JP2002070634A - Controller for lean combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller for a lean combustion engine capable of preventing deterioration of exhaust gas after a restart of the lean combustion engine in an idle stop system-equipped automobile, a hybrid electric vehicle or the like, which has the lean combustion engine. SOLUTION: In this controller, an active state decision means 66 pseudo- decides that an air-fuel ratio sensor is in an active state regardless of output of the air-fuel ratio sensor just after an automatic stop/restart means 61 automatically restarts the engine, and allows selection of a feedback mode. When the engine is brought into a specific operation state, a combustion mode selection means 62 selects the feedback mode.

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 a lean burn engine which is suitable for use as an engine for an idle stop system or a hybrid electric vehicle.

[0002]

2. Description of the Related Art In recent years, idle stop systems and hybrid electric vehicles (HEV) have been developed for the purpose of reducing exhaust gas, suppressing fuel consumption, and reducing noise. In the idle stop system, the engine is automatically stopped (idling is stopped) when the vehicle stops such as waiting for a traffic light or congestion.

[0003] In the HEV, when the engine is used for power generation, the engine is started or stopped according to the remaining capacity of the battery, and when the engine is used for traveling, the engine is automatically started according to the output demand of the vehicle. Start or stop. Thus, the idle stop system and the HEV
In this case, the operation of the engine is automatically started and stopped according to the situation, regardless of the driver's engine stop operation.

On the other hand, a lean-burn engine has been developed as an engine (internal combustion engine) capable of reducing fuel consumption.
In such an engine, as the combustion control mode,
A stoichiometric mode (feedback mode) in which the air-fuel ratio is controlled by O ₂ feedback so that the air-fuel ratio becomes stoichiometric, or a lean mode in which the air-fuel ratio is controlled by an open loop so that the air-fuel ratio becomes leaner than the stoichiometric ratio. In addition, there is an open loop mode (including an enrichment mode) in which the air-fuel ratio is controlled by an open loop so that the air-fuel ratio is in a rich state near stoichiometry or on the richer side than stoichiometry. I have. In the case of a spark-ignition in-cylinder injection engine, a super-lean mode (compression lean mode) is also set, in which fuel is injected in the compression stroke immediately before spark ignition to perform stratified combustion and achieve a significantly lean air-fuel ratio. it can.

When the engine speed and the engine load are small, the super lean mode or the lean mode is selected. When the engine speed and the engine load are large, the stoichiometric mode is selected, and the engine speed and the engine load are reduced. If it becomes larger, the open loop mode enrich mode is selected. In an engine applied to an idle stop system or an HEV, an engine that controls the engine in each of these operation modes has been developed.

For example, FIG. 6 is a schematic diagram showing a configuration example of a drive system of an HEV having an idle stop system.
As shown in FIG. 6, the HEV includes a motor 101, a transmission 102, a clutch 103, and a differential (differential) on a rotating shaft 101A of the motor 101.
Driving wheels 105 and 105 are connected through a 104, and an engine 107 is connected to a rotating shaft 101A of the motor 101 through a clutch 106. An O ₂ sensor 40 and an exhaust gas purifying catalyst 29 are interposed in the exhaust passage 108 of the engine 107 from the upstream.

Normally, the clutch 106 between the motor 101 and the engine 107 is released, and the motor 1
The clutch 106 is connected to use the canter power of the engine 107 when the vehicle travels only with the canter power of 01 and a large driving force is required, or when the remaining capacity of the battery (not shown) is reduced. I do. That is, when the driving force is requested, the engine 107 is used for the driving force of the vehicle, and when the remaining capacity of the battery is small, the motor 107 is used.
01 functions as a generator, and the engine 107 is used as a power generation engine.

When a predetermined idle stop condition is satisfied during traveling, that is, when the vehicle stops and the operating engine 107 enters an idle state and the shift lever position becomes neutral, idle stop (engine stop) is performed. When the idle stop condition is not satisfied (normally, when the shift lever position is shifted from the neutral position to the traveling position), the idle stop is released (the engine is started).

The control mode of the engine 107 (combustion
Mode), as described above, _TwoFrom the sensor 40
O based on output_TwoAir-fuel ratio by feedback control
The stoichiometric mode for controlling near the stoichiometric and the open
Lean mode that controls the air-fuel ratio lean by loop control
(Including super lean mode) and open loop control
To control the air-fuel ratio near stoichiometric or rich.
Equipped with the open loop mode, the output of the engine 107 is required.
Demand (small engine load) or engine
If the number of turns is low, lean mode is selected and engine
Output demand (engine load) of the
If the engine speed increases, the stoichiometric mode or open
The loop mode is selected.

A general O ₂ sensor 40 (for example, a zirconia oxygen sensor) used in the stoichiometric mode generally changes its output voltage stepwise when the amount of oxygen in the exhaust gas becomes small. ₂ sensors 4
The output voltage value of 0 becomes small on the lean side of the stoichiometric air-fuel ratio at the boundary of the stoichiometric air-fuel ratio, and becomes larger than a predetermined value on the rich side of the stoichiometric air-fuel ratio.

Therefore, in O ₂ feedback control, O ₂
When the output voltage value of the sensor 40 exceeds a predetermined value, the target air-fuel ratio is corrected so that the air-fuel ratio increases on the assumption that the air-fuel ratio is richer than the stoichiometric value, and the output voltage value of the O ₂ sensor 40 is lower than the predetermined value. , The air-fuel ratio is on the leaner side than the stoichiometric ratio, and the target air-fuel ratio is corrected so that the air-fuel ratio decreases to control the fuel injection amount and the like.

[0012] Thus, the O ₂ feedback control of the stoichiometric mode, O ₂ and is essential detected by the sensor 40, O ₂ sensor 40 is an O ₂ feedback control is not reliably react In the active state You cannot do it. If the O ₂ sensor 40 is active, reacts with the air-fuel ratio becomes rich (output voltage is generated) because, O ₂
If the sensor 19 shows a reaction of a certain level or more, that is, if the output voltage of the O ₂ sensor 40 becomes a predetermined value or more, the O ₂ sensor 40
Determined is determined to be in the active state, if the O ₂ sensor 40 is not shown above a certain reaction, i.e. if the output voltage of the O ₂ sensor 19 is less than the predetermined value, the O ₂ sensor 40 is in the inactive state can do.

Therefore, when the engine is started, such activation determination is performed until the O ₂ sensor 40 is activated (that is, until the output voltage of the O ₂ sensor 40 becomes higher than a predetermined value). Is designed to prohibit selection of a stoichiometric mode for performing O ₂ feedback control.

[0014]

In the above-described HEV with an idle stop system, for example, when the vehicle is started when the engine is idle stopped, first, the shift lever is switched from the neutral position to the traveling position, and thereafter, The driver will start by depressing the accelerator pedal. In this case, engine control is performed, for example, as shown in FIG.

That is, when the shift lever is switched, t
_{At 1} , the stopped engine starts. Immediately after the completion of the start (time t ₂ ), unless the accelerator pedal is depressed by a predetermined opening degree or more, the engine load becomes small, so that the lean mode is selected, and the actual A / F becomes lean. Thereafter, if the accelerator pedal is depressed by a predetermined degree or more (time point t ₃ ), the output becomes insufficient in the lean mode and the vehicle exits the lean mode.

After exiting the lean mode, the stoichiometric mode is normally selected. However, as described above, the O ₂ feedback control (O ₂ feedback control) is performed until it is confirmed that the O ₂ sensor 40 is in the active state after the engine is started. (Stoichiometric mode)
In this case, when exiting the lean mode, the open loop mode is selected by the open loop control to make the air-fuel ratio near stoichiometric or rich. In other words, in lean mode after starting the engine,
Since the output of the O ₂ sensor 40 is 0 (the output voltage is almost 0), the O ₂ sensor 40 is determined to be inactive, and the A / F feedback flag (stoichiometric mode flag) is prohibited (stoichiometric mode selection prohibited). Therefore, when leaving the lean mode, the open loop mode is selected.

As described above, when the open-loop mode is selected, although the air-fuel ratio is set close to stoichiometry, the actual air-fuel ratio is not confirmed and the control is performed as in the case of O ₂ feedback control, but the fuel injection amount is reduced. Since the fuel ratio feedback correction coefficient (A / F / F / B coefficient) C _FB is held at 1 (no correction), when the actual value of the base air-fuel ratio is shifted to the lean side, for example, the lean mode is exited. Also,
The output of the O ₂ sensor 40 remains 0 and the O ₂ sensor 40
May be continuously determined to be in the inactive state. in this case,
The A / F feedback flag remains in the prohibited state. Therefore, even after exiting the lean mode, the stoichiometric mode by the O ₂ feedback control is not easily selected,
Since the operation state that is slightly leaner than the stoichiometric state (of course, the operation state closer to stoichiometric than the lean mode) continues,
NOx emissions will increase significantly.

As described above, the engine is restarted after stopping.
If you leave Lean mode later, _TwoInactivate sensor 40
The situation in which the gender determination state continues is the idle stop system.
Only at idle stop in HEV with stem
To general cars (cars driven only by the engine)
Driving at idle stop or HEV
It can also occur when the engine driving force is added to the vehicle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and can prevent deterioration of exhaust gas after restarting an engine in a vehicle equipped with an idle stop system or a hybrid electric vehicle equipped with a lean burn engine. An object of the present invention is to provide a control device for a lean burn engine.

[0020]

For this reason, in the control apparatus for a lean burn engine of the present invention, the combustion mode selecting means includes:
A lean combustion mode in which the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio to perform combustion based on the operating state of the engine detected by the operating state detecting means, and the air-fuel ratio is controlled by feedback control based on the detection result of the air-fuel ratio sensor. Either the feedback mode, in which the fuel ratio is controlled near the stoichiometric air-fuel ratio, and combustion, or the open-loop mode, in which the air-fuel ratio is controlled near the stoichiometric air-fuel ratio or enriched from the stoichiometric air-fuel ratio by open-loop control to perform combustion. Select the combustion mode. At this time, whether or not the air-fuel ratio sensor is in an active state is determined by the active state determining means, and when the engine is in a specific operating state, the combustion mode selecting means determines whether the air-fuel ratio sensor is in a specific operating state according to the determination result of the active state determining means. The feedback mode is selected when the air-fuel ratio sensor is active, and the open-loop mode is selected when the air-fuel ratio sensor is inactive.

The automatic stopping / restarting means automatically stops and restarts the engine under predetermined conditions, and the activation state determining means always makes the engine idle based on the output of the air-fuel ratio sensor. It is determined whether or not the fuel ratio sensor is in an active state. Immediately after the engine is automatically restarted by the automatic stop / restart means, regardless of the output of the air / fuel ratio sensor, Is pseudo-determined to be in the active state. Accordingly, the combustion mode selection means is configured to execute the feedback mode immediately after the engine is automatically restarted, when the engine enters a specific operating state based on the result of the pseudo determination by the activation state determination means. Is selected (above, claim 1).

The automatic stop and restart of the engine by the automatic stop / restart means includes, for example, idle stop and release of idle stop in an idle stop system, and a vehicle driving or power generation engine in a hybrid electric vehicle. Automatic stop and automatic restart. Further, for example, the air-fuel ratio sensor has a characteristic in which the output changes suddenly in the vicinity of the stoichiometric air-fuel ratio, and the activity of the air-fuel ratio sensor is determined based on whether the output of the air-fuel ratio sensor changes suddenly. It is preferable that the determination be made based on the fact that the output of the air-fuel ratio sensor has reached a predetermined level.

Further, it is preferable that after the pseudo determination that the air-fuel ratio sensor is in the active state immediately after the restart, the activation state determining means shifts to a normal determination based on the output of the air-fuel ratio sensor. Thereby, when the air-fuel ratio sensor is actually in an inactive state when the engine is automatically restarted, the inactive state can be quickly and reliably determined. In the combustion mode selection means, the inconvenience of selecting the open loop mode without fail and selecting the feedback mode in an inactive state is avoided (claim 2).

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a lean-burn engine control apparatus according to an embodiment of the present invention; FIG. The lean burn engine according to the present embodiment is a spark ignition type direct injection gasoline engine (hereinafter also referred to as a direct injection gasoline engine or simply an engine), and the engine is mounted on an automobile. First,
The configuration of the engine will be described.

As shown in FIG. 2, the cylinder head 2 of the engine 1 is provided with a fuel injection valve 6 as a fuel injection means which opens directly into a combustion chamber 5 together with a spark plug 4 for each cylinder 3. The ignition plug 4 is driven by an ignition coil 4A, and the fuel injection valve 6 is driven by a driver 6A. A piston 8 connected to a crankshaft 7 is provided in the cylinder 3, and a hemispherically concave cavity 9 is formed on a top surface of the piston 8. The fuel injection valve 6 can inject fuel directly into the cylinder during the intake stroke of the engine, and also functions as intake stroke fuel injection means.

The cylinder head 2 has an intake port 11 that can communicate with the combustion chamber 5 via an intake valve 10 and an exhaust port 13 that can communicate with the combustion chamber 5 via an exhaust valve 12. The intake port 11 is disposed substantially vertically above the combustion chamber 5, and cooperates with the cavity 9 on the top surface of the piston 8 to form a reverse tumble flow by intake air in the combustion chamber 5. A water temperature sensor 16 for detecting a cooling water temperature is provided on a water jacket 15 on the outer periphery of the cylinder 3, and a crank angle sensor 17 for outputting a signal at a predetermined crank angle position is provided on the crankshaft 7. Each of the camshafts 18 and 19 for driving the cylinder 12 is provided with a cylinder identification sensor (cam angle sensor) 20 for outputting a cylinder identification signal according to the position of the camshaft. Since the engine rotation speed can be calculated based on the crank angle signal, the crank angle sensor 17 also functions as engine rotation speed detection means.

The intake system includes an air cleaner 21,
Intake pipe 22, throttle body 23, surge tank 2
4, the intake manifold 25 is arranged in this order, and the intake port 11 is provided at the downstream end of the intake manifold 25. The throttle body 23 is provided with an electronically controlled throttle valve (ETV) 30 as air amount adjusting means for adjusting the amount of air flowing into the combustion chamber 5.
The opening degree control of 0 can perform not only control according to the accelerator opening degree, but also idle speed control and control for introducing a large amount of intake air during lean operation, which will be described later.

Further, immediately downstream of the air cleaner 21, an air flow sensor 37 for detecting an intake air flow rate is provided.
The throttle body 23 has a throttle position sensor 38 for detecting the throttle opening of the ETV 30 and an ETV 3
And an idle switch 39 for detecting the fully closed state of 0 and outputting an idle signal. Since the volume efficiency Ev can be calculated from the intake air flow rate, the air flow sensor 3
7 also functions as a volume efficiency calculating means.

The exhaust system includes an exhaust manifold 26 having an exhaust port 13 and an exhaust pipe 27 in this order from the upstream side. A three-way catalyst 29 for purifying exhaust gas is interposed in the exhaust pipe 27, and the exhaust manifold 26 is provided in the exhaust manifold 26. And an O ₂ sensor 40 as an air-fuel ratio sensor. Although the fuel supply system is not shown, fuel whose pressure has been adjusted to a predetermined high pressure (about several tens of atmospheres (for example, about 2 to 7 MPa)) is guided to the fuel injection valve 6, and the high-pressure fuel is supplied from the fuel injection valve 6. Is to be injected.

Further, there are provided an accelerator position sensor (hereinafter, referred to as APS) 42 for detecting an accelerator pedal depression amount (accelerator position) θap, and a shift lever position sensor 43 for detecting a shift lever position of the transmission. . Then, the spark plug 4, the fuel injection valve 6, the E
An electronic control unit (ECU) 60 having a function as an engine control unit is provided to control the operation of each engine control element such as a TV 30 and a starter (not shown). The ECU 60 includes an input / output device, a storage device for storing a control program, a control map, and the like;
A central processing unit, a timer, a counter, and the like are provided. The ECU 60 controls each of the above-described engine control elements based on detection information from the various sensors described above, key switch position information, and the like. It has become.

In particular, the present engine is a direct injection engine, which can perform fuel injection at an arbitrary timing, and atomizes fuel and mixes it with air by fuel injection (intake stroke injection) centering on the intake stroke. In addition to performing uniform combustion by promoting uniform combustion while accelerating fuel injection, the air-fuel mixture is collected in the vicinity of the spark plug 4 by fuel injection (compression stroke injection) centering on the compression stroke, utilizing the above-described reverse tumble flow to achieve stratified combustion. Can be performed. As an operation mode (combustion mode) of the present engine, an O ₂ feedback mode (stoichiometric mode) in which the air-fuel ratio is kept close to the stoichiometric air-fuel ratio by feedback control based on information detected by the O ₂ sensor 40.
An open-loop mode (including an enrichment mode) in which the air-fuel ratio is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and a lean-burn mode in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio to perform lean combustion by uniform combustion ( (Intake lean mode) and super-lean combustion (super-lean operation) using the above-mentioned stratified combustion with the air-fuel ratio being significantly leaner than the stoichiometric air-fuel ratio
And a lean burn mode (compression lean mode).

In the ECU 60, based on a map (not shown), one of the operation modes according to the engine speed (hereinafter referred to as engine speed) Ne and the target value (target Pe) of the average effective pressure Pe indicating the engine load state. When the engine speed Ne is small and the target Pe is small, the lean mode is selected. As the engine speed Ne and the target Pe increase, the operation mode is selected in the order of stoichiometry and enrichment. I will do it.

The engine speed Ne is calculated from the output signal of the crank angle sensor 17, and the target Pe is calculated from the engine speed Ne and the accelerator position (accelerator opening) detected by the APS 42. Further, it is assumed that the engine according to the present embodiment is provided in, for example, an HEV having an idle stop system as shown in FIG. That is, as shown in FIG. 6, the HEV is connected to the motor 101 and the transmission 10 by the rotating shaft 101A of the motor 101.
2, clutch 103 and differential (differential) 10
4 and an engine 107 connected via a clutch 16 to a rotating shaft 101A of the motor 101. An O ₂ sensor 40 is provided in an exhaust passage 108 of the engine 107 from upstream. , An exhaust gas purification catalyst 29 is interposed.

Normally, the clutch 106 is released and the vehicle travels only by the canter power of the motor 101. When a large driving force is required, the clutch 106 is connected and the engine 107 is connected to the driving force of the vehicle. When the remaining capacity of the battery is low, the clutch 106 is connected to make the motor 101 function as a generator, and the engine 107 is used as a power generating engine.

In the course of driving by the engine,
If the idle stop condition that the vehicle is stopped, the engine 107 is idle and the shift lever position is neutral is satisfied, the idle stop is executed, and if any of the conditions is not satisfied, the idle stop is released. In order to realize such engine control,
The ECU 60 is provided with a function of automatically starting, stopping, and restarting the engine (automatic stop / restart means).

Here, a control device for the lean burn engine of the present embodiment for performing such engine control will be described with reference to FIG. As shown in FIG.
The automatic stop / restart means 61 for automatically starting, stopping and restarting the engine, the combustion mode selecting means 62 for setting a combustion mode (operation mode) from the engine operating state, and the combustion mode selecting means 62 Fuel injection valve 6, spark plug 4, ETV based on the operation mode set in
Each functional element such as a fuel injection valve control means 63, an ignition plug control means 64, and an ETV control means 65 for controlling the operation of the fuel injection valve 30 is provided. Of course, in addition to this, the ECU 60 also has a function of controlling various other engine control elements.

The automatic stop / restart means 61 includes an engine request response control section 61a and an idle stop control section 61a.
b is provided. The engine demand response control unit 61a increases the driving torque of the vehicle when the driving torque of the vehicle is insufficient only with the canter power of the motor 101, or increases the remaining power of the battery (not shown). In order to drive 101 as a generator,
Starting the stopped engine, and then starting the motor 10
The engine is stopped when the driving torque is satisfied with only one canter power or when the remaining capacity of the battery has recovered to a predetermined remaining capacity. In the idle stop control unit 61b,
Based on information from a crank angle sensor (engine rotational speed detecting means) 17 as an engine operating state detecting means, an idle switch 39, and a shift lever position sensor 43, the vehicle is stopped, the engine is in an idle state, and the shift lever position is neutral. The idle stop condition is determined. If the idle stop condition (&&) is satisfied during the operation of the engine, the idle stop (engine stop) is performed. If the idle stop condition is not satisfied during the idle stop, the engine is restarted.

In the combustion mode selection means 62, as described above, the feedback control mode (stoichiometric mode) is performed using a map or the like according to the engine operating state, that is, the engine speed Ne and the engine load (for example, the target Pe). ,
One of the operation modes is selected from the open loop control mode (including the enrichment mode), the lean burn control mode (intake lean mode), and the lean burn control mode (compression lean mode).

However, since the stoichiometric mode is a feedback control based on the detection result of the O ₂ sensor (air-fuel ratio sensor) 40, the control is established unless the O ₂ sensor 40 is in an active state and cannot output correct detection information. do not do. That is, if the O ₂ sensor 40 is out of order due to a failure or a malfunction, the erroneous detection information is output from the O ₂ sensor 40, and feedback is performed based on such erroneous detection information. When the control is performed, the actual air-fuel ratio gradually departs from the stoichiometric air-fuel ratio (stoichiometric), and the combustion deteriorates, leading to a reduction in fuel consumption performance and exhaust gas performance. As described above, when the O ₂ sensor (air-fuel ratio sensor) 40 is inactive, controlling the air-fuel ratio A / F in an open loop gives a better combustion state, and improves the fuel efficiency and exhaust gas performance. Can be secured.

Therefore, the O ₂ sensor 4 is provided in the ECU 60.
A function (active state determining means) 66 for determining whether or not 0 is in an active state is provided.
The selection of the stoichiometric mode is allowed or prohibited. That is, when the O ₂ sensor 40 is in the active state, the air-fuel ratio feedback control permission flag (A / FF-B / F flag) relating to whether or not the stoichiometric mode can be selected by the air-fuel ratio feedback control (O ₂ feedback control) is set as follows: Turn on (stoichiometric mode selection permitted). If the O ₂ sensor 40 is in an inactive state, A / F-F
The / B flag is turned off (selection of the stoichiometric mode is prohibited).

In general, the O ₂ sensor (air-fuel ratio sensor) 40 depends on the temperature, but when a predetermined temperature is reached, the O ₂ sensor switches between the lean side and the rich side beyond the stoichiometric (stoichiometric air-fuel ratio). The output changes suddenly, producing an almost on / off output signal. Therefore, when thus the output value of the O ₂ sensor 40 changes suddenly, although the O ₂ sensor can be determined to be in the active state, more simple, the O ₂ sensor 4
When the output value of 0 exceeds a predetermined value, it can be determined that the O ₂ sensor 40 is in the active state.

In this embodiment, when the air-fuel ratio goes from the lean side to the rich side with respect to stoichiometry (the amount of oxygen in the exhaust gas becomes small) as in a zirconia oxygen sensor generally widely used, the output voltage value becomes large. An active state determination unit 66 uses a sensor having a characteristic that increases stepwise from substantially zero.
In Once beyond the O ₂ sensor output values 40 (output voltage) is a preset reference value, O ₂ sensor 40 is adapted to determined to be in the active state (this is called in the active mode) .

Conversely, the fact that the output value (output voltage) of the O ₂ sensor 40 does not exceed the preset reference value is due to the fact that the O ₂ sensor 40 has actually failed. The O ₂ sensor 40 is normal, but it is not clear whether it is because the air-fuel ratio is simply lean or not. However, during the O ₂ feedback control, the output voltage value of the O ₂ sensor 40 must always exceed the reference value periodically, and during the O ₂ feedback control, the output voltage value of the O ₂ sensor 40 exceeds the reference value for a long time. If not, these can be determined to be due to a failure of the O ₂ sensor 40. Therefore, the activation state determining means 66 determines that O ₂
During feedback control, that is, during stoichiometric mode,
_{When the} state in which the output voltage value of the ₂ sensor 40 does not exceed the reference value continues for a predetermined time or more, the O ₂ sensor 40
Is determined to be inactive due to a failure (this is referred to as an inactive mode).

As described above, since the determination of the activation / inactivation of the O ₂ sensor 40 cannot be performed under the predetermined condition, the activation state determination means 66 holds the latest determination result unless the engine is stopped. It is supposed to. Although it is impossible to determine the activation of the O ₂ sensor 40 when the engine is stopped, in the present embodiment, when the engine is stopped,
The O ₂ sensor 40 is set to be inactive (inactive mode). Therefore, when starting the engine,
Assuming that the O ₂ sensor 40 is inactive, the engine control is started. This takes into account the cold start of the engine, and the O ₂ sensor 40 becomes inactive in the cold state even if it has not failed, and does not react even if the air-fuel ratio is rich (the output voltage is low). Does not increase). Therefore, when starting the engine, in principle, the O ₂ sensor 40
Is pseudo-determined to be inactive and performs engine control.

However, in addition to stopping and starting the engine by operating the driver,
As described above, the automatic stop / restart means 61 starts the engine when the engine output is requested, and stops the engine when the engine output request is stopped. When the idle stop condition (&&) is satisfied, an idle stop (engine stop) is performed, and when the idle stop condition is not satisfied during the idle stop, the engine is restarted.

Such an automatic engine stop or engine start can occur many times during one run (between the time the driver starts the engine and the time it is stopped). It is unlikely that the O ₂ sensor 40 is cold. In particular, by setting the idle stop to be executed on condition that the engine is warmed up, even if the activation determination of the O ₂ sensor 40 is impossible, the O ₂ sensor In most cases, 40 is in an active state.

Even in such a case, if the O ₂ sensor 40 is falsely determined to be inactive at the time of engine start, most of the time, the O ₂ sensor 40 is in the active state and the stoichiometric mode is set. Although it can be selected, this is prohibited and the open loop mode is selected. When the O ₂ sensor 40 is in the active state, the stoichiometric mode can perform combustion more efficiently than the open loop mode, and is surely advantageous in terms of exhaust gas and fuel efficiency.

[0048] Therefore, in the active state determining unit 66, the automatic stop and restart means 61, when the engine is restarted, O ₂ sensor 40 is adapted to If it is active pseudo determination. Of course, starting not according to the automatic stop and restart means 61, i.e., at start-up by the driver of the operation, as described above, in consideration of the time cold-start of the engine, in the active state determining unit 66, O ₂ sensor 40
Are pseudo-determined to be inactive.

Therefore, the combustion mode selection means 62 determines the activation state based on the determination result of the activation state determination means 66.
When the engine is restarted by the automatic stop / restart means 61, the stoichiometric mode is promptly selected when the engine is in an operating state corresponding to the stoichiometric mode. Even if a corresponding operation state is established, the stoichiometric mode is not selected until the activation state of the O ₂ sensor 40 is confirmed.

In the activation state determining means 66, the O ₂ sensor 4
0 even when the pseudo determined If it is active, since then be selected stoichiometric mode immediately active and non-active of the O ₂ sensor 40 can be determined from the actual output of the O ₂ sensor 40, O ₂ sensor Even when 40 is actually inactive, this can be quickly determined to avoid inappropriate mode selection. Further, even when the O ₂ sensor 40 is pseudo-determined to be in the inactive state, by executing the enriched open loop mode, the O ₂ sensor 40
Unless failed, the O ₂ sensor 40 rises in temperature and becomes active, so that the output voltage of the O ₂ sensor 40 exceeds a predetermined value, and the O ₂ sensor 40 is in the active state by the active state determination means 66. Is determined, and the stoichiometric mode can be selected.

The fuel injection valve control means 63 uses the maps and the like provided according to the set operation mode to determine the engine operation state, that is, the engine speed Ne, the engine load [for example, the target Pe or Ev ( Volumetric efficiency)]
And controls the fuel injection valve 6 by setting the fuel injection amount and the fuel injection timing. Specifically, the start timing and the end timing of the fuel injection (both corresponding to the crank angle) are set, and the fuel injection valve 6 is controlled based on this.

The ignition plug control means 64 also uses the map provided according to the set operation mode and the like, based on the engine operation state, that is, the engine speed Ne and the engine load (for example, target Pe or Ev). The ignition plug 4 is controlled by setting the ignition timing. ETV control means 6
5, the accelerator opening and the engine operation state, that is, the engine speed Ne and the engine load (for example, the target P) are determined using a map provided according to the set operation mode.
e or Ev), the target opening of the ETV 30 is set and the ETV 30 is controlled.

The control device for the lean burn engine as one embodiment of the present invention is configured as described above.
For example, as shown in FIGS. 3 and 4, the activation / inactivation of the O ₂ sensor (air-fuel ratio sensor) 40 is determined. That is, as shown in FIG.
As a result of 10), when the engine is stopped, it is simulated that the O ₂ sensor 40 is in the inactive state (step A20).

When the engine is started, as shown in FIG. 4, it is determined whether or not the engine is being started (before the start is completed) (step B10). If the engine is being started, the process proceeds to step B20 to start the engine. It is determined whether or not the automatic start is performed by the automatic stop / restart means 61. If the start is automatic, the process proceeds to step B30, where it is determined that the O ₂ sensor 40 is in the active state, and the inactivity timer (timer value T ₀₂ ) is reset to 0 (step B14).
0).

If it is not an automatic start, that is, if it is a start by a driver's operation, the process proceeds from step B20 to step B40, in which the O ₂ sensor 40 is falsely determined to be in an inactive state, and an inactivity timer ( The timer value T ₀₂ is reset to 0 (step B140). On the other hand, if the engine is not being started, it means that the engine is operating (after the start is completed), and the process proceeds to step B50 to determine whether or not the operation mode of the engine is the stoichiometric mode. If the operation mode is the stoichiometric mode, the process proceeds to step B60 to determine whether the output voltage value V _O2 of the O ₂ sensor 40 is less than the predetermined value V ₁ .

Here, if the output voltage value V _O2 is less than the predetermined value V ₁ , the air-fuel ratio is leaner than the stoichiometric value, so the routine proceeds to step B80, where the air-fuel ratio feedback of the fuel injection amount (fuel injector driving time) is performed. The use correction coefficient C _FB is increased by a predetermined minute amount to increase the fuel injection amount. That is, a value obtained by adding a predetermined minute amount α to the correction coefficient C _FB (n−1) of the previous control cycle is used as the correction coefficient C _FB of the current control cycle.
_FB as _{(n) [C FB (n} ) = C FB (n-1) + α],
Set the fuel injection amount.

[0057] Then, increments the value T ₀₂ of inactivity timer (step B100), inactivity timer value T ₀₂ is whether it is ₁ or greater than a predetermined value T is determined (step B 110). If the stoichiometric mode is continued, the output voltage value V _O2 of the O ₂ sensor 40 is controlled by the feedback control.
There if a predetermined value V _1, less than the output voltage value V _O2 until a predetermined value V ₁ above, increases corrects the fuel injection amount (step B8
0) so, O ₂ sensor 40 is in the normal (active state), then the output voltage V _O2 is not able to continue longer than a predetermined time the state less than the predetermined value V _1.

The value T ₀₂ of the inactivity timer is equal to the output voltage value V _O2
There shows the time the state of less than the predetermined value V ₁ is continued. Therefore, determining the value T ₀₂ inactive timer Once becomes ₁ or greater than a predetermined value T, O ₂ sensor 40 is not normal and (in an inactive state) (step B 120). Then, the inactivity timer (timer value T ₀₂ ) is reset to 0 (step B140).

The value T of the inactivity timer₀₂Is a predetermined value T₁Above
If not, O_TwoThe activity and inactivity of the sensor 40
The judgment result up to this point is retained. On the other hand, the operation mode
In the live mode, in step B60,_TwoSensor 4
0 output voltage value V_O2Is the predetermined value V₁Was not less than
Air-fuel ratio is richer than stoichiometric,
Proceeding to step B90, the fuel injection amount (fuel injector drive time)
Correction coefficient C for air-fuel ratio feedback_FBThe predetermined minute amount
Only to decrease the fuel injection amount. That is,
Control cycle correction coefficient C_FB(N-1) is a predetermined minute amount α
The subtracted value is used as the correction coefficient C for the current control cycle._FB(N)
As [C _FB(N) = C_FB(N-1) -α], fuel injection
Set the amount.

Then, the output voltage value V _O2 of the O ₂ sensor 40
Since but a predetermined value V ₁ or more, it is determined that the O ₂ sensor 40 is normal (in an active state) (step B 130),
The inactivity timer (timer value T ₀₂ ) is reset to 0 (step B150). On the other hand, if it is determined that the operation mode of the engine is not the stoichiometric mode at step B50 while the engine is operating (after the start is completed),
Proceeding to 70, it is determined whether the output voltage value V _O2 of the O ₂ sensor 40 is equal to or greater than a predetermined value V ₁ . Here, the output voltage value V _O2
There if a predetermined value V ₁ or more, O ₂ sensor 40 is normal is determined (the is active) (step B 130), the inactivity timer (timer value T ₀₂₎ is reset to 0 (step B150).

[0061] Also, to reset when the output voltage value V _O2 of the O ₂ sensor 40 in step B70 is determined not to be a predetermined value V ₁ or more inert timer (timer value T ₀₂₎ to 0 (step B150), The results of the previous determination regarding the activation / inactivation of the O ₂ sensor 40 are retained. In this way, when the engine is restarted by the automatic control, it is simulated that the O ₂ sensor 40 is in the active state. Therefore, the combustion mode selection means 62 allows the selection of the stoichiometric mode immediately after the restart. When the operating state of the engine (engine speed or engine load) becomes suitable for the stoichiometric mode, the stoichiometric mode is immediately selected,
By the O ₂ feedback control, the air-fuel ratio is accurately controlled to be close to the stoichiometric state, and the engine is operated.

For example, FIG. 5 is a time chart showing the situation when such an engine is restarted. The solid line shows the present embodiment, and the dashed line shows the conventional technique (see FIG. 7). As shown in FIG. 5, the shift lever is switched at time t _1, an engine that has been stopped by the idle stop control is assumed to start. In this case, usually, start the engine when there is a predetermined response delay, start completed at a later time t _2. At this time, from the start start command (time t ₁ ), it is pseudo-determined that the O ₂ sensor 40 is in the active state (active mode), so that the A / F feedback flag (stoichiometric mode) is started from the engine start completion time t _2. Flag) is turned on (stoichiometric mode selection permitted).

Immediately after the start, unless the accelerator pedal is depressed by a predetermined opening degree or more, the engine load becomes small, so that the lean mode is selected and the actual air-fuel ratio (actual A / A /
F) The actual A / F becomes lean. However, if the accelerator pedal is depressed by a predetermined opening degree or more (time point t ₃ ), the output becomes insufficient in the lean mode and the vehicle exits the lean mode.
Since the / F feedback flag indicates that stoichiometric mode selection is permitted, the stoichiometric mode is normally selected (unless the accelerator pedal is depressed to the maximum opening degree).

When the stoichiometric mode is selected, the stoichiometric mode is executed after a response delay, the actual A / F changes from lean to rich, and thereafter, based on the output of the O ₂ sensor 40 responding to the actual A / F. Thus, the air-fuel ratio feedback correction coefficient (A / FF-B coefficient) C _{FB of} the fuel injection amount is set so that the air-fuel ratio swings rich and lean near the stoichiometric ratio.

Therefore, the air-fuel ratio can be kept well in the vicinity of the stoichiometric ratio, the combustion can be performed efficiently and satisfactorily, and the three-way catalyst 29 also operates efficiently.
As shown by the solid line, the amount of NOx emission is greatly reduced as compared with the related art (see the dashed line). Further, the engine output and the fuel efficiency are compatible. Further, after the pseudo determination that the air-fuel ratio sensor 40 is in the active state immediately after the restart of the engine, the activation determination of the air-fuel ratio sensor 40 is performed as usual based on the output of the air-fuel ratio sensor 40.
If the air-fuel ratio sensor 40 is actually in an inactive state when the engine is automatically restarted, the inactive state can be quickly and reliably determined. As a result, a problem that the feedback mode is selected even when the air-fuel ratio sensor 40 is inactive is avoided, and inappropriate feedback control can be selected. It is possible to suppress deterioration of fuel efficiency and exhaust gas.

The above-described embodiment is an example, and the present invention is not limited to this embodiment. Various modifications of the above-described embodiment may be made without departing from the spirit of the present invention. be able to. For example, in the above-described embodiment, when the engine is automatically stopped, the air-fuel ratio sensor 40 is falsely determined to be in an inactive state. However, from the time of automatic engine stop, the air-fuel ratio sensor 40 is falsely determined to be active. You may.

In the above-described embodiment, when the engine is restarted from an automatic stop, the air-fuel ratio sensor 40 is always pseudo-determined to be in an active state immediately after the restart. Air-fuel ratio sensor 4
Although it is pseudo-determined that the air-fuel ratio sensor 40 is in an inactive state, it is necessary to pseudo-determine that the air-fuel ratio sensor 40 is in an inactive state. , The air-fuel ratio sensor 40 is pseudo-determined to be inactive, and if the engine has been warmed up, the air-fuel ratio sensor 4
You may comprise so that 0 may be pseudo-determined that it is an active state.

When the engine is started by the driver's operation, the air-fuel ratio sensor 40 is always pseudo-determined to be in an inactive state.
If the engine is not cold (i.e., if the warm-up is completed), the pseudo determination may be made immediately after the restart that the air-fuel ratio sensor 40 is in the active state. In this case, the cold state of the engine may be determined to be cold if the cooling water temperature (or oil temperature) is equal to or lower than a predetermined temperature using the cooling water temperature of the engine or the oil temperature of the engine oil. If the stop time is longer than a predetermined time, it may be determined that the engine is cold.

[0069]

As described above in detail, according to the control system for a lean burn engine of the present invention, it is always determined whether or not the air-fuel ratio sensor is in an active state based on the output of the air-fuel ratio sensor. Immediately after the engine is automatically restarted by the automatic stop / restart means, the pseudo-determination is made that the air-fuel ratio sensor is in the active state regardless of the output of the air-fuel ratio sensor. When the engine is in a specific operating state, the feedback mode is selected if the air-fuel ratio sensor is active, and the open-loop mode is selected if the air-fuel ratio sensor is inactive. . Therefore, the feedback mode can be selected immediately after the restart of the engine, and immediately after the restart of the engine, the engine output and the fuel efficiency are balanced while the air-fuel ratio is feedback-controlled near the stoichiometric air-fuel ratio. Exhaust gas purification can be promoted (claim 1).

After a pseudo determination that the air-fuel ratio sensor is in an active state immediately after restarting the engine, the routine automatically shifts to a normal determination based on the output of the air-fuel ratio sensor. When the air-fuel ratio sensor is actually in an inactive state, the inactive state can be promptly and reliably determined. Select a mode,
The problem of selecting the feedback mode in the inactive state is avoided, inappropriate feedback control can be avoided, deterioration of combustion can be suppressed, and fuel consumption and exhaust gas can be suppressed ( Claim 2).

[Brief description of the drawings]

FIG. 1 is a control block diagram showing a control device for a direct injection engine as one embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a direct injection engine according to an embodiment of the present invention.

FIG. 3 is a flowchart showing control contents according to a control device for a lean burn engine as one embodiment of the present invention.

FIG. 4 is a flowchart showing control contents according to a control device for a lean burn engine as one embodiment of the present invention.

FIG. 5 is a time chart showing a specific example of engine control according to the control device for a lean-burn engine as one embodiment of the present invention, where (a) shows NOx emissions and (b)
Indicates an air-fuel ratio feedback correction coefficient C _FB of the fuel injection amount, (c) indicates an O ₂ sensor output, (d) indicates an air-fuel ratio feedback flag (A / F-F / B flag), e) shows the state of the O ₂ sensor activity judgment, and (f)
Indicates an actual air-fuel ratio (actual A / F), (g) indicates an engine operation mode (combustion mode), (h) indicates an engine speed, and (i) indicates a throttle opening (TPS). Show.

FIG. 6 is a schematic diagram illustrating a configuration example of a drive system of a hybrid electric vehicle.

7A and 7B are time charts for explaining a problem in the control of the conventional lean burn engine, in which FIG. 7A shows the NOx emission amount, FIG. 7B shows the air-fuel ratio feedback correction coefficient C _FB of the fuel injection amount, (C) shows the O ₂ sensor output,
(D) is an air-fuel ratio feedback flag (A / F-F /
B), (e) shows the state of the O ₂ sensor activation determination, (f) shows the actual air-fuel ratio (actual A / F),
(G) shows the operation mode (combustion mode) of the engine,
(H) shows the engine speed, and (i) shows the throttle opening (TPS).

[Explanation of symbols]

Reference Signs List 1 engine 17 crank angle sensor (engine rotation speed detecting means) as engine operating state detecting means 39 idle switch 40 O ₂ sensor as air-fuel ratio sensor 43 shift lever position sensor 61 automatic stop / restart means 62 combustion mode selecting means 66 Active state determination means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/14 310 F02D 41/14 310B (72) Inventor Satoshi Yoshikawa 5-33-8 Shiba 5-chome, Minato-ku, Tokyo No. Mitsubishi Motors Industry Co., Ltd. (72) Inventor Kazuhiko Kawasaki 4-21-1, Shimomaruko, Ota-ku, Tokyo Mitsubishi Motors Engineering Co., Ltd. (72) Taketoshi Hirata 4-2-1, Shimomaruko, Ota-ku, Tokyo Mitsubishi 3G084 AA04 BA09 BA13 BA17 BA28 CA01 CA02 DA02 DA10 EA07 EB12 FA02 FA03 FA06 FA07 FA10 FA20 FA26 FA29 FA36 FA38 FA39 3G093 AA04 AA07 BA19 BA20 BA21 BA22 CA01 CA02 CA03 DA01 DA11 DA09 DA11 DA13 DB06 DB12 EA03 EA04 EA05 EA09 EA12 EC02 FA06 FA08 FA11 FB01 FB02 3G301 HA01 HA04 HA15 H A16 JA02 JA25 JA26 JA29 KA01 KA04 LA03 LB04 LC02 LC04 MA01 MA14 NA07 NA08 NB05 NC04 ND04 ND13 NE13 NE15 PA01Z PA11A PA11Z PA14Z PD02A PD02Z PD13Z PE01Z PE03Z PE04Z PE08Z PE09Z PF01Z PF03Z PF10Z PF10Z PF10Z

Claims (2)

[Claims] An air-fuel ratio sensor for detecting an air-fuel ratio of a combustion mixture by detecting an exhaust gas component, a lean combustion mode for performing combustion by controlling the air-fuel ratio to be leaner than a stoichiometric air-fuel ratio; A feedback mode in which the air-fuel ratio is controlled to near the stoichiometric air-fuel ratio by feedback control based on the detection result of the fuel ratio sensor to perform combustion, and an open-loop control controls the air-fuel ratio to near the stoichiometric air-fuel ratio or to a richer side than the stoichiometric air-fuel ratio An activation state determining means for determining whether or not the air-fuel ratio sensor is in an active state; and an operating state of the engine. Operating state detecting means for detecting the combustion mode; and setting the combustion mode based on the detection result of the operating state detecting means, and when the engine is in a specific operating state. A combustion mode selecting means for selecting the feedback mode when the air-fuel ratio sensor is active, and selecting the open loop mode when the air-fuel ratio sensor is inactive, according to a determination result of the activation state determining means; Automatic stop / restart means for automatically stopping and restarting the engine under the following conditions: the activation state determination means always activates the air-fuel ratio sensor based on the output of the air-fuel ratio sensor. It is determined that the air-fuel ratio sensor is in an active state immediately after the engine is automatically restarted by the automatic stop / restart means regardless of the output of the air-fuel ratio sensor. In addition to the pseudo determination, the combustion mode selection means sets the engine to a specific operating state immediately after the engine is automatically restarted based on the result of the pseudo determination by the activation state determination means. And selects the feedback mode Once Tsu,
Control device for lean burn engine. 2. The method according to claim 2, wherein the activation state determination means determines that the air-fuel ratio sensor is in an activation state immediately after the restart.
2. The control device for a lean-burn engine according to claim 1, wherein the control shifts to a normal determination based on an output of the air-fuel ratio sensor.