U.S. patent application number 10/840621 was filed with the patent office on 2004-12-16 for nonresonant type knock sensor.
This patent application is currently assigned to NGK SPARK PLUG CO., LTD.. Invention is credited to Aoi, Katsuki, Harada, Sadamitsu, Hirata, Tomohiro, Ito, Yasuo.
Application Number | 20040250603 10/840621 |
Document ID | / |
Family ID | 29219475 |
Filed Date | 2004-12-16 |
United States Patent
Application |
20040250603 |
Kind Code |
A1 |
Harada, Sadamitsu ; et
al. |
December 16, 2004 |
Nonresonant type knock sensor
Abstract
A knock sensor comprises a sensor body having a metallic shell
including a cylindrical portion and a flange portion formed at an
end of the cylindrical portion, an annular piezoelectric element
fitted around the cylindrical portion and an annular weighting
member fitted around the cylindrical portion to hold the
piezoelectric element between the weighting member and the flange
portion, and a resin-molded sensor casing arranged
circumferentially around the sensor body. The resin-molded sensor
casing includes a weighting portion located nearer to the weighting
member than to the piezoelectric element with respect to an axial
direction of the cylindrical portion, and at least the weighting
portion of the resin-molded sensor casing is made of a resin
containing at least one of metal powder and metal oxide powder and
has a density of 2.0 g/cm.sup.3 or higher.
Inventors: |
Harada, Sadamitsu; (Gifu,
JP) ; Aoi, Katsuki; (Aichi, JP) ; Hirata,
Tomohiro; (Aichi, JP) ; Ito, Yasuo; (Aichi,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NGK SPARK PLUG CO., LTD.
|
Family ID: |
29219475 |
Appl. No.: |
10/840621 |
Filed: |
May 7, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10840621 |
May 7, 2004 |
|
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|
10422806 |
Apr 25, 2003 |
|
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|
6752005 |
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Current U.S.
Class: |
73/35.11 |
Current CPC
Class: |
G01L 23/222
20130101 |
Class at
Publication: |
073/035.11 |
International
Class: |
G01L 023/22 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2002 |
JP |
2002-127301 |
Aug 23, 2002 |
JP |
2002-243746 |
Aug 29, 2002 |
JP |
2002-251320 |
Claims
1. (canceled).
2. (canceled).
3. (canceled).
4. (canceled).
5. (canceled).
6. (canceled).
7. (canceled).
8. (canceled).
9. (canceled).
10. (canceled).
11. A knock sensor, comprising: a metallic shell including a
cylindrical portion and a flange portion formed at an end of the
cylindrical portion; an annular piezoelectric element fitted around
the cylindrical portion; and an annular weighting member fitted
around the cylindrical portion to hold the piezoelectric element
between the weighting member and the flange portion, wherein the
flange portion has at least one cut formed therein to reduce the
weight of the flange portion.
12. The knock sensor according to claim 11, wherein said at least
one cut is formed in a side of the flange portion opposite to a
side facing toward the piezoelectric element.
13. The knock sensor according to claim 11, wherein said at least
one cut is a groove formed around the cylindrical portion.
14. The knock sensor according to claim 11, wherein said at least
one cut includes a plurality of depressions.
15. The knock sensor according to claim 11, wherein at least the
flange portion of the metallic shell is made of a material having a
lower specific gravity than that of iron.
16. The knock sensor according to claim 11, wherein the
piezoelectric element is made of a sintered piezoelectric ceramic
material mainly composed of (Bi.sub.0.5Na.sub.0.5)TiO.sub.3,
(Bi.sub.0.5K.sub.0.5)TiO.sub- .3 and BaTiO.sub.3.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/422,806 filed Apr. 25, 2003, the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a nonresonant type knock
sensor that detects the occurrence of knocking in an internal
combustion engine.
[0003] A knock sensor with a piezoelectric element is commonly used
in an ignition control system of an internal combustion engine so
as to detect the occurrence of knocking in the engine and thereby
allow the control system to provide optimal ignition timing for the
engine. There are two types of knock sensors: a resonant type and a
nonresonant type. In the case of the nonresonant type knock sensor,
the piezoelectric element receives a mechanical load due to engine
vibrations caused by the knocking, converts the mechanical load
into an electrical signal and outputs the electrical signal to the
control system via a band-pass filter so that the control system
reads the signal output in a frequency band corresponding to the
knocking vibrations to find the occurrence of knocking in the
engine.
SUMMARY OF THE INVENTION
[0004] Recently, there have been strict environmental regulations.
When the piezoelectric element is made free from lead so as to be
compliant with such strict environmental regulations, there is a
possibility that the signal outputted from the lead-free
piezoelectric element is so weak that the control system cannot
determine whether the knocking is actually occurring in the engine.
In order to avoid such a possibility, it is desired to improve the
signal output characteristic of the nonresonant type knock
sensor.
[0005] In consideration of the fact that the intensity of the
output signal from the piezoelectric element depends on the
mechanical load applied to the piezoelectric element, one
conceivable way to improve the signal output characteristic of the
sensor would be to increase the size of any part or portion of the
sensor that weights down the piezoelectric element (such as a
weighting member or resin-molded sensor casing) so as to add to its
weight and thereby increase the mechanical load on the
piezoelectric element as disclosed in Japanese Laid-Open Patent
Publication No. 2-173530. However, this results in upsizing of the
sensor. As there is only a limited space for mounting the knock
sensor in the engine, it is difficult to improve the signal output
characteristic of the sensor to a sufficient degree in the
above-mentioned way.
[0006] The present invention has been made allowing for the
above-mentioned circumstances, and an object of the present
invention is to provide a nonresonant type knock sensor that has an
increased mechanical load on its piezoelectric element without
upsizing of the sensor for improvement in signal output
characteristic.
[0007] According to a first aspect of the invention, there is
provided a knock sensor, comprising: a sensor body having: a
metallic shell including a cylindrical portion and a flange portion
formed at an end of the cylindrical portion; an annular
piezoelectric element fitted around the cylindrical portion; and an
annular weighting member fitted around the cylindrical portion to
hold the piezoelectric element between the weighting member and the
flange portion; and a resin-molded sensor casing arranged
circumferentially around the sensor body, wherein the resin-molded
sensor casing includes a weighting portion located nearer to the
weighting member than to the piezoelectric element with respect to
an axial direction of the cylindrical portion, and at least the
weighting portion of the resin-molded sensor casing is made of a
resin containing at least one of metal powder and metal oxide
powder and has a density of 2.0 g/cm.sup.3 or higher.
[0008] According to a second aspect of the invention, there is
provided a knock sensor, comprising: a metallic shell including a
cylindrical portion and a flange portion formed at an end of the
cylindrical portion; an annular piezoelectric element fitted around
the cylindrical portion; and an annular weighting member fitted
around the cylindrical portion to hold the piezoelectric element
between the weighting member and the flange portion, wherein at
least the flange portion of the metallic shell is made of a
material having a lower specific gravity than that of iron.
[0009] According to a third aspect of the invention, there is
provided a knock sensor, comprising: a metallic shell including a
cylindrical portion and a flange portion formed at an end of the
cylindrical portion; an annular piezoelectric element fitted around
the cylindrical portion; and an annular weighting member fitted
around the cylindrical portion to hold the piezoelectric element
between the weighting member and the flange portion, wherein the
flange portion has at least one cut formed therein to reduce the
weight of the flange portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a sectional view of a nonresonant type knock
sensor according to a first or second embodiment of the present
invention.
[0011] FIG. 2 is an exploded view of a sensor body of the knock
sensor of
[0012] FIG. 3 is an illustration showing the operation of the
nonresonant type knock sensor.
[0013] FIG. 4 is a graph showing an improvement in signal output
achieved by the knock sensor according to the second embodiment of
the present invention under room temperature conditions.
[0014] FIG. 5 is a graph showing an improvement in signal output
achieved by the knock sensor according to the second embodiment of
the present invention under high temperature conditions.
[0015] FIG. 6 is a sectional view of a nonresonant type knock
sensor according to a third embodiment of the present
invention.
[0016] FIG. 7A is a sectional view of a metallic shell of the knock
sensor of FIG. 6.
[0017] FIG. 7B is a bottom view of the metallic shell of FIG.
7A.
[0018] FIG. 8A is a sectional view of a metallic shell according to
a modification of the third embodiment.
[0019] FIG. 8B is a bottom view of the metallic shell of FIG.
8A.
[0020] FIG. 9A is a sectional view of a metallic shell according to
another modification of the third embodiment.
[0021] FIG. 9B is a bottom view of the metallic shell of FIG.
9B.
DESCRIPTION OF THE EMBODIMENTS
[0022] The present invention will be described below with reference
to the drawings. In the following first to third embodiments, like
parts and portions are designated by like reference numerals, and
repeated descriptions thereof are omitted.
[0023] A nonresonant type knock sensor 100 according to the first
embodiment of the invention will be first explained.
[0024] As shown in FIGS. 1 and 2, the knock sensor 100 comprises a
sensor body 190 having a metallic shell 120, an insulation sleeve
131, annular insulation plates 130 and 135, an annular
piezoelectric element 150, annular electrode plates 140 and 160, an
annular weighting member 170, a conical spring washer 180 and a nut
185, and a resin-molded sensor casing 110.
[0025] The metallic shell 120 includes a cylindrical portion 121
and an annular flange portion 122 formed radially outwardly at an
end 121c of the cylindrical portion 121. The cylindrical portion
121 has a thread 121b formed on an outer circumferential surface
thereof. Further, a through hole 120b is formed in the metallic
shell 120 along an axial direction of the cylindrical portion 121
in order for the knock sensor 100 to be attached to a cylinder
block of an internal combustion engine (not shown) by using a bolt
(not shown) through the hole 120b and thereby vibrate together with
the cylinder block at the occurrence of knocking. It is noted that
the knock sensor 100 is mounted on the cylinder block in such an
orientation that the flange portion 122 abuts at its bottom side on
the cylinder block.
[0026] The insulation plate 130, the electrode plate 140, the
piezoelectric element 150, the electrode plate 160, the insulation
plate 135, the weighting member 170 and the spring washer 180 are
fitted around the cylindrical portion 121 of the metallic shell 120
in the order of mention from the flange-portion side. The
insulation sleeve 131 is interposed between the cylindrical portion
121 of the metallic shell 120 and the electrode plate 140, the
piezoelectric element 150 and the electrode plate 160 so as to keep
the electrode plates 140 and 160 and the piezoelectric element 150
electrically insulated from the metallic shell 120. The nut 185 has
a thread 185b formed on an inner circumferential surface thereof,
and is screwed down against the spring washer 180 in such a manner
as to fix the insulation plate 130, the electrode plate 140, the
piezoelectric element 150, the electrode plate 160, the insulation
plate 135 and the weighting member 170 between the flange portion
122 and the nut 185 by engagement of the threads 121b and 185b. The
electrode plates 140 and 160 has output terminals 141 and 161,
respectively, formed extendingly to output a signal from the
piezoelectric element 150 (i.e. a voltage developed between the
electrode plates 140 and 160) to an electronic control unit (ECU,
not shown) via a band-pass filter (not shown).
[0027] The sensor casing 110 is arranged circumferentially around
the sensor body 190 with the hole 120b exposed externally of the
sensor casing 110. The sensor casing 110 includes a connector
portion 113 in which the output terminals 141 and 161 are
accommodated for connection of the knock sensor 100 to the ECU. The
sensor casing 110 further includes a weighting portion 111 located
nearer to the weighting member 170 than to the piezoelectric
element 150 with respect to the axial direction of the cylindrical
portion 121 of the metallic shell 120 to contribute to the
application of a load to the piezoelectric element 150.
[0028] In the first embodiment, at least the weighting portion 111
of the sensor casing 110 is made of a resin containing at least one
of metal powder and metal oxide powder and has a density of 2.0
g/cm.sup.3 or higher at room temperature. The weighting portion 111
can be formed integral with the other portions of the sensor casing
110 (the whole of the sensor casing 110 can be molded of the resin
containing metal and/or metal oxide powder). Alternatively, the
weighting portion 111 may be formed separately from the other
portions of the sensor casing 110 to have e.g. a layer structure
(only the weighting portion 111 may be molded of the resin
containing metal and/or metal oxide powder).
[0029] A resin-molded sensor casing of a conventional knock sensor
is generally made of nylon and has a density of about 1.5
g/cm.sup.3, whereas at least the weighting portion 111 of the
sensor casing 110 is made of the resin containing metal and/or
metal oxide powder and has a density of 2.0 g/cm.sup.3 or higher as
described above. Accordingly, the sensor casing 110 becomes able to
apply an increased mechanical load to the piezoelectric element 150
even when the sensor casing 110 is made in the same size as the
above conventional sensor casing. This makes it possible to improve
the signal output characteristic of the knock sensor 100 without
upsizing of the sensor 100. This also makes it possible to downsize
the knock sensor 100 while maintaining the signal output
characteristic of the sensor 100 at the same level as that of the
conventional knock sensor.
[0030] Specific examples of the metal powder usable in the resin
include tungsten powder, molybdenum powder, iron powder, stainless
steel powder and the like. Specific examples of the metal oxide
powder usable in the resin include tungstic oxide powder,
molybdenum oxide powder, ferrite powder and the like. These metal
and metal oxide powders can be used alone or in any combination
thereof.
[0031] The metal and/or metal oxide powder added in the resin
preferably has a true density of 10.0 g/cm.sup.3 or higher at room
temperature. If the volume content of the metal and/or metal oxide
powder in the resin is relatively large, there is a possibility
that the resin may become difficult to mold. When the metal and/or
metal oxide powder has a true density of 10.0 g/cm.sup.3 or higher,
however, it becomes possible to control the density of at least the
weighting portion 111 of the metallic shell 110 to 2.0 g/cm.sup.3
or higher without adding a large amount of the metal and/or metal
oxide powder in the resin and thereby possible to avoid a
deterioration in the moldability of the resin. Herein, the "true
density" is defined as the density of a solid substance that forms
particles of the powder.
[0032] The metal and/or metal oxide powder added in the resin can
be either electrically conductive or insulative, but the sensor
casing 110 preferably has an insulating property in order to
provide the insulation between axially opposite sides of the
piezoelectric element 150 (e.g. to keep the insulation resistance
between the opposite sides of the piezoelectric element 150 of 1
M.OMEGA. or higher) and to prevent the electrode plates 140 and 160
from electrically conducting via the sensor casing 110. In the case
of the metal and/or metal oxide powder being electrically
conductive, it is thus preferable to control the amount, particle
size and particle shape of the metal and/or metal oxide powder
added. Especially when the sensor casing 110 is molded in one
piece, it is desirable that the metal and/or metal oxide powder is
electrically insulative so as to secure the insulating property of
the sensor casing 110 without regard to the amount, particle size
and particle shape of the metal and/or metal oxide powder added in
the resin. It becomes therefore possible to control the density of
the resin-molding sensor casing 110 to any desired value where the
resin is moldable and adjust the mechanical load on the
piezoelectric element 150 as appropriate. In particular, the
electrically insulative metal oxide powder (such as tungstic oxide,
molybdenum oxide and/or ferrite) is desirably used.
[0033] In consideration of effects on the human body, the metal
and/or metal oxide powder added in the resin is preferably free of
lead.
[0034] As the resin of the sensor casing 110, a commercially
available resin, such as "MC102K07 (high-density resin with a
density of 6.0 g/cm.sup.3, prepared by adding tungsten powder to
electrically insulative nylon 6)" from Kanebo., Ltd., can be
used.
[0035] Further, the weighting member 170 preferably has a density
of 10 g/cm.sup.3 or higher at room temperature.
[0036] A weighting member of a conventional knock sensor is made of
e.g. brass and has a density of about 8.0 g/cm.sup.3, whereas the
weighting member 170 has a density of 10 g/cm.sup.3 or higher.
Accordingly, the weighting member 170 becomes able to apply an
increased mechanical load to the piezoelectric element 150 even
when the weighting member 170 is made in the same size as the above
conventional weighting member. This makes it possible to improve
the signal output characteristic of the knock sensor 100 without
upsizing of the sensor 100. In order to control the density of the
weighting member 170 to 10 g/cm.sup.3 or higher, the weighting
member 170 can be made of a heavy metal (such as tungsten or
molybdenum), an alloy thereof or a sintered metal thereof. In
consideration of effects on the human body, the weighting member
170 is preferably free of lead.
[0037] Furthermore, the piezoelectric element 150 is desirably made
of a sintered piezoelectric ceramic material mainly composed of
(Bi.sub.0.5Na.sub.0.5)TiO.sub.3, (Bi.sub.0.5Ko.sub.0.5)TiO.sub.3
and BaTiO.sub.3 (hereinafter referred to as "BNT", "BKT" and "BT",
respectively).
[0038] Although the use of a lead-free piezoelectric element in a
knock sensor being examined as an environmental protection measure,
the knock sensor with the lead-free piezoelectric element generally
shows a lower signal output characteristic than that with a
lead-containing piezoelectric element as described above. With the
piezoelectric element 150 made of the BNT-BKT-BT sintered
piezoelectric ceramic material to be lead-free, however, it becomes
possible for the knock sensor 100 to attain the signal output
characteristic at the same level as that with the lead-containing
piezoelectric element. Herein, the term "lead-free piezoelectric
element" means a piezoelectric element containing lead in an amount
of less than 0.001% by mass, as measured by fluorescent X-ray
analysis, based on the total mass of the piezoelectric element.
[0039] It is assumed that the chemical composition of the main
BNT-BKT-BT constituent of the sintered piezoelectric ceramic
material is expressed as BNT.sub.xBKT.sub.yBT.sub.z where x, y and
z (x+y+z=1) represent the mole fractions of the BNT, BKT and BT
components, respectively. In order for the piezoelectric element
150 to attain high sensitivity and heat-resistance, it is desirable
to control the mole fractions of the BNT, BKT and BT components in
such a manner as to satisfy the following expressions:
0.5.ltoreq.X.ltoreq.0.9, 0.ltoreq.y.ltoreq.0.5 and
0.ltoreq.z.ltoreq.0.5. This allows the knock sensor 100 to show
high sensitivity and heat resistance.
[0040] Next, a nonresonant-type knock sensor 200 according to the
second embodiment of the invention will be explained. The knock
sensor 200 is structurally similar to the knock sensor 100 as shown
in FIG. 1, except that at least of a flange portion 222 of a
metallic shell 220 of the knock sensor 200 is made of a material
having a lower specific gravity than that of iron. The flange
portion 222 can be formed integral with a cylindrical portion 221
of the metallic shell 220 (the whole of the metallic shell 220 can
be formed from the material having a lower specific gravity than
that of iron). Alternatively, the cylindrical portion 221 and the
flange portion 222 can be formed separately and joined together by
e.g. adhesive bonding or welding (only the flange portion 222 can
be formed from the material having a lower specific gravity than
that of iron).
[0041] The operation of the knock sensor 200 will be now described
below with reference to FIG. 3 in order to facilitate the
understanding of the second embodiment. Herein, the effect of a
sensor casing 210 is left out of consideration. When the knock
sensor 200 receives an acceleration A with the operation of the
engine, the piezoelectric element 150 receives a mechanical load F
that can be expressed as the difference between a force Ft acting
on the weighting member 170 and a force Fs acting on the flange
portion 222 (F=Ft-Fs). Then, the piezoelectric element 150 develops
a voltage output V responsive to the mechanical load F exerted on
the piezoelectric element 150. As the forces Ft and Fs acting on
the weighting member 170 and the flange portion 222 are
proportional to a weight Wt of the weighting member 170 and a
weight Ws of the flange portion 222, respectively, it is concluded
that the voltage output V from the piezoelectric element 150 is in
proportion to the difference between the weight Wt of the weighting
member 170 and the weight Ws of the flange portion 222
(V.varies.Wt-Ws). Accordingly, the signal output from the
piezoelectric sensor 150 can be increased with decrease in the
weight of the flange portion 222.
[0042] A metallic shell of a conventional knock sensor is generally
made of iron or brass, whereas at least the flange portion 222 of
the metallic shell 220 is made of the material having a lower
specific gravity than that of iron. The flange portion 222 is
therefore made lighter in weight so that the signal output
characteristic of the knock sensor 200 can be improved without
upsizing of the sensor 200 as described above.
[0043] The material having a lower specific gravity than that of
iron can be exemplified by a resinous material (such as
polyphenylene sulfide: PPS) and a metallic material. In
consideration of heat resistance, it is desirable to use the
metallic material, preferably aluminum. The specific gravity of
aluminum (about 2.7) is as low as only about 35% of the specific
gravity of iron (about 7.9). The use of aluminum thus offers
sufficient weight reduction of the flange portion 222 for
improvement of the signal output characteristic of the knock sensor
200. Further, aluminum is suitable for the metallic shell 222
because of its hardness and availability. In addition, aluminum is
highly resistant to corrosion. Although the metallic shell made of
iron needs to be given plating (such as zinc chromate plating) so
as to improve corrosion resistance, such plating becomes
unnecessary through the use of aluminum. It becomes possible to
simplify the manufacturing process of the knock sensor 200.
[0044] A nonresonant-type knock sensor 300 according to the third
embodiment of the invention will be described. The knock sensor 300
is structurally similar to the knock sensors 100 and 200 as shown
in FIG. 6, except that a metallic shell 320 of the knock sensor 300
has at least one cut formed in its flange portion 322 so that the
flange portion 322 can be made lighter in weight. This makes it
possible to improve the signal output characteristic of the knock
sensor 300 without upsizing of the sensor 300 for the same reason
as described above in the second embodiment.
[0045] There may be edges and burrs caused by forming the cut or
cuts in the flange portion 322. In such a case, it is desirable
that such edges and burrs are given chamfering so that the flange
portion 322 is closely held onto the piezoelectric element 150 and
the cylinder block for stable signal output characteristic of the
knock sensor 300.
[0046] The cut or cuts are preferably formed in one side of the
flange portion 322 opposite to the side facing toward the
piezoelectric element 150. If the cut or cuts are formed in the
side of the flange portion 322 facing toward the piezoelectric
element 150, the piezoelectric element 150 becomes less prone to
vibrations caused by the knocking. Accordingly, there arises a
possibility that the output voltage of the piezoelectric element
150 may be lowered and/or the waveform of the output voltage of the
piezoelectric element 150 may be distorted. With the cut or cuts
formed in the side of the flange portion 322 opposite to the side
facing toward the piezoelectric element 150, however, it becomes
possible to effectively prevent the output voltage of the
piezoelectric element 150 from being lowered or distorted and, at
the same time, to reduce the weight of the flange portion 322 for
improvement in the signal output characteristic of the knock sensor
300.
[0047] As shown in FIGS. 7A and 7B, a single cut groove 322d may be
formed around a cylindrical portion 321 of the metallic shell 320
in order to improve the signal output characteristic of the knock
sensor 300 effectively by reducing the weight of the flange portion
322 while keeping the weight balance of the flange portion 322. The
groove 322d can be of any form, such as cyclic, star or polygonal
form. Alternatively, a plurality of circumferentially evenly spaced
depressions 322e may be formed around the cylindrical portion 321
as shown in FIGS. 8A and 8B. The shape of the depressions 322e is
not limited to round shape, and can be any other shape, such as
star or polygonal shape. As shown in FIGS. 9A and 9B, a plurality
of grooves 322f may be formed around the cylindrical portion 322f.
In such cases, it is also possible to use the depressions 322e or
322f for e.g. the fixing and positioning of the metallic shell 320
during the assembly of the knock sensor 300 in addition to reducing
the weight of the flange portion 322.
[0048] Instead of forming at least one cut in the flange portion
322, one side of the flange portion 322 can be cut away in such a
manner as to reduce the thickness of the flange portion 322 and
thereby reduce the weight of the flange portion 322.
[0049] Further, the metallic shell 320 preferably has at least the
flange portion 322 made of the material having a lower specific
gravity than that of iron, more preferably aluminum, in the same
manner as in the second embodiment to further reduce the weight of
the flange portion 322.
[0050] The present invention will be described in more detail by
reference to the following examples. It should be however noted
that the following examples are only illustrative and not intended
to limit the invention thereto.
EXAMPLES
[0051] Various samples of knock sensors were manufactured and
tested for performance as follows.
[0052] A sample of the knock-sensor 100 (SAMPLE 1) was manufactured
by the following procedure. The respective sensor body parts were
first prepared using the following materials: soft iron for the
metallic shell 120 and the nut 185; polyolefin for the insulation
sleeve 131; polyethylene terephthalate (PET) for the insulation
plates 130 and 135; 42Ni--Fe alloy for the electrode plates 140 and
160; lead zirconate titanate (PZT) for the piezoelectric element
150; and tungsten (density: about 19.2 g/cm.sup.3) for the
weighting member 170. The prepared body parts were assembled into
the sensor body 190, by: putting the insulation sleeve 131 on the
cylindrical portion 121 of the metallic shell 120; fitting the
insulation plate 130, the electrode plate 140, the piezoelectric
element 150, the electrode plate 160 and the insulation plate 135
around the insulation sleeve 131 in the order of mention; placing
the weighting member 170 on the insulation plate 135 to hold the
piezoelectric element 150, the insulation plates 130 and 135 and
the electrode plates 140 and 160 between the weighting member 170
and the flange portion 122; putting the spring washer 180 on the
weighting member 170; and then screwing the nut 185 against the
washer 180 in such a manner as to hold the insulation plates 130
and 135, the electrode plates 140 and 160, the piezoelectric
element 150, the weighting member 170 and the washer 180 between
the flange portion 122 and the nut 185 with a predetermined load
imposed on the piezoelectric element 150. Then, a resin was
prepared by mixing tungsten powder (true density: about 19.2
g/cm.sup.3) into nylon in such a manner that the density of the
resin was controlled to about 2.1 g/cm.sup.3. The sensor casing 110
was integrally molded of the prepared tungsten-powder containing
nylon resin by injection molding according to a known molding
method, so as to circumferentially surround the sensor body 190
with the hole 120b of the metallic shell 120 exposed externally of
the sensor casing 110.
[0053] For reference purposes, a knock sensor was prepared as
REFERENCE SAMPLE by the same procedure and with the same dimensions
as used for SAMPLE 1, except that the corresponding weighting
member and sensor casing were made of brass (density: about 8.0
g/cm.sup.3) and nylon (density: about 1.5 g/cm.sup.3),
respectively. The metallic shell of REFERENCE SAMPLE had no
groove/depression formed in its flange portion for weight reduction
of the flange portion.
[0054] Performance comparisons were made between SAMPLE 1 and
REFERENCE SAMPLE. The weighting portion 111 of SAMPLE 1 had a
density of about 2.1 g/cm.sup.3 that was larger than that of the
corresponding portion of REFERENCE SAMPLE (about 1.5 g/cm.sup.3),
so that the weighting portion 111 of SAMPLE 1 weighed more than the
corresponding portion of REFERENCE SAMPLE even in the same size.
The weighting member 170 of SAMPLE 1 had a density of about 19.2
g/cm.sup.3 that was larger than that of the corresponding member of
REFERENCE SAMPLE (about 8.0 g/cm.sup.3), so that the weighting
portion 170 weighed more than the corresponding member of REFERENCE
SAMPLE even in the same size. SAMPLE 1 was therefore able to apply
an increased mechanical load to the piezoelectric element 150 under
the load of the weighting portion 111 and the weighting member 170
without increasing in size and then to achieve an improved signal
output characteristic.
[0055] Further, the density of the resin of the sensor casing 110
was controlled to about 2.1 g/cm.sup.3 by adding a very small
amount of the tungsten powder with a true density of about 19.2
g/cm.sup.3. The volume content of the tungsten powder in the resin
was so low that the resin was molded into the sensor casing 100
without trouble and did not cause deterioration in the insulation
resistance between the opposite sides of the piezoelectric element
150.
[0056] Another sample of the knock sensor 100 (SAMPLE 2) was
manufactured by the same procedure and with the same dimensions as
used for SAMPLE 1, except that the electrically insulative tungstic
oxide (WO.sub.3) powder was used in place of the tungsten
powder.
[0057] As compared to REFERENCE SAMPLE mentioned above, SAMPLE 2
was able to attain an improved signal output characteristic in the
same manner as SAMPLE 1. In addition, the insulation property of
the sensor casing 110 was secured assuredly by the use of the
electrically insulative tungstic oxide powder. There was no fear of
electrical conduction between the electrode plates 140 and 160 via
the sensor casing 110 and no fear of insufficient insulation of the
connector portion 113. The density of the sensor casing 110 was
controlled as appropriate without regard to the amount of the
tungstic oxide powder added to apply an increased mechanical load
to the piezoelectric element 150, while the moldability of the
resin was maintained.
[0058] Next, a sample of the knock sensor 200 (SAMPLE 3) was
manufactured by the same procedure and with the same dimensions as
used for SAMPLE 1, except that the metallic shell 220, the
weighting member 170 and the sensor casing 210 were made of
aluminum (available as "KS27" from Furukawa Electric Co., Ltd.
according to JIS H4040), brass and nylon, respectively. In other
words, SAMPLE 3 differed from REFERENCE SAMPLE in that: the
corresponding metallic shell of REFERENCE SAMPLE was made of iron,
whereas the metallic shell 220 of SAMPLE 3 was made of aluminum to
reduce the weight of the flange portion 222.
[0059] Performance comparisons were made between SAMPLE 3 and
REFERENCE SAMPLE as follows. Each of SAMPLE 3 and REFERENCE SAMPLE
was mounted in the cylinder head of an internal combustion engine,
and the signal outputs from SAMPLE 3 and REFERENCE SAMPLE were
measured at room temperature with respect to varying engine
vibration frequencies. The average of the measured signal outputs
was calculated against each vibration frequency. Then, the signal
output ratio of SAMPLE 3 to REFERENCE SAMPLE at room temperature
were calculated by the following expression:
Output ratio=(Al.sub.avg-Fe.sub.avg).times.100/Fe.sub.avg
[0060] where Al.sub.avg is the average of the signal outputs from
SAMPLE 3 at a given engine vibration frequency; and Fe.sub.avg is
the average of the signal outputs from REFERENCE SAMPLE at the
given engine vibration frequency. The results are shown in FIG. 4.
Further, the signal output ratio of SAMPLE 3 to REFERENCE SAMPLE
was determined at 125.degree. C. in the same way as above. The
results are shown in FIG. 5. As is apparent from FIGS. 4 and 5,
SAMPLE 3 had 15% or more of improvement in signal output at room
temperature and 23% or more of improvement in signal output at
125.degree. C. as compared to REFERENCE SAMPLE. SAMPLE 3 was able
to apply an increased mechanical load to the piezoelectric element
150 by reducing the flange portion 222 in weight without increasing
in size, and therefore able to attain an improved signal output
characteristic. Further, aluminum was suitably used for the
metallic shell 220 due to its hardness and availability. There was
no need to give plating treatment in the preparation of the
metallic shell 222 because of high corrosion resistance of
aluminum, so that the manufacturing process of SAMPLE 3 was
simplified.
[0061] A sample of the knock sensor 300 (SAMPLE 4) was manufactured
by the same procedure and with the same dimensions as used for
SAMPLE 1, except that the weighting member 170 and a sensor casing
310 were made of brass and nylon, respectively, and that the
metallic shell 320 had a groove 322d formed in one side of the
flange portion 322 opposite to the side facing toward the
piezoelectric element 150. In other words, SAMPLE 4 differed from
Reference example in that: the corresponding portion of REFERENCE
SAMPLE had no groove, whereas the flange portion 322 of the SAMPLE
4 had the groove 322d formed therein to reduce the weight of the
flange portion 322.
[0062] As compared to REFERENCE SAMPLE, SAMPLE 4 was able to apply
an increased mechanical load on the piezoelectric element 150 by
reducing the flange portion 322 in weight without increasing in
size, and therefore able to attain an improved signal output
characteristic.
[0063] Another sample of the knock sensor (SAMPLE 5) was
manufactured by the same procedure and with the same dimensions as
used for SAMPLE 4, except that the metallic shell 320 was made of
aluminum so as to further reduce the weight of the flange portion
322. Accordingly, SAMPLE 5 was able to attain more improvement in
the signal output characteristic than that attained by SAMPLE
4.
[0064] Still another sample of the knock sensor 300 (SAMPLE 6) was
by the same procedure and with the same dimensions as used for
SAMPLE 5, expect that the piezoelectric element 150 was made of a
sintered piezoelectric ceramic material mainly composed of BNT, BKT
and BT as follows. The BNT-BKT-BT sintered piezoelectric ceramic
material was prepared by using as starting materials BaCO.sub.3
powder, K.sub.2CO.sub.3 powder, Na.sub.2CO.sub.3 powder and
TiO.sub.2 powder. The BaCO.sub.3 powder, K.sub.2CO.sub.3 powder,
Na.sub.2CO.sub.3 powder and TiO.sub.2 powder were dispensed so that
the ratio of mole fractions x, y and z of BZT, BKT and BT
components in the ceramic material was controlled to
x:y:z=0.80:0.10:0.10. Ethanol was added to the BaCO.sub.3 powder,
K.sub.2CO.sub.3 powder, Na.sub.2CO.sub.3 powder and TiO.sub.2
powder and subjected to wet blending for 15 hours by using a ball
mill. The resultant mixture was put in hot water, dried, and
calcinated at 800.degree. C. for 2 hours. The calcinated mixture
was subjected to wet milling for 15 hours by using a boll mill, put
in hot water and then dried to obtain a granulation of the
BNT-BKT-BT sintered piezoelectric ceramic material. The granulation
was formed to a predetermined size by uniaxial pressing with a
pressure of 1 GPa and subjected to cold isostatical press (CIP)
with a pressure of 15 GPa. The thus-obtained formed article was
sintered at 1050 to 1250.degree. C. for 2 hours. Silver electrodes
were formed on the sintered article and subjected to polarization
process, thereby completing the piezoelectric element 150.
[0065] Although the piezoelectric element 150 of SAMPLE 6 was
lead-free, SAMPLE 6 was able to attain the same level of signal
output characteristic as that of SAMPLE 5. As there was no
dispersion of lead during the sintering of the ceramic material,
SAMPLE 6 was more environmentally friendly. Further, the
piezoelectric element 150 of SAMPLE 6 satisfied the following
expressions: 0.5.ltoreq.X.ltoreq.0.9, 0.ltoreq.y.ltoreq.0.5 and
0.ltoreq.z.ltoreq.0.5 so that the piezoelectric element 150 had
high sensitivity and heat resistance. Namely, SAMPLE 6 showed high
sensitivity and heat resistance.
[0066] The entire contents of Japanese Patent Application Nos.
2002-127301 (filed on Apr. 26, 2002), 2002-243746 (filed on Aug.
23, 2002) and 2002-251320 (filed on Aug. 29, 2002) are herein
incorporated by reference.
[0067] Although the present invention has been described with
reference to specific embodiments of the invention, the invention
is not limited to the above-described embodiments. Various
modification and variation of the embodiment described above will
occur to those skilled in the art in light of the above teaching.
For example, the weighting member 170, the conical spring washer
180 and the nut 185 may be formed into one piece so as to reduce
the parts count of the sensor. The scope of the invention is
defined with reference to the following claims.
* * * * *