JPH062639A - Engine controller - Google Patents

Abstract

PURPOSE:To keep off a torque shock with the transfer of an air-fuel ratio as preventing any fear of a misfire attending on this air-fuel ratio transfer from the rich side to the lean side by selecting the air-fuel ratio to the lean side and the rich side according to a driving state in a reciprocal manner. CONSTITUTION:An air-fuel ratio is constituted so as to transfer it to the lean side and the rich side from the theoretical air-fuel ratio reciprocally according to the driving state. In this connection, this is one that increasedly controls an EGR rate of reflux gas by an exhaust gas recirculation(EGR) means 19, and it is provided with an EGR rate increment control means 36 being operated at an area adjacent to at least a lean area of a rich area. In addition, at the time of transference from the rich area to the lean area in an air-fuel ratio control means 33, it is provided with an ignition energy increasing control means 35 controlling the ignition energy of an ignition means 26 for increment temporarily. With this constitution, torque-down and torque-up attending on the air-fuel ratio transference to the rich side are offset, thus a torque shock is relievable in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an engine configured to switch the air-fuel ratio between the lean side and the rich side relative to the stoichiometric air-fuel ratio in accordance with the operating condition.

[0002]

2. Description of the Related Art Conventionally, as an engine control device of this type, the air-fuel ratio is switched between lean side and rich side depending on the operating condition, thereby improving fuel efficiency by lean burn and high output by rich side air-fuel ratio. It is known that the increase of nitrogen oxides (NOx) is suppressed while securing the
Above all, the torque shock on the up side when switching the air-fuel ratio from the lean side to the rich side and the torque shock on the down side when switching the air-fuel ratio from the rich side to the lean side are alleviated by retarding the ignition timing. There are known ones (see JP-A-60-13953).
This is because the ignition timing is retarded in the air-fuel ratio switching from the lean side to the rich side to cause torque down,
This torque reduction is offset by the torque increase due to the air-fuel ratio switching from the lean side to the rich side, and the ignition timing is gradually retarded in advance before the switching in the air-fuel ratio switching from the rich side to the lean side. ,afterwards,
By performing the air-fuel ratio switching and the ignition timing advance at once, the torque reduction due to the air-fuel ratio switching and the torque increase due to the ignition timing advance are offset.

[0003]

However, since the retard control of the ignition timing retards the ignition timing, the torque that should be originally obtained is suppressed and the output is lowered and the fuel consumption is deteriorated. There is an inconvenience.

In order to eliminate the inconvenience of deteriorating fuel efficiency, exhaust gas recirculation (Exhaust Gas Recirculat)
ion; hereinafter referred to as EGR), and by increasing the EGR rate when changing the air-fuel ratio from the lean side to the rich side, the torque when changing the air-fuel ratio from the lean side to the rich side. It is possible to reduce the shock. That is, it is conceivable that the torque shock on the up side due to the air-fuel ratio switching is offset by slowing the combustion by increasing the circulating gas that is an inert gas at the same time as the air-fuel ratio switching.

However, in this case, conversely to the above, even if the control for reducing the increased EGR rate at once is performed in synchronization with the air-fuel ratio switching from the rich side to the lean side, it remains in the piping system of the EGR means. Recirculated gas, that is, E
The recirculation gas that remains in the piping system downstream of the GR valve during the above-described increase control may be introduced into the combustion chamber, and the introduced recirculation gas may temporarily cause over EGR. When this over EGR occurs, the EGR flow rate increases by the amount of the residual recirculation gas, even though the air-fuel ratio is switched from the rich side to the lean side at once and the ratio of the fuel amount to the intake air amount is reduced at once. For,
There is a risk of misfire. When a misfire occurs, a large torque shock is generated accordingly.

The present invention has been made in view of such circumstances, and an object of the present invention is to switch the air-fuel ratio between the lean side and the rich side depending on the operating condition. While preventing the risk of misfire due to the air-fuel ratio switching from the air-fuel ratio to the lean side, the torque shock due to the air-fuel ratio switching is prevented.

[0007]

In order to achieve the above object, the invention according to claim 1 is a lean region in which an air-fuel ratio on the lean side of the stoichiometric air-fuel ratio is set, and a region adjacent to the lean region. An air-fuel ratio control unit that switches between each other in accordance with an operating state in a rich region where an air-fuel ratio that is richer than a stoichiometric air-fuel ratio including the stoichiometric air-fuel ratio is set, and an EGR unit that recirculates exhaust gas, It is premised that an ignition means for igniting a spark plug is provided. In this configuration, an EGR rate increase control means for increasing the EGR rate of the circulating gas by the EGR means is provided, which is operated in at least an area adjacent to the lean area of the rich area. And, when the air-fuel ratio control means is switched from the rich region to the lean region, the ignition energy increase control means for temporarily increasing the ignition energy of the ignition means is provided.

Further, in the invention described in claim 2, in the invention described in claim 1, the air-fuel ratio in the lean range in the air-fuel ratio control means is set to a value excluding the air-fuel ratio value 16 and larger than the air-fuel ratio value 16. . Then, the EGR ratio in the lean region in the EGR means is set to be smaller than the EGR ratio in the rich region.

Further, in the invention described in claim 3, in the invention described in claim 1, the rich region in the air-fuel ratio control means is set adjacent to the lean region so that the air-fuel ratio is substantially equal to the theoretical air-fuel ratio. A set λ = 1 region and an enriched region that is set adjacent to the λ = 1 region and does not include the set air-fuel ratio of the λ = 1 region and that an air-fuel ratio richer than the stoichiometric air-fuel ratio is set. It consists of and. The EGR rate increase control means is operated in the λ = 1 region to maximize the EGR rate.

[0010]

With the above construction, in the invention according to claim 1,
When the air-fuel ratio control means switches the air-fuel ratio from the lean region to the rich region in accordance with the operating state, the EGR rate increase control means is operated in accordance with this air-fuel ratio switching to increase the EGR rate. The increase in the EGR rate increases the amount of the circulating gas, which is the inert gas introduced into the combustion chamber, so that the combustion becomes slower, and the resulting torque reduction and the torque increase due to the air-fuel ratio switching to the rich side are offset. Torque shock is prevented. Moreover, since the EGR rate is increased and the amount of recirculated gas introduced into the combustion chamber is increased, the increase in combustion temperature is suppressed, the increase in NOx is suppressed, and the fuel economy is improved.

On the other hand, when the air-fuel ratio is switched from the rich region to the lean region by the air-fuel ratio control means, the operation of the EGR rate increase control means is stopped along with the change of the air-fuel ratio and the state before the increase is returned. The ignition energy increase control means temporarily increases the ignition energy of the ignition means. Therefore, the increase of the EGR rate is stopped, combustion is activated, and the torque is increased accordingly.
This torque increase and the torque decrease due to the air-fuel ratio switching to the lean region are canceled out to prevent torque shock. In this case, even if the residual reflux gas in the state where the EGR rate is increased is introduced into the combustion chamber after the EGR rate is reduced and temporarily becomes the over EGR state, the ignition energy is temporarily increased and the ignitability is increased. As a result, misfire is prevented.

According to the second aspect of the present invention, in addition to the operation of the first aspect of the present invention, the air-fuel ratio in which the NOx generation is maximized when the lean region and the rich region are switched by the air-fuel ratio control means. Since the value 16 is skipped and the process is performed at once, the increase in NOx is effectively suppressed. Moreover, since the EGR rate in the lean region is set to be smaller than that in the rich region, it is possible to prevent instability of combustion while improving fuel efficiency.

Further, according to the third aspect of the invention, in addition to the operation according to the first aspect of the invention, the air-fuel ratio control means controls the lean region, the λ = 1 region and the enriched region according to the operating condition. The fuel economy can be further improved by switching to. Moreover, in the above λ = 1 region, EGR
Since the rate becomes maximum, the increase of the combustion temperature in the vicinity of the air-fuel ratio region where the generation of NOx becomes maximum is suppressed, and the increase in NOx can be suppressed more effectively.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an engine to which an engine control device according to an embodiment of the present invention is applied. In the figure, 1
Is an engine, the engine 1 includes a cylinder block 3 forming a cylinder 2, a cylinder head 4 joined to an upper surface of the cylinder block 3, and the cylinder 2
And a piston 5 that reciprocates inside. In the cylinder 2, the combustion chamber 6 is defined by the lower surface of the cylinder head 4 and the top surface of the piston 5.
Is formed, and an ignition plug 7 whose ignition is controlled with a predetermined ignition timing and a predetermined ignition energy is attached to the top surface of the combustion chamber 6.

An intake port 9 forming the downstream end of the intake passage 8 and an exhaust port 11 forming the upstream end of the exhaust passage 10 are opened in the combustion chamber 6. An intake valve 12 is provided at the opening of the combustion chamber 6 of the intake port 9, and an exhaust valve 13 is provided at the opening of the combustion chamber 6 of the exhaust port 11.
Are provided respectively. These intake and exhaust valves 12, 13
Is opened and closed at a predetermined timing by a valve mechanism (not shown) to introduce intake air into the combustion chamber 6 and exhaust exhaust gas.

The upstream end of the intake passage 8 is the air cleaner 1.
An air flow meter 15 that is opened to the atmosphere via the air cleaner 14 and detects the intake air amount (load) downstream of the air cleaner 14, and a throttle valve 16 that adjusts the intake air amount.
And a fuel injection valve 17 for injecting fuel toward the opening of the combustion chamber 6 of the intake port 9 based on a predetermined set air-fuel ratio are arranged in this order. In addition, the exhaust passage 10
Has a downstream end opened to the atmosphere via the catalyst 18.

Numeral 19 is an EGR means for recirculating the exhaust gas in the exhaust passage 10 to the intake passage 8. This E
The GR means 19 has an EGR passage 20 having an upstream end opened to the exhaust passage 10 on the upstream side of the catalyst 18 and a downstream end opened to the intake passage 8 at the downstream position of the throttle valve 16, and the EGR passage 20. Of the amount of exhaust gas recirculation (EG
EGR valve 21 for adjusting the R amount) and this EGR valve 21.
First and second solenoid valves 22 and 23 for supplying a negative pressure as an operation source for operating the valve 21 to a predetermined opening degree
It consists of and.

The first solenoid valve 22 introduces negative pressure from the intake passage 8 located downstream of the throttle valve 16, and the second solenoid valve 23 introduces negative air from the intake passage 8 located upstream of the throttle valve 16. The solenoid valve 22, 23 is controlled in its opening degree by a signal output from a control unit (hereinafter referred to as an ECU) 24, so that the EGR valve 21 has a predetermined negative pressure. Pressure is supplied to open and close the EGR valve 21 at an opening degree based on a predetermined set EGR rate (ratio of EGR flow rate to intake air flow rate). An EGR valve opening sensor 25 that detects the opening of the EGR valve 21 is connected to the ECU 24. Based on the output from the EGR valve opening sensor 25, the EGR valve 21 has a predetermined value based on the set EGR rate. Both solenoid valves 2 so that the opening is
Opening / closing control of 2 and 23 is performed.

Further, reference numeral 26 is an ignition means for igniting the ignition plug 7 in a normal ignition state and an up ignition state in which ignition energy is increased from the normal ignition state. As shown in detail in FIG. 2, the ignition means 26 includes an igniter 27, a DC-DC converter 28, a coil 29, and a distributor 30 (FIG. 1) for distributing the secondary current from the coil 29 to each ignition plug. See) and.

The igniter 27 receives the output of the normal ignition signal IGT from the ECU 24 and receives the coil 2 from the normal ignition signal IGT.
An ON signal for energizing 9 is given. Further, the DC-DC converter 28 receives the output of the up ignition signal IGE from the ECU 24, and in addition to the normal ignition signal IGT, energization of the coil 29 is turned ON.
The signal is forcibly given a predetermined number of times. That is, the time for energizing the coil 29 is lengthened. As a result, as shown in FIG. 3, in the up-ignition state based on the up-ignition signal IGE (indicated by the dashed line in the figure), the discharge time for the secondary current from the coil 29 is the normal ignition signal. It is longer than the normal ignition state based on the IGT (the case indicated by the solid line in the figure) by a predetermined time, and as a result, the ignition energy in the spark plug 7 is increased.

The ECU 24 is connected to an operating state detecting means 32 composed of the air flow meter 15 and an engine speed sensor 31 for detecting the engine speed. Then, the ECU 24, as shown in FIG. 4, the air-fuel ratio control means 33 for setting the air-fuel ratio region in accordance with the operating state specified by the load from the operating state detecting means 32 and the engine speed, and the above-mentioned. An EGR control means 34 for controlling the opening degree of the EGR valve 21 of the EGR means 19 to an opening degree based on a predetermined set EGR rate according to an operating state, and the ignition means 26 according to the air-fuel ratio range.
And an ignition energy increase control means 35 for bringing the above into an up ignition state.

The air-fuel ratio control means 33 is leaner than the stoichiometric air-fuel ratio, that is, the lean side air-fuel ratio is set such that the λ value, which is the ratio of the set air-fuel ratio to the theoretical air-fuel ratio, is greater than 1. A region, a λ = 1 region where an air-fuel ratio substantially equal to the theoretical air-fuel ratio is set, and a rich side of the theoretical air-fuel ratio, that is, a predetermined rich-side air-fuel ratio where the λ value is smaller than 1 is set. The air-fuel ratio region with the enriched region is set according to the operating state, and the air-fuel ratio is switched according to this air-fuel ratio region. The setting of the air-fuel ratio region is performed based on a map stored in advance. In this map, as shown in FIG. 5, the low rotation / low load region in which the engine speed is lower than a predetermined rotation speed and the load is lower than a predetermined load is a lean region A, and the high rotation speed of the lean region A is high. The medium rotation / medium load region adjacent to the high side or the high load side is defined as λ = 1 region B, and this λ
The high rotation / high load region adjacent to the high rotation side or the high load side of the = 1 region B is defined as the enrichment region C. Then, the fuel is supplied to the fuel injection valve 17 based on the set air-fuel ratio in each of these regions A, B, and C.

The lean side air-fuel ratio is 16 except for the air-fuel ratio value of around 16 at which NOx generation becomes maximum.
A larger value, for example, a value of 23 to 25 is set, and the rich side air-fuel ratio is set to, for example, a value of 14 or less when the stoichiometric air-fuel ratio is set to a value of 15, and the lean side air-fuel ratio is set according to the operating state. By switching the stoichiometric air-fuel ratio and the rich side air-fuel ratio at once, the air-fuel ratio range in which the amount of NOx generated is maximized is skipped to suppress the generation of NOx.

The EGR control means 34 sets a relatively small predetermined EGR rate a in the lean region A to the λ
The maximum EGR rate b obtained by adding a predetermined increase to the EGR rate a in the = 1 region B and the predetermined EGR rate c smaller than the EGR rate b in the enriched region C are set. That is, the EGR rate is switched in synchronization with the switching of the air-fuel ratio region by the air-fuel ratio control means 33.

The ignition energy increase control means 35 is
When the air-fuel ratio control means 33 switches from the λ = 1 region B to the lean region A, the DC-DC converter 28 for a predetermined short time immediately after the switching.
The up ignition signal IGE is output to.
As shown in FIG. 6, the time for outputting the up ignition signal IGE is switched from the EGR rate b to the EGR rate a by the EGR control means 34 in accordance with the switching from the λ = 1 region B to the lean region A. From the time point t ₁ before switching E remaining in the EGR passage 20 on the downstream side of the EGR valve 21.
The recirculated gas at the GR rate b (the portion in the shaded area indicated by G in the figure) is discharged into the combustion chamber 6 through the intake passage 8 and the above E
The time is set to be almost equal to the short time until the time point t ₂ at which the EGR amount becomes the GR rate a. Then, after the elapse of this time, the up ignition signal IGE is turned off, and normal ignition is performed by the normal ignition signal IGT. That is, the ignition energy is increased during a time (between time points t _{1 and} t ₂ ) at which misfire may occur due to the over EGR resulting from the residual circulating gas.

Next, the control by the air-fuel ratio control means 33, the EGR control means 34 and the ignition energy increase control means 35 will be concretely described with reference to FIG. First, in step S1, the intake air amount from the air flow meter 15 and the engine speed from the engine speed sensor 31 are read, and the air-fuel ratio is set according to the current operating state based on these detected values in step S2. To do. This air-fuel ratio is set based on the above-described map shown in FIG. 5 which is stored in advance, and the current operating state is in the lean region A, λ =
The air-fuel ratio determined according to each region is set depending on whether it is in the 1st region B or the enriched region C. This step S2 constitutes the air-fuel ratio control means 33.

Next, in step S3, the EGR rate for the current operating state is set according to the air-fuel ratio range set in step S2. This EGR rate is set based on the map previously set as the EGR rate corresponding to the air-fuel ratio range. If the current operating state is the lean range A, the EGR rate a is set to λ = 1 range B. If it exists, the EGR rate b is set, and if it is the enriched region C, the EGR rate c is set.

Then, in steps S4 to S6, it is determined whether or not the current operating state is the switching time point from the λ = 1 area B to the lean area A. If it is the switching time point, the ignition energy increase control means 35 is activated. Let That is, the set air-fuel ratio in the previous operating state is read in step S4, and it is determined in step S5 whether or not the previous set air-fuel ratio is in the λ = 1 region. If the previous set air-fuel ratio is λ = 1, the process proceeds to step S6, and it is determined in step S6 whether the current set air-fuel ratio is in the lean range. If it is the lean side air-fuel ratio, it is determined that the operating state has just been switched from the λ = 1 region B to the lean region A, and the routine proceeds to step S7. In step S7, the EGR means 19 is controlled based on the EGR rate a set in step S3. This control is performed by outputting a control signal to the first and second solenoid valves 22 and 23 of the EGR means 19 so that the EGR flow rate is based on the EGR rate a. Then, in step S8, the up ignition signal IGE is output to the DC-DC converter 29, and the up ignition signal IGE is output.
Is continued for a predetermined integration time of the timer set in step S9. When this accumulated time has elapsed, step S10
Then, the output of the up ignition signal IGE is stopped and the process returns.

On the other hand, if the previously set air-fuel ratio is not in the λ = 1 region B in step S5, step S11
It is determined whether or not the current set air-fuel ratio is the lean side air-fuel ratio. If the current set air-fuel ratio is the lean side air-fuel ratio, in step S12 the EGR rate a set in step S3 is set.
If it is not the lean side air-fuel ratio, the EGR means 19 is determined based on the EGR rate b or c in step S13.
And then return. In addition, when the current set air-fuel ratio is not the lean side air-fuel ratio in step S6, that is, when the operating state is continuously in the λ = 1 region or when the λ = 1 region is changed to the enriched region, In step S14, the E set in step S3 is set.
The EGR means 19 is operated based on the GR rate b or c and the process returns.

That is, when the current operating state is the switching time point from the λ = 1 region B to the lean region A, the EGR rate is switched from b to a, and the ignition means 26 is set to the up ignition state to step the ignition energy. It is designed to be increased for a predetermined time in S9, and in other cases, EG is performed at each EGR rate a, b, c set according to the air-fuel ratio region.
The R means 19 is controlled. Of the above controls, the steps S3, S7, S12, S13 and S14 make the EGR control means 34 the step S3.
8, S9 and S10 are ignition energy increase control means 3
5, respectively. Further, of the EGR control means 34, steps S3, S13 and 14 constitute EGR rate increase control means 36 for increasing the EGR rate in the λ = 1 region.

Reference numeral 37 in FIG. 1 indicates a battery.

In the engine control device having the above structure,
When the operating state is in the low rotation / low load region, the air-fuel ratio control unit 33 sets the lean region A to set the lean side air-fuel ratio, and the EGR control unit 34 sets E.
The GR rate a is set, and EGR is performed based on this EGR rate a. Therefore, in addition to the fuel consumption improvement by lean burn, as shown in FIG. 8, the fuel consumption improvement by EGR can be achieved. Moreover, the EGR rate a is set to the other region B.
Since it is set to a smaller value than
It is possible to prevent the instability of combustion due to the EGR in the above and to prevent deterioration of drivability.

Then, when the operating state shifts to the high rotation side or the high load side and the lean region A is switched to the λ = 1 region B by the air-fuel ratio control means 33, the above-mentioned switching is performed in synchronization with this switching. The EGR control means 34 via the EGR rate increase control means 36 increases the EGR rate from a to b. Due to this increase in the EGR rate, the EGR amount of the exhaust gas, which is an inert gas, increases and combustion becomes slow. While this combustion is suddenly slowed down at the time of the above switching, torque down occurs, while torque up occurs as the air-fuel ratio is switched to the rich side. And as a result of both being offset,
It is possible to reduce or prevent the torque shock caused by switching from the lean region A to the λ = 1 region B.

In the λ = 1 region B, the air-fuel ratio is set to a value close to the air-fuel ratio that maximizes NOx generation. The EGR rate set by the EGR control means 34 is the maximum EGR rate b. Therefore, the increase in combustion temperature can be effectively suppressed, and the increase in NOx can be effectively suppressed. In addition, the maximum EGR rate b in the λ = 1 region B
By doing so, it is possible to improve fuel efficiency not only in the lean region A but also in the λ = 1 region B.

On the contrary, when the operating state shifts from the λ = 1 region B to the low rotation side or the low load side and is switched to the lean region A by the air-fuel ratio control means 33, the EGR is synchronized with this switching. The EGR rate is switched from b to a and reduced by the control means 34. As a result, combustion is activated to the extent that the EGR rate is reduced, and the torque is increased accordingly. For this reason, the torque increase and the torque decrease due to the switching of the air-fuel ratio to the lean side are canceled out, so that the torque shock can be alleviated or prevented. Further, at the time of the above switching, even if the residual reflux gas at the EGR rate b before the EGR rate switching is introduced into the combustion chamber after the EGR rate switching and temporarily becomes the over EGR state, the air-fuel ratio and the EGR rate are switched. At the same time, since the discharge time is increased by the ignition energy increasing means 35 and the ignition energy is temporarily increased for a predetermined time, it is possible to prevent the occurrence of misfire and improve the combustibility. That is, as shown in FIG. 9, it is possible to prevent an increase in torque fluctuation when the EGR amount is larger than S ₁ and a misfire occurs due to the over EGR by improving the combustibility. This can contribute to alleviation of the torque shock.

The present invention is not limited to the above embodiment, but includes various other modifications. That is, in the above embodiment, the case where the EGR is performed in the lean region A is also shown, but the present invention is not limited to this.
For example, EGR is stopped in the lean region, that is, E
The GR rate may be set to 0, and the EGR may be performed for the first time based on the EGR rate increase amount increased by the EGR rate increase control means in the λ = 1 region. Even in this case, the above-mentioned measures are taken to alleviate the torque shock caused by the mutual switching of the air-fuel ratios between the above-mentioned regions and prevent the occurrence of misfire due to the residual circulating gas when switching from the λ = 1 region to the lean region. The same can be done as in the example.

In the above-described embodiment, the EGR is performed based on the EGR rate c even in the enriched region C, but the present invention is not limited to this, and the EGR may be stopped in the enriched region.

In the above embodiment, the rich region is divided into the λ = 1 region B and the enriched region C. However, the present invention is not limited to this, and one rich side air-fuel ratio is set as the rich region without being divided into the regions B and C. May be set.

In the above embodiment, the ignition energy is increased by lengthening the energization time to the coil 29, but the invention is not limited to this, and may be increased by increasing the current value, for example.

Further, in the above-described embodiment, the load is detected by the operating state detecting means 32 by the intake air amount by the air flow meter 27, but the present invention is not limited to this, and based on the shaft torque detection value by the shaft torque sensor, for example. The load may be detected.

Further, in the above embodiment, the air-fuel ratio control means 33 sets one air-fuel ratio value in each of the lean region A or the enriched region C, but the present invention is not limited to this, and for example, each Two or more values may be set in a stepwise manner in accordance with the operating state.

[0043]

As described above, according to the engine control device of the present invention, when the air-fuel ratio is switched from the lean region to the rich region by the air-fuel ratio control means according to the operating condition, E due to air-fuel ratio switching
Since the GR rate increase control means is operated to increase the EGR rate, the combustion can be suddenly slowed down due to the increase of the circulating gas which is an inert gas, resulting in torque reduction and emptying to the rich side. Torque shock can be mitigated by canceling out the torque increase due to the fuel ratio switching.

On the contrary, when the air-fuel ratio is switched from the rich region to the lean region, the EG
Since the increase of the EGR rate is stopped by stopping the operation of the R rate increase control means, and the ignition energy of the ignition means is temporarily increased by the ignition energy increase control means,
Torque can be increased by the increase in combustion due to the stop of the increase in the EGR rate, and the torque shock can be mitigated by canceling this torque increase and the torque decrease accompanying the air-fuel ratio switching to the lean region. . Moreover, in this case, even if the EGR state is temporarily increased due to the residual recirculation gas before the stop, the misfire can be prevented from occurring due to the increase in the ignition energy, and the torque shock can be prevented and the fuel consumption can be reduced. Can contribute to the improvement of.

In addition to these effects, the increase of the EGR rate by the operation of the EGR rate increase control means can contribute to the improvement of fuel consumption, and the operation of the EGR rate increase control means is adjacent to the lean region. Since it is performed in the region immediately after switching to the rich region, the increase of the combustion temperature can be suppressed by the circulating gas which is the inert gas introduced into the combustion chamber, and the increase of NOx can be suppressed.

According to the second aspect of the invention, in addition to the effect of the first aspect of the invention, the switching between the lean region and the rich region by the air-fuel ratio control means is NOx.
Since the air-fuel ratio value 16 that maximizes the occurrence of NO is skipped and is performed at once, it is possible to effectively suppress the increase in NOx. Moreover, since the EGR rate in the lean region is set to be smaller than that in the rich region, it is possible to prevent instability of combustion while improving fuel efficiency.

Furthermore, according to the invention of claim 3, in addition to the effect of the invention of claim 1, the air-fuel ratio control means sets the lean region, the λ = 1 region and the enriched region according to the operating condition. Since the switching can be performed, the fuel efficiency can be further improved. Moreover, in the above λ = 1 region, EGR
Since the rate becomes maximum, the increase in NOx can be suppressed more effectively by suppressing the increase in the combustion temperature in the vicinity of the air-fuel ratio region in which the generation of NOx becomes maximum.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an engine to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing an ignition means.

FIG. 3 is a relationship diagram between a secondary current and a discharge time in a normal ignition state and an up ignition state.

FIG. 4 is a simplified block configuration diagram showing a control device of the above embodiment.

FIG. 5 is a map of an air-fuel ratio region and a set EGR rate in the relationship between load and engine speed.

FIG. 6 is a relationship diagram of changes in EGR amount, air-fuel ratio, and ignition energy and time when switching from the λ = 1 region to the lean region.

FIG. 7 is a flowchart showing control in the ECU.

FIG. 8 is a relationship diagram between an EGR amount and a fuel consumption rate when the operating state is in a λ = 1 region and a lean region.

FIG. 9 is a relationship diagram between EGR amount and torque fluctuation when the operating state is in a λ = 1 region and a lean region.

[Explanation of symbols]

 1 Engine 7 Spark Plug 19 EGR Means 26 Ignition Means 33 Air-Fuel Ratio Control Means 35 Ignition Energy Increase Control Means 36 EGR Rate Increase Control Means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location F02D 43/00 A 7536-3G F02M 25/07 550 R F02P 3/00 B (72) Inventor Yamamoto Juei Hide 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation

Claims (3)

[Claims] 1. A lean region in which an air-fuel ratio on the lean side of the stoichiometric air-fuel ratio is set, and an air-fuel ratio on the rich side of the stoichiometric air-fuel ratio which is set adjacent to the lean region and includes the stoichiometric air-fuel ratio. An engine control device comprising: an air-fuel ratio control means for mutually switching to a rich region to be set according to an operating state; an EGR means for recirculating exhaust gas; and an ignition means for igniting an ignition plug, the EGR means comprising: For increasing the EGR rate of the recirculation gas by means of EGR rate increasing control means operated in at least an area adjacent to the lean area in the rich area, and from the rich area to the lean area in the air-fuel ratio control means. And an ignition energy increase control means for temporarily increasing the ignition energy of the ignition means at the time of switching to The control device of the engine. 2. The air-fuel ratio in the lean range in the air-fuel ratio control means is set to a value excluding the air-fuel ratio value 16 and larger than the air-fuel ratio value 16, and the EGR rate in the lean range in the EGR means is the EGR rate in the rich range. The engine control means according to claim 1, wherein the control means is set smaller. 3. The rich region in the air-fuel ratio control means,
The λ = 1 region in which the region is set adjacent to the lean region and the air-fuel ratio is set to be substantially equal to the stoichiometric air-fuel ratio, and the set air-fuel ratio in the region of λ = 1 is set adjacent to the λ = 1 region. And an enrichment region in which the air-fuel ratio on the rich side of the stoichiometric air-fuel ratio is set, and the EGR rate increase control means is operated in the λ = 1 region to maximize the EGR rate. The control device for the engine according to claim 1.