JPH10267746A - Knocking detecting sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-resonant knocking detecting sensor which is difficult to produce a resonance point in the characteristics of output frequency, and therefore can certainly accurately detect knocking. SOLUTION: A knocking detecting sensor 1 is equipped with a piezoelectric element plate 8 for detecting a vibration caused by knocking and a main body metal fitting to support the above plate 8 on the side of its one plate face, and the support face 11 of the main body metal fitting to the plate 8 is formed in a tapered face whose inside is recessed more than its outside. Since the support face 11 is formed in the above shape, a resonance point becomes difficult to occur in a sensor output, and flat output frequency characteristics can therefore be stably obtained, and as a result, the occurrence of the knocking can be certainly accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-resonant knock detection sensor which is attached to an internal combustion engine and electrically detects knocking of the engine.

[0002]

2. Description of the Related Art Conventionally, as a sensor for detecting knocking generated in an internal combustion engine of an automobile or the like, a sensor that detects vibration caused by knocking using a piezoelectric element has been widely used. Among them, the non-resonant type disclosed in Japanese Patent Application Laid-Open No. 221819/1990 is, for example, a ring-shaped metal shell having a flange-shaped receiving portion formed at the lower end side. The piezoelectric element is extrapolated, and one surface thereof is supported by the flange-shaped receiving portion, and a nut member screwed to the outer peripheral surface of the metal shell via a washer-shaped pressing member is tightened to the other surface side. ,
This has a structure in which it is pressed and held between the receiving member and the nut member. Such a knocking detection sensor has a relatively flat output characteristic without a specific resonance frequency as shown in FIG. 7, for example, and extracts a sensor output in a frequency band corresponding to knocking using a bandpass filter. By doing so, the detection is performed.

[0003]

By the way, in the above-mentioned knock detection sensor of the non-resonance type, it is desirable that its output frequency characteristic be as flat as possible, as inferred from its detection principle. Here, most conventional non-resonance knock detection sensors have a flat supporting surface for the above-described receiving portion for the piezoelectric element, and in such a structure, resonance tends to occur at a specific frequency. It has been known. Then, as shown in FIG.
When resonance occurs at a frequency other than the intended detection band, there is a problem that the detection output level in the knocking band is reduced or the resonance is susceptible to noise, resulting in detection failure.

An object of the present invention is to provide a non-resonance type knock detection sensor which is less likely to generate a resonance point in output frequency characteristics, and which can reliably detect knocking with high accuracy.

[0005]

In order to solve the above-described problems, a knocking detection sensor according to the present invention includes a piezoelectric element plate for detecting vibrations due to knocking, and a piezoelectric element plate for detecting vibration. A metal shell supported on one of the plate surfaces, wherein a support surface of the metal shell for the piezoelectric element plate has a tapered surface in which an inner portion is recessed from an outer portion. By making the supporting surface of the metal shell to the piezoelectric element plate as described above, a resonance point is hardly generated in the sensor output, a flat output frequency characteristic can be stably obtained, and the occurrence of knocking can be reliably detected with high accuracy. be able to.

Specifically, the piezoelectric element plate is formed in a ring shape, and the metal shell is formed integrally with a cylindrical or columnar insertion portion at one end of the insertion portion. And a flange portion extending outward in the circumferential direction. In this case, the piezoelectric element plate has a hole formed in the center thereof, with respect to the insertion portion of the metal shell,
It is extrapolated from the side opposite to where the flange is formed. The flange portion has a ring-shaped end surface facing the externally inserted piezoelectric element plate forming a support surface, and the support surface is inclined in the radial direction such that the inner edge side is retracted from the outer edge side. It is a tapered surface. And
The piezoelectric element plate is supported, for example, at the outer edge of the tapered surface.

In this case, it is desirable that the tapered surface be adjusted to have a radial inclination angle with respect to the reference surface in the range of 0.1 to 1.3 ° with respect to a surface perpendicular to the axis of the insertion portion. . If the inclination angle exceeds 1.3 °, the contact state between the electrode of the piezoelectric element plate and the metal shell deteriorates, and stable sensor output characteristics cannot be obtained. On the other hand, 0.1 °
Below this, a resonance point tends to occur in the output frequency characteristic, and the sensor output tends to vary. Therefore,
The angle of inclination is preferably adjusted in the range of 0.1 to 1.3 °, more preferably in the range of 0.2 to 1.0 °, and even more preferably in the range of 0.2 to 0.7 °. Is good.

[0008]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a cross-sectional structure of a knocking detection sensor (hereinafter, also simply referred to as a sensor) 1 according to one embodiment of the present invention. The sensor 1 includes a synthetic resin case (hereinafter also simply referred to as a case) 2, a metal shell 5, a piezoelectric element plate 8, a connection terminal 22, and the like. The case 2 includes a main body 3 formed in a cylindrical shape.
And a tubular portion 25 which is formed integrally with the side wall so as to protrude laterally from the side surface thereof, and is formed, for example, by integral injection molding with the metal shell 5 and the piezoelectric element plate 8 after assembly. Have been.

The metallic shell 5 has a cylindrical insertion portion 7 having a through-hole 6 formed in the axial direction thereof, and is formed integrally with the lower end of the insertion portion 7 in the circumferential direction of the insertion portion 7. And a flange portion 10 extending outwardly along the line. The flange portion 10 has a tapered surface 1 that is inclined in a radial direction at a ring-shaped upper end surface (support surface) facing the piezoelectric element plate 8 so that an inner edge side is retracted from an outer edge side.
It is set to 1. A plurality of uneven portions 7 are provided along the axial direction on the outer periphery of the distal end portion of the insertion portion 7 and the outer periphery of the flange portion 10.
a and 10a are formed, respectively, and serve to improve the bonding strength by injecting the constituent resin of the injection molded case 2 here. Further, a screw portion 13 is formed slightly above the intermediate portion of the insertion portion 7 and along the circumferential direction below the uneven portion 7a.

As shown in FIG. 1, the piezoelectric element plate 8 has a ring shape in which a hole 8a is formed in the center thereof, and electrode plates 9a and 9b are arranged on the front and back surfaces thereof. In the state, the flange portion 10 is inserted into the insertion portion 7 of the metal shell 5.
Is extrapolated from the end opposite to the side on which is formed, and further on top thereof, an insulating plate 16, a weight 17, and a washer 1
8 are extrapolated and stacked in this order. When the nut member 20 is tightened from the distal end of the insertion portion 7 to the screw portion 13 formed on the outer periphery of the nut member 20, the above members are nipped and held between the tapered surface 11 and the lower surface of the nut member 20. In addition, the end face of the piezoelectric element plate 8 on the electrode plate 9b side is supported by the tapered surface 11 of the flange portion 10.

As shown in FIG. 2, the tapered surface 11 of the flange portion 10 has a surface perpendicular to the axis of the insertion portion 7 as a reference surface M, and the inclination angle θ in the radial direction with respect to the reference surface M is, for example, 0.1. The angle is adjusted in the range of about 1.3 °, preferably in the range of 0.2 ° to 1.0 ° (in the figure, the inclination angle of the tapered surface is exaggerated for convenience of explanation).

Next, as shown in FIG. 1, two connection terminal portions 22 (FIG. 3: 22a, 22b) for taking out the output from the piezoelectric element plate 8 are provided with electrode plates 9a, 9b via a built-in resistor 24, and the other end of the cylindrical portion 25
The connector portion 23 is formed so as to protrude inward, and forms a connector portion 23 together with the tubular portion 25. Then, by fitting the female coupler 27 into the connector portion 23, the connection terminal portion 22 and the circuit portion (not shown) are electrically connected. Note that the built-in resistor 24 does not necessarily need to be provided, and may be omitted.

Hereinafter, a method of using the knocking detection sensor 1 will be described. As shown in FIG. 4, by inserting a screw member 33 into the through hole 6 of the metal shell 5 and screwing the screw portion 31 of the internal combustion engine 30, the sensor 1
Vibration generated by knocking of the internal combustion engine 30 is transmitted to the piezoelectric element plate 8 via the metal shell 5. The piezoelectric element plate 8 converts the vibration into an electric signal by a piezoelectric effect, and the electric signal is output from the connection terminal section 22 to a circuit section (not shown) via a cable. Here, a band-pass filter (band-pass filter) is provided in a circuit section for detecting the output signal of the sensor 1, and only a signal in a detection frequency band (FIG. 7) corresponding to knocking is detected. In the sensor 1 of the present invention, since the support surface of the metal shell 5 for the piezoelectric element plate 8 is the tapered surface 11, a resonance point is less likely to be generated in its output characteristics.
Knocking can be reliably detected with high accuracy.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Each part of the knocking detection sensor 1 having the shape shown in FIG. 1 was manufactured with the following dimensions and materials. First, the piezoelectric element plate 8 has an outer diameter of 22.7 mmφ and an inner diameter of 15.15 mm.
A PZT sintered body having a diameter of 2.4 mm was obtained. The metal shell 5 is formed by forging and cutting so that the outer diameter of the flange portion 10 is 23 mm and the inner diameter is 13.8 mm, and the angle of the tapered surface 11 is in a range of -4.0 to +4.0. Was adjusted.

Next, such a knocking sensor 1 is held on a vibrator via a predetermined jig, and a frequency of 17 k
Hz sine wave is input from the signal generator via the amplifier, and when the vibration of the vibrator is set to 3G, the output voltage of the sensor 1 is measured at n = 10 for each taper angle, The value of the standard deviation was calculated and used as an index of variation. FIG. 5 shows the result. From the measurement results, it can be seen that there is little variation when the taper angle is in the range of 0.1 to 1.3 °. Note that a negative taper angle indicates that the inner side is tapered in a direction opposite to the above, which protrudes from the outer side.

When a sine wave having a frequency of 4.5 kHz or 17 kHz is input from a signal generator via an amplifier to the sensor 1 held by the vibrator, and the vibration of the vibrator is set to 3G. The output voltage of the sensor 1 was measured. Then, α = (output value at the time of 3G excitation at 17 kHz /
Flatness α defined by 4.5 kHz 3G excitation) was obtained for each taper angle. In the non-resonance knock sensor, the smaller the value of the flatness α, the flatter the output frequency characteristic, which means that the knock detection characteristic is better. FIG. 6 shows the measurement results of the flatness α for each taper angle. From this result, it is understood that the flatness α is better as the taper angle is closer to 0. However, if the taper angle is too close to 0, the variation in the output value will increase from the measurement results in FIG. Therefore, by setting the taper angle in the range of 0.1 to 1.3 °, it can be seen that it is possible to suppress the variation in the output while maintaining the flatness.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an example of a knocking detection sensor according to the present invention.

FIG. 2 is an explanatory diagram exaggerating a main part of the knocking detection sensor of FIG. 1;

FIG. 3 is a conceptual diagram schematically showing a method of connecting a piezoelectric element plate to connection terminals.

FIG. 4 is a conceptual diagram showing a mounting state of a knocking detection sensor.

FIG. 5 is a graph showing the results of an experiment in which the relationship between the output variation of the knocking detection sensor and the taper angle was examined.

FIG. 6 is a graph showing the results of an experiment in which the relationship between the flatness of the output of the knocking detection sensor and the taper angle was examined.

FIG. 7 is an explanatory diagram illustrating an example of output characteristics of a non-resonant knock detection sensor.

FIG. 8 is an explanatory diagram showing a case where resonance occurs in the output characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Knocking detection sensor 5 Metal shell 7 Insertion part 8 Piezoelectric element plate 10 Flange part 11 Tapered surface

Claims (3)

[Claims] 1. A sensor for detecting knocking occurring in an internal combustion engine, comprising: a piezoelectric element plate for detecting vibration caused by the knocking; and a metal shell for supporting the piezoelectric element plate on one of its plate surfaces. A knocking detection sensor, wherein a supporting surface of the metal shell for the piezoelectric element plate has a tapered surface in which an inner portion is recessed from an outer portion. 2. The piezoelectric element plate is formed in a ring shape, and the metal shell is formed integrally with a cylindrical or columnar insertion portion at one end side of the insertion portion. A flange portion extending outwardly along a direction, wherein the piezoelectric element plate has a hole formed in the center thereof and an insertion portion of the metal shell, wherein the flange is formed. The flange portion has a ring-shaped end face facing the externally inserted piezoelectric element plate forming the support surface, and the support surface has an inner edge side larger than an outer edge side. 2. The knocking detection sensor according to claim 1, wherein the knocking detection sensor has a tapered surface inclined in a radial direction so as to be retracted. 3. The tapered surface has a tilt angle in a radial direction with respect to a reference surface that is perpendicular to an axis of the insertion portion in a range of 0.1 to 1.3 ° with respect to the reference surface. 2. The knocking detection sensor according to 2.