode of MAP look-up table PID, the error between the target EGR valve opening and the pre-control EGR valve opening can be rapidly eliminated, so that the EGR system can rapidly respond to the target EGR valve opening corresponding to the current running condition of the gasoline engine; (3) by pre-controlling the EGR control system, the problem of transient response of EGR can be effectively solved, and the dynamic property, the fuel economy and the emission of the engine can be effectively improved.

In the electronically controlled EGR system shown in fig. 6, the data acquisition module performs digital filtering on the acquired data and determines the fault of the sensor. The control module judges the real-time working condition of the engine according to the data processed by the data acquisition module, inquires the related EGR valve opening degree map and calculates the target EGR valve opening degree and the pre-control EGR valve opening degree. And the PID module compares the pre-control EGR valve opening degree with the target EGR valve opening degree to perform PID adjustment on the error. The EGR valve driving module adjusts an opening degree of the EGR valve through a driving motor by using a pulse modulation signal (PWM). The communication module is used for realizing information interaction between the EGR control module and other EMS (engine management system) function modules. The diagnosis module is mainly used for diagnosing whether CAN communication is normal or not and detecting whether abnormal seating phenomena such as blockage and the like occur in the EGR valve or not.