JP2005069029A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an engine output torque change and an exhaust gas property deterioration at changing of an air fuel ratio. <P>SOLUTION: An NO<SB>x</SB>occluding reduction catalyst 17 is arranged in an exhaust gas pipe 15 of a supercharged lean burn engine 1 to control emission. An electronic control unit (ECU) 30 of the engine operates the period with a theoretical air-fuel ratio until an engine suction air quantity reaches a predetermined value from the start of air fuel ratio change to reduce and control emission of the occluded NO<SB>x</SB>of the NO<SB>x</SB>occluded reduction catalyst and to prevent the output torque change corresponding to the change of the air-fuel ratio at restoring from a rich spike to a lean air fuel ratio operation when operating the rich spike for changing the operation air fuel ratio of the engine from a short time lean air fuel ratio into the lean air fuel ratio, and retardes an ignition timing as needed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine control device, and more particularly to an internal combustion engine control device that switches an operating air-fuel ratio during engine operation.
[0002]
[Prior art]
In an internal combustion engine (lean burn engine) that operates with a lean air-fuel ratio air-fuel mixture, a lean air-fuel ratio operation is performed in most of the operating region. In addition, a supercharged lean burn engine provided with a supercharger for the purpose of expanding the lean air-fuel ratio operation region enables lean air-fuel ratio operation even during high load operation. For this reason, in a supercharged lean burn engine, lean air-fuel ratio operation is performed in almost all operating regions except that the lean air-fuel mixture is operated with the stoichiometric air-fuel mixture in some light load regions where combustion tends to be unstable. Is done. For this reason, for example, when the engine load increases due to acceleration from the light load region (theoretical air-fuel ratio operation region), switching from the theoretical air-fuel ratio to the lean air-fuel ratio may occur during engine operation.
[0003]
Further, when the inflowing exhaust air-fuel ratio is lean, nitrogen oxides (NO in the exhaust) _X ) Is absorbed or absorbed, and when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or rich air-fuel ratio, NO is stored by reducing components such as CO or HC components in the exhaust. _X NO to reduce and purify _X When the storage reduction catalyst is used as an exhaust purification catalyst, NO is applied during lean air-fuel ratio operation. _X NO stored by the storage reduction catalyst _X The air-fuel ratio is switched to the rich air-fuel ratio for a short time each time the amount of _X NO stored in the catalyst by supplying rich air-fuel ratio exhaust gas to the storage reduction catalyst _X It is necessary to perform a rich spike operation to reduce and purify.
[0004]
For this reason, NO _X In a lean burn engine using an occlusion reduction catalyst as an exhaust purification catalyst, the operating air-fuel ratio is switched between the stoichiometric air-fuel ratio or the rich air-fuel ratio and the lean air-fuel ratio relatively frequently every time the rich spike operation is executed.
However, in the case of a supercharged lean burn engine, there arises a problem that the fluctuation of the engine output torque becomes large when the air-fuel ratio is switched, particularly when the rich or stoichiometric air-fuel ratio is switched to the lean air-fuel ratio, compared to the case of natural intake.
[0005]
The engine output torque is determined by the amount of fuel combusted in the combustion chamber. Therefore, when switching from rich or stoichiometric air-fuel ratio to a lean air-fuel ratio during acceleration, the air-fuel ratio is made lean to prevent fluctuations in engine output torque (ie, to maintain the same fuel amount). Therefore, it is necessary to greatly increase the intake air amount of the engine. Further, in acceleration from the stoichiometric air-fuel ratio operation region, etc., it is necessary to increase the amount of fuel. Therefore, it is necessary to further increase the intake air amount of the engine.
[0006]
For this reason, the throttle valve opening greatly increases when switching to the lean air-fuel ratio. However, in the supercharged lean burn engine, in addition to the response delay of the increase in the intake air amount with respect to the normal change in the throttle valve opening, a delay in the increase in the intake air amount occurs due to the so-called turbo lag due to the increase in the boost pressure. The amount of fuel supplied to the engine is determined according to the intake air amount and the air-fuel ratio. However, at the time of switching to the lean air-fuel ratio, the fuel supply amount to the engine is controlled to an amount that maintains the air-fuel ratio lean relative to the actual intake air amount until the intake air amount reaches the target value after switching. Therefore, after the switching, the fuel supply amount is reduced as compared with before the switching until the intake air amount reaches the target value.
[0007]
For this reason, after the air-fuel ratio switching, the engine output torque temporarily decreases, and in a vehicle-mounted engine or the like, there is a problem that the vehicle acceleration performance deteriorates, the driving force fluctuates and the driving performance deteriorates.
In order to compensate for the shortage of engine output torque, for example, in the case of an engine that can drive a vehicle with both an electric motor and an engine, such as a hybrid vehicle, the engine In addition, motor-assisted operation is effective to operate the electric motor to compensate for the lack of engine output.
[0008]
However, even in a hybrid vehicle, when the amount of charge (SOC) of a storage battery (battery) that supplies electric power to the electric motor decreases, the motor cannot be operated, and motor-assisted operation cannot be performed.
Although not related to the lean burn engine, for example, Patent Document 1 discloses a countermeasure against the problem that the motor assist operation cannot be performed when the SOC of the hybrid vehicle is lowered.
[0009]
In Patent Document 1, for example, in a hybrid vehicle, the amount of accelerator operation, etc., in each operation mode such as traveling only with an engine, traveling with both an engine and a motor (motor assist), traveling only with a motor, charging during engine traveling, etc. If the driving force of the vehicle is controlled to be constant at the same driving conditions, the characteristics of the electronically controlled throttle valve and the speed change characteristics of the transmission can be changed when the SOC is lowered and motor assist cannot be performed. By changing, a control device is disclosed in which the driving force of the vehicle is always kept substantially constant.
[0010]
[Patent Document 1]
JP-A-10-3776
[0011]
[Problems to be solved by the invention]
However, only a relatively small increase in driving force can be obtained by changing the characteristics of the electronically controlled throttle valve and the speed change characteristics of the transmission as in Patent Document 1. For this reason, it is not possible to compensate for relatively rapid and large torque fluctuations such as when switching from rich or stoichiometric air-fuel ratio to lean air-fuel ratio in a lean burn engine, particularly a supercharged lean burn engine, and the battery SOC decreases. If the motor assist cannot be used due to, for example, a problem that causes a drop in the drivability of the vehicle occurs.
[0012]
By the way, in actuality, when the air-fuel ratio is switched from the rich or stoichiometric air-fuel ratio to the lean air-fuel ratio, the target air-fuel ratio is gradually adjusted according to the change speed of the intake air amount so that the fuel supply amount to the engine does not change greatly. If it is changed, it is possible to reduce the fluctuation of the engine output torque accompanying the air-fuel ratio switching.
However, when the engine air-fuel ratio is gradually changed in this way, the engine air-fuel ratio becomes longer during the period from the rich or stoichiometric air-fuel ratio to the target lean air-fuel ratio after switching. There is. NO as an exhaust purification catalyst _X When using an NOx storage reduction catalyst, the lean air-fuel ratio will reduce NO in the exhaust. _X In fact, the catalyst NO _X When the amount of occlusion increases, the catalyst NO _X The storage capacity is reduced. For this reason, the catalyst NO _X When the amount of occlusion increases, in an atmosphere of a lean air-fuel ratio that is relatively close to the stoichiometric air-fuel ratio (for example, a so-called weak lean region having an air-fuel ratio of about 15 to 20), the engine NO _X NO due to increased emissions _X NO from the storage reduction catalyst _X May be released without being purified. Usually, in the lean air-fuel ratio operation, the target air-fuel ratio is set to a so-called strong lean air-fuel ratio of 20 or more. However, when the air-fuel ratio is switched from the rich or stoichiometric air-fuel ratio to the lean air-fuel ratio, the time remaining in this weak lean air-fuel ratio region The longer it gets, the more NO released into the atmosphere _X This is not preferable because the amount may increase.
[0013]
Therefore, it is necessary to avoid the air-fuel ratio from staying in the weak lean air-fuel ratio region as much as possible at the time of air-fuel ratio switching, and it is not possible to adopt a countermeasure that gradually changes the air-fuel ratio and suppresses fluctuations in engine output torque.
In view of the above problems, the present invention prevents a decrease in engine output torque when switching an air-fuel ratio in a lean burn engine, particularly when switching from a rich or stoichiometric air-fuel ratio to a lean air-fuel ratio, thereby reducing the drivability of the vehicle. It is an object of the present invention to provide a control device for an internal combustion engine that can prevent the deterioration of exhaust properties due to air-fuel ratio switching by reducing the time during which the exhaust air-fuel ratio remains in a weak lean air-fuel ratio region.
[0014]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a control device for an internal combustion engine that switches an operating air-fuel ratio between a stoichiometric air-fuel ratio or a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio during engine operation, The engine intake air amount is adjusted at the time of air-fuel ratio switching, the engine driving force at the air-fuel ratio after switching is adjusted, and the engine is theoretically operated from the start of the air-fuel ratio switching until the intake air amount reaches a predetermined value. A control device for an internal combustion engine is provided that prevents engine output fluctuations during air-fuel ratio switching by operating at an air-fuel ratio.
[0015]
That is, in the first aspect of the invention, the fuel supply amount to the engine is controlled so that the engine air-fuel ratio becomes the target air-fuel ratio after switching (for example, the strong lean air-fuel ratio) simultaneously with the start of switching at the time of air-fuel ratio switching. However, the amount of fuel supplied to the engine is controlled so that the engine air-fuel ratio becomes the stoichiometric air-fuel ratio while the engine intake air amount at the beginning of switching is not sufficiently increased. As a result, a decrease in engine output torque at the time of air-fuel ratio switching is suppressed.
[0016]
In the present invention, the stoichiometric air-fuel ratio operation at the time of switching the air-fuel ratio is stopped when the intake air amount increases to an extent that the reduction range of the engine output torque can be tolerated when switching to the target lean air-fuel ratio. The air-fuel ratio is switched from the stoichiometric air-fuel ratio to the target lean air-fuel ratio. This minimizes the time that the engine is operated at an intermediate air / fuel ratio (e.g., a weak lean air / fuel ratio). _X Even when an occlusion reduction catalyst is used, deterioration of exhaust properties is prevented.
[0017]
According to the second aspect of the present invention, the engine intake air amount is smaller than the predetermined value during the theoretical air-fuel ratio operation when the air-fuel ratio is switched from the rich air-fuel ratio or the stoichiometric air-fuel ratio to the lean air-fuel ratio. The control apparatus for an internal combustion engine according to claim 1, wherein the engine ignition timing is further retarded when the value exceeds the value.
[0018]
Further, the engine ignition timing is retarded when the engine intake air amount exceeds a predetermined value. As a result, the engine output torque is prevented from significantly increasing by performing the theoretical air-fuel ratio operation at the time of switching to the lean air-fuel ratio. For example, when the engine is operated at a stoichiometric air-fuel ratio, the predetermined value for starting the retard of the ignition timing is a target intake air amount that is set according to the accelerator pedal depression amount (accelerator opening) of the driver. .
[0019]
According to a third aspect of the present invention, the engine includes an electric assist motor that assists rotation of the engine output shaft, a storage battery that supplies electric power to the assist motor, and a charge amount of the storage battery is predetermined. When the air-fuel ratio is greater than or equal to the value, the theoretical air-fuel ratio operation is not performed when the air-fuel ratio is switched, the engine assist shaft rotation is assisted by the electric assist motor, and the air-fuel ratio is immediately switched to the air-fuel ratio after switching. 3. The control device for an internal combustion engine according to claim 1, wherein the stoichiometric air-fuel ratio operation is performed when the air-fuel ratio is switched when the charge amount of the engine is equal to or less than the predetermined value.
[0020]
That is, according to the third aspect of the present invention, when switching the air-fuel ratio in an engine equipped with an electric assist motor such as a hybrid vehicle engine, if the SOC of the battery is sufficiently high, the motor assist is performed when the air-fuel ratio is switched. To prevent the engine output torque from fluctuating (decreasing) and temporarily holding the air-fuel ratio of claim 1 or 2 at the stoichiometric air-fuel ratio when the air-fuel ratio is switched only when the SOC is lowered and the motor assist cannot be used. Control.
As a result, even in the hybrid vehicle, both the torque fluctuation at the time of switching the air-fuel ratio and the deterioration of the exhaust gas property are prevented regardless of the presence or absence of the SOC.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration when the present invention is applied to an internal combustion engine for a hybrid vehicle.
In FIG. 1, 100 denotes the entire hybrid vehicle, 101 denotes a vehicle body of the vehicle 100, 103 denotes a wheel, and 10 denotes a power unit mounted on the vehicle body 101 of the vehicle 100.
The power unit 10 includes an internal combustion engine 1, a motor generator (motor / generator) 5 connected to the output shaft of the engine 1 via a power switching mechanism 3, and output power when the motor generator 5 operates as a generator. (AC power) is converted to DC power to charge the battery 9, and when the motor generator 5 operates as a motor, the DC current from the battery 9 is converted to AC power having an arbitrary voltage and frequency. And an inverter 7 with a converter for supplying to the generator 5.
[0022]
In this embodiment, the internal combustion engine 1 is a four-cylinder four-cycle supercharged gasoline engine, and is a supercharged lean burn engine that can be operated in a wide air-fuel ratio range from a rich air-fuel ratio to a lean air-fuel ratio.
The output shaft of the engine 1 and the input / output shaft of the motor generator 5 are connected to the transmission 2 that drives the wheels 103 of the vehicle 100 via the power switching mechanism 3.
[0023]
The power mechanism 3 connects and disconnects the transmission 2, the engine 1 output shaft, and the input / output shaft of the motor generator 5. In other words, the power switching mechanism 3 connects only the output shaft of the internal combustion engine 1 or only the input / output shaft of the motor generator 5 or both to the transmission 2 at the same time to drive the wheels 103, or the output shaft of the internal combustion engine 1 and the motor The input / output shaft of the generator 5 is connected in a state where it is disconnected from the transmission 2 so that the power generation by the motor generator 5 and the cranking at the start of the engine 1 can be performed.
[0024]
In the present embodiment, NO is provided in the exhaust pipe 15 of the internal combustion engine 1. _X An occlusion reduction catalyst 17 is arranged. NO _X The occlusion reduction catalyst 17 is configured to detect NO in the exhaust when the exhaust air-fuel ratio of the engine 1 is lean. _X NO is occluded in the catalyst by absorbing and / or adsorbing components, and occluded using reducing components such as HC components and CO in the exhaust when the exhaust air-fuel ratio of the engine 1 becomes rich _X It is a catalyst that reduces and purifies.
[0025]
1 is an electronic control unit (ECU) that controls the engine 1. The ECU 30 is a microcomputer having a known configuration in the present embodiment, and controls the operation mode of each device such as the power switching mechanism 3, the motor generator 5, the inverter 7 with a converter, and the like, which will be described later in the present embodiment. Torque fluctuation suppression control at the time of switching the air-fuel ratio is performed.
[0026]
As shown in FIG. 2, in order to execute these controls on the input / output port of the ECU 30, a signal corresponding to the engine intake air amount from the air flow meter 301 arranged in the intake passage of the engine 1 is also sent to the accelerator pedal ( A signal indicating an accelerator pedal depression amount (accelerator opening) of the vehicle driver from an accelerator opening sensor 303 arranged in the vicinity of the throttle valve (not shown) in the engine intake passage and a throttle valve (not shown) in the vicinity of the engine intake passage. Signals representing the throttle valve opening are input from the opening sensor 305, respectively.
[0027]
Further, the ECU 30 receives a pulse signal corresponding to the crankshaft rotational speed from a crank angle sensor 307 provided in the vicinity of a crankshaft (not shown) of the engine 1 and an exhaust air / fuel ratio sensor 309 provided in the engine exhaust passage. In addition to a signal indicating the exhaust air-fuel ratio (operating air-fuel ratio), a signal indicating the state of charge (SOC) of the battery is input from the battery controller 311.
[0028]
The input / output port of the ECU 30 is connected to the fuel injection valve 331 and the ignition circuit 333 of the engine 1 to control the fuel injection amount, the fuel injection timing, and the ignition timing of the engine 1, respectively. It is connected to the actuator of the throttle valve 335.
The electronically controlled throttle valve 335 includes an actuator such as a stepper motor, and is a throttle valve that can take an opening degree according to a command from the ECU 30 without being mechanically connected to an accelerator pedal.
[0029]
Further, the input / output port of the ECU 30 is connected to the hybrid control computer 340. The hybrid control computer 340 controls the motor generator 5 and the power switching mechanism 3 of the power unit 10 in accordance with a command from the ECU 30, and travel modes of the hybrid vehicle 100 (engine travel, motor assist travel, motor travel, charging travel, etc.). In the present embodiment, the motor assist operation is performed when the air-fuel ratio of the engine 1 is switched as described later.
[0030]
Next, switching of the air-fuel ratio in this embodiment will be described.
In the present embodiment, the engine 1 is operated in the theoretical air-fuel ratio operation in a part of the light load operation region where the rotational speed of the supercharger is low, and the lean air-fuel ratio (air-fuel ratio of 20 or more) in almost all other regions. Driving is performed.
Therefore, at the time of acceleration from the light load region, the operating air-fuel ratio is switched from the stoichiometric air-fuel ratio to the lean air-fuel ratio in order to increase the engine output torque.
In such lean air-fuel ratio switching for acceleration, it is necessary to increase the engine output torque immediately after switching.
[0031]
In the present embodiment, NO _X The storage reduction catalyst 17 is used, but when the engine is operated at a lean air-fuel ratio, NO _X The lean air-fuel ratio exhaust gas flows into the storage reduction catalyst 17, and the NO in the exhaust gas _X Ingredient is NO _X Since it is occluded by the occlusion reduction catalyst 17, NO _X NO of storage reduction catalyst 17 _X The amount of occlusion increases.
[0032]
For this reason, the lean air-fuel ratio operation of the engine 1 continues to some extent and NO _X NO of storage reduction catalyst 17 _X When the storage amount increases to a predetermined level, the ECU 30 operates the engine 1 for a short time at a rich air-fuel ratio, and NO _X The NO stored in the catalyst 17 is obtained by performing a rich spike operation for supplying the rich air-fuel ratio exhaust gas to the storage reduction catalyst 17. _X It is necessary to reduce and purify. That is, NO _X When the rich reduction spike of the storage reduction catalyst 17 is executed, the air-fuel ratio of the engine is switched between the lean air-fuel ratio and the rich air-fuel ratio.
[0033]
In this case, the lean air-fuel ratio operation is resumed after the end of the rich spike operation, so that the rich air-fuel ratio is switched to the lean air-fuel ratio. At this time, the engine output torque may be the same before and after the switching. preferable.
As described above, it is necessary to significantly increase the engine intake air amount in order to maintain the same engine output torque (fuel amount) when switching (returning) from the rich air-fuel ratio or the stoichiometric air-fuel ratio to the lean air-fuel ratio. is there. Further, in order to increase the engine output after switching such as during acceleration, it is necessary to further increase the intake air amount.
[0034]
However, especially when a supercharged lean burn engine is used as in the present embodiment, a delay due to a turbo lag occurs in addition to a normal response delay of the intake system, and the intake air amount is relatively moderate. Does not increase.
For this reason, immediately after switching, the amount of fuel is reduced to maintain the target lean air-fuel ratio, resulting in a problem that the engine output torque is reduced. FIG. 3 is a timing chart for explaining the decrease in the engine output torque, taking as an example the switching from the stoichiometric air-fuel ratio during acceleration to a lean air-fuel ratio.
[0035]
In FIG. 3, curve A represents a change in throttle valve opening TA during acceleration, B represents a change in intake air amount Ga, and C represents a change in fuel injection correction amount FAF. In the present embodiment, the ECU 30 determines the fuel injection amount QINJ to the engine according to the engine intake air amount Ga. That is, in the present embodiment, the fuel injection amount QINJ is calculated as QINJ = Ga × FAF. The engine air-fuel ratio is adjusted by changing the value of the fuel injection correction amount FAF.
[0036]
For example, if the FAF value in the stoichiometric air-fuel ratio (air-fuel ratio A / F = 14.6) operation is FAFS, the FAF value FAFL in the lean air-fuel ratio operation (A / F = 25) is FAFL = (14.6 / 25 ) FAFS.
Also, curves D and DL in FIG. 3 show changes in engine output torque TQ, curve D shows an ideal torque change (increase) during acceleration, and curve DL shows an actual torque change.
[0037]
Further, curve E shows the change in engine air-fuel ratio A / F.
Curves A to E show switching from the stoichiometric air-fuel ratio operation to the lean air-fuel ratio at the time of acceleration, and the horizontal axis (time axis) ts during steady operation at the stoichiometric air-fuel ratio (A / F = 14.6). The case where acceleration starts at a point is shown.
When acceleration is started (ts), the throttle valve opening TA (curve A) is changed to the target opening TA after switching. ₀ The fuel injection correction amount FAF is decreased stepwise from FAFS to FAFL (curve C). Further, since the throttle valve opening TA has increased, the engine intake air amount Ga starts to increase. However, because of the turbo lag, the increase speed is relatively slow, and the target intake air amount Ga corresponding to the throttle valve opening TA. ₀ The time point te is reached (curve B).
[0038]
For this reason, at the start of acceleration (ts), although the intake air amount Ga does not increase, the fuel injection amount is greatly reduced because the FAF is stepped down to FAFL, and the engine output torque TQ Falls significantly (curve DL).
Thereafter, the intake air amount Ga increases with the passage of time, and the actual engine output TQ also increases and reaches the target torque at the time te, but the torque change necessary for obtaining smooth acceleration (curve D) As compared with, the decrease in torque becomes larger and the time to reach the target torque becomes longer.
[0039]
However, in this case, the air-fuel ratio A / F is switched from the stoichiometric air-fuel ratio (A / F = 14.6) to the lean air-fuel ratio (A / F = 25) in a stepped manner, and the time during which the air-fuel ratio remains at the intermediate air-fuel ratio Is minimized (curve E).
As described above, even if the air-fuel ratio is not switched stepwise in the case of FIG. 3, the engine output torque is prevented from changing if the air-fuel ratio is gradually switched according to the increase of the intake air amount Ga. However, in this embodiment, NO _X Since exhaust gas purification using the storage reduction catalyst 17 is performed, at an air-fuel ratio of weak lean air-fuel ratio (A / F = about 15 to 20), NO _X Unpurified NO from the storage reduction catalyst 17 _X May be released. For this reason, when the air-fuel ratio is switched, the air-fuel ratio is changed from the stoichiometric air-fuel ratio to a strong lean air-fuel ratio stepwise as shown in curve E in order to shorten the time during which the air-fuel ratio stays at the intermediate weak lean air-fuel ratio as much as possible. The air-fuel ratio is switched to A / F = 25.
[0040]
In the present embodiment, when the battery SOC is sufficiently high, the motor generator 5 is operated at the time of air-fuel ratio switching to perform motor assist so that the driving torque of the vehicle 100 matches the ideal curve D. That is, by compensating for the shortage (shaded portion) of the engine output torque with the output of the motor generator 5, fluctuations in the drive torque are suppressed and smooth acceleration is obtained.
[0041]
However, when the battery SOC is insufficient, the motor assist cannot be performed, so that there is a problem that the vehicle driving torque has a torque fluctuation like the curve DL.
In the present embodiment, the torque fluctuation can be suppressed even when the motor assist cannot be performed by maintaining the operating air-fuel ratio at the theoretical air-fuel ratio for a predetermined time when switching to the lean air-fuel ratio.
[0042]
FIG. 4 is a timing chart similar to FIG. 3 for explaining the air-fuel ratio switching operation without motor assistance in the present embodiment. In FIG. 4, curves A to E represent the throttle valve opening TA, the intake air amount Ga, the fuel injection correction amount FAF, the engine output torque TQ, and the air-fuel ratio A / F, respectively, as in FIG. Indicates the ignition timing of the engine. In the engine output torque curve, D represents an ideal output torque change, DL represents the same conventional actual torque change as in FIG. 3, and DS represents the engine output torque change of the present embodiment.
[0043]
In the acceleration of FIG. 4, the throttle valve opening TA is set to TA at the acceleration start time ts. ₀ The fuel correction amount FAF is set to the theoretical air-fuel ratio equivalent value FAFS (curve C).
For this reason, in this embodiment, since the air-fuel ratio does not become lean at the time of switching, the fuel injection amount does not decrease. Therefore, the actual engine output torque DS increases without decreasing, becomes larger than the conventional torque change DL, and becomes slightly higher than the ideal torque change.
[0044]
However, if the intake air amount Ga increases while maintaining the FAF at the stoichiometric air-fuel ratio equivalent value FAFS, the output torque of the engine becomes excessive, and a driving torque more than expected by the driver is generated. Therefore, in the present embodiment, at time t1, the ignition timing is retarded as shown by curve I.
Here, the time point t1 is a time point when the engine intake air amount Ga reaches the stoichiometric air-fuel ratio equivalent air amount Gas (curve B).
[0045]
As described above, an electronically controlled throttle valve is used in this embodiment, and the throttle valve opening is not mechanically connected to the accelerator pedal. In this embodiment, the throttle valve opening is set in advance according to the accelerator pedal depression amount (accelerator opening) of the driver, the engine speed, and the engine operating air-fuel ratio. In this case, even if the accelerator opening and the engine speed are the same, the throttle valve opening is set small and the intake air amount is small in the theoretical air-fuel ratio operation, but the fuel injection amount is the same as the accelerator opening and the engine speed. If the numbers are the same, they are almost the same regardless of the engine air-fuel ratio.
[0046]
The stoichiometric air-fuel ratio equivalent air amount Gas is a target intake air amount when the stoichiometric air-fuel ratio operation is performed at the same accelerator opening as the throttle valve opening (curve A) at the target lean air-fuel ratio. As described above, if the fuel injection amount of the engine is the same, the engine output torque is almost the same regardless of whether it is the theoretical air-fuel ratio operation or the lean air-fuel ratio operation. The theoretical air-fuel ratio equivalent air amount is the target intake air amount Ga at the target lean air-fuel ratio during acceleration. ₀ This is the intake air amount when the theoretical air-fuel ratio operation is performed with the same amount of fuel that is injected into the engine.
[0047]
In other words, the engine output torque when the theoretical air-fuel ratio operation is performed with the intake air amount Gas is the target intake air amount Ga during the lean air-fuel ratio operation. ₀ The engine output torque when the lean air-fuel ratio operation is performed is almost the same.
That is, in this embodiment, since the theoretical air-fuel ratio operation is continued even after the acceleration is started, the engine intake air amount is set to the target Ga. ₀ The final target torque TQ for the lean air-fuel ratio operation at the time t1 when the gas reaches smaller Gas ₀ If (curve DS) is reached and the intake air amount further increases, the engine output torque becomes excessive.
In order to prevent this, in the present embodiment, the theoretical air-fuel ratio operation is continued even after the acceleration is started, but the retard of the ignition timing IG is started from the time (t1) when the intake air amount reaches the stoichiometric air-fuel ratio equivalent air amount Gas. Then, the retard amount is increased in accordance with the increase of the intake air amount Ga, and the engine output torque during the theoretical air-fuel ratio operation becomes the final target torque TQ. ₀ Torque control is performed so as not to become above.
[0048]
Thereby, after the time point t1, even if the intake air amount Ga increases, the engine output torque is almost the final target torque TQ. ₀ Will be maintained.
At time t2 in this state, the retard of the ignition timing is stopped, and the fuel correction amount FAF is reduced stepwise to a predetermined value FAF2 between the theoretical air-fuel ratio equivalent value FAFS and the lean air-fuel ratio equivalent value FAFL. Here, FAF2 is set to a value at which an air-fuel ratio slightly higher than the weak lean air-fuel ratio can be obtained. At time t2, even if the value of the intake air amount Ga changes the fuel injection correction amount and the ignition timing in steps, This is the time when the engine output torque fluctuation before and after the change falls within the allowable range, and is determined in detail by an experiment using an actual engine.
[0049]
That is, at the time point t2, the ignition timing retardation is stopped and the fuel injection correction amount FAF is reduced stepwise, but the engine output torque DS hardly changes and the air-fuel ratio A / F (curve E) is further reduced. The air-fuel ratio changes stepwise from the stoichiometric air-fuel ratio to a slightly higher air-fuel ratio than the weak lean air-fuel ratio.
Thereafter, the fuel injection correction amount FAF is gradually reduced as the intake air amount Ga increases, and the intake air amount becomes the final target air amount Ga. ₀ At the time te when the air-fuel ratio reaches the lean air-fuel ratio equivalent value FAFL (curve C), the air-fuel ratio reaches the lean air-fuel ratio (A / F = 25) which is the lean operation target air-fuel ratio.
[0050]
As shown in FIG. 4, in the present embodiment, when switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio at the time of acceleration, the stoichiometric air-fuel ratio is reached from the start of switching until the engine intake air amount reaches a predetermined value (time point t2). While the operation is continued, after the air amount reaches the stoichiometric air-fuel ratio equivalent air amount Gas (time point t1), the ignition timing is retarded, so that the engine output fluctuation and the exhaust property at the time of air-fuel ratio switching without motor assist are performed. And prevent the deterioration.
[0051]
Next, FIG. _X Occlusion NO of Occlusion Reduction Catalyst 17 _X FIG. 5 is a timing chart similar to FIG. 4 showing a switching operation from a rich air-fuel ratio to a lean air-fuel ratio at the end of a rich spike operation for reduction.
As shown in FIG. 5, during the rich spike operation (before time ts), the intake air amount Ga is maintained the same as when the stoichiometric air-fuel ratio operation is performed, and the fuel injection correction amount FAF is the rich air-fuel ratio equivalent value FAFR. (Curve C), the engine operating air-fuel ratio A / F is maintained at a rich air-fuel ratio of about 13, for example. In this case, the ignition timing IG is held at a retarded angle (curve I) in order to prevent an increase in engine output accompanying an increase in fuel.
[0052]
When the rich spike ends in this state (time point ts), the throttle valve opening is stepped to the target opening TA during lean air-fuel ratio operation. ₀ (Curve A), and the intake air amount Ga starts to increase from the stoichiometric air-fuel ratio equivalent air amount Gas (curve B). The fuel injection correction amount FAF is reduced stepwise from the rich air-fuel ratio equivalent value FAFR to the stoichiometric air-fuel ratio equivalent value FAFS (curve C), and the air-fuel ratio A / F becomes the stoichiometric air-fuel ratio (curve E). In this state, since the air amount has already reached the stoichiometric air-fuel ratio equivalent value Gas, after the engine ignition timing IG is once returned to zero, the retard amount is increased according to the increase in the air amount Ga. Increasing (Curve I).
[0053]
As a result, the engine output torque TQ is substantially constant TQ. ₀ (Curve DS). A curve DL in FIG. 5 shows a case where the fuel injection correction amount is reduced stepwise to the lean air-fuel ratio equivalent value FAFL immediately after the end of the rich spike. In this case, a large torque fluctuation occurs, but in this embodiment (curve DS), the torque fluctuation is prevented from occurring.
[0054]
Also in the present embodiment, when the time t1 is reached, the retard of the ignition timing is stopped, and the fuel injection correction amount FAF is reduced stepwise from the stoichiometric air-fuel ratio equivalent value to the same FAF2 as in FIG. 4, and then the intake air amount It is gradually reduced to a lean air-fuel ratio equivalent value FAFL as Ga increases. That is, also in this embodiment, the same operation as the period from time t2 to te in FIG. 4 is performed in the period from time t1 to te.
[0055]
As a result, even in this embodiment, it is possible to prevent engine output torque fluctuations and deterioration of exhaust properties when switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio when motor assist cannot be obtained.
FIG. 6 is a flowchart illustrating the air-fuel ratio switching operation of the present embodiment that is executed by the ECU 30. In the present embodiment, at the time of switching from the rich or stoichiometric air-fuel ratio to the lean air-fuel ratio, if the battery SOC is greater than or equal to a predetermined value, the motor generator 5 is operated to perform air-fuel ratio switching while performing motor assist, When the SOC is equal to or less than the predetermined value, the air-fuel ratio switching control described with reference to FIGS. 4 and 5 is performed.
[0056]
In the switching operation of FIG. 6, first, at step 601, it is determined whether or not the engine is currently operating at the rich air fuel ratio or the stoichiometric air fuel ratio. When the engine is not operated at the rich air-fuel ratio or the stoichiometric air-fuel ratio, switching to the lean air-fuel ratio does not occur, so this operation is immediately terminated.
If the current engine is operating at a rich air-fuel ratio or a lean air-fuel ratio, it is next determined in step 603 whether switching to the current lean air-fuel ratio is requested (eg, acceleration start, rich spike end, etc.). Is determined, and if there is no request for switching to the lean air-fuel ratio, this operation is terminated as it is.
[0057]
If there is a request for switching to the lean air-fuel ratio in step 603, then in step 605, the current battery SOC is set to a predetermined value SOC. ₀ It is determined whether or not the following is true. SOC ₀ Is a lower limit value of the SOC in which the motor generator 5 can be used.
In step 605, SOC ≧ SOC ₀ If this is the case, that is, if the motor generator 5 can be used at the time of air-fuel ratio switching, the process proceeds to step 607 to switch to a lean air-fuel ratio and perform motor assist operation. As a result, as shown in FIG. 3, the engine air-fuel ratio is immediately switched to the lean air-fuel ratio operation target value, and although the engine output fluctuates greatly, torque is applied by the motor generator 5, so that the curve D in FIG. Such an ideal driving force change can be obtained.
[0058]
In step 605, SOC <SOC ₀ If this is the case, that is, if the charge amount of the battery is low and the motor assist cannot be used, the process proceeds to step 609 and the stoichiometric air-fuel ratio is performed without performing the motor assist as shown in FIGS. Switch to lean air-fuel ratio through operation at As a result, even if motor assist cannot be obtained, fluctuations in output torque and deterioration of exhaust properties associated with air-fuel ratio switching are prevented.
[0059]
【The invention's effect】
According to the invention described in each claim, there is a common excellent effect that can prevent fluctuations in engine output torque and deterioration of exhaust gas properties at the time of air-fuel ratio switching without using motor assist.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration outline of an embodiment when the present invention is applied to an internal combustion engine for a hybrid vehicle.
FIG. 2 is a diagram illustrating input and output of an electronic control unit (ECU).
FIG. 3 is a diagram illustrating air-fuel ratio switching with motor assist.
FIG. 4 is a diagram illustrating an air-fuel ratio switching operation from a theoretical air-fuel ratio to a lean air-fuel ratio without using motor assist.
FIG. 5 is a diagram illustrating an air-fuel ratio switching operation from a rich air-fuel ratio to a lean air-fuel ratio without using motor assist.
FIG. 6 is a flowchart illustrating air-fuel ratio switching control according to the present embodiment.
[Explanation of symbols]
1. Internal combustion engine
3. Power switching mechanism
5. Motor generator
9 ... Battery
17 ... NO _X Occlusion reduction catalyst
30 ... Electronic control unit (ECU)

Claims (3)

A control device for an internal combustion engine that switches an operating air-fuel ratio between a stoichiometric air-fuel ratio or a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio during engine operation,
Adjusting the engine intake air amount at the time of air-fuel ratio switching and adjusting the engine driving force at the air-fuel ratio after switching,
A control apparatus for an internal combustion engine, which prevents engine output fluctuation at the time of air-fuel ratio switching by operating the engine at a stoichiometric air-fuel ratio from the start of the air-fuel ratio switching until the intake air amount reaches a predetermined value. When the stoichiometric air-fuel ratio operation at the time of the air-fuel ratio switching from the rich air-fuel ratio or the stoichiometric air-fuel ratio to the lean air-fuel ratio, the engine ignition timing is further increased when the engine intake air amount becomes a predetermined value smaller than the predetermined value. The control device for an internal combustion engine according to claim 1, wherein the retardation of the internal combustion engine is performed. The engine includes an electric assist motor that assists rotation of the engine output shaft, and a storage battery that supplies electric power to the assist motor.
Further, when the charge amount of the storage battery is equal to or greater than a predetermined value, the theoretical air-fuel ratio operation is not performed when the air-fuel ratio is switched, the engine assist shaft rotation is assisted by the electric assist motor, and the air-fuel ratio is immediately set. 3. The internal combustion engine according to claim 1, wherein when the charge amount of the storage battery is equal to or less than the predetermined value, the theoretical air-fuel ratio operation is performed when the air-fuel ratio is switched. Control device.

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