JPH04370350A - Misfire state detecting device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a misfire state detecting device whereby a misfire state can be promptly detected without using an exhaust temperature sensor. CONSTITUTION:A lean output duration time CM of an O2 sensor 13 in the upstream part is measured under execution of air-fuel ratio feedback control based on an output of the O2 sensor 13 in the upstream part. In the point of time (CM=CM0) when this duration time reaches predetermined time CM0, whether an output V2 of an O2 sensor 15 in the downstream part is rich (misfire) or lean (base air-fuel ratio A/F is lean), is discriminated.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a misfire in an internal combustion engine that detects a misfire in an air-fuel ratio sensor system that feedback-controls an engine air-fuel ratio according to the output of an air-fuel ratio sensor provided at least upstream of a catalytic converter. The present invention relates to a state detection device.

0002

[Prior Art] When a misfire occurs in an internal combustion engine,
Although the exhaust temperature decreases, unburned components such as HC and CO
As the components react in the three-way catalyst, the catalyst temperature increases. Therefore, conventional misfire detection methods for internal combustion engines include detecting the exhaust temperature upstream of the catalyst and the temperature inside the catalyst, and determining that the engine is in a misfire state when the temperature inside the catalyst is higher than the exhaust temperature upstream of the catalyst. (Reference: JP-A-60-102
Publication No. 538).

0003

[Problems to be Solved by the Invention] However, it is difficult to provide a temperature sensor with good responsiveness in the exhaust system, such as the exhaust temperature upstream of the catalyst and the temperature inside the catalyst. There is a problem in that it takes time to detect the temperature inside the catalyst, and as a result, the detection of a misfire condition is delayed, and the countermeasures are also delayed.

[0004] Accordingly, an object of the present invention is to provide a misfire condition detection device that can quickly detect a misfire condition.

[0005]

Means for Solving the Problems A means for solving the above problems is shown in FIG. That is, an upstream air-fuel ratio sensor 13 for detecting the air-fuel ratio of the engine by detecting the oxygen concentration in the exhaust gas is provided in the exhaust passage upstream of the three-way catalyst CCRO provided in the exhaust passage of the engine. A downstream air-fuel ratio sensor 15 is provided in the exhaust passage downstream of the main catalyst CCRO to detect the air-fuel ratio of the engine by detecting the oxygen concentration in the exhaust gas. The air-fuel ratio feedback control means feedback-controls the air-fuel ratio of the engine according to at least the output V1 of the upstream air-fuel ratio sensor 13. The lean state continuation determining means determines whether the lean state of the output V1 of the upstream air-fuel ratio sensor 13 continues for a predetermined period of time. As a result, when the lean state of the output V1 of the upstream air-fuel ratio sensor 13 continues for a predetermined period of time, the rich determining means determines whether the output V2 of the downstream air-fuel ratio sensor 15 is rich. As a result, the output V1 of the downstream air-fuel ratio sensor 15
When the engine is rich, it is determined and detected as an engine misfire condition.

[0006]

[Operation] The operation of the above-mentioned means will be explained below. An air-fuel ratio sensor that detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas upstream of the catalyst emits a signal indicating that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio in the following two cases. (1) When the engine misfires (2) When the air-fuel ratio given to the engine (hereinafter referred to as the basic air-fuel ratio) is leaner than the stoichiometric air-fuel ratio, that is, when a misfire condition occurs in the engine, the basic air-fuel ratio Regardless of whether the exhaust gas is rich or lean, unburned components (HC) and oxygen (O2) are present in the exhaust gas, and the air-fuel ratio sensor upstream of the catalyst detects the oxygen and outputs a lean output. On the other hand, even if no misfire has occurred in the engine, if the air-fuel ratio given to the engine (hereinafter referred to as the basic air-fuel ratio) is leaner than the stoichiometric air-fuel ratio, O2 (oxygen ) component will be present, so the upstream air-fuel ratio sensor will issue a lean output.

Under these circumstances, when air-fuel ratio feedback control is performed so that the basic air-fuel ratio becomes the stoichiometric air-fuel ratio using the lean output of the upstream air-fuel ratio sensor, the output of the downstream air-fuel ratio sensor is determined depending on the presence or absence of a misfire condition. I will explain it separately. (1) When no misfire condition has occurred in the engine In this case, even if the basic air-fuel ratio is lean, the basic air-fuel ratio is made rich by air-fuel ratio feedback control based on the lean output of the upstream air-fuel ratio sensor. After a predetermined period of time, the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. Since the air-fuel ratio on the downstream side of the catalyst changes later than the air-fuel ratio on the upstream side, the downstream air-fuel ratio sensor does not generate a rich output before the upstream air-fuel ratio sensor indicates a rich output. In other words, when the upstream air-fuel ratio sensor maintains a lean output for a predetermined period of time or longer, the downstream air-fuel ratio sensor will not output a rich output, so it will not be mistakenly determined to be a misfire.

(2) When a misfire condition occurs in the engine On the other hand, when a misfire condition occurs in the engine,
Even if the basic air-fuel ratio becomes rich due to air-fuel ratio feedback control, the lean output from the upstream air-fuel ratio sensor continues because O2 components are present in the exhaust gas upstream of the catalyst. However, since that O2 is consumed in the catalyst by unburned components (HC), no O2 is present in the exhaust gas downstream of the catalyst, and the catalyst downstream air-fuel ratio sensor will generate a rich output. In other words, if the downstream air-fuel ratio sensor outputs a rich output while the upstream air-fuel ratio sensor continues to provide a lean output for a predetermined period of time or more, it can be determined that a misfire has occurred.

[0009] The reason why the continuation of the lean output of the upstream air-fuel ratio sensor is one of the conditions for determining a misfire is that even if a misfire has not occurred due to engine operating conditions, the upstream air-fuel ratio may momentarily become lean. Moreover, since the basic air-fuel ratio is rich, this is to avoid misjudging a case where the downstream air-fuel ratio sensor shows a rich output as a misfire state.

0010

Embodiment FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In Figure 2,
An air flow meter 3 is provided in the intake passage 2 of the engine body 1. The air flow meter 3 directly measures the intake air amount, and includes, for example, a built-in potentiometer to generate an analog voltage output signal proportional to the intake air amount. This output signal is provided to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose axis generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 720 degrees in terms of crank angle.
A crank angle sensor 6 is provided that generates a pulse signal for detecting a reference position at each time. These crank angle sensors 5,
The pulse signal 6 is supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder. Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. The water temperature sensor 9 generates an analog voltage electrical signal according to the temperature THW of the cooling water. This output is also supplied to the A/D converter 101.

[0012] The exhaust system downstream of the exhaust manifold 11 contains three harmful components HC, CO, and NOx in the exhaust gas.
A catalytic converter 12 is provided that accommodates a three-way catalyst that simultaneously purifies the air. A first O2 sensor 13 is provided in the exhaust manifold 11, that is, upstream of the catalytic converter 12, and a second O2 sensor 15 is provided in the exhaust pipe 14 downstream of the catalytic converter 12. The O2 sensors 13 and 15 generate electrical signals according to the concentration of oxygen components in the exhaust gas. That is, the O2 sensors 13 and 15 output different output voltages to the A/F of the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
This occurs in the D converter 101. In this embodiment, the upstream O2 sensor 13 is used for air-fuel ratio feedback control and misfire state determination, but the downstream O2 sensor 15 is used only for misfire state determination.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, and an RO.
M104, RAM105, backup RAM106,
A clock generation circuit 107 and the like are provided. Also,
The throttle valve 16 of the intake passage 2 has a throttle valve 16
An idle switch 17 is provided that generates a signal LL indicating whether or not the door is fully closed. This idle state output signal L
L is supplied to the input/output interface 102 of the control circuit 10.

Reference numeral 18 denotes a secondary air intake valve, which supplies secondary air to the exhaust pipe 11 during deceleration or idling to reduce HC and CO emissions. This secondary air introduction intake valve 18 is turned on by a switch 19 using the negative pressure of the surge tank 2a of the intake passage 2.
It will be turned off. Further, this switch 19 is controlled by the output of the input/output interface 102 of the control circuit 10.

An alarm 20 is activated when the engine misfires. Furthermore, in the control circuit 10, a down counter 108, a flip-flop 109
, and a drive circuit 110 for controlling the fuel injection valve 7. That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and flip-flop 10
9 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, down counter 1
08 counts a clock signal (not shown) and finally, when its borrow-out terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110
stops the energization of the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the amount of the fuel injection valve TAU mentioned above, and therefore, the amount of fuel corresponding to the fuel injection valve TAU is sent into the combustion chamber of the engine body 1.

[0016] Incidentally, the occurrence of an interrupt in the CPU 103 is
For example, when the input/output interface 102 receives a pulse signal from the crank angle sensor 6 after the A/D conversion of the D converter 101 is completed. The intake air amount data Q and cooling water temperature data THW of the air flow sensor 3 are taken in by an A/D conversion routine executed at a predetermined time or every predetermined crank angle, and stored in a predetermined area of the RAM 105. In other words, data Q and TH in RAM 105
W is updated at predetermined intervals. Further, the rotational speed data Ne is calculated by the interruption of the crank angle sensor 6 every 30° CA, and is stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 2 will be explained below. FIG. 3 shows a routine for performing air-fuel ratio feedback control based on the output V1 of the upstream O2 sensor 13, and calculates the air-fuel ratio correction coefficient FAF according to the output V1 of the upstream O2 sensor 13. This routine is performed every predetermined time, for example, 4 ms. First, step 30
1, 302, it is determined whether the air-fuel ratio closed loop (feedback) condition by the upstream O2 sensor 13 is satisfied. That is, in step 301, RA
Read the cooling water temperature THW from M105 and set it to the predetermined value THW.
For example, it is determined whether the temperature is 40°C or higher, and step 302
Now, it is determined whether other closed loop conditions are satisfied. For example, when the output signal of the upstream O2 sensor 13 has never been inverted (when the output signal of the upstream O2 sensor 13 has never been reversed), (due to inactivity), fuel cut, etc., the closed loop condition does not hold, and in other cases, the closed loop condition holds. Step 301, 3
If the closed loop condition is not satisfied in step 02, step 3
Proceed directly to 15. Note that the air-fuel ratio correction coefficient FAF is set to 1.
It may be set to 0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 303.

In step 303, the output V1 of the upstream O2 sensor 13 is A/D converted and taken in, and in step 304, V1 is set to the comparison voltage VR1, for example 0.45.
It is determined whether the air-fuel ratio is below V, that is, it is determined whether the air-fuel ratio is rich or lean. In other words, lean (V1 ≦ VR1)
If so, in step 305 the air-fuel ratio flag F1 is set to “
0” (lean). On the other hand, rich (V1 > VR1
), the air-fuel ratio flag F1 is set to "1" (rich) in step 306.

In step 306', the air-fuel ratio flag F
It is determined whether the sign of 1 has been reversed, that is, the determination is made by comparing it with the previous air-fuel ratio flag F10. If the air-fuel ratio is reversed, in step 307, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F1. If it is a reversal from rich to lean, the rich skip amount RSR is read from the backup RAM 106 in step 308 and increased in a skip manner as FAF←FAF+RSR.On the other hand, if it is a reversal from lean to rich, the process goes to step 309. Read the lean skip amount RSL from the backup RAM 106 and set FAF ← FAF-RSL.
and decrease it in a skip manner. In other words, skip processing is performed.

If the sign of the air-fuel ratio flag F1 is not inverted in step 306, steps 310 and 311
, 312 performs integration processing. That is, step 3
10, it is determined whether F1="0" or not, and F1="0" is determined.
” (lean), FAF in step 311 ←
FAF+KIR, and on the other hand, if F1="1" (rich), in step 312 FAF ← FAF-
KIL. Here, the integral constants KIR and KIL are set sufficiently small compared to the skip amounts RSR and RSL, that is, KIR (KIL) < RSR (RSL).
It is. Therefore, step 311 is in the lean state (F1
="0"), the fuel injection amount is gradually increased, and step 3
12 gradually reduces the fuel injection amount in a rich state (F1="1").

Next, steps 308, 309, 31
In step 313, the air-fuel ratio correction coefficient FAF calculated in step 1 and 312 is guarded at a minimum value, for example, 0.8, and is also guarded at a maximum value, for example, 1.2. As a result, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

In step 314, in preparation for the next execution,
F10 ← F1. FAF calculated as above
is stored in the RAM 105, and the loop ends at step 315. FIG. 4 shows an injection amount calculation routine, which is executed at a predetermined crank angle, for example, 360° CA. In step 401, the intake air amount data Q and rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TAUP. For example, TAUP←α・Q/Ne
(α is a constant). In step 402, the final injection amount TAU is determined as TAU ←TAUP・FAF・β+γ
Calculate by Note that β and γ are correction amounts determined by other operating state parameters. Then step 40
At step 3, the injection amount TAU is set in the down counter 108, and the flip-flop 109 is also set to start fuel injection. The routine then ends at step 404.

As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the borrow-out signal from the gown counter 108, and the fuel injection ends. FIG. 5 shows a routine for detecting a misfire state of the engine, which is executed every predetermined period of time, for example, every 4 ms. In steps 501 and 502, similarly to steps 301 and 302 in FIG. 3, it is determined whether the air-fuel ratio closed loop condition by the upstream O2 sensor 13 is satisfied. In other words, detection of a misfire condition is based on the premise that air-fuel ratio feedback control is being performed by the upstream O2 sensor 13. Therefore, the upstream O2 sensor 13
Proceed to step 503 only if all the air-fuel ratio closed loop conditions are satisfied; otherwise, proceed to step 51.
Proceed directly to step 1.

[0024] In step 503, the output V1 of the upstream O2 sensor 13 is A/D converted and taken in, and in step 504, it is determined whether the output V1 of the upstream O2 sensor 13 is lean (V1 ≦ VR1) or rich. . As a result, in the case of lean (V1 ≦VR1), the counter CM is counted up by +1 in step 505, and conversely, in the case of rich (V1 > VR1), step 50
Clear the counter CM at 6. Furthermore, in the case of lean, it is determined in step 507 whether the counter CM has exceeded a predetermined value CM0. That is, if the engine is in a misfire state, regardless of whether the basic air-fuel ratio is rich or lean, the exhaust gas contains O2 components, so the output V1 of the upstream O2 sensor 13 will be lean (V1 ≦ VR1). Therefore, if the engine misfire condition continues, the determination at step 507 will satisfy CM>CM0. However, if there is no misfire and the basic air-fuel ratio is lean, and the lean condition continues, the flow will still proceed from step 504 to step 507, and CM>CM0 will be satisfied.

In steps 508 and 509, it is determined whether the engine is in a misfire state or the basic air-fuel ratio is in a lean state. That is, in step 508, the output V2 of the downstream O2 sensor 15 is A/D converted and taken in, and in step 509, it is determined whether the air-fuel ratio downstream of the catalyst is rich (V2 > VR2) or lean (V2 ≦ VR2). . Note that the comparison voltage VR2 is 0.55V or 0.45V like VR1.
shall be. As a result, if it is rich, it is determined that it is a misfire condition,
If it is lean, it is determined that the basic air-fuel ratio is lean. In other words, when the misfire state of the engine continues for a predetermined period of time (CM=CM0), during this period the basic air-fuel ratio becomes rich due to the air-fuel ratio feedback control based on the upstream O2 sensor 13, and therefore, the unburned components HC and CO in the three-way catalyst After reacting with O2 components, unburned components HC are released downstream of the catalyst.
, CO remains, and no O2 component remains. As a result, in step 509, V2 > VR2 (rich), so it is possible to determine whether the engine is misfiring. On the other hand, when the basic air-fuel ratio is lean, the unburned components HC and CO do not remain, but the O2 component remains upstream and downstream of the three-way catalyst. As a result, in step 509, V2 ≦
Since it becomes VR2 (lean), it is possible to determine the lean state of the basic air-fuel ratio. In addition, if a misfire condition has not occurred and the upstream air-fuel ratio sensor output is lean, the upstream air-fuel ratio sensor output will change when the basic air-fuel ratio becomes rich due to air-fuel ratio feedback control. , the rich output is shown prior to the output of the downstream air-fuel ratio sensor, so a negative determination is made in step 504 and the process directly proceeds to step 511, so that a misfire condition will not be erroneously detected. That is, to repeat once more, the case where it is determined that there is a misfire state is the case where the downstream air-fuel ratio sensor outputs a rich output when the upstream air-fuel ratio sensor output is lean for a predetermined period of time or more.

Only when it is determined that a misfire has occurred, the alarm 20 is activated in step 510 to notify the driver of the occurrence of a misfire. Incidentally, in step 510, in order to know later that a misfire occurred while the engine was operating, the information may be stored and retained in the backup ram so that the information can be recalled as necessary. . The routine then ends at step 511.

FIG. 6 is a modification of FIG. 5, in which steps 601, 602, 603, and
604 is added. The routine of FIG. 6 is linked with the secondary air introduction control (ASC) shown in the routine of FIG. 7, which will be described later. In other words, when the engine misfires, unburned components HC and CO increase, so secondary air is introduced to reduce the amount of HC and CO caused by misfire.
Reduces unburned components such as CO. In other words, in the secondary air introduction control area, unburned components such as HC and CO have already been reduced, so in FIG. Air is introduced to reduce unburned components such as HC and CO.

[0028] Steps 501, 502, 601,
At 602, it is determined whether or not the air-fuel ratio feedback control region by the upstream O2 sensor 13 (steps 501, 502) is outside the secondary air introduction control region (step 50).
1, 601, 602). In other words, 2
The next air introduction is as described below: i) When the cooling water temperature THW is less than a predetermined value THW0, ii)
) When the cooling water temperature THW is equal to or higher than the predetermined value THW0, the idle switch LL is on (LL=“1”) and the engine rotational speed Ne is the predetermined value N0, for example 1000 rpm.
This is done when the number is greater than or equal to m.

[0029] Therefore, the cooling water temperature THW is equal to the predetermined value THW0.
When the above conditions are met and the idle switch LL is off or the engine speed Ne is less than N0, secondary air is not introduced normally, so steps 503 to 511 are performed.
Execute the misfire state determination detection flow. As a result, when a misfire is detected, the misfire detection flag XM is set ("1") at step 603, and on the other hand, when no misfire is detected, the misfire detection flag
Reset M (“0”). As a result, even if the secondary air is outside the secondary air introduction control range, secondary air is introduced by the routine shown in FIG. 7, which will be described later, to reduce unburned components HC and CO due to misfire.

FIG. 7 shows a secondary air introduction control routine, which is executed every predetermined period of time, for example, 4 ms. Step 7
01 to 703, it is determined whether or not it is in the normal secondary air introduction control region, that is, whether or not the above-mentioned conditions i) and ii) are satisfied. As a result, if it is in the secondary air introduction control area, proceed to step 704 and switch 1.
9 is turned on, the secondary air introduction intake valve 18 is opened, and secondary air is introduced to reduce unburned components. On the other hand, if it is not in the secondary air introduction control region, it is determined in step 705 whether or not the misfire detection flag XM is "1" (misfire). As a result, if it is a misfire condition (XM="1"), the process proceeds to step 704 and the secondary air introduction intake valve 18 is opened. Only in other cases, the process proceeds to step 706 and the secondary air introduction intake valve 18 is closed.

[0031] Then, in step 707, this routine ends. FIG. 8 shows secondary air introduction outside the normal secondary air introduction control area where the cooling water temperature THW is greater than or equal to the predetermined value THW0 and the rotational speed Ne is less than the predetermined value N0 when the routines in FIGS. 6 and 7 are used. FIG. 2 is a timing diagram for explanation. In other words, assume that a misfire condition occurs during deceleration.

Before time t0, the cooling water temperature THW is also higher than the predetermined value THW0 and the idle switch LL is off (LL="0"), so the flow in FIG. 7 continues through steps 701, 702 and 705. In step 706, the secondary air introduction intake valve 18 is turned off (closed).
shall be. Furthermore, the misfire detection flag XM is reset (“0”).
). Next, at time t0,
When the vehicle enters a deceleration state (LL="1"), both the rotational speed Ne and the vehicle speed SPD decrease. At this time, if a misfire condition occurs, the upstream O2 sensor 13 detects the remaining O2 of the exhaust gas.
2 The output V1 becomes lean in response to the component. During the initial period of deceleration (t0 to t1), LL="1"
” and Ne ≧N0 (in this case, THW≧THW0)
Therefore, in the routine of FIG. 7, the normal secondary air introduction control area is set, and the flow of FIG.
The process proceeds to step 704 via steps 702 and 703, where the secondary air intake valve 18 is turned on (opened), and as a result, unburned components such as HC and CO in the exhaust gas are reduced.

At time t1, the rotational speed Ne becomes N
0, which is outside the area of normal secondary air introduction control, and the flow of FIG. 7 goes to steps 701, 702, 703,
The process proceeds to step 706 via step 705, where the secondary air intake valve 18 is turned off (closed), and as a result, the exhaust gas HC
, CO, and other unburned components will increase. From this time t1, the counter CM in Fig. 6 starts, and the upstream O2
The lean output time of the output V1 of the sensor 13 is measured.

At time t2, when the lean output time of the output V2 of the upstream O2 sensor 13 reaches a predetermined value (CM=CM0), the downstream O2 sensor 1 at this time
The above-mentioned upstream O
2. Determine whether the lean output of the sensor 13 is due to a misfire condition or due to a lean basic air-fuel ratio. As shown in FIG. 8, the output V2 of the downstream O2 sensor 15 at time t2 is rich, and therefore, when it is determined that there is a misfire state, the misfire detection flag
M is set (XM="1"). As a result, the flow in FIG. 7 is as follows: steps 701, 702
, 703, and 705 to step 704, the secondary air introduction intake valve 18 is turned on (opened), and secondary air is introduced. Therefore, unburned components such as HC (CO) are reduced again. Turning on (opening) this secondary air introduction intake valve 18
is the time t when the output of the downstream O2 sensor 15 becomes lean
Continues until 3. That is, the misfire detection flag XM is reset at step 604 in FIG. 6 at this time t3.

As described above, according to the routines shown in FIGS. 6 and 7, even if it is outside the normal secondary air introduction control area, if a misfire condition occurs during deceleration, secondary air is introduced and the H
Unburnt components such as C and CO are reduced. Note that the hatched portion of the HC component in FIG. 8 is the case where secondary air is not introduced even if a misfire condition occurs during deceleration.

As described above, according to the routines shown in FIGS. 6 and 7, it is possible to reduce unburned components such as HC and CO that accompany a misfire condition, and even when secondary air is introduced due to a misfire condition, the upstream Since the air-fuel ratio feedback control based on the side O2 sensor is not stopped, it is possible to reduce overall emissions.Furthermore, since the air-fuel ratio is made lean in the misfire state during low speed driving (including idling), the catalyst exhaust odor is reduced. It also helps reduce

[0037] Note that under normal secondary air introduction control conditions (Fig.
If steps 701 to 703) are different, steps 501, 601, 602 in FIG.
All you have to do is change.

[0038]

As explained above, according to the present invention, a misfire condition can be quickly detected without using an exhaust temperature sensor.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention.

FIG. 2 is an overall schematic diagram showing an embodiment of a misfire state detection device for an internal combustion engine according to the present invention.

FIG. 3 is a flowchart showing the operation of the control circuit of FIG. 2;

FIG. 4 is a flowchart showing the operation of the control circuit in FIG. 2;

FIG. 5 is a flowchart showing the operation of the control circuit in FIG. 2;

FIG. 6 is a flowchart showing the operation of the control circuit of FIG. 2;

FIG. 7 is a flowchart showing the operation of the control circuit in FIG. 2;

8 is a timing diagram supplementary explanation of the flowcharts of FIGS. 6 and 7; FIG.

[Explanation of symbols]

1... Engine body 2...Air flow meter 4...Distributor 5, 6...Crank angle sensor 10...Control circuit 12...Catalytic converter 13...Upstream O2 sensor 15...Downstream O2 sensor 17...Idle switch 18...Secondary air intake intake valve 19...Switch 20...Alarm

Claims (1)

[Claims] Claim 1: Provided in the exhaust passage of an internal combustion engine,
A three-way catalyst (CCRO) having a storage effect; and an upstream air-fuel ratio sensor (which is installed in the exhaust passage upstream of the three-way catalyst and detects the air-fuel ratio of the engine by detecting the oxygen concentration in the exhaust gas). 13), a downstream air-fuel ratio sensor (15) that is provided in the exhaust passage on the downstream side of the three-way catalyst and detects the air-fuel ratio of the engine by detecting the oxygen concentration in the exhaust gas, and at least the upstream side an air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine according to the output of the air-fuel ratio sensor; and a lean state persistence determination for determining whether the lean state of the output of the upstream air-fuel ratio sensor continues for a predetermined period of time. rich determination means for determining whether or not the output of the downstream air-fuel ratio sensor is rich when the output of the upstream air-fuel ratio sensor remains lean for a predetermined period of time; A misfire state detection device for an internal combustion engine, which determines and detects a misfire state of the engine when the output of an air-fuel ratio sensor is rich.