JP3617240B2 - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation control device that controls the exhaust gas recirculation amount while detecting the concentration of NOx discharged from an internal combustion engine.
[0002]
[Prior art]
In order to reduce NOx emitted from internal combustion engines such as diesel engines and gasoline engines, exhaust gas recirculation (EGR) devices that recirculate part of the exhaust gas into the intake air and reduce the maximum combustion temperature and pressure are known. .
[0003]
In a diesel engine, when EGR is performed to reduce NOx, the combustion atmosphere becomes oxygen-deficient, and thus exhaust particulates (particulates: PM) and other exhaust components generally tend to deteriorate. In particular, the trade-off relationship between NOx and PM becomes more prominent as the amount of EGR is larger or the excess air ratio is lower. Therefore, to reduce the NOx and PM emissions in a well-balanced manner, it is necessary to precisely control the EGR according to the operating conditions.
[0004]
Therefore, conventionally, for example, according to Japanese Patent Application Laid-Open No. 61-27967, the EG rate is determined based on the engine speed, the load, and the intake air pressure, and the opening degree of the EGR valve is controlled accordingly. Control is performed so as to be a predetermined value or less. Further, if the engine intake charging efficiency changes due to atmospheric pressure, the required EGR rate for reducing NOx without changing smoke and PM also changes, so that the atmospheric pressure is reduced according to Japanese Patent Laid-Open No. 63-239353. Some monitors monitor and correct EGR when driving at high altitudes.
[0005]
However, even if EGR control is performed in this way, since there are many open controls, the actual EGR amount does not always match the target value, and the NOx emission amount varies from engine to engine.
[0006]
Even if the EGR amount is feedback controlled, for example, if the combustion conditions of the engine fluctuate due to moisture in the air, the actual emission amount of NOx and PM changes even if the EGR amount is the same. There is also.
[0007]
Further, when the opening degree of the EGR valve is controlled by the step motor, the number of steps corresponding to the target value is determined, so that the opening degree of the EGR valve is also determined correspondingly and can be controlled to the EGR valve opening degree as the target. However, since the EGR valve does not have an abnormality or failure due to step-out of the step motor or the like, as countermeasures against these problems, as disclosed in JP-A-6-249077 and JP-A-6-229323, intake and exhaust The EGR valve failure is determined by detecting the differential pressure of the EGR, or the failure diagnosis is performed by detecting the EGR temperature as disclosed in Japanese Patent Laid-Open No. 7-42622, or measured as disclosed in Japanese Patent Laid-Open No. 6-137219. Some have diagnosed a failure by comparing the EGR amount with the predicted EGR amount.
[0008]
However, providing a new sensor or diagnostic logic for diagnosing a failure of the EGR valve in this way is not preferable because it complicates the control and increases the cost.
[0009]
[Problems to be solved by the invention]
In any case, the conventional EGR device does not actually detect the NOx emission state even if the control accuracy of the EGR amount is improved by feedback control of the EGR amount. Even if EGR control is performed, NOx emissions may not reach the specified level depending on the engine, and it may not always be possible to stably reduce NOx over a long period of time, including engine deterioration. .
[0010]
By the way, in recent years, NOx sensors for measuring NOx concentration in exhaust gas have been developed. For example, a solid electrolyte type NOx sensor such as that disclosed in SAE960344, or a simple one as proposed in Japanese Patent Application Laid-Open No. 7-325059. A substance that detects a NOx concentration using a substance having a crystal-like structure as a NOx sensitive body is known.
[0011]
Therefore, the present invention calculates the actual NOx emission amount based on the NOx concentration in the exhaust gas, and performs feedback control so that the NOx emission amount matches the target value according to the operating conditions, thereby reducing the NOx emission amount. The purpose is to reduce the variation without variation.
[0012]
Another object of the present invention is to avoid instability of control due to a delay in response of NOx emission amount or detection error from the detection characteristics of the NOx concentration sensor.
[0013]
Another object of the present invention is to make it possible to reliably diagnose an EGR valve abnormality without adding a special sensor.
[0014]
[Means for Solving the Problems]
FirstOr secondThe invention includes means for detecting the engine speed, means for detecting the engine load, means for detecting the intake air amount of the engine, means for calculating the amount of fuel supplied to the engine based on these, In an exhaust gas recirculation control device for an internal combustion engine that includes an exhaust gas recirculation passage that partially recirculates into intake air and an exhaust gas recirculation control valve that adjusts the exhaust gas recirculation amount, the NOx concentration in the exhaust gas flowing through the exhaust passage is detected. NOx concentration detection means, engine speed, negativeTo loadA means for setting a target NOx emission amount accordingly;Correction means for correcting the target NOx emission based on the difference between the target control value of the fuel injection timing of the diesel engine or the intake swirl ratio and the actually measured control value;Means for calculating an actual NOx emission amount based on the engine speed, the intake air amount, and the NOx concentration obtained by correcting the response delay of the NOx concentration sensor;The correctedMeans for feedback-controlling the opening degree of the exhaust gas recirculation control valve so as to coincide with the target NOx emission amount.
[0018]
ThirdAccording to the invention, the feedback control means of the exhaust gas recirculation control valve stops the feedback control when the oxygen concentration in the exhaust gas is high, such as at least during deceleration operation, and the opening degree of the exhaust gas recirculation control valve according to the engine speed and load Open control to.
[0019]
4thThe present invention further comprises means for determining and warning that the exhaust gas recirculation control valve is in failure when the difference between the target NOx emission amount and the measured NOx emission amount is equal to or greater than a preset value.
[0020]
5thIn this invention, the failure determination warning means stops the failure determination during transient operation.
[0021]
[Operation and effect of the invention]
FirstOr secondIn the invention, when the target NOx emission amount is set according to the operating state of the engine, the opening degree of the exhaust gas recirculation control valve is adjusted, and a part of the exhaust gas is recirculated into the intake air from the exhaust gas recirculation passage. Reduce the maximum combustion temperature and pressure of the engine to reduce NOx generated during combustion. On the other hand, the NOx concentration in the exhaust gas is detected, and the NOx emission amount is calculated based on the NOx concentration, the engine speed at this time, and the intake air amount. If the calculated NOx emission amount is larger than the target NOx emission amount, the opening degree of the exhaust gas recirculation control valve is increased, and the exhaust gas recirculation amount recirculated into the intake air is increased to generate NOx. Reduce the amount. On the contrary, when the NOx emission amount is smaller than the target emission amount, the opening degree of the exhaust gas recirculation control valve is decreased to decrease the exhaust gas recirculation amount.
[0022]
In this way, by controlling the exhaust gas recirculation amount so as to always achieve the target NOx emission amount, the drivability due to excessive exhaust gas recirculation and other exhaust components are prevented from being deteriorated. The fluctuation of the NOx emission amount due to the influence of the atmospheric pressure can be prevented, and the NOx emission amount can be accurately reduced to the target state.
[0023]
Also,Since the NOx emission amount is calculated in consideration of the response delay of the NOx concentration sensor, the actual NOx emission amount can be accurately grasped, and the control accuracy can be improved.
[0025]
further,For example, when the fuel injection timing is earlier than the target injection timing, NOx increases relatively, and when the intake swirl ratio increases, NOx also increases. At this time, if the target NOx emission amount is left as it is, the exhaust gas recirculation amount increases due to feedback control, and particulates and smoke increase. Therefore, by correcting the target NOx emission amount to the decreasing side, these The increase can be suppressed.
[0026]
ThirdIn this invention, when the oxygen concentration in the exhaust gas is high, such as when the fuel is cut by deceleration operation, the NOx concentration sensor does not work normally, and an error in detecting the NOx concentration excessively occurs. For this reason, exhaust gas recirculation becomes excessive immediately after resumption of fuel supply after deceleration, and the drivability and particulates deteriorate. Therefore, the feedback control of the exhaust gas recirculation amount is stopped during the deceleration operation, and the open control is performed by the engine speed and the load, so that the opening degree of the exhaust gas recirculation control valve becomes excessively large when resuming the fuel supply after the deceleration. Prevent and ensure good drivability.
[0027]
4thIn this invention, when the difference between the target NOx emission amount and the actually measured NOx emission amount is large due to the feedback control of the exhaust gas recirculation amount, the control system including the exhaust gas recirculation control valve fails. It can be considered that an abnormality such as has occurred. If the failure remains, it is impossible to control the NOx emission amount to the target value. Therefore, in such a case, a failure is determined and a warning is given to prompt repair or the like.
[0028]
5thIn the present invention, during the transient operation, the measured value is likely to cause an error with respect to the target NOx emission amount including the response of the feedback control. Even at this time, if a failure is determined from these differences, an accurate determination cannot be made. Therefore, in such a case, the reliability of the failure determination can be improved by stopping the failure determination.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment when the present invention is applied to a diesel engine will be described.
[0030]
First, FIG. 1 shows a diesel engine fuel injection system.
[0031]
In FIG. 1, a feed pump 6 that preloads fuel is attached to an input shaft 6a of a fuel injection pump 1 that is driven to rotate in synchronization with engine rotation, and further rotates coaxially with the input shaft 6a. At the same time, a plunger 2 connected so as to reciprocate in the axial direction is arranged.
[0032]
The feed pump 6 feeds pressurized fuel to the pump chamber 7, and surplus fuel is returned to a fuel tank (not shown) to maintain the pressure in the pump chamber 7 constant.
[0033]
The plunger 2 is coaxially provided with a face cam 2a having a cam crest corresponding to the number of cylinders, and the plunger 2 reciprocates in the axial direction every time the face cam 2a rides on the roller 8a. For example, in the case of a six-cylinder engine, when the input shaft 6a rotates once, the face cam 2a rides on the roller 8a only six times during this time, and the plunger 2 reciprocates six times. Each time the plunger 2 reciprocates, fuel is sucked into the plunger chamber 2b and pressurized. Reference numeral 2k denotes a return spring that pushes back the plunger 2 against the face cam 2a.
[0034]
In the extension stroke of the plunger 2, the fuel from the pump chamber 7 is sucked into the plunger chamber 2 b via the fuel stop valve 10 and the slit 2 j provided in the plunger 2.
[0035]
On the other hand, in order to pressurize the pressurized fuel in the plunger chamber 2b to the fuel injection nozzle 11 of each cylinder in the compression stroke of the plunger 2, the communication passage 2c communicating with the plunger chamber 2b along the axis of the plunger 2 is provided. The communication passage 2c is formed with a high-pressure passage 2d branched in the radial direction in the middle, and a discharge passage 2e penetrating in the radial direction is formed at the tip.
[0036]
A number of ports 2g corresponding to the number of engine cylinders are equally arranged on the inner periphery of the cylinder 2f around the plunger 2 so as to be selectively connected to the high-pressure passage 2d according to the rotational position of the plunger 2. Each port 2g is connected to a delivery valve 2h (only one is shown), and fuel is pumped from the delivery valve 2h to the fuel injection nozzle 11.
[0037]
The plunger 2 reciprocates six times for each rotation, and pressurizes the fuel sucked each time. The pressurized fuel is pushed into the high-pressure passage 2d from the communication passage 2c, and at this time, the port 2g communicates with the rotation position of the plunger 2. Pressurized fuel is fed to the fuel injection nozzle 11 via the corresponding delivery valve 2h.
[0038]
On the other hand, the control sleeve 3 is slidably fitted on the outer periphery of the plunger 2 and normally closes by covering the discharge passage 2e. However, due to the movement of the plunger 2 in the compression direction, the discharge passage 2e is eventually opened. release. As a result, the pressure in the plunger chamber 2b is released, and the pumping of fuel from the delivery valve 2h to the fuel injection nozzle 11 is completed.
[0039]
Accordingly, the amount of fuel fed into the fuel injection nozzle 11 varies depending on the position of the control sleeve 3, and if the release passage 2e is released early when the plunger 2 moves in the compression direction, the fuel injection amount is small and conversely When the release timing of the discharge passage 2e is delayed, the fuel injection amount increases.
[0040]
In order to control the fuel injection amount, a rotary solenoid 4 for freely changing the position of the control sleeve 3 is provided, and a fuel injection signal from a fuel injection amount control unit 18 is supplied to the rotary solenoid 4. The position of the control sleeve 3 is changed accordingly. The position of the control sleeve 3 is detected by the position sensor 5 and fed back to the control unit 18.
[0041]
Next, the roller 8a on which the face cam 2a rides is controlled by the timer piston 8 in the circumferential direction of the face cam 2a. The illustrated timer piston 8 is rotated by 90 degrees from the actual position for convenience of explanation. A low-pressure chamber 8b and a high-pressure chamber 8c are provided on both sides of the timer piston 8, and the pressure in the high-pressure chamber 8c is adjusted by controlling the amount by which a part of the high-pressure fuel is released to the low-pressure chamber 8b by the control valve 9. As a result, the position of the timer piston 8 changes.
[0042]
When the position of the timer piston 8 changes and the position of the roller 8a is advanced in the rotational direction of the face cam 2a, the position at which the face cam 2a rides on the roller 8a is relatively delayed, and the fuel pressurization start timing by the plunger 2, that is, If the fuel injection timing is delayed and the position of the roller 8a is delayed in the direction opposite to the rotation of the face cam 2a, the pressurization start timing by the plunger 2 is advanced, and the fuel injection timing is advanced.
[0043]
The operation of the control valve 9 is controlled according to the operating state by the signal from the control unit 18 described above, the position of the timer piston 8 is adjusted, and the fuel injection timing is advanced and retarded.
[0044]
The control unit 18 includes a nozzle lift sensor 12 that detects the valve opening timing of the fuel injection nozzle 11, a fuel temperature sensor 15 that detects the temperature of the fuel supplied to the fuel injection pump 1, and an engine coolant temperature. Signals from the coolant temperature sensor 13 that performs the operation, the accelerator opening sensor 16 that detects the accelerator opening, the rotational speed sensor 14 that detects the pump rotational speed, and the like are input. Based on these signals, the fuel injection amount and the injection described above are input. Calculate and output the timing control signal.
[0045]
In this way, the fuel injection amount and injection timing for the engine are controlled in accordance with the operating state, and an exhaust gas recirculation amount control system controlled corresponding to this will be described with reference to FIG.
[0046]
FIG. 2 shows an exhaust gas recirculation system, in which 51 is a diesel engine, 52 is an intake air passage, 53 is an exhaust air passage, and 54 is an exhaust gas recirculation passage for returning a part of the exhaust gas in the exhaust air passage 53 to the intake air passage 52. It is.
[0047]
The intake passage 52 is provided with an air flow meter 55 for measuring the amount of intake air, and an intake throttle valve 56 for restricting intake air in two stages is provided downstream thereof. The exhaust gas recirculation passage 54 is connected to the downstream side of the intake throttle valve 56, and an exhaust gas recirculation control valve (EGR valve) 57 for controlling the exhaust gas recirculation amount is interposed in the exhaust gas recirculation passage 54. .
[0048]
Therefore, the recirculation amount of the exhaust gas flowing from the exhaust passage 53 to the intake passage 52 depends on the differential pressure between the suction negative pressure generated according to the opening of the intake throttle valve 56 and the exhaust pressure of the exhaust passage 53, and Is determined in accordance with the opening degree of the EGR valve 57 at the time.
[0049]
The opening of the intake throttle valve 56 is controlled in two stages by a negative pressure actuator 56a, and a first negative pressure passage for leading negative pressure from a vacuum pump (not shown) to the negative pressure actuator 56a via a first electromagnetic valve 61. 62 and a second negative pressure passage 64 that guides negative pressure through the second electromagnetic valve 63 are connected to each other, and the opening degree of the intake throttle valve 56 is controlled by the negative pressure adjusted by the electromagnetic valves 61 and 63. Is controlled in two stages, and the suction negative pressure generated downstream thereof is controlled.
[0050]
For example, when the first electromagnetic valve 61 stops introducing negative pressure, introduces atmospheric pressure, and the second electromagnetic valve 63 introduces negative pressure, the negative pressure of the negative pressure actuator 56a is weak and the intake throttle is reduced. On the other hand, the opening degree of the valve 56 is relatively large. On the other hand, when the first electromagnetic valve 61 also introduces a negative pressure, the negative pressure is strong and the opening degree of the intake throttle valve 56 is small. When both the first and second electromagnetic valves 61 and 63 are introducing atmospheric pressure, the intake throttle valve 56 is held in the fully open position by the return spring.
[0051]
The lift amount of the EGR valve 57 is changed by the rotation of the step motor 57a, the opening degree thereof is adjusted, and the exhaust gas recirculation amount flowing into the intake air through the exhaust gas recirculation passage 54 is increased or decreased according to the opening degree.
[0052]
Reference numeral 70 denotes a controller which controls the operation of the first and second electromagnetic valves 61 and 63 and the step motor 57a to control the exhaust gas recirculation amount. A NOx concentration sensor 59 for detecting the NOx concentration in the exhaust gas is provided, and the NOx emission amount contained in the exhaust gas is calculated based on the output of the NOx concentration sensor 59, as will be described later. The exhaust gas recirculation amount is feedback-controlled so as to coincide with the NOx emission amount set in advance corresponding to the operating state.
[0053]
For this reason, the controller 70 receives signals from an air flow meter 55, an engine speed sensor (not shown), and an accelerator opening sensor (refer to FIG. 1) for detecting the engine load. A signal from the provided NOx concentration sensor 59 is also input, thereby setting the target NOx emission amount according to the operating state and calculating the NOx emission amount contained in the exhaust gas from the exhaust gas flow rate and the NOx concentration. Then, the opening degree of the EGR valve 57 is feedback-controlled so that the target NOx emission amount and the measured NOx emission amount coincide with each other.
[0054]
The contents controlled by the controller 70 can be expressed as a block diagram of FIG.
[0055]
That is, based on outputs from the rotation speed detection means and the load detection means, the target NOx emission amount search means searches for the target NOx emission amount according to the operating state. Furthermore, means for dynamically compensating for this target value is provided. The outputs from the intake air amount detecting means and the NOx concentration detecting means are compensated by the response delay compensating means, respectively, and the measured NOx exhaust amount calculating means calculates the NOx exhaust amount contained in the exhaust gas from the intake air amount and the NOx concentration. Is done. Then, in the comparison means, the target NOx emission amount is compared with the actually measured NOx emission amount, and the target lift amount of the EGR valve is calculated so that the difference therebetween is eliminated. That is, when the actual NOx emission amount is larger than the target NOx emission amount, the lift amount (valve opening degree) of the EGR valve is increased, and conversely, when the actual NOx emission amount is smaller, the EGR valve lift amount is reduced. This result is output to the EGR valve driving means, and based on this, the lift amount of the EGR valve is feedback-controlled.
[0056]
These control contents in the controller 70 will be described in more detail with reference to the following flowchart.
[0057]
4 to 18 show a first embodiment.
[0058]
First, FIG. 4 is a flow for calculating the cylinder intake fresh air amount Qac, which is executed in synchronization with the engine rotation (Ref. Job).
[0059]
In step 1, the output of the air flow meter AMF is read, and in step 2, the intake air amount is calculated from the output voltage by table conversion. In step 3, the load average value Qas0 is calculated by performing the load average process of the intake air amount.
[0060]
In step 4, the engine speed Ne is read. In step 5, the intake air amount Qac0 per cylinder is calculated as Qac0 = Qas0 / Ne × KCON # from Qas0, Ne and the constant KCON #. In step 6, the fresh air amount Qacn at the intake collector inlet is calculated by performing a delay process for n times of Qas0.
[0061]
In step 7, the cylinder intake fresh air amount Qac and the fresh air amount Qacn obtained in step 6 are calculated as follows using the volume ratio Kvol and the volume efficiency equivalent value Kin.
[0062]
Qac = Qac_n-1× (1-Kvol × Kin) + Qacn × Kvol × Kin
However, Kvol = Vc / Vm, Vc represents 1 cylinder volume, and Vm represents the intake system volume.
[0063]
In this way, the cylinder intake fresh air amount Qac is obtained, and the process ends.
[0064]
FIG. 5 is a flow for calculating the fuel injection amount Qsol (Ref. Job).
[0065]
First, in step 1, the engine speed Ne and the control lever opening (accelerator opening) CL are read. In step 2, a fuel injection characteristic map as shown in FIG. 6 is searched from these Ne and CL to calculate a basic fuel injection amount Mqdrv.
[0066]
In step 3, the basic fuel injection amount is corrected by the water temperature or the like to obtain Qsol1. Further, in step 4, the maximum fuel injection amount is limited according to the maximum fuel injection amount map as shown in FIG. 7, and the corrected Qsol1 is limited so as not to exceed the maximum injection amount QsolMAX. The fuel injection amount Qsol is set, and the process is terminated.
[0067]
Next, FIG. 8 is a flow for calculating the target NOx emission amount determined by the operating state (Ref. Job).
[0068]
In Step 1, the engine speed Ne and the fuel injection amount Qsol are read. In Step 2, the target NOx emission amount NOx_t0 is searched from the target NOx emission amount map as shown in FIG. 9 based on Ne and Qsol. The process ends.
[0069]
FIG. 10 is a flow for determining the transient operation of the engine in order to correct the target NOx emission amount during the transient operation (Ref. Job).
[0070]
In step 1, the fuel injection amount Qsol, accelerator opening TVO, and engine speed Ne are read. In step 2, the fuel injection amount Qsolzk, accelerator opening TVOzm, and engine speed Nezn before a predetermined calculation cycle are set. Read.
[0071]
In step 3, the differences dQsol, dTVO, and dNe are calculated as follows from the fuel injection Qsol, the accelerator opening TVO, and the engine rotation speed Ne before the predetermined cycle.
[0072]
dQsol = Qsol-Qsl-Qsolzk, dTVO = TVO-TVOzm, dNe = Ne-Nezn
In order to determine whether or not the driving state is in a transient state, in step 4, it is determined whether each of dQsol, dTVO, and dNe is in a steady region or an acceleration (transient) region by using a determination table as shown in FIG. Then, the AND of these results is taken, for example, when two or more of these are transient, it is determined as transient and a transient determination flag F_tr is set.
[0073]
Next, FIG. 12 is a flow for calculating a target NOx emission amount (Ref. Job).
[0074]
In Step 1, the transient flag F_tr is read, and in Step 2, it is determined whether or not the operation is transient. If the operation is transient, the process proceeds to Step 3 and the advance of the target NOx emission is corrected. Proceed to step 5.
[0075]
In step 3, the first-order delay equivalent value R_NOx_t of the EGR control system for the searched target NOx emission amount NOx_t is calculated as follows.
[0076]
R_NOx_t = R_NOx_t_n-1× (1-K_NOxt #) + NOx_t0 × K_NOxt #
However, K_NOxt # is an EGR control system time constant equivalent value. In step 4, the target NOx emission amount is advanced and corrected by the correction gain corresponding to the delay of the EGR control system, and this is set as NOx_t which is the target NOx emission amount after the delay correction of the EGR control system. NOx_t is obtained as follows.
[0077]
NOx_t = GK_NOx # × NOx_t0− (GK_NOx # −1) × R_NOx_t_n-1
GK_NOx # is a lead correction gain. In this way, during transient operation, the target NOx emission amount is corrected to the advance side corresponding to the delay of the EGR control system, and the response delay is compensated.
[0078]
In addition, when it progresses to step 5 (at the time of steady state), it sets NOx_t = NOx_t0 as it is, and complete | finishes a process.
[0079]
FIG. 13 shows a flow of the cycle processing of the fuel injection amount and the intake air amount. This calculation operation is executed every 10 ms.
[0080]
In order to calculate the NOx emission amount contained in the exhaust gas based on the NOx concentration in the exhaust gas, the intake fresh air amount and the fuel injection amount are subjected to cycle processing so as to match the time lag.
[0081]
In step 1, the intake fresh air amount Qac and the fuel injection amount Qsol are read. In step 2, cycle processing is performed on Qac and Qsol, and Qac performs delay processing by subtracting 1 from the number of cylinders and Qsol by subtracting 2 from the same. That is, the process ends with the intake air amount Qace = Qac · Z_ (CYLN # _1) and the fuel injection amount Qf0 = Qsol · Z_ (CYLN # _2).
[0082]
FIG. 14 is a flow for calculating the NOx discharge amount actually discharged from the NOx concentration, the intake air amount, and the rotational speed based on the results of these cycle processes (Ref. Job).
[0083]
In step 1, the intake air amount Qace and the fuel injection amount Qf0 obtained in FIG. 13 are read, and in step 2, the intake air amount weight is converted as the intake dry molar flow rate M_Qac according to the following equation.
[0084]
M_Qac = (Qace / MolAir #) − Qf0 / 1000 × HF / (CF + HF) × AH / 4
However, HF has a mass ratio of 1.85, CF has a mass ratio of C of 12.00, and AH has an atomic weight of 1.0079. MolAir # means an apparent molecular weight.
[0085]
Next, at step 3, the engine speed Ne is read, and at step 4, the output NOx_i1 of the NOx concentration sensor is read. In step 5, the NOx concentration C_NOx is obtained by voltage conversion from a table giving the relationship between the sensor output voltage NOx_i1 and the NOx concentration.
[0086]
In step 6, the NOx emission weight NOx_i0 is calculated as follows based on the intake dry molar flow rate M_Qac, the engine speed Ne, and the NOx concentration C_NOx.
[0087]
NOx_i0 = M_Qac × C_NOx × (AN + 2 × A0) × Ne × Nz / 3600/2
AN represents the molecular weight of N, AO represents the molecular weight of O, and Nz represents the number of cylinders.
[0088]
If the NOx concentration in the exhaust gas is known, the NOx emission amount can be calculated from the relationship between this and the exhaust gas flow rate, and the exhaust gas flow rate can be calculated from the intake air amount, the engine speed, and the like.
[0089]
In step 7, the response delay of the output of the NOx concentration sensor is regarded as a first-order delay, and advance processing is performed by the amount corresponding to the time constant as shown in the following equation to obtain the measured NOx emission amount NOx_i.
[0090]
NOx_i = [NOx_i0−NOx_i_n-1(1-K_NOxi #)] / K_NOxi #
Next, FIG. 15 is a flow for calculating the lift amount of the exhaust gas recirculation control valve (EGR valve) based on the target NOx emission amount and the measured NOx emission amount obtained as described above (Ref. Job). .
[0091]
First, in step 1, the target NOx emission amount NOx_t and the measured NOx emission amount NOx_i obtained as described above are read, and in step 2, the difference dNOx between the target value and the actual measurement value is obtained. dNOx = NOx_t−NOx_i.
[0092]
In step 3, based on the difference dNOx between the target value and the actual measurement value, a proportional term (P) is used as a control term for feedback control of the opening degree of the EGR valve from a table as shown in FIG. Min), integral term (I min), and differential term (D min), and based on the measured NOx emission amount NOx_i, according to the table of FIG. 16B, the respective P min, I min, D min Correction values, Phos, Ihos, Dhos are obtained, and from these, PID processing is performed as (P minutes × P minutes correction value) + (I minutes × I minutes correction value) + (D minutes × D minutes correction value). Based on these, the control target value Lift of the EGR valve is calculated in step 4 so that the difference dNOx described above becomes zero.
[0093]
In this way, the opening degree (lift amount) of the EGR valve is feedback-controlled so that the target NOx emission amount and the measured NOx emission amount coincide.
[0094]
Next, the overall operation will be described.
[0095]
When the target NOx emission amount is set according to the operating state of the engine, the opening degree (lift amount) of the EGR valve 57 is adjusted accordingly. As a result, part of the exhaust gas is recirculated from the exhaust passage 53 to the intake passage 52.
[0096]
Exhaust gas is recirculated according to the pressure difference between the exhaust passage 53 and the intake passage 52. However, in general, a diesel engine has a low intake negative pressure, and even if the opening of the EGR valve 57 is increased, the exhaust gas recirculation amount is reduced. May not increase as required. Therefore, in an operating state where the required exhaust gas recirculation amount is large, the opening degree of the intake throttle valve 56 is throttled from the fully open position, and the negative pressure generated downstream thereof is adjusted.
[0097]
When a part of the exhaust gas is recirculated into the intake air, the maximum temperature and pressure of combustion are lowered, and the amount of NOx generated is suppressed. On the other hand, when the exhaust gas recirculation amount increases, particulates (PM) and other exhaust components also deteriorate.
[0098]
If the NOx emission amount can be suppressed to a predetermined state, further increasing the exhaust gas recirculation amount will only cause deterioration of PM.
[0099]
Therefore, the NOx emission amount contained in the exhaust gas is calculated based on the output of the NOx concentration sensor 59 and the exhaust gas flow rate, and the EGR valve 57 is set so that the NOx emission amount matches the target NOx emission amount. The opening is feedback controlled.
[0100]
For this reason, when the actual NOx emission amount is larger than the target value, the opening degree of the EGR valve 57 is increased to increase the exhaust gas recirculation amount, thereby reducing the NOx emission amount to the target value, and conversely the actual NOx amount. When the discharge amount is smaller than the target value, it means that the exhaust gas recirculation is excessively performed, and the opening degree of the EGR valve 57 is reduced, and the NOx discharge amount is controlled to coincide with the target value.
[0101]
In this way, the exhaust gas recirculation control is performed so that the target NOx emission amount is always achieved. In this case, the dynamic behavior of the NOx concentration sensor 59, the EGR valve 57, and the working fluid (intake air, exhaust gas) is controlled. By measuring (calculating) the amount of NOx emissions using a physical model that takes into account, accurate feedback control is performed without causing a phase delay with respect to a predetermined target NOx emission amount, not only during steady operation but also during transient operation. can do. For this reason, compared with the conventional exhaust gas recirculation control device, it is possible to significantly suppress the variation in the accuracy of the component parts and the variation in the NOx emission amount due to the deterioration with time.
[0102]
Further, since the NOx emission amount is directly measured and feedback controlled, there is no need to correct for environmental changes such as atmospheric pressure and humidity as shown in FIGS. That is, in general, as the atmospheric pressure decreases, the oxygen concentration decreases, and the NOx emission amount decreases with respect to the same EGR amount, but the PM emission amount tends to increase, but the target NOx emission amount is always constant. By performing EGR so as to become, even if the atmospheric pressure changes, fluctuations in PM emission can be prevented. Similarly, as the humidity in the intake air increases, the combustion temperature relatively decreases, and for the same EGR amount, the NOx emission amount decreases, while PM increases, but the target NOx emission amount is reached. By controlling the EGR, it is possible to prevent the PM emission amount from changing even if the humidity changes.
[0103]
As a result, EGR correction based on atmospheric pressure and humidity is not required, and an atmospheric pressure and humidity sensor for that purpose are not required, while deterioration of PM and smoke can be avoided.
[0104]
Next, another embodiment will be described.
[0105]
In the case of a diesel engine, the control parameter having the greatest influence on the NOx emission amount is the EGR rate, but it is also affected by the fuel injection timing or the strength of the intake swirl. Now, if the NOx emission amount fluctuates due to the fuel injection timing, this is naturally reflected in the output of the NOx concentration sensor 59. For example, since the injection timing is advanced from the set value, NOx If the amount of emissions increases, the EGR amount will be increased by that amount to reduce NOx, but smoke and PM will worsen accordingly, especially when accelerating compared to the steady state. .
[0106]
Therefore, in the present embodiment, it is determined whether or not the control parameter that affects the NOx emission amount other than EGR matches the target value and the actual measurement value, and the target NOx emission amount is corrected according to this difference. To prevent smoke and PM deterioration.
[0107]
19 to 21 are for controlling the target NOx emission amount by taking the fuel injection timing as an example of the control parameter.
[0108]
First, FIG. 19 is a flow for calculating the target NOx emission amount (Ref. Job).
[0109]
In step 1, the engine speed Ne and the fuel injection amount Qsol are read, and based on these, the map as shown in FIG. 9 is searched to read the target NOx emission amount NOx_tM. In step 3, a target NOx correction value NOx_hos obtained in accordance with FIG. In step 4, the target NOx emission amount is corrected as follows.
[0110]
NOx_t0 = NOx_tM × NOx_hos
In this way, the target NOx emission amount is corrected, and the calculation ends as NOx_t0.
[0111]
FIG. 20 is a flow for calculating the correction value NOx_hos for the target NOx (Ref. Job).
[0112]
The target fuel injection timing ITs set in accordance with the operating state in step 1 and the actual fuel injection timing ITi obtained from the output of the nozzle lift sensor are read. In step 2, the target fuel injection timing and the actual fuel injection timing are measured. Is obtained as Dit = ITs−ITi.
[0113]
In step 3, based on this Dit, the target NOx correction value NOx_hos set with the characteristics shown in FIG. 21 is obtained from the table, and the calculation is terminated.
[0114]
Note that NOx_hos takes 1.0 when the difference between the target fuel injection timing and the actually measured fuel injection timing is zero, and increases as the deviation amount increases in both the advance side and the retard side. Therefore, the target NOx emission amount adjusted based on this correction value increases as the shift to the advance side or the retard side increases. This characteristic varies depending on the combustion concept of the engine.
[0115]
Other control operations are the same as those in the first embodiment.
[0116]
In this way, when the fuel injection timing deviates from the target injection timing, the target NOx emission amount is corrected to the increase side accordingly, and for example, the amount of NOx generated due to the deviation of the fuel injection timing increases. However, the amount of EGR is not increased, and therefore it is possible to avoid an increase in smoke and PM due to an increase in the amount of EGR. In particular, smoke and PM are extremely deteriorated by increasing the amount of EGR, such as when the amount of NOx emission increases due to an error in the fuel injection timing, in areas where the amount of fuel injection is likely to occur, such as during acceleration. Can prevent problems.
[0117]
In addition, although the NOx emission amount increases due to the correction of the target NOx emission amount, the target NOx emission amount is relatively increased in anticipation of this amount, such as in the steady state where the smoke does not increase much even if the EGR is increased. If set to a small value, an increase in the total NOx emission can be suppressed.
[0118]
In this example, the fuel injection timing has been described as a control parameter that affects the NOx emission amount, but control of the intake swirl ratio and the like can be performed in the same manner.
[0119]
The third embodiment will be described with reference to FIGS.
[0120]
In the type in which the NOx concentration sensor 59 is a solid electrolyte type and detects the NOx concentration from the oxygen passage amount, when the fuel supplied to the engine at the time of deceleration is cut and the oxygen concentration in the exhaust becomes the same as the atmosphere, the oxygen pump It has a characteristic that it does not work properly and the sensor output shifts to the upper limit value. For this reason, at the time of deceleration, the NOx emission amount is erroneously recognized as a result, the EGR valve is lifted to the maximum, and the valve opening is increased.
[0121]
When the fuel is cut at the time of deceleration, there is no NOx emission from the engine, and even if the fuel is not cut, the NOx emission should be reduced relatively, so there is no need to open the EGR valve in this way, On the other hand, at the time of fuel recovery, even if the EGR valve closes suddenly from the maximum lift state, the EGR is excessively performed during the response delay, the combustion deteriorates due to a large amount of EGR, and misfires and white smoke occur. Much smoke is generated during deceleration and re-acceleration.
[0122]
Therefore, in this embodiment, when the deceleration operation is detected, the feedback control of the EGR valve by the NOx concentration sensor is stopped, and the EGR valve opening degree is controlled by the engine rotation and the load so that the fuel from the deceleration fuel cut state can be obtained. Eliminate these problems that occur during recovery.
[0123]
First, FIG. 22 is a flow for determining a deceleration operation (Ref. Job).
In step 1, the fuel injection amount Qsol, accelerator opening TVO, and engine speed Ne are read. In step 2, the fuel injection amount Qsolzk, accelerator opening TVOzm, and engine speed Nezn before the set calculation cycle are read. In step 3, the differences dQsol, dTVO, and dNe of these values before the setting cycle are calculated as dQsol = Qsol−Qsolzk, dTVO = TVO−TVOzm, and dNe = Ne−Nedn, respectively.
[0124]
In step 4, these dQsol, dTVO, and dNe are compared with predetermined values to determine whether or not the vehicle is decelerating. When the vehicle is decelerating, the flag F_da is set. When shifting to the deceleration operation, the fuel injection amount, the accelerator opening degree, and the engine speed are reduced from those before the predetermined cycle, and therefore the above-described differences are increased.
[0125]
FIG. 23 is a control flow of the EGR valve during deceleration (Ref. Job).
[0126]
When the deceleration operation determination flag F_da is set in FIG. 22, the process proceeds to the flow of FIG. 23. In step 1, the engine speed Ne and the fuel injection amount Qsol are read. Then, in step 2, the lift amount of the target EGR valve is retrieved from the Ne and Qsol from the lift map of the EGR valve as shown in FIG.
[0127]
The lift amount of the EGR valve at the time of deceleration decreases as the fuel injection amount and the rotational speed increase (the valve opening decreases), and the lift amount in a state close to idle rotation increases.
[0128]
When the lift amount of the target EGR valve is determined, the lift amount of the EGR valve is open-controlled based on this. During this deceleration, feedback control of the EGR valve for making the NOx emission amount coincide with the target value is stopped.
[0129]
In this way, the feedback control of the EGR valve by the NOx concentration sensor is stopped at the time of deceleration, and the EGR valve opening is controlled by the open loop by the engine rotation and the load, so that at the time of fuel recovery from the deceleration fuel cut state, etc. The error of the NOx concentration sensor prevents the EGR valve from opening up to the maximum opening, and prevents the combustion state from deteriorating due to excessive opening of the EGR valve.
[0130]
Next, an embodiment for performing failure determination of the EGR valve will be described with reference to FIGS.
[0131]
Since the NOx emission amount is feedback-controlled, the measured NOx emission amount should match the target value. However, the measured NOx emission amount greatly deviates from the target value in the EGR valve failure state.
[0132]
Therefore, in this embodiment, the failure of the EGR valve is determined from the difference between the target NOx emission amount and the measured NOx emission amount.
[0133]
First, FIG. 25 is a flow (Ref. Job) for determining whether or not the vehicle is in a transient operation state. In step 1, the fuel injection amount Qsol, the accelerator opening TVO, and the engine speed Ne are read. In step 2, The set fuel injection amount Qsolzk, accelerator opening TVOzm, and engine speed Nezn before the calculation cycle are read. In step 3, the differences dQsol, dTVO, and dNe of these values before the setting cycle are calculated as dQsol = Qsol−Qsolzk, dTVO = TVO−TVOzm, and dNe = Ne−Nedn, respectively. In step 4, these dQsol, dTVO, and dNe are compared with predetermined values, and when the difference is equal to or larger than the predetermined value, it is determined as transient operation in the same manner as in FIG. 10 described above, and a transient operation flag F_trl is set.
[0134]
FIG. 26 is a flowchart for determining an EGR valve failure (Ref. Job). First, in step 1, it is determined from the result of the flag in FIG.
[0135]
During transient operation, even if the operation of the EGR valve is normal, the target NOx emission amount and the actually measured NOx emission amount may greatly deviate, so the failure determination is stopped.
[0136]
When the transient operation is not being performed, the process proceeds to Step 2 to read the difference dNOx between the target NOx emission amount NOx_t of the previous time or a predetermined cycle and the measured NOx emission amount NOx_i. In step 3, the ratio between the difference dNOx and the measured NOx_i, that is, dNOx / NOx_i is compared with a preset failure determination threshold value DIAG_EGR.
[0137]
When the ratio of the difference dNOx to the measured NOx emission amount is equal to or less than the predetermined value, the process proceeds to Step 5 where the difference between the target NOx emission amount and the measured NOx emission amount is small and the EGR control is normally performed, that is, the EGR valve. It is judged that the operation is normal.
[0138]
However, when the ratio of dNOx to the measured NOx emission amount is equal to or greater than the predetermined value, the process proceeds to step 6 and there is a large difference between the target NOx emission amount and the actually measured NOx emission amount even though feedback control is being performed. It is determined that the control is not normal, and an abnormal state is notified by turning on a warning lamp in step 7. If necessary, the fuel injection amount may be limited at this time, and a fail mode may be set to urge repair for failure.
[0139]
In this way, an abnormality such as a failure of the EGR valve can be determined with a simple configuration.
[0140]
In addition, about the above, although the case where it applied to a diesel engine was demonstrated, this invention is applicable similarly to a gasoline engine.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a fuel supply system according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram showing an exhaust gas recirculation control system.
FIG. 3 is a block diagram of a control system of the present invention.
FIG. 4 is a flowchart for calculating a cylinder intake air amount, showing the control content of the first embodiment.
FIG. 5 is a flowchart for calculating a fuel injection amount.
FIG. 6 is a characteristic diagram that similarly shows fuel injection characteristics;
FIG. 7 is a characteristic diagram showing the maximum injection amount characteristic.
FIG. 8 is a flowchart for calculating a target NOx emission amount.
FIG. 9 is a characteristic diagram that similarly shows the target NOx emission amount characteristic;
FIG. 10 is a flowchart for determining a transient operation in the same manner.
FIG. 11 is also a characteristic diagram of a transient operation determination flag.
FIG. 12 is a flowchart for calculating a target NOx emission advance process.
FIG. 13 is a flowchart for performing cycle processing in the same manner.
FIG. 14 is a flowchart for calculating a NOx emission amount.
FIG. 15 is a flowchart for calculating the lift amount of the EGR valve.
FIG. I. This shows the characteristics of the D constant. I. D minutes, (B) I. The correction value for D is shown.
FIG. 17 is an explanatory view showing the relationship between atmospheric pressure and NOx emission characteristics.
FIG. 18 is an explanatory view showing the relationship between humidity and NOx emission characteristics.
FIG. 19 is a flowchart for calculating a target NOx emission amount, showing the control content of the second embodiment.
FIG. 20 is a flowchart for calculating a correction value for the target NOx emission amount.
FIG. 21 is a characteristic diagram showing characteristics of correction values in the same manner.
FIG. 22 is a flowchart for determining the deceleration operation state, showing the control content of the third embodiment.
FIG. 23 is a flowchart for calculating a target EGR valve lift amount in the same deceleration state.
FIG. 24 is a characteristic diagram in which lift characteristics of the target EGR valve are set similarly.
FIG. 25 is a flowchart for determining the transient operation state, showing the control content of the fourth embodiment.
FIG. 26 is a flowchart for determining a failure of the EGR valve.
[Explanation of symbols]
51 diesel engine
52 Air intake passage
53 Exhaust passage
54 Exhaust gas recirculation passage
55 Air Flow Meter
57 Exhaust gas recirculation control valve
57a Step motor
59 Exhaust concentration sensor
70 controller

Claims (5)

Means for detecting the engine speed, means for detecting the engine load, means for detecting the intake air amount of the engine, means for calculating the amount of fuel supplied to the engine based on these, and a part of the exhaust In an exhaust gas recirculation control device for an internal combustion engine having an exhaust gas recirculation passage that recirculates into intake air and an exhaust gas recirculation control valve that adjusts the exhaust gas recirculation amount, NOx concentration detection that detects the NOx concentration in the exhaust gas flowing through the exhaust passage The target NOx emission amount is corrected based on the difference between the means, the means for setting the target NOx emission amount according to the engine speed and the load, and the target control value of the fuel injection timing of the diesel engine and the actually measured control value. correction means and, the engine speed and the intake air amount and the NOx concentration means for calculating the actual NOx emission amount based on the NOx concentration determined by correcting the response delay of the sensor , Exhaust gas recirculation control device for an internal combustion engine actual NOx emissions, characterized in that it comprises a means for feedback controlling the opening degree of the exhaust gas recirculation control valve so as to coincide with the corrected target NOx emissions. Means for detecting the engine speed, means for detecting the engine load, means for detecting the intake air amount of the engine, means for calculating the amount of fuel supplied to the engine based on these, and a part of the exhaust In an exhaust gas recirculation control device for an internal combustion engine having an exhaust gas recirculation passage that recirculates into intake air and an exhaust gas recirculation control valve that adjusts the exhaust gas recirculation amount, NOx concentration detection that detects the NOx concentration in the exhaust gas flowing through the exhaust passage correcting means, engine speed, and means for setting the NOx emissions target in accordance with the load, the target NOx emissions based on the difference of the target control value of the intake swirl ratio of the diesel engine and the measured control value calculating a correction unit, the actual NOx emission amount based on the NOx concentration determined by correcting the response delay of the engine speed and the intake air amount and the NOx concentration sensor for Stage and, exhaust gas recirculation control device for an internal combustion engine actual NOx emissions, characterized in that it comprises a means for feedback controlling the opening degree of the exhaust gas recirculation control valve so as to coincide with the corrected target NOx emissions. It said feedback control means of the exhaust gas recirculation control valve, stops the feedback control when the oxygen concentration in the exhaust gas such as at least decelerated while driving high, open control the opening degree of the exhaust gas recirculation control valve in response to engine speed and load The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 1 or 2 . 4. The apparatus according to claim 1 , further comprising a means for determining and warning that the exhaust gas recirculation control valve is faulty when a difference between the corrected target NOx emission amount and the measured NOx emission amount is equal to or greater than a preset value. exhaust gas recirculation control apparatus for an internal combustion engine according to one or. The exhaust gas recirculation control device for an internal combustion engine according to claim 4 , wherein the failure determination warning means stops the failure determination during transient operation.

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