JPH11280524A - Air/fuel ratio control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means capable of accelerating warming-up of an engine or a temperature rise of an exhaust emission purifying catalyst and quickly starting feedback control of air/fuel ratio while suppressing a torque fluctuation in a permissible range regardless of a nature or the like of fuel. SOLUTION: In a engine system A, ignition timing of a spark plug 7 is markedly delayed when an engine 1 is cold started, in this way, warming up of the engine 1 and a temperature rise of three-way catalytic converter in a catalytic converter 27 are accelerated. Roughness control is performed by an ECU35, a torque fluctuation caused by a marked delay angle of the ignition timing is suppressed, and the torque fluctuation is controlled in a permissible range. Here, feedback control of air/fuel ratio is started when a roughness controlled variable becomes zero in all cylinders, and the feedback control can be early started while suppressing the torque fluctuation in a permissible range regardless of a nature or the like of fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention promotes warming-up of an engine or temperature rise of an exhaust gas purifying catalyst by performing a feedback control of an air-fuel ratio and greatly retarding an ignition timing at a cold start. The present invention relates to an air-fuel ratio control device for an engine in which torque fluctuation (roughness) is stabilized by roughness control using at least an air-fuel ratio as a control amount.

[0002]

2. Description of the Related Art Generally, in an automobile engine,
O ₂ obtains the actual air-fuel ratio (actual air-fuel ratio) from the O ₂ concentration in the exhaust gas detected by the sensor, so as to eliminate the deviation based on the deviation of the target air-fuel ratio of the actual air-fuel ratio, that is, the actual air-fuel ratio Feedback control of the air-fuel ratio is performed so as to match the target air-fuel ratio (for example, actual
22546). As described above, when the air-fuel ratio feedback control is performed, the air-fuel ratio is substantially maintained at the target air-fuel ratio, that is, the optimum air-fuel ratio, so that the combustibility of the air-fuel mixture is improved, fuel efficiency is improved, and hydrocarbons are improved.
The emission amount of air pollutants such as (HC), carbon monoxide (CO), and nitrogen oxide (NOx) is reduced, and emission performance is improved.

However, if the air-fuel ratio feedback control is performed in an engine in which the air-fuel ratio feedback control is performed after the engine is started and the engine is still in a cold state, the combustibility of the air-fuel mixture becomes sufficiently stable. As a result, the torque fluctuation (roughness) becomes large, causing a problem that the smooth operation of the engine is impaired. Therefore, in the engine disclosed in Japanese Utility Model Laid-Open No. 6-22546, the start timing of the feedback control of the air-fuel ratio is set according to the lean ratio of the air-fuel ratio. However, in general, the properties or quality of fuel (gasoline) used in an automobile engine vary considerably, and the performance or characteristics of each engine have individual differences. It is very difficult to set properly.

On the other hand, in an automobile engine, a catalytic converter having an exhaust gas purifying catalyst is provided in an exhaust passage for purifying exhaust gas. As such an exhaust gas purifying catalyst, HC, CO and N
Three-way catalysts that can simultaneously purify Ox are widely used, but the three-way catalysts have a relatively low catalytic activity at low temperatures and have the characteristic that they cannot sufficiently exhibit exhaust gas purification performance. . Therefore, in a catalytic converter using a three-way catalyst as an exhaust gas purifying catalyst, when the engine is started from a cold state (during a cold start), the temperature of the exhaust gas is quickly increased after the engine is started. It is necessary to promote the temperature rise (activation) of the purification catalyst. In addition, it is conceivable to provide an electric heater for heating the exhaust gas purifying catalyst to promote the temperature rise of the exhaust gas purifying catalyst. However, in this case, the cost is increased and the power consumption is increased. Occurs.

[0005] In general, when the engine is started from a cold state, it is preferable to start the vehicle after the engine temperature (engine water temperature) has risen to some extent from the viewpoint of improving fuel efficiency and the like. Therefore, in an automobile engine, it is necessary to quickly raise the engine temperature.

Therefore, there has been proposed an engine system in which the ignition timing is greatly retarded at the time of a cold start of the engine to promote an increase in the engine temperature or the exhaust gas temperature (for example, Japanese Patent Application Laid-Open No. 8-218995). Reference). That is, if the ignition timing is greatly retarded in this way, the conversion rate of thermal energy generated by the ignition and combustion of the air-fuel mixture in the combustion chamber to mechanical energy decreases,
To that extent, the thermal energy transmitted to the engine cooling water or the exhaust gas increases, and the warm-up of the engine is promoted, and the temperature rise of the exhaust gas and, consequently, the temperature of the exhaust gas purifying catalyst are promoted.

However, if the ignition timing is greatly retarded in order to promote the warming of the engine or the temperature rise of the exhaust gas purifying catalyst, the output torque of the engine decreases and the combustibility becomes unstable. At low output (low load /
At low revolutions), for example, at the time of idling, torque fluctuation (roughness) becomes large, causing a problem that the smooth operation of the engine is impaired. Therefore, for example, Japanese Patent Laid-Open No. 8-2
In an engine system such as the engine system disclosed in Japanese Patent Application Laid-Open No. 18995, the ignition timing is greatly retarded in order to quickly increase the engine temperature or the exhaust gas temperature at the time of a cold start. Roughness control is performed such that the output torque of the engine is controlled so that the torque fluctuation falls within an allowable limit.

[0008]

By the way, in an engine in which the feedback control of the air-fuel ratio is performed, while the ignition timing is greatly retarded and the roughness control is performed during the cold start, the feedback control of the air-fuel ratio is performed. It is very difficult to set a start time. That is, if the start time of the feedback control of the air-fuel ratio is advanced, the fuel efficiency can be improved and the generation amount of air pollutants such as HC, CO, and NOx can be reduced.
It becomes difficult to suppress torque fluctuations and perform stable roughness control, and, consequently, the temperature rise (activation) of the exhaust gas purification catalyst
As a result, the emission of air pollutants into the atmosphere is not reduced so much. Conversely, delaying the start timing of the air-fuel ratio feedback control stabilizes the roughness control and promotes the temperature rise of the exhaust gas purification catalyst, but increases the amount of air pollutants such as HC, CO, and NOx. As a result, there arises a problem that the emission amount of air pollutants into the atmosphere is not reduced so much.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and performs feedback control of the air-fuel ratio and performs roughness control while significantly retarding the ignition timing during cold start of the engine. Regarding the engine to be performed, it is possible to promote the warm-up of the engine or the temperature rise of the exhaust gas purification catalyst while keeping the torque fluctuation within an allowable range, regardless of the properties of the fuel or individual differences of the engine, and It is an object of the present invention to provide a means for quickly starting the air-fuel ratio feedback control.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an air-fuel ratio control means for controlling an air-fuel ratio and a predetermined engine operating range when the engine is cold (including a semi-warmed state). And a roughness control means for performing roughness control by correcting the air-fuel ratio so that the torque fluctuation state falls within an allowable limit by the roughness control amount (the air-fuel ratio basic value) of the roughness control means. correction amount) exceeds a predetermined value for (e.g., 0) when it becomes reduced to the air-fuel ratio control means O ₂ sensor (e.g., lambda
The air-fuel ratio is feedback-controlled by an O ₂ sensor or a linear O ₂ sensor.

In this air-fuel ratio control device for an engine, the feedback control of the air-fuel ratio is started when the roughness control amount becomes small, so that the torque fluctuation is within an allowable range irrespective of the properties of the fuel or individual differences of the engine. It is possible to promote the warm-up of the engine or the temperature rise of the exhaust gas purifying catalyst while keeping the temperature within the range, and to promptly start the feedback control of the air-fuel ratio. For this reason, fuel economy performance and emission performance are greatly improved.

In the above-described air-fuel ratio control device for an engine, the roughness control means uses, for example, a stoichiometric air-fuel ratio (λ = 1, A / F = 14.7) or an air-fuel ratio (near the stoichiometric air-fuel ratio) based on the stoichiometric air-fuel ratio. For example, it is preferable that roughness control is performed by correcting the air-fuel ratio basic value with A / F = 14) as the air-fuel ratio basic value. If you do this,
In both the λO ₂ sensor and the linear O ₂ sensor, the detection accuracy of the O ₂ concentration (air-fuel ratio) is good near the stoichiometric air-fuel ratio, so the control accuracy of the roughness control is increased, and the fuel efficiency and emission performance are further improved. Enhanced. further,
The transition from the roughness control based on the air-fuel ratio to the feedback control of the air-fuel ratio using the stoichiometric air-fuel ratio as the target air-fuel ratio is facilitated.

In the above-described air-fuel ratio control device for an engine, when the roughness control means performs the roughness control by correcting the air-fuel ratio to the rich side, when the roughness control amount decreases to a predetermined value, the air-fuel ratio is reduced. The control means is O
_It is preferable that feedback control of the air-fuel ratio by _two sensors is performed. In this case, it is more preferable that the air-fuel ratio control means performs the feedback control of the air-fuel ratio by the O ₂ sensor when the roughness control amount is reduced to the predetermined value in all the cylinders. By doing so, warming up the engine or raising the temperature of the exhaust gas purification catalyst is further promoted, and the transition from roughness control of the air-fuel ratio to feedback control of the air-fuel ratio is further facilitated.

In the above-described air-fuel ratio control device for an engine, it is preferable that the air-fuel ratio control means performs open control of the air-fuel ratio when the roughness control amount is larger than a predetermined value for at least one cylinder. By doing so, the roughness control becomes easy.

It is particularly preferable that the air-fuel ratio control device for an engine be provided in an engine in which a catalytic converter having an exhaust gas purifying catalyst is provided in an exhaust passage. In this case, for example, when the engine is started from a cold state, it is possible to promote the temperature rise of the exhaust gas purification catalyst,
Emission performance can be improved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. As shown in FIG. 1, an in-vehicle engine system A equipped with an air-fuel ratio control device according to the present invention is provided with an in-line four-cylinder four-cycle engine 1 using gasoline as fuel. Although not shown in detail, the engine 1 has four cylinders 2 (only one is shown).
Cylinder block 3 provided with
And a cylinder head 4 mounted on the upper surface of the cylinder head. A piston 5 is inserted into each cylinder 2 so as to be able to reciprocate.
Defines a combustion chamber 6. An ignition plug 7 is provided on the ceiling of each combustion chamber 6, and the ignition plug 7 is connected to an ignition circuit 8 including an igniter capable of electronically controlling the ignition timing.

The engine system A further includes a single common intake passage 9 for taking in air from the atmosphere to supply air (intake) to the combustion chamber 6 of each cylinder 2, and a common intake passage 9. And an independent intake passage 10 for each cylinder for receiving air from the cylinder. Here, the upstream end of the common intake passage 9 is connected to an air cleaner 11 for removing dust in the air, and the downstream end is connected to a surge tank 15 for stabilizing the flow of air. The upstream end of each independent intake passage 10 is connected to a surge tank 15, respectively.
The downstream ends respectively communicate with the combustion chamber 6 via the intake valve 12.

In the common intake passage 9, the flow rate of the air (the amount of intake air actually taken into the engine 1) is sequentially stored in the common intake passage 9 from the upstream side in the air flow direction (leftward in the positional relationship in FIG. 1). A hot wire type air flow sensor 13 for detecting, and a throttle valve 14 which is opened and closed according to the depression amount of an accelerator pedal (not shown) to narrow the common intake passage 9
Are provided. Each of the independent intake passages 10 is provided with an injector 16 (fuel injection valve) that receives a fuel injection signal (injection pulse) from an ECU 35 (engine control unit) to be described later and injects fuel. I have. The air cleaner 11 is provided with an intake air temperature sensor 17 for detecting an intake air temperature (air temperature).

Each of the independent intake passages 10 is branched into a first intake passage (intake port) (not shown) and a second intake passage 10a (intake port) (not shown) in the vicinity of the downstream end thereof.
An on-off valve 18 (intake flow enhancement control valve), which is opened and closed by an actuator 18a, is disposed upstream of the branch portion of the two intake passages and immediately upstream of the injector 16.
Here, the open / close valve 18 is notched at the upper end when the valve is closed so that a gap is formed to allow the intake air to flow toward the injector 16 when the valve is closed. When the on-off valve 18 is closed, the air is substantially supplied to the combustion chamber 6 from the cutout, and at this time, a strong tumble is generated in the combustion chamber 6 and the combustibility of the air-fuel mixture is enhanced. .

The portion of the common intake passage 9 upstream and downstream of the throttle valve 14 is an ISC (Idle Speed
Control) connected by a bypass passage 20 and the ISC
The ISC bypass passage 20 is opened and closed by an actuator 21 a to open and close the ISC bypass passage 20.
An SC valve 21 is provided. This ISC valve 2
By controlling the opening degree of the engine 1, the idle speed of the engine 1 is controlled. An idle switch 22 for detecting the fully closed state of the throttle valve 14 is provided near the throttle valve 14 in the common intake passage 9.
And a throttle opening sensor 23 for detecting the opening of the throttle valve 14 (throttle opening).

Further, the engine system A is provided with an exhaust passage 25 for discharging the exhaust gas of the engine 1 into the atmosphere, and the exhaust passage 25 is provided in the exhaust gas flow direction (FIG. 1).
In the vicinity of the upstream end when viewed from the left (in the middle positional relationship), there are four branches near the upstream end, and each of these upstream ends (exhaust ports) communicates with the corresponding combustion chamber 6 via an exhaust valve 24. In the exhaust passage 25, an O ₂ sensor 26 (λO ₂ sensor, linear O ₂ sensor, etc.) for detecting the oxygen concentration (and, consequently, the air-fuel ratio) in the exhaust gas in order from the upstream side in the flow direction of the exhaust gas. And a catalytic converter 27 for purifying the exhaust gas. The O ₂ sensor 26 detects the air-fuel ratio in the combustion chamber 6 based on the oxygen concentration in the exhaust gas. The λO ₂ sensor is an O ₂ sensor of a type in which the output suddenly changes near the stoichiometric air-fuel ratio (λ = 1) and detects whether the air-fuel ratio is substantially higher or lower than the stoichiometric air-fuel ratio. The linear O ₂ sensor is basically the O ₂ sensor of the type capable of detecting the O ₂ concentration in a linear, especially the detection accuracy of the O ₂ concentration in the vicinity of the stoichiometric air-fuel ratio becomes higher (i.e. , The output change with respect to the change in O ₂ concentration is large). The catalytic converter 27 uses a three-way catalyst capable of simultaneously purifying hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) in exhaust gas as an exhaust gas purifying catalyst. In addition, those having a performance of purifying NOx even in a lean state are used.

Further, the engine 1 is provided with a crank angle sensor 30 composed of an electromagnetic pickup or the like. The crank angle sensor 30 is arranged at a position corresponding to the outer periphery of the plate to be detected 31 attached to the end of the crankshaft (not shown), and the plate to be detected 31 rotates with the rotation of the crankshaft. Occasionally, a pulse signal is output with the passage of the four projections 31a provided on the outer periphery. Further, the engine 1 is provided with a water temperature sensor 32 for detecting the temperature of the cooling water in the water jacket (engine water temperature).

An ECU 35 (engine control unit) composed of a microcomputer or the like is provided for performing various controls of the engine system A to the engine 1. As shown in FIG.
U35 includes an air flow sensor 13, an intake air temperature sensor 1
7, idle switch 22, throttle opening sensor 2
3, O ₂ sensor 26, a crank angle sensor 30, so that the output signals of such a water temperature sensor 32 are input.
On the other hand, the ECU 35 outputs a signal (pulse signal) for controlling the fuel injection to the injector 16, outputs a signal for controlling the ignition timing to the ignition circuit 8, and further outputs the signal to the actuator 21 a of the ISC valve 21.
A control signal is also output to the actuator 18a of the on-off valve 18.

Specifically, the ECU 35 includes the on-off valve 18
Opening / closing valve controller 36 for controlling the actuator 18a
A roughness detecting section 37 for detecting a crank angular velocity fluctuation state or a torque fluctuation state (hereinafter referred to as “roughness” or “roughness value”) of the engine 1, and air for controlling a fuel injection amount of the injector 16, that is, an air-fuel ratio. Fuel ratio control section 38, ignition circuit 8 or spark plug 7
And an ISC control unit 40 for controlling the actuator 21a of the ISC valve 21.

Hereinafter, an outline of various controls of the engine system A or the engine 1 executed by the ECU 35 will be described. In other words, the on-off valve control unit 36 causes the actuator 18a of each cylinder 2 to substantially close the on-off valve 18 in a predetermined low output area (low load / low rotation area), and substantially closes the combustion chamber 6 from the notch. Supply air. For example, as shown in FIG. 15, the on-off valve closing area (low output area)
Is the engine speed and intake charge efficiency (engine load)
And the engine water temperature. The on-off valve closing region is set by searching a map using the engine speed, the intake charging efficiency, and the engine water temperature as parameters.

At this time, a strong tumble is formed in the combustion chamber 6 to enhance the flow of intake air, thereby greatly improving the combustibility of the air-fuel mixture. At this time, the high-speed air flowing into the combustion chamber 6 through the notch of the on-off valve 18 causes
Evaporation and atomization of the fuel injected from the injector 16 are promoted, and the combustibility of the air-fuel mixture is also enhanced.
On the other hand, when the operating state of the engine 1 is not in the predetermined low output region, the on-off valve 18 is opened, a sufficient amount of air is supplied to the combustion chamber 6, and the intake charging efficiency and, consequently, the engine output are increased.

The roughness detector 37 detects a roughness value of the engine 1 and outputs the roughness value to an air-fuel ratio controller 38 and an ignition timing controller 39, as described later. The air-fuel ratio controller 38 and the ignition timing controller 39
Performs normal air-fuel ratio control and ignition timing control, while performing roughness control (see FIGS. 3 to 8) described later.

The air-fuel ratio controller 38 basically determines the air-fuel ratio of the air-fuel mixture supplied to each combustion chamber 6 based on the intake air amount detected by the air flow sensor 13 to a predetermined target air-fuel ratio (for example, , Λ = 1 and A / F = 14.7) are controlled. In a predetermined operation range, feedback control of the air-fuel ratio is performed based on the O ₂ concentration in the exhaust gas detected by the O ₂ sensor 26, that is, the deviation of the actual air-fuel ratio from the target air-fuel ratio. . As described later, the air-fuel ratio control unit 38 performs the A / F roughness control by changing (correcting) the air-fuel ratio (basic value) when the engine 1 is cold started. Has become.

The ignition timing control unit 39 basically calculates the ignition timing IGT of each cylinder 2 according to the following equation (1) or (1 ').
(N) is calculated, and the ignition plug 7 is energized at the ignition timing IGT (n) to ignite and burn the air-fuel mixture in the combustion chamber 6.

[Number 1] _{IGT (n) = θ BASE -θ} IDFB -θ RTD + θ rough (n) .................. Formula _{1 IGT (n) = θ BASE} -θ IDFB -θ RTD + θ 'rough (n) ... ... Equation 1 ′ In Equation 1, n is an integer of 1 to 4, and corresponds to the cylinder numbers of the four cylinders of the engine 1 in the order of ignition. For example, when n = 1 corresponds to the first cylinder, n = 2 corresponds to the third cylinder, n = 3 corresponds to the fourth cylinder, and n = 4 corresponds to the second cylinder.

In equation (1), θ _BASE is a basic ignition timing, that is, a basic set value of the ignition timing, and is usually an MBT for each cylinder, that is, an ignition timing at which the engine 1 outputs the maximum torque (for example, top dead center). The angle is set slightly later than (before 10 °) according to the engine speed and the intake charging efficiency using a basic ignition timing setting map (not shown). The basic ignition timing θ _BASE is, as described later, between an idle state and a non-idle state (off-idle state).
Are set individually so as to be suitable for each operation state.

In Equation 1, θ _IDFB is a feedback control amount (correction amount) of the ignition timing for _performing feedback control so that the engine speed (idle speed) follows the target idle speed during idling. For example, as shown in FIG. 16, the target idle speed is set so as to linearly decrease with an increase in the engine water temperature according to the engine water temperature (engine temperature). When the engine 1 is in a warm-up state, for example, when the engine water temperature exceeds 60 ° C., the target idle speed is set to a constant value within a range of, for example, 650 to 700 rpm.

For example, as shown in FIG. 17, the feedback control amount θ _IDFB is preferably set according to the deviation of the engine speed (idling speed) from the target idling speed during idling. As is clear from FIG. 17, for example, when the idling speed is higher than the target idling speed (the deviation is +), θ _IDFB is changed in the retard direction, whereby the output torque of the engine 1 is reduced and the idling speed is reduced. The number decreases and approaches the target idle speed.
On the other hand, when the idle speed is lower than the target idle speed (the deviation is −), θ _IDFB is changed in the advance direction,
As a result, the output torque of the engine 1 increases, and the idle speed increases to approach the target idle speed. For example, as shown in FIG. 18, on the retard side from MBT (ignition timing at which the output torque becomes maximum), the output torque of the engine 1 decreases as the ignition timing is retarded. The idle speed can be controlled by making the angle or the retard angle.

In Equation 1, θ _RTD is a temperature-rise promotion control amount. This engine system A or engine 1
Then, when starting from a cold state, that is, during a cold start, the ignition timing is greatly retarded (for example, approximately 15 °).
CA), thereby increasing the rate of transfer of thermal energy generated by the combustion of the air-fuel mixture to the engine cooling water or the exhaust gas, thereby promoting warming-up of the engine 1 and promoting the temperature rise of the exhaust gas temperature to form a catalyst. The temperature of the three-way catalyst in the converter 27 is promoted.

For example, as shown in the graph G ₁ in FIG. 19, except when the engine water temperature is very low, the temperature increase promotion control variable theta _RTD is set to significantly retard side depending on the engine coolant temperature, As a result, the warm-up of the engine 1 or the temperature rise of the three-way catalyst in the catalytic converter 27 is promoted. Thereby, the emission performance and the fuel efficiency of the engine system A or the engine 1 are improved.

However, if the ignition timing is greatly retarded to promote warming-up of the engine 1 or increase in temperature of the three-way catalyst in the catalytic converter 27, the output torque of the engine 1 becomes relatively low. Fluctuations in fuel properties (whether heavy or light), changes in the combustion state of the air-fuel mixture in the combustion chamber 6, etc., cause fluctuations in crank angular speed or torque fluctuations (roughness), and impair the smooth operation of the engine 1. May be Therefore, as shown in Equation 1 or Equation 1 ′, (θ
_BASE −θ _IDFB −θ _RTD ) and the IG roughness control amount θ _rough (n)
Alternatively, the roughness is suppressed by correcting with θ ′ _rough (n). The IG roughness control amount θ
_{The rough} (n) or θ ′ _rough (n) is set in a roughness control routine (FIGS. 3 to 8) described later.

Thus, the ignition timing control section 39 determines whether or not the ignition timing IGT (n) has been reached based on the signal input from the crank angle sensor 30, and when the ignition timing has come, the ignition circuit 8 Then, the ignition plug 7 is energized to ignite and burn the air-fuel mixture for each cylinder. The ISC control unit 4
0 is calculated using the well-known ordinary ISC control method.
The flow rate of bypass air flowing in the SC bypass passage 20 is controlled.

By the way, in the engine system A or the engine 1, as described above, the ignition timing is greatly retarded to promote the warm-up of the engine 1 or the temperature rise of the three-way catalyst in the catalytic converter 27. As a result, in the low output region, fluctuations in crank angular velocity or fluctuations in torque (roughness) are likely to occur, and the rotational stability of the engine may be impaired. Therefore,
In a predetermined low output area (roughness control area), the ignition timing or the air-fuel ratio is corrected to perform the roughness control such that the roughness is suppressed and the rotational stability of the engine is increased.

Hereinafter, a specific control method of the roughness control will be described with reference to flowcharts shown in FIGS. As shown in FIGS. 3 to 8, in this roughness control, first, in step S <b> 1, the crank angle after the top dead center changes from 104 ° to 174 ° (ATDC 104 ° CA to 100 ° C.) based on the output signal of the crank angle sensor 30. ATDC 174 °
A time interval T (i) until CA) is measured. Subsequently, in step S2, using the following equation 2, step S1
The crank angular velocity ω (i) is calculated based on the time interval T (i) measured in (1).

Ω (i) = 70 · 10 ⁶ / T (i) ··················· Equation 2 T (i): Time interval [microseconds] ω (i) : Crank angular velocity [Crank angle (° CA) /
Seconds]

Here, a preferred method of setting the crank angle period for detecting the crank angular speed ω (i) is as follows.
This will be described with reference to FIGS. FIG. 9 is a diagram illustrating an example of a change characteristic of a torque and an angular velocity with respect to a crank angle (ATDC CA) after the top dead center for an in-line four-cylinder four-cycle engine. As shown in FIG. 9, the combined torque of the inertia torque (dashed line) and the gas pressure torque (dashed line) in each cylinder is 180 ° CA during normal combustion, as indicated by the thick solid line in FIG. Changes periodically at intervals,
The angular speed of the crankshaft rotated by this combined torque
(Solid line A) also changes periodically. On the other hand, for example, when the combustion state becomes unstable in the first cylinder and a state close to misfire occurs, the combined torque of the engine becomes extremely low as shown by a two-dot chain line in FIG. . As a result, the crank angular velocity remarkably decreases from the middle of the expansion stroke of the first cylinder as shown by the broken line B, and the difference from the normal combustion time increases. In the cylinder to be ignited next (third cylinder),
Although the angular velocity decreases throughout the expansion stroke in which the influence of the previously ignited cylinder (first cylinder) remains, the value gradually approaches a normal value as the stroke progresses.

FIG. 10 is a graph showing the correlation between the combustion pressure and the angular velocity fluctuation (roughness state). In FIG. 10, the horizontal axis represents the value after the compression top dead center (AT
DC) represents the crank angle (ATDC CA), and the vertical axis represents the correlation coefficient indicating the degree of influence of the combustion state (gas pressure) of the cylinder on the angular velocity. Here, if the correlation coefficient is positive, it means that there is a high correlation between the fluctuation of the combustion pressure of the cylinder and the fluctuation of the angular velocity. On the other hand, if the correlation coefficient is negative, the fluctuation of the combustion pressure of the preceding cylinder is higher than that of the cylinder. Significant impact.

As is apparent from FIGS. 9 and 10, the crank angle at which combustion is almost completed (ATDC 40 ° C.)
A) to the crank angle (about 200 ° CA ATDC) near the combustion start timing of the cylinder to be ignited next, the correlation between the combustion pressure and the angular velocity fluctuation is high, and especially the torque after the gas pressure torque decreases. Inflection point (ATDC 90 ° CA
), A period X (A
(TDC 100 ° CA to ATDC 200 ° CA), the correlation is high. Thus, for example, A
If the angular velocity is detected within the range of TDC 100 ° CA to ATDC 200 ° CA, the combustion state of the cylinder can be accurately determined based on the fluctuation of the angular velocity (roughness state). In addition, in order to sufficiently secure the angular velocity detection time, the crank angle period for detecting the angular velocity is preferably set to 60 ° CA or more.

Therefore, as shown in FIG. 11, for example, in this embodiment, the ATDC 104 ° CA and the AT
Each projection 31a of the plate to be detected 31 is provided so that DC 174 ° CA is detected, and the ATD
The crank angular velocity during a period of 70 ° CA from C104 ° CA to 174 ° CA is detected.

Next, in step S3, the difference dω (c) of the crank angular velocity ω (i) is obtained by comb filter processing for removing an element that becomes a noise for the determination of the combustion state for each cylinder using the following equation 3. i), that is, the crank angular velocity fluctuation dω (i) is calculated. The cylinder identification is
This is performed based on a signal from a sensor that detects the rotation angle of the camshaft (not shown).

Dω (i) = ω (i−4) −ω (i) Equation 3ω (i−4): Calculation of crank angle speed four times before Value ω (i): Current calculated value of crank angular velocity

Here, factors that cause angular velocity fluctuations other than fluctuations in the combustion state include angular velocity fluctuations caused by resonance caused by an explosion as an excitation source, and angular velocity caused by wheel rotation caused by imbalance of wheels and a drive system. Fluctuation, and angular velocity fluctuation due to the influence of vibration acting on the tire from the road surface.
As shown in FIG. 12, the noise of the explosion rotation order component caused by the resonance occurs at the 0.5th order of the engine rotation and a frequency that is an integral multiple thereof, and the noise caused by the wheel rotation caused by the imbalance and the noise caused by the road surface. Is 0,0 of engine speed.
Occurs in the lower frequency range than the fifth order.

Therefore, in step S3, the crank angular velocity fluctuation dω is removed while removing the 0.5th order engine speed and its integral multiple frequency components by engine comb processing.
(I) is calculated. That is, as shown in FIG. 13, the deviation between the present value ω (i) and the previous value ω (i−4) of the crank angular velocity in the same cylinder is obtained, and the 0.5th order and the 0.5th of the engine rotation are obtained by the comb filter processing. The data of the crank angular velocity variation dω (i) excluding the frequency component of an integral multiple thereof is obtained.

Subsequently, in step S4, the roughness value dωf is obtained by high-pass filtering using the following equation (4).
(I) is calculated. That is, in order to remove noise of a frequency component lower than the 0.5th order of the engine rotation, a smoothing process is performed based on the data up to eight cycles before the crank angular speed fluctuation dω (i) obtained in step S3. , The roughness value dωf (i) is calculated.

[Number 4] _{dωf (i) = k 1 ·} dω (i-4) + k 2 · (dω (i-3) + dω (i-5)) + k 3 · (dω (i-2) + dω (i −6)) + k ₄ · (dω (i−1) + dω (i−7)) + k ₅ · (dω (i) + dω (i−8)) Equation 4 Equation 4 , K _{1 to} k _{5 are} averaging coefficients (constants).

As shown in FIG. 14, the high-pass filter process sufficiently attenuates and removes frequency components lower than the 0.5th order of the engine speed. In this way, the roughness value dωf reflecting the combustion state with high accuracy for each cylinder
(I), that is, a crank angular velocity fluctuation value or a torque fluctuation value can be obtained.

Next, in steps S5 and S6,
The roughness value dωf (i) calculated in step S4 is
It is determined whether the value exceeds the upper threshold value dωfmax, is equal to or lower than the lower threshold value dωfmin, or exceeds the lower threshold value dωfmin within a range equal to or lower than the upper threshold value dωfmax. Here, when the roughness value exceeds the upper limit threshold value dωfmax, the crank angular speed fluctuation or torque fluctuation (roughness) becomes extremely large, and smooth operation of the engine 1 may be impaired. Is the limit value required to be reduced to The upper threshold dωfmax is preferably set according to the engine speed and the intake charging efficiency by searching a map using the engine speed and the intake charging efficiency (engine load) as parameters.

On the other hand, the lower limit threshold value dωfmin is considered that when the roughness value is less than this, the crank angular speed fluctuation or the torque fluctuation becomes very small and the operation of the engine 1 is sufficiently stabilized. Is a limit value at which it is considered possible to alleviate the suppression. The lower threshold dωfmin is preferably set according to the engine speed and the intake charging efficiency by searching a map using the engine speed and the intake charging efficiency (engine load) as parameters.

Thus, in step S5, the roughness value d
If .omega.f (i) is determined to exceed the upper threshold dωfmax (YES in step S5), 1 the roughness large determination flag F ₁ is set in step S7, followed by roughness small determination in step S8 flag F ₂ to 0 are set.

If it is determined in steps S5 and S6 that the roughness value dωf (i) is equal to or smaller than the lower threshold dωfmin (NO in step S5 and YES in step S6), the roughness is increased in step S9. determination flag F ₁ to 0 is set, followed by 1 to roughness small determination flag F ₂ in step S10 is set.

In steps S5 and S6,
When it is determined that the roughness value dωf (i) exceeds the lower threshold dωfmin within the range of the upper threshold dωfmax or less (NO in step S5 and NO in step S6), the roughness is increased in step S11. determination flag F ₁ to 0 is set and subsequently set 0 and the roughness small determination flag F ₂ in step S12.

Thereafter, in step S13, it is determined whether the condition for executing the roughness control is satisfied. In this roughness control, when the following three conditions are satisfied, it is determined that the roughness control execution condition is satisfied, and the roughness control is executed.

<Roughness Control Execution Conditions> (1) At the time of engine start, a predetermined time (for example, one second) has elapsed after the complete explosion. Here, it is determined that a complete explosion has occurred when the engine speed has increased to 500 rpm after cranking. This is because the rotation of the engine 1 is relatively unstable immediately after the complete explosion, and it is not preferable to execute the roughness control in such a case. (2) The engine water temperature is equal to or lower than a predetermined temperature (for example, 60 ° C.). In other words, the engine warm-up flag F ₄ is described below is 0. The engine warm-up flag F ₄
As shown in FIG. 8, when it is determined in step S51 that the engine coolant temperature exceeds a predetermined temperature K (for example, 60 ° C.), 1 is set in step S52, and it is determined that the temperature is not higher than the predetermined temperature K. When it is done, step S53
Is a flag for which 0 is set. When the engine water temperature exceeds the predetermined temperature, the engine 1 has already been warmed up, so that the ignition timing for warming up the engine 1 or promoting the temperature rise of the three-way catalyst is not significantly retarded. Therefore, it is not necessary to perform roughness control. (3) The operating state of the engine 1 is in the on-off valve closing area (intake air flow enhancement area) in FIG. This is because when performing the roughness control, it is necessary to increase the combustibility of the air-fuel mixture in the combustion chamber 6 in order to increase the rotational stability of the engine 1.

Thus, when it is determined in step S13 that the roughness control execution condition is not satisfied (N
O), that is, when at least one of the above roughness control execution conditions is not satisfied, the process skips to step S32 described later to temporarily stop or end the roughness control.

On the other hand, if it is determined in step S13 that the roughness control execution condition is satisfied (YES), that is, if all the roughness control execution conditions are satisfied, step S14 is executed. In this step S14, the operating state of the engine 1 is in the IG roughness control region where roughness control should be performed by controlling the ignition timing, or the A / F should perform roughness control by controlling the air-fuel ratio (fuel injection amount). It is determined whether it is in the roughness control area.

[0057] In the step S14, IG roughness control inhibition flag F ₃ is 0 and performs IG roughness control when the engine 1 is idling, while IG
Whether the roughness control inhibition flag F ₃ is 1, or the engine 1 is when in a non-idle (off-idle) state is to perform the A / F roughness control. IG
Roughness control inhibition flag F ₃ is a flag that is set to 1 when the roughness control amount in IG roughness control (correction amount) becomes maximum advance side. Therefore, when the IG roughness control inhibition flag F ₃ is 1, it is not possible to increase the output torque of the engine 1 by controlling the ignition timing, thus IG roughness control is substantially impossible.

Thus, in step S14, the engine 1
Is determined to be in the IG roughness control region (YES), Steps S15 to S
At 24, the IG roughness control amount is calculated or held (maintained as it is). Specifically, roughness large determination flag F ₁ is determined whether it is 1 first, in step S15.
If roughness atmospheric determination flag F ₁ is determined to be 1 (YES), i.e. if so the ignition timing is advanced to increase the torque, in step S17, this cylinder using Equation 5 follows IG roughness control amount θ _rough (i)
Is calculated. The IG roughness control amount θ for each cylinder
_{The rough} (i) is basically obtained by correcting the previous IG roughness control amount θ _rough (i-1) for each cylinder toward the advance side.

[0059]

Θ _rough (i) = θ _rough (i−1) + min [K ₁ · (dωf (i) −dωfmax), Δigad] Equation 5 θ _rough (i): For each cylinder IG roughness control amount θ _rough (i-1): Previous IG roughness control amount for each cylinder min [α, β, ...]: Minimum value of α, β, ... K ₁ : Proportional constant dωf (i) : Roughness value dfmax: Upper limit threshold value Δigad: Advancing correction amount Δigad is preferably set according to the engine speed and the intake charging efficiency by searching a map using the engine speed and the intake charging efficiency as parameters. Is done.

Where θ for each cylinder calculated by equation (5)
_When the calculated value of _rough (i) is larger than the predetermined limit value IMX, θ _rough (i) is set to IMX. Here, the limit value IMX is a limit value of θ _rough (i) to the advance side of each cylinder, that is, a limiter. When θ _rough (i) reaches IMX, θ _rough (i) is It cannot be changed to the advance side.

Next, in step S18, the current IG roughness control amount θ ' _rough (i) of all cylinders is calculated using the following equation (6). The IG roughness control amount θ ' _{rough for} all cylinders
(I) is basically obtained by correcting the previous IG roughness control amount θ ′ _rough (i−1) of all cylinders to the advance side. In the IG roughness control (ignition timing control), the IG roughness control amount θ _rough (i) for each cylinder and the IG roughness control amount θ ′ _rough (i) for all cylinders are used selectively or alternatively. Can be

Θ ′ _rough (i) = θ ′ _rough (i−1) + min [K ₁ · (dωf (i) −dωfmax), Δigad] Equation 6 θ ′ _rough (i): this time IG roughness control amount of all cylinders θ ′ _rough (i−1): previous IG roughness control amount of all cylinders min [α, β,...]: Minimum value of α, β,... K ₁ : proportionality constant dωf (i): roughness value dfmax: upper threshold value Δigad: advance angle correction amount

Also in this step S18, the calculated value of θ ' _rough (i) for all cylinders calculated by the equation 6 is equal to the limit value IMX.
When it is larger than θ ′ _rough (i), it is set to IMX. Therefore, when θ ′ _rough (i) reaches IMX, θ ′ _rough (i) cannot be changed further to the advance side.

Next, in step S19, step S18
IG roughness control amount θ 'calculated for all cylinders
whether _rough (i) is equal to the limit value IMX is determined, if _{θ 'rough (i) = IMX} (YES), 1 is set in the IG roughness control inhibition flag F ₃ in step S20. _Unless θ ′ _rough (i) = IMX (NO), step S20 is skipped. The IG roughness control inhibition flag F ₃ is, since a flag is set to 1 when the roughness control amount in IG roughness control (correction amount) becomes the advance angle side to the maximum, the IG roughness control inhibition flag F _{When 3} is 1, the output torque of the engine 1 cannot be increased by controlling the ignition timing, and the IG roughness control cannot be executed. Therefore, when this IG roughness control inhibition flag F ₃ 1 is set, so that the later of the A / F roughness control is executed. Thereafter, the control proceeds to step S44.

[0064] In step S15 described above, if the roughness large determination flag F ₁ is determined not 1 (NO), the roughness small determination flag F ₂ in step S16 it is determined whether it is 1. Here, the small roughness determination flag F ₂
Is determined to be 1 (YES), that is, if the torque should be decreased by retarding the ignition timing, in step S21, the current IG roughness control amount θ for each cylinder using the following equation 7 _rough (i) is calculated. The IG roughness control amount θ _rough (i) for each cylinder is basically
IG roughness control amount for the previous cylinder θ _rough (i-1)
Is corrected to the retard side.

Equation 7 θ _rough (i) = θ _rough (i−1) −Δigret Equation 7 θ _rough (i): IG roughness control amount for each cylinder this time θ _rough (i -1): previous IG roughness control amount for each cylinder Δigret: retard angle correction amount

Note that Δigret is preferably set according to the engine speed and the intake charging efficiency by searching a map using the engine speed and the intake charging efficiency as parameters. However, when the calculated value of θ _rough (i) for each cylinder calculated by Expression 7 is smaller than the predetermined limit value IMN, θ _rough (i) is set to IMN.
Here, the limit value IMN is a limit value to the retard side of θ _rough (i) for each cylinder, that is, a limiter.
_{When rough} (i) reaches IMN, θ _rough (i)
Can no longer be changed to the retard side.

Next, in step S22, the current IG roughness control amount θ ' _rough (i) of all cylinders is calculated using the following equation (8). The IG roughness control amount θ ' _{rough for} all cylinders
(I) is basically a correction of the previous IG roughness control amount θ ′ _rough (i−1) of all cylinders to the retard side.

Equation 8 θ ′ _rough (i) = θ ′ _rough (i−1) −Δigret] Equation 8 θ ′ _rough (i): IG roughness control amount of all cylinders this time θ ′ _rough (i-1): previous IG roughness control amount of all cylinders Δigret: retard angle correction amount

Also in this step S22, the calculated value of θ ' _rough (i) for all cylinders calculated by equation (8) is equal to the limit value IMN
When it is smaller than θ ′ _rough (i), it is set to IMN. Therefore, when θ ′ _rough (i) reaches IMN, θ ′ _rough (i) cannot be changed further to the retard side. Thereafter, the control proceeds to step S44.

[0068] If the roughness small determination flag F ₂ is determined not 1 in step S16 of the (NO), ie the roughness value is not more than the upper threshold value Diomegafmax,
If it is determined that the difference exceeds the lower threshold dωfmin, the crank angular velocity fluctuation or torque fluctuation (roughness) is not so large and not small enough to further retard the ignition timing. IG
The roughness control amount is kept as it is.

That is, in this case, step S23
Thus, the previous cylinder-specific IG roughness control amount θ _rough (i−
1) is the current IG roughness control amount θ for each cylinder
_rough (i). Subsequently, in step S24, the previous IG roughness control amount θ ′ _rough (i−1) of all cylinders is set as the current IG roughness control amount θ ′ _rough (i) of all cylinders. Thereafter, the control proceeds to step S44.

Thus, in step S44, it is determined whether or not the operation state of the engine is in the idle range. If the engine is in the idle range (YES), the on-off valve 18 is closed in step S45 (FIG. 15). It is determined whether or not it is in the valve closing area (see YE).
S) In step S46, the basic ignition timing for idling when the on-off valve 18 is closed is set as the basic ignition timing θ _BASE . On the other hand, if it is not in the valve closing area (N
O) In step S47, the basic ignition timing for idling when the on-off valve 18 is opened is set as the basic ignition timing θ _BASE . If it is determined in step S44 that the operating state of the engine 1 is in the non-idle range (NO),
In step S48, similarly to step S45, it is determined whether or not the on-off valve 18 is in the valve closing area. If it is in the valve closing area (YES), the on-off valve 18 is set to the basic ignition timing θ _BASE in step S49. A non-idle ignition timing basic value at the time of valve closing is set. On the other hand, if it is not in the valve closing region (NO), the basic ignition timing θ is determined in step S50.
_The base value of the ignition timing for the non-idle state when the on-off valve 18 is opened is set in _BASE . In the engine system A or the engine 1, the basic ignition timing θ _BASE is set to be more advanced than at the time of idling in order to increase the engine output at the time of non-idling. In addition, on-off valve 1
When the valve 8 is closed, the combustion speed increases due to the effect of the notch, so that the basic ignition timing θ _BASE is set to be more retarded than when the on-off valve 18 is opened. Therefore, step S
In steps S44 to S50, the basic ignition timing θ _BASE is individually set according to whether the engine is idling or non-idling and according to the open / close state of the on-off valve 18. Thereafter, the process returns to step S1, and the control is continued.

When it is determined in step S14 that the operating state of the engine 1 is not in the IG roughness control area (NO), that is, when it is determined that the engine 1 is in the A / F roughness control area. Is the step S
In step 25 to step S31, the A / F roughness control amount is calculated or held (maintained as it is). That is, in this case, it is difficult or substantially impossible to perform the roughness control by changing the ignition timing. Therefore, the roughness control is performed by changing the air-fuel ratio to increase or decrease the output torque.

[0072] Specifically, roughness large determination flag F ₁ is determined whether it is 1 first, in step S25. If roughness atmospheric determination flag F ₁ is determined to be 1 (YES), i.e. if the air-fuel ratio (A / F) should be increased torque is varied to the rich side, the step S2
In step 7, the following A / F roughness control amount λ _rough (i) for each cylinder is calculated using the following equation 9. A /
The F roughness control amount λ _rough (i) is basically obtained by correcting the previous A / F roughness control amount λ _rough (i-1) for each cylinder by a fixed amount toward the rich side.

Λ _rough (i) = λ _rough (i−1) + KL Equation 9 λ _rough (i): A / F roughness control amount for each cylinder λ _rough (I-1): A / F roughness control amount for each previous cylinder KL: Rich-side roughness control amount correction value (constant value)

Where λ for each cylinder calculated by equation (9)
_When the calculated value of _rough (i) is larger than a predetermined limit value FMX, λ _rough (i) is set to FMX. Here, the limit value FMX is a limit value on the rich side of λ _rough (i) for each cylinder, that is, a limiter, and λ _rough (i)
Reaches FMX, λ _rough (i) cannot be changed further to the rich side. Thereafter, the control proceeds to step S39.

[0074] In step S25 described above, if the roughness large determination flag F ₁ is determined not 1 (NO), the roughness small determination flag F ₂ in step S26 it is determined whether it is 1. Here, the small roughness determination flag F ₂
Is determined to be 1 (YES), that is, when the torque should be reduced by changing the air-fuel ratio to the lean side, in step S28, the A / F for each cylinder at this time is obtained by using the following Expression 10. The roughness control amount λ _rough (i) is calculated. A / F roughness control amount λ _rough (i) for each cylinder
Is basically obtained by correcting the previous cylinder-specific A / F roughness control amount λ _rough (i−1) by a fixed amount toward the lean side.

Λ _rough (i) = λ _rough (i−1) −KR (10) λ _rough (i): A / F roughness control amount λ for each cylinder this time _rough (i-1): previous A / F roughness control amount for each cylinder KR: lean side roughness control amount correction value (constant value)

Next, at step S29, A / A
Whether F roughness control variable is 0 is determined, if 0 is A / F roughness control variable with all the cylinders (YES), 0 to IG roughness control inhibition flag F ₃ in step S30 is set. If the A / F roughness control amount of at least one cylinder is not 0 (NO), step S30
To skip. In step S30, when this IG roughness control inhibition flag F ₃ 0 is set it will return to the IG roughness control of the. Thereafter, the control proceeds to step S39.

[0076] If the roughness small determination flag F ₂ is determined not 1 at step S26 of the (NO), ie the roughness value is not more than the upper threshold value Diomegafmax,
If it is determined that the difference exceeds the lower threshold dωfmin, the change in the crank angular speed or the change in the torque (roughness) is not so large and not so small, so that the current A / F roughness control amount remains unchanged. Will be retained. That is, in this case, in step S31, the previous A / F roughness control amount λ _rough (i-1) for each cylinder
Is the A / F roughness control amount λ _rough (i) for each cylinder
It is said. Thereafter, the control proceeds to step S39.

[0077] At step S39, the air-fuel ratio feedback control flag F ₅ is determined whether it is 1. The air-fuel ratio feedback control flag F _5, when 1 is set is allowed feedback control of the air-fuel ratio,
When 0 is set, this is a flag for prohibiting the feedback control of the air-fuel ratio. In this A / F roughness control, the feedback control of the air-fuel ratio is prohibited when the A / F roughness control amount of at least one cylinder exceeds a predetermined set value, and the A / F roughness control amount is set to 0 for all cylinders. Then, the feedback control of the air-fuel ratio is permitted when.

[0078] Thus, in step S39, when the air-fuel ratio feedback control flag F ₅ is determined to be 1 (YES), that is, when in the state in which the feedback control of the air-fuel ratio is permitted, at least one in step S40 It is determined whether the A / F roughness control amount of the cylinder exceeds a predetermined set value. Here, if A / F roughness control variable of at least one cylinder exceeds a predetermined setting value (YES), the set air-fuel ratio feedback control flag F ₅ to 0 in step S41, thus the air-fuel ratio feedback control Is prohibited (open control is performed). On the other hand, in step S40, A
If the / F roughness control amount is equal to or less than a predetermined set value, (N
O), skipping step S41, the air-fuel ratio feedback control flag F ₅ is held at 1, thus the feedback control of the air-fuel ratio is continued. Thereafter, after steps S44 to S50 are executed, the process returns to step S1 and the control is continued.

[0079] In step S39 described above, when the air-fuel ratio feedback control flag F ₅ is determined not 1 (N
O), that is, when the feedback control of the air-fuel ratio is prohibited, the A / A
It is determined whether the F roughness control amount is 0 or not. Here, if the A / F roughness control amounts of all cylinders are 0 (YE
S), 1 to the air-fuel ratio feedback control flag F ₅ is set at step S43, thus the feedback control of the air-fuel ratio is allowed. On the other hand, in step S42, unless A / F roughness control variable of at least one cylinder is 0 (NO), skips step S43, is held air-fuel ratio feedback control flag F ₅ is kept zero, therefore the air-fuel ratio Feedback control remains prohibited. Thereafter, steps S44 to S50 are performed.
Is executed, the process returns to step S1 and the control is continued.

As described above, steps S32 to S
At 43, the A / F roughness control amount λ _rough (i) is calculated, and at the time of cold start, switching control from A / F roughness control to air-fuel ratio feedback control is performed. That is, the feedback control of the air-fuel ratio by the O ₂ sensor 26 is started when the A / F roughness control amount λ _rough (i), that is, the correction amount with respect to the air-fuel ratio basic value is reduced to 0 for all cylinders. Has become. As described above, the roughness control amount λ _rough
When (i) is larger than the set value for at least one cylinder, A / F roughness control, that is, open control is continued.

That is, in the method of switching from the A / F roughness control to the feedback control of the air-fuel ratio, the roughness control amount λ _rough (i) is set to 0 for all cylinders.
The feedback control of the air-fuel ratio is started at the time of, the warm-up of the engine 1 or the catalytic converter 27 while keeping the torque fluctuation (roughness value) within an allowable range irrespective of the properties of the fuel or individual differences of the engine. The temperature of the three-way catalyst can be accelerated, and the air-fuel ratio feedback control using the stoichiometric air-fuel ratio or an air-fuel ratio in the vicinity thereof as the target air-fuel ratio can be started immediately.

For example, as shown in FIG.
As a general tendency, the fluctuation rate of the indicated mean effective pressure Pi becomes larger as the air-fuel ratio (A / F) becomes leaner, but the property of the fuel (gasoline), for example, whether it is heavy or light It depends greatly on. Therefore, the roughness value varies greatly depending on the properties of the fuel. Further, the roughness value greatly differs depending on the individual difference of the engine 1. For this reason, it is inherently difficult to set the start timing of the air-fuel ratio feedback control. However, according to the A / F roughness control or the feedback control of the air-fuel ratio, the torque variation (roughness) is not affected irrespective of the property of the fuel or the individual difference of the engine.
Can be shifted from the A / F roughness control to the feedback control of the air-fuel ratio at an early stage, while keeping within the allowable range.

Here, the roughness control amount λ _rough (i)
Is based on a stoichiometric air-fuel ratio (λ = 1, A / F = 14.7) or an air-fuel ratio (for example, A / F = 14) in the vicinity of the stoichiometric air-fuel ratio and corrects the basic value to perform A / F roughness control. It is supposed to do. Therefore, it is either O ₂ sensor 26 is .lamda.o ₂ sensor and the linear O ₂ sensor, since they have the detection accuracy of the O ₂ concentration in the vicinity of the stoichiometric air-fuel ratio (air-fuel ratio) is good, the A / F The control accuracy of the roughness control is improved, and the fuel consumption performance and emission performance are improved. Then, the transition from the A / F roughness control to the feedback control of the air-fuel ratio using the stoichiometric air-fuel ratio or the air-fuel ratio in the vicinity thereof as the target air-fuel ratio is facilitated.

When it is determined in step S13 that the roughness control execution condition is not satisfied (NO), that is, when at least one of the roughness control execution conditions is not satisfied, the roughness control is temporarily stopped. Or terminated. In this case, first, step S32
In the engine warming-up flag F ₄ is whether 1,
That is, the engine water temperature is a predetermined temperature (eg, 60 ° C.)
Is determined, the engine warm-up flag F
_{If 4} is not 1 (NO), the roughness control is temporarily stopped, and in steps S33 to S35, the IG roughness control amount for each cylinder, the IG roughness control amount for all cylinders, and the A value for each cylinder, respectively. / F roughness control amount is maintained (maintained as is).

That is, in step S33, the previous cylinder-based IG roughness control amount θ _rough (i-1) is set to the current cylinder-based IG roughness control amount θ _rough (i).
In step S34, the previous IG roughness control amount θ ′ _rough (i−1) of all cylinders is set as the current IG roughness control amount θ ′ _rough (i) of all cylinders. In step S35, the A / F roughness control amount λ _rough (i
-1) is the A / F roughness control amount λ _rough for each cylinder this time.
(I).

Thereafter, after the above-described steps S39 to S50 are executed, the process returns to step S1. However, in this case, since the roughness control is temporarily stopped as described above, steps S33 to S33 are performed.
The roughness control amounts held at 35 are not used for roughness control. That is, when the roughness control is temporarily stopped, the respective roughness control amounts immediately before the stop are retained, but these roughness control amounts are retained (stored) in preparation for the subsequent restart of the roughness control.
It is just being done.

As described above, after the roughness control execution condition is not satisfied and the roughness control is temporarily stopped, and when the roughness control condition is satisfied again, the roughness control is resumed using the held roughness control amount. Is done. As a result, the roughness control is stabilized at an early stage, and thus the responsiveness of the control is enhanced, and the engine 1 is warmed up or the temperature of the three-way catalyst in the catalytic converter 27 is increased while keeping the torque fluctuation within an allowable range. Can greatly facilitate
Emission performance and fuel efficiency can be improved.

[0088] In step S32 described above, if the engine warming-up flag F ₄ is determined to be 1 (YES), there already warmed-up state of the engine 1, also the three-way catalyst in the catalytic converter 27 is also sufficiently , The roughness control is terminated. However,
When the roughness control is suddenly (stepwise) terminated,
Since the roughness control amount suddenly disappears, the output torque may suddenly change and a torque shock may occur. Therefore, in this case, in steps S36 to S38, the IG roughness control amount for each cylinder, the IG roughness control amount for all cylinders, and the A / F roughness control amount for each cylinder are gradually reduced (gradual decrease). Reset) to end the roughness control relatively slowly. This prevents the occurrence of torque shock at the end of the roughness control.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine system including a control device according to the present invention.

FIG. 2 is a functional block diagram of an ECU provided in the engine system shown in FIG.

FIG. 3 is a part of a flowchart showing a control method of roughness control by an ECU.

FIG. 4 is a part of a flowchart showing a control method of roughness control by an ECU.

FIG. 5 is a part of a flowchart showing a control method of roughness control by an ECU.

FIG. 6 is a part of a flowchart showing a control method of roughness control by an ECU.

FIG. 7 is a part of a flowchart showing a control method of roughness control by the ECU.

FIG. 8 is a flowchart illustrating a method of setting an engine warm-up flag in roughness control by an ECU.

FIG. 9 is a diagram showing a stroke of each cylinder of an in-line four-cylinder four-cycle engine, and changes in torque and angular velocity with respect to changes in crank angle.

FIG. 10 is a diagram showing a correlation between combustion pressure and angular velocity fluctuation.

FIG. 11 is a view showing a schematic configuration of a plate to be detected and a crank angle sensor for detecting a crank angle.

FIG. 12 is a diagram showing a change in angular velocity due to a noise factor;

FIG. 13 is a diagram showing an attenuation characteristic after passing through a comb filter in order to remove a 0.5-order component of engine rotation and an integral multiple thereof from the detected angular velocity data.

14 is a diagram illustrating an attenuation characteristic after passing through a high-pass filter in order to remove a frequency component lower than the 0.5th order of engine rotation from the data illustrated in FIG. 13;

FIG. 15 is a diagram showing a valve opening region and a valve closing region of an on-off valve, using an engine speed, an intake charging efficiency, and an engine water temperature as parameters.

FIG. 16 is a graph showing a change characteristic of a target idle speed with respect to an engine water temperature during a cold start.

FIG. 17 is a diagram showing a change characteristic of a feedback control amount of an ignition timing with respect to an idle speed deviation;

FIG. 18 is a diagram showing the dependence of the output torque of the engine on the ignition timing.

FIG. 19 is a view showing a change characteristic of a control amount of a temperature rise promotion of an ignition timing with respect to an engine water temperature.

FIG. 20 is a diagram showing a change characteristic of the indicated average effective pressure fluctuation rate with respect to the air-fuel ratio, using a property of fuel as a parameter.

[Explanation of symbols]

A: engine system, 1 ... engine, 2 ... cylinder, 3 ...
Cylinder block, 4 ... cylinder head, 5 ... piston, 6 ... combustion chamber, 7 ... spark plug, 8 ... ignition circuit, 9 ...
Common intake passage, 10 independent intake passage, 10a second independent intake passage, 11 air cleaner, 12 intake valve, 13 ...
Air flow sensor, 14 ... throttle valve, 15 ... surge tank, 16 ... injector, 17 ... intake air temperature sensor, 1
8 open / close valve, 18a actuator, 20 ISC bypass passage, 21 ISC valve, 21a actuator, 22 idle switch, 23 throttle opening sensor, 24 exhaust valve, 25 exhaust passage, 26 O ₂ Sensor, 27: Catalytic converter, 30: Crank angle sensor, 31: Plate to be detected, 31a: Projection, 32: Water temperature sensor, 35: ECU, 36: Open / close valve control unit, 37 ...
Roughness detector, 38: air-fuel ratio controller, 39: ignition timing controller, 40: ISC controller.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 305 F02D 41/04 305Z 45/00 312 45/00 312B F02P 5/15 F02P 5/15 E

Claims (6)

[Claims] An air-fuel ratio control means for controlling an air-fuel ratio, and a roughness control means for performing a roughness control by correcting the air-fuel ratio so that a torque fluctuation state falls within an allowable limit in a predetermined engine operation region when the engine is cold. the air-fuel ratio control apparatus for provided an engine, when the roughness control variable of the roughness control means is reduced to a predetermined value, so the air-fuel ratio control means performs a feedback control of the air-fuel ratio by the O ₂ sensor An air-fuel ratio control device for an engine, comprising: 2. The engine air-fuel ratio control device according to claim 1, wherein the roughness control means performs the roughness control by correcting the air-fuel ratio based on a stoichiometric air-fuel ratio. . 3. When the roughness control means performs the roughness control by correcting the air-fuel ratio to the rich side,
When the roughness control variable is reduced to a predetermined value, the engine according to claim 1 or 2, characterized in that the air-fuel ratio control means is adapted to perform feedback control of the air-fuel ratio by the O ₂ sensor Air-fuel ratio control device. 4. The air-fuel ratio control means performs feedback control of an air-fuel ratio by an O ₂ sensor when the roughness control amount is reduced to a predetermined value for all cylinders. Item 4. An air-fuel ratio control device for an engine according to item 3. 5. The air-fuel ratio control means according to claim 1, wherein said air-fuel ratio control means performs open control of said air-fuel ratio when said roughness control amount is larger than a predetermined value for at least one cylinder. An air-fuel ratio control device for an engine according to any one of the preceding claims. 6. The engine according to claim 1, wherein a catalytic converter having an exhaust gas purifying catalyst is provided in the engine provided in the exhaust passage. Fuel ratio control device.