JP3769820B2 - Engine misfire diagnostic device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a misfire diagnostic equipment of the engine to diagnose whether a misfire in the engine has occurred.
[0002]
[Prior art]
In general, when an engine, a spark plug, or the like deteriorates or fails in an engine, intermittent misfire can occur. As such misfires occur more frequently, the emission of exhaust gas deteriorates, and unburned gas in the catalytic converter burns, causing damage to the converter, so early detection is very important. It becomes.
[0003]
By the way, the misfire may be temporarily generated in an unstable operation state such as when the engine is started, or may be semipermanently caused by deterioration of the injector or the spark plug. Of these, it is only the latter that can be regarded as a failure that can essentially have an adverse effect on the operating state of the engine, and it is reasonable to regard the former as normal without actually judging it as misfire.
[0004]
Therefore, Japanese Patent Laid-Open No. 4-36044 discloses a period from the start of driving the starter motor to the elapse of a predetermined time after the start of driving of the motor as a misfire determination stop period. During this misfire determination stop period, the misfire determination is determined. A device that is considered to diagnose a misfire determination only when a misfire that can be regarded as a failure that actually has an adverse effect on the operating state of the engine by prohibiting the above is disclosed.
[0005]
[Problems to be solved by the invention]
A brake booster for boosting the brake operation using the intake negative pressure may be connected to the intake system of the engine. This brake booster assists the pedal effort by using the differential pressure between the intake negative pressure and the atmospheric pressure when the brake pedal is depressed, and when the pedal is returned (that is, the brake is turned on). When switching from OFF to OFF), the air (atmosphere) is discharged into the intake system to store negative pressure.
[0006]
Therefore, in an engine equipped with such a brake booster, when the brake is switched from on to off, the exhaled air flows into the cylinder, and the air-fuel ratio may be temporarily reduced to cause misfire. Such a misfire is a temporary phenomenon that occurs only when the brake is switched from on to off, and therefore it is appropriate to regard it as normal without actually determining that a misfire has occurred (failure has occurred).
[0007]
However, in the device disclosed in the above publication, after the misfire determination stop period has elapsed, the misfire determination is always performed based on a certain determination condition regardless of whether the brake is turned on or off. There is also a risk of misdiagnosis as a fault misfire due to temporary leaning of the air-fuel ratio due to a brake operation.
[0008]
On the other hand, the increase in intake air due to the discharge of the brake booster as described above is not detected by an air flow sensor or the like arranged upstream of the discharge position, so the air-fuel ratio is temporarily reduced by the discharge air. In the case of leaning, the response is delayed, and an unstable combustion state may be left for a relatively long time.
[0009]
Japanese Patent Laid-Open No. 4-203252 discloses a technique that prohibits misfire determination for a while when the brake is switched from off to on to prevent misfire misdiagnosis due to rotational fluctuation during sudden braking. This device cannot solve the inconvenience caused by the air discharged from the brake booster to the intake system.
[0010]
In view of such circumstances, and an object thereof is to provide a misfire diagnostic equipment of the engine which can avoid a disadvantage due to the discharging of air to the intake system from the brake booster.
[0011]
[Means for Solving the Problems]
As a means for solving the above-described problems, the present invention provides an engine misfire diagnosis apparatus for determining misfire of an engine in which a brake booster using the intake negative pressure is connected to an intake system. When the preset misfire judgment condition is satisfied, when the crank angular speed fluctuation value exceeds the preset judgment value, misfire judgment means for judging that misfire has occurred, and switching when the brake is switched from on to off Until the predetermined period from the time point, the misfire determination value by the misfire determination means is set to be larger than the other period only when the intake air amount is a certain value or less and the misfire diagnosis is performed. Is greater than a certain value, it comprises a judgment restricting means for executing a misfire diagnosis based on a normal judgment value even before the predetermined period has elapsed .
[0012]
The “misfire” determined in this device is a temporary phenomenon caused when the air-fuel ratio becomes lean when the brake is switched from on to off, that is, when air is discharged from the brake booster to the intake system. It shall not include any misfires, but shall refer only to misfires that actually have an adverse effect on engine operating conditions, that is, misfires that can be regarded as malfunctions.
[0013]
According to this device, when the brake is switched from on to off, that is, when air is discharged from the brake booster to the intake system, the intake air amount is a constant value until a predetermined period elapses from the switching time. Only in the following cases, the misfire judgment value is made larger than the normal period and the misfire judgment is performed, so that the temporary misfire caused by the leaning of the air-fuel ratio due to the inflow of the air into the cylinder becomes a fault misfire. As well as a misfire determination opportunity can be secured.
[0014]
In particular, when the intake air amount detecting means for detecting the intake air amount is provided in the intake system, and the brake booster is connected at a position downstream of the detection position by the intake air amount detecting means. In this case, the air increase due to the discharge of air from the brake booster is not detected at all by the intake air amount detection means, and the fuel injection increase control is not performed based on the detection of the intake air amount. The present invention is particularly useful.
[0017]
The predetermined period can be set as appropriate, but this period is substantially equal to the period during which air is discharged from the brake booster to the intake system when the brake is switched from on to off. Thus, the misfire determination regulation period can be minimized to the extent that the misdiagnosis can be reliably prevented.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS.
[0025]
An engine body 10 shown in FIG. 1 includes a plurality of cylinders, each of which contains a piston 12, and a combustion chamber 14 is formed above the piston 12. An intake port 15 and an exhaust port 16 face the combustion chamber 14, and the intake port 15 and the exhaust port 16 are opened and closed by an intake valve 17 and an exhaust valve 18, respectively. Further, a crank angle sensor 13 and a water temperature sensor 19 for detecting the engine water temperature τw are disposed at appropriate positions of the engine body 10.
[0026]
An intake passage 20 is connected to the intake port 15. In this intake passage 20, an air cleaner 21, an air flow sensor (intake air amount detection means) 22, a throttle valve 23, a surge tank 24, and an intake manifold 25 are provided in this order from the upstream side toward the intake port 15. The injector 26 is arranged. The throttle valve 23 is bypassed by a bypass passage 27, and an idle speed control bypass valve 28 is provided in the middle of the bypass passage 27. The air cleaner 21 is provided with an intake air temperature sensor 29.
[0027]
An exhaust passage 30 is connected to the exhaust port 16. The exhaust passage 30 is provided with a catalytic converter 31, and an O ₂ sensor 32 is provided upstream thereof.
[0028]
A brake booster 34 is connected to an appropriate position of the intake system (in this embodiment, the surge tank 24 on the downstream side of the air flow sensor 22). The brake booster 34 is connected to a brake pedal 36. When the brake pedal 36 is depressed, the brake booster 34 assists the pedal depression force by using a differential pressure between the intake negative pressure and the atmospheric pressure. When 36 is released (that is, when the brake is switched from on to off), the air (air) is discharged into the surge tank 24 and the negative pressure is stored again.
[0029]
A brake switch 38 is provided in the vicinity of the brake pedal 36 to detect the presence or absence of depression (brake on / off).
[0030]
This engine is equipped with an ECU (control unit) 40 formed of a microcomputer. The ECU 40 performs fuel injection control from the injector 26, opening / closing control of the bypass valve 28, and the like based on the detection signals of the sensors, and determines whether or not misfiring that can be regarded as a failure has occurred in the engine body 10. As a function related to this, a determination regulation unit 41 and a misfire determination unit 42 are provided.
[0031]
The misfire determination means 42 determines that a misfire has occurred only when the current operating state matches a preset misfire determination condition, and turns on a warning lamp 44 provided in the cab or the like. When the brake switch 38 is switched from on to off, that is, when the brake is switched from on to off, the determination restricting means 41, as a rule, until a predetermined determination restricting period elapses from the switching point. The misfire determination by the misfire determination means 42 is restricted , and the determination restriction period starts from the time when the brake is switched from on to off, and the air flow from the brake booster 34 to the surge tank 24 associated therewith. It is set to a period substantially equivalent to the period when the discharge ends.
[0032]
Next, a specific misfire diagnosis operation performed by the ECU 40 will be described with reference to the flowchart of FIG. 2 and the time charts of FIGS.
[0033]
First, various detection signals are captured (step S1 in FIG. 2), and the misfire diagnosis operation is started from the point in time when the actual operation state matches the preset misfire monitoring conditions (YES in step S2).
[0034]
As a feature of this device, when the brake is switched from on to off (YES in step S3), as shown in FIG. 3A, a timer count TC for measuring the misfire determination regulation period is set to the misfire. The count value A corresponding to the determination regulation period is set (step S4 in FIG. 2), and thereafter, the timer count TC is decreased by 1 (step S5). If the timer count TC does not reach 0 (NO in step S6) and the intake air amount Qa does not reach the preset value B (YES in step S7), the brake booster 34 It can be determined that the air is exhaled and that the air has a large effect on the air-fuel ratio (that is, the air-fuel ratio is remarkably made lean), and it is expected that the combustion state is temporarily destabilized due to the lean air-fuel ratio. Therefore, during this period, the misfire determination value is set to be larger than that in other periods ( step S15 ), and the misfire diagnosis is executed.
[0035]
On the other hand, when the timer count TC reaches 0 (YES in step S6), that is, when the misfire determination regulation period has elapsed and it can be considered that the discharge of air from the brake booster 34 has ended, If the intake air amount Qa is greater than or equal to the above value B (NO in step S7), that is, even if air is discharged from the brake booster 34, the entire intake air amount Qa is large, which greatly affects the air-fuel ratio. Can be regarded as not being given, a misfire diagnosis is executed based on a normal determination value Rf (described later) (step S16).
[0036]
As shown in FIG. 3B, when the brake is operated many times at a pitch shorter than the misfire determination regulation period, that is, when the pumping brake is performed, the period is multiplied by the brake multiple. Since air continues to be discharged intermittently from the force device 34, the misfire monitoring may be started after the misfire determination regulation period has elapsed since the last switching from brake on to off.
[0037]
As a specific operation of the misfire monitor, the count number is integrated (ignition number) every time ignition by an unillustrated spark plug is performed, and the number of times that misfire has occurred (misfire number) is also counted. In the present invention, based on a detection signal outputted from the crank angle sensor 13, calculates the [Delta] [omega (difference between the crank angular speed and the previous crank rotation of the crank angular speed of this crank rotation) variation of the crank angular speed, the variation Means is used such that the number of misfires is counted each time the value Δω exceeds a preset determination value Rf.
[0038]
Each time the number of ignitions reaches a predetermined value C (YES in step S10), the number of misfires counted so far is compared with a preset allowable value D. If the number of misfires is larger ( If YES in step S11), it is determined that a failure has occurred (that is, misfire in a narrow sense) (step S12), and if the number of misfires is less than or equal to the allowable value D (NO in step S11), it is determined that it is normal (step S13). Each time such a determination is made, the count values for the number of ignitions and the number of misfires are reset to 0 (step S14) to prepare for the next misfire determination.
[0039]
According to such a device, until the predetermined misfire determination regulation period elapses from the time when the brake is switched from on to off, in principle, the determination value for misfire determination is set larger than usual , It is possible to prevent a misdiagnosis in which a temporary misfire caused by the air discharged from the brake booster 34 is determined as a failure misfire, and an appropriate misfire diagnosis can always be performed.
[0040]
Moreover, even during the above SL misfire determination regulatory period, when the intake air amount Qa is large, i.e., if the above discharging air is not significant perturbation of the air-fuel ratio, since by usual misfire determination, More appropriate misfire diagnosis is possible by preventing more than necessary misfire judgment regulations.
[0041]
In other words , the “determination regulating means” in the present invention does not completely prohibit misfire determination as described above, but makes the condition for judging misfire for a predetermined period after the brake is switched from on to off. there are, in the case the intake air amount in the above SL predetermined period is less than a predetermined value, and a determination value to be compared with the crank angular speed variation Δω is larger than other periods.
[0042]
Further, between the engine misfire identification restriction period may be set as appropriate, but this time, as described above, by setting the period substantially equal to the period until discharging of air from the brake booster 34 is completed For example, there is an advantage that a period for suppressing the misfire determination can be set in a short time while reliably preventing misdiagnosis caused by the exhaled air.
[0043]
Next, a second embodiment will be described with reference to FIGS. In this embodiment, an unstable combustion state caused by the discharged air is positively eliminated by using a fuel control means 43 that controls fuel injection from the injector 26. Specifically, when the brake switch 38 is switched from on to off, the fuel control means 43 injects fuel asynchronously until a preset air-fuel ratio correction period elapses from the switching point in principle. (That is, the fuel is injected at a timing different from the original fuel injection timing).
[0044]
The specific control operation is shown in the flowchart of FIG. In the figure, the brake on / off determination (step S3) and the check of the intake air amount Qa (step S7) are exactly the same as in the first embodiment, but in this second embodiment, the brake is on. When the intake air amount Qa is less than the predetermined value B (YES in step S7), the above-described asynchronous fuel injection is performed (step Sij). By such temporary injection of fuel, leaning of the air-fuel ratio due to air discharge from the brake booster 34 is quickly eliminated or alleviated, and an unstable combustion state is prevented from continuing for a long time. Further, when the misfire diagnosis is performed simultaneously with the air-fuel ratio control as in this embodiment, misdiagnosis caused by the lean air-fuel ratio can also be prevented.
[0045]
Moreover, in this embodiment, when the intake air amount Qa is large, that is, when the above-mentioned discharged air does not affect the air-fuel ratio so much, asynchronous fuel injection is not performed, so that there is an advantage that fuel consumption can be saved correspondingly. can get.
[0046]
Note that the “air-fuel ratio correction means” in the present invention is not limited to the temporary injection of fuel asynchronously as described above, and may be, for example, an increase in the fuel injection amount at the regular fuel injection timing. The illustrated bypass valve 28 may be closed to temporarily reduce the intake air amount.
[0047]
【The invention's effect】
As described above, according to the present invention, in the engine misfire diagnosis device to which the brake booster using the intake negative pressure is connected, when the brake is switched from on to off, that is, the air from the brake booster to the intake system. Since the misfire determination is restricted until a predetermined period elapses from the switching point, the temporary misfire caused by the lean air-fuel ratio due to the inflow of air into the cylinder. Can be prevented from being determined as a fault misfire. In particular, the misfire determination value is restricted by setting the misfire determination value larger than normal only when the intake air amount is a certain value or less, so the operating range in which the misfire determination can be performed can be expanded while preventing the misdiagnosis. An effect is obtained.
[0050]
According to the predetermined period, when the brake is switched from on to off, a period substantially equivalent to the period during which air is discharged from the brake booster to the intake system is set. As long as it can be prevented, it is possible to minimize the period during which misfire determination is restricted .
[0055]
The misfire diagnostic equipment of the engine according to the present invention, together with the intake air amount detecting means for detecting an intake air amount to the intake system is provided, at a position downstream of the detection point by this intake air amount detecting means When the brake booster is connected, that is, when the increase in air due to the air discharged from the brake booster is not detected by the intake air amount detection means, the effect is particularly remarkable.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an engine according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing a misfire diagnosis operation performed in the engine.
FIGS. 3A and 3B are time charts showing a setting example of a misfire determination regulation period in the misfire diagnosis operation. FIGS.
FIG. 4 is an overall configuration diagram of an engine according to a second embodiment of the present invention.
FIG. 5 is a flowchart showing a misfire diagnosis operation performed in the second embodiment of the present invention.

Claims (3)

In the engine misfire diagnosis device that performs misfire determination of an engine in which a brake booster that uses the intake negative pressure is connected to the intake system, when the engine operating state satisfies a preset misfire determination condition , the crank angular speed When the fluctuation value exceeds a preset determination value, misfire determination means for determining that misfire has occurred, and when the brake is switched from on to off, the amount of intake air is reduced until a predetermined period elapses from the switching point. Only when the value is below a certain value, the misfiring judgment value by the misfire judgment means is made larger than the other period to execute the misfire diagnosis. An engine misfire diagnostic apparatus comprising: a judgment restricting means for executing a misfire diagnosis based on a normal judgment value even before the engine is run . 2. The engine misfire diagnosis apparatus according to claim 1, wherein intake air amount detection means for detecting an intake air amount is provided in the intake system, and the brake is disposed at a position downstream of a detection point by the intake air amount detection means. An engine misfire diagnostic device, characterized in that a booster is connected. 3. The engine misfire diagnostic apparatus according to claim 1 or 2, wherein the predetermined period is substantially equivalent to a period during which air is discharged from the brake booster to the intake system when the brake is switched from on to off. Engine misfire diagnostic device characterized by the period.

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