JP3314449B2 - Air-fuel ratio control device for internal combustion engine - 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 internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as an air-fuel ratio control device for an internal combustion engine, Japanese Patent Publication No. 4-54056 discloses that an activation judgment is made based on the output of a lean sensor during fuel cut.

[0003]

However, as shown in FIG. 8, the sensor applied voltage for obtaining the sensor output during the fuel cut is relatively large, and it is necessary to set the sensor supply power supply capacity large, which increases the cost. Is concerned. or,
When the engine speed at the time of deceleration is low as in an A / T vehicle, there is little opportunity to perform fuel cut, and there is a problem that it takes time from activation of the sensor to determination of activation.

It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can determine the activation of a limit current type lean sensor frequently without increasing the voltage applied to the sensor. .

[0005]

According to the present invention, as shown in FIG. 9, a limiting current type lean sensor M1 is attached to an exhaust passage of an internal combustion engine, and the limiting current type lean sensor M1 detects the oxygen concentration in the exhaust gas. The air-fuel ratio control of the internal combustion engine, wherein the air-fuel ratio of the air-fuel mixture supplied to the cylinder of the internal combustion engine is feedback-controlled by the feedback control means M2 so that the oxygen concentration in the exhaust passage becomes a constant value. A deceleration detecting means for detecting deceleration of the internal combustion engine; and a lean control for controlling the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio and flammable when the internal combustion engine is decelerated by the deceleration detecting means M3. Control means M4
A sensor activation determining means M5 for determining whether or not the output value of the limiting current type lean sensor M1 is within a predetermined range during the air-fuel ratio control that is leaner than the stoichiometric air-fuel ratio and combustible by the lean control means M4. And a feedback control stop for stopping the feedback control of the air-fuel ratio by the feedback control means M2 assuming that the sensor is in an inactive state when the output value of the limit current type lean sensor M1 is out of a predetermined range by the sensor activity determination means M5. The gist is an air-fuel ratio control device for an internal combustion engine including the means M6.

[0006]

The deceleration detecting means M3 detects the deceleration of the internal combustion engine,
When the internal combustion engine is decelerated by the deceleration detecting means M3, the lean control means M4 controls the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio and to allow combustion. Then, the sensor activity determining means M5 determines whether or not the output value of the limit current lean sensor M1 is within a predetermined range at the time of air-fuel ratio control leaner than the stoichiometric air-fuel ratio by the lean control means M4. Thereafter, the feedback control stopping means M6 is turned on by the sensor activation determining means M5.
When the output value of 1 is out of the predetermined range, it is determined that the sensor is in the inactive state, and the feedback control of the air-fuel ratio by the feedback control means M2 is stopped.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram around the engine. The engine body 1 is provided with an intake pipe 2 and an exhaust pipe 3. A fuel injection valve 4 is arranged at an intake port of the intake pipe 2. The fuel injection valve 4 is controlled by the output signal of the electronic control unit 5, and fuel is injected from the fuel injection valve 4. The fuel injection amount is determined by a rotation speed sensor 6 and a pressure sensor 8 for measuring the pressure in the surge tank 7.
The basic injection amount τ stored in advance is retrieved from the map in accordance with the signal (1). Further, when the engine is warmed up and a lean control execution condition such as a steady state is satisfied, a lean correction coefficient K (K ≦ 1.0) stored as shown in FIG. 3 is searched from the engine speed and the pressure sensor signal. The lean air-fuel ratio is realized by multiplying the basic injection amount τ.

Further, a limiting current type lean sensor 9 is provided in the exhaust pipe 3, and the actual air-fuel ratio is measured by the limiting current type lean sensor 9. Then, the target air-fuel ratio obtained from the lean correction coefficient K is compared with the actual air-fuel ratio, and the feedback correction coefficient α is further set to τ so that the actual air-fuel ratio approaches the target air-fuel ratio.
Calculate the fuel injection amount by adding or subtracting from K. That is, it is determined by the fuel injection amount TAV (= τ · K ± α).

A throttle valve 10 provided in the intake pipe 2 is provided with a throttle opening sensor 11. The output signal of the throttle opening sensor 11 is taken into the electronic control unit 5, and the electronic control unit 5 detects the throttle opening and the on / off of the idle switch. Further, a water temperature sensor 19 is provided in the engine body 1, and the water temperature sensor 19 detects an engine cooling water temperature.
The detection signal is taken into the electronic control unit 5.

The electronic control unit 5 includes a lean sensor drive circuit 12 and a microcomputer 13. FIG.
3 shows details of the lean sensor drive circuit 12. In FIG. 2, the limiting current type lean sensor 9 and the applied voltage supply power source 1
4 are connected via a switch 15. And
When the switch 15 is switched to the position shown by the solid line in FIG. 2, the voltage of the battery 14 is applied to the limit current type lean sensor 9. When the switch 15 is switched to the position shown by the broken line in FIG.
, The voltage of the battery 14 is not applied.

In FIG. 2, two resistors 16 and 17 are connected in parallel between the plus and minus terminals of the battery 14 and can be switched by a switch 18. Switching of the switches 15 and 18 is controlled by the microcomputer 13. Further, the output voltage V of the limit current type lean sensor 9 is detected by the microcomputer 13.

In this embodiment, the microcomputer 13 comprises feedback control means, deceleration detection means, lean control means, sensor activation determination means, and feedback control stop means.

Next, the operation of the air-fuel ratio control device for an internal combustion engine thus configured will be described. FIG. 4 shows a process (flowchart) executed by the microcomputer 13. This process is 8
It is started every msec.

In step 100, the microcomputer 13 determines whether or not the engine cooling water temperature is 80 ° C. or higher, and if it is 80 ° C. or higher, determines that the engine warm-up is completed. Further, when the microcomputer 13 determines that the engine warm-up is completed, it determines in step 101 whether or not the amount of change in the throttle opening is within a predetermined amount, and if not, determines that the engine is in a steady state.

If the microcomputer 13 determines that the engine warm-up is not completed in step 100 or is not in the steady state in step 101,
The routine proceeds to step 103, where stoichiometric air-fuel ratio control (lean correction coefficient K = 1.0) is performed.

On the other hand, if the microcomputer 13 determines that the engine has been warmed up in step 100 and is in a steady state in step 101, the microcomputer 13 proceeds to step 102 and performs lean control (K <
1.0).

Further, the microcomputer 13 determines in step 104 whether or not the limit current type lean sensor 9 is in an active state. When the microcomputer 13 determines that the sensor is active, it performs feedback control by comparing the target air-fuel ratio obtained from the lean correction coefficient K with the actual air-fuel ratio obtained from the output of the limiting current lean sensor 9 in step 105. That is, the air-fuel ratio of the air-fuel mixture supplied to the cylinder of the engine is feedback-controlled so that the oxygen concentration in the exhaust passage becomes a constant value.

When the sensor is inactive, the microcomputer 13 performs open loop control in step 106. Next, FIG.
The method of determining lean sensor activity in step 104 will be described with reference to FIG. This process is started every 8 msec.

The microcomputer 13 determines in step 200 whether the engine is in a decelerating state. Here, as an example of the detection of the deceleration state, when the change in the throttle opening is equal to or less than a predetermined value ((current throttle opening) − (previous throttle opening) ≦ predetermined value), or the change in the intake pipe negative pressure is reduced. A case where the value is equal to or less than a predetermined value ((current negative pressure value) − (previous negative pressure value) ≦ predetermined value) is exemplified.

When the microcomputer 13 is in the deceleration state, the air-fuel ratio is made lean in step 201 with the lean correction coefficient K = K _ACT . Here, K _ACT is the smallest value of K stored in advance as a map based on the engine speed and the pressure in the surge tank, that is, the leanest air-fuel ratio that can be feedback-controlled (K = 0.7 in FIG. 3). When the activity is determined based on this air-fuel ratio, the output of the lean sensor at the entire controllable air-fuel ratio is guaranteed.

Next, the microcomputer 13 determines in step 202 whether or not the lean sensor output at this time is equal to or more than a predetermined value. If the output is equal to or more than the predetermined value, the microcomputer 13 sets the sensor to active in step 203. In step 204, it is determined to be inactive. Here, the predetermined value is determined by the feedback and sensor output characteristics of FIG. 7, and is the lean sensor output in the active state at the leanest air-fuel ratio for performing the feedback control. For example, taking the case of FIG. 7 as an example, A / F =
When 21 is the leanest air-fuel ratio, the threshold value is I ₂₁ .

Thus, the limiting current type lean sensor 9
Is determined. FIG. 6 is a flowchart showing the relationship between deceleration for performing the activity determination and fuel cut.
That is, since the lean sensor activation determination cannot be performed when the fuel cut condition is satisfied and the fuel cut is performed, the predetermined air-fuel ratio for performing the activation determination when the lean sensor 9 is not activated even when the fuel cut execution condition is satisfied. (The air-fuel ratio that is leaner than λ = 1 and combustible) is used to determine the activity.

First, the microcomputer 13 determines in step 300 whether or not the fuel cut execution condition is satisfied. If the condition is not satisfied, the microcomputer 13 proceeds to step 305. Here, as an example of the fuel cut execution condition, it is determined that the fuel cut condition is satisfied when the idle switch is on and the engine speed is equal to or higher than a predetermined value.

When the microcomputer 13 determines in step 300 that the fuel cut execution condition has been satisfied, the microcomputer 13 determines in step 301 whether the lean sensor 9 was previously activated and whether the lean sensor 9 has been activated. That is, it is determined whether or not the current lean sensor 9 is determined to be in the active state. If the microcomputer 13 determines that the lean sensor 9 has already been activated, the microcomputer 13 executes a fuel cut in step 302.

If the lean sensor 9 has not been determined to be active, the routine proceeds to step 303, where it is determined whether or not a deceleration state for determining lean sensor activation has been established.

If the microcomputer 13 determines in step 303 that the vehicle is in the decelerating state, the microcomputer 13 executes a lean sensor activation determination in step 304. On the other hand, if the fuel cut execution condition is not satisfied in step 300, the microcomputer 13 proceeds to step 305. The microcomputer 13 determines in step 305 whether or not the vehicle is in a deceleration state. If it is determined that the vehicle is in a deceleration state, the microcomputer 13 determines in step 306 whether or not the lean sensor 9 has already been determined to be active. If the microcomputer 13 has not determined that the lean sensor is active, the microcomputer 13 performs lean activation determination in step 307.

Next, the voltage applied to the lean sensor will be described. In order to supply an output current that is substantially proportional to the air-fuel ratio to the lean sensor 9, it is necessary to apply a voltage having a magnitude corresponding to the air-fuel ratio as shown in FIG. Actually, when the control is performed with a lean air-fuel ratio, the applied voltage is not switched, and the voltage value is set so that the control can be performed with the same applied voltage.

On the other hand, when performing feedback control at the stoichiometric air-fuel ratio, no voltage is applied to the lean sensor 9 and the rich / lean determination is made based on the electromotive force as an O ₂ sensor (used as an oxygen concentration cell). Therefore, the voltage applied to the lean sensor 9 switches between the time of the lean control and the time other than the time of the lean control (the time of the stoichiometric air-fuel ratio feedback, the time of the open control). However, in the lean activation determination according to the present embodiment, the lean sensor 9 is operated in the deceleration state in which the open control is performed.
Therefore, it is necessary to apply the same voltage as that during the lean control even when the open control is performed, even when the activity is determined. That is, switching of the applied voltage of the lean sensor 9 includes (1) at the time of lean control and at the time of activation determination,
(2) Switching is performed in two ways: at the time of stoichiometric air-fuel ratio feedback and at the time of open control other than at the time of activity determination.

The switching of the applied voltage to the lean sensor 9 will be described with reference to FIG. (1) At the time of lean control and at the time of activation determination: switch 1
5 is set to B1, and a voltage is applied to the lean sensor 9.
(2) At the time of open control other than at the time of stoichiometric air-fuel ratio feedback and at the time of activation determination ... Switch 15 is set to B2, and voltage application to lean sensor 9 is stopped.

Here, since the sensor output measures the voltage applied to a resistor in series with the lean sensor 9, the sensor output detection resistor is switched by the switch 18 at the same time as the applied voltage is switched. (1) At the time of lean control and at the time of activation determination: switch 1
8 is B1, and the current flowing through the sensor is measured by the voltage across the 100Ω resistor. (2) At the time of open control other than the stoichiometric air-fuel ratio feedback and the activity determination time: The switch 18 is set to B2, and the electromotive force of the lean sensor is 1.5 MΩ.
Measure with the voltage across the resistor.

As described above, in this embodiment, the microcomputer 13
(Feedback control means, deceleration detection means, lean control means, sensor activation determination means, feedback control stop means) detects the deceleration of the engine (step 20 in FIG. 5).
0) When the engine is in a deceleration state, the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio and combustible (step 201 in FIG. 5). The microcomputer 13 is leaner than the stoichiometric air-fuel ratio, and, when combustible air-fuel ratio control, either in the output value is a predetermined range of the limiting current type lean sensor 9, that is, determines whether or not 7 the I ₂₁ or more (Step 202 in FIG. 5). Further, the microcomputer 13 outputs values of the limiting current type lean sensor 9 is out of the predetermined range (less than in Figure 7 I ₂₁₎ and the sensor stops the feedback control of the air-fuel ratio is in the inactive state (in FIG. 4 Step 10
Therefore, in the conventional method, the activation is determined based on the output of the lean sensor during the fuel cut. Therefore, as shown in FIG. 8, the sensor applied voltage for obtaining the sensor output during the fuel cut is compared. Therefore, it is necessary to set the sensor power supply capacity large (indicated by I3 in FIG. 8). However, in the present embodiment, the air-fuel ratio leaner than the stoichiometric air-fuel ratio and combustible, that is, the leanest air-fuel ratio A / F =
21, the voltage applied to the sensor for obtaining the sensor output is small (indicated by I4 in FIG. 8). Further, in the prior art, when the engine speed at the time of deceleration is low as in the case of an A / T vehicle, there is little opportunity to perform fuel cut, and there is a problem that it takes time from activation of the sensor to determination of activation. However, in the present embodiment, the determination of the sensor activity is performed not when the fuel is cut but when the engine is in a deceleration state, so that the determination of the sensor activity can be performed with high frequency.

As described above, in this embodiment, the activation of the limiting current type lean sensor can be determined frequently without increasing the voltage applied to the sensor.

[0033]

As described in detail above, according to the present invention,
An excellent effect that the limit current type lean sensor can be activated frequently without increasing the voltage applied to the sensor is exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram around an engine.

FIG. 2 is a diagram illustrating a lean sensor drive circuit.

FIG. 3 is a map for obtaining a K value.

FIG. 4 is a flowchart illustrating an operation.

FIG. 5 is a flowchart for explaining an operation.

FIG. 6 is a flowchart for explaining an operation.

FIG. 7 is a relationship diagram between an air-fuel ratio and a lean sensor output.

FIG. 8 is a relationship diagram between a lean sensor applied voltage and a lean sensor output.

FIG. 9 is a block diagram corresponding to a claim.

[Explanation of symbols]

9 Limit current type lean sensor 13 A microcomputer as feedback control means, deceleration detection means, lean control means, sensor activation determination means, feedback control stop means.

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI G01N 27/26 361 G01N 27/46 325P (56) References JP-A-59-29746 (JP, A) JP-A-4-36651 JP-A-1-232138 (JP, A) JP-A-62-162955 (JP, A) JP-A-62-1103565 (JP, A) JP-A-6-174678 (JP, A) 58-161859 (JP, A) JP 4-54056 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/41 F02D 41/12 330 F02D 41/14 310 F02D 45/00 368 G01N 27/26 361

Claims (1)

(57) [Claims] 1. A limiting current type lean sensor is attached to an exhaust passage of an internal combustion engine, an oxygen concentration in exhaust gas is detected by the limit current type lean sensor, and an oxygen concentration in the exhaust passage is kept constant by feedback control means. An air-fuel ratio control device for the internal combustion engine, wherein the air-fuel ratio of the air-fuel mixture supplied to the cylinder of the internal combustion engine is feedback-controlled so as to obtain a value. When the internal combustion engine is in a deceleration state by the means,
Lean control means for controlling to an air-fuel ratio leaner than the stoichiometric air-fuel ratio and combustible, and leaner than the stoichiometric air-fuel ratio by the lean control means,
And, at the time of air-fuel ratio control capable of combusting, a sensor activity determining means for determining whether an output value of the limiting current type lean sensor is within a predetermined range, and an output value of the limiting current type lean sensor is determined by the sensor activity determining means. An air-fuel ratio control device for an internal combustion engine, comprising: feedback control stopping means for stopping the feedback control of the air-fuel ratio by the feedback control means when the sensor is in an inactive state when the sensor deviates from a predetermined range.