JPH07139416A - Misfire detection device for internal combustion engine - Google Patents

Abstract

PURPOSE:To utilize a combustion temperature for which detection sensitivity is high and variation rate is low so as to improve detection accuracy by detecting inter-cylinder pressure of an internal combustion engine, calculating the combustion temperature based on this inter-cylinder pressure, and detecting existence of misfire based on the combustion temperature. CONSTITUTION:Pressures in respective cylinders in an internal combustion engine are detected by an inter-cylinder detection means A. Combustion temperature is calculated by a combustion temperature calculation means B based on the detected inter-cylinder pressures. Existence of misfire is detected by a misfire detection means C based on the calculated combustion temperature. Detection sensitivity of combustion variation is improved by the combustion temperature in the internal combustion engine, since a variation width of the combustion temperature against for the variation width of the combustion pressure is amplified. The change rate of combustion temperature is decreased from that of the combustion pressure for variation of an operational condition. Therefore, judgement accuracy is thus improved since the judgement reference value of the combustion temperature need not be changed more remarkably than that of the combustion pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in a device for detecting misfire of an internal combustion engine.

[0002]

2. Description of the Related Art Generally, when a misfire occurs in an internal combustion engine, various problems such as an increase in harmful components of exhaust gas due to discharge of unburned fuel, overheating of a catalytic converter, afterburning, and fluctuation in rotation occur. Therefore, the occurrence of misfire is detected, and when the misfire is detected, the fuel injection amount, the ignition timing, etc. are corrected and controlled so as to suppress the occurrence of misfire.

Conventionally, as a device for detecting misfire, a device for detecting misfire from rotation fluctuation of a crankshaft (rotational fluctuation detection system), fluctuation of cylinder pressure (for example, Japanese Patent Laid-Open No. 3-31564). There is a method for detecting a misfire (cylinder pressure detection method) or a method for detecting a misfire from a change in the air-fuel ratio of exhaust gas (air-fuel ratio detection method).

[0004]

However, each of the above misfire detection devices has the following problems. In other words, in the rotational fluctuation detection method, misfire is detected based on the detection result of the rotational fluctuation of the crankshaft, so there is a case that it is erroneously detected due to a reverse input from the drive system (during traveling on an irregular road surface). The accuracy of misfire detection was low.

Further, in the in-cylinder pressure detection system, it is difficult to distinguish between misfire and normal combustion in a region where the increase in combustion pressure such as an idle operation region is small, and the misfire detection accuracy is low. Further, in the air-fuel ratio detection system, the response delay is large because the oxygen concentration in the exhaust gas is detected. Further, when performing lean air-fuel ratio control, the output of the air-fuel ratio sensor is kept lean as in the case of misfire, so there is a problem that misfire detection is difficult.

The present invention has been made in view of the above conventional circumstances, and an object of the present invention is to provide a misfire detecting device for an internal combustion engine capable of detecting misfire with high accuracy in the entire operating range.

[0007]

Therefore, as shown in FIG. 1, the internal combustion engine misfire detection device according to the present invention detects in-cylinder pressure detection means A for detecting the pressure in each cylinder of the internal combustion engine.
And a combustion temperature calculating means B for calculating a combustion temperature based on the cylinder pressure detected by the cylinder pressure detecting means A,
Misfire detection means C for detecting the presence or absence of misfire based on the combustion temperature calculated by the combustion temperature calculation means B.

[0008]

In the present invention having such a structure, the cylinder pressure (combustion pressure) P is detected by the cylinder pressure detection means, and PV = G
The combustion temperature (cylinder temperature) T is calculated by the combustion temperature calculation means from the equation of RT, and the combustion temperature P is calculated by the misfire detection means.
Detects misfire based on. As a result, it is possible to improve the detection sensitivity of misfire as compared with the case of detecting the misfire based on the change of the in-cylinder pressure (or the indicated mean effective pressure). Even in an operating region where the increase width is small, it is possible to favorably distinguish between misfire and normal combustion.

In other words, even an Otto cycle engine actually has a combined cycle, and therefore, isobaric combustion (even if heat is supplied to the cylinder interior gas by combustion during a predetermined period after top dead center in the combustion stroke). , Because the volume V increases,
Combustion is performed close to a state in which the combustion pressure P does not change. That is, during this period, even if the in-cylinder pressure (combustion pressure) P detected by the in-cylinder pressure detection means is substantially constant near the maximum pressure Pmax, the combustion temperature (in-cylinder temperature) T is the highest combustion during this period. This means that the temperature continues to rise toward Tmax. Therefore, the fluctuation range of the combustion pressure P (for example, the difference between the in-cylinder pressure at the beginning and end of compression or the maximum pressure at misfire and the maximum pressure Pmax at combustion)
Compared with the above, the fluctuation range of the combustion temperature T (for example, the difference between the maximum temperature Tmax and the in-cylinder temperature at the beginning or end of compression or the maximum temperature at the time of misfire) is amplified, so the in-cylinder pressure Therefore, the detection sensitivity of the combustion change is improved as compared with the case where the change of the combustion state is detected based on.

Further, the rate at which the combustion temperature T changes according to changes in operating conditions (rotational speed and load) is smaller than the combustion pressure P. That is, for example, when the rotation speed or the load is small, the combustion pressure P and the gas weight G (intake air flow rate + fuel weight) become small.
Is smaller, it means that the combustion temperature T is increased from the relationship of PV = GRT. Further, for example, when the rotation speed or the load is large, the combustion pressure P and the gas weight G increase, but the increase of G acts in the direction of decreasing the combustion temperature T from the relationship of PV = GRT. It will be. Therefore, between the rate at which the combustion pressure P changes according to the change in the operating state and the rate at which the combustion temperature T changes, the rate at which the combustion temperature T changes is significantly smaller.

Therefore, when the change in the combustion state is detected, in the case where the change is based on the combustion pressure (cylinder pressure) P, it is necessary to greatly change the judgment reference value according to the magnitude of the change in the operating state. Since it is not necessary to greatly change the judgment reference value based on the combustion temperature T, in this respect as well,
The determination accuracy will be improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, air is sucked into the engine 1 from an air cleaner (not shown) through an air flow meter 2 that detects an intake air flow rate Q, an intake duct 3, a throttle valve 4, and an intake manifold 5. At each branch portion of the intake manifold 5, a fuel injection valve 6 is provided for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid to open the valve, is deenergized and is closed, and is energized and opened by a drive pulse signal from a control unit 50 described later, Fuel that is pressure-fed from the fuel pump and is controlled to a predetermined pressure by the pressure regulator is injected and supplied to the engine 1.

A spark plug 7 is provided in each combustion chamber of the engine 1, and sparks are ignited and burned in the air-fuel mixture based on an ignition signal from the control unit 50. The spark plug 7 is provided with an in-cylinder pressure sensor 8 of a spark plug washer type using a piezo element. The output signal of the in-cylinder pressure sensor 8 is input to the control unit 50. Exhaust gas is exhausted from the engine 1 into the atmosphere via the exhaust manifold 9, the exhaust pipe 10, the three-way catalyst 11 as an exhaust gas purification catalyst, and a noise reduction device (not shown).

A REF signal crank angle sensor 12 for outputting a pulse signal for cylinder discrimination (REF signal) is output to a cam shaft or crank shaft (not shown in FIG. 2).
And a POS signal crank angle sensor 13 that outputs a pulse signal for each crank angle of 1 degree (POS signal). The output signals of these sensors are input to the control unit 50.

The control unit 50 includes a CPU and RO
A microcomputer including an M, a RAM, an A / D converter, an input / output interface, and the like is provided, which receives input signals from various sensors, receives fuel injection valves 6, and spark plugs 7.
Control the operation of. By the way, the injection amount control of the fuel injection valve 6 is performed in the following manner. That is, the control unit 50 determines the basic fuel injection amount from the intake air flow rate Q detected by the air flow meter 2 and the engine rotation speed N obtained by counting the pulse signal of the crank angle sensor 12 for POS signal for a certain period of time. Tp (Tp = k
× Q / N, k is a constant) and the basic fuel injection amount Tp is calculated.
Is corrected by various correction factors (for example, air-fuel ratio feedback correction factor, water temperature correction factor, learning correction factor, load correction factor, etc.) to the fuel injection valve 6 as a drive pulse signal. I am supposed to send it.

The control unit 50 has a function as a misfire detecting means. The misfire detection means according to the present invention detects the cylinder internal pressure P, and PV = GR
The combustion temperature (cylinder temperature) T is calculated from the equation T, and misfire is detected based on the combustion temperature (cylinder temperature) T. This is the cylinder pressure (or indicated mean effective pressure)
It is possible to improve the detection sensitivity of misfire as compared to the case of detecting misfire based on the change of This is because it can be distinguished from normal combustion well. That is, since the actual combustion cycle is a combined cycle, isobaric combustion is carried out for a predetermined period after the top dead center of the combustion stroke (even if the amount of heat is supplied to the cylinder interior gas by combustion, the volume V increases, so the combustion pressure P (A state that does not change), combustion will be performed close to. That is, during this period, even if the in-cylinder pressure (combustion pressure) P detected by the in-cylinder pressure sensor 8 is substantially constant near the maximum pressure Pmax, the combustion temperature (in-cylinder temperature) T is the highest during this period. This means that the temperature continues to rise toward Tmax.
Therefore, the combustion temperature T is compared with the fluctuation range of the combustion pressure P (for example, the difference between the in-cylinder pressure at the beginning and end of compression or the maximum pressure at the time of misfire and the maximum pressure Pmax at the time of combustion).
The fluctuation range (for example, the difference between the maximum temperature at the beginning of compression or the end of compression or the maximum temperature at the time of misfire and the maximum temperature Tmax at the time of combustion) is amplified. Therefore, the detection sensitivity of the combustion change is improved as compared with the case of detecting the change of.

Further, as described above, the rate at which the combustion temperature T changes due to the change in the operating state is smaller than the combustion pressure P, so that when the change in the combustion state is detected, the combustion pressure (in the cylinder In the case of the one based on the pressure P, it is necessary to greatly change the judgment reference value in accordance with the magnitude of the change in the operating state, whereas in the case of the one based on the combustion temperature T, it is not necessary to greatly change the judgment reference value. Therefore, also in this respect, the determination accuracy is improved.

Here, the misfire detection control executed by the control unit 50 as the misfire detecting means will be described with reference to the flowchart of FIG. The flow is based on the RE
It is executed every time a signal is input from the crank angle sensor 13 for F signal. Step 1 (denoted as S1 in the figure.
As well. ), The output value of the cylinder pressure sensor 8 (cylinder pressure)
P (θ) is sampled for each predetermined crank angle (θ). The angle θ may be any angle as long as the misfire determination can be accurately performed. Further, the sampling section may be limited to a section related to combustion such as compression / expansion stroke, whereby only the combustion component excluding the influence of pumping loss in the bottoming cycle (intake / exhaust stroke) can be extracted. Therefore, the combustion fluctuation detection accuracy can be made higher, and the memory capacity of the control unit 50 and the calculation time can be reduced.

In step 2, the intake air flow rate Q is sampled from the air flow meter 2. In step 3,
The sampled P (θ) and crank angle (θ)
In-cylinder volume V (θ) and gas weight G [= intake air flow rate Q + residual gas weight + vaporized fuel weight (corresponding to Tp). In a 4-cycle engine, the residual gas weight can be omitted. ], And the combustion temperature (cylinder temperature) T (θ) is calculated from the following equation.

T (θ) = P (θ) · V (θ) / (R ·
G) R: Gas constant Incidentally, the average combustion temperature, the maximum combustion temperature or the like is obtained from the combustion temperature T (θ) for each predetermined crank angle thus obtained and stored as the actual combustion temperature Te. In step 4, the combustion temperature T theoretically obtained (from the calorific value of the actually injected fuel, etc.) from simulation calculation, etc.
_th (average combustion temperature or maximum combustion temperature, etc.) is set and stored in a map or the like in advance based on the engine speed N and the basic fuel injection amount Tp for each ignition timing, and the theory is referred to with reference to the map. The combustion temperature T _th is searched. Of course,
The calculation may be made each time.

In step 5, the difference SA (= T _th -Te) between the theoretical combustion temperature T _th and the actual combustion temperature Te is calculated. In step 6, SA obtained in step 5
, Is determined to be greater than a preset determination value. If YES, go to step 7. If NO, the process proceeds to step 8. In step 7, it is determined that the actual combustion temperature Te has not risen sufficiently and misfire has occurred, the misfire determination flag MISS is set to 1, and this flow ends. .

In step 8, the actual combustion temperature T (θ)
Is sufficiently increased to near the theoretical combustion temperature T _th , it is determined that the combustion is normally performed, the misfire determination flag MISS is set to 0, and this flow is ended. In the control unit 50, when a misfire is detected by the above flow,
By controlling the fuel injection amount, ignition timing, etc., it is possible to suppress the occurrence of misfiring, and to suppress the increase in harmful components of exhaust gas due to the discharge of unburned fuel, the overheating of the catalytic converter, the afterburn, the fluctuation in rotation, etc. ing.

As described above, according to the present embodiment, the presence or absence of misfire is detected based on the actual combustion temperature (in-cylinder temperature) Te obtained from the in-cylinder pressure P. Therefore, the in-cylinder pressure (or It is possible to detect a change in the combustion state with higher accuracy than that in which the indicated average effective pressure) is detected, and thus it is possible to improve the accuracy of misfire determination in the entire operating range. In other words, the actual combustion process of the engine 1 is a combined cycle, and therefore, isobaric combustion is performed for a predetermined period after the top dead center of the combustion stroke (even if the heat quantity is supplied to the cylinder interior gas by combustion, the volume V
Is increased, the combustion close to the state where the combustion pressure P does not change) is performed. That is, during this period, even if the in-cylinder pressure (combustion pressure) P detected by the in-cylinder pressure sensor 8 is substantially constant at the maximum pressure Pmax, the combustion temperature (in-cylinder temperature) Te is still the highest combustion temperature during this period. Tmax
Will continue to rise towards. Therefore, the fluctuation range of the combustion temperature Te is amplified as compared with the fluctuation range of the in-cylinder pressure P, so that the combustion change is detected as compared with the case of detecting the change of the combustion state based on the in-cylinder pressure P. The detection sensitivity of is improved.

Further, the rate at which the combustion temperature Te changes due to a change in the operating state is smaller than the combustion pressure P, so that when the change in the combustion state is detected, it is based on the combustion pressure (cylinder pressure) P. In this case, the judgment reference value needs to be greatly changed according to the magnitude of the change in the operating state, whereas in the case of the one based on the combustion temperature T, the judgment reference value does not need to be changed greatly. Therefore, the determination accuracy is improved.

In this embodiment, the combustion temperature T _th theoretically obtained from the operating state of the engine 1 is compared with the combustion temperature Te obtained from the actual in-cylinder pressure P. The in-cylinder temperature obtained from the in-cylinder pressure P at the time of occurrence of fire is detected and stored in advance by an experiment or the like, and the misfire is detected by comparing the in-cylinder temperature at the time of the misfire with the combustion temperature Te. It is also possible to do. Further, when the theoretical combustion temperature T _th and the combustion temperature Te obtained from the actual in-cylinder pressure P are compared, the average combustion temperature or the maximum combustion temperatures are described as being compared with each other, but the invention is not limited to this. Instead, it is obvious that the combustion temperatures at predetermined crank angles set in advance may be compared with each other.

[0026]

As described above, according to the present invention,
Since the combustion temperature is calculated based on the cylinder pressure, and the presence or absence of misfire is determined based on the calculated combustion temperature,
Since it is possible to detect changes in the combustion state with high accuracy,
As a result, misfire can be detected with high accuracy in all operating regions including the region where the cylinder pressure change due to combustion during idle operation is small.

[Brief description of drawings]

FIG. 1 is a block diagram according to the present invention.

FIG. 2 is an overall configuration diagram of an embodiment according to the present invention.

FIG. 3 is a flowchart showing misfire detection control in the above embodiment.

FIG. 4 is a diagram showing a misfire undetectable region of a device that detects misfire due to cylinder pressure fluctuation.

[Explanation of symbols]

 1 Engine 8 In-cylinder pressure sensor 12 REF signal crank angle sensor 13 POS signal crank angle sensor 50 Control unit

Claims (1)

[Claims] 1. In-cylinder pressure detecting means for detecting the pressure in each cylinder of an internal combustion engine; combustion temperature calculating means for calculating a combustion temperature based on the in-cylinder pressure detected by the in-cylinder pressure detecting means. A misfire detecting device for an internal combustion engine, comprising: misfire detecting means for detecting the presence or absence of misfire based on the combustion temperature calculated by the combustion temperature calculating means.