Misfire detector for multi-cylinder engine

A misfire detector prevents catalysts from being heated to damaging high temperatures. The misfire detector for a multi-cylinder engine includes a fuel cut control to stop supplying fuel to misfiring cylinders, a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and a retard control to retard the ignition timing based on the extent that misfire occurs or the air-fuel ratio. The retard control can be replaced by a throttle opening control for misfire to limit the throttle opening angle. The retard control can also be replaced by an engine or vehicle speed control to limit the engine or vehicle speed below a predetermined engine or vehicle speed, respectively, irrespective of the throttle position.

FIELD OF THE INVENTION

This invention relates to misfire detectors for a multi-cylinder engine, and more particularly to a misfire detector for the multi-cylinder engine to prevent a catalyst from being heated to high temperatures and avoid detriment or damage of the catalyst.

BACKGROUND OF THE INVENTION

In an engine mounted on a vehicle, there may be caused misfires due to unstable combustion of the fuel in a combustion chamber due to various factors such as lean mixture of the air-fuel ratio by driving under lean combustion, a malfunction of ignition systems or fuel systems, and a failure of components of the engine. When misfire of the engine occurs, unburned gas flows to the catalyst in the exhaust system and burns which causes a rise in catalyst temperature that detriments the performance or damages the catalyst. For this reason, some engines are provided with misfire detectors to detect the misfire and control the fuel.

In prior misfire detectors for the multi-cylinder engine, “fuel feedback control prevention” and “fuel cut” are chosen based on the rate of misfire so as to protect the catalyst from the high temperature or damage (for example, see JP Laid-Open No. H05-10180).

Also, there is another prior misfire detector for the multi-cylinder engine in which fuel feedback control is stopped based on the misfire rate and the fuel cut, or halt of fuel supply, is performed to protect the catalyst, and the driver is informed of short of fuel due to the misfire so as to reduce cost for repair (for example, see JP Laid-Open No. 2002-138894).

Further, there is fuel control while the fuel cut is performed to protect the catalyst.

Here, control of the prior misfire detector for the multi-cylinder engine is explained below. Referring toFIG. 13, a control program for the misfire detector for the multi-cylinder engine starts in step502. Rate of misfire is calculated for each cylinder in step504. Then a determination is made in step506as to whether the rate of misfire is more than or equal to a criteria A by which to judge whether the catalyst may be damaged.

Rate of misfire is calculated for every 200 engine revolutions for each cylinder, including the cylinder for which the fuel cut is performed due to the misfire. For a V-type engine, the rate of misfire is calculated for each cylinder bank. The rate of misfire is determined from a table depending on the engine speed and the engine load.

The determination is made in step506as to whether the misfire rate is more than or equal to the damaging criteria A. In this step, the cylinder for which the fuel cut should be performed (fuel cut cylinder) is determined through a determination process for the fuel cut cylinder as shown inFIG. 14. In order to determine the fuel cut cylinder, a determination program starts in step602. In step604, the misfire rate for each cylinder is calculated by dividing the number of misfires by the number of ignitions (for every 200 revolutions of engine speed). Then a determination is made in step606as to whether the rate of misfire is more than or equal to the damaging misfire criteria A. Further, another determination is made in step608as to whether the number of misfires for each cylinder SIKCYLi (wherein i is a cylinder number) is greater than a set rate B (e.g. 30%) of the number of misfires of all cylinders for every 200 revolutions of engine speed.

If both of the determinations in steps606and608are “YES”, then the misfire cylinder is determined in step610and the determination process ends in step612. If either the determination in step606or608is “NO”, then the process returns to step604.

If the misfire cylinder is determined and the determination in step506is “YES”, a fuel feed back control (F/B) for the fuel cut cylinder is halted and is initialized in step508. In this initialization of the fuel feed back control, the correction value is set at zero or a default value.

Then, in step510a learning control to learn the quantity of fuel feed back for the cylinder for which the fuel cut should be performed is prevented. The correction value of learning is initialized to an unlearned state in step512. In this initialization of the learning control correction value, the correction value is set at zero or a default value. Also, the learning control is set at the initial state as in the state at start of the engine or the state at which a battery is changed.

Then the fuel cut for the misfire cylinder is performed in step514. Increase in the fuel supply to the cylinders for which the fuel cut is not performed is prevented in step516, and the process returns to step504. In this fuel increase prevention process, the fuel increases for acceleration, enrichment, and other conditions are prevented.

In the calculation of the misfire rate after the implement of the fuel cut for the misfire cylinder in step514, the calculation of the misfire rate in step504includes the cylinder for which the fuel cut is performed, and a determination is made in step506as to whether the calculated misfire rate is more than or equal to the criteria A by which to judge whether the catalyst may be damaged.

If the determination in step506is “YES”, the processes in steps508–516are performed. In contrast, if the determination in step506is “NO”, the effect of the misfire on the catalyst is not significant, so that the fuel cut for the misfire cylinder is canceled in step518, the fuel feed back control is resumed in step520, the learning control is resumed in step522, the fuel increase control prevention is canceled in step524, and the process returns to step504.

At this time, the process in step518to cancel the fuel cut for the misfire cylinder may be replaced by a condition based on set engine speed and set engine load, instead of the damaging criteria A (FIG. 5).

According to the above-mentioned prior control, the fuel cut control, the fuel feed back prevention control, the fuel learning prevention control, and the fuel increase prevention control are performed when misfire occurs to prevent a rise in the catalyst temperature. However, the air-fuel (A/F) ratio becomes lean and results in undesirable engine knocking, as shown in a time chart inFIG. 15. At this time, no ignition timing control is performed to prevent the knocking.

Moreover, even if the fuel cut control, the fuel feed back prevention control, the fuel learning prevention control, and the fuel increase prevention control are performed when the misfire occurs, the vehicle speed can be increased by depressing a throttle pedal in case the misfire frequency is low or the engine has a large piston displacement. This results in not only a bad influence on the engine and the catalyst but also emission of the exhaust gas in a large amount in the ambient, since the normal appropriate control for exhaust gas is not performed.

SUMMARY OF THE INVENTION

In order to obviate or at least minimize the above inconveniences, the present invention provides a misfire detector for a multi-cylinder engine having a misfire detecting means to detect the misfire for each cylinder, and performs a misfire control if the frequency of the misfire detected by the misfire detecting means is more than a predetermined value. The misfire control includes (1) a fuel cut control for misfiring cylinders having a fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a retard control to retard the ignition timing by a retard quantity set based on the extent the misfire occurs or the air-fuel ratio.

Also, in a misfire detector for a multi-cylinder engine having a misfire detecting means to detect the misfire for each cylinder, and performing a misfire control if the frequency of the misfire detected by the misfire detecting means is more than a predetermined value. The misfire control includes (1) a fuel cut control for misfiring cylinders having a fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a throttle opening control for misfire to limit the throttle opening angle as compared to a normal throttle opening angle, in accordance with an acceleration degree.

Further, in a misfire detector for a multi-cylinder engine having a misfire detecting means to detect the misfire for each cylinder, and performing a misfire control if the frequency of the misfire detected by the misfire detecting means is more than a predetermined value, the misfire control includes (1) a fuel cut control for misfire cylinders by a fuel cut means to stop supplying the fuel to the misfire cylinders, (2) a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) an engine speed control to limit the engine speed below a predetermined engine speed irrespective of the opening degree of the throttle.

Furthermore, in a misfire detector for a multi-cylinder engine having a misfire detecting means to detect misfire for each cylinder, and performing a misfire control if the frequency of the misfire detected by the misfire detecting means is more than a predetermined value, the misfire control includes (1) a fuel cut control for misfiring cylinders by a fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a vehicle speed control to limit the vehicle speed below a predetermined speed irrespective of the opening degree of the throttle.

According to the present invention, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, the misfire control includes (1) the fuel cut control for misfire cylinders by the fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the retard control to retard the ignition timing by the retard quantity set based on the extent the misfire occurs or the air-fuel ratio. Accordingly, the catalyst is not heated to high temperatures, which prevents detriment or damage of the catalyst.

Also, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, the misfire control includes (1) the fuel cut control for misfire cylinders by the fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the throttle opening control for misfire to limit the throttle opening angle as compared to the normal opening in accordance with the acceleration degree. Accordingly, when the misfire is detected, a rise is avoided in the catalyst temperature owing to the driving at high speed under heavy engine load in a situation where the driver depresses an acceleration pedal when he feels power down due to the misfires. This prevents detriment or damage of the catalyst.

Further, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, the misfire control includes (1) the fuel cut control for misfire cylinders by the fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) a control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the engine speed control to limit the engine speed below the predetermined engine speed irrespective of the opening degree of the throttle. Accordingly, when the misfire is detected, a rise is avoided in the catalyst temperature owing to driving at high speed under heavy engine load in a situation where the driver depresses the acceleration pedal when he feels power down due to the misfires. This prevents detriment or damage of the catalyst.

Furthermore, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, the misfire control includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the vehicle speed control to limit the engine speed below the predetermined speed irrespective of the opening degree of the throttle. Accordingly, when misfire is detected, the driver is prevented from driving at high speed which is contrary to the misfire control for avoiding problems resulting from the misfires. Thereby, the catalyst is not heated to high temperatures, which prevents detriment or damage of the catalyst.

According to the present invention, when the misfire control is performed, executed are (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the retard control to retard the ignition timing by the retard quantity set based on the extent the misfire occurs or the air-fuel ratio. Thereby, the catalyst is not heated to high temperatures, which prevents detriment or damage of the catalyst.

Also, when the misfire control is performed, executed are (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the throttle opening control for misfire to limit the throttle opening angle as compared to the normal opening in accordance with the acceleration degree. Accordingly, when misfire is detected, a rise is avoided in the catalyst temperature owing to the driving at high speed under heavy engine load in a situation where the driver depresses the acceleration pedal when he feels power down due to the misfires. This prevents detriment or damage of the catalyst.

Further, when the misfire control is performed, executed are (1) the fuel cut control for misfiring cylinders by the fuel cut means to stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the engine speed control to limit the engine speed below the predetermined engine speed irrespective of the opening degree of the throttle. Accordingly, when misfire is detected, a rise is avoided in the catalyst temperature owing to the driving at high speed under heavy engine load in a situation where the driver depresses the acceleration pedal when he feels power down due to the misfires. This prevents detriment or damage of the catalyst.

Furthermore, when the misfire control is performed, executed are (1) the fuel cut control for misfire cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the vehicle speed control to limit the vehicle speed below the predetermined speed irrespective of the opening degree of the throttle. Accordingly, when misfire is detected, the driver is prevented from driving at high speed which is contrary to the misfire control for avoiding problems due to the misfires. Thereby, the catalyst is not heated to high temperatures, which prevents detriment or damage of the catalyst.

DETAILED DESCRIPTION

FIGS. 1–7illustrate an embodiment of the present invention.FIGS. 3 and 4show a multi-cylinder engine (internal combustion engine)2mounted on a vehicle (not shown).

Firstly, a system of the multi-cylinder engine2is described below. The multi-cylinder engine2includes an intake passage4and an exhaust passage6. The engine2is a V-type engine, in which a first cylinder bank8-1and a second cylinder bank8-2are formed in a V-shape.

The intake passage4has an air cleaner10at an upstream end thereof, a throttle valve12in a generally middle portion, and two branched intake passages, i.e., first and second intake branch passages4-1,4-2at a downstream end. The first intake branch passage4-1has a downstream end connected to a combustion chamber (not shown) in the first cylinder bank8-1, while the second intake branch passage4-2has a downstream end connected to a combustion chamber (not shown) in the second cylinder bank8-2.

Also, the intake passage4includes a bypass air passage14that bypasses the throttle valve12to connect the upstream and downstream sides of the intake passage4. In the bypass air passage14, an idle control valve16is disposed so as to regulate the air flowing through the bypass air passage14. This idle control valve16is connected to a control means68mentioned later.

Also, the exhaust passage6is divided on an upstream side into two branched passages, i.e., first and second exhaust branch passages6-1,6-2. The first exhaust branch passage6-1has an upstream end connected to the combustion chamber in the first cylinder bank8-1, while the second exhaust branch passage6-2has an upstream end connected to the combustion chamber in the second cylinder bank8-2. The first and second exhaust branch passages6-1,6-2are merged at downstream ends.

The first exhaust branch passage6-1includes: a first three-way catalyst18-1for a first warming-up device; a first front oxygen sensor20-1on an upstream side of the first three-way catalyst18-1; and a first rear oxygen sensor22-1on a downstream side of the first three-way catalyst18-1.

The second exhaust branch passage6-2includes: a second three-way catalyst18-2for a second warming-up device; a second front oxygen sensor20-2on an upstream side of the second three-way catalyst18-2; and a second rear oxygen sensor22-2on a downstream side of the second three-way catalyst18-2.

The first and second front oxygen sensors20-1,20-2measure the concentration of oxygen in the exhaust gas in the first and second exhaust branch passages6-1,6-2and feed reversed rich and lean signals. Also, the first and second rear oxygen sensors22-1,22-2measure the concentration of oxygen in the exhaust gas in the first and second exhaust branch passage6-1,6-2on the downstream sides of the first and second three-way catalysts18-1,18-2, and feed reversed rich and lean signals. The exhaust passage6includes a three-way catalyst24toward a downstream side from a junction of the first and second exhaust branch passages6-1,6-2.

Further, the multi-cylinder engine2, includes first and second fuel injection valves26-1,26-2facing the combustion chambers in the first and second cylinder banks8-1,8-2, respectively. The first and second fuel injection valves26-1,26-2are connected to a fuel tank30through a fuel supply passage28. The fuel in the fuel tank30is forced to the fuel supply passage28by a fuel pump32, and is filtered by a fuel filter34to remove dust therein, and is supplied to the first and second fuel injection valves26-1,26-2.

In the fuel supply passage28, a fuel pressure regulator36is disposed which regulates the pressure of the fuel. This fuel pressure regulator36regulates the pressure of the fuel to a predetermined pressure by utilizing the intake pipe pressure that is introduced from a pressure introducing passage38in connection with the intake passage4. Surplus fuel is returned through a fuel return passage40to the fuel tank30.

The fuel tank30is connected to a canister44through an evaporative passage42. A tank pressure control valve46is disposed on the evaporative passage42. The tank pressure control valve46with an opened or closed solenoid valve50regulates the intake pipe pressure introduced through a pressure passage48in communication with the intake passage4. The canister44is connected through a purge passage52to the intake passage4on a downstream side of the throttle valve12. On the purge passage52, a purge control valve54is disposed. The canister44includes an atmosphere valve56to regulate the air being introduced.

The multi-cylinder engine2includes an EGR passage58that connects the second exhaust branch passage6-2, on an upstream side of the second front oxygen sensor20-1forming an exhaust system, with a junction of the first and second intake branch passages4-1,4-2forming an intake system. The EGR passage58includes an EGR control valve60that regulates the amount of the exhaust gas recirculated to the intake system from the exhaust system.

In addition, the multi-cylinder engine2includes first and second ignition coils62-1,62-2to spark an ignition plug (not shown) positioned in each combustion chamber in the first and second cylinder banks8-1,8-2. In the second cylinder bank8-2, a PCV valve64is positioned.

A control means68, forming a misfire detector66for the multi-cylinder engine2, is connected to the idle control valve16, the first and second front oxygen sensors20-1,20-2, the first and second rear oxygen sensors22-1,22-2, the first and second fuel injection valves26-1,26-2, the fuel pump32, the purge control valve54, the EGR control valve60, and the first and second ignition coils62-1,62-2.

The control means68is connected to an intake temperature sensor70to detect the intake air temperature, an intake air flow sensor72to detect the amount of the intake air, a throttle opening sensor74to detect opening angle of the throttle, a cam angle sensor76to detect the angle of a cam, an intake air pressure sensor78to detect the pressure in an intake pipe, a coolant temperature sensor80to detect the temperature of a coolant for the multi-cylinder engine2, a crank angle sensor82to detect the angle of a crank of the multi-cylinder engine2which also functions as an engine speed sensor, a fuel level sensor84to detect the fuel level of the fuel tank30, and a pressure sensor86to detect the pressure in the fuel tank30.

The control means68is also connected to an indication lamp88, an electric load90, a power steering pressure switch92, a heater blower fan switch94, a vehicle speed sensor96, a combination meter98, a cruise control module100, an A/C condenser fan relay102, an A/C controller104, a data link controller106, an ABS control module108, a main relay110, an ignition switch112, a P/N position switch114, a battery116, a starter magnet switch118, an O/D off lamp120, a power lamp122, a light switch124, a stop lamp switch126, an O/D cut switch128, a power/normal change switch130, a four-wheel-drive low switch132, a transmission range switch134, a first solenoid valve136, a second solenoid valve138, a TCC solenoid valve140, an A/T input rotational speed sensor142, and an A/T output rotational speed sensor144.

As shown inFIG. 4showing the misfire detector66for the multi-cylinder engine2, the control means68includes an atmosphere pressure sensor146, a misfire detecting means148to detect the misfires in each cylinder of the engine2based on the variation of the engine speed and the variation of the pressure in the cylinders, and a misfire control that is executed if the frequency of the misfire detected by the misfire detecting means148is greater than a predetermined value.

Here is explained a general structure of the misfire detector66of the multi-cylinder engine2. As shown inFIG. 3, the multi-cylinder engine2includes the intake passage4and the exhaust passage6. In the intake passage4, disposed are the intake airflow sensor72that detects the amount of the intake air from the upstream side, and the throttle valve12. Adjacent the throttle valve12, the throttle opening angle sensor74is disposed as an electric-controlled throttle sensor to detect the opening angle of the throttle.

In the exhaust passage6, disposed are the catalysts, e.g., the first and second three-way catalysts18-1,18-2for the first and second warming-up devices, and the three-way catalyst24. Toward the upstream side of the three-way catalysts18-1,18-2,24, disposed is either one of the oxygen sensor (O2 sensor) and the air-fuel ratio sensor, e.g., the first and second front oxygen sensors20-1,20-2, and the first and second rear oxygen sensors22-1,22-2.

The control means (also referred to as ECU; electronic control unit)68of the misfire detector66for the multi-cylinder engine2includes a misfire calculation means68a, a misfire rate calculation means68b, a fuel control means68c, an ignition timing control means68d, and the throttle control means68e. The misfire detecting means148thus includes the misfire calculation means68a, and the misfire rate calculation means68b. The fuel control means68cexecutes fuel cut control by the fuel cut control means152, fuel feedback control, and fuel learning control, mentioned later.

The control means68receives information from the engine2on the engine speed and ignition timing components. The control means68is connected on an input side to: a knock sensor150; the intake air flow sensor72; the throttle opening sensor74or the electronic controlled throttle sensor; the sensors such as the first and second front and rear oxygen sensors20-1,20-2,22-1,22-2; the intake air temperature sensor70; the coolant temperature sensor80; the atmosphere pressure sensor146; and the vehicle speed sensor96.

The control means68is connected on an output side to: the first and second fuel injection valves26-1,26-2; and the throttle opening sensor74or the electronic controlled throttle sensor.

The misfire detector66includes the control means68which performs the misfire control, the misfire control including (1) a fuel cut control for misfiring cylinders by having the fuel cut means152stop supplying the fuel to the misfiring cylinders, (2) a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a retard control to retard the ignition timing by a retard quantity set based on the extent the misfire occurs or the air-fuel ratio.

More particularly, the control means68: detects the misfire in each cylinder of the multi-cylinder engine2by means of the misfire calculation means68aof the misfire detecting means148based on the variation of the engine speed and the pressure in the cylinder; calculates the rate of misfire for every 200 revolutions of the engine speed by means of the misfire rate calculation means68b; and executes the misfire control if the frequency of the misfire detected by the misfire rate calculation means68bof the misfire detecting means148is greater than the predetermined value.

It is noted that the misfire rate is calculated for each cylinder in connection with the catalyst, and the misfire rate is also calculated for each cylinder bank when the multi-cylinder engine2is a V-type engine with the catalysts disposed for each cylinder bank.

As shown inFIG. 5, the predetermined value is a damaging misfire criteria A % that is a ratio at which the catalyst can be damaged. By comparing the misfire rate, i.e., the frequency of the misfire detected by the misfire rate calculation means68bof the misfire detecting means148, with the damaging misfire criteria A %, the misfire control is performed when the misfire rate is greater than or equal to the damaging misfire criteria A %.

In misfire control, performed are (1) a fuel cut control for misfire cylinders by the fuel cut means152to stop supplying the fuel to the misfiring cylinders, (2) a control to prevent a fuel feed back control and a fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a retard control to retard the ignition timing by a retard quantity set based on the extent the misfire occurs or the air-fuel ratio.

More particularly, the fuel cut means152included in the fuel control means68cperforms the fuel cut for the misfire cylinder, and the fuel feed back control is stopped and is initialized. This initialization is to set a correction value at zero or default value.

Also, the fuel control means68cstops the fuel learning control and the correction value is initialized to an unlearned state. This initialization is to set a correction value for learning at zero or default value. Moreover, the learning control is set at the initial state as in the state at start of the engine and the state for a battery is changed.

Further, the fuel control means68cprevents the fuel increasing control, e.g., the fuel increases for acceleration, the enrichment, and other factors are prevented.

Furthermore, the ignition timing control means68dretards the ignition timing by a retard amount set based on the extent of the misfire or the air-fuel ratio. The amount of the retard is set at a fixed value preset by the control means68or a value based on the misfire rate or the air-fuel ratio.

If the ignition timing retard control is performed under a knock control, the range of the ignition timing retard for knock is expanded.

After start of the fuel cut control when the misfire occurs, as shown inFIG. 6, a fuel cut cancel condition for misfire is considered to be satisfied when time “Treset” has elapsed and the driving in each divided section continues for more than 60 seconds. Then the fuel cut is canceled and the catalyst protection control is also canceled.

Operation of one embodiment of the present invention is explained with reference toFIG. 1illustrating a flow chart for the fuel cut control etc. for misfire by the misfire detector66of the multi-cylinder engine2.

A program for fuel cut control for misfire starts in step102. The rate of misfire for each cylinder is calculated in step104. In step106, a determination is made as to whether this misfire rate is greater than or equal to the damaging misfire criteria A at which the catalyst may be damaged.

The rate of misfire is calculated for every 200 revolutions of the engine speed for each cylinder. This calculation includes the cylinder for which the fuel cut is performed. For the V-type engine, the misfire rate is calculated for each cylinder bank. Also, the misfire rate is calculated for each cylinder that shares the catalyst. The damaging misfire criteria A is calculated from a table based on the engine speed and the engine load, as shown inFIG. 5.

In the determination in step106as to whether the misfire rate is greater or equal to the damaging misfire criteria A, the fuel cut cylinder is determined from a flow chart for determination of the fuel cut cylinder, as shown inFIG. 2.

In the flow chart for the determination of the cylinder in which the fuel supply should be stopped, a program for determination starts in step202. Rate of misfire is calculated for each cylinder by dividing the number of misfires by the number of ignitions (for every 200 revolutions of the engine speed) in step204. In step206, a determination is made as to whether the misfire rate for each cylinder is greater or equal to the damaging misfire criteria A. In step208, another determination is made as to whether the number of misfires for each cylinder SIKCYLi (wherein i designates the cylinder number) is greater than a predetermined ratio (e.g. 30%) of the number of the misfires of all cylinders for every 200 revolutions of the engine speed.

If the determination in step206and the determination in step208both are “YES”, then the cylinder for which the fuel cut should be performed is determined in step210, and the program ends in step212. If the determination in step206or the determination in step208is “NO”, the process returns to step204.

After the fuel cut cylinder is determined and when the determination in step106is “YES”, then the fuel feed back control for the fuel cut cylinder is halted in step108, and the fuel feed back control is initialized. At this initialization of the fuel feed back control, the correction value is set at zero or a default value.

Then, the learning control of the amount of the fuel feed back control for the fuel-cut cylinder is stopped in step110. In step112, the correction value of learning is initialized to an unlearned state. This initialization is to set a correction value for learning at zero or a default value. Also, the learning control is set at the initial state as in the state at start of the engine and the state for the battery is changed.

Then fuel cut is performed for the misfire cylinder in step114. Prevented is the fuel increase control for the cylinder that the fuel cut is not performed in step116. In this fuel increase prevention process, the fuel increases for acceleration, enrichment, and other factors are prevented.

In step118, the ignition timing control means68dretards the ignition timing. When the ignition timing retard control is performed for the knock control, then the range of ignition timing retard for knock is expanded in step120. Then a determination is made in step122as to whether the fuel cut cancel condition is met.

After start of the fuel cut control when the misfire occurs, as shown inFIG. 6, a fuel cut cancel condition for misfire is considered to be satisfied in step122when time “Treset” has elapsed and the driving in each divided section continues for more than 60 seconds. Then the fuel cut is canceled and the catalyst protection control is also canceled.

If the determination in step122is “NO”, then the program returns to step104. If the determination in step122is “YES”, the fuel feed back control is resumed in step124, and the fuel learn control is resumed in step126. The fuel increase control prevention is canceled in step128, and the ignition timing retard control is canceled in step130. Expansion of the ignition timing retard range is canceled in step132if the ignition timing regard control for the knock control is performed. Then the program returns to step104.

As a result, in the misfire detector6for the multi-cylinder engine2having the misfire detecting means148to detect the misfire for each cylinder, and performing a misfire control if the frequency of the misfire detected by the misfire detecting means148is more than a predetermined value, when the misfire control is performed, executed are (1) the fuel cut control for misfiring cylinders by having the fuel cut means152stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the retard control to retard the ignition timing by the retard quantity set based on the extent the misfire occurs or the air-fuel ratio. Accordingly, the catalyst is not heated to high temperatures, which prevents detriment or damage of the catalyst.

FIGS. 8–10illustrate a second embodiment of the present invention. The same reference numerals are hereinafter utilized for features identical or similar in function to those described in the first embodiment.

According to the first embodiment of the present invention, in the misfire detector for the multi-cylinder engine, the misfire control performed by the control means includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means152stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the retard control to retard the ignition timing by the retard quantity set based on the extent the misfire occurs or the air-fuel ratio. In contrast, the second embodiment is characterized in that in the misfire detector for the multi-cylinder engine, the misfire control performed by the control means includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a throttle opening control for misfire to limit the throttle opening angle as compared to a normal throttle opening in accordance with an acceleration degree.

More particularly, in the second embodiment, the retard of the ignition timing according to the first embodiment based on the extent of the misfire or the air-fuel ratio is replaced by a control regarding the electronic controlled throttle when the misfire is determined.

Operation of the second embodiment is explained with reference to a flowchart ofFIG. 8for throttle control of the misfire detector when misfiring. A program for the throttle control for misfire starts in step302. The rate of misfire for each cylinder is calculated in step304. Then a determination is made in step306as to whether this misfire rate is greater than or equal to the damaging misfire criteria A at which the catalyst may be damaged.

The rate of misfire is calculated for every 200 revolutions of the engine speed for each cylinder. This calculation includes the cylinder for which the fuel cut is performed. For the V-type engine, the misfire rate is calculated for each cylinder bank. Also, the misfire rate is calculated for each cylinder that shares the catalyst. The damaging misfire criteria A is calculated from a table based on the engine speed and the engine load (seeFIG. 5).

In the determination in step306as to whether the misfire rate is greater or equal to the damaging misfire criteria A, the cylinder for which the fuel cut should be performed is determined from the flow chart for determination of the fuel cut cylinder shown inFIG. 2.

After the fuel cut cylinder is determined and when the determination in step306is “YES” as shown inFIG. 10, the throttle opening angle control for misfire is performed in step308so that the throttle opening angle is at a misfire opening angle at which the throttle opening angle is limited with respect to the normal opening angle in accordance with the acceleration opening degree.

Then the fuel cut is performed for the misfiring cylinder. Prevented is the fuel increase control for the cylinder that the fuel cut is not performed. In this fuel increase prevention process, the fuel increases due to the increasing speed, enrichment, and other factors are prevented.

Then a determination is made in step310as to whether the fuel cut cancel condition is met. After start of the fuel cut control when the misfire occurs, as shown inFIG. 6, a fuel cut cancel condition for misfire is considered to be satisfied in step310when time “Treset” has elapsed and the driving in each divided section continues for more than 60 seconds. Then the fuel cut is canceled and the catalyst protection control is also canceled.

If the determination in step310is “NO”, then the program returns to step304. If the determination in step310is “YES”, the fuel feed back control is resumed and the fuel-learn control is resumed. The fuel increase control prevention is canceled, and the throttle opening angle control for misfire is canceled in step312. Then the program returns to step304.

As a result, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, when the misfire control is performed, executed are (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the throttle opening control for misfire to limit the throttle opening angle as compared to the normal opening in accordance with the acceleration degree. Accordingly, when the misfire is detected, avoided is rise in the catalyst temperature owing to the driving at high speed under heavy engine load in a situation where the driver depresses an acceleration pedal when he feels power down due to the misfires. This prevents detriment or damage of the catalyst.

FIGS. 11 and 12illustrate a third embodiment of the present invention.

The third embodiment of the present invention is characterized in that in the misfire detector for the multi-cylinder engine, the misfire control includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) an engine speed control to limit the engine speed below a predetermined engine speed irrespective of the opening degree of the throttle. Alternatively, the third embodiment of the present invention is characterized in that in the misfire detector for the multi-cylinder engine, the misfire control includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) a vehicle speed control to limit the vehicle speed below a predetermined speed irrespective of the opening degree of the throttle.

More particularly, according to the third embodiment, the engine speed control limits the engine speed below the predetermined engine speed irrespective of the opening degree of the throttle, or the vehicle speed control limits the vehicle speed below the predetermined vehicle speed irrespective of the opening degree of the throttle, instead of the ignition timing retard control based on the extent of the misfire or the air-fuel ratio according to the first embodiment, or the electric controlled throttle control for misfire according to the second embodiment.

Operation of the third embodiment is explained with reference to a flowchart ofFIG. 11for the vehicle speed limit control of the misfire detector when misfiring. A program for the vehicle speed limit control for misfire starts in step402. The rate of misfire for each cylinder is calculated in step404. Then a determination is made in step406as to whether this misfire rate is greater than or equal to the damaging misfire criteria A at which the catalyst may be damaged.

The rate of misfire is calculated for every 200 revolutions of the engine speed for each cylinder. This calculation includes the cylinder for which the fuel cut is performed. For the V-type engine, the misfire rate is calculated for each cylinder bank. Also, the misfire rate is calculated for each cylinder that shares the catalyst. The damaging misfire criteria A is calculated from a table based on the engine speed and the engine load (seeFIG. 5).

In the determination in step406as to whether the misfire rate is greater or equal to the damaging misfire criteria A, the cylinder for which the fuel cut should be performed is determined from the flow chart for determination of the fuel cut cylinder shown inFIG. 2.

After the fuel cut cylinder is determined and when the determination in step406is “YES”, then the vehicle speed is limited below the predetermined speed, i.e., the vehicle speed limit control for misfire, irrespective of the opening of the throttle in step408. In the vehicle speed control by the throttle control or the fuel cut control, the predetermined speed is, e.g., 50 km/h, so that the vehicle speed is limited below 50 km/h irrespective of the opening degree of the throttle.

Prevented is the fuel increase control for the cylinder that the fuel cut is not performed. In this fuel increase prevention process, fuel increases due to the increasing speed, enrichment, and other factors are prevented.

Then a determination is made in step410as to whether the fuel cut cancel condition is met. After start of the fuel cut control when the misfire occurs as shown inFIG. 6, a fuel cut cancel condition for misfire is considered to be satisfied in step410when time “Treset” has elapsed and the driving in each divided section continues for more than 60 seconds. Then the fuel cut is canceled and the catalyst protection control is also canceled.

If the determination in step410is “NO”, then the program returns to step404. If the determination in step410is “YES”, the fuel feed back control is resumed and the fuel-learn control is resumed. The fuel increase control prevention is canceled, and the throttle opening angle control for misfire is canceled in step412. Then the program returns to step404.

As a result, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, the misfire control includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) a control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the engine speed control to limit the engine speed below the predetermined engine speed irrespective of the opening degree of the throttle. Accordingly, when the misfire is detected, a rise is avoided in the catalyst temperature owing to the driving at high speed under heavy engine load in a situation where the driver depresses the acceleration pedal when he feels power down due to the misfires. This prevents detriment or damage of the catalyst.

Furthermore, in the misfire detector for the multi-cylinder engine having the misfire detecting means to detect the misfire for each cylinder, and performing the misfire control if the frequency of the misfire detected by the misfire detecting means is more than the predetermined value, the misfire control includes (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, and (3) the vehicle speed control to limit the vehicle speed below the predetermined speed irrespective of the opening degree of the throttle. Accordingly, when the misfire is detected, the driver is prevented from driving at high speed which is contrary to the misfire control for avoiding problems due to the misfires. Thereby, the catalyst is not heated to high temperatures, which prevents detriment or damage of the catalyst.

The present invention is not limited to the above-mentioned first, second, and third embodiments, but is adaptable for various applications and variations or modifications.

For example, in the above-mentioned embodiments of the present invention, when the misfire control is executed, in addition to two controls, i.e., (1) the fuel cut control for misfiring cylinders by the fuel cut means to stop supplying the fuel to the misfiring cylinders, and (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, the third control includes (3) the retard control to retard the ignition timing by the retard quantity set based on the extent the misfire occurs or the air-fuel ratio, (3) the throttle opening control for misfire to limit the throttle opening angle as compared to the normal opening in accordance with the acceleration degree, (3) the engine speed control to limit the engine speed below the predetermined engine speed irrespective of the opening degree of the throttle, or (3) the vehicle speed control to limit the engine speed below the predetermined speed irrespective of the opening degree of the throttle. However, the third control may be combined as a special configuration.

When implementing the misfire control, in addition to two controls, i.e., (1) the fuel cut control for misfiring cylinders by having the fuel cut means stop supplying the fuel to the misfiring cylinders, and (2) the control to prevent the fuel feed back control and the fuel learning control and to initialize the correction values of both the fuel feed back control and the fuel learning control, as the third control, combined can be (3) the retard control to retard the ignition timing by the retard quantity set based on the extent the misfire occurs or the air-fuel ratio and (3) the throttle opening control for misfire to limit the throttle opening angle as compared to the normal throttle opening, in accordance with the acceleration degree, for example.

This contributes the improvement of the reliability of the misfire control, so that the catalyst is prevented from being heated to high temperatures with reliability in order to avoid detriment or the damage of the catalyst.