JP2007309298A - Ignition timing control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ignition timing control device for an engine capable of smoothly shifting to EGR on state or EGR off state while restraining over-advanced timing and performing sufficient combustion in start and stop of EGR. <P>SOLUTION: The ignition timing control device for the engine for generating electrical spark from an ignition plug 115 in prescribed ignition timing so as to perform combustion is provided with EGR means 142 for recirculating a part of exhaust gas (EGR) from an exhaust passage 122 to a suction passage 121, and an ignition timing correction means for advancing the ignition timing in performing EGR and performing moderating control for gradually approximating a timing advance amount to a target value in start and stop of EGR, and a moderating degree in moderating control is set to be relatively larger when EGR is started compared to when EGR is stopped. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ignition timing control device for an engine that generates electric sparks from an ignition plug at a predetermined ignition timing and performs combustion. In particular, the present invention relates to an EGR that recirculates a part of exhaust gas from an exhaust passage to an intake passage. The present invention relates to an operation for advancing the ignition timing during execution of the EGR.

  Conventionally, a technique for performing EGR for the purpose of reducing nitrogen oxide (NOx) in exhaust gas or improving fuel consumption is known. In EGR, a part of the exhaust gas is recirculated from the exhaust passage to the intake passage and recirculated. In general, when EGR is performed, the inactive components in the intake air increase, so that the combustion temperature decreases, so that the generation of NOx can be suppressed. Further, when EGR is performed, the intake negative pressure is reduced and the pumping loss is suppressed, so that the fuel consumption can be improved.

  In addition, since the combustion speed becomes slower when EGR is performed than when it is not performed, a technique is also known in which ignition timing is advanced (accelerated) in accordance therewith to achieve appropriate combustion.

  Incidentally, as EGR means for performing EGR, it is common to provide an EGR passage that connects the exhaust passage and the intake passage, and an EGR valve that opens and closes the EGR passage. In such a configuration, a certain amount of time is required until the actual EGR amount (or EGR rate) reaches the target value after the EGR valve is opened and closed. On the other hand, the ignition timing can be immediately changed to the target advance amount. Therefore, if the ignition timing is advanced in synchronism with the opening / closing of the EGR valve, the result will be relatively earlier than the advance amount suitable for the actual EGR amount. That is, when the EGR is started, the engine is over-advanced, and when the EGR is stopped, the engine is under-advanced.

With respect to such a problem, for the purpose of following the actual change in the EGR amount, processing for gradually bringing the ignition timing advance amount close to the target value (hereinafter, such processing is referred to as “annealing processing”). ) Is also known. For example, Japanese Patent Application Laid-Open No. H10-228561 discloses a method for performing an annealing process that gradually brings the ignition timing closer to the target value in accordance with the change rate of the intake state.
JP 7-197876 A

  However, research by the present inventor has revealed that conventional annealing may be inconvenient. Even if the opening degree of the EGR valve and other operating conditions are the same, the actual EGR amount (hereinafter referred to as the actual EGR amount) varies between when EGR starts (when on) and when EGR stops (when off). This is due to the difference in speed, that is, responsiveness. The response of the actual EGR amount is higher when EGR is off than when EGR is on.

  Therefore, when the smoothing degree of the annealing process is set based on the time when EGR is on, the follow-up change of the ignition timing is relatively delayed when EGR is off with high responsiveness of the actual GER amount. When the EGR is off, control is performed to return the increased advance amount to the normal advance amount. Therefore, delaying this means that the advance amount is relatively too large (over advance angle). . This excessive advance angle is not preferable because it causes abnormal combustion such as knocking.

  On the other hand, when the smoothing degree is set based on the time when EGR is off, the follow-up change of the ignition timing is relatively preceded when EGR is on when the responsiveness of the actual GER amount is low. When EGR is on, control to increase the advance angle amount is performed, so that this precedes it means that the advance angle is relatively over.

  That is, in either case, if the degree of smoothing is set with one as a reference, the other is over-advanced, and problems such as knocking are likely to occur.

  The present invention has been made in view of the above circumstances, and at the time of start and stop of EGR, it is possible to smoothly shift to the EGR on or off state while suppressing the advance angle and performing good combustion. It is an object of the present invention to provide an engine ignition timing control device.

  According to a first aspect of the present invention for solving the above-mentioned problem, in an ignition timing control device for an engine that performs combustion by generating an electric spark from an ignition plug at a predetermined ignition timing, a part of the exhaust gas is discharged from the exhaust passage. EGR means for performing EGR to recirculate to the intake passage, and an annealing process for advancing the ignition timing during execution of the EGR and gradually bringing the advance amount toward the target value at the start and stop of the EGR And an ignition timing correction means for performing the above-mentioned, wherein the smoothing degree in the smoothing process is set so as to be relatively larger when the EGR is started than when the EGR is stopped.

  The annealing process is a process for gradually bringing the advance amount of the ignition timing closer to the target value. The degree of annealing refers to the degree of gradual change in ignition timing. The greater the degree of annealing, the closer to the target value.

  The invention according to claim 2 is the engine ignition timing control device according to claim 1, further comprising EGR control means for adjusting an EGR amount by the EGR means, wherein the EGR amount is higher or higher than that in an idle operation state. In the operating region of the rotational speed, it is set according to the engine rotational speed and the engine load, and the degree of change of the EGR rate with respect to the change of the engine load is relatively larger on the high load side than on the low load side. It is characterized by being set to.

  According to a third aspect of the present invention, in the engine ignition timing control device according to the second aspect, the smoothing degree is set to be relatively larger on the increase side of the EGR amount than on the decrease side. It is characterized by.

  According to a fourth aspect of the present invention, in the engine ignition timing control device according to any one of the first to third aspects, the smoothing degree is relatively larger at the low speed side of the engine speed than at the high speed side. It is set so that it may become.

  According to the first aspect of the present invention, as described below, when the EGR is on and off, it is possible to smoothly shift to the EGR on or off state while suppressing the over-advanced angle and performing good combustion.

  According to the configuration of the present invention, when EGR is turned on, which has relatively low responsiveness to changes in the EGR amount, the degree of smoothing of the smoothing process can be increased and the ignition timing can be gradually brought closer to the target advance amount. In addition, when EGR is off, which has a relatively high responsiveness to changes in the EGR amount, the degree of smoothing can be reduced to quickly return the ignition timing to the normal advance amount. In this way, it is possible to easily set the change degree of the ignition timing according to the responsiveness of the EGR amount change. Therefore, the excessive advance angle when EGR is on and off is suppressed, and abnormal combustion such as knocking can be effectively prevented.

  According to the invention of claim 2, as will be described below, it is possible to perform effective EGR according to the operating state, and to effectively suppress the excessive advance angle on the increase side and decrease side of the EGR amount.

  According to the configuration of the present invention, since the EGR amount is set according to the engine rotation speed and the engine load, effective EGR according to the driving state can be performed. For example, in the low / medium load region, by performing EGR, the combustion temperature can be reduced to suppress NOx emission, and the pumping loss can be reduced to improve fuel efficiency. In this case, it is preferable to increase the EGR rate as the engine speed and the load increase. In such control on the EGR increase side (including switching from OFF to ON), the ignition timing can be gradually increased by performing an annealing process with a relatively large degree of annealing. It is possible to effectively suppress the excessive advance angle due to excessively.

  On the other hand, in the high load region, the EGR rate can be reduced (including the stop of EGR) to increase the fresh air ratio, and high torque and high output can be obtained. The degree of change in the EGR rate with respect to the change in engine load at that time is preferably larger than that in the low / medium load region. This is because EGR can be quickly turned off at the time of transition from the medium load region to the high load region. In such control on the EGR reduction side (including switching from on to off), the ignition timing advance angle can be quickly returned to the normal value by performing an annealing process with a relatively low degree of annealing. The over-advance angle due to the delay can be effectively suppressed.

  According to the invention of claim 3, as will be described below, it is possible to perform the smoothing process of the ignition timing according to the changing direction of the EGR amount, and smoothly shift to the destination EGR state while performing good combustion. be able to.

  When changing the EGR amount, the response of the actual EGR amount change is higher when the EGR is decreased than when the EGR is increased. According to the configuration of the present invention, when the EGR is increased, the degree of smoothing of the relative smoothing process is relatively increased and the ignition timing is gradually brought closer to the target advance amount, and when the EGR is decreased, the degree of smoothing is decreased and the speed is quickly increased. The ignition timing is returned to the normal advance amount. Accordingly, it is possible to easily set the degree of change in the ignition timing according to the actual degree of change in the EGR amount both when the EGR is increased and when the amount is decreased, and it is possible to perform good combustion that is unlikely to cause knocking or the like.

  According to the invention of claim 4, as described below, the ignition timing smoothing process according to the engine rotation speed can be performed, and the transition to the destination EGR state can be smoothly performed while performing good combustion. it can.

  Since the scavenging amount per unit time increases as the engine rotation speed increases, the response of the actual EGR amount change becomes higher. According to the configuration of the present invention, the smoothing degree of the smoothing process is relatively increased on the low speed side of the engine speed, and the ignition timing is gradually brought closer to the target advance amount, and the smoothing degree is decreased on the high speed side. As a result, the ignition timing is quickly returned to the normal advance amount. Accordingly, it is possible to easily set the degree of change in the ignition timing according to the degree of change in the actual EGR amount in a wide speed range from low speed to high speed, and it is possible to perform good combustion that is unlikely to cause knocking or the like.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an engine 100 according to an embodiment of the present invention. The schematic configuration of the engine 100 includes an engine body 110, an intake passage 121, and an exhaust passage 122. The engine main body 110 is constituted by a cylinder head, a cylinder block, or the like, and is provided with a plurality of (for example, four) cylinders 112. A combustion chamber 114 is formed in each cylinder 112, and a spark plug 115 is provided at the top. The air-fuel mixture in the combustion chamber 114 is combusted by ignition of the spark plug 115, and the combustion energy is output to the engine output shaft 101 (crankshaft) via the piston 113 and the like.

  The engine body 110 includes a crank angle sensor 130 that detects the rotation angle of the engine output shaft 101, a cam angle sensor 132 that detects the cam angle, a knock sensor 131 that detects knocking, and a water temperature sensor 133 that detects the cooling water temperature. Is provided.

  An intake passage 121 is connected to the intake side of each combustion chamber 114, and an exhaust passage 122 is connected to the exhaust side. An air cleaner 120 that purifies the intake air is provided in the uppermost stream of the intake passage 121, and an air flow sensor 125 that detects the intake air amount is provided downstream thereof.

  A throttle valve 123 that adjusts the intake air amount is provided downstream of the air flow sensor 125. An intake manifold 121a branched toward each cylinder 112 via a surge tank is formed further downstream of the throttle valve 123.

  The intake manifold 121a is provided with an intake pressure sensor 126 that detects intake pressure. The intake pressure sensor 126 is also called a MAP sensor, and detects the absolute pressure of the intake manifold 121a. The intake air amount can be obtained from the absolute pressure and the engine speed.

  A fuel injection valve 116 that supplies fuel to each combustion chamber 114 is provided at a position near each cylinder 112 in the intake passage 121. The downstream intake passage 121 is connected to each combustion chamber 114 via an intake valve 117.

On the other hand, an exhaust passage 122 is connected to the exhaust side of each combustion chamber 114 via an exhaust valve 118. The exhaust passage 122 is provided with an exhaust purification device 152 for purifying exhaust. A linear O ₂ sensor 151 is provided on the upstream side of the exhaust purification device 152, and a lambda O ₂ sensor 153 is provided on the downstream side, and each detects the oxygen concentration in the exhaust gas.

  Further, an EGR passage 141 that connects the intake passage 121 and the exhaust passage 122 is provided. An EGR valve 142 for opening and closing the EGR passage 141 is provided on the EGR passage 141. The EGR passage 141 and the EGR valve 142 constitute EGR means for performing EGR. That is, by opening the EGR valve 142, a part of the exhaust gas (EGR gas) flowing through the exhaust passage 122 is returned to the intake passage 121 through the EGR passage 141, and EGR is performed. The EGR gas merges with fresh air in the intake passage 121 and is guided again to the combustion chamber 114 to become an inert gas component during combustion. As the opening degree of the EGR valve 142 is increased, the EGR gas amount (EGR amount) increases. Also, the EGR rate (the ratio of EGR gas to fresh air) increases. When the EGR valve 142 is closed, the recirculation of the EGR gas is interrupted and the EGR is stopped.

  FIG. 2 is a control block diagram of a PCM (powertrain control module) 700 that controls the engine 100.

  The PCM 700 is a control module that integrally controls the operation of the engine 100 and an automatic transmission (not shown), and includes a computer having a CPU, a ROM, a RAM, and the like. Specifically, a program stored in advance in a ROM (or RAM) is executed by the CPU, whereby the operation of each part of the power train is controlled.

In the following description of the PCM 700, the portion closely related to the present invention will be mainly described. The PCM 700 includes detections from the air flow sensor 125, the intake pressure sensor 126, the crank angle sensor 130, the knock sensor 131, the cam angle sensor 132, the water temperature sensor 133, the linear O ₂ sensor 151, and the lambda O ₂ sensor 153 shown in FIG. A signal is input. Further, a detection signal from an accelerator opening sensor 134 for detecting the accelerator depression amount (accelerator opening) and a vehicle speed sensor 138 for detecting the vehicle speed, which are not shown, are also input to the PCM 700.

  The PCM 700 functionally includes an intake air amount control unit 710, a fuel injection control unit 715, an ignition timing control unit 720, and an EGR control unit 730.

  The intake air amount control unit 710 sets an appropriate intake air amount based on the operating state such as the engine speed Ne and the accelerator opening, and adjusts the opening of the throttle valve 123 (throttle opening TVO) according to the intake air amount. To do. When performing EGR, the throttle opening TVO is set in consideration of the amount of EGR gas recirculated to the intake passage 121.

The fuel injection control unit 715 sets an appropriate fuel injection amount according to the intake air amount, and injects fuel from each fuel injection valve 116 at an appropriate injection timing for each cylinder 112. In a predetermined feedback operation region, the oxygen concentration detected by the linear O ₂ sensor 151 and the lambda O ₂ sensor 153 is referred to, and the fuel in each cylinder 112 is set to a predetermined air-fuel ratio, for example, the stoichiometric air-fuel ratio. The injection amount is feedback controlled.

  The ignition timing control unit 720 sets an appropriate ignition timing and generates an electric spark (spark) at the spark plug 115 of each cylinder 112. During normal operation of engine 100, the ignition timing is set to a timing earlier than the compression top dead center by a predetermined advance amount. This ignition timing is obtained by adding a correction by an ignition timing correction unit 721, which will be described later, to the base basic ignition timing. The basic ignition timing is set in advance as a map value using, for example, the engine rotation speed Ne and the engine load CE as parameters, and is obtained by reading them.

  The ignition timing control unit 720 includes an ignition timing correction unit 721 (ignition timing correction means). The ignition timing correction unit 721 performs various corrections according to the operation state on the basic ignition timing to set a final ignition timing (final ignition timing).

  Here, correction when performing EGR, that is, ignition timing EGR correction will be described. When EGR is performed, the combustion speed becomes slower than when EGR is not performed, so the ignition timing is advanced to compensate for this. That is, correction is performed to advance the ignition timing further than the basic ignition timing. The target value Δtgt of the ignition timing EGR correction amount is set in advance as a map value using, for example, the engine speed Ne, the engine load CE, and the EGR valve opening EVO as parameters, and is set by reading this.

  However, when the EGR valve opening EVO is in a transient state, that is, when the EGR valve 142 is switched from on to off or off to on, and when the EGR valve opening EVO fluctuates, the ignition timing EGR correction amount Δtg is set. A predetermined annealing process is performed. In the annealing process, considering that there is a time difference between the change in the EGR valve opening EVO and the change in the actual EGR amount, the EGR correction amount Δtg is gradually brought closer to the target value to follow the change in the actual EGR amount. It is a process to make. As a result, the final ignition timing gradually approaches the target value.

  By the annealing process of this embodiment, the ignition timing EGR correction amount Δtg is obtained by the following (Equation 1).

Δtg (i) = α · Δtg (i−1) + (1−α) · Δtgt (i) (Equation 1)
In (Expression 1), α is a smoothing coefficient, and Δtgt is a target value of the ignition timing EGR correction amount. The subscript (i) represents the current value in the processing routine, and (i-1) represents the previous value.

  As is apparent from (Expression 1), the ignition timing EGR correction amount Δtg (i) is obtained by changing the previous value Δtg (i−1) and the current target value Δtgt (i) by a ratio of α: (1−α). Is a weighted average.

  When the annealing coefficient α = 0, Δtg (i) = Δtgt (i). That is, the ignition timing EGR correction amount Δtg (i) is the current target value itself, which means that the annealing process is not actually performed.

  On the other hand, when the smoothing coefficient α> 0, substantial smoothing processing is performed. The greater the annealing coefficient α, the stronger the previous value Δtg (i−1) is reflected in the ignition timing EGR correction amount Δtg (i). Accordingly, the ignition timing EGR correction amount Δtg is more gently changed while the rapid change is suppressed. That is, the degree of smoothing increases as the smoothing coefficient α increases.

  The EGR control unit 730 determines whether or not EGR is necessary, and when performing EGR, opens the EGR valve 142 so that the predetermined EGR valve opening EVO (or EGR rate) is obtained. The EGR valve opening EVO is set in advance as a map value using, for example, the engine rotational speed Ne and the engine load CE as parameters, and is obtained by reading them.

  FIG. 3 is a graph showing the relationship between the engine load CE and the EGR rate at the steady engine speed. This graph shows a case where the engine rotation speed Ne = 1500 rpm. The horizontal axis represents the engine load CE (CE = 1 and full load), and the vertical axis represents the EGR rate (%).

  As shown in this graph, when the engine load CE = 0, the EGR rate = 0%. That is, EGR is off and the EGR valve 142 is closed. In the region of 0 <CE ≦ 0.75, EGR is turned on and the EGR valve 142 is opened. Among these, in the low / medium load region where 0 <CE ≦ 0.7, the EGR rate is set to increase as the engine load CE increases. Conversely, in a high load region where 0.7 <CE ≦ 0.75, the EGR rate is set to be lower as the engine load CE is higher. At this time, the degree of change in the EGR rate with respect to the change in the engine load CE is set to be much larger than that on the low load side. Further, EGR is stopped when 0.7 <CE ≦ 1 in the high load side region.

  Thus, since the EGR rate (EGR amount) is set according to the engine load CE, it is possible to perform effective EGR according to the operating state. For example, in the low / medium load region, by performing EGR, the combustion temperature can be reduced to suppress NOx emission, and the pumping loss can be reduced to improve fuel efficiency. In this case, it is preferable to increase the EGR rate as the engine rotational speed Ne and the engine load CE are larger.

  On the other hand, in the high load region, the EGR rate can be reduced (including the stop of EGR) to increase the fresh air ratio, and high torque and high output can be obtained. The degree of change in the EGR rate with respect to the change in the engine load CE at that time is preferably larger than that in the low / medium load region as shown in FIG. This is because EGR can be quickly turned off at the time of transition from the medium load region to the high load region.

  Next, setting of the ignition timing by the ignition timing control unit 720 will be described focusing on the operation of the ignition timing correction unit 721. When EGR is on, the ignition timing EGR correction amount Δtg is set by the ignition timing correction unit 721 as described above, and the ignition timing is corrected to the advance side. If the EGR rate is in a steady state where there is no temporal change, the smoothing process is not performed, and the smoothing coefficient α = 0 in (Expression 1). Therefore, the ignition timing EGR correction amount Δtg = target value Δtgt.

  On the other hand, when the EGR rate is in a transient state that changes with time, the annealing process is performed. Next, the smoothing coefficient α used for the smoothing process will be described. In the present embodiment, three types of smoothing coefficients α, that is, α1, α2, and α3 are set (α1 <α2 <α3) except when α = 0. The smoothing coefficients α1, α2, and α3 are selectively used depending on the type of transient state. That is, even if the EGR rate is the same, the value of the applied smoothing coefficient α may be different if the type of transient state is different.

  Next, five typical transient states are listed according to the graph of FIG. 3, and the smoothing coefficient α applied at that time will be described.

  The first transient state is a change (arrow A1 in FIG. 3) in which the engine load CE increases from the EGR off state in the no-load state (engine load CE = 0) to turn on the EGR. At this time, since the degree of change in the actual EGR amount is moderate, the largest smoothing coefficient α3 is applied correspondingly. By doing so, the ignition timing EGR correction amount gradually approaches the target value, so that the over-advanced angle of the ignition timing is suppressed.

  The second transient state is a change (arrow A2 in FIG. 3) in which the engine load CE increases from the EGR on state and the EGR rate increases. In this case as well, as in the first transient state, the degree of change in the actual EGR amount is moderate, and the corresponding smoothing coefficient α3 is applied.

  The third transient state is a change (arrow A3 in FIG. 3) in which the engine load CE decreases from the EGR on state and the EGR rate decreases. In this case, the degree of change in the actual EGR amount is quicker than in the second transient state. Accordingly, the second largest smoothing coefficient α2 is applied correspondingly. By doing so, the ignition timing EGR correction amount approaches the target value more promptly than in the second transient state, and thus the ignition timing over-advance angle is suppressed.

  The fourth transient state is a change (arrow A4 in FIG. 3) in which the engine load CE is decreased from the EGR on state and the EGR is off. In this case, the degree of change in the actual EGR amount is further quicker than in the third transient state. Also, since there is little concern about abnormal combustion such as knocking, the annealing coefficient α = 0 is applied. By doing so, the annealing process is not performed, and the ignition timing can be immediately returned to the target value.

  The fifth transient state is a change (arrow A5 in FIG. 3) in which the engine load CE increases from the EGR on state and then goes through a high load region where the EGR rate rapidly decreases. In this case, the degree of change in the actual EGR amount is further quicker than in the third transient state. Accordingly, the smallest smoothing coefficient α1 is applied correspondingly. By doing so, an appropriate smoothing process following the change in the actual EGR amount is performed, and the excessive advance angle of the ignition timing is suppressed. As a result, abnormal combustion such as knocking is effectively suppressed.

  As described above, the five transient states have been described as examples. However, since there are various transient states in which the EGR rate changes, an appropriate smoothing coefficient α is set in each case. Further, the change in the EGR rate does not necessarily occur under the condition that the engine speed Ne is constant, but also occurs due to the change in the engine speed Ne, and more generally, the change in the engine load CE and the change in the engine speed Ne. The final degree of change in the EGR rate is determined by the combination. Therefore, it is necessary to set the smoothing coefficient α in consideration of the engine speed Ne.

  FIG. 4 is a graph showing the relationship between the engine speed Ne and the smoothing coefficient α. The horizontal axis represents the engine speed Ne, and the vertical axis represents the value of the smoothing coefficient α (0 <α <1).

  As shown in this graph, the smoothing coefficients α1, α2, and α3 are set so as to be larger on the low speed side as a whole and smaller as the speed increases while maintaining the relationship of α1 <α2 <α3. This reflects the fact that the scavenging amount per unit time increases as the engine rotational speed Ne increases, and the responsiveness to changes in the actual EGR amount increases. By doing so, the smoothing degree is relatively increased on the low speed side and the ignition timing is gradually brought closer to the target advance amount, and the smoothing degree is reduced on the high speed side and the ignition timing is quickly adjusted to the normal advance angle. Can be returned to the quantity. Therefore, the ignition timing is set according to the actual EGR amount change degree in a wide speed range from low speed to high speed, and good combustion that is unlikely to cause knocking or the like can be performed.

  FIG. 5 is a time chart of a transient state in a low load region. The horizontal axis represents time t, and the vertical axis represents engine speed Ne, engine load CE, throttle opening TVO, EGR valve opening EVO, and ignition timing EGR correction amount Δtg in order from the top. The respective characteristics are indicated by Ne1, CE1, TVO1, EVO1, and Δtg1.

  This time chart corresponds to the first transient state (arrow A1 in FIG. 3), and is set with the smoothing coefficient α = α3 = 0.93. Further, in order to clearly confirm the effect of the annealing process, ignition timing correction other than the ignition timing EGR correction is not performed.

  As shown in this time chart, as the throttle opening TVO1 gradually increases, the engine load CE1 increases, and the EGR is switched from OFF to ON in the vicinity of time t1. That is, the EGR valve 142 is opened, and the EGR valve opening EVO1> 0. Along with this, the actual EGR amount gradually increases. The ignition timing EGR correction amount Δtg1 gradually increases while being processed with a large degree of smoothing. By doing so, the rate of increase in the advance amount of the ignition timing becomes moderate, and good combustion with suppressed over-advance is performed.

  As reference characteristics, the ignition timing EGR correction amount Δtg1 'when the smoothing coefficient α is reduced (α = 0.5) is indicated by a broken line. The ignition timing EGR correction amount Δtg1 ′ has a rising characteristic that is steeper than the ignition timing EGR correction amount Δtg1 where the smoothing coefficient α = 0.93. At this time, knocking due to excessive advance (too much advance of the advance amount) occurred. As a result, the knocking suppression effect due to the annealing coefficient α = α3 = 0.93 was confirmed.

  FIG. 6 is a time chart of a transient state in a high load region. The horizontal axis represents time t, and the vertical axis represents engine speed Ne, engine load CE, throttle opening TVO, EGR valve opening EVO, and ignition timing EGR correction amount Δtg in order from the top. Each characteristic is indicated by Ne2, CE2, TVO2, EVO2, and Δtg2.

  This time chart corresponds to the fifth transient state (arrow A5 in FIG. 3), and is set with the smoothing coefficient α = α1 = 0.5. Further, in order to clearly confirm the effect of the annealing process, correction of the ignition timing other than the ignition timing EGR correction is not performed.

  As shown in this time chart, as the throttle opening TVO2 rapidly increases, the engine load CE2 increases, the EGR valve opening EVO starts decreasing near the time point t2, and finally the EGR valve opening EVO = 0. After time t2, the actual EGR amount also decreases rapidly. Then, the ignition timing EGR correction amount Δtg2 decreases while being subjected to a smoothing process with a small smoothing degree. By doing so, the return speed of the advance amount of the ignition timing becomes rapid, and a good combustion transient characteristic in which the excessive advance angle is suppressed is obtained.

  As a reference characteristic, the ignition timing EGR correction amount Δtg2 'when the annealing coefficient α is larger than α1 (α = 0.93, corresponding to α3) is indicated by a broken line. The ignition timing EGR correction amount Δtg2 'has a gentler return characteristic than the ignition timing EGR correction amount Δtg2 where the smoothing coefficient α = 0.5. At this time, knocking due to over-advance (advance amount return delay) occurred. As a result, the knocking suppression effect due to the annealing coefficient α = α1 = 0.5 was confirmed.

  As described above with reference to FIGS. 5 and 6, when the EGR amount change response is relatively low and when the EGR rate is increased, the degree of smoothing (smoothing coefficient α) is increased gradually. The ignition timing can be brought close to the target advance amount. In addition, when the EGR amount change response is relatively high, when the EGR is off or when the EGR rate is decreased, the degree of smoothing can be reduced to quickly return the ignition timing to the normal advance amount. In this way, it is possible to easily set the change degree of the ignition timing according to the responsiveness of the EGR amount change. Therefore, the excessive advance angle when EGR is on and off is suppressed, and abnormal combustion such as knocking can be effectively prevented.

  FIG. 7 is a flowchart of the ignition timing setting by the ignition timing control unit 720 when there is a transient change in the EGR rate. When this flowchart is started, first, various necessary signal data such as the engine speed Ne and the throttle opening TVO are read (step S1), and then the basic ignition timing not considering the correction of the ignition timing is read from the map. Is set (step S2).

  Next, it is determined whether or not the operating state is an EGR region where EGR is performed (step S3). If YES, an EGR rate is further set (step S4). Subsequently, the target value Δtgt of the ignition timing EGR correction amount Δtg is read from a map or the like and set (step S5).

  Next, it is determined whether or not the transient state is such that the EGR rate increases (step S6). If YES (corresponding to arrows A1 and A2 in FIG. 3), α3 (for example, α3 = 0.93) is set (step S7). Then, an annealing process is performed using (Equation 1) to which the annealing coefficient α3 is applied (step S9).

  Further, although omitted in the above description, if there is an ignition timing correction other than the ignition timing EGR correction (for example, ignition timing control at the time of shifting of the automatic transmission), it is additionally set (step S10). A final ignition timing is set (step S11). Then, ignition is performed at the final ignition timing by the spark plug 115 (step S12).

  Going back to step S6, if NO, that is, a transient state in which the EGR rate decreases (corresponding to the arrow A3 in FIG. 3), α2 (eg, α2 = 0.7) is set as the smoothing coefficient (step S8). ), The process proceeds to step S9.

  Further retroactively, if NO in step S3, that is, if the current operating state is not in the EGR region, first, the target value of the EGR rate is set to 0% (step S21). When the EGR valve 142 is open, it is closed. Then, it is determined whether or not it is on the high load side (step S22). If NO (corresponding to the arrow A4 in FIG. 3), the annealing process is not performed and the ignition timing EGR correction amount Δtg is the target value. The value itself, that is, 0 is set (step S25), and the process proceeds to step S10.

  If YES in step S22, that is, on the high load side, it is further determined whether or not the current actual EGR amount is greater than 0 (step S23). For example, this is determined to be YES when the time (measured by a timer or the like) after the EGR valve 142 is closed is within a predetermined value. If YES in step S23 (corresponding to arrow A5 in FIG. 3), α1 (eg, α1 = 0.5) is set as the smoothing coefficient (step S24), and the process proceeds to step S9. On the other hand, if NO in step S23, it is considered that the transient state has already been completed, the process proceeds to step S25, and the ignition timing EGR correction amount Δtg = 0 is set.

  Although this flowchart is for controlling a transient state, it can be used by appropriately omitting this flowchart even in a steady state. In that case, for example, in the case of YES in step S3, the process may proceed to step S10 after steps S4 and S5. If NO in step S3, the ignition timing EGR correction amount Δtg = 0 may be set and the process proceeds to step S10.

  As mentioned above, although embodiment of this invention was described, this embodiment can be suitably changed in the range which does not deviate from the summary of this invention.

  For example, in the above-described embodiment, (Equation 1) is used to perform the annealing process, but it is not always necessary to use this equation, and the ignition timing EGR correction amount Δtg gradually increases to the target value Δtgt according to the degree of annealing. Other methods may be used as long as they are close. In addition, although three kinds of α1, α2, and α3 are set as the annealing coefficient α, other values may be set, and specific values thereof are not limited to the above values.

  Further, the characteristics of the EGR rate with respect to the engine load CE are not necessarily limited to those shown in FIG. 3, and may be set as appropriate according to the purpose of the EGR. However, as in the characteristics shown in FIG. 3, the effect of the present invention is remarkably exhibited when there is a large difference in the degree of change in the EGR rate between when EGR is on (arrow A1) and when EGR is off (arrow A5). be able to.

It is a figure showing a schematic structure of an engine concerning an embodiment of the present invention. It is a control block diagram of the powertrain control module which controls an engine. It is a graph which shows the relationship between the engine load in a steady engine speed, and an EGR rate. It is a graph which shows the relationship between an engine speed and an annealing coefficient. It is a time chart of the transient state in a low load area | region. It is a time chart of the transient state in a high load area | region. It is a flowchart of ignition timing setting in the case of accompanied with a transient change of the EGR rate.

Explanation of symbols

100 Engine 115 Spark plug 121 Intake passage 122 Exhaust passage 141 EGR passage (EGR means)
142 EGR valve (EGR means)
721 Ignition timing correction unit (ignition timing correction means)
730 EGR controller (EGR controller means)
Ne Engine speed CE Engine load

Claims (4)

In an engine ignition timing control device that generates electric sparks from an ignition plug at a predetermined ignition timing and performs combustion,
EGR means for performing EGR to recirculate a part of the exhaust gas from the exhaust passage to the intake passage;
Ignition timing correction means for advancing the ignition timing during execution of the EGR and performing an annealing process for gradually bringing the advance amount toward the target value at the start and stop of the EGR;
An ignition timing control device for an engine, characterized in that the smoothing degree in the smoothing process is set to be relatively greater when the EGR starts than when the EGR is stopped. EGR control means for adjusting the amount of EGR by the EGR means,
The EGR amount is set according to the engine rotation speed and the engine load in an operation region where the load is higher than the idle operation state or at a higher rotation speed, and the degree of change in the EGR rate with respect to the change in the engine load is higher. 2. The ignition timing control device for an engine according to claim 1, wherein the ignition timing control device is set to be relatively large on the side with respect to the low load side.   3. The engine ignition timing control device according to claim 2, wherein the smoothing degree is set so as to be relatively larger on the increase side of the EGR amount than on the decrease side.   The engine ignition timing according to any one of claims 1 to 3, wherein the smoothing degree is set so as to be relatively larger on the low speed side of the engine speed than on the high speed side. Control device.

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