JPH04124441A - Misfire detecting device for engine - Google Patents

Abstract

PURPOSE:To improve accuracy of judgement in misfire condition, by correcting cylinder pressure for judging misfire condition, which is detected in an optional crank angle position after termination of compression stroke in its reducing direction according to detected pressure after termination of compression stroke. CONSTITUTION:In an engine misfire detecting device 9, respective cylinder pressures which are detected by pressure indicating sensors 7 in crank angle positions of optional two points in front and rear of the upper dead point in compression stroke, are compared with each other so as to detect misfire condition of the engine. At this time, cylinder pressure for judging the misfire condition, which is detected in the optional crank angle position after termination of compression stroke, is corrected in its reducing direction according to detected pressure after termination of the compression stroke. Hence, for example, when the temperature in a combustion engine 3 is raised rapidly by acceleration or the like, error detection caused by an increase of the output value of the pressure indicating sensor 7, can be corrected in reducing direction pertinently. It is thus possible to improve accuracy of judgement on misfire condition.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an engine misfire detection device.

(Prior Art) In order to extract the thermal energy generated by combustion within the cylinder of an engine most effectively as driving output, it is desirable to set the maximum pressure generation point due to combustion to a position slightly later than compression top dead center TDC ( (See Figure 4).

For example, the relationship between the ignition timing and the combustion pressure in the cylinder in a four-stroke engine is specifically illustrated in FIG. 4.

At the end of the intake stroke, the cylinder is filled with a negative pressure air-fuel mixture that has been throttled by the throttle valve.

The intake valve actually closes about 40-60' after bottom dead center. Compression eventually begins, and the pressure and temperature of the mixture confined within the cylinder increases, and the gasoline in the mixture evaporates.

Then, when the compression pressure increases, an electric spark is sent to the spark plug. It takes a certain amount of time after the spark flies until the air-fuel mixture starts to actively burn.

This is ignition delay.

Once the ignition delay time has passed and combustion begins, the cylinder pressure increases rapidly. Next, when combustion ends, the piston has already entered its downward stroke, so the cylinder volume increases and the cylinder pressure decreases.

During the compression stroke, the piston does work by compressing the air-fuel mixture. However, during the expansion stroke, the combustion gas expands, pushing the piston and performing work on the outside.

The exhaust valve opens at 40 to 60 degrees before bottom dead center, and the residual pressure releases the combustion gases from the exhaust system into the atmosphere.

During the next upward stroke (exhaust stroke), the combustion gases are forced out by the piston. As the engine approaches top dead center, the intake valves begin to open, and as the engine approaches top dead center, the exhaust valves close.

In the case of ignition timing at the illustrated crank angle position, the maximum combustion pressure appears at a position slightly later than compression top dead center TDC, and the greatest combustion work is performed by sufficiently high combustion pressure until the exhaust valve opens. . On the other hand, if the ignition timing is advanced by a predetermined angle beyond the indicated ignition timing, the maximum combustion pressure will be the highest, but on the other hand, knocking will occur.

On the other hand, if the ignition timing is delayed by a predetermined amount from the ignition timing shown in the figure, knocking as described above will not occur, but the generated combustion pressure will be greatly reduced and the amount of work will also be reduced.

Therefore, the ignition timing of the engine is generally set at an optimal position before compression top dead center TDC, as shown in the figure, taking into account the ignition delay and combustion time.

Therefore, when the air-fuel mixture is ignited and combusted normally, the internal cylinder pressure of the engine changes greatly across the compression top dead center TDC, as shown by the solid line in FIG. On the other hand, in the case of a misfire, on the other hand, the output change within the cylinder becomes symmetrical with respect to the compression top dead center TDC.

Therefore, for example, as shown in FIG. 5, pressure values P1. at any two points before and after compression top dead center. By detecting Pt with, for example, a finger pressure sensor and comparing them, it is possible to detect a misfire state of the engine (for example, as disclosed in Japanese Patent Application Laid-Open No. 61-238).
(See Publication No. 76).

(Problem to be Solved by the Invention) However, when the temperature of the combustion gas near the acupressure sensor changes rapidly, for example during acceleration, the output signal of the acupressure sensor changes as shown in FIG. There is a problem in that the temperature changes upward, making it impossible to distinguish between normal combustion and misfire, leading to such detection.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above problems, and involves comparing cylinder pressures at arbitrary two crank angle positions before and after compression top dead center. In an engine misfire detection device for detecting a misfire state of an engine, the cylinder pressure at the end of a compression stroke is detected, and the misfire state is determined at an arbitrary crank angle position after the end of the compression stroke according to the detected pressure. The present invention is characterized in that a determination pressure correction means is provided for correcting the cylinder pressure for use in a downward direction.

(Function) In the configuration of the engine misfire detection device of the present invention described above, the cylinder pressure at the end of the compression stroke is detected, and the misfire judgment pressure at an arbitrary crank angle position after the end of the compression stroke is determined in accordance with the detected value. Since the correction is made in the downward direction, even when the temperature of the combustion chamber rises rapidly, such as during acceleration, false detections based on the high value of the shiatsu sensor output are appropriately corrected in the downward direction. It becomes possible to do so.

(Effects of the Invention) Therefore, according to the present invention, it is possible to provide an engine misfire state detection device with high determination accuracy (and high reliability).

(Embodiment) FIGS. 1 to 3 show an engine misfire detection device according to an embodiment of the present invention.

First of all, Fig. 1 shows the overall system configuration of the detection device, where 1 is the cylinder of a 4-cycle engine, 2 is the cylinder of the 4-cycle engine,
is the piston of the same engine, 3 is the combustion chamber of the same engine, 4
5 is the same spark plug, and 5 is a connecting rod that supports the piston 2 on the crankshaft via a piston pin 6. Further, reference numeral 7 is a finger pressure sensor for detecting cylinder pressure provided at the upper part of the engine combustion chamber 3.

On the other hand, reference numeral 9 denotes an engine misfire detection device (control unit), and the engine misfire detection device 9 is formed of, for example, a microcomputer, and detects the detection signal (/cylinder pressure P) of the finger pressure sensor 7, the engine crank By inputting the angle θ, etc., a misfire detection operation as shown in FIG. 2 is performed.

As a result, when a misfire state of the engine is appropriately detected, a warning device 10 such as a cluster indicator is activated to notify the driver that the engine is in a misfire state.

Next, the engine misfire state detection function of the engine misfire detection device 9 will be explained in detail with reference to the functional block diagram of FIG.

In FIG. 2, first, reference numeral 20 is an engine, and the crank angle θ of the engine 20 is determined by the crank angle detection means 11, and at each stroke position of the engine 20 (■ At the start of compression, ■ Before compression top dead center, ■ After compression top dead center, ■At the end of expansion)
The shiatsu pressure (cylinder pressure P) at is accurately determined by the shiatsu pressure detection means 13 at the beginning of compression, the shiatsu pressure detection means 15 before compression upper row point, the shiatsu pressure detection means 16 after compression top dead center, the shiatsu pressure detection means 14 at the end of inflation, etc., respectively. (Actually, the above-mentioned shiatsu sensor 7 is detected at each corresponding crank angle timing.)
).

The respective detected pressures P,, P, of the above-mentioned compression upper row point acupressure detection means 15 and compression top dead center acupressure detection means 16 are inputted to the pressure value comparison means 17, and their deviations ΔP=P, -P,
is calculated. The calculated value ΔP is input to the output correction means 18, and after being subjected to output correction based on predetermined characteristics described below, is supplied to the above-mentioned warning device 10 as a drive signal.

Reference numeral 12 denotes a compression start/expansion end output difference calculation means for calculating an output correction signal ΔV to be supplied to the output correction means 18, and the cylinder pressure detection signal ■1 at point a at the start of compression shown in FIG. Calculate the output difference ΔV=V, -V with the cylinder pressure detection signal V at the end point, and apply the output difference Δ■ to the output value ΔP of the pressure value comparison means 17 as a characteristic correction signal. By adding (ΔP+ΔV)L, the upper output error of the acupressure sensor output due to the sudden increase in the combustion temperature near the acupressure sensor 7 during acceleration is corrected.

As a result, the output from the output correcting means 18, ie, the warning device drive signal, always accurately corresponds to the engine misfire condition and has high reliability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the overall system configuration of an engine misfire detection device according to an embodiment of the present invention, and FIG.
Figure 3 is a functional block diagram showing the configuration of the main parts of the device.
A characteristic diagram showing the operation of the main parts of the device, Figure 4 is a characteristic diagram showing the general combustion pressure (cylinder pressure) characteristics of a 4-cycle engine, and Figure 5 is a characteristic diagram showing the combustion pressure characteristics of Figure 4. FIG. 6 is an explanatory diagram illustrating the principle of detecting a misfire state of an engine. FIG. 6 is an explanatory diagram illustrating problems with the conventional misfire detection device based on the principle of FIG. 5. 1...Cylinder 2...Piston 3...Combustion chamber 7...Shiatsu sensor warning device 20...◆Engine Figure 5 (P,)P,)... Misjudgment Figure 6

Claims (1)

[Claims] 1. In an engine misfire detection device that detects an engine misfire condition by mutually comparing cylinder pressures at arbitrary two crank angle positions before and after compression top dead center, the cylinder pressure at the end of the compression stroke is detected. , a misfire detection for an engine, characterized in that a determination pressure correction means is provided for correcting the cylinder pressure for determining the misfire state detected at an arbitrary crank angle position after the end of the compression stroke in a downward direction according to the detected pressure. Device.