JPH04276158A - Engine misfire detector - Google Patents

Abstract

PURPOSE:To accurately judge generation of misfire even during idling run by mutually comparing pressures inside a combustion chamber, at front and rear crank angular positions respectively apart from the top dead point by substantially the same angle, and judging generation of misfire when the pressure difference is less than a specified judging level. CONSTITUTION:A cylinder internal pressure sensor 22 which detects pressure inside a combustion chamber 18 is installed in the washer position of an ignition plug 20. Also a crank angle sensor 24 for detecting the crank angle of the crank shaft of an engine 2 is provided. It is controlled in a control part 26 that respective detection signals of the cylinder internal pressure sensor 22 and the crank angle sensor 24 are inputted, and pressures inside the combustion chamber, at front and rear crank angular positions respectively apart from the top dead point by the same angle are compared with each other, and generation of misfire is judged when the pressure difference is less than a specified judging level. Consequently, generation of the misfire can be accurately judged even during idling run where no large difference is present between the maximum values of the pressure inside the cylinder under the misfire and ignition condition respectively.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to an engine misfire detection device, and in particular detects fluctuations in engine operating conditions such as pressure in a combustion chamber and rotational angular velocity of a crankshaft, and inputs this detection signal to a control unit to detect a misfire. The present invention relates to an engine misfire detection device that detects a state.

0002

2. Description of the Related Art In internal combustion engines of vehicles, the generation of harmful exhaust gas components is reduced and fuel efficiency is improved by operating the engine with a lean air-fuel mixture.

However, if the air-fuel mixture is too lean, combustion within the combustion chamber will be poor, and there is a risk that unburned gas will flow to the exhaust system and cause a misfire. In this way, when a misfire occurs, it causes functional deterioration and damage to the catalyst body, so a fuse sensor is installed downstream of the catalyst body, and when the temperature of the catalyst body rises above the set value due to a misfire, this fuse sensor is activated. When the temperature condition is detected, it is displayed on the meter or a warning lamp is lit on the panel to notify the driver of the occurrence of a misfire.

[0004] Furthermore, as an engine misfire detection device, there is one disclosed in Japanese Patent Laid-Open No. 60-45750. The fuel injection control method for an internal combustion engine disclosed in this publication determines a misfire at the time of starting the engine from the combustion pressure in the engine combustion chamber, and reduces the amount of fuel to be injected below a predetermined value when a misfire is determined. This prevents the air-fuel ratio in the engine combustion chamber from becoming too rich, ensuring startability.

[0005]

By the way, some conventional engine misfire detection devices detect variations in the rotational angular velocity of the engine crankshaft.

However, it is generally difficult to detect fluctuations in the rotational angular velocity of the crankshaft of the engine and to determine which cylinder is misfiring from the detected fluctuations in the rotational angular velocity, especially in multi-cylinder engines. As the torque fluctuation decreases, the determination accuracy decreases, making it more difficult to determine whether there is a misfire, which requires a large amount of time for maintenance and inspection, which is disadvantageous in practice.

[0007]

[Means for Solving the Problems] Therefore, in order to eliminate the above-mentioned disadvantages, the present invention provides an engine misfire detection device that detects misfires based on fluctuations in engine operating conditions, in which the pressure inside the combustion chamber is applied to the washer part of the spark plug. A cylinder pressure sensor is provided to detect the crank angle of the crankshaft of the engine, and a crank angle sensor is provided to detect the crank angle of the crankshaft of the engine, and detection signals from the cylinder pressure sensor and the crank angle sensor are inputted to the engine so that the cylinder is separated from the top dead center by approximately the same angle. The present invention is characterized in that a control section is provided that compares the pressures in the combustion chamber at the front and rear crank angle positions and determines that a misfire has occurred if the pressure difference is less than a predetermined determination level.

[0008]

[Operation] With the invention as described above, the pressure in the combustion chamber of the front and rear crank angle parts that are approximately the same angle away from top dead center is compared, and if the pressure difference is less than a predetermined judgment level, the control section It is determined that a misfire has occurred, and the cylinder where the misfire occurred is clearly known, making maintenance and inspection easier.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 to 9 show embodiments of the present invention. In FIG. 1, 2 is an internal combustion engine; 4 is an internal combustion engine;
1 is a cylinder block, 6 is a cylinder head, 8 is a piston, 10 is an intake port, 12 is an intake valve, 14 is an exhaust port, and 16 is an exhaust valve.

The cylinder head 6 of the engine 2 includes:
A spark plug 20 is provided to protrude into the combustion chamber 18 .

At this time, an in-cylinder pressure sensor 22 for detecting the pressure within the combustion chamber 18 is provided at the washer portion of the spark plug 20, and a crank angle sensor 24 for detecting the crank angle of a crankshaft (not shown) of the engine 2 is provided. .

The cylinder pressure sensor 22 and crank angle sensor 24 are connected to a control unit (ECU) 26, and a warning display lamp 28 is also connected to notify the driver of the occurrence of a misfire.

The control section 26 also controls the cylinder pressure sensor 2.
2 and the crank angle sensor 24, and compare the pressures in the combustion chamber at the front and rear crank angle positions that are approximately the same angle away from top dead center. If the pressure difference is less than a predetermined judgment level, a misfire occurs. It has a configuration that controls to determine that this has occurred.

More specifically, as shown in FIGS. 2 and 3, the cylinder pressure sensor 22 has a main body 22A connected to an annular upper member 3.
0 and a lower member 32, and these upper and lower members 3
0 and 32, first and second piezoelectric elements 34-1 and 34-
2, and an electrode member 36 interposed between the first and second piezoelectric elements 34-1 and 34-2.

At this time, the upper and lower members 30 and 32 are
(minus) side electrode, and the electrode member 36 is
The in-cylinder pressure sensor 22 is connected to the control section 26 by a lead wire 38, which is a (positive) side electrode.

The control section 26 also controls the cylinder pressure sensor 2.
When the detection signals from the combustion chamber 18 and the combustion chamber 18 are input, the cylinder pressure sensor output voltages VA and VB at the front and rear crank angle positions A and B, which are approximately the same angle away from the top dead center, are compared. This is to compare the pressure inside.

Then, the cylinder pressure sensor output voltages VA and V
If the difference ΔV from B is less than a predetermined determination level VH, it is determined that a misfire has occurred, and this misfire status is outputted to the display lamp 28, which is controlled to be turned on, for example.

In general, the relationship between the in-cylinder pressure sensor output voltage and the crank angle appears in an asymmetrical shape before and after top dead center at the time of ignition, as shown by the broken line in FIG. As shown, the shape appears approximately symmetrical before and after the top dead center, and the cylinder pressure sensor output voltage VA becomes VA1.

For this reason, the difference ΔV between the cylinder pressure sensor output voltages VA and VB is set to a predetermined judgment level VH,
A misfire is determined when the cylinder pressure sensor output voltage VA decreases and the difference ΔV becomes small and becomes less than the determination level VH.

Incidentally, stress is applied to the cylinder pressure sensor 22 in advance by the spark plug 20 when the spark plug 20 is installed, and a bias is applied to the output voltage.

Therefore, since the output voltage changes depending on the tightening torque of the spark plug 20, it is not possible to measure the absolute value of the cylinder pressure, but it is possible to measure changes in the cylinder pressure.

In addition, for example, in detail regarding a three-cylinder engine, when calculating the measurement timing, as shown in FIGS. 8 and 9, the rise θr and fall θs of the crank angle detection signal of the electromagnetic pickup type crank angle sensor are Both are before top dead center TDC.

[0024] Then, the prediction periods T1F and T2F are expressed by the formula ────────────── Equation 1 ────
Calculated by ────────────.

After this calculation, the measurement times A and B are calculated using the formula ──
──────────── Number 2 ──────
────────── and ──────────────
─ The measurement timing is determined by calculating each using the number 3 ────────────────.

Next, the operation will be explained.

First, input capture interrupt (ICI) will be explained with reference to FIG.

An input capture interrupt (ICI) (100) is operated to input the crank angle detection signal from the crank angle sensor 24, and it is determined whether the input edge is in a rising state or a falling state (102). .

If it is determined in this judgment (102) that it is in the rising state, the cylinder is judged (104) and the formula ────────────── Equation 3 -
────────────── measurement time B makes TB
is calculated (106).

[0030] Then, in TB due to this measurement time B, F
RC is added to obtain OCR (108).

Thereafter, the input edge is set to a falling state (110), and the process proceeds to RTI (118), which will be described later.

Further, in the above judgment (102), if it is judged that it is in the falling state, the formula ──────
────────── Number 2 ────────
Calculate TA from measurement time A of ──────── (
112).

[0033] Then, in TA due to this measurement time A, F
RC is added to obtain OCR (114).

Thereafter, the input edge is set to a rising state (116), and the transition is made to RTI (118).

The output compare interrupt (OCI) will also be explained with reference to FIG.

First, run the output compare interrupt (OCI) (200) program to determine whether the crank angle is before or after top dead center (20
2) Do.

If it is determined in this judgment (202) that the position is before top dead center, the cylinder pressure sensor output voltage VB
(204), and this in-cylinder pressure sensor output voltage V
The measured value of B is stored in RAM (random access memory).
is stored (206) and transferred to RTI (208).

If it is determined in the above judgment (202) that the position is after top dead center, the cylinder pressure sensor output voltage VA
(210), and this cylinder pressure sensor output voltage VA
The difference ΔV is obtained by subtracting the cylinder pressure sensor output voltage VB before top dead center (212).

[0039] Then, this difference ΔV is a predetermined judgment level V
It is determined whether or not it is less than H (214), and if this determination (214) is NO, it is RTI (216), and if the determination (214) is YES, one misfire has occurred At the same time, the misfire flag is set (218
)do.

At this time, for example, the control section 26 outputs a misfire signal to the indicator lamp 28, causing the indicator lamp 28 to light up.

[0041] After the processing (218), RTI (2
20).

As a result, in the above two flowcharts, the difference ΔV was calculated from the relationship between the cylinder pressure sensor output voltage and the crank angle as shown in FIG. 6 during normal operation, but as shown in FIG. Even during idling, when there is not a large difference in the maximum value of the cylinder pressure between the misfire state and the ignition state, the above-mentioned method makes it possible to clearly determine the occurrence of a misfire.

Furthermore, even in a multi-cylinder engine, the misfire state can be determined independently for each cylinder by the in-cylinder pressure sensor 22 provided in the washer of the spark plug 20 for each cylinder, and the cylinder in which the misfire has occurred can be detected independently. This makes maintenance and inspection easier, which is advantageous in practice, and there is no risk of deterioration in misfire detection accuracy.
Good usability can be maintained.

Furthermore, in a system equipped with a cylinder pressure sensor for performing knock control, for example, the cylinder pressure sensor can perform knock control and misfire detection, so the cylinder pressure sensor can be shared, and the configuration can be simplified. It is economically advantageous because it does not become complicated and the cost can be reduced.

[0045]

As described in detail above, according to the present invention, an in-cylinder pressure sensor for detecting the pressure in the combustion chamber is provided at the washer portion of the spark plug, and a crank angle sensor for detecting the crank angle of the engine crankshaft is provided. The sensor inputs the detection signals from the cylinder pressure sensor and crank angle sensor, compares the pressure in the combustion chamber at the front and rear crank angle positions that are approximately the same angle away from top dead center, and determines if the pressure difference is less than a predetermined judgment level. In this case, a control unit is provided to determine that a misfire has occurred, so that the control unit can determine that a misfire has occurred, not only during normal operation, but also during idling, where there is not a large difference in the maximum cylinder pressure between the misfire state and the ignition state. , it is possible to clearly determine the occurrence of misfire. Furthermore, even in multi-cylinder engines, the misfire status can be determined independently for each cylinder using the in-cylinder pressure sensor installed in the washer of the spark plug for each cylinder, making it possible to clearly identify the cylinder in which the misfire occurred. This makes maintenance and inspection easier, which is advantageous in practice, and there is no risk of deterioration in misfire determination accuracy, allowing good usability to be maintained. Furthermore, in a system equipped with a cylinder pressure sensor to perform knock control, for example, since the cylinder pressure sensor can perform knock control and misfire detection, the cylinder pressure sensor can be shared, reducing the complexity of the configuration. First, the cost can be kept low and it is economically advantageous.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an engine misfire detection device showing an embodiment of the present invention.

FIG. 2 is a schematic perspective view of a cylinder pressure sensor.

FIG. 3 is an enlarged cross-sectional view of the cylinder pressure sensor taken along the line ⓓ-ⓓ of FIG. 2;

[Figure 4] Input capture interrupt (IC
It is a flowchart of I).

[Figure 5] Output compare interrupt (OC
It is a flowchart of I).

FIG. 6 is a diagram showing the relationship between cylinder pressure sensor output voltage and crank angle.

FIG. 7 is a diagram showing the relationship between the cylinder pressure sensor output voltage and the crank angle during idling.

FIG. 8 is a time chart showing a method for calculating measurement timing in a three-cylinder engine.

FIG. 9 is a schematic diagram showing each numerical value in relation to the crank angle.

[Explanation of symbols]

2 Engine 4 Cylinder block 6 Cylinder head 8 Piston 20 Spark plug 22 Cylinder pressure sensor 22A main body 24 Crank angle sensor 26 Control unit (ECU) 30 Upper member 32 Lower member 34-1 First piezoelectric element 34-2 Second piezoelectric element 36 Electrode member

[Math 1]

[Math 2]

[Math 3]

Claims (1)

[Claims] Claim 1: An engine misfire detection device that detects misfires due to changes in engine operating conditions, comprising: a cylinder pressure sensor that detects the pressure inside the combustion chamber provided at the washer portion of the spark plug;
A crank angle sensor is provided to detect the crank angle of the engine crankshaft, and detection signals from the cylinder pressure sensor and the crank angle sensor are inputted to detect combustion at the front and rear crank angle portions that are approximately the same angle away from top dead center. An engine misfire detection device comprising a control section that compares pressures in a room and determines that a misfire has occurred if the pressure difference is less than a predetermined determination level.