JP3864706B2 - In-cylinder direct injection internal combustion engine exhaust purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification apparatus for a direct injection type internal combustion engine, and more particularly to an apparatus for raising the temperature of a catalyst by combustion in an exhaust system of unburned fuel.
[0002]
[Prior art]
Conventionally, as an apparatus for raising the temperature of a catalyst by combustion in an exhaust system of unburned fuel, there has been one disclosed in Japanese Patent Laid-Open No. 11-294157.
In a direct injection internal combustion engine, a cylinder is provided with a volume portion in an exhaust passage between an exhaust purification catalyst and a combustion chamber, and a main injection is performed in an expansion stroke when a temperature rise of the catalyst is required. In addition to this, an additional fuel injection is performed.
[0003]
The additionally injected fuel is released into the exhaust passage when the exhaust valve is opened while a part of the oxygen contained in the exhaust gas reacts, and the unburned portion remaining unburned in the exhaust passage is the volume portion. Where the exhaust gas supplied to the catalyst is heated.
[0004]
[Problems to be solved by the invention]
By the way, in the above-mentioned conventional device, in order to achieve complete combustion of unburned fuel, a volume part in which unburned fuel and combustion gas stay is provided, but whether or not unburned fuel is completely burned in the volume part, Because it depends on the exhaust gas temperature at the inlet of the volume and the concentration of unburned fuel (see FIG. 5), it is difficult to stably burn the unburned fuel stably and the emission may deteriorate due to unburned fuel. There was a problem.
[0005]
For example, when the exhaust gas temperature is low, the oxidation reaction takes time, so the oxidation reaction upstream of the volume part of the exhaust discharged from the combustion chamber becomes insufficient, and as a result, the temperature rise of the volume part is small and the volume part Instability in combustion becomes unstable, and the amount of unburned fuel increases. On the other hand, when the exhaust gas temperature is relatively high, the oxidation reaction is promoted, but as a result, the oxidation reaction upstream of the volume part increases and the concentration of unburned fuel at the volume part inlet decreases. Combustion at the part becomes unstable, and the amount of unburned fuel increases.
[0006]
In order to solve the increase in the unburned residue when the exhaust temperature is relatively high, it is necessary to suppress the oxidation reaction upstream of the volume, but the exhaust temperature is forcibly lowered to suppress the oxidation reaction. Then, there is a possibility that unburned residue may increase for the reasons described above, and a method for forcibly reducing the exhaust temperature is not preferable.
The present invention has been made in view of the above problems, and when performing additional fuel injection for raising the temperature of the catalyst, it is possible to avoid the occurrence of unburned residue in the volume portion due to the exhaust gas temperature and worsening of emissions. An object of the present invention is to provide an exhaust purification device for a direct injection type internal combustion engine.
[0007]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, in a direct injection type internal combustion engine, a volume portion is provided in the exhaust passage on the upstream side of the catalyst, and when the temperature of the catalyst is required to be raised, during the expansion stroke or the exhaust stroke. Let the fuel injection valve perform additional fuel injection and depending on the exhaust temperatureBy changing the arrival time of exhaust from the combustion chamber to the volume part,The combustion ratio of unburned fuel on the upstream side of the volume was adjusted.
[0008]
According to such a configuration, the combustion ratio of the unburned fuel on the upstream side of the volume part corresponds to the fact that the oxidation reaction on the upstream side of the volume part takes time when the exhaust gas temperature is low and is accelerated when the exhaust temperature is high. Adjust.
Specifically, when the exhaust gas temperature is low, the combustion temperature of the unburned fuel on the upstream side of the volume part is increased to increase the temperature of the volume part, and conversely, the oxidation temperature is high and the oxidation reaction upstream of the volume part. Is excessive and the unburned fuel concentration at the inlet of the volume decreases, the combustion ratio of the unburned fuel at the upstream of the volume is decreased.
[0009]
here,The arrival time of the exhaust gas from the combustion chamber to the volume part is the time for the exhaust gas to oxidize until it reaches the volume part. When the exhaust gas temperature is low and the oxidation reaction rate is slow, if the arrival time is lengthened, the slow reaction time The combustion rate of unburned fuel can be increased and changed by compensating for the speed. Conversely, when the exhaust time is high and the oxidation reaction rate is fast, if the arrival time is shortened, the unburned fuel before reaching the volume portion The combustion of is suppressed.According to a second aspect of the present invention, the exhaust arrival time from the combustion chamber to the volume portion is shortened as the exhaust temperature is higher.
[0010]
In the invention according to claim 3, the arrival time to the volume part is changed by changing the opening characteristic of the exhaust valve.
According to such a configuration, by changing the opening characteristic of the exhaust valve, the flow rate characteristic when exhaust is discharged into the exhaust passage changes, and the arrival time of the exhaust to the volume changes.
[0011]
According to the invention of claim 4, the opening area of the exhaust valve is changed as the opening characteristic of the exhaust valve.
According to such a configuration, for example, if the opening area of the exhaust valve at the initial valve opening is increased, the exhaust gas is discharged all at once and the arrival time to the volume portion is shortened.
In the invention according to claim 5, the arrival time to the volume part is changed by changing the cross-sectional area of the exhaust passage from the combustion chamber to the volume part.
[0012]
According to such a configuration, by changing the cross-sectional area of the exhaust passage, the flow rate of the exhaust gas is adjusted, and the arrival time to the volume part is changed.
According to the sixth aspect of the present invention, the cross-sectional area of the exhaust passage from the combustion chamber to the volume portion is changed by providing a plurality of exhaust valves for each cylinder and changing the number of exhaust valves to be opened. The configuration.
[0013]
According to such a configuration, the cross-sectional area of the exhaust passage in the exhaust stroke is reduced by reducing the number of exhaust valves to be opened, and conversely, the exhaust stroke is increased by increasing the number of exhaust valves to be opened. Increase the cross-sectional area of the exhaust passage at.
In the invention according to claim 7, the length of the exhaust passage from the combustion chamber to the volume part is changed to change the arrival time to the volume part.
[0014]
According to such a configuration, even when the exhaust flow velocity is the same, the arrival time to the volume portion changes due to the different exhaust passage lengths.
In the invention according to claim 8, a plurality of exhaust passages having different lengths are provided in parallel as exhaust passages connecting the combustion chamber and the volume portion, and one of the plurality of exhaust passages is selectively opened. Thus, the length of the exhaust passage from the combustion chamber to the volume portion is changed.
[0015]
According to such a configuration, a plurality of exhaust passages having different lengths are provided in parallel in advance, and when the arrival time to the volume portion is increased, the longer one of the plurality of exhaust passages is opened, and the reverse In addition, when it is desired to shorten the arrival time to the volume portion, the long exhaust passage is closed and the short passage is opened instead.
According to the ninth aspect of the present invention, the exhaust arrival time is changed by changing the rotational speed and / or intake air amount of the engine.
[0016]
According to this configuration, the exhaust flow rate changes due to changes in the engine speed and the intake air amount, and the arrival time to the volume changes.
According to a tenth aspect of the present invention, an exhaust arrival time target is determined based on the exhaust temperature, and when the determined target exceeds a predetermined range, the engine exhaust is set so that the target is within the predetermined range. It was set as the structure which changes temperature.
[0017]
According to this configuration, when the arrival time required from the exhaust temperature is set, if this arrival time exceeds a predetermined range, for example, if it is outside the controllable range, the target temperature can be achieved by changing the engine temperature. As a result, a target in accordance with the exhaust temperature is realized by setting the value within the predetermined range (controllable range).
In the invention described in claim 11, the exhaust gas temperature is changed by changing the ignition timing of the engine and / or the timing of additional fuel injection.
[0018]
According to this configuration, the exhaust gas temperature is changed so that the target of the arrival time is within a predetermined range by the advance / retard control of the ignition timing and / or the additional fuel injection timing.
The invention according to claim 12 is configured such that a target of the exhaust arrival time is determined based on the exhaust temperature, and the additional fuel injection is stopped when the determined target exceeds a predetermined range.
[0019]
According to this configuration, when the arrival time required from the exhaust temperature is set, if this arrival time exceeds a predetermined range, for example, if it is outside the controllable range, the target arrival time (in other words, unburned fuel) (Combustion rate target) cannot be realized, and even if the additional injection is performed as it is, the amount of unburned fuel is increased. Therefore, the additional fuel injection is stopped.
[0020]
In the invention described in claim 13, the exhaust gas temperature is estimated based on the operating condition of the engine.
According to such a configuration, instead of directly detecting the exhaust gas temperature with the temperature sensor, the exhaust gas temperature is estimated from the engine operating conditions (for example, the rotational speed, the intake air amount, the air-fuel ratio, etc.).
[0021]
【The invention's effect】
Claim1, 2According to the described invention,Corresponding to the difference in reaction speed due to the difference in exhaust temperature, the exhaust arrival time to the volume part, that is, the reaction time is changed, so the concentration of unburned fuel and the exhaust temperature at the volume part inlet can be accurately and easily Can be controlled to the optimum value,There is an effect that the temperature of the catalyst can be raised after sufficiently avoiding the generation of unburned residue.
[0022]
According to invention of Claim 3, 4,There is an effect that the exhaust flow rate can be adjusted by changing the opening characteristic of the exhaust valve, and the arrival time of the exhaust gas to the volume portion can be changed to a value corresponding to the difference in the exhaust gas temperature (reaction rate).
[0023]
According to the fifth and sixth aspects of the invention, the exhaust flow velocity is changed by changing the cross-sectional area of the exhaust passage, and the exhaust arrival time to the volume portion is set to a value corresponding to the difference in the exhaust temperature (reaction rate). There is an effect that it can be changed.
According to the seventh and eighth aspects of the invention, by changing the length of the exhaust passage, it is possible to change the arrival time of the exhaust to the volume portion to a value corresponding to the difference in the exhaust temperature (reaction rate). effective.
[0024]
According to the ninth aspect of the present invention, the exhaust flow rate is changed by changing the rotational speed and the intake air amount, and the exhaust arrival time to the volume part is changed to a value corresponding to the difference in the exhaust temperature (reaction speed). There is an effect that can be made.
According to the invention of claim 10, the exhaust gas temperature is forced when the combustion rate of the unburned fuel on the upstream side of the volume cannot be controlled to the optimum value even if the exhaust arrival time is controlled to the maximum. Therefore, the target of the arrival time is changed, so that the combustion ratio of the unburned fuel can be controlled to the optimum value within the control range of the arrival time.
[0025]
According to the eleventh aspect of the present invention, there is an effect that the target of the arrival time can be changed to the exhaust temperature within the control range by the retard / advance control of the ignition timing and / or the additional injection timing.
According to the twelfth aspect of the invention, the additional injection is stopped in a state where the combustion ratio of the unburned fuel on the upstream side of the volume portion cannot be controlled to the optimum value by controlling the arrival time, and the increase in the amount of unburned fuel is increased. There is an effect that inviting additional injection can be prevented in advance.
[0026]
According to the invention of claim 13, since the exhaust gas temperature is estimated without using a temperature sensor, there is an effect that the system configuration can be simplified.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a direct injection type internal combustion engine to which the present invention is applied.
In FIG. 1, the air sucked into the engine 1 passes through an air cleaner 2, and then the flow rate is measured by an air flow meter 3, guided to a throttle chamber 4, and the amount of air by a throttle valve 4 a interposed in the throttle chamber 4. Is controlled.
[0028]
The intake air is then introduced when the intake valve 8 is opened in the cylinder 7 through the intake collector 5 and the intake passage 6.
The cylinder 7 is provided with a piston 9 that reciprocates.
A fuel injection valve 10 that directly injects fuel into a combustion chamber constituted by the piston 9 and the cylinder 7 is provided, and the fuel injection valve 10 injects fuel into the air in the cylinder 7. An air-fuel mixture is formed, and the air-fuel mixture burns by spark ignition of the spark plug 11.
[0029]
The combustion exhaust is discharged to the exhaust port 13 when the exhaust valve 12 is opened.
An EGR (exhaust gas recirculation) passage 14 is connected to the exhaust port 13, and a part of the exhaust gas is recirculated to the intake collector 5 through the EGR passage 14. The exhaust gas recirculation amount is controlled by an EGR valve 15 interposed in the middle of the EGR passage 14.
The exhaust passage 16 connected downstream of the exhaust port 13 is provided with an oxygen sensor 17 for detecting the oxygen concentration in the exhaust gas correlated with the air-fuel ratio of the combustion mixture. The air-fuel ratio is detected from the oxygen concentration detection signal, and the air-fuel ratio detection result is used for air-fuel ratio feedback control.
[0030]
A volume 18 is provided on the downstream side of the oxygen sensor 17, and a catalyst 19 for purifying exhaust gas is further provided on the downstream of the volume 18.
The engine control unit 20 controls the injection amount and injection timing in the fuel injection valve 10, the ignition timing of the spark plug 1, and the opening degree of the EGR valve 15 that adjusts the exhaust gas recirculation amount.
[0031]
In addition to the intake air amount signal from the air flow meter 3 and the oxygen concentration signal from the oxygen sensor 17, the engine control unit 20 includes a crank angle sensor signal for detecting the engine speed and crank angle, and a coolant temperature. A signal, an accelerator pedal opening signal, and the like are input, and each control is performed based on these signals.
In the present embodiment, a variable valve mechanism 21 is provided that can switch the lift characteristic of the exhaust valve 12 to the two characteristics shown in FIG.
[0032]
The variable valve mechanism 21 is configured such that, for example, two cams having different profiles can be switched and used.
The two lift characteristics shown in FIG. 2 are the valve opening timing and the valve closing timing, and the maximum lift amount is the same, but the characteristic b is the initial lift amount (opening area) compared to the characteristic a. Is set to be large.
[0033]
The variable valve mechanism 21 is also controlled by the engine control unit 20.
The engine control unit 20 is configured to perform additional fuel injection in the expansion stroke or the exhaust stroke when the temperature of the catalyst 19 is to be raised separately from the normal main fuel injection. Will be described with reference to the flowchart of FIG.
[0034]
In the flowchart of FIG. 3, in step S1, the engine speed Ne, the intake air amount Qa, the air-fuel ratio A / F, and the cooling water temperature Tw are read as parameters indicating the operating conditions of the engine 1.
In step S2, the coolant temperature Twst at the time of engine start is read.
In step S3, it is determined whether or not the coolant temperature Twst at the time of starting the engine is lower than a predetermined temperature Twstlow.
[0035]
If it is determined in step S3 that the cooling water temperature Twst at the time of starting the engine is lower than the predetermined temperature Twstlow, it is determined that the cooling device is being started, and the process proceeds to step S4.
On the other hand, if it is determined that the coolant temperature Twst at the time of starting the engine is equal to or higher than the predetermined temperature Twstlow, it is determined that the catalyst 19 is in an active state at the time of restart immediately after the engine is stopped, and the temperature of the catalyst 19 is increased. Without proceeding to steps S11 and S12. Details of steps S11 and S12 will be described later.
[0036]
In step S4, it is determined whether or not the temperature increase control execution duration CntON is less than a predetermined value CntON0. If it is determined in step S4 that the continuation time CntON is equal to or greater than the predetermined value CntON0, the temperature rise control is terminated and the process proceeds to steps S11 and S12. In step S11, the change in the arrival time of the exhaust from the combustion chamber to the volume portion 18 is canceled, and the arrival time is set to the normal value.return.
[0037]
In step S12, the duration CntON is reset to zero.
On the other hand, if it is determined in step S4 that the duration CntON is less than the predetermined value CntON0, the process proceeds to step S5.
In step S3, the active state of the catalyst 19 is determined from the cooling water temperature Twst at the start, and in step S4, it is estimated whether or not the catalyst 19 has been heated to the activation temperature from the execution duration CntON of the temperature increase control. Therefore, a catalyst temperature sensor that directly detects the temperature of the catalyst 19 may be provided, and when the temperature of the catalyst 19 is lower than the activation temperature, temperature increase control for performing additional injection may be executed.
[0038]
In step S5, the exhaust temperature Texp at the time of performing additional injection is estimated based on the operating conditions of the engine 1.
The exhaust temperature Texp at the time of the additional injection changes according to the engine speed Ne, the intake air amount Qa, the ignition timing ADV, the additional injection timing IT2, the additional injection air-fuel ratio (additional injection amount), and the exhaust temperature for each parameter. Since the change shows characteristics as shown in FIGS. 4A to 4E, the exhaust temperature Texp at the time of execution of the additional injection can be estimated from these characteristics.
[0039]
In step S6, it is determined whether or not the estimated exhaust temperature Texp during execution of the additional injection is higher than a threshold value TexpSL.
When the exhaust gas temperature Texp is high, the oxidation reaction rate on the upstream side of the volume 18 is high, and the concentration of unburned fuel at the inlet of the volume 18 is lowered, so that combustion in the volume 18 becomes unstable and burns. The remaining amount increases (see FIG. 5). Conversely, when the exhaust gas temperature Texp is low, the oxidation reaction rate on the upstream side of the volume 18 is slow, and as a result, the temperature rise of the volume 18 is small and the combustion in the volume 18 becomes unstable. However, the unburned amount increases (see FIG. 5).
[0040]
Therefore, when the exhaust gas temperature Texp is high and the reaction rate is fast, it is necessary to reduce the unburned fuel concentration ratio at the inlet of the volume 18 by reducing the combustion ratio of the unburned fuel upstream of the volume 18. On the contrary, when the exhaust temperature Texp is low and the reaction rate is slow, it is necessary to increase the combustion rate of unburned fuel on the upstream side of the volume 18 to increase the temperature of the volume 18.
[0041]
In the present embodiment, the combustion rate of unburned fuel on the upstream side of the volume 18 is adjusted by changing the time until the exhaust reaches the volume 18 from the combustion chamber with respect to the change in the reaction speed.
That is, when the exhaust temperature Texp is high and the reaction rate is fast, the combustion time of unburned fuel can be reduced by shortening the arrival time and shortening the oxidation reaction time upstream of the volume 18. If the exhaust temperature Texp is low and the reaction rate is slow, the combustion time of unburned fuel can be increased by increasing the arrival time and increasing the oxidation reaction time upstream of the volume 18. it can.
[0042]
Therefore, when it is determined in step S6 that the exhaust temperature Texp at the time of performing additional injection is higher than the threshold value TexpSL, the routine proceeds to step S7, where the arrival time is set to the short side, and the exhaust temperature at the time of performing additional injection is set. When it is determined that Texp is equal to or less than the threshold value TexpSL, the process proceeds to step S10, and the arrival time is set to the longer side.
The switching of the arrival time is made by switching the lift characteristic of the exhaust valve 12 by the variable valve mechanism 21.
[0043]
When a short side is required as the arrival time, by selecting a characteristic b having a larger lift amount (opening area) at the initial stage of valve opening from among the lift characteristics shown in FIG. 2, the exhaust flow rate at the initial stage of opening the valve is increased. The arrival time is set to the short side.
Conversely, when a longer side is required as the arrival time, by selecting a characteristic a having a smaller lift amount (opening area) in the initial stage of valve opening from among the lift characteristics shown in FIG. The flow rate is reduced and the arrival time is set on the longer side.
[0044]
In step S8, additional fuel injection is performed in the expansion stroke or the exhaust stroke.
In step S9, the continuation time CntON is counted up. When the continuation time CntON becomes equal to or greater than a predetermined value CntON0, the process proceeds from step S4 to steps S11 and S12, and the additional injection control is stopped and the arrival time, that is, the exhaust gas The lift characteristic of the valve 12 is returned to the normal characteristic a.
[0045]
As described above, the arrival time is switched corresponding to the difference in the reaction rate depending on the exhaust temperature Texp, and the combustion ratio of unburned fuel on the upstream side of the volume 18 is adjusted so that no unburned fuel remains in the volume 18. The fuel can be burned, and the temperature of the catalyst 19 can be increased without deteriorating the emission.
By the way, in the above-described embodiment, the lift characteristic (open characteristic) of the exhaust valve 12 is switched as means for changing the exhaust arrival time from the combustion chamber to the volume portion 18. However, the means shown in FIG. It is also possible to switch the arrival time.
[0046]
FIG. 6 shows a configuration including two exhaust ports 13 and two exhaust valves 12 for each cylinder, and one of the two exhaust valves 12 is stopped by the variable valve mechanism 21 and closed. Be able to keep
That is, a characteristic a in which the two exhaust valves 12 are both opened / closed and a characteristic b in which one of the two exhaust valves 12 is normally opened / closed but the other is stopped and held in the closed state are switched. It is.
[0047]
Here, in the case of the characteristic b in which one of the two exhaust valves 12 is deactivated, the number of valves opened in the exhaust stroke is halved compared to the characteristic a, so that the cross-sectional area of the exhaust passage through which the exhaust can be discharged is halved. Becomes faster and the arrival time becomes shorter.
Therefore, when it is determined in step S6 that the exhaust gas temperature Texp at the time of performing the additional injection is higher than the threshold value TexpSL, the characteristic b that stops one of the two exhaust valves 12 is selected in step S7. Thus, the oxidation reaction time on the upstream side of the volume portion 18 can be shortened, and the combustion ratio of unburned fuel can be suppressed.
[0048]
In step S6, when it is determined that the exhaust temperature Texp at the time of the additional injection is equal to or lower than the threshold value TexpSL, the characteristic a that normally opens and closes both the two exhaust valves 12 is selected in step S10. By doing so, a sufficient oxidation reaction time on the upstream side of the volume portion 18 can be secured.
Further, as means for changing the arrival time of the exhaust gas from the combustion chamber to the volume portion 18, a configuration in which the length of the exhaust passage 16 from the combustion chamber to the volume portion 18 is switched as shown in FIG. 7 may be used. .
[0049]
In FIG. 7, as an exhaust passage 16 from the combustion chamber to the volume 18, an exhaust passage 16 a that is normally used and an exhaust passage 16 b that is shorter than the exhaust passage 16 a are provided in parallel, and the exhaust passage 16 a A switching valve 25 is provided for selecting which of the exhaust passage 16b and exhaust gas is to flow.
According to such a configuration, if the exhaust gas is allowed to flow toward the exhaust passage 16b, the arrival time to the volume portion 18 is shortened. Therefore, in step S6, it is determined that the exhaust gas temperature Texp at the time of performing additional injection is higher than the threshold value TexpSL. At this time, if the short side exhaust passage 16b is opened in step S7, the oxidation reaction time on the upstream side of the volume portion 18 can be shortened and the combustion ratio of unburned fuel can be suppressed.
[0050]
If it is determined in step S6 that the exhaust temperature Texp during execution of the additional injection is equal to or lower than the threshold value TexpSL, if the exhaust passage 16a is opened in step S10, the upstream side of the volume 18 A sufficient oxidation reaction time can be secured.
Further, the exhaust flow rate is changed by forcibly changing the rotational speed Ne and / or the intake air amount Qa of the engine 1 without using the special arrival time variable mechanism as described above, so that the arrival time can be changed. It is possible to change the configuration.
[0051]
The flowcharts of FIGS. 8 and 9 show temperature rise control particularly suitable for a configuration in which the arrival time is changed by forcibly changing the rotational speed Ne and / or the intake air amount Qa of the engine 1 as described above.
8 and 9, in step S21, the engine speed Ne, the intake air amount Qa, the air-fuel ratio A / F, and the coolant temperature Tw are read as parameters indicating the operating conditions of the engine 1.
[0052]
In step S22, the exhaust temperature Tex at that time is estimated from each parameter read in step S21.
The correlations between the engine speed Ne, the intake air amount Qa, the air-fuel ratio A / F, the cooling water temperature Tw, and the exhaust temperature Tex show the characteristics shown in FIGS. 10 (a) to 10 (d). The exhaust temperature Tex can be estimated from the above characteristics.
[0053]
In step S23, it is determined whether or not the exhaust temperature Tex is lower than a predetermined temperature Tlow.
When it is determined in step S23 that the exhaust gas temperature Tex is equal to or higher than the predetermined temperature Tlow, it is estimated that the catalyst 19 has reached the activation temperature, so that the process proceeds to steps S37 and S38, and the temperature rise control of the catalyst 19 is performed. Quit this program without
[0054]
In steps S37 and S38, an execution duration time CntON and a suspension duration time CntOFF of temperature increase control described later are reset to 0, respectively.
On the other hand, if it is determined that the exhaust temperature Tex is lower than the predetermined temperature Tlow, the process proceeds to step S24, and it is determined whether or not the engine 1 is within a predetermined time since the engine 1 is started.
When the elapsed time after the start exceeds the predetermined time, the process proceeds to step S32, and it is determined whether the execution duration CntON is equal to or less than the predetermined time CntON0 or whether the stop duration CntOFF is equal to or greater than the predetermined time CntOFF0. To do.
[0055]
Here, when the execution duration CntON exceeds the predetermined time CntON0, or when the stop duration CntOFF is less than the predetermined time CntOFF0, the process proceeds to step S36, and the stop is performed without executing the temperature increase control. Count up the duration time CntOFF and end this program.
On the other hand, when the engine 1 is within a predetermined time since the start or when a predetermined time or more has elapsed since the start, the execution duration CntON is less than the predetermined time CntON0 or the stop duration CntOFF is If it is equal to or longer than the predetermined time CntOFF0, the process proceeds to step S25.
[0056]
In step S25, similarly to step S5, the exhaust temperature Texp at the time of executing the additional injection is estimated based on the operating conditions of the engine 1.
In the next step S26, the target value TMtgt of the exhaust arrival time from the combustion chamber to the volume portion 18 is determined from the exhaust temperature Texp at the time of execution of the additional injection.
As shown in FIG. 11, the target value TMtgt is set shorter as the exhaust temperature Texp is higher.
[0057]
That is, since the oxidation reaction proceeds in a short time when the exhaust temperature Texp is high, it is required to reach the volume 18 in a short time in order to suppress excessive oxidation upstream of the volume 18. Since the oxidation reaction takes time when Texp is low, it is necessary to secure a longer time to reach the volume 18 in order to promote oxidation on the upstream side of the volume 18.
[0058]
In step S27, it is determined whether or not the target value TMtgt is within a range between the minimum value TMlwr and the maximum value TMupr.
The minimum value TMlwr and the maximum value TMupr are parameters set according to, for example, torque, and the lower limit / upper limit of the exhaust arrival time within the control range of the intake air amount and the rotational speed capable of generating the current torque. Means.
[0059]
That is, if it is within the range between the minimum value TMlwr and the maximum value TMupr, by changing the intake air amount and the rotational speed within a range in which the torque is not greatly changed, the exhaust flow rate is changed and the target is changed. It will be possible to control the arrival time.
If it is determined in step S27 that the target value TMtgt is not within the range between the minimum value TMlwr and the maximum value TMupr, the process proceeds to step S33, and the target value is determined from the range between the minimum value TMlwr and the maximum value TMupr. Based on how far the TMtgt is, it is determined whether or not the target value TMtgt is within a correctable range.
[0060]
The target value TMtgt is corrected by forcibly changing the exhaust temperature Texp at the time of additional injection, and the target value TMtgt corresponding to the changed exhaust temperature Texp is sandwiched between the minimum value TMlwr and the maximum value TMupr Indicates that it is within.
In the present embodiment, since the exhaust gas temperature Texp is forcibly changed by changing the ignition timing ADV and / or the additional injection timing IT2, as will be described later, it can be changed by changing the ignition timing ADV and / or the additional injection timing IT2. In step S33, it is determined whether or not the target value TMtgt can be within the range between the minimum value TMlwr and the maximum value TMupr by changing the exhaust temperature within the range.
[0061]
When it is determined in step S33 that the correction is not possible, that is, even if the ignition timing ADV and / or the additional injection timing IT2 are changed to the maximum within a range not impairing the combustibility, the exhaust temperature at that time is supported. When the target value TMtgt to be performed does not fall within the range between the minimum value TMlwr and the maximum value TMupr, unburned fuel will be generated even if the additional injection is forcibly executed, so the process proceeds to step S36 without performing the additional injection.
[0062]
On the other hand, if it is determined in step S33 that the correction can be made, the process proceeds to step S34, and the ignition timing ADV and / or the additional injection timing IT2 is set so that the target value TMtgt is within the range between the minimum value TMlwr and the maximum value TMupr. To change.
For example, when the target value TMtgt of the arrival time is larger than the maximum value TMupr, it is necessary to increase the exhaust gas temperature. Therefore, as shown in FIG. 4, the ignition timing ADV is retarded or the additional injection timing IT2 is set. Delay.
[0063]
In step S35, a target value TMtgt corresponding to the exhaust temperature Texp after the change of the ignition timing ADV and / or the additional injection timing IT2 is set.
In the above embodiment, if it is determined in step S27 that the target value TMtgt is not within the range between the minimum value TMlwr and the maximum value TMupr, and it is determined in step S33 that it is within the correctable range, the exhaust temperature The target value TMtgt is changed to change the target value TMtgt and the temperature increase control is performed. However, when it is determined in step S27 that the target value TMtgt is not within the range between the minimum value TMlwr and the maximum value TMupr, It may be configured to determine execution stop.
[0064]
In step S28, in order to make the actual arrival time coincide with the target value TMtgt, the intake air amount Qa and / or the engine rotational speed Ne of the engine 1 is controlled by controlling the throttle opening (idle control valve), the main injection amount, and the like. The exhaust flow rate is changed by forcibly changing it.
In step S29, additional fuel injection is performed in the expansion stroke or the exhaust stroke.
[0065]
In step S30, the execution duration CntON is counted up, and in step S31, the suspension duration CntOFF is reset to zero.
As a result, the execution duration CntON measures the total time of additional injection, and the stop duration CntOFF measures the time since the additional injection was stopped.
[0066]
If the predetermined time CntOFF0 or more does not elapse after the additional injection is stopped, the additional injection will not be performed, and if the execution duration CntON exceeds the predetermined time CntON0, the additional injection will not be performed. The execution of frequent additional injection after a predetermined time has elapsed from the start is avoided, and deterioration due to excessive temperature rise of the catalyst 19 and deterioration of fuel consumption are prevented.
[0067]
In the embodiment shown in the flowcharts of FIGS. 8 and 9, the arrival time is changed by changing the intake air amount Qa and / or the engine rotational speed Ne, so that no special variable mechanism is required, and the upstream side of the volume portion 18 is not required. The combustion rate of the unburned fuel can be adjusted to increase the temperature of the catalyst 19 without generating unburned residue.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an internal combustion engine in an embodiment.
FIG. 2 is a lift characteristic diagram of an exhaust valve in the embodiment.
FIG. 3 is a flowchart showing details of catalyst temperature rise control.
FIG. 4 is a diagram showing a correlation between an exhaust temperature during additional injection and operating conditions.
FIG. 5 is a diagram showing the correlation between the amount of unburned fuel and the concentration of unburned components at the volume inlet and the exhaust temperature.
FIG. 6 is a diagram illustrating an exhaust arrival time variable mechanism by exhaust valve suspension control.
FIG. 7 is a view showing a variable mechanism of an exhaust arrival time by switching an exhaust passage.
FIG. 8 is a flowchart showing another embodiment of catalyst temperature increase control.
FIG. 9 is a flowchart showing another embodiment of catalyst temperature increase control.
FIG. 10 is a diagram showing a correlation between exhaust temperature and operating conditions.
FIG. 11 is a diagram showing a correlation between an exhaust temperature and a target value of arrival time.
[Explanation of symbols]
1. Internal combustion engine
2 ... Air cleaner
3 ... Air flow meter
4 ... Throttle chamber
5 ... Intake collector
6 ... Intake passage
7 ... Cylinder
8 ... Intake valve
9 ... Piston
10 ... Fuel injection valve
11 ... Spark plug
12 ... Exhaust valve
13 ... Exhaust port
14 ... EGR passage
15 ... EGR valve
16 ... Exhaust passage
17 ... Oxygen sensor
18 ... Volume part
19 ... Catalyst
20 ... Engine control unit
21 ... Variable valve mechanism

Claims (13)

In a cylinder direct injection internal combustion engine having a fuel injection valve for directly injecting fuel into the combustion chamber and having a catalyst for purifying exhaust in the exhaust passage, a volume portion is provided in the exhaust passage on the upstream side of the catalyst, When a temperature increase of the catalyst is required, additional fuel injection is performed from the fuel injection valve during the expansion stroke or exhaust stroke, and the exhaust reaches from the combustion chamber to the volume portion according to the exhaust temperature. An exhaust purification device for a direct injection type internal combustion engine, characterized in that the combustion ratio of unburned fuel on the upstream side of the volume part is adjusted by changing the time . The exhaust purification apparatus for a direct injection type internal combustion engine according to claim 1, wherein the exhaust arrival time from the combustion chamber to the volume portion is shortened as the exhaust temperature is higher . The exhaust purification device for a direct injection type internal combustion engine according to claim 1 or 2 , wherein the exhaust arrival time is changed by changing an opening characteristic of the exhaust valve. 4. The exhaust purification apparatus for a direct injection type internal combustion engine according to claim 3, wherein the opening area of the exhaust valve is changed as an opening characteristic of the exhaust valve. The exhaust purification of a direct injection type internal combustion engine according to claim 1 or 2 , wherein the exhaust arrival time is changed by changing a cross-sectional area of the exhaust passage from the combustion chamber to the volume portion. apparatus. 6. A plurality of exhaust valves are provided for each cylinder, and the cross-sectional area of the exhaust passage from the combustion chamber to the volume portion is changed by changing the number of exhaust valves to be opened. An exhaust purification apparatus for a direct injection type internal combustion engine as described. The exhaust purification of a direct injection type internal combustion engine according to claim 1 or 2 , wherein the exhaust arrival time is changed by changing a length of an exhaust passage from the combustion chamber to the volume portion. apparatus. As the exhaust passage connecting the combustion chamber and the volume portion, a plurality of exhaust passages having different lengths are provided in parallel, and one of the plurality of exhaust passages is selectively opened, whereby the combustion chamber 8. An exhaust purification apparatus for a direct injection type internal combustion engine according to claim 7, wherein the length of the exhaust passage from the cylinder to the volume portion is changed. The exhaust purification device for a direct injection type internal combustion engine according to claim 1 or 2 , wherein the exhaust arrival time is changed by changing a rotational speed of the engine and / or an intake air amount. A target of the exhaust arrival time is determined based on the exhaust temperature, and when the determined target exceeds a predetermined range, the exhaust temperature of the engine is changed so that the target is within the predetermined range. The exhaust purification apparatus for a direct injection type internal combustion engine according to any one of claims 1 to 9, wherein the exhaust purification apparatus is a direct injection type internal combustion engine. The exhaust emission control device for a direct injection type internal combustion engine according to claim 10, wherein the exhaust gas temperature is changed by changing an ignition timing of the engine and / or a timing of additional fuel injection. Wherein determining a target arrival time on the basis of the exhaust temperature exhaust, when the target which is the determined exceeds a predetermined range, one of the claim 1-9, characterized in that for stopping said additional fuel injection An exhaust emission control device for a direct injection type internal combustion engine, according to claim 1. The exhaust emission control device for a direct injection type internal combustion engine according to any one of claims 1 to 12, wherein the exhaust gas temperature is estimated based on operating conditions of the engine.

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