JPS6152926B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibration sensor for detecting knocking vibrations of, for example, an automobile engine.

A system has been proposed that advances the ignition timing while detecting the knocking state of the engine, and operates the engine in a state that provides the best fuel efficiency within a range that does not exceed the knocking limit. As a means for determining, a vibration sensor that detects knocking vibration is often used.

Conventionally, there is a device as shown in FIG. 1 as this vibration sensor.

A sensor body 2 has an anchor bolt 1 for attachment to an engine cylinder block, etc., and a vibrating part support 3 is integrally formed in the center thereof.

A diaphragm 5 is clamped between the support base 3 and the retainer 4, and its base end is fixed in a cantilever supported state by bolts 6.

The diaphragm 5 has a rectangular shape as a whole, and is made by bonding a thin metal plate 7 and a piezoelectric element 8 of substantially the same shape.

Both surfaces of the piezoelectric element 8 are coated with silver or the like to form electrodes, and each time the piezoelectric element 8 bends integrally with the metal plate 7, a potential is generated between the two electrodes.

In order to take out the potential generated by this vibration as an output, an output terminal 9 is connected to the metal plate 7 in contact with one electrode, and the other electrode is body grounded to the engine via the support stand 3 and the sensor body 2. .

The center of the retainer 4 is formed into a cylindrical shape, and the entire retainer 4 is made of an insulating material to keep both electrodes insulated from each other.

The space containing these diaphragms 5 is sealed by a cover cap 2A.

In this way, the diaphragm 5 is vibrated by the engine vibration transmitted to the sensor body 2, and a corresponding frequency output change is extracted. Since it is fixed to the high sensor body 2, only the output corresponding to the vibration input is generated.

Therefore, although the resonance frequency of the diaphragm 5 is made to correspond to engine knocking vibration, the S/N ratio, which is the level ratio between the output during sensor resonance and the normal vibration noise output, is as low as about 7. As a result,
There was a problem in which it was often difficult to determine engine knocking.

Therefore, the present invention provides a vibration sensor in which a vibration detection section is attached to a part that mechanically resonates with a specific vibration component such as engine knocking vibration, and output can be obtained under double resonance or a state close to it. , aims to solve the above problems.

Embodiments of the present invention will be described below based on the drawings.

A first embodiment is shown in FIGS. 2 to 4. An anchor bolt 1 is attached to the metal cylindrical case body 10.
1 is integrally formed, and a relatively thin disk-shaped cover plate 14 is fixed to the end of the cylindrical wall portion 13 of the case body 10 by caulking its peripheral edge 12.

The support diameter D, wall thickness t, and weight of the central portion of the cover plate 14 are appropriately set in advance so that the cover plate 14 vibrates at or near mechanical resonance in a specific measurement target frequency range, for example, a knocking frequency range. It is something.

And this cover plate (vibration plate)
In the central part of 14, there is a support base 1 formed concentrically.
5 is provided, and a diaphragm 16 serving as a vibration detection section is held between a retainer 17 and fixed by bolts 18 and nuts 19.

The diaphragm 16 itself has basically the same structure as the one shown in FIG. Its width, length, thickness, etc. are set so that the frequency matches the knocking vibration frequency range.

The piezoelectric element 21 has electrode surfaces 21A and 22B coated with silver or the like on both sides, and one electrode surface 22A is connected to an engine block or the like via the metal plate 20, the support base 15, the cover plate 14, and the sensor body 10. The body is grounded and the other electrode surface 22B
is connected to the connection connector 24 via the retainer 17, nut 19, and bolt 18.

Therefore, the retainer 17, nut 19, bolt 18, cover plate 14, sensor body 10, etc. are all made of conductive material (metal).

An insulating sleeve 25 is inserted through the bolt 18, and an insulating ring 27 is interposed between the bolt tightening flange 26 and the cover plate 14, thereby maintaining insulation between the electrodes.

The support stand 15 and the retainer 17 have a diaphragm 1
Flat parts (notches) 28 and 29 are formed to accurately determine the fixing position of the diaphragm 16.
Tighten nut 19 while aligning.

The sensor body 10 and the cover plate 14 are vibrated by the vibration of the engine, and the diaphragm 16 attached to the cover plate 14 is also vibrated accordingly.

The potential of the piezoelectric element 21 changes in response to vibration, and this is taken out as an output via the connection connector 24.

When vibrations due to knocking occur, the cover plate 14 is set to resonate in this vibration range, so the amplitude of the membrane vibration increases significantly compared to other ranges.

For this reason, the diaphragm 16 attached to it also vibrates greatly and at the same time resonates with this vibration, so the amplitude of the diaphragm 16 becomes double resonance or a state close to it, and as a result, the piezoelectric element 2
The absolute value of the output of 1 increases significantly compared to the non-resonant region.

FIG. 5 shows the thickness of the cover plate 14 being changed (t
= 1.5, 1.8, 3.0 mm), and it shows that as the plate thickness t becomes thinner, the resonant frequency shifts to a lower range. Further, it can be seen that the resonance characteristic of the cover plate 14 does not have a sharp peak unlike that of a rectangular plate, but has a relatively broad characteristic. Therefore, even if the resonant frequency of the cover plate 14 deviates somewhat from the knocking frequency range, the sensor output can be improved. This is shown in FIG.

Figure 6 shows the results of a vibration experiment with the diaphragm 16 attached to the cover plate 14 with thicknesses of t = 1.5, 1.8, and 3.0 mm.When the plate thickness was t = 1.5 mm, each resonance frequency was Because they matched at 8KHz, the output at resonance became significantly large, and the S/N ratio also decreased.
666, which is a significant improvement.

Furthermore, when the plate thickness is 1.8 mm, the resonance point of the diaphragm 16 is 8KHz and the resonance point of the cover plate 14 is 10KHz, so although two peaks appear, the S/N is The ratio was 31, which is a relatively good value.

Note that when the plate thickness t = 3 mm, the resonance point of the cover plate 14 is 16KHz, which is considerably shifted from the resonance point of the diaphragm 16 of 8KHz, but still.
The S/N ratio has improved from 7 to 10, and some effect can be recognized.

However, in the above explanation, the plate thickness itself is a relative value determined in relation to other conditions (support diameter, etc.), and these values are merely examples under specific conditions.

Next, the embodiments shown in FIGS. 7 and 8 will be explained. In this case, instead of the diaphragm 16, the cover plate 14 has a resonant frequency set on the back or front surface of the cover plate 14 so that the resonance frequency is in the knocking frequency range (for example, 8 KHz). A resonance type G sensor (gravitational acceleration sensor) 30 is attached via a stud 31. 32 is a lead wire for outputting output. In this case as well, the same effects as in the previous embodiment can be obtained.

In each of the above embodiments, an example of detecting engine knocking vibration has been described, but it is of course possible to apply the present invention to detecting other vibrations.

As explained above, according to the present invention, the sensor output can be amplified using mechanical resonance, and a specific vibration to be measured such as knocking vibration can be clearly distinguished.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional device, Fig. 2A is a sectional view of the first embodiment of the present invention, Fig. 2B is an enlarged view of section E, and Fig. 3 is a sectional view taken along line FF in Fig. 1. 4 is an exploded perspective view of the main parts, FIG. 5 is an explanatory diagram showing the resonance characteristics of the cover plate, FIG. 6 is an explanatory diagram showing the output characteristics of the sensor of the present invention, and FIGS. 7 and 8 are FIG. 3 is a cross-sectional view of the second and third embodiments. DESCRIPTION OF SYMBOLS 10... Case body, 14... Cover plate, 16... Vibration plate, 18... Bolt 19... Nut, 20... Metal plate, 21... Piezoelectric element.

Claims (1)

[Claims] 1. In a vibration sensor that detects knocking vibration of an engine, the sensor cover covering the space formed in the sensor body is used as a vibration plate, and the resonance frequency of the vibration plate is set to be at or near the knocking frequency of the engine. A vibration sensor characterized in that a vibration detection section that resonates at a knocking frequency of an engine is attached to the vibration plate.