JP2768098B2 - Engine air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an engine which controls an air-fuel ratio based on a detection result from an air-fuel ratio sensor provided in an engine exhaust system.

[0002]

2. Description of the Related Art Conventionally, there have been proposed a large number of sensors that perform air-fuel ratio control based on detection results from an O ₂ sensor (air-fuel ratio sensor) provided in an engine exhaust system. On the other hand, it has also been proposed to perform the air-fuel ratio feedback control by the O ₂ sensor at a low engine temperature due to a demand for measures against exhaust gas.

[0003]

However, when the air-fuel ratio feedback control by the O ₂ sensor is performed from a time when the engine temperature is low as described above, there are the following problems. That is, when the engine is at a low temperature, an air-fuel ratio that tends to be rich is generally given in many cases. Therefore, an overshoot may occur when the air-fuel ratio is controlled to the lean side by the air-fuel ratio feedback control, and the engine may be over-lean. If the output state deteriorates, or if an acceleration operation or the like is performed from this state, drivability may be degraded.

The present invention has been made in view of the above problems, and even when the air-fuel ratio feedback control is performed by an air-fuel ratio sensor from a low engine temperature, the engine output state deteriorates or drivability during acceleration is reduced. It is an object of the present invention to provide an air-fuel ratio control device for an engine, which does not cause deterioration of the engine.

[0005]

Therefore, an air-fuel ratio control apparatus for an engine according to the present invention is provided in an engine exhaust system.
And an air-fuel ratio sensor.
-Fuel ratio control that performs air-fuel ratio control based on detection results from
Means, wherein the air-fuel ratio control means includes a first engine temperature.
Air-fuel ratio based on the detection results from the air-fuel ratio sensor
Control and the first engine
The air-fuel ratio will not exceed the specified value above the gin temperature.
Air-fuel ratio clip means,
When the engine temperature rises, the fuel
To shift the value of the air-fuel ratio that should be
And the air-fuel ratio control means is a first engine
Air-fuel based on the detection result from the air-fuel ratio sensor at or above the temperature
The air-fuel ratio is controlled for a predetermined time after the engine is started.
Prohibit air-fuel ratio control based on detection results from sensors
And at a temperature lower than the first engine temperature.
Higher than second engine temperature, lower than warm-up temperature
At a higher temperature than when the temperature is equal to or higher than the second engine temperature.
It is characterized in that the time for prohibiting the air-fuel ratio control is set to be long .

[0006]

[0007]

[0008]

In the above-described air-fuel ratio control apparatus for an engine according to the present invention (claim 1) , the first engine is controlled by the air-fuel ratio control means.
Air-fuel ratio based on the detection result from the air-fuel ratio sensor above the temperature
Control and air-fuel above the first engine temperature
Make sure that the ratio does not exceed the specified value, and
As the air temperature increases, the air-fuel ratio value to be clipped is
To the right side.

[0009]

[0010] is et al., The air-fuel ratio control apparatus for an engine of the present invention (claim 1), by the air-fuel ratio control means performs air-fuel ratio control based on the detection result from the air-fuel ratio sensor at a first engine temperature or higher However, the air-fuel ratio control based on the detection result from the air-fuel ratio sensor is prohibited for a predetermined time after the engine is started. Then, at a temperature lower than the second engine temperature higher than the first engine temperature and lower than the post-warm-up temperature,
The time during which the air-fuel ratio control is prohibited is longer than when the temperature is equal to or higher than the second engine temperature.

[0011]

1 to 6 show an air-fuel ratio control device for an engine according to an embodiment of the present invention, and FIG. 1 shows a control system thereof. FIG. 2 is a hardware block diagram of the control system, FIG. 3 is an overall configuration diagram of an engine system having the present apparatus, FIGS. 4 and 5 are flowcharts each explaining a control procedure thereof, and FIG. FIG.

FIG. 3 shows an engine system having the present apparatus. In FIG. 3, an engine (internal combustion engine) EG has an intake passage 2 and an exhaust passage 3 leading to a combustion chamber 1 of the engine. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4, and the communication between the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5.

The intake passage 2 is provided with an air cleaner 6, a throttle valve 7, and an electromagnetic fuel injection valve (injector) 8 in this order from the upstream side. A catalytic converter (three-way catalyst) 9 and a muffler (muffler) (not shown) are provided. The intake passage 2 has a surge tank 2
a is provided.

Further, the injectors 8 are provided in the intake manifold portion by the number of cylinders. Now, assuming that the engine EG of this embodiment is an in-line four-cylinder engine, four injectors 8 are provided. That is, it can be said that the engine is a so-called multi-point fuel injection (MPI) type multi-cylinder engine. Also, the throttle valve 7
Is connected to the accelerator pedal via a wire cable, so that the opening changes according to the amount of depression of the accelerator pedal, and is further opened and closed by an idle speed control motor (ISC motor). Thus, the opening of the throttle valve 7 can be changed without depressing the accelerator pedal during idling.

With such a configuration, the air sucked through the air cleaner 6 according to the opening degree of the throttle valve 7 is mixed with the fuel from the injector 8 at the intake manifold so as to have an appropriate air-fuel ratio. By igniting the spark plug 35 at an appropriate timing, the fuel is burned to generate engine torque, and then the air-fuel mixture is discharged to the exhaust passage 3 as exhaust gas. , NOx are purified, then muffled by a muffler and released to the atmosphere.

Further, various sensors are provided to control the engine EG. First, on the side of the intake passage 2, an air flow sensor (intake amount sensor) 11 for detecting an intake air amount from Karman vortex information, an intake air temperature sensor 12 for detecting an intake air temperature, and an atmospheric pressure are provided in an air cleaner portion. An atmospheric pressure sensor 13 is provided, and a potentiometer type throttle sensor 1 for detecting an opening degree of a throttle valve 7 is provided at a portion where the throttle valve is provided.
4. Idle switch 15 for detecting idling state
Etc. are provided.

On the exhaust passage 3 side, an oxygen concentration sensor (air-fuel ratio sensor) 17 (hereinafter, referred to as an air-fuel ratio sensor) for detecting the oxygen concentration (O ₂ concentration) in the exhaust gas is provided upstream of the catalytic converter 9.
Simply O of ₂ sensor 17) is provided. In addition,
As the O ₂ sensor 17, a sensor with a heater or a sensor without a heater may be used. further,
As other sensors, a water temperature sensor 19 for detecting an engine cooling water temperature, and a crank angle sensor 21 for detecting a crank angle as shown in FIG.
1 is also a rotation speed sensor for detecting the engine rotation speed) and T for detecting the top dead center of the first cylinder (reference cylinder).
A DC sensor (cylinder discrimination sensor) 22 is provided in each distributor.

The detection signals from these sensors are input to an electronic control unit (ECU) 23. The ECU 23 is also supplied with a voltage signal from a battery sensor 25 for detecting the voltage of the battery and a signal from a cranking switch 20 or an ignition switch (key switch) for detecting the start time.

The hardware configuration of the ECU 23 is as shown in FIG. 2. The ECU 23 has a CPU 27 as its main part. The CPU 27 has an intake air temperature sensor 12, an atmospheric pressure sensor 13, a throttle sensor 14, O ₂ sensor 17, together with detection signals from the water temperature sensor 19 and the battery sensor 25 is input through an input interface 28 and the a / D converter 30, an air flow sensor 11, a crank angle sensor 2
1, detection signals from a TDC sensor 22, an idle switch 15, a cranking switch 20, an ignition switch, and the like are input via an input interface 29.

Further, the CPU 27 has a ROM for storing program data and fixed value data via a bus line.
31, data is exchanged between a battery 32 and a battery backup RAM (not shown) which is backed up by holding the stored contents while the battery 32 is connected. Has become.

The data in the RAM 32 disappears and is reset when the ignition switch is turned off. The fuel injection control signal based on the calculation result by the CPU 27 is transmitted to the solenoid (injector solenoid) 8 of the injector 8 via the four injection drivers 34.
a (more precisely, a transistor for the injector solenoid 8a).

Focusing on fuel injection control (air-fuel ratio control), a control signal for fuel injection calculated by a method described later is output from the CPU 27 to the injector solenoid 8a via the driver 34, and the four injectors 8 are controlled. Are sequentially driven. For such fuel injection control (injector drive time control), the ECU 23
As shown in FIG. 1, first, the intake air from the basic drive time has a basic driving time determining means 51 for determining the T _B, the basic drive time determining means 51 the air flow sensor 11 for an injector 8 determine the amount a information and the intake air quantity a / N information per revolution engine from the engine speed N information from the crank angle sensor 21, it is to determine the basic drive time T _B based on this information.

A feedback air-fuel ratio correction coefficient setting means 52 for setting a feedback correction coefficient K _FB (= K _AF ) in accordance with the result of comparison between the output of the O ₂ sensor 17 and the judgment voltage (reference voltage) is provided. In addition, air-fuel ratio correction coefficient setting means 53 for setting an air-fuel ratio correction coefficient K _AFM (= K _AF ) based on the engine speed N and the engine load A / N is provided.
59, the output of one of the feedback air-fuel ratio correction coefficient setting means 52 and the air-fuel ratio correction coefficient setting means 53 is selected.

Further, a warm-up correction coefficient setting means 55 for setting a warm-up correction coefficient K _TW according to the engine cooling water temperature Tw detected by the water temperature sensor 19, the intake air temperature detected by the intake air temperature sensor 12, and the atmospheric pressure sensor 13 correction means 56 is provided for setting the correction coefficient K in accordance with the atmospheric pressure or the like detected by the further sets the dead time (dead time) T _D for correcting the driving time according to the battery voltage Dead time correction means 57 is also provided.

Although not shown, the engine is started during the start.
Set the start-up fuel injection time according to the cooling water temperature
A start-up injection time setting means is also provided.
In the setting at this start time injection time setting means
Fuel is injected during the fuel injection time at startup, and after startup,
Drive time T_B, Air-fuel ratio correction coefficient K_AF, Water temperature correction coefficient K _TW
Fuel injection time T determined by_inj(= T_B× K_AF× K_TW×
K + T_D), The fuel is injected.

As described above, the ECU 23 sets the O
_{2 It} has the function of the air-fuel ratio control means for performing the air-fuel ratio control based on the detection result from the sensor 17,
The air-fuel ratio control means is provided with a function of an air-fuel ratio clip means for preventing the air-fuel ratio from becoming larger than a predetermined value when the engine temperature is low. More specifically, the air-fuel ratio control means performs the air-fuel ratio control based on the detection result from the O ₂ sensor 17 when the engine coolant temperature Tw is equal to or higher than a first temperature ((first engine temperature; for example, about 30 ° C.) T1). And an air-fuel ratio clipping means for preventing the air-fuel ratio from becoming larger than a predetermined value at the first temperature T1 or higher.
The air-fuel ratio clipping means is configured to shift the value of the air-fuel ratio to be clipped to the lean side when the engine cooling water temperature Tw increases. The air-fuel ratio clipping means is configured to shift the value of the air-fuel ratio to be clipped to the lean side stepwise (two steps in this example) according to the engine cooling water temperature Tw.

Further, the air-fuel ratio control means, air at a first temperature T1 or perform an air-fuel ratio control based on the detection result from the O ₂ sensor 17, but after the engine is started a predetermined time based on the detection result from the O ₂ sensor The fuel ratio control is configured to be prohibited, and the post-warm-up temperature T3 higher than the first temperature T1 is set.
At a temperature lower than the second temperature (second engine temperature; for example, about 50 ° C.) T2 lower than (eg, 80 ° C.) T2, the time during which the air-fuel ratio control is prohibited is longer than at a temperature equal to or higher than the second temperature T2. It is set long.

If the relationship between the temperatures T1, T2, and T3 is expressed by an inequality, T1 <T2 <T3. less than,
This fuel injection control will be described with reference to the flowcharts shown in FIGS. First, after inputting the operating state information in step A1, it is determined in step A2 whether the engine is being started (cranking). If so, in step A3, the engine coolant temperature Tw is set to a predetermined value T2 ( Second temperature; for example, about 50 ° C.) or more. If Tw <T2, step A4
Then, the timer value TIM is set to TIM1, and if Tw ≧ T2, the timer value TIM is set to TIM2 in step A5. Here, when TIM1> TIM2, for example, T
IM1 is set to about 30 seconds, and TIM2 is set to about 15 seconds.

Thereafter, a starting fuel pulse width corresponding to the engine cooling water temperature Tw is set, this is input to the injection time T _inj (step A6), and the feedback flag FFB is set to 0 (step A7). Then, in step A17, the injector 8 is driven according to the fuel injection time T _inj . On the other hand, after starting the engine, step A
At 8, it is determined whether the timer value TIM is greater than zero. At first, since a predetermined timer value is set in step A4 or step A5, the timer value TIM is decremented in step A9, and then in step A10.
Then, the feedback flag FFB is set to 0, and in steps A11 and A12, the air-fuel ratio correction coefficient K corresponding to the intake air amount A / N and the engine speed N per one revolution of the engine.
Set the _AFM, put it to the K _FB.

Furthermore, in step A13, setting the warm-up correction factor K _TW corresponding to the engine coolant temperature Tw, even in step A14, setting the other correction coefficient K, T _D, also in step A15, the basic after setting the driving time T _B, in step A16, the fuel injection time _{T inj T B × K AF ×} K
Determined from _TW × K + T _D, in step A17, by driving the injector 8 in accordance with the fuel injection time T _inj, desired fuel is injected.

When the timer value TIM becomes 0 after the completion of the start and the time TIM1 or TIM2 has elapsed, the timer value TIM is reset to 0 in step A18, and then the engine cooling water temperature Tw is reduced in step A19. Feedback start temperature T1 (first temperature; for example, 30 °)
C) or more. The relationship between the temperatures T1 and T2 is T1 <T2 <T3 as described above. Here, T3 is a temperature after warm-up, for example, about 80 ° C.

If Tw ≧ T1, step A20
In, O ₂ sensor 17 to determine whether the activity, if O ₂
If the sensor active, in step A21, a feedback control operation zone with O ₂ sensor 17 -; determines whether the (feedback zone down F / B zone), if the feedback zone - if it is down, at step A22 ,
The feedback flag FFB is set to 1.

If Tw <T1, the O ₂ sensor 17 is inactive, or the feedback zone is not used, it is determined that the feedback control by the O ₂ sensor 17 cannot be performed, and steps A10 to A17 are performed. Is performed. After setting the feedback flag FFB to 1 as described above, it is determined that feedback control by the O ₂ sensor 17 is possible, and in step A23,
The O ₂ sensor output is compared with the reference voltage value (0.5 volt). If the O ₂ sensor output is equal to or less than the reference voltage value, in step A24, the feedback correction coefficient K _{FB is set} to 1 + I
+ While placing the P / 2, O ₂ when the sensor output is greater than the reference voltage value, in step A25, placing the feedback during correction coefficient K _FB and 1 + I-P / 2.

Here, P is a proportional control value, and I is an integral control value. The integral control value I is updated by an integration routine shown in FIG. That is, in step B1 shown in FIG.
It is determined whether or not feedback control by the O ₂ sensor 17 is possible.
Assuming that feedback control by the _two sensors 17 is possible, the output of the O ₂ sensor is compared with the reference voltage value (0.5 volt) in step B2, and if the output of the O ₂ sensor is equal to or less than the reference voltage value, step B3 in, while the integral gain ΔI is added to the integral control value I, O ₂ when the sensor output is greater than the reference voltage value, in step B4, the integral gain ΔI is subtracted from the integral control value I.

After step B3, it is determined whether or not the integral control value I is greater than the maximum clip value IMAX (step B5). If so, step B6
And I = IMAX. After step B4, it is determined whether or not the integral control value I is smaller than the minimum clip value IMIN (step B7).
At step B8, I = IMIN.

Thus, the integral control value I becomes IMAX and I
While taking the value between MIN and _TwoSensor output is reference
When the voltage is equal to or less than the voltage value, the integral control value I is increased,
O_TwoIf the sensor output is higher than the reference voltage,
The control value I is reduced. As a result, the feed
Back correction coefficient K_FBAlso O_TwoSensor output is reference voltage value
In the following cases, it increases and O_TwoWhen the sensor output is
If it is greater than the pressure value, it will decrease.

If FFB = 0 in step B1, it is determined that feedback control by the O ₂ sensor 17 is impossible, and the integral control value I is set to 0 in step B9. Incidentally, step A24 or A25 in FIG.
Thereafter, in step A26, it is determined whether the engine cooling water temperature Tw is equal to or higher than T2. If Tw ≧ T2, in step A27, the feedback-time correction coefficient minimum clip value K _FBMIN is _set to MIN1.
If <T2, in step A28, the feedback-time correction coefficient clip value K _FBMIN is _set to MIN2.

Here, MIN1 <MIN2 <1. Further, this MIN1 is 0 <IMIN + 1 <MIN1.
<K _FBMAX <1 + IMAX is satisfied. In addition,
K _{FBMA X} is feedback during correction coefficient maximum clip value, a K _FBMAX> 1. Then, step A27,
After A28, it is determined whether or not the feedback-time correction coefficient K _FB is smaller than the feedback-time correction coefficient minimum clip value K _FBMIN (step A29). If so, in step A30, K _FB = K _FBMIN is set. .

Further, at step A31, the feedback
Correction coefficient K_FBIs the maximum correction coefficient for feedback.
Top value K_FBMAXIs determined to be greater than
If there is, in step A32, K_FB= K_FBMAXIt is said.
After that, this K_FBTo K_AF(Step A3
3) In step A13, according to the engine cooling water temperature Tw
Warm-up correction coefficient K_TWIs set, and further, Step A14
And the other correction coefficients K and T_DAnd step A15
And the basic drive time T _BIs set, and then step A16
And the fuel injection time T_injTo T_B× K_AF× K_TW× K + T_D
In step A17, the fuel injection time T_inj
By driving the injector 8 according to the
Is injected.

Therefore, during the start of the engine, the fuel injection time T _inj is set based on the fuel pulse width data for start corresponding to the engine cooling water temperature Tw, and the injector 8 is driven according to this time T _inj. Is completed, the feedback control by the O ₂ sensor 17 is prohibited for a certain time (TIM1 or TIM2). While the feedback control is prohibited, the air-fuel ratio is actively set to rich. Further, in this case, from the relationship of TIM1> TIM2, when the engine cooling water temperature Tw is lower than the second temperature T2 which is higher than the first temperature T1 and lower than the post-warm-up temperature T3, the engine cooling water temperature Tw is higher than the second temperature T2. This means that the time during which the feedback air-fuel ratio control is prohibited is set longer than at the time.

Further, when the time for prohibiting the feedback air-fuel ratio control elapses, the feedback air-fuel ratio control based on the detection result from the O ₂ sensor 17 is performed when the engine cooling water temperature Tw is equal to or higher than the first temperature T1. The fuel ratio does not become larger (lean) than a predetermined value. Thus, even when the air-fuel ratio feedback control by the air-fuel ratio sensor is performed from a time when the engine is at a low temperature, the engine output state does not deteriorate and drivability does not deteriorate during acceleration.

When the engine cooling water temperature Tw as the engine temperature increases, the value of the air-fuel ratio to be clipped is shifted to the lean side. Specifically, the value of the air-fuel ratio to be clipped is shifted to the lean side when Tw is higher than T2 than when the engine cooling water temperature Tw is equal to or lower than T2. Thereby, according to the engine cooling water temperature Tw,
The shift of the value of the air-fuel ratio to be clipped to the lean side is performed stepwise.

When the engine cooling water temperature Tw becomes higher than T2, the clip to the lean side may be removed. When the engine is started in a state where the engine cooling water temperature Tw is equal to or lower than T1, the engine cooling water temperature Tw rises as shown in the characteristics of FIG. 6, but in this case, the feedback flag FFB and the air-fuel ratio correction coefficient K FIG. 6 shows how the _AF changes over time.

When the engine cooling water temperature Tw is T1 <Tw
When the engine is started in the state of <T2, the engine cooling water temperature Tw increases as shown in the characteristic of FIG.
FIG. 6 shows how the feedback flag FFB and the air-fuel ratio correction coefficient K _AF change over time in this case. Further, when the engine is started in a state where the engine cooling water temperature Tw is higher than T2, the engine cooling water temperature Tw rises as shown in the characteristic of FIG. 6, but in this case, the feedback flag FFB and the air-fuel ratio correction coefficient K FIG. 6 shows how the _AF changes over time.

[0045]

As described above in detail, according to the air-fuel ratio control apparatus for an engine of the present invention, when the engine temperature is low,
Since the air-fuel ratio is clipped so that it does not become larger than the predetermined value, even when the air-fuel ratio feedback control is performed by the air-fuel ratio sensor from when the engine is low, the engine output state deteriorates and drivability deteriorates during acceleration. There is an advantage that it does not invite.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control system of an air-fuel ratio control device for an engine as one embodiment of the present invention.

FIG. 2 is a hardware block diagram showing a control system of an engine air-fuel ratio control device as one embodiment of the present invention.

FIG. 3 is an overall configuration diagram of an engine system having an air-fuel ratio control device of the present engine.

FIG. 4 is a flowchart illustrating a control procedure according to an embodiment of the present invention.

FIG. 5 is a flowchart illustrating a control procedure according to an embodiment of the present invention.

FIG. 6 is an operation explanatory view of one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Intake passage 2a Surge tank 3 Exhaust passage 4 Intake valve 5 Exhaust valve 6 Air cleaner 7 Throttle valve 8 Injector 8a Injector solenoid 9 Catalytic converter 10 Canister 10A Purge introduction path 11 Air flow sensor (intake amount sensor) 12 Intake temperature sensor 13 Atmospheric pressure sensor 14 Throttle sensor 15 Idle switch 16 Purge control solenoid valve 16a Purge solenoid 17 O ₂ sensor 19 Water temperature sensor 20 Cranking switch 21 Crank angle sensor (engine speed sensor) 22 Cylinder discrimination sensor 23 Electronic control unit (ECU) 25 Battery sensor 27 CPU 28, 29 Input interface 30 A / D converter 31 ROM 32 RAM 34 Injection driver 35 Ignition plug 51 Driving time decision means 52 feedback time air-fuel ratio correction coefficient setting means 53 the air-fuel ratio correction coefficient setting means 55 warmup correction coefficient setting means 56 correction means 57 a dead time compensation means 58 the switching means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/14 310 F02D 45/00 368

Claims (1)

(57) [Claims] An engine exhaust system includes an air-fuel ratio sensor, and air-fuel ratio control means for performing air-fuel ratio control based on a detection result from the air-fuel ratio sensor. Air-fuel ratio control means for performing air-fuel ratio control based on a detection result from the air-fuel ratio sensor at a temperature equal to or higher than the temperature, and air-fuel ratio clipping means for preventing the air-fuel ratio from becoming larger than a predetermined value at a temperature equal to or higher than the first engine temperature. The air-fuel ratio clipping means, when the engine temperature becomes high,
The value of the air-fuel ratio to be clipped is configured to shift to the lean side, and, the air-fuel ratio control means, detecting binding of the air-fuel ratio sensor at a first engine temperature or higher
Air-fuel ratio control based on the
The time is based on the air-fuel ratio based on the detection result from the air-fuel ratio sensor.
Control is prohibited, and the first
The second engine is higher than the engine temperature and lower than the temperature after warm-up.
At temperatures lower than the engine temperature,
The time during which the air-fuel ratio control is prohibited is set longer than in the above case.
An air-fuel ratio control device for an engine, characterized in that it is specified .