JPS6226410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an ignition ignition system for an internal combustion engine that has a function of detecting knocking by vibrations generated outside the cylinder due to internal cylinder pressure of the internal combustion engine and adjusting the ignition timing to a predetermined knocking level. This invention relates to knocking detectors used in timing control devices and the like.

It is generally known that there is a strong correlation between ignition timing and cylinder pressure, but when the air-fuel mixture is exploded, the cylinder pressure will be harmonic (usually 4KHz to 10KHz or 11KHz) when no knocking occurs.
This is a frequency component of ~13KHz, which is caused by the bore diameter of the engine cylinder and intermittent rapid combustion. Vibration or noise is generated outside the cylinder. If we look closely at the internal pressure signal generated within the cylinder or the vibration or noise generated outside the cylinder, we can see that knocking (trace knock) begins at the engine crank angle where the internal pressure reaches its maximum value, and gradually increases. When knocking occurs (light knock, heavy knock), the harmonics become large in front of the maximum internal pressure (that is, on the ignition side). Therefore, if the vibrations and noise generated outside the cylinder due to this knocking are accurately detected and feedback is used to control the ignition timing, engine efficiency can be greatly improved. Currently, there is no detector that can detect this and operate stably under the harsh environmental conditions required for vehicles.

Conventionally, piezoelectric acceleration detectors commonly used for vibration detection have been used for this type of detection, and the frequency characteristics of this detector are higher than the knocking frequency.
There are two types: one in which the characteristics become flat below the resonance point (hereinafter referred to as a non-resonant type), and the other in which the resonance characteristics are matched to the knocking frequency under consideration by the present inventors.
In the non-resonant type, the resonance point is higher than the knocking frequency, so the sensitivity in the low frequency band including the knocking frequency below this resonance point is almost constant. Therefore, in principle, knocking can be detected over the entire knocking frequency range. However, during engine operation, a lot of vibration noise such as valve seating vibration occurs, and the S/N ratio between vibration noise and knocking deteriorates, so it is practically impossible to detect knocking at high speeds with the non-resonant type. be. In addition, the overall detection sensitivity is low, making it difficult to detect slight knocking even at low rotation speeds.

In the resonance type, detection sensitivity is greatly improved for a specific frequency near the resonance point, vibration noise at other frequencies is difficult to detect, and both the S/N ratio and sensitivity against knocking are greatly improved.

However, resonance also has the disadvantage that the higher the degree of resonance (resonance sharpness Q), the narrower the detection frequency width will inevitably be. A slight shift in frequency makes it difficult to detect knocking.

In other words, an ideal detector is required to have a wide range within the entire knocking frequency band and to have an S/N ratio and sensitivity similar to that of a resonant type.

Therefore, in view of the above points, the present invention provides multiple resonance characteristics within the knocking frequency band to expand the frequency detection width, and S/
It has a good N ratio and sensitivity, and can detect weak knocking.In addition, by fixing piezoelectric elements to each diaphragm part with a different resonance frequency, sufficient strength can be obtained with a small structure, and performance and performance are improved. It is desired to provide a detector with excellent features in terms of manufacturing method, price, etc. For this reason, a device according to Japanese Patent Application Laid-open No. 157737/1983 has been developed, but since it has a plurality of diaphragm sections, it has to be large in size in order to prevent interference with the sensor itself.

Therefore, an object of the present invention is to provide a knocking detector for an internal combustion engine that can prevent mutual interference during resonance in a device having a plurality of diaphragm portions, and can be downsized.

The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 is a block diagram of a knock feedback ignition system using a knocking detector according to the present invention. 1 in the figure is a four-cylinder in-line internal combustion engine, and a knocking detection unit 2 is installed in the cylinder block of the engine 1.
is attached by means such as screws. 3 is a knocking detection circuit that detects engine knocking from the output signal of the knocking detector 2; 4 is an ignition timing control device that advances or retards the ignition timing in accordance with the output of the detection circuit 3 to control it to an optimum position. The output signal of the control device 4 is passed through a known ignition device 5 to ignite the air-fuel mixture by a spark plug attached to the engine 1. The knocking detection circuit 3 used in this system detects an ignition signal (not shown), and detects noise components caused by engine vibration using the output of the detector 2 at a predetermined time period immediately after ignition at which knocking does not occur or at a predetermined crank angle. The ratio of this to the output of the sensor at a predetermined time or at a predetermined angle after top dead center TDC (after the peak of shiatsu pressure) where knocking is likely to occur (an integral value, that is, an averaged value may be used) is calculated. The presence or absence of knocking is detected. Alternatively, the presence or absence of knocking may be processed stochastically, rather than simply based on a single signal. for example
The presence or absence of knocking is determined based on what percentage of knocking occurs in 100 ignitions. The ignition timing control device 4 advances or retards the ignition timing depending on the presence or absence of this knocking. The detailed configurations of the knocking detection circuit 3 and the ignition timing control device 4 are well known and will not be described here; however, this detector can be used in any system that detects knocking and controls the ignition timing. It is clear that it is possible.

Next, the knocking detector of the present invention will be explained in detail. In the first embodiment shown in FIG. 2, reference numeral 21 denotes each diaphragm section 2 having a plurality of resonance points that resonate at knocking frequencies of 4 to 10 KHz and 11 to 13 KHz.
1a, and each of the diaphragm portions 21
a is a thicker ring-shaped support portion 21b;
It extends more towards the center. This vibrating body 21 is formed by cutting or stamping a metal flat plate such as iron (light alloy such as aluminum, resin, ceramic, etc.), and the resonance characteristics are determined by the shape of each vibrating plate portion 21a, the thickness h , length l (equivalent length from the fulcrum), and material. The resonance frequency is approximately determined by αh/l ² . Vibration plate part 21
The resonance frequency of a is determined by the support part 2 of each vibration plate part 21a.
The width near 1b and the width at the tip are arbitrarily made different to provide mutually different resonance frequencies. Reference numeral 22 denotes a bottom housing made of metal such as iron and having a substantially cylindrical outer circumferential wall, and the outer circumferential wall and the bottom wall include a hexagonal part 22a for using a wrench and a threaded part 22b for attaching to the engine block. The inner peripheral surface is provided with a support portion 21b of the vibrating body 21.
The vibrating body 2 is provided with a stepped portion 22c in contact with the
One support portion 21b is driven into the housing 22. Reference numeral 23 denotes a ring-shaped presser spacer made of a metal material (or resin may be used), which is driven into the housing 22 from above the support portion 21b of the vibrating body 21, so that the spacer 23 and the stepped portion 22c of the housing 22 are connected to each other. The support portion 21b of the vibrating body 21 is held between the two. Reference numeral 24 denotes a piezoelectric element that is individually fixed to the upper surface of each diaphragm section 21 with a conductive adhesive (sputtering or vacuum deposition may be used). The other electrode is connected to the internal terminal 2 of the connector 26 via each lead wire 25.
7 are commonly connected to each other. A cap 28 is placed on the spacer 23 to prevent the lead wire 25 from coming into contact with the diaphragm portion 21a. 29 is a sealing O-ring interposed between the cap 28 and the connector 26. The connector 26 is fixed to the upper end of the housing 22 by caulking the entire circumference of the open end of the housing 22. This detector is firmly attached to the engine block by a threaded portion 22b provided in the housing 22, and the knocking vibration of the internal combustion engine is detected by the housing 22.
2 to the vibrating body 21.

According to the above configuration, engine vibration due to knocking is transmitted to the vibrating body 21 via the housing 22, and each vibrating plate portion 21a of the vibrating body 21 vibrates. Each of the diaphragm portions 21a vibrates independently in response to the knocking vibration. That is, among the knocking frequency components, the diaphragm portion closer to the resonance frequency vibrates more strongly. Then, each diaphragm section 2
The vibration of 1a applies stress to each piezoelectric element 24 fixed to each diaphragm part 21a in accordance with the magnitude of the vibration of each diaphragm part 21a, and generates an electrical output in accordance with the magnitude of this vibration. , each electrical output is connected to the internal terminal 2 of the connector 26 via each lead wire 25.
7 and taken out to the outside. Since this embodiment has three diaphragm portions 21a, it has three resonant frequencies in the knocking frequency band, and knocking detection outputs with a good S/N ratio are generated in the vicinity of these three resonant frequencies. The number of resonance frequencies is simply determined by the number of diaphragm portions 21a, and there is no limit to the number. Therefore, 4-10KHz and 11-13KHz are within the frequency band of knocking.
An appropriate number (1KHz, or
By providing 5 diaphragm portions 21a (500KHz pitch, etc.), knocking can be easily detected with high sensitivity over the entire frequency range. And the vibrating part 21
If the width, material, thickness, and shape of a are defined, its resonance point is determined solely by the length.

Therefore, setting the resonance frequency is easy.

In addition, the resonance characteristics are sharp, and the knocking detection sensitivity is improved, while the sensitivity to vibration noise components at other frequencies is reduced. Therefore, not only weak knocking can be detected sufficiently, but also the frequency width to be detected can be widened in total. Sufficient sensitivity and S/N ratio can be obtained over the entire knocking frequency band, and the knocking detection accuracy can be greatly improved. do. Further, even if the knocking frequency changes depending on the combustion process, it can be sufficiently detected. Also,
Since the piezoelectric element 24, which is relatively weak against vibrations and shocks, is fixed to the diaphragm 21, which is stronger and easier to manufacture, sufficient strength against vibrations and shocks can be obtained, and manufacturing is also relatively simple.

FIG. 3 shows another example of the vibrating body 21 portion designed with the relationship between the width l ₁ near the base and the width l ₂ near the tip of each 3-resonance type diaphragm 21a as l ₁ < l ₂ . It is something.

Figure 4 shows the vibrating body 21 designed as l ₁ > l ₂ .
This shows still another embodiment of the section, and in the one shown in FIG. 4, piezoelectric elements 24 are individually fixed to one entire surface of each diaphragm section 21a by sputtering. In both of FIGS. 3 and 4, the basic thickness of the diaphragm portion 21a is determined, and the dimensions of the tip and root portions are changed to adjust the resonance frequency to be different for each diaphragm portion 21a. The one shown in Fig. 3 is generally used when making the diaphragm 21 thicker, and the one shown in Fig. 4 is used when the plate thickness is thinner and the resonant frequency is increased.
These can be changed depending on the material of the vibrating body 21. Each of the above-mentioned vibrating bodies 21 has a vibration plate portion 21a.
Although an R is attached to the connection part between the support part 21b and the support part 21b,
This is to eliminate the influence (cutting) caused by the notch action of the vibrating body 21, but if there is no problem in terms of strength, R can be omitted.

In FIG. 5, a notch 21c is provided in the support portion 21b to constitute the vibrating body 21, and the vibrating body 21 is attached to the housing 2.
2, when the support part 21b is inserted into the notch 21c.
It is designed to absorb distortion during implantation by shrinking.

In FIG. 6, the vibrating body 21 is constructed by increasing the thickness of the support portion 21b by the thickness of the spacer 23, and when this vibrating body 21 is used, the spacer 23 can be omitted.

FIG. 7 shows another example of the vibrating body 21 in which four diaphragm portions 21a are arranged radially at intervals of 90° to obtain four resonant frequencies.
In the illustrated example, the piezoelectric elements 24 are continuously formed by sputtering over almost the entire plane of each diaphragm 21a and the support 21b, except for each support base 21b where each diaphragm 21a of the support 21b extends. Furthermore, a thin film electrode 24a made of silver paste or silver is fixed to the surface of the piezoelectric element 24, and the output of the piezoelectric element 24 is taken out from this electrode 24a through a single lead wire 25. . It goes without saying that thin film electrodes are fixed to the connection surfaces of the lead wires 25 in piezoelectric elements 24 other than those shown in FIG. 7, although not shown. Further, a holding spacer 23 as shown in FIG. 8 is used for the vibrating body 21 shown in FIG. This spacer 23 is integrally provided with each presser protrusion 23a facing each support base 21d and having a presser surface slightly smaller than the area of each support base 21d. vibrating body 2 in contact with
1 support portion 21b is connected to the stepped portion 22c of the housing 22.
It is made to be pressed down. When the piezoelectric element 24 is fixed up to the support portion 21b in this manner, the spacer 23 must be made of an electrical insulator such as resin or ceramic.

FIG. 9 shows a second embodiment of the detector of the present invention, in which a piezoelectric element 24 is fixed to the entire surface of a vibrating body 21 by sputtering, and a presser spacer 23 made of a metal material and a piezoelectric element of the vibrating body 21 are fixed. A ring-shaped spacer 23A made of a material such as ceramic or resin is interposed between the support portion 21b to which the element 24 is fixed.

FIG. 10 shows the configuration of main parts of the third embodiment of the detector of the present invention, in which a vibrating body 21 having a predetermined shape forming a flat central electrode is provided with respective oscillators having approximately the same shape as the vibrating body 21 on both sides. It has a bimorph structure in which the piezoelectric element 24 is fixed. Each piezoelectric element 24
Although not shown, a thin film electrode is fixed to the lower surface of the lower piezoelectric element, and this electrode is grounded through the housing 22, and a thin film electrode is fixed to the upper surface of the upper piezoelectric element. This electrode is also grounded via the holding space 23 made of metal (conductor) and the housing 22, and the upper surface of the lower piezoelectric element and the lower surface of the upper piezoelectric element are grounded via the diaphragm 21 that forms the center electrode. The vibration detection output is connected to a lead wire 25 from which the vibration detection output is taken out.

FIG. 11 shows a fourth embodiment of the detector of the present invention, in which diaphragm portions 21a forming rectangular flat center electrodes having different lengths are individually provided,
The diaphragm portion 2 is placed on both sides of each diaphragm portion 21a.
Each piezoelectric element 24 having substantially the same shape as 1a is fixed to form a bimorph structure, and one end of each piezoelectric element structure having a bimorph structure is fitted into a plurality of recesses 22d formed in the stepped portion 21c of the housing 22. , and is pressed down with a holding spacer 23 made of a metal (conductor) such as aluminum, iron, or brass.

As described above, in the present invention, the configuration has a plurality of resonant frequencies within the frequency band in which knocking occurs, and since knocking is detected by combining the respective resonance outputs, a non-resonant detector without resonance characteristics is used. The disadvantage of not being able to detect weak knocking due to vibration noise during vehicle operation (e.g. valve seating vibration) has been greatly improved, and
As the Q of resonance increases, the sensitivity improves only at frequencies near the resonance point, making it difficult to detect noise, but on the other hand, the detection frequency range becomes narrower, and knocking occurs depending on the shift of the resonance point and the combustion process. If the target knocking frequency shifts due to a change in frequency, the high Q and narrow frequency width can sometimes make it difficult to detect knocking. Since the highly sensitive frequency detection width is expanded, detection can be made within any resonance characteristic, and as a result, the knocking detection performance is greatly improved. In addition, since a plurality of diaphragm sections are provided that branch from the ring-shaped support section radially toward the center, that is, inward, the roots of the diaphragm sections, or the branch sections, can be sufficiently separated from each other, thereby preventing mutual interference. This has the special effect of making it possible to create a detector that suppresses as much as possible. This has the effect that it can be constructed in a compact size.

Furthermore, since a piezoelectric element is fixed to each diaphragm part to detect the vibration of each diaphragm part, it is possible to use a vibrating body that is resistant to vibrations and shocks and is easy to manufacture. Despite using a piezoelectric element that is vulnerable to vibration and shock, by fixing this piezoelectric element to the diaphragm, sufficient strength against vibration and shock can be obtained, and manufacturing is relatively simple and compact. It has the excellent effect of being

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a knock-feedback ignition system to which a detector of the present invention is applied, and FIGS. 2A and 2B are a cross-sectional view and a longitudinal cross-sectional view showing a first embodiment of the detector of the present invention. Figures 3 to 7 each show five examples of the vibrating body part applied to the detector shown in Figure 2. Figure 3A is a front view of the first example, and Figure 3B is a front view of the first example. Figure 3A is a longitudinal cross-sectional view taken along the line A-A' shown in Figure 4A, Figure 4A is a front view showing the second example, Figure 4B is a longitudinal cross-section taken along the line B-B' shown in Figure 4A. Figure 5 is a front view showing the third example;
FIG. 6A is a front view showing the fourth example, FIG. 6B is a longitudinal cross-sectional view taken along line C-C' shown in FIG. 6A,
FIG. 7A is a front view showing the fifth example, and FIG. 7B is a longitudinal sectional view taken along the line DD' shown in FIG. 7A. FIG. 8 is a vertical sectional view showing a holding spacer combined with the vibrating body portion shown in FIGS. 7A and B, FIG. 9 is a vertical sectional view showing a second embodiment of the detector of the present invention, and FIG. 10 A is a front view showing the configuration of main parts of the third embodiment of the detector of the present invention, FIG. 10B is a longitudinal cross-sectional view taken along the line EE' shown in FIG. 10A, and FIG. 11A is the detection of the present invention Cross-sectional view showing the fourth embodiment of the vessel, No. 11
FIG. B is a longitudinal cross-sectional view showing the main part configuration of the illustrated detector 11A. 1...Internal combustion engine, 2...Knocking detector, 2
1... Vibrating body, 21a... Vibration plate section, 21b...
Support part, 22... Housing, 23... Spacer for presser, 24... Piezoelectric element.

Claims (1)

[Scope of Claims] 1. A vibrating body having a plurality of diaphragm parts that vibrate in response to vibrations caused by knocking of an internal combustion engine and having mutually different resonance frequencies within the knocking frequency band, and each diaphragm part of this vibrating body. A knocking detector for an internal combustion engine includes a piezoelectric element that is fixed to a piezoelectric element and generates an electric output in accordance with the vibration of each diaphragm, wherein the vibrating body includes a ring-shaped support for supporting the diaphragm. What is claimed is: 1. A knocking detector for an internal combustion engine, characterized in that the knocking detector has a plurality of diaphragm portions, and a plurality of diaphragm portions are integrally provided, branching radially from the support portion toward the center. 2. The knocking detector for an internal combustion engine according to claim 1, wherein the supporting portion of the vibrating body has a thicker plate thickness than each of the vibrating plate portions. 3. Each of the diaphragm sections has a different resonant frequency by making the width of the root portion and the width of the tip different for each diaphragm section. The knocking detector for an internal combustion engine according to item 1 or 2.