JPH04175440A - Combustion condition detecting device - Google Patents

Abstract

PURPOSE:To detect the operating condition of an internal combustion engine securely with receiving almost no influence by an external cause by forming a light radiated from a light radiating body provided in a combustion chamber to a signal precessing circuit through a light transmitting body, and detecting the combustion condition by observing from the outer side. CONSTITUTION:A sensor is installed by penetrating the wall 1 of a cylinder head, and the tip of the sensor is projected in a combustion chamber 2. In this case, a light radiating body 4 is provided and formed at the top end of a rod-form heatproof light transmitting body 3. And the light transmitting body 3 is held by a holding member 5, and the holding member 5 is screwed to the wall 1 through a washer 6. Furthermore, an optical connector 7 is screwed to the holding member 5, and the light transmitting body 3 is connected to an optical fiber 8 optically. On the other hand, at the outgoing side of the optical fiber 8, a lens 9, a filter 10, and a lens 11 are provided, and a specific wave-length light of the transmitting light is entered to a light detector 12. And the electric signal of the light detector 12 is amplified by an amplifier 13, and fed to a signal precessing circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a combustion state detection device for an internal combustion engine, and particularly to a combustion state detection device that can accurately detect abnormal combustion associated with knocking.

(Prior art) In internal combustion engines installed in automobiles, the ignition timing is set at the ignition timing (M, B, T, ) that can generate the maximum torque.
It is necessary to control the advance angle until the maximum fuel efficiency and output performance are achieved. However, the optimal ignition timing differs depending on the driving conditions of the vehicle and the operating state of the internal combustion engine. For example, in a relatively low speed range, the ignition timing limit at which knocking occurs is higher than M, B, or T. Since it is on the delayed side, if the ignition timing is set to M, B, or T, knocking will occur, resulting in a significant drop in fuel efficiency and output performance.

Therefore, there is a strong demand for the development of an internal combustion engine operating state detection device that can accurately detect abnormal operation of the internal combustion engine, particularly the occurrence of knocking.

- In an ignition type internal combustion engine, a flame is generated by the activation of a spark plug, and combustion occurs as the flame propagates within the combustion chamber. On the other hand, abnormal combustion that causes abnormal operation such as knocking is caused by combustion due to flame propagation as well as combustion due to self-ignition near the cylinder wall surface. Therefore, abnormal operations such as knocking are conventionally detected by detecting pressure vibrations such as knocking sounds.

Special Publication No. 41-515 as a sensor for detecting knocking
A sensor using a piezoelectric element disclosed in Publication No. 4 is known. In this sensor, a washer-shaped piezoelectric element is installed in the spark plug, and pressure changes occurring within the combustion chamber are converted into electrical signals.The pressure changes occurring within the combustion chamber are detected from the detected electrical signals.

Furthermore, as another knocking detection device, a knocking detection device using a vibration sensor composed of a piezoelectric element is known, and the electrical signal from the vibration sensor is passed through various filter circuits and a signal with a frequency component corresponding to knocking is detected. The occurrence of knocking is detected through a knocking determination circuit.

(Problem to be Solved by the Invention) The knocking detection device using the pressure sensor or vibration sensor described above detects the pressure change occurring in the combustion chamber by fixing the sensor to the cylinder head. The problem was that vibrations other than combustion were also detected at the same time, resulting in an extremely poor signal-to-noise ratio. Moreover,
The detection output of vibration sensors and pressure sensors is generated as an electrical signal, and this electrical signal is generated at the position of the cylinder head, so noise is likely to occur even while the electrical signal, which is the output signal, is sent to the signal processing circuit. A problem occurred in that the S/N ratio decreased significantly. For this reason, complex signal processing is required to extract the pressure and vibration components corresponding to knocking, which has the disadvantage of making the processing circuit complex and expensive. Furthermore, since complex signal processing is required,
Signal processing takes a long time, resulting in poor responsiveness.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned drawbacks and to provide an internal combustion engine capable of detecting the combustion state of an internal combustion engine, particularly abnormal combustion related to knocking, with a simple configuration without requiring complicated signal processing, and with high accuracy. The present invention provides a combustion state detection device.

(Means for Solving the Problems) A combustion state detection device according to the present invention is a combustion state detection device that detects a combustion state in a combustion chamber of an internal combustion engine, and is arranged near an ignition means in the combustion chamber, and is arranged in a predetermined wavelength range. an opaque light emitter; a light transmitter supporting the light emitter at its tip and transmitting light in the predetermined wavelength range; and a photodetector optically coupled to the rear end of the light transmitter. , signal processing means for time-differentiating the output signal from the photodetector and detecting the combustion state of the internal combustion engine based on the time-differentiated signal.

The light emitter functions to emit light according to its own temperature without transmitting chemiluminescent light caused by combustion, and is made of a material such as platinum or rhodium at the tip of a heat-resistant light transmitter such as a sapphire rod. It can be formed by sputtering a high melting point material.

This light emitter must be placed near the ignition means,
For example, approximately 1 of the time it takes to complete combustion due to flame propagation after ignition.
It is desirable to place it in a position where the flame can reach it within a time of /2.

In addition, the optical transmission body is made of a material that is transparent to the wavelength light (usually infrared light of 0.5 to 5 μm) detected by the photodetector placed in the subsequent stage, and in some cases, multiple transmission It can be used by optically coupling the bodies.

Furthermore, the signal processing means can be constructed of an analog circuit, or can be constructed of a circuit that amplifies the output signal from the photodetector, performs A/D conversion, performs digitization processing, and then performs digital arithmetic processing.

Furthermore, since two peaks occur at a time interval in the time-differentiated signal when abnormal combustion occurs, the signal processing means of the present invention determines whether or not two peaks occur during one combustion cycle. The occurrence of abnormal combustion is detected by providing a detection means.

Furthermore, it was confirmed that the amplitude of the second peak that occurs after the first peak corresponds to the square root of the knocking intensity, so by providing a means to hold the second peak value, the knocking intensity and the degree of abnormal combustion can be improved. can be detected.

(Function) As mentioned above, in an ignition type internal combustion engine, during normal combustion only combustion occurs due to flame propagation, and during abnormal combustion, localized and rapid combustion occurs along with combustion due to flame propagation. This local combustion occurs after flame propagation combustion occurs.
It has been found that this occurs after a considerable amount of time has passed. As a result of various experiments and analyses, the present inventor discovered that flame propagation combustion and local combustion can be clearly separated and detected by appropriately setting the placement position of the light emitter. . In other words, if the light emitter is placed far away from the ignition means, for example, near the cylinder wall, the light emitter will receive combustion heat due to flame propagation and combustion heat due to local combustion in an extremely short period of time. Only combustion heat flows in, making it impossible to distinguish between flame propagation combustion and local combustion. On the other hand, when the light emitter is placed near the ignition means, after a considerable amount of time has elapsed after the flame passes through the light emitter, heat due to post-local combustion flows into the light emitter. Therefore, flame propagation combustion and local combustion can be detected separately, and by detecting the occurrence of local combustion, it is possible to detect the occurrence of abnormal combustion.

When combustion heat flows into the light emitter, the light emitter emits light corresponding to its own temperature, so the photoelectric output signal from the photodetector that receives the light emitted from the light emitter also becomes light. Corresponds to the amount of heat flowing into the radiator. Therefore, when the photoelectric output signal from the photodetector is time-differentiated, a peak will occur in the time-differentiated signal that corresponds to rapid heat inflow into the light emitter, ie, flame propagation and local combustion. As a result, local combustion, that is, abnormal combustion, can be detected by detecting whether two peaks occur in the time differential signal during the combustion cycle (2).

In this way, in the present invention, the combustion state is determined by optically detecting the combustion state and processing the photoelectric output signal from the photodetector, so that weak abnormal combustion that cannot be detected by a pressure sensor can be detected. can be detected with high precision. In particular, since combustion information is detected optically, the combustion state can be detected with an extremely high S/N ratio without being affected by mechanical vibrations, electric fields, or magnetic fields.

(Embodiment) FIG. 1 is a diagram showing the overall configuration of a combustion state detection device for an internal combustion engine according to the present invention. The sensor is installed so as to penetrate through the wall 1 of the cylinder head, and the tip of the sensor is attached to the combustion chamber 2.
protrude inward. This sensor is placed near the spark plug so that the flame generated by the actuation of the spark plug reaches the sensor in the shortest possible time. This sensor has a heat-resistant rod-shaped light transmitting body 3 made of a sapphire rod, and a light emitting body 4 is formed at the tip thereof. The light emitter 4 is formed by sputtering an optically transparent high melting point material such as platinum or rhodium to a thickness of several μm. Note that it is preferable that the light emitter 4 be arranged so as to protrude from the boundary layer of combustion gas formed on the cylinder wall surface. The reason for this is that by protruding, detection can be performed without being affected by the boundary layer that exists near the wall surface. The optical transmitter 3 is supported by a support member 5 made of a metal material such as stainless steel.

A thread is formed on the outer periphery of the support member 5 and a thread groove is formed on the wall 1 of the cylinder head, and the support member 5 is screwed onto the wall 1 via a washer 6. Further, the optical connector 7 is screwed onto the support member 5 to optically couple the optical transmission body 3 to the optical fiber 8. When the spark plug attached to the cylinder head is activated, a flame is generated near the spark plug and the flame propagates toward the opposing wall. As the flame propagates, the flame reaches the surface of the light emitter 4, and the temperature of the light emitter increases depending on the temperature and pressure of the generated combustion gas. Since the light emitter 4 is formed of a noble metal thin film with an extremely small heat capacity, it responds extremely quickly. When the temperature of the light emitter 4 rises, the light emitter emits light whose intensity corresponds to the temperature and pressure of the combustion gas,
The generated light propagates through the rod-shaped light transmission body 3 and the optical fiber 8. A lens 9 and a filter I are installed on the output side of the optical fiber 8.
O and a lens 11 are arranged, and light of a specific wavelength among the propagating light is made to enter the photodetector 31. Since the light emitter 4 emits light with an intensity corresponding to the temperature and pressure of the combustion gas, the photodetector 12 generates an electrical signal representing the combustion state within the combustion chamber. Supply this telegram.

Fig. 2 shows the arrangement position of the sensor in the engine combustion chamber, Fig. 2a is a diagram schematically showing the arrangement position, and Fig. 2 is a diagram showing other arrangement positions. The ignition type engine has a spark plug 20, an intake valve 21, and an exhaust valve 22.
is installed. The first sensor 23A is attached near the spark plug 20, and the second sensor 23B is attached at a position farther away than the spark plug 20. Note that the second sensor 23B is not an essential component of the present invention, but is a reference member provided for explaining the present invention.

When the spark plug 20 operates and the combustion gas ignites, 102
A relatively low temperature flame of about 0° is generated and propagates inside the cylinder like a wave surface. This flame propagation is coded 2
4a and 24b. Since the flame is generated near the spark plug 20 and gradually propagates toward the side far from the spark plug, the generated flame passes through the first sensor 23A and after a predetermined period of time passes through the second sensor. On the other hand, in a knocking state, after the spark plug is activated, self-ignition occurs near the cylinder wall before the flame reaches the opposing cylinder wall, resulting in short-term rapid combustion that occurs explosively. In other words, we believe that combustion in a relatively small area around the spark plug rapidly accelerates the oxidation reaction of unburned gas in the opposing cylinders and near the walls, causing the unburned gas to explode in a short period of time. It will be done. Combustion gas due to this self-ignition propagates inside the cylinder at a much higher speed than flame propagation due to normal combustion. Therefore, the first sensor 23A placed near the spark plug detects only combustion due to normal flame propagation during normal combustion. Furthermore, in the event of abnormal combustion, it detects combustion due to normal flame propagation as well as local combustion due to self-ignition that occurs afterwards. - side, a second sensor 23 located farther away than the spark plug 20;
B detects combustion due to flame propagation during normal combustion, and detects combustion due to flame propagation and abnormal combustion almost simultaneously or with an extremely short time interval during abnormal combustion. Therefore, if the sensor is placed farther away than the spark plug, it is difficult to clearly distinguish between normal combustion and abnormal combustion. On the other hand, if a sensor is placed near the spark plug, normal combustion due to flame propagation can be clearly distinguished and detected.

Next, the results of an experiment in which the operating state of an internal combustion engine was measured using the above-mentioned combustion state detection device will be explained.

The conditions are as follows.

1) Internal combustion engine used: single-cylinder engine with a displacement of 612cc 2) Number of revolutions: 750 r, p, m.

3) Compression ratio near, 0 4) Air/fuel efficiency: 12.7 5) Two types of engine operating states were tested: normal operating state and knocking state (trace knock) by changing the gasoline octane number and ignition angle. And so.

(i) Normal operating state octane number: 100 ignition angle knee 12° (ii) Knocking state octane number: 80 ignition angle knee 15° 6) Detect the output signal from the amplified photodetector and record the detected value over time Differentiate to generate a differential output signal,
At the same time, a pressure sensor was attached to the cylinder head to measure pressure fluctuations occurring in the combustion chamber. Data from the crank angle detection sensor was also measured.

Figures 3a to 3d show experimental results when knocking occurs. Figures 3a and 3b show detection signals for the entire 1 cycle, and Figures 3c and d show enlarged views of the state before and after the combustion cycle. In the drawing, the horizontal axis is .

The crank angle is shown, and the vertical axis shows the relative value of each detected value. The curve indicated by the symbol p indicates the pressure change measured by the pressure sensor, and the symbol TA indicates the detected value from the photodetector of the first sensor located near the spark plug,
The symbol TB indicates the detection value from the photodetector of the second sensor placed at a far position, and the symbols dTA/dt, dTB/dt
indicates a signal obtained by time-differentiating the detected values TA and Te from the photodetector, and PH is a high frequency component signal of the detected value from the pressure sensor (signal after passing through a bypass filter,
Usually used as a value representative of knocking strength. )
shows. In the pressure curve P, a peak occurs near a crank angle of -10', and minute vibrations peculiar to knocking are superimposed on the peak. Therefore, it can be understood that knocking occurs. Furthermore, in the detected value TA of the first sensor, as shown in FIG. There is. Also, the time differential curve dTA/dt
Also, two peaks were clearly observed corresponding to these rising points. On the other hand, the time differential curve dTa / of the second sensor
For dt, a peak was observed only at approximately the same position as the second peak position.

Note that the timing at which the second peak occurs is slightly delayed from the generation of the high frequency component PH, but this is considered to be due to the delay caused by the processing of the differentiating circuit.

Figure 4 shows an enlarged view of the actual measurement results during normal combustion.

The pressure curve P rises gently and reaches its peak at around 32'' crank angle.In addition, only an extremely small amplitude is observed in the high frequency component PH, and no knocking is observed.Time differentiation The curve dTA/dt only has a peak near the crank angle θ°, and shows a nearly flat characteristic after that.The dTs/dt curve also shows a nearly flat characteristic after ignition, and at a crank angle of 44 A peak occurs at °.

The peaks of these time differential curves dTA/dt and dTB/dt are due to normal flame propagation. Therefore, the third
From the experimental results shown in FIG. 4 and FIG. 4, the following technical matters become clear.

■If the light emitter is placed further away than the spark plug, the peak due to flame propagation, which is normal combustion, and the peak due to abnormal combustion cannot be distinguished, so normal combustion and abnormal combustion cannot be distinguished.

(2) If the light emitter is placed close to the spark plug, the peak due to flame propagation and the peak due to abnormal combustion can be detected with a considerable time interval, and therefore the occurrence of abnormal combustion can be clearly detected.

(2) Whether or not abnormal combustion is occurring can be determined by determining whether or not two peaks occur in the signal obtained by time-differentiating the detected value from the photodetector during one combustion cycle.

Next, knocking intensity determination will be explained.

FIG. 5 is a graph showing the relationship between the second peak value of the time differential of the detection value from the photodetector and the peak-to-peak value of the high frequency component of the detection value from the pressure sensor, which is commonly used as the knocking intensity. Figure 5a shows the relationship between the time-differentiated peak value of the first sensor placed near the spark plug and the high frequency component of the pressure sensor, and Figure 5a shows the time-differentiated peak value of the second sensor placed far away. The relationship between the value and the high frequency component of the pressure sensor is shown. In FIGS. 5a and 5b, the horizontal axis indicates the amplitude of the high frequency component of the pressure sensor in a logarithmic manner, and the vertical axis indicates the peak value of the second peak of the time differential in a logarithmic manner. Fifth
As is clear from Figures a and b, the peak value of the time differential is approximately proportional to the 1/2 power of the amplitude of the high frequency component. Therefore, the Ritzking strength can be determined by measuring the peak value of the time differential of the detected value from the photodetector.

6 and 7 show the configuration of an example of the signal processing circuit of the combustion state detection device according to the present invention, FIG. 6 is a waveform diagram showing the detection principle, and FIG. 7 is a circuit diagram. In this example, the detected value from the photodetector is differentiated twice, and the second-order differential signal d
Find T2/d2t. As shown in Figure 6, the slope of the -th derivative signal is large near the peak, so by comparing the second-order derivative signal with a preset limit value, it can be determined that a peak has occurred in the first-order derivative signal. Can be detected. Then, it is compared with a limit value, and the pulse is raised based on the comparison result, and is lowered at the zero cross point of the second-order differential signal.

The falling timing of the pulse thus formed coincides with the timing of the peak value of the first-order differential signal. By using the pulse signal configured in this manner as sampling, even if various noises occur in the width of the -order differential signal, the first peak and the second peak included in the -order differential signal can be accurately detected.

Next, the circuit configuration will be explained based on FIG. 7. After amplifying the output signal from a photodetector that receives light emitted from a light emitter placed near the spark plug, the first differentiation circuit 30 forms a first-order differential signal, and this -order differential dT
/dt signal is supplied to the sample hold circuit 31. Furthermore, the negative differential signal is also supplied to the second differential circuit 32 to form a second differential signal dT2/d2t. This second-order differential signal is supplied to the hysteresis comparator 33, where it is compared with a set limit and returned at the zero-crossing point, generating a pulse signal that falls in response to the peak included in the -order differential signal. The generated pulse signal is supplied to a pulse width identification/setting circuit 34, and it is determined based on the width whether the generated pulse is noise or not. The output pulse from this pulse width identification/setting circuit is supplied to a counter circuit 35.

This counter circuit is configured to generate an output signal when two pulse signals are input, and to be reset by a signal corresponding to the start of a combustion cycle, such as an ignition pulse signal. Therefore, when a pulse signal due to the first peak in the -th differential signal is inputted, and then a pulse signal due to the second peak is inputted, an output signal is generated from the counter circuit 35, and the output signal is applied to the AND gate 36. is supplied to one input terminal of the Further, the output signal of the pulse width identification/selection circuit 34 is supplied to the other input terminal of the AND gate 36. The falling timing of the output of this AND gate coincides with the timing of the second peak. This AN
By supplying the output signal of the D gate to the sample and hold circuit 31, the peak value of the first-order differential signal at the time of the second peak can be outputted from the sample and hold circuit 3I. Therefore, the peak value of the second peak in the first-order differential signal can be determined based on the output signal of the sample-and-hold circuit. Note that the output signal of the AND gate can also be used as the abnormal combustion detection signal. In this example, the rising edge of the second peak is used to generate a sampling pulse, and the pulse width is identified and selected to detect the occurrence of the second peak, but the falling edge of the second peak is used to generate the sampling pulse. It is also possible to detect the occurrence of the second peak by generating a sampling pulse and identifying and selecting the pulse width from the zero cross point.

FIG. 8 is a circuit diagram showing a modification of the signal processing circuit. In this example, a low-pass filter 40 is connected after the first differentiating circuit 30 to cut high frequency signals of 5 KHz or higher. That is, if a light emitter is placed near a spark plug, a flash of light will occur due to ignition, resulting in noise. Since this flash has an extremely short pulse width, the low-pass filter 4
By connecting 0, it is possible to cut out the noise caused by the flash caused by ignition. Furthermore, in this example, a monostable multi-bibreak 41 is used instead of the counter circuit. This monostable multivibrator is triggered by the falling edge of the pulse signal due to the first peak and generates a pulse with a constant time width. This configuration eliminates the need for a reset signal.

The present invention is not limited to the embodiments described above, and various modifications and changes are possible. For example, in the above embodiment, an example was explained in which combustion due to self-ignition is detected after a considerable period of time has passed after ignition, but it is also possible to detect abnormal combustion due to early self-ignition that occurs before the spark plug operates. It is. In this case, early combustion can be detected by temporally comparing the first peak that occurs in the time differential signal and the operating timing of the spark plug.

(Effects of the Invention) The effects of the present invention explained above are summarized as follows.

(1) A light emitter is placed inside the combustion chamber, and the combustion state is detected by observing the light emitted from the light emitter from the outside via a light transmitter, so it is almost unaffected by external factors. The operating state of the internal combustion engine can be accurately detected. In particular, in the signal obtained by time-differentiating the output signal of the photodetector, two
Since it can be detected based on whether or not these peaks occur, it is possible to accurately detect abnormal combustion related to knocking that is too weak to be detected by a pressure sensor.

(2) The occurrence of abnormal combustion can be detected by time-differentiating the photoelectric output signal from the photodetector and determining whether or not two peaks occur in this -order differential signal, and the peak value is related to knocking. Since it corresponds to the degree of abnormal combustion that occurs, it is possible to accurately detect the occurrence and degree of abnormal combustion.

(3) Unlike a detection sensor, a pressure sensor, or a vibration sensor, it does not have a moving part, so it is possible to realize operating state detection that is less susceptible to noise and has excellent reliability and durability.

(4) Since the light emitter can be composed of an optically opaque high-melting point material coating, it is virtually unaffected by the adhesion of soot generated by combustion and chemiluminescence, realizing an operating state detection device with excellent durability. can do.

(5) Since the detection signal is the optical energy emitted from the light emitter, the detection signal can be transmitted to any position using an optical fiber, and is not affected by external factors during transmission. Therefore, knocking detection with a high -layer S/N ratio can be achieved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the overall configuration of the combustion state detection device according to the present invention, Figs. 2 a and b are diagrams showing the arrangement positions of the sensors, and Figs. 3 a to d are graphs showing detection signals during knocking. , Figure 4 is a graph showing the detection signal during normal operation, Figure 5 a and b are graphs showing the relationship between the amplitude of the high frequency component and the peak value of the time differential signal, and Figure 6 is the principle of sampling the detection signal. FIG. 7 is a circuit diagram showing the configuration of the signal processing circuit, and FIG. 8 is a circuit diagram showing a modification of the signal processing circuit. 1... Cylinder wall 2... Combustion chamber 3... Light transmission body 4... Light emitter 5... Support member
7... Optical connector 8... Optical fiber
12... Photodetector 30, 32... Differential circuit
31...Sample/Hold circuit 32...Hysteris comparator 35...Counter circuit 36...AND gate 23A (Ku 1t Souse°) Figure 2 O (Output @ Wentun) - ζr S This value Figure 4a Figure 5

Claims (1)

[Scope of Claims] 1. A combustion state detection device for detecting a combustion state in a combustion chamber of an internal combustion engine, comprising: a light emitter disposed near an ignition means in the combustion chamber and opaque in a predetermined wavelength range; an optical transmission body supporting a light emitter at its tip and transmitting light in the predetermined wavelength range; a photodetector optically coupled to a rear end of the optical transmission body; and an output signal from the photodetector. A combustion state detection device comprising a signal processing means for time-differentiating the signal and detecting a combustion state of an internal combustion engine based on the time-differentiated signal.