JPH04334745A - Combustion state monitor device of multicylinder internal combustion engine - Google Patents

Abstract

PURPOSE:To precisely detect a change of pressure while reducing the number of input circuits by supplying output combining pressure sensor outputs of cylinders explosion strokes of which are reciprocally separated from each other by 240 deg. at a crank angle to an amplifier. CONSTITUTION:A pressure sensor 3 is provided for each of cylinders, and it converts cylinder internal pressure of each of the cylinders to an electrical signal and detects it. Additionally, an analog switch circuit 6 passes an output signal from the pressure sensor 3 through a charge amplifier 4 for a specified period of time of more or less than the top dead center of each of the cylinders on the basis of a signal from a crank angle sensor 5. hereby, outputs of the pressure sensors 3 of the cylinders explosion strokes of which are reciprocally separated from each other by 240 degrees at a crank angle are combined and this combined output is supplied to the charge amplifier 4. Consequently, as seat noise of an intake valve and a discharge valve does not superimpose on the signal with a constitution that the number of the charge amplifier 4 is smaller than the number of the pressure sensors, it is possible to precisely detect a change of pressure.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state monitoring device for an internal combustion engine that detects cylinder internal pressure to detect combustion abnormalities such as misfires and knocks in the internal combustion engine.

0002

[Prior Art] Conventionally, a pressure sensor made of a piezoelectric element is inserted into the washer of a spark plug of an internal combustion engine such as a two-stroke engine, a four-stroke engine, or a rotary engine, and the spark plug is tightened to detect the cylinder internal pressure. There are devices that detect combustion conditions such as misfire and knocking. In order to simplify the circuit, conventional devices of this type connect the outputs of the pressure sensors installed in each cylinder to an amplifier (charge-voltage amplifier), and then use the output to integrate circuits, arithmetic judgment circuits, etc. There was one that was connected to the engine to detect combustion conditions such as misfire. However, in this case, high frequency output due to seating of intake valves and exhaust valves of other cylinders will be superimposed on the in-cylinder pressure output of the cylinder during the combustion stroke. Therefore, a filter has been added to the input circuit to remove the high frequency output. Further, Japanese Utility Model Publication No. 59-155532 proposes a system in which the outputs of the pressure sensors are collectively input to the input circuit for each cylinder in which the explosion stroke and the compression stroke do not overlap.

0003

[Problems to be Solved by the Invention] However, when a filter is added to the input circuit, there are problems in that the input circuit becomes complicated and it becomes difficult to detect knocking. In addition, if the explosion stroke and compression stroke are simply grouped by cylinder, excluding 2-stroke engines without intake valves and exhaust valves, and rotary engines, for example, 6
When applied to a cylinder internal combustion engine, intake valve seating noise or exhaust valve seating noise will be superimposed. For example, as shown in Fig. 3, when the pressure sensors of the first and fifth cylinders are connected, the fifth cylinder is placed in the range A1 from 60 degrees before top dead center to 60 degrees after top dead center where the combustion state is monitored. Intake valve seating noise C5 is superimposed. On the other hand, as shown in Fig. 4, when the pressure sensors of the first and sixth cylinders are connected, the first cylinder is placed in the range A6 from 60 degrees before top dead center to 60 degrees after top dead center where the combustion state is monitored. There is a problem in that the exhaust valve seating noise B1 is superimposed. The present invention has been made in order to solve the above problems, and its purpose is to reduce the number of input circuits by inputting several pressure sensors into one input circuit, and to reduce the number of input circuits. To provide a combustion state monitoring device for a multi-cylinder internal combustion engine, which can eliminate superimposition of valve seating noise and exhaust valve seating noise, accurately detect pressure changes, and make highly reliable combustion state determinations. There is a particular thing.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a pressure sensor that is provided for each cylinder and detects the cylinder internal pressure of each cylinder by converting it into an electric signal corresponding to the pressure value, and an internal combustion sensor. A crank angle sensor that detects the crank angle of the engine, an amplifier to which the output of the pressure sensor for each cylinder is connected and input, and a predetermined period of time before and after top dead center of each cylinder based on the signal from the crank angle sensor. In the combustion state monitoring device for a multi-cylinder internal combustion engine, the outputs of the pressure sensors of the cylinders whose explosion strokes are separated from each other by 240 degrees in crank angle are combined, and the combined output is obtained. There is provided a combustion state monitoring device for a multi-cylinder internal combustion engine, characterized in that the combustion condition is supplied to the amplifier.

[0005]

[Operation] In the combustion state monitoring device for a multi-cylinder internal combustion engine configured as described above, the explosion strokes are 240 degrees apart in crank angle.
The outputs of the pressure sensors of three cylinders separated by degrees are input to one amplifier. Since the intake valve seating noise and exhaust valve seating noise of the three cylinders occur at a position away from the top dead center of each cylinder, they are eliminated by the selection means and are not superimposed on the output signal.

[0006]

Embodiments Examples of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a combustion state monitoring device. A pressure sensor 3 is attached to each spark plug 2 of a six-cylinder internal combustion engine 1. This pressure sensor 3 is a piezoelectric sensor installed instead of a washer between the spark plug 2 and the cylinder block, and generates an electric charge Q proportional to the internal pressure of each cylinder. The outputs of the six pressure sensors 3 for each cylinder are connected three in parallel and input to a charge amplifier (charge-voltage amplifier) 4. The pressure sensors 3 for the first, second and third cylinders are connected to the first charge amplifier 4, and the pressure sensors 3 for the fourth and third cylinders are connected to the second charge amplifier 4'.
The pressure sensors 3 of the fifth and sixth cylinders are connected. The charge amplifier 4 is composed of an operational amplifier 41, a feedback resistor 42 for preventing zero point drift, and a feedback capacitor 43, and converts the charge Q output from each pressure sensor 3 into a voltage V according to the relationship V=Q/C.
Convert and amplify.

The crank angle sensor 5 optically detects the rotation angle of the crankshaft and sends out a crank angle signal K corresponding to the rotation angle. Analog switch circuits 6 and 6', to which the outputs of charge amplifiers 4 and 4' are input, determine the angle of 60 degrees before top dead center in the combustion state of each cylinder based on the crank angle signal K.
A pressure signal from 60° after top dead center is input to the combustion state determination circuit 7. The combustion state determination circuit 7 includes a bandpass filter 71, a knock determination circuit 72, and a display circuit 73. Signals from a speed sensor 81, an intake air amount sensor 82, etc. are input to the knock determination circuit 72. The display circuit 73 has, for example, six LEDs, and lights up the LED corresponding to the cylinder in which the knock occurs based on the signal from the knock determination circuit 72 and the crank angle signal K.

FIG. 2 is a timing chart showing the relationship between the stroke of each cylinder and seating noise. Since it is a six-cylinder engine, the firing order is the first, fifth, third, sixth, second, and fourth cylinders, and the strokes of each cylinder are shifted by 120 degrees of crank angle. The section from 60 degrees before compression top dead center to 60 degrees after compression top dead center, which is a section necessary for monitoring the combustion state, is indicated by diagonal lines A1 to A6 in the figure. Exhaust valve seating noise occurs at the beginning of each intake stroke, and is indicated by arrows B1 to B6 in the figure.
Indicated by Further, intake valve seating noise occurs at the beginning of each compression stroke, and is indicated by arrows C1 to C6 in the figure. Then, three cylinders whose strokes are separated by 240 degrees from each other, for example, the first cylinder,
When the signals of the third and second cylinders are combined, combustion state monitoring sections A1, A3, and A2 appear at exactly 120 degree intervals, and each exhaust valve seating noise B1 to B3 and intake valve seating noise C1 appear at the 120 degree interval. ~C3 occurs. Each noise B1 to B3, C1 to C is generated in the combustion state monitoring sections A1, A3, and A2.
3 do not overlap, it becomes possible to accurately grasp the combustion state. The same holds true for the combination of the fourth, fifth, and sixth cylinders whose strokes are 240 degrees apart from each other.

Although the above embodiment has been explained using a six-cylinder engine as an example, it is clear that the same applies to a three-cylinder engine. In the case of a three-cylinder engine, the strokes of each cylinder are shifted by 240 degrees of crank angle, so the outputs of the pressure sensors of the three cylinders may be combined into one.

In the above embodiment, the analog switch circuit 6 detects the cylinder pressure at equal intervals of 60° before and after the top dead center, but these crank angles can be adjusted appropriately depending on the number of cylinders of the internal combustion engine. The detection angle may be changed before and after the top dead center. Further, it is also possible to detect the pressure state in an arbitrary crank angle range.

[0011]

[Effects of the Invention] The present invention combines the outputs of the pressure sensors of the cylinders having the above-mentioned configuration whose explosion strokes are separated from each other by 240 degrees in crank angle, and supplies the combined output to an amplifier. Therefore, with a configuration in which the number of amplifiers is smaller than the number of pressure sensors, the seating noise of the intake valve and exhaust valve will not be superimposed on the signal, and there is an excellent effect that the combustion state can be accurately monitored.

[Brief explanation of drawings]

[Figure 1] Block diagram showing the combustion condition monitoring device,

[Figure 2] Timing chart showing the relationship between the stroke of each cylinder and seating noise

[Figure 3] Timing chart,

[Figure 4] Timing chart.

[Explanation of symbols]

1. ．． Internal combustion engine, 2. ．． Spark plug, 3.
．． pressure sensor, 4. ．． charge amplifier (amplifier),
5. ．． Crank angle sensor, 6. ．． Analog switch circuit (selection means), 7. ．． Combustion state determination circuit.

Claims (1)

[Claims] 1. A pressure sensor provided for each cylinder that converts and detects the cylinder internal pressure of each cylinder into an electrical signal corresponding to the pressure value; a crank angle sensor that detects the crank angle of an internal combustion engine; a multiplier comprising an amplifier connected to and inputted with the output of the pressure sensor; and selection means for passing the output signal from the amplifier for a predetermined period before and after top dead center of each cylinder based on the signal from the crank angle sensor. A combustion state monitoring device for a cylinder internal combustion engine, characterized in that outputs of pressure sensors of cylinders whose explosion strokes are separated from each other by 240 degrees in crank angle are combined, and the combined output is supplied to the amplifier. Combustion status monitoring device for internal combustion engines.