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Description of Invention
Vibration sensor
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibration sensor
for detecting vibrations such as knocking of an internal combustion engine. In general, if the
strong knocking state continues during operation of the internal combustion engine, the
durability of the engine is adversely affected, but in the slight knocking state in a relatively low
speed engine rotation region, the engine output and fuel consumption characteristics are the
best. It is known to be. Therefore, conventionally, focusing on the ignition timing that is closely
related to the occurrence of knocking, the ignition timing is made to advance and retract
correspondingly while detecting the contact knocking state, and the slight knocking state is
always maintained. An apparatus has been proposed which is intended to improve fuel efficiency
and output characteristics. In such a device, a sensor for detecting the knocking state of the
engine is indispensable, so the present applicant has presented a sensor as shown in the s8gi
diagram, which is accompanied by knocking F! It is designed to detect seki oscillations. In the
figure, reference numeral 1 denotes a diaphragm made of a circular thin plate-like piezoelectric
element, and a silver coating, for example, is decorated on both surfaces thereof to form an
electrode surface. EndPage: 1 This diaphragm 1 is housed in a case main body 3 having a circular
recess 2, held in the circumference between electrodes 5 and 7 having a flange 4 corresponding
to the recess 2, and transmitted to the case main body 3 The membrane is designed to vibrate.
One electrode surface of the diaphragm 1 is in contact with the conductive case main body 3%
and the other electrode surface is in contact only with the electrode 5 0 and the electrode 5 is
fixed so as to fix the diaphragm 1 with a certain clamping force. On the outer side of the
insulator 6 covering the plate, a flat spring 9 is interposed between the ring-shaped spring seat 7
and the retainer 8 and caulked and fixed from the outer side of the retainer 8 through the edge
10 of the case body 3 It is The diaphragm 1 is held at a constant pressure by the elastic force of
the disc spring 9 to prevent the fluctuation of the resonance frequency due to the change of the
fixed load. Further, the inner diameter of the concave portion 2 and the inner diameter of the
flange portion 4 are set to be the same, and the support end of the diaphragm 1 is made to
coincide with the case where the upper and lower surfaces are distorted. The resonance
frequency of the diaphragm 1 determined by the inner diameter of the support is selected so as
to be included in the normal engine knocking frequency range (5 to 9 I (Hz)). The vibration
sensor having such a configuration is attached to the engine body by the anchor bolt 11
integrally formed with the case body 3. The anchor bolt base 33 of the case body 3 has a
hexagonal nut shape for mounting. When the diaphragm 1 vibrates as the engine vibrates and is
bent up and down with the peripheral surface as a fulcrum, a potential difference is generated
between the upper and lower electrode surfaces of the piezoelectric element based on the
amount of deformation.
Since one of the electrode surfaces is grounded via the case main body 3, the vibration of the
diaphragm (piezoelectric element) 1 can be electrically isolated as a voltage between the
electrode 5 and the body ground. Moreover, since the diaphragm 1 resonates in the engine
knocking frequency range to increase the output, the vibration component based on knocking
can be amplified and detected with high accuracy. 3- In this case, in this case, the resonance
frequency largely changes due to the change of the support inner diameter of the diaphragm 1
and the support load, so high management accuracy is required at the time of assembly etc., and
productivity tends to decrease. . The peak vibration region due to knocking is a relatively narrow
range / concave, and the variation in the resonance frequency exerts a large bulging portion on
the detection accuracy. In order to solve this problem, the present invention embeds the
periphery of the diaphragm integrally at the time of forming the synthetic resin force a of the
case main body so as to suppress the support inner diameter of the diaphragm and the support
load as much as possible 151]. It is an object of the present invention to provide a vibration
sensor. Hereinafter, the present invention will be described based on all the embodiments of the
present invention. In the first embodiment of FIGS. 2 to 4, 20 is a diaphragm in which electrodes
21A and 21B are coated on the upper and lower surfaces of the piezoelectric element The
periphery of the goo 2 main body 22 formed by injection molding of a synthetic resin is
integrally embedded and fixed. The ring body 22 has a circular hollow portion 23 formed in the
central portion, and the diaphragm 20 is housed in the hollow portion 23. Both sides of the
cavity 23 are sealed by case covers 25A and 25B. Further, mounting holes 27 are respectively
provided in the bracket portion 26 of the case main body 22. Lead wires 29A and 29B are
bonded to the electrodes 21A and 21B of the diaphragm 20 by soldering, for example, and these
bonding portions are also integrally embedded at the time of the injection molding. The part of
the leader line extends to the outside. The diaphragm 20 is drawn between the male mold 31 and
the female mold 32 for injection molding as shown in FIG. 5 in a state in which the lead wires
29A and 29B are previously bonded, and injection of the molten resin is performed. Along with
the molding of the case body 22, the periphery is fixed. In this case, the inner diameter of the
hollow portion 23 of the case main body 22 significantly affects the support inner diameter of
the diaphragm 20 and the resonance frequency. Therefore, the shrinkage rate of the case main
body 22 after injection molding is considered. The dimensional accuracy of and 32 is strictly
controlled by instrumentation. Thus, since the diaphragm 20 is integrally cast and formed
EndPage: 2 and the peripheral portion thereof is held by the bonding force accompanying the
assimilation of the synthetic resin in the fluid state, its supporting load (pressure) is mechanically
Unlike fixing, it can always be made substantially constant, and as a result, coupled with the
dimensional accuracy of the support inner diameter, the resonance frequency of the diaphragm
20 can be made to correspond exactly to the knocking oscillation frequency.
Further, from the viewpoint of productivity as well, since the fixing of the diaphragm 20 is also
completed simultaneously with the injection molding of the case body 22, the mass productivity
is excellent and the yield is also good. In addition, the diaphragm 20 vibrates in a film due to the
vibration transmitted to the p1 case main body 22 due to the attachment to the engine main
body, and the output change of the piezoelectric element is generated accordingly, and the
vibration can be detected as an electrical output. The diaphragm 20 is the same as that shown in
FIG. 1 in the above description. Although a thin plate-like piezoelectric element in which a stain
pole is formed by silver coating on both sides is described as an example, the present invention is
not limited to this, but using one as shown in FIG. It is also good. That is, the diaphragm 20
shown in FIG. 6 (5) has the sheet metal plate 52 fixed to one surface of the electrode 51 of the
piezoelectric element 50 with a conductive adhesive, as shown in FIG. 6 (B). The diaphragm 20
shown in FIG. 6 (q and q shows a diaphragm in which two electrodes 51. 51 of the same polarity
of the piezoelectric element 50. 50 are fixed (so-called bimorph) with a conductive adhesive.
Reference numeral 20 denotes a metal plate 52 fixed to the middle or one side of the
piezoelectric element 50.50 shown in FIG. 6) with an isoelectric adhesive, and any of them can
increase the output. . The second embodiment shown in FIGS. 7 and 8 will now be described. In
this embodiment, a metal plate 40 serving also as an electrode is bonded to the back surface of
the piezoelectric element 42 as a diaphragm 20 '. The diameter d of the electrode 41 to be coated
was set according to the stress distribution at the time of deformation of the diaphragm 20 ', and
the output value of the vibration detection was increased. The stress generated by the film
vibration of the diaphragm 20 'fixed at the periphery changes in direction at the inflection point
of the deformation curve of the diaphragm 20'. 7-Therefore, if the diameter of the electrode 41 is
determined so as not to take out only the output of the part in which the stress in the same
direction occurs, the output of the piezoelectric element does not cancel out by the stress in the
reverse direction. The output of the piezoelectric element is increased. The other configuration is
the same as in the first embodiment, and the diaphragm 20 'is integrally fixed at the time of
injection molding of the case body 22. As understood from the above description, according to
the present invention, since the fixing of the diaphragm is integrally performed at the time of
molding of the case main body, it is possible to extremely reduce the variation of the fixing load
and the support inner diameter of the diaphragm. , Very good resonance with engine knocking
vibration. Therefore, there is an effect that a vibration sensor with high knocking detection
accuracy and excellent mass productivity can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a conventional
apparatus, FIG. 2 is a plan view of a first embodiment of the present invention, and FIGS. 3 and 4
are AA and B-B of FIG. Line cross-sectional view, FIG. 5 is an explanatory view of the case 8-case
molding state, FIGS. 6 (5) to (6) are cross-sectional views showing other structural examples of
the diaphragm, and FIG. Partial cross section of the example, Figure 8 is the same CC &! FIG.
DESCRIPTION OF SYMBOLS 20 ... Diaphragm, 21A, 21B ... Electrode% 22 ... Case main body, 23 ...
Hollow part, 29A, 29B ... Lead wire, 31.32 ... Mold. Patent applicant Nissan Motor Co., Ltd.
EndPage: 3 Fig. 4 Fig. 4 Fig. 5 Fig. 6 5052 End Page: 4 Fig. 7 Fig. 8 Fig. 5 B85-EndPage: 5
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