JP3064782B2 - Control method for lean burn engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a lean burn engine, and more particularly, to a method for easily switching an engine between a stoichiometric operation and a lean operation while suppressing fluctuations in engine output and generation of nitrogen oxides. The present invention relates to a lean burn engine control method which can be performed by a simple control system.

[0002]

2. Description of the Related Art In order to improve the exhaust gas characteristics or fuel efficiency of an internal combustion engine, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio.
It is known to operate an engine lean (lean combustion operation). In this type of air-fuel ratio control, the engine is controlled to have a stoichiometric air-fuel ratio near the stoichiometric air-fuel ratio in the acceleration operation region or the like so that the engine output is not insufficient in the engine acceleration operation region or the like, and the engine is operated in a stoichiometric operation. Like that. Therefore, for example, when the accelerator pedal is released and the vehicle is released from the acceleration operation region, only the fuel amount is reduced, and the transition from the stoichiometric operation to the lean operation is performed. In this case, the engine output suddenly drops, causing a shock and hindering drivability.

Therefore, in order to keep the engine output constant during the transition from the stoichiometric operation to the lean operation, an air-fuel ratio control device that changes only the intake air amount without changing the fuel supply amount to the engine, JP-A-5-1872
No. 95. The proposed device performs a stoichiometric operation when the engine is in a specific operation state and performs a lean operation at other times. The proposed device includes two bypass passages that bypass the throttle valve, and one of the bypass passages includes an idle rotation passage. A number control (ISC) valve is provided, and a negative pressure responsive valve is provided in the other bypass passage. During a lean operation, a bypass valve provided in a control pressure passage that connects a portion of the intake passage with a throttle valve and a control chamber of a negative pressure responsive valve is opened. Is supplied to the engine via the bypass passage on the negative pressure responsive valve side. Further, the target intake air amount for achieving the air-fuel ratio on the lean side is calculated according to the throttle valve opening, and the valve opening of the ISC valve is determined according to the deviation between the target intake air amount and the actual intake air amount. Is subjected to duty control, whereby the target intake air amount is supplied to the engine.

[0004] The above proposed device uses an air bypass valve (ABV) comprising a bypass valve and a negative pressure responsive valve as a device for supplying lean air. The engine is used when switching between stoichiometric operation and lean operation. There is an advantage that output torque fluctuation is small and this switching can be performed in a short time. FIG. 1 exemplifies a time change of an intake air amount, an ignition timing, an air-fuel ratio (A / F), and an engine output torque at the time of transition from the stoichiometric operation to the lean operation when the ignition timing control is introduced into the proposed device. As shown in the drawing, the intake air amount increases with a first-order lag as the ISC opening increases. Further, the torque fluctuation during the transition from the stoichiometric operation to the lean operation is small.

[0005]

Although the proposed device has the above-mentioned advantages, the ISC is required to accurately measure the bypass air necessary for maintaining the same torque during the lean operation and the stoichiometric operation. An auxiliary device such as a valve is required, and the device configuration becomes complicated. In order to simplify the configuration of the apparatus, it is conceivable that the air bypass valve is removed and the bypass air is supplied only by the ISC valve in the proposed apparatus. However, ISC
Since the response of the intake air amount to the change in the valve opening is slow, in this case, as shown by the solid line in FIG. 2, the engine output torque suddenly drops when switching between the lean operation and the stoichiometric operation, causing a shock. become. Further, as shown by the broken line in FIG. 2, when the air-fuel ratio is made leaner in accordance with the increase in the intake air amount, the torque drop is small,
Since the engine is operated for a long time in the air-fuel ratio region where the amount of generated nitrogen oxides is large, the amount of discharged nitrogen oxides increases.

Accordingly, the present invention provides a method for controlling a lean burn engine, wherein the switching between the stoichiometric operation and the lean operation of the engine can be executed by a simple control system while suppressing fluctuations in engine output and generation of nitrogen oxides. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an engine operating system.
Engine should be stoichiometric based on rolling state
Stoichiometric operation based on the first basic ignition timing basic air-fuel ratio and the first of is performed when it is determined that the region, en
When it is determined that the gin is in the region in which the lean operation is to be performed, the second basic air-fuel ratio is set on the lean side of the first basic air-fuel ratio and is set on the advance side of the first basic ignition timing. Lean- burn engine that controls the engine so that lean operation is performed based on the second basic ignition timing
In the control method, when the control is switched from the stoichiometric operation to the lean operation, the intake air is operated under the operation at the first basic air-fuel ratio and the first basic ignition timing.
The control for increasing the amount is started, and after the control for increasing the amount is started.
The ignition timing is increased at the timing when the actual intake air amount starts increasing.
After once changing to the retard side from the first basic ignition timing
The air-fuel ratio and the ignition timing are controlled to the second basic air-fuel ratio and the second basic ignition timing.

[0008]

When the operation is shifted from the stoichiometric operation range to the lean operation range, the control for increasing the intake air amount is started under the operation at the first basic air-fuel ratio and the first basic ignition timing.
After the start of the increase control of
At the start timing, the ignition timing is changed to a more retarded side than the first basic ignition timing. Next, the air-fuel ratio is controlled to a second basic air-fuel ratio set leaner than the first basic air-fuel ratio, and the ignition timing is set to a more advanced angle than the first basic ignition timing. Control is performed at the second basic ignition timing, whereby the operation shifts to the lean operation.

[0009]

Referring to FIG. 3, an electromagnetic fuel injection valve 3 is provided for each cylinder in an intake manifold 2a connected to each cylinder of the engine 1, and a fuel pressure regulator (not shown) is provided from a fuel pump (not shown). A constant-pressure fuel is supplied to each fuel injection valve 3 via an unillustrated illustration). The intake manifold 2a is connected to an intake pipe 2b, which cooperates with the intake manifold 2a, via a surge tank 2c. An air cleaner 4 is provided at an outer end of the intake pipe 2b. A throttle valve 5 is provided in the middle of the intake pipe 2b. The ignition plug 6 mounted on each cylinder of the engine 1 is connected to an igniter 8 via a distributor 7.
The high voltage generated in the secondary coil when the supply current to the primary coil of the igniter 8 is cut off causes the spark plug 6 to spark and ignite the mixture in the engine cylinder.

A control device for implementing the control method according to the first embodiment of the present invention is an electronic control unit (ECU) having functions such as an operation range determining means and an operation control means in air-fuel ratio / ignition timing control described later. The control unit 10 includes a central processing unit, a storage device including a non-volatile battery backup ram for storing various control programs and the like, an input / output device, and the like (all not shown).

The control device further includes an ISC valve 30 disposed in a bypass passage 20 provided in the intake pipe 2b, bypassing the throttle valve 5. The ISC valve 30 constitutes an intake air amount increasing / decreasing means in cooperation with the control unit 10, and opens and closes the bypass passage 20 to permit or prevent air supply to the engine 1 through the bypass passage 20. It includes a body 31 and a pulse motor 32 for driving the body 31 to open and close. The pulse motor 32 is connected to the output side of the control unit 10 together with the fuel injection valve 3 and the igniter 8.

Further, the control device has various sensors as engine operating state detecting means. These sensors are, for example, air flow sensors 41 provided on the intake passage 2 side for detecting the amount of intake air from Karman vortex information.
And a potentiometer type throttle sensor 42 attached to the throttle valve 5 for detecting the throttle opening.
An O2 sensor 43 provided on the exhaust passage 9 side of the engine 1 for detecting the oxygen concentration in the exhaust gas, a water temperature sensor 44 for detecting the engine cooling water temperature, and a predetermined crank angle position provided on the distributor 7, for example. Includes a crank angle sensor 45 that outputs a pulse signal (TDC signal) every time a top dead center is detected, and a cylinder discrimination sensor 46 for detecting that a specific cylinder, for example, the first cylinder is at a predetermined crank angle position. . Reference numeral 47 denotes a boost sensor used for performing the control method according to the second embodiment of the present invention.
c, which detects the negative pressure in the intake pipe downstream of the throttle valve 5. The various sensors described above are connected to the input side of the electronic control unit 10.

The electronic control unit 10 is provided with a TDC transmitted from the crank angle sensor 45 every 180 degrees of the crank angle.
The engine speed is calculated from the stroke cycle of the engine detected based on the signal generation interval, and the ignition / fuel supply is then determined based on the output from the cylinder discrimination sensor 46 and the preset ignition / fuel supply sequence in the engine cylinder. The cylinder to be used is determined.

Further, the electronic control unit 10 performs an idle operation state, a high load operation state,
Various engine operation states such as a low load operation state, a deceleration fuel cut operation state, and an O2 feedback control operation state are detected, and the fuel injection amount according to the detected engine operation state, that is, the opening time of the fuel injection valve 3 and the optimum Calculate the ignition timing,
A drive signal corresponding to the calculated valve opening time is supplied to each fuel injection valve 3 to supply a required amount of fuel to each cylinder, and a drive signal corresponding to the calculated ignition timing is supplied from the drive circuit to the igniter 8. To ignite the mixture.

The operation of the control device having the above configuration will be described below. During the operation of the engine 1, the electronic control unit 10 executes an engine operation control routine shown in FIG. 4 at a predetermined cycle. In this control routine, the control unit 10
First, it is determined whether or not the flag F1 is a value "1" indicating that the switching control from the stoichiometric operation to the lean operation is being performed (step S1). The flag value F2n set as described later in the last cycle of the routine and stored in the present flag value storage area (not shown) of the storage device of the control unit 10 is
The previous flag value F2n- is stored in a previous flag value storage area (not shown).
It is stored as 1 (step S2). The flag F2 indicates the engine operating range, and its initial value is, for example, "1".

Next, the control unit 10 reads the outputs from the throttle sensor 42 and the crank angle sensor 45 (step S3), detects the cycle of the output of the crank angle sensor, and calculates the engine speed Ne from the detected cycle. (Step S4). Further, the control unit 10
The stoichiometric operation of the engine 1 is performed based on the throttle sensor output read in step S3, that is, the throttle opening α and the engine speed Ne calculated in step S4.
It is determined whether or not the vehicle is operating in a region to be performed (stoichiometric operation region) (step S5). The stoichiometric operation range is set in advance by an engine operation state parameter such as a throttle opening α and an engine speed Ne so as to correspond to a sudden start operation state, a rapid acceleration operation state, and the like of the engine 1.

If the result of the determination in step S5 is affirmative, the control unit 10 sets the current flag value F2n to a value "1" representing the stoichiometric operation range, and stores this in the current flag value storage area. (Step S6) Next, stoichiometric operation control is performed (Step S7). In the stoichiometric operation control, the electronic control unit 10 supplies an amount of basic auxiliary air suitable for the operation state to the engine 1 via the bypass passage 20 in accordance with the engine operation state parameters such as the throttle opening α and the engine speed Ne. The opening degree of the ISC valve 30 is controlled to the basic opening degree PBAS corresponding to the basic auxiliary air amount, so that the engine speed is rapidly reduced due to the rapid closing operation of the throttle valve 5. Prevent stop.

The electronic control unit 10 calculates the valve opening time Tinj of the fuel injection valve 3 according to the following equation. Tinj = (A / Nm ÷ λS) × K1 × K2 + T0 Here, A / Nm is sucked into the cylinder obtained from the Karman vortex frequency detected by the air flow sensor 41 and the engine speed Ne calculated in step S4. This is the amount of air per intake stroke. λS is a target air-fuel ratio (first basic air-fuel ratio), which is set to a stoichiometric air-fuel ratio or a value near the stoichiometric air-fuel ratio (for example, an air-fuel ratio of 14.7). K1 represents a coefficient for converting the fuel flow rate into the valve opening time. K2 is a correction coefficient value set by various parameters representing the engine operating state, and is set according to, for example, the engine water temperature TW detected by the engine water temperature sensor 44, the oxygen concentration in the exhaust gas detected by the O2 sensor 43, and the like. You. T0
Is a correction value set according to a battery voltage or the like detected by a battery sensor (not shown).

The electronic control unit 10 supplies a drive signal corresponding to the valve opening time Tinj calculated as described above to the fuel injection valve 3 and supplies a fuel amount corresponding to the valve opening time Tinj this time. The engine 1 is supplied to the cylinder to perform the stoichiometric operation of the engine 1. During the stoichiometric operation, the control unit 10 sends a drive signal to the igniter 8 based on the first basic ignition timing θIG1 set in advance as a function of the engine speed Ne or the like, and the control unit 10 transmits the drive signal at the crank angle position corresponding to the ignition timing θIG1. The ignition timing is controlled so that the ignition is performed.

Referring again to FIG. 4, the control routine will be further described. If the determination result in step S5 is negative, that is, if it is determined that the engine 1 is not operating in the stoichiometric operation range, the control unit 10 sets the current flag value F
2n is set to a value “0” representing a lean operation area (an area where lean operation is to be performed) , and this is stored in a current flag value storage area (step S8), and then stored in a previous flag value storage area in step S2. It is determined whether or not the previous flag value F2n-1 is the value "1" representing the stoichiometric operation range (step S9). If the determination result is affirmative, the flag F1 is set to the value "1" in step S10. Then, the execution of the present control routine in the current cycle ends.

In step S1 of the next cycle, the flag F
Since it is determined that the value of 1 is “1”, the control unit 11 performs the switching control shown in detail in FIGS. 5 to 8 for shifting from the stoichiometric operation to the lean operation (step S11). In this switching control, the control unit 1
0 is the throttle opening α detected in step S3 of FIG.
A response delay time T1 of the intake air amount with respect to the ISC valve opening operation is determined from an α · Ne-T1 map (not shown) based on the engine speed Ne calculated in step S4 and
From the α · Ne-T2 map (not shown), the retard control time T2
, And an advance control time T3 is obtained from an α · Ne-T3 map (not shown) (step S21).

Next, based on the throttle opening α and the engine speed Ne, the control unit 10 controls the I-state from the start of switching from the stoichiometric operation to the lean operation to the completion of the switching.
The SC valve opening amount ΔPISC is calculated (step S2).
2). In the calculation of the ISC valve opening amount ΔPISC, the target intake air amount A / NL at the time of lean operation is stored in the storage device of the control unit 10 in advance based on the throttle opening α and the engine speed Ne. Ne-A /
It is read from an NL map (not shown). This map preferably keeps the fuel supply amount to the engine 1 substantially constant so as to give the air amount necessary for obtaining substantially the same torque as the engine torque in the stoichiometric operation in the lean operation. On the other hand, the stoichiometric operation is switched to the lean operation by increasing only the air amount so that the engine shock can be prevented.

It should be noted that the target intake air amount A /
NL may be set according to the engine operating state. In this case, the intake air amount A / NS during the stoichiometric operation read from the α · Ne-A / NS map (not shown) based on the throttle valve opening α and the engine speed Ne, and the target air amount during the lean operation. Based on the fuel ratio λL and the target air-fuel ratio (second basic air-fuel ratio) λS during the stoichiometric operation, the target intake air amount A / NL is calculated from the following equation. Note that the target air-fuel ratio λL
Is set to a predetermined value on the fuel lean side of the stoichiometric air-fuel ratio (for example, the air-fuel ratio 22).

A / NL = (A / NS ÷ λS) × λL When the target intake air amount A / NL is obtained as described above,
The control unit 10 obtains a deviation ΔA / N between the target intake air amount A / NL and the actual intake air amount A / Nm, and then calculates an ISC valve opening amount ΔPISC according to the deviation ΔA / N by, for example, the following equation. Is calculated from

ΔPISC = KP · ΔA / N where KP is a feedback proportional term gain. The gain KP may be variably set according to the engine speed Ne, for example. When the ISC valve opening operation amount ΔPISC is obtained in step S22, the control unit 10 calculates the target ISC valve opening PISC at the time of completion of the switching control from the following equation in step S23.

PISC = PBAS + ΔPISC Next, the ISC valve opening operation amount ΔPISC and step S
21, the response delay time T1, the retard control time T2, and the advance control time T3, and the control operation cycle ΔT
Based on the above, the ISC valve opening change amount ΔDISC per one control operation cycle ΔT is calculated (step S2).
3).

In step S24, the retard control time T2 and the preset retard control amount Δ per one control operation cycle ΔT
The retard amount during the retard control time T2 is calculated based on θL (or the retard control amount ΔθL per one control operation cycle ΔT is calculated based on the preset retard amount and the retard control time T2). Next, the retard amount, the target ignition timing (second basic ignition timing) θIG2 during the lean operation, and the advance control time T
3 and the advance control amount Δ per one control operation cycle ΔT
θA is calculated.

In step S25, the target air-fuel ratio (first basic air-fuel ratio) λS during stoichiometric operation, the target air-fuel ratio (second basic air-fuel ratio) λL during lean operation, and the advance control time (air-fuel ratio leaning) Based on the control time T3, the air-fuel ratio control amount Δλ per one control operation period ΔT is calculated.
Next, the control unit 10 sets a rounded value T1 'obtained by dividing the response delay time T1 obtained in step S21 by the control operation period ΔT in a timer (not shown) (step S26). It is determined whether or not the stored value T1 ′ is “0” (step S27). Immediately after the response delay time T1 is set, the result of the determination in step S25 is negative, so that the control unit 10 waits for the control operation period ΔT and then subtracts “1” from the stored value T1 ′ of the timer (step S28, S29), the sum of the currently set ISC valve opening DISC (the initial value corresponds to the basic opening PBAS) and the ISC valve opening change amount ΔDISC is set as a new set ISC valve opening DISC (step S30). ), ISC
A drive signal corresponding to the valve opening change amount ΔDISC is sent to the pulse motor 32 to increase the opening of the ISC valve 30 (step S31). Thus, the opening operation of the ISC valve 30 in the switching control is started from the switching control start time (time t0 in FIG. 9).

Thereafter, steps S27 to S31 are repeatedly executed, and the ISC valve opening is controlled in an open loop such that the ISC valve opening gradually increases with time as shown in FIG. If it is determined in step S27 that the stored value T1 'of the timer has become "0", a value T2' corresponding to the retard control time T2 is set in the timer (step S32), and the stored value T2 'of the timer is set. "0"
Is determined (step S33). Immediately after the retard control time T2 is set, the result of the determination in step S33 is negative, so that the control unit 10 waits for the control operation period ΔT and then subtracts “1” from the stored value T2 ′ of the timer ( Steps S34 and S35), a value obtained by subtracting a preset retard control amount ΔθL per one control operation cycle ΔT from the current set ignition timing θIG (the initial value is the same as the first basic ignition timing θIG1) The new set ignition timing θIG is set, and the sum of the currently set ISC valve opening DISC and the ISC valve opening change amount ΔDISC is set as a new set ISC valve opening DISC (step S36). A drive signal corresponding to the ignition timing θIG is sent to the igniter 8 to retard the ignition timing, and a drive signal corresponding to the ISC valve opening change amount ΔDISC is sent to the pulse motor 32 to output the IS signal. The C valve opening is increased (step S37). Thus, when the response delay time T1 of the intake air amount to the change in the ISC valve opening elapses from the switching control start time t0 and the intake air amount starts to increase (time t1), the intake air amount is continuously increased. At the same time, the retard control is started in order to suppress an increase in torque due to the increase in the intake air amount.

Thereafter, steps S33 to S37 are repeatedly executed, and the ignition timing is controlled to be delayed with respect to the first ignition timing θIG1 as time passes, as shown in FIG.
A torque fluctuation due to an increase in the intake air amount is prevented. If it is determined in step S33 that the stored value T2 'of the timer has become "0", a value T3' corresponding to the advance control time T3 is set in the timer (step S38), and the stored value T2 'of the timer is set. It is determined whether it is "0" (step S39). Immediately after the advance control time T3 is set, the result of the determination in step S39 is negative, so that the control unit 10 subtracts “1” from the stored value T3 ′ of the timer after waiting for the control operation period ΔT ( (Steps S40 and S41), the sum of the current set ignition timing θIG (initial value is equal to θIG1−ΔθL · (T2 / ΔT)) and the retard control amount ΔθA per one control operation cycle ΔT calculated in step S24. A new set ignition timing θIG is set (step S42), and then the current target air-fuel ratio λ (the initial value is the same as the target air-fuel ratio (first basic air-fuel ratio) λS during stoichiometric operation) and step S25. The sum with the calculated air-fuel ratio control amount Δλ per one control operation cycle ΔT is set as a new target air-fuel ratio λ (step S43). Then, the control unit 10 sets the set ISC valve opening DISC
Is determined to have reached the target ISC valve opening PISC (step S44). If the determination result is negative, the set ISC valve opening DISC is updated and the drive signal corresponding to the ISC valve opening change amount ΔDISC is determined. If the determination result is affirmative, the update of the set ISC valve opening and the transmission of the drive signal are terminated (step S45),
Until the target ISC valve opening PISC is reached, a drive signal corresponding to the set ignition timing θIG is sent to the igniter 8 to advance the ignition timing while the ISC valve opening is increased, and the air-fuel ratio is set to the target air-fuel ratio λ. A drive signal corresponding to the valve opening time is sent to the fuel injection valve 3 to make the air-fuel ratio lean (step S46).

As described above, the leaning of the air-fuel ratio is started at the time point t2 when the time T2 has elapsed from the time point t1 at which the intake air amount starts to increase, in other words, when the intake air amount has increased considerably. Is done. In addition, the ignition timing is advanced as the lean operation proceeds. Therefore, unlike the case where the leaning is started at the same time as the opening of the ISC valve as shown by the solid line in FIG. 2, a large torque drop does not occur. That is, as shown in FIG. 9, the drop in torque is small, and the occurrence of shock is avoided. Further, as compared with the case shown by the broken line in FIG. 2, the time required for switching the air-fuel ratio, and hence the engine operation time in the air-fuel ratio region where the nitrogen oxides increase, is shorter, and the emission of nitrogen oxides is suppressed.

Thereafter, steps S39 to S44 are repeatedly executed, and as shown in FIG. 9, the ignition timing is changed from the value on the delay side with respect to the first basic ignition timing θIG1 suitable for the stoichiometric operation to the second suitable for the lean operation. Basic ignition timing θ
The advance angle is controlled toward IG2, and the air-fuel ratio A / F is controlled to be lean from a first basic air-fuel ratio suitable for stoichiometric operation to a second basic air-fuel ratio suitable for lean operation.

When it is determined in step S39 that T3 '= 0, the switching control routine shown in FIGS.
The control unit 10 returns to the control routine of
Is set to a value "0" indicating the completion of the switching control (step S12 in FIG. 4). At the time point when this switching control is completed (time point t3 in FIG. 9), since the intake air amount has not completely reached the target intake air amount A / NL during the lean operation, the engine output torque drops as shown in FIG. . However, a considerable amount of intake air has been supplied to the engine 1 after a considerable period of time has elapsed since the start of the opening operation of the ISC valve 30, and the drop in the torque is slight, so that the occurrence of a shock may not occur. Absent.

After the completion of the switching control, the control routine of FIG. 4 is executed again. Since the value of the flag F1 is set to "0" when the switching control is completed, the steps of the control routine execution cycle immediately after the completion of the switching control are performed. The determination result in S1 is negative. Then, in step S2, the F2 flag value 0 at the start of the switching control is stored as F2n-1 and
Since it is determined in step S5 that the vehicle is not in the stoichiometric operation range and the flag value F2n is set to "0" in step S8, the determination result in step S9 is negative. Therefore, the lean operation control (step S
13) will be executed.

In this lean operation control, the electronic control unit 10 controls the opening degree of the ISC valve 30 so that the intake air amount becomes the target intake air amount A / NL during the lean operation, and the air-fuel ratio becomes lean. The opening time of the fuel injection valve 3 so that the target air-fuel ratio λL at the time of operation, that is, the engine 1
The ignition timing is controlled to the target ignition timing θIG2 during the lean operation.

Hereinafter, a method for controlling a lean burn engine according to a second embodiment of the present invention will be described. The control method according to this embodiment is similar to the control method shown in FIG.
Can be implemented by a control device additionally equipped with the control device, and therefore, the description of the device configuration is omitted. The method of the present embodiment is basically the same as that of the first embodiment, and executes the control procedure shown in FIG. 4 and performs the switching control (steps S11 to S12 in FIG. 4) shown in FIG. Some of which are shown in detail)
Are partially different from those shown in FIGS.

Referring to FIGS. 10 to 12, step S121 of the switching control corresponds to step S21 of FIG.
The electronic control unit 10 reads the output from the boost sensor 47 representing the intake pipe negative pressure PB0 at the start of the switching control, stores the output, and stores the pressure data PB0 and the engine speed calculated in step S4 in FIG. Based on the number Ne, the set value ΔP of the intake pipe negative pressure rise amount in the period from the switching control start time t0 to the air-fuel ratio lean control start time t2 is obtained from a PB0 · Ne-ΔP map (not shown) and not shown. An advance control time T3 is obtained from the PB0 Ne-T3 map.

Next, steps S122 to S125 corresponding to steps S22 to S25 in FIG. 5 are sequentially executed, and the ISC from the switching control start time t0 to the completion time t3 is performed.
Valve opening amount ΔPISC, ISC valve opening change amount ΔDISC per control operation period ΔT, advance angle control amount ΔθA
And the air-fuel ratio control amount Δλ is determined. Next, the electronic control unit 10 reads the boost sensor output PB (step S126), and the pressure data PB is stored in the step S12.
It is determined whether the pressure data exceeds the pressure data PB0 stored in step 1 (step S127). Immediately after the start of the switching control, the result of this determination is negative, so that the control unit 10 sequentially executes steps S128 to S130 respectively corresponding to steps S28, S30 and S31 in FIG. Start the valve opening operation.

Thereafter, steps S126 to S130 are repeatedly executed, and the ISC valve opening gradually increases with time. Then, near the time point t1 in FIG. 9, the intake air amount and, consequently, the negative pressure PB in the intake pipe begin to increase, and step S12
The determination result at 7 becomes positive. In this case, the control unit 10 transmits the pressure data PB read in step S126.
Is determined to have reached the sum of the pressure data PB0 at the switching control start time t0 and the pressure increase amount ΔP determined in step S121 (step S131).

In the vicinity of the time point t1 at which the intake air amount starts to increase, the increase in the intake pipe pressure due to the increase in the intake air amount is not yet large, so that the determination result in step S131 is negative. Therefore, the control unit 1 executes step S1 corresponding to steps S34, S36 and S37 in FIG.
32 to S134 are sequentially executed to start the ignition timing retard control in the switching control while increasing the ISC valve opening, then read the boost sensor output PB (step S135), and execute the above steps S131 to S135. Execute repeatedly.

Then, in step S131, when it is determined that the pressure data PB has reached the sum of the pressure data PB0 and the pressure increase amount ΔP, and therefore, it is necessary to start leaning the air-fuel ratio, the control unit 10 proceeds to step S131. Step S3 of 8
8 to S46 are sequentially executed to perform the lean control of the air-fuel ratio while performing the ISC valve opening control and the ignition timing advance control.

The present invention is not limited to the first and second embodiments, but can be variously modified, and is also applicable to a drive-by-wire type throttle control system, that is, a throttle valve direct-acting system. For example, in both embodiments, the bypass passage 20 and the ISC
The switching control from the stoichiometric operation to the lean operation and the air supply control in the lean operation control are performed using the valve 30, but this may be performed using a dedicated bypass passage and a valve. Also, a small flow rate air bypass valve may be used in combination.

[0043]

According to the present invention as described above, the present invention is, luck of the engine
Engine should be stoichiometric based on rolling state
Stoichiometric operation based on the first basic ignition timing basic air-fuel ratio and the first of is performed when it is determined that the region, en
When it is determined that the gin is in the region in which the lean operation is to be performed, the second basic air-fuel ratio is set on the lean side of the first basic air-fuel ratio and is set on the advance side of the first basic ignition timing. Lean- burn engine that controls the engine so that lean operation is performed based on the second basic ignition timing
In the control method, when the control is switched from the stoichiometric operation to the lean operation, the intake air is operated under the operation at the first basic air-fuel ratio and the first basic ignition timing.
The control for increasing the amount is started, and after the control for increasing the amount is started.
The ignition timing is increased at the timing when the actual intake air amount starts increasing.
After once changing to the retard side from the first basic ignition timing
In addition, since the air-fuel ratio and the ignition timing are controlled to the second basic air-fuel ratio and the second basic ignition timing, the stoichiometric operation of the engine while suppressing the fluctuation of the engine output and the generation of nitrogen oxides. Switching to lean operation can be performed by a simple control system.

[Brief description of the drawings]

FIG. 1 is a graph exemplifying a change over time of an intake air amount, an ignition timing, an air-fuel ratio, and an engine output torque when a transition is made from a stoichiometric operation to a lean operation when ignition timing control is introduced into a conventional device.

FIG. 2 is a graph similar to FIG. 1 exemplifying a temporal change of an intake air amount or the like when bypass air is supplied only by an ISC valve in the conventional apparatus related to FIG. 1;

FIG. 3 is a schematic diagram showing a control device for carrying out the control method of the present invention, with a block diagram showing a part together with peripheral elements.

FIG. 4 is a flowchart showing an engine operation control routine executed by the electronic control unit 10 shown in FIG. 3 in the control method according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing a part of a control procedure in switching control in the engine operation control routine shown in FIG. 4;

FIG. 6 is a flowchart showing a control procedure in the switching control following the control procedure shown in FIG.

FIG. 7 is a flowchart showing a control procedure in the switching control following the control procedure shown in FIG.

FIG. 8 is a flowchart showing a control procedure in the switching control following the control procedure shown in FIG.

FIG. 9 shows the ISC valve opening degree, intake air amount, ignition timing, before and after the switching control in the control method according to the first embodiment of the present invention;
4 is a graph illustrating the time change of the air-fuel ratio and the engine output torque.

FIG. 10 is a flowchart showing a part of a control procedure in switching control in a control method according to a second embodiment of the present invention.

FIG. 11 is a flowchart showing a control procedure in the switching control following the control procedure of FIG.

FIG. 12 is a flowchart showing a control procedure in the switching control following the control procedure of FIG. 11;

[Explanation of symbols]

 Reference Signs List 1 engine 2 intake passage 3 fuel injection valve 5 throttle valve 6 spark plug 8 igniter 10 electronic control unit 20 bypass passage 30 ISC valve 41 air flow sensor 42 throttle sensor 45 crank angle sensor 47 boost sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02P 5/15 F02P 5/15 B

Claims (1)

(57) [Claims] 1. The engine according to claim 1 , wherein
When it is determined that the gin is in the region where the stoichiometric operation is to be performed, the stoichiometric operation is performed based on the first basic air-fuel ratio and the first basic ignition timing, and the engine operates in the lean operation.
The set in the first second basic air-fuel ratio and the first advance side of the basic ignition timing set by leaner than the basic air-fuel ratio when it is determined that the area to be Second, a lean-burn engine control method for controlling the engine so that lean operation is performed based on the basic ignition timing.
Oite, when the switching control to the lean operation from the stoichiometric operation to start increasing control of the intake air amount under the operation at timing the first basic air-fuel ratio and the first basic ignition
And the actual intake air amount after the start of the increase control.
At the start timing, the ignition timing is set to the first basic ignition timing.
And controlling the air-fuel ratio and the ignition timing to the second basic air-fuel ratio and the second basic ignition timing, respectively, after once changing the ignition timing to a more retarded side .