JP3951616B2 - Control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention Switching between spark ignition combustion and compression self-ignition combustion according to operating conditions The present invention relates to a technique for enriching control of an exhaust air-fuel ratio for regeneration of a NOx trap catalyst in an internal combustion engine.
[0002]
[Prior art]
In view of increasing environmental problems in recent years, there is an increasing demand for internal combustion engines to improve fuel consumption and exhaust emissions.
In order to improve the thermal efficiency of a gasoline engine, a method is known in which the air-fuel mixture is leaned to reduce pump loss and to increase the specific heat ratio of the working gas to increase the theoretical thermal efficiency.
[0003]
However, in the conventional spark ignition engine, if the air-fuel ratio is made lean, the combustion period becomes longer and the combustion stability deteriorates. For this reason, there is a limit to the lean air-fuel ratio.
As a technique for solving the above problem, as shown in JP-A-7-71279, means for causing premixed compression self-ignition combustion is proposed. In a two-cycle engine, an exhaust control valve capable of controlling the opening degree of the exhaust port is provided in the vicinity of the exhaust port, and by controlling the exhaust control valve, the in-cylinder pressure is controlled to cause self-ignition combustion. ing.
[0004]
In premixed compression self-ignition combustion, combustion reactions occur from multiple positions, so even when the air-fuel ratio is made lean, the combustion period is not prolonged compared to spark ignition combustion, and combustion at a leaner air-fuel ratio is performed. Is possible. Further, since the air-fuel ratio is lean, the combustion temperature is lowered and NOx can be greatly reduced.
On the other hand, NOx trap catalysts that trap NOx contained in exhaust gas when the exhaust air-fuel ratio is lean and desorb and purify trapped NOx by making the exhaust air-fuel ratio rich are known. According to this technique, NOx contained in the exhaust gas during lean combustion can be effectively purified.
[0005]
[Problems to be solved by the invention]
However, when the above two technologies are combined, it is necessary to enrich the exhaust air-fuel ratio for regeneration of the NOx trap catalyst. When rich control is performed while performing compression auto-ignition combustion, compression auto-ignition combustion There is a problem that the ignition timing is advanced and knocking occurs.
[0006]
It is also possible to end compression self-ignition combustion once and switch to spark ignition combustion, but in this case, it is necessary to switch the in-cylinder temperature, in-cylinder pressure, air-fuel ratio, etc. significantly and instantaneously, which improves operability. It was more likely to cause deterioration. In addition, in order to start compression self-ignition combustion again, it is necessary to adjust the in-cylinder temperature, in-cylinder pressure, air-fuel ratio, etc. to the optimum conditions for self-ignition, and it takes time to start self-ignition. Since there is no compression self-ignition combustion with good fuel consumption in the section up to, there is a problem of causing deterioration in fuel consumption.
[0007]
The present invention has been made in view of such a problem, and provides a clean internal combustion engine that can continue compression self-ignition combustion, has high fuel efficiency, even when the exhaust air-fuel ratio is enriched from the requirements of the exhaust system. For the purpose.
[0008]
[Means for Solving the Problems]
For this reason, in the invention of claim 1, Switching between spark ignition combustion and compression self-ignition combustion according to operating conditions In an internal combustion engine control device, the exhaust air-fuel ratio is enriched and controlled. Request was during compression auto-ignition combustion In this case, the air-fuel ratio is controlled to be rich while continuing compression self-ignition combustion. In this case, the air-fuel ratio selection means for selecting an air-fuel ratio that provides an ignitability equivalent to the ignitability during normal compression self-ignition combustion without performing the enrichment control is provided as the enriched air-fuel ratio. It is characterized by that.
[0009]
Claim 2 In the invention of During compression self-ignition combustion When the exhaust air-fuel ratio is controlled to be rich, the engine torque during normal compression self-ignition combustion without rich control is Equivalent Intake air amount limiting means for reducing the intake air amount so as to obtain engine torque is provided.
Claim 3 In the invention, a fuel injection valve capable of directly injecting fuel into the cylinder is provided, During compression self-ignition combustion When the exhaust air-fuel ratio is controlled to be rich, by controlling the fuel injection timing in the compression stroke, the ignitability and engine torque during normal compression self-ignition combustion without the rich control are Equivalent It has a fuel injection timing control means for forming a rich air-fuel mixture layer in a part of the cylinder so that ignitability and engine torque can be obtained.
[0010]
Claim 4 In the invention of During compression self-ignition combustion A means for controlling at least one of the in-cylinder temperature (intake air temperature) or the in-cylinder pressure to a predetermined value is provided.
Claim 5 In this invention, the exhaust system is provided with a NOx trap catalyst that traps NOx when the exhaust air-fuel ratio is lean and desorbs and purifies NOx trapped when the exhaust air-fuel ratio is rich. Therefore, the exhaust air-fuel ratio is controlled to be enriched.
[0011]
【The invention's effect】
According to the invention of claim 1, There was a demand to enrich the exhaust air-fuel ratio during compression auto-ignition combustion In this case, the air-fuel ratio is enriched while continuing the compression self-ignition combustion, so the compression self-ignition can be continued even after the enrichment control is completed. Can do.
[0012]
Also during compression self-ignition combustion When the exhaust air-fuel ratio is controlled to be rich, the ignitability during normal compression self-ignition combustion without rich control is Equivalent Since the air-fuel ratio at which ignitability is obtained is selected, the exhaust air-fuel ratio enrichment control can be performed while continuing good self-ignition without causing premature ignition timing in self-ignition.
Claim 2 According to the invention of During compression self-ignition combustion When the exhaust air-fuel ratio is controlled to be rich, the engine torque during normal compression self-ignition combustion without rich control is Equivalent Since the intake air amount is temporarily reduced so that the engine torque can be obtained, the exhaust air-fuel ratio enrichment control can be performed without deteriorating the drivability.
[0013]
Claim 3 According to the invention, a direct injection type fuel injection valve is used, During compression self-ignition combustion When the exhaust air-fuel ratio is controlled to be rich, by controlling the fuel injection timing in the compression stroke, the ignitability and engine torque during normal compression self-ignition combustion without the rich control are Equivalent A rich mixture layer is formed in a part of the cylinder so that ignitability and engine torque can be obtained. Claim 2 The exhaust air-fuel ratio enrichment control can be performed without further deterioration of the drivability as compared with the present invention.
[0014]
Claim 4 According to the invention, by providing the means for controlling at least one of the in-cylinder temperature (intake air temperature) or the in-cylinder pressure to a predetermined value, it is possible to control the conditions so that self-ignition easily occurs, while the equivalent ignitability is obtained. When selecting the obtained air-fuel ratio, selection errors can be reduced by matching the conditions.
Claim 5 According to this invention, by using it for regeneration of the NOx trap catalyst, the NOx trap ability of the NOx trap catalyst can always be maintained, and emission can be improved by improving the NOx purification efficiency.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
First, a first embodiment of the present invention will be described.
FIG. 1 is a system diagram of an internal combustion engine (hereinafter referred to as an engine) showing a first embodiment of the present invention.
[0016]
The intake passage 2 of the engine 1 is provided with an electric throttle valve 3 that controls the amount of intake air, and an intake air temperature controller 4 that can adjust the temperature of intake air (intake air temperature). A fuel injection valve 5 for injecting and supplying fuel toward an intake port of each cylinder is provided in a manifold portion that distributes intake air to each cylinder on the downstream side. Furthermore, a spark plug 6 for spark ignition combustion is provided in the combustion chamber of each cylinder. These are driven by a control unit (hereinafter referred to as C / U) 7.
[0017]
The C / U 7 includes an accelerator opening signal (Aps) from the accelerator pedal sensor 8, a crank angle signal from the crank angle sensor 9 (from which the engine speed Ne can be calculated), and an air flow meter 10 provided in the intake passage 2. The intake air amount signal (Qa), the intake air temperature signal (Ta) from the intake air temperature sensor 11, the engine coolant temperature signal (Tw) from the water temperature sensor 12, and the like are input.
[0018]
In the C / U 7, based on these input signals, the opening degree of the electric throttle valve 3, the fuel injection amount and the injection timing of the fuel injection valve 5 are set so as to realize the target torque and the air-fuel ratio according to the operating conditions. Further, the ignition timing of the spark plug 6 is controlled at the time of spark ignition combustion. In particular, when the fuel injection valve 5 is controlled, the fuel injection amount is controlled so that the intake air amount Qa detected by the air flow meter 10 has a desired air-fuel ratio corresponding to the operating conditions.
[0019]
Further, the C / U 7 controls the intake air temperature controller 4 based on the signal from the intake air temperature sensor 11 so that the desired intake air temperature (and thus the desired in-cylinder temperature) is obtained.
Exhaust gas from the engine 1 is exhausted from an exhaust passage 13. The exhaust passage 13 is provided with a three-way catalyst 14 on the downstream side of a manifold portion that collects exhaust from each cylinder, and further on the downstream side. The NOx trap catalyst 15 is provided, and the exhaust gas is exhausted into the atmosphere after passing through these.
[0020]
The three-way catalyst 14 has a characteristic of efficiently purifying HC, CO, and NOx simultaneously when the exhaust air-fuel ratio is substantially stoichiometric.
The NOx trap catalyst 15 has a characteristic of trapping NOx when the exhaust air-fuel ratio is lean, desorbing NOx trapped when the exhaust air-fuel ratio is rich, and reducing and purifying NOx by catalytic action at this time. ing.
[0021]
In the above configuration, after warm-up, the engine 1 performs compression self-ignition combustion (hereinafter simply referred to as self-ignition combustion). In the self-ignition combustion, since the air-fuel ratio can be made lean, the NOx emission amount can be greatly reduced as compared with the spark ignition combustion. However, as described above, the three-way catalyst 14 and the NOx trap catalyst are used for further emission improvement. 15 is provided to purify harmful substances discharged from the engine 1.
[0022]
The NOx trap catalyst 15 can trap NOx in the exhaust gas when the exhaust air-fuel ratio is lean. However, if this NOx trap is continued, the NOx trapping capability is saturated, and eventually NOx cannot be trapped. In this case, the trapped NOx can be desorbed and purified by enriching the exhaust air-fuel ratio.
Therefore, in this embodiment, for example, as shown in FIG. 2, the NOx emission amount map in which the NOx emission amount per unit time is obtained and stored in advance from the engine speed and the torque is referred to, and the NOx emission amount is integrated. Thus, the NOx trap amount in the NOx trap catalyst 15 is estimated, and when the NOx trap amount approaches the saturation amount, it is determined that the NOx trap catalyst 15 is saturated (trap limit), and the exhaust air-fuel ratio is rich. Control.
[0023]
Next, the relationship among the intake air temperature, the air-fuel ratio, and the ignition timing (ignition delay period) in the self-ignition engine will be described with reference to FIG.
FIG. 3 shows ignition timings when the intake air temperature is 25 ° C., 100 ° C., and 200 ° C., for example, and the air-fuel ratio (A / F) of the air-fuel mixture is changed at each intake air temperature.
According to this, when the intake air temperature is 25 ° C., self-ignition is possible when the air-fuel ratio of the air-fuel mixture is close to the stoichiometric ratio, but it almost coincides with the stability limit line. Is possible. However, since the air-fuel ratio can be operated only at the stoichiometric ratio and lean combustion, which is a merit of self-ignition, cannot be performed, the actual operation at this intake air temperature is not performed because there is no fuel savings.
[0024]
When the intake air temperature is 100 ° C., the point indicated by (1) in the figure is the point where the air-fuel ratio of the air-fuel mixture is on the lean side and below the stability limit line, and this point is the point where the air-fuel ratio is lean and This is the air-fuel ratio set point during normal self-ignition combustion that falls within the stability limit.
On the other hand, if the air-fuel ratio of the air-fuel mixture is enriched, the ignition timing will gradually become early and knocking will occur, causing the possibility of engine damage and the combustion timing being too early. Therefore, it is not desirable to drive here because the gain of fuel consumption decreases. Usually, it is difficult to perform self-ignition combustion on the richer side than this region, and switching to spark ignition is common.
[0025]
However, when the air-fuel ratio of the air-fuel mixture is further enriched, the richness is caused by the balance between the tendency of the in-cylinder temperature to drop due to fuel vaporization and the ignition timing to be delayed, and the tendency to reduce the ignition delay due to the richness of the air-fuel ratio. The more it becomes, the more the ignition timing tends to be delayed.
In this rich region, since lean combustion is not performed in normal operation as described above, there is no gain in terms of fuel consumption, but when the exhaust air-fuel ratio is enriched based on self-ignition combustion, There is an advantage that the exhaust air-fuel ratio can be enriched while continuing the self-ignition combustion. In this embodiment, the point indicated by (2) in the figure is the air-fuel ratio set point when the exhaust air-fuel ratio is enriched. Thus, it is possible to obtain an ignitability that is substantially equivalent to the ignitability during normal self-ignition combustion when the enrichment control is not performed, and to enrich the exhaust air-fuel ratio while continuing the self-ignition combustion.
[0026]
When the air-fuel ratio is selected so that the ignitability is substantially equivalent, the difference in ignition timing is, for example, within about ± 5 ° CA on the low rotation side and within about ± 15 ° CA on the high rotation side. It is desirable to do.
Therefore, in the present embodiment, when the exhaust air-fuel ratio is controlled to be enriched for regeneration of the NOx trap catalyst 15, the intake air temperature is controlled to a predetermined temperature (for example, 100 ° C.) by the intake air temperature regulator 4 while the rich air / fuel ratio is controlled. The air-fuel ratio (the air-fuel ratio at the point (2) in FIG. 3) at which an ignitability substantially equivalent to the ignitability at the time of self-ignition combustion at the normal lean air-fuel ratio without performing the control is selected The air-fuel ratio is controlled to be rich while continuing the ignition combustion.
[0027]
According to this, since the combustion is not switched to spark ignition in order to enrich the exhaust air-fuel ratio, self-ignition combustion can be performed immediately after the enrichment control is finished, so that the self-ignition type with good fuel efficiency and cleanness The engine becomes feasible.
In the above description, it is difficult to follow the rapid change of the intake air temperature as in the rich spike, so the intake air temperature is controlled to be constant here, but the intake air temperature is also changed as necessary. It doesn't matter.
[0028]
FIG. 3 shows the relationship under a certain operating condition. Such a map is provided for each operating condition, and the rich air-fuel ratio is referred to from the map corresponding to the operating condition in the enrichment control. do it. In addition, instead of having a large number of maps for each operating condition as described above, one map showing the air-fuel ratio for each operating condition may be prepared. Is possible.
[0029]
Next, a second embodiment of the present invention will be described.
In the present embodiment, as in the first embodiment described above, when the exhaust air-fuel ratio is controlled to be enriched, an ignitability substantially equivalent to the ignitability at the time of self-ignition combustion without performing the enrichment control is obtained. In addition, by restricting the intake air amount by the electric throttle valve 3 or the like, an engine torque substantially equivalent to the engine torque at the time of self-ignition combustion without rich control is obtained.
[0030]
However, by selecting the air-fuel ratio that keeps the ignitability equivalent by limiting the amount of intake air so that the torque used for the driving force is kept equivalent, the selection is performed as follows.
Referring to FIG. 4, in the first embodiment, the air-fuel ratio at the point (1) in the figure is selected during normal self-ignition combustion, and the air-fuel ratio at the point (2) in the figure is selected during the enrichment control. In the present embodiment, even if the intake air temperature is constant (for example, 100 ° C.), the temperature rise due to adiabatic compression decreases with the intake air restriction by the intake air throttle, so the ignition timing shifts as shown by the upward arrow in the figure. This is almost the same phenomenon as when the intake air temperature shown in FIG. 3 is lowered. For this reason, in the present embodiment, the air-fuel ratio at the point indicated by (3) in the figure is selected during the enrichment control.
[0031]
Accordingly, for each operating condition, an intake air reduction amount that is commensurate with the torque generated during the enrichment control and an air-fuel ratio that does not reach the stability limit at that time are obtained in advance by experiment, and are stored in the C / U 7 as data. Store it in.
When it is determined that the enrichment control is necessary, the intake air amount is limited as described above, and the air-fuel ratio corresponding to the intake air reduction amount is obtained. By controlling to the rich air-fuel ratio at the point (3) that is substantially equivalent to 1), it becomes possible to perform enrichment control while maintaining the self-ignition combustion and maintaining the torque used for the driving force substantially constant. .
[0032]
The intake air amount may be limited by the electric throttle valve 3 or by changing the operation characteristics of the intake valve. It is also possible to reduce the amount of intake air by raising the intake air temperature. However, if the intake air temperature is changed stepwise, the intake pipe and intake port of the engine and the heat capacity inside the engine Since the temperature changes with a first order delay, it is not suitable for this embodiment.
[0033]
Next, a third embodiment of the present invention will be described.
The present embodiment is more specific based on the control of the second embodiment described above, and is shown as a flowchart of the air-fuel ratio control in FIGS.
In order to realize such control, in this embodiment, the intake air temperature controller 4 described above is used as the in-cylinder temperature control means. Further, as the in-cylinder pressure control means, a supercharger or a variable compression ratio mechanism not shown in FIG. 1 is used.
[0034]
FIG. 5 is a flowchart of the main routine of air-fuel ratio control, which will be described first.
In S1, signals from various sensors, specifically, accelerator opening Aps, engine speed Ne, intake air amount Qa, intake air temperature Ta, cooling water temperature Tw, and the like are read.
In S2, a target torque TTC which is a driver's request is calculated mainly based on the accelerator opening Aps.
[0035]
In S3, from a map having the engine speed Ne and the target torque TTC as parameters, based on the operation region, a low-medium rotation, a low-medium load auto-ignition combustion region, or a high-rotation or high-load spark ignition combustion (homogeneous combustion). ) In the case of the self-ignition combustion region, the combustion flag FCmb = 0 is set, and in the case of the spark ignition combustion region, the combustion flag FCmb = 1 is set.
[0036]
In S4, a target fuel-air ratio TFBYA necessary for fuel injection amount control is set based on the operating region from a map using the engine speed Ne and the target torque TTC as parameters.
The fuel-air ratio here is the reciprocal of the excess air ratio λ, and the fuel-air ratio = 14.6 / air-fuel ratio when the stoichiometric air-fuel ratio is 14.6. Therefore, TFBYA = 1 when the target air-fuel ratio is stoichiometric, smaller than 1 when lean, and larger than 1 when rich. Then, the fuel injection amount for obtaining the target air-fuel ratio can be calculated by multiplying the fuel injection amount equivalent to the stoichiometric amount with respect to the intake air amount Qa by TFBYA.
[0037]
In S5, the current coolant temperature Tw is compared with the warm-up determination threshold value TwL, and when Tw ≧ TwL (after warm-up), the current combustion flag FCmb and the target fuel-air ratio TFBYA are maintained. However, when Tw <TwL (before warm-up), the routine proceeds to S6, where the combustion flag FCmb = 1 is set, and the target fuel-air ratio TFBYA = 1 (stoichiometric) is set.
[0038]
That is, in S6, when Tw <TwL and it is determined that the engine is not warmed up, it is difficult to stably perform self-ignition combustion. In this case, it is provided for performing spark ignition combustion (FCmb = 1).
In S7, it is determined whether or not the combustion flag FCmb = 0 (self-ignition combustion). If FCmb = 0, the process proceeds to S8 to enter the control for self-ignition combustion.
[0039]
In S8, processing is performed according to the self-ignition determination control subroutine of FIG.
A description will be given along the self-ignition determination control subroutine of FIG. Here, first, it is determined whether or not self-ignition combustion can be started immediately (self-ignition is possible) when entering the self-ignition combustion region.
In S101, the cylinder temperature is estimated every moment by the cylinder temperature estimating means. Specifically, the in-cylinder temperature is estimated based on engine operating conditions (engine speed Ne, target torque TTC, target fuel-air ratio TFBYA, etc.), intake air temperature Ta, and the like.
[0040]
In S102, the cylinder pressure is estimated every moment by the cylinder pressure estimating means. Specifically, the in-cylinder pressure is estimated based on engine operating conditions (engine speed Ne, target torque TTC, target fuel-air ratio TFBYA, etc.), intake air temperature Ta, crank angle, and the like. Note that the in-cylinder pressure at a predetermined crank angle may be estimated instead of the in-cylinder pressure every moment.
[0041]
In S103, the target fuel-air ratio TFBYA is read from the engine speed Ne and the target torque TTC with reference to the map used in S4.
In S104, for each target fuel-air ratio TFBYA, a map in which 1 / τ (the reciprocal of the ignition delay period τ) is stored in advance with the in-cylinder temperature and the in-cylinder pressure as parameters is referred to, and the target in the current operating state is determined. Find 1 / τ at the current in-cylinder temperature and in-cylinder pressure at the fuel-air ratio TFBYA. Several maps used here are prepared according to TFBYA, and 1 / τ is obtained by interpolating the value of TFBYA. In addition, the point “◯” on the map shown in S104 of FIG. 6 indicates the target point of the in-cylinder temperature and the in-cylinder pressure.
[0042]
In S105, the values of 1 / τ obtained in S104 are integrated (∫1 / τ = ∫1 / τ + 1 / τ).
In S106, it is determined whether or not the integrated value of 1 / τ (∫1 / τ) exceeds a predetermined value (1 / τth). Here, when 1 / τ exceeds a predetermined value, self-ignition combustion is performed, and when 1 / τ does not exceed the predetermined value, self-ignition combustion does not occur. Therefore, the determination is made with the integrated value.
[0043]
As a result of this determination, if ∫1 / τ <1 / τth (self-ignition is not possible), the process proceeds to S107 to S109, and the following processing is performed in order to enable self-ignition.
That is, in S107, the in-cylinder temperature control means (intake air temperature controller 4) increases the in-cylinder temperature by a predetermined value, and in S111, the in-cylinder pressure control means (supercharger or variable compression ratio mechanism) controls the cylinder. The internal pressure is increased by a predetermined value. This is because the in-cylinder temperature and the in-cylinder pressure are considered not to rise to the levels necessary for self-ignition combustion, so that the in-cylinder temperature and the in-cylinder pressure are increased so that self-ignition easily occurs.
[0044]
Further, in S109, the combustion flag FCmb = 1 is set, and the target fuel-air ratio TFBYA = 1 (stoichiometric) is set. This is because the spark ignition combustion is performed without starting the self-ignition combustion until the self-ignition condition is reached by the increase in the in-cylinder temperature and the in-cylinder pressure.
If it is determined in S106 that ∫1 / τ ≧ 1 / τth (self-ignition can occur), the process proceeds to S110 to S112, and the following processing is performed to maintain a state in which self-ignition can be generated.
[0045]
That is, in S110, the in-cylinder temperature is controlled to a predetermined value T1 by the in-cylinder temperature control means (intake air temperature controller 4), and in S111, the in-cylinder pressure control means (supercharger or variable compression ratio mechanism) controls the cylinder. The internal pressure is controlled to a predetermined value P1. The predetermined values T1 and P1 here are respective target values, and the in-cylinder temperature and the in-cylinder pressure are controlled so as to fall within a range of a predetermined width including the target values.
[0046]
In S112, an instruction is given to perform the operation by self-ignition combustion. At this time, the in-cylinder temperature and the in-cylinder pressure are controlled at the target point (point) on the map shown in S104 of FIG. 6, and the ignition delay period is controlled to the optimum state. It does not occur.
This is the end of the description of the self-ignition determination control subroutine of FIG. 6, and the description returns to the flowchart of the main routine of FIG.
[0047]
Although omitted in the flow, the operation by the spark ignition combustion is instructed except when the operation by the self-ignition combustion is instructed in S112 described above.
In S9, it is determined whether or not it is the regeneration timing of the NOx trap catalyst 15, that is, whether or not the NOx trap amount of the NOx trap catalyst 15 has reached a predetermined value in a state where self-ignition combustion or spark ignition combustion is being performed. Do.
[0048]
That is, as already described, the NOx emission map (FIG. 2) in which the NOx emission amount per unit time is obtained in advance from the engine speed (Ne) and torque (TTC) and stored is stored (see FIG. 2). By accumulating the amount, the NOx trap amount in the NOx trap catalyst 15 is estimated. Further, the NOx emission amount obtained from the map for each operating condition may be multiplied by a ratio (trap rate) at which the NOx trap catalyst 15 can trap NOx, and this may be integrated to obtain the NOx trap amount. . Of course, it may be estimated or measured by other known methods.
[0049]
Then, the amount of NOx trap is compared with a threshold value for determining the regeneration time, and when it becomes equal to or greater than the threshold value, the regeneration time is determined. The threshold value of the NOx trap amount here is set to a value of, for example, about 80% of the trappable amount so that NOx discharged during the regeneration process can also be trapped.
If it is determined in this determination that it is not the regeneration timing of the NOx trap catalyst 15, this routine is terminated without performing regeneration control (exhaust air-fuel ratio enrichment control). If it is determined, the process proceeds to S10 for regeneration control (exhaust air-fuel ratio enrichment control).
[0050]
In S10, in order to select the regeneration method according to the combustion method, it is determined whether the combustion method is self-ignition combustion (FCmb = 0) or spark ignition combustion (FCmb = 1).
As a result, in the case of self-ignition combustion (FCmb = 0), the process proceeds to S11, and in the case of spark ignition combustion, the process proceeds to S12.
[0051]
In S11, enrichment control by self-ignition combustion is performed for a predetermined period according to the self-ignition enrichment control subroutine of FIG. This will be described later.
In S12, enrichment control by spark ignition combustion is performed for a predetermined period. In this case, normal rich control may be performed by setting the target fuel-air ratio TFBYA to a predetermined rich equivalent TFBYArich.
[0052]
The self-ignition enrichment control subroutine of FIG. 7 will be described.
In S201, for each operating condition, a table showing the relationship between the air-fuel ratio (target air-fuel ratio TFBYA) and the ignition delay (ignition timing θ10) is referred to, and the lean-side TFBYA during normal self-ignition combustion (● points) Is obtained, and the target fuel-air ratio TFBYA is set to this rich TFBYA (◯ point). Specifically, it is set at the point (2) in FIG. 3 shown as the first embodiment or the point (3) in FIG. 4 shown as the second embodiment. This portion corresponds to air-fuel ratio selection means at the time of enrichment control.
[0053]
In S202, an amount of reduction of the intake air amount corresponding to the difference between the engine generated torque in the rich TTFYA determined in S201 and the engine generated torque during normal self-ignition combustion is obtained in advance through experiments or the like. The correction target intake air amount Qa ′ for equalizing the engine torque is obtained by referring to a map storing the corrected target intake air amount Qa ′ using the engine speed Ne and the target torque TTC as parameters. Control to get. This portion corresponds to intake air amount limiting means.
[0054]
In S203, the in-cylinder temperature is controlled to a predetermined value T2 (where T2> T1) by the in-cylinder temperature control means (intake air temperature controller 4).
In S204, the in-cylinder pressure is controlled to a predetermined value P2 (where P2> P1) by the in-cylinder pressure control means (supercharger or variable compression ratio mechanism).
The operations of S203 and S204 increase the in-cylinder temperature and the in-cylinder pressure as compared with normal self-ignition combustion because the amount of compressed working gas decreases as the intake air amount into the cylinder decreases. Because it is necessary to let go. Accordingly, T2> T1 and P2> P1 are set, but these values are set according to the engine used.
[0055]
By performing the above-described operation, it is possible to perform enrichment control while continuing self-ignition combustion, so that the fuel efficiency gain increases and the torque is controlled to be kept substantially constant. Can realize rich control of self-igniting engine.
Next, a fourth embodiment of the present invention will be described.
[0056]
The configuration is different from the first embodiment in that a fuel injection valve 5 ′ (see FIG. 1) capable of directly injecting fuel into the cylinder is provided.
When self-ignition combustion is performed, fuel injection timing control means is provided for controlling the fuel injection timing by performing fuel injection from the direct injection fuel injection valve 5 'in the compression stroke.
[0057]
Here, by advancing the fuel injection timing in the compression stroke, the range in which the air-fuel mixture exists (air-fuel mixture layer) can be made relatively wide as shown in FIG. By retarding, the range in which the air-fuel mixture exists (air-fuel mixture layer) can be made relatively narrow as shown in FIG. 8B, and the air-fuel mixture range can be made variable by controlling the fuel injection timing. The structure to be taken is taken.
[0058]
Next, the operation of this embodiment will be described.
The process up to the determination of the exhaust air-fuel ratio enrichment control is the same as in the first embodiment. In this embodiment, when it is determined that the enrichment control is necessary, the air-fuel ratio is enriched as in the first embodiment. However, the air-fuel ratio in the range where the air-fuel mixture exists is enriched at this time, and is not the average air-fuel ratio in the cylinder.
[0059]
That is, when the enrichment control is performed, based on the fuel injection timing in the case where normal self-ignition combustion is performed, the fuel injection timing is relatively retarded, so that in FIG. As described above, if the range in which the air-fuel mixture exists is narrowed, and thus the fuel injection amount is the same, the air-fuel ratio in the range in which the air-fuel mixture exists can be enriched.
[0060]
In the present embodiment, when the exhaust air-fuel ratio is controlled to be enriched, the fuel injection amount is increased. This increase is caused by retarding the fuel injection timing so that the air-fuel ratio within the range where the air-fuel mixture exists is increased. The desired air-fuel ratio is set, and the generated torque is set to be equivalent to that during normal self-ignition combustion. The fuel injection timing and the fuel injection amount may be stored in the C / U 7 as a map obtained in advance by experiments.
[0061]
Here, since the air-fuel ratio in the range where the air-fuel mixture exists is much richer than stoichiometric, it cannot be fully combusted in the cylinder, so the generated torque does not change significantly from the case of lean combustion, and Since unburned fuel is discharged up to the exhaust, it is suitable for NOx reduction.
According to the present embodiment, the exhaust air-fuel ratio can be enriched and controlled while the self-ignition combustion is continued while maintaining the ignitability of the rich air-fuel mixture equivalent to that during normal self-ignition combustion. A clean self-ignition engine can be realized.
[Brief description of the drawings]
FIG. 1 is a system diagram of an engine showing a first embodiment.
FIG. 2 is a graph showing the characteristics of NOx emissions from the engine
FIG. 3 is a diagram showing the relationship between intake air temperature, air-fuel ratio, and ignition timing in self-ignition combustion as the first embodiment.
FIG. 4 is a diagram showing a change in characteristics of self-ignition combustion when intake air is limited as a second embodiment.
FIG. 5 is a flowchart of a main routine of air-fuel ratio control according to the third embodiment.
FIG. 6 is a flowchart of a self-ignition determination control subroutine.
FIG. 7 is a flowchart of a self-ignition enrichment control subroutine.
FIG. 8 is a diagram showing an air-fuel mixture formation region in the fourth embodiment.
[Explanation of symbols]
1 engine
2 Intake passage
3 Electric throttle valve
4 Intake air temperature controller
5 Fuel injection valve
5 'direct fuel injection valve
6 Spark plug
7 C / U
8 Accelerator position sensor
9 Crank angle sensor
10 Air flow meter
11 Intake air temperature sensor
12 Cooling water temperature sensor
13 Exhaust passage
14 Three-way catalyst
15 NOx trap catalyst

Claims (5)

In an internal combustion engine that switches between spark ignition combustion and compression self-ignition combustion according to operating conditions ,
When there is a request to enrich the exhaust air-fuel ratio during the compression auto-ignition combustion, the air-fuel ratio is enriched and controlled while continuing the compression auto-ignition combustion ,
An internal combustion engine characterized by comprising an air-fuel ratio selection means for selecting an air-fuel ratio that provides an ignitability equivalent to that in normal compression self-ignition combustion without performing enrichment control as the enriched air-fuel ratio in this case Engine control device. When the exhaust air-fuel ratio is controlled to be enriched during compressed self-ignition combustion, the intake air amount is reduced so that the engine torque equivalent to the engine torque during normal compression self-ignition combustion without enrichment control is obtained. 2. The control apparatus for an internal combustion engine according to claim 1, further comprising air amount limiting means. A fuel injection valve capable of directly injecting fuel into the cylinder is provided, and when the exhaust air-fuel ratio is enriched during compression self-ignition combustion , the enrichment control is performed by controlling the fuel injection timing in the compression stroke It has fuel injection timing control means for forming a rich air-fuel mixture layer in a part of the cylinder so as to obtain ignitability during normal compression self-ignition combustion and engine torque equivalent to engine torque. 2. The control apparatus for an internal combustion engine according to claim 1 , wherein the control apparatus is an internal combustion engine. The control device for an internal combustion engine according to any one of claims 1 to 3 , further comprising means for controlling at least one of the in-cylinder temperature and the in-cylinder pressure to a predetermined value during the compression self-ignition combustion. . The exhaust system includes a NOx trap catalyst that traps NOx when the exhaust air-fuel ratio is lean, and desorbs and purifies NOx trapped when the exhaust air-fuel ratio is rich, and exhausts the NOx trap catalyst for regeneration. The control apparatus for an internal combustion engine according to any one of claims 1 to 4 , wherein the air-fuel ratio is controlled to be enriched.

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