Note: Descriptions are shown in the official language in which they were submitted.
.
' 1
~d o~ ~ . .
. . . .
~ ven~ion r~la~s to a me~hod o~ and appa~atu~
lS or det~cting t~a pre~ehce o~ corl~duct~e particles ~ an oll
1aw s~te~ , or e~ample, i~ the l~ricatillg ~seem o~
~ter~al co~libustion or ~et engi~ and m~re pa~ti$uiax~ sr to ~
~uch a ~ snd app~ra~2s adapted to gi~7e a~: ~dicatioYl of ; - `.
. t~he qua~tity o such co~au~tive partiele~ pre~e~t,` ~-
~ presence of metal particles ~ th~ lubricatl~g
~ystem of lnt~r~ol ca~ibwtion or ~et e~gine~ not o~ly
h~rmful to ~u~h engine~ i~ operatiarl but aD ixlcrea~i~g q!iEmtit:~
. - . . . :
~ ' ~ . ' :" : ' . : ~ ~
~707~
of ~uch particle~ ~ ~dlca~ e o Qxces~ive wear of ~ricti~al
~u~ace~ o~ ~uch e~g~e~. ~hQ d~1:ec~io~ of ~8 pre~e~ce oE
~uch par~icle~ and particularly of a~ i~cre~g qua~ti~y of
such part~cle~ will erlable their rem~7al bot~h to pr~vent d~magQ
to ~he engi~e and for a~algsi~ ~n order to determ~e ~Le co~ditio~
o~ th~ en8ine. S~ce dlffere~ fricti~nal surface3 of t~h~
engi~e are mad~ of ,~iff~ra~ me~ , lt: would be po~3~1e to
de~ec~ a defe~t ill a p~rt~culæ part oi. 1~B e~g~ h as t~
p~s~o~, cy~i~der~ bearing e~c. by a~ s of me1:al part~:le~
pre3~t i~ ~e oil flaw o t~he l~brlcati:ng ~y8tem t~hereof uposi
det~ct~o~ of ~m i~creasi~g qua tity o~ pætiel~.
Apparat~ or t~his puxpose here'co~or@ pro~posad i~ t~
prior art ha8 b~en ba~ lectrical 8~n~i~g o~ m~tal
particle~ a~. ~y pa~8 t~ough 8t:ructure~ terpo~ed ~ the oll
E~aw a~d comprls~g ~paced el~c~rically co~duc~Lv~ bodi~ or
electrodes. For e~ample, U.g. Paten~ No. 2,349,992 l~o Schcader
disclo~ v~riow e~ibodlmeats oE ~uch a device i~ whlch ~e
presence o~ metal particl~ he o~l flaw ~hrough t~he volume
defi:Qed be~een 8paced ~lectrode3 result~3 ~ caparitive or
re~i~tiYe cha~8e~ t~at ar~ electrically se~ed.
Ho~ever, t~ha,electrode~ of such devlce~ must be
phy~ically clo~e 8paced ~rom each o*ler in order ~o pravide tha
8e~it:1vi~ r~quired tc~ detl3ct mi~ute metal pætlcle~ d~
i~ t~he oil ~low. The re8ult ls t~ c 8uch dev~ce~ tend ~o act
a~ fluld il~ " co~l~cti~g bo~h ~e~al pa~ticle~s a~d-
non~tallic GOllt~lli31a~. ~ku9, ~;uch device~ d to indicats
~e pre~e~ce of a~ exce~siv~ antit~r of metal particle~, eve~
undex normal e~gine c~nditlon~, or to become clogged Wi~L
no~etallic c~t~m~ts.
' ':
:`
. . .
, . . .
1(37~6
According to the teaching of U,S, patent no.
3,457,504 to Arthur et al, an attempt is made to overcome the
inherent problem described above by accenting the fluid filter
characteristics of the device and decreasing the sensitivity
of the electrical elements thereof. However, such an approach
only tends to transfer the problem from the electrical elements
to the filter element thereof since the relative condition of
the filter element at any point in time will tend to determine
the operating characteristics of the device. Thus, if the
filter is made fine enough to trap the large quantity of minute
particles of metal required to produce the desired electrical
output, it will also trap a large quantity of non-metallic
contaminants, thereby tending to reduce the oil flow therethrough
and effectively deactivatiny the device Eor the purpose intended.
It is an object of -this invention to pro~ride an
improved method and apparatus for de-tecting the presence and
- quantity of minute metal particles in an oil flow system.
It is another object of this invention to provide an
- improved method Eor detecting the presence and quantity of
minute metal particles in an oil flow system without the use
of fluid filter structures or inherent fluid filter action.
To this end the inven-tion consists of the m~thod of
sensing the presence and quantity of conductive materials in a
flow system for high electrical resistance fluid comprising
the steps of: a. positioning an electrically insulating
substrate having a major surface with a plurality of elongated
close spaced substantially parallel electrically conductive
surfaces thereon below the normal level of fluid at a point
in said system where the fluid flow is relatively static
30 whereby conductive materials having a higher specific gravity
than said fluid may contact said major surface of said
,.,
f ~ - 3 -
.~ .
"' ~
, .
'
-" ~V7~ 6
substrate; b. electrically connecting each of said elongated
conductive surfaces at the junction between a different pair
of a plurality of series connected electrical resistance
elements providing a given total electrical resistance;
c. electrically isolating said plurality of series connected
electrical resistance elements from said fluid of said flow
system; d. passing a given electrical current flow through said
series connected electrical resistance elements; and e. sensing
effective decreases in said given total electrical resistance
due to conductive materials which contact sai~ substrate in a
position to bridge the space between adjacent ones of said
elongated close spaced substantially parallel conductive
surfaces thereon.
The invention also consists of apparatus for sensing
the presence and quantity of conductive materials .in a flow
system for high electrical resistance fluid comprising: a. an
insulating substrate having a major surface with a plurality
of elongated close spaced substantially parallel electrically ~ ,
conductive surfaces thereon positioned within said fluid flow
system below the normal level of fluid at a point in said
system where said fluid flow is relatively static whereby
conductive materials having a higher specific gravity than
said fluid may contact said major surface of said substrate;
b. a plurality of electrical resistance elements electrically
connected in series to provide a given total electrical
resistance with the junction between each pair of said
plurality of electrical resistance elements comprising a
different one of said plurality of elongated close spaced
substantially parallel electrically conductive surfaces on said
one major surface of said electrically insulating substrate;
c. means electrically isolating said plurality of electrical
~ - 3a -
96
resistance elements from said fluid of said flow system; d.
means for passing a given electrical current flow through said
series connected electrical resistance elements; and e. means
for sensing and indicating the effective decreases in said given
total electrical resistance of said series connected electrical
resistance elements due to conductive materials which contact
said major surface of said substrate in a position to bridge
the space between ad~acent ones of said elongated close
spaced substantially parallel conductive surfaces thereon.
The invention also relates to a sensor for use in
apparatus for sensing conductive particles in a flow system for
high electrical resistance fluid, said sensor comprising:
a. an insulating body having a planar surface; b. an array of
a plurality of elongated close spaced generally parallel
electrically conductive surfaces mounted on said planar surface
of said insulating body; c. a plurality of electrical resistance
elements each electrically connected between a different pair
of said plurality of elongated close spaced generally parallel
electrically conductive surfaces; d. protective means isolating
said plurality of electrical resistance elements from their
environment; and e. means for making electrical connections
to the ultimate one of said plurality of conductive surfaces
at each side of said array of said plurality of conductive
surfaces.
r
~ .
,........................................................................ .
"', .
:'~
:, .
~)7~796
Thus, in the prefe~ed fo~m of this invention, the
presence and quantity of conductive materials in an oil flow
system are sensed by allowing such materials to settle ou-t of
the oil at a point in the system where such oil is relatively
static onto a generally planar insulatîng surface having an
array of elongated close spaced substantially parallel
electrically conductive surface portions thereon. A plurality
of discrete electrically resistive elements are electrically
connected in series with each other and each junction between
a pair of serially connected electrically resistive elements
is electrically connected to a different one of the elongated
electrically conductive surface portions. Thus, conductive
metal particles settling on such planar surface will tend to
electrically connect the elongated conductive surface
portions, changing the total electrical resistance of the
series connected electricall~ resistive elements and such
changes in total resistance is sensed in order to sense the
presence of metal particles in the oil flow system. The value
of the total resistance sensed will be an inverse function of ,
the quantity of metal particles in the oil flow system thus
providing for the sensing of the quantity of metal particles
in the system.
Brief Description of the Drawing
The foregoing and other objects and features of this `!
invention will be more clearly apparent from a reading of the
following detailed description of preferred embodiments in
conjunction with the attached drawing wherein:
_ 4 _
..
107~)7'36
FIG. 1 is a perspective view of a preferred embodi-
ment of the apparatus of this invention wi-th the sensor shown
separately from the remainder of the apparatus which is
enclosed in an appropriate housing and with the electrical
connections between the sensor and the remainder of the
apparatus indicated schematically.
FIG. 2 is a schematic representation of a general-
ized oil flow system to which this invention is applicable and
including a showing OL the preferred locat.ion of the sensor
according to the teaching of this invention.
FIG. 3 is an enlarged cross-sectional view in
elevation of the sensor according to the preferred embodiment
of this invention shown in FIG. 1.
FIG. 4 is an enlarged top plan view of the elec~
trically active element of the sensor of FIG. 3 showing a
preferred arrangement of the electrically conductive surfaces
on an insulating disc with the resistive elements and other
electrical portions of the apparatus shown in generalized
schematic form.
FIG. 5 is a detailed schematic representation of
the apparatus according to a preferred embodiment of this
invention including a schematic representation of the
sensor.
FIG. 6 is an enlarged top plan view showing a
preferred structure for the e:Lectrically active element of
the sensor in which both the conductive surfaces and the
: resistive elements are provided on a major surface of an
insulating disc by printed circuit techniques.
Detailed Description of Preferred E,mbodiments
Referring to FIG. 1, a preferred embodiment of the
sensor element 10 according to the teaching of thls invention
is shown in perspective, with a housing 11 containing the
., .
~0'71~796
remainder of the apparatus according to this invention also
shown in perspective. A schematic representation of the
electrical interconnection including a battery 12 between
the sensor 10 and remainder of the apparatus contained in
the housing 11 is included in FIG. 1.
In actual use, the sensor 10 wil:L be installed in
an appropriate place in the oil flow system of an engine
or other mechanism in accordance with the teaching of this
invention and the housing ll containing the remainder of
the apparatus will be mounted at a point where it may be
conveniently observed by the operator of the engine or other
machine. For example, where the teaching of this invention
is applied to an internal combustion engine, the sensor 10
would be mounted in the oil pan of the engine and the housing
ll could be mounted on the dashboard or instrument panel toge-
ther with the other instruments which monitor the operation
of the engine. If a battery is not associa-ted with the
engine or other machine to which this invention is applied,
then an appropriate battery or other source of DC electrical
energy must be provided.
Referring to FIG. 2, the essential elements of an
oil flow system to which this invention is applicable are
shown in generalized form. Thus, such oil flow system must
include a portion such as an oil reservoir or oil pan
represented at 14 where a quantity of the oil in the system
is in a relatively static state. Represented at 16 is a pump
~ or other appropriate means for urging oil to flow from the
i reservoir 14 -to an engine or other machine represented at 18
~ for the lubrication thereof after which the oil returns to
i 30 the reservoir 14. According to the teaching of this invention,
the sensor 1~ is mounted in a wall of the reservoir 14 where
' ' .
, . .
~7~7S~!~
the force of gravity will cause relatively heavy metal
particles to settle out of the relatively static quantity
of oil in the reservoir 14 onto the sensor 10. Thus, the
sensor 10 is preferably mounted at ~he point in the reservoir
14 normally occupied by the drain plug provided in the prior
art for draining the oil from the oil flow system. However,
the sensor 10 may be located at any point in the wall of
the reservoir where it will be exposed to the settling of a
representative amount of heavy metal particles from the oil
by the force of gravity.
Referring to FI~. 3, a preferred embodiment of the
sensor 10 according to the teaching of this invention is
shown in enlarged cross-section. Such sensor 10 comprises
a metallic body 20 in the form of a threaded plug with a
hexagonal head, as best shown in FIG. 1, similar to the drain
plugs conventionally used in oil flow systems. In fact,
according to the preferred embodiment of this invention~
the sensor 10 actually comprises the drain plug of the
oil flow system suitably modified to include the electrical
elements according to the teaching of this invention as will
be more fully discussed hereinbelow. In any event, the
metallic body 20 serves as the mount for the sensor pill 22
with a ma~or surface thereof exposed to the oil in the
reservoir or other relatively static point in the oil flow.
Referring to FIG. 4, an enlarged top plan view
of the major surface of the sensor pill 22 which is exposed
to the oil is shown. Such sensor pill comprises a planar
array of a plurality of elongated mutually spaced electrically
conductive surfaces 24. According to the preferred embodiment
o~ this invention, such planar array of electrically conductive
surfaces 24 are provided on an appropriate insulating substrate
such as a mica disk, for example. Such electrica:Lly conductive
-- 7
,.~...
~)7V79~
surfaces 24 are preferably made of copper coated with gold
in order to provide high electrical conductivity and resis-
tance to corrosion or other chemical effects due to their
direct contact with the oil of the oil flow system. Conven-
tional technlques such as the photographic printing and
etching techniques conventionally used in making printed
circuit boards may be conveniently used in fabricating the
sensor pill 22 according to the teaching o.f this invention.
As shown in ~IG. 4, the sensor pill 22 also includes
10 a plurality of electrically resistive elements 26. According
to the teaching of this invention, such electrically resistive
elemen-ts axe electrically connected in series with each other
across the battery 12 or other source of DC electrical energy
through the remaining por-tion of the apparatus of this invention
schematically indicated in FIG. 4 by the ammeter 11'. ~ccording
to this invention, the junction between each pair o:E series
connected electrically resistive elements 26 is electrically :
connected to a different one of the electrically conductive
surfaces 24. In fact, in the embodiment shown in FIG. 4, the
20 electrically conductive surfaces 24 each form the junction
between a different pair of electrically resistive elements
26. Thus, in operation, a DC electrical current is estab- .
lished by the battery ].2 or other source through the apparatus
which current flow is essentially determined by the total
resistance of the electrically resistive elements 26 and may
be indicated by an ammeter such as that represented generally
at 11' in FIG. 4.
If a metal particle or plurality of metal particles
settle onto the sensor pill 22 in such a way as to form an
~: 30 electrically conductive bridge between any pair of elec-
, . trically conductive surfaces 24, they will tend to establish
-- 8
.`;
., .
J~117(~96
a low resistance electrical current path therebetween in
parallel with one of the electrically resistive elements 26
thereby tending to reduce the total resistance of the apparatus
and increase the current flow therethrough. If a large
quantity of metal particles are present in the oil, they will
tend to settle over -the surface of the pill 22 resulting in
a large reduction in the total resistance of the apparatus
and a large current flow therethrough whereas a lesser number
of metal particles will result in a lesser reduction in
resistance and a lesser current flow therethrough. Thus a
. change in the total resistance of the apparatus will indicate
the presence of metal particles in the.oil and the total
value of such resistance will be an inverse function of the
quantity of such metal particles.
Referring to FIG. 5, a detailed schematic diagram
of a preferred embodiment of the appara-tus of this invention
is shown in which the sensor element is indicated schemati-
cally at 10. Such sensor 10 is connected across the source ~-
of DC electrical energy which may be a 12 volt battery, for
example, through a current limiting resistor 30, the purpose
of which is to reduce the current drain on the DC source.
The junction between the sensor 10 and -the resistor 30 is
connected -to the inverting input of an operational amplifier
31 through an input resistor 32. The non-inverting input of
the DC amplifier 31 is connected to the adjustable tap of
a potentiometer 33 which potentiometer is connected in series
with a current limiting resistor 34 and a bias resistor 35
across the source of DC electrical energy. The output of the
amplifier 31 is connected to the base of a transistor 36
through an output resistor 37 and across an input resistor
38. The potentiometer 33 is adjusted so that there is no
: output from the amplifier 31 to cause the transistor 36 to
_ g _
, .
107~79~; ~
conduct when the resi~tance of the sensor 10 is at full value.
The accumulation of metal particles on the surface of the
sensor 10 will reduce the total resistance thereof, thereby
reducing the voltage which is developed thereacross and
applied to the inverting input of the amplifier 31. This
will result in an increased output from such amplifier 31
eausing the transistor 36 to conduet in di:reet proportion
to sueh output. The transistor 36 is eonnleeted aeross the
source of DC eleetrical energy through the solenoid of a
10 milliammeter indicated generally at 40. Thus, as the ,
resistance of the sensor 10 decreases from its normal
value to a lower value due to the accumulation of metal
particles thereon, the amount of current conducted through
the transistor 36 and solenoid 40 of the milliammeter will
inerease, resulting in a eorresponding inerease in the
reading of the milliammeter from 0.
. The output of the amplifier 31 is also eonneeted
through a reverse biased zener diode 41 to the base of a
: seeond transistor 42. The seeond transistor 42 is eonneeted
in series with a light emitting diode 43 aeross the souree
of DC eleetrical energy through a voltage limiting resistor
44. The transistor 42 is in a non-condueting eondition when
there is no output from the amplifier 31 and the. resistanee
of the sensor is at its maximum value. As metal partieles
aeeumulate on the sensor 10 redueing the resistance thereof,
: the voltage output of the amplifier 31 increases until the
;. threshold voltage of the zener diode 41 is reached eausing
it to eonduct and apply the output of the amplifier 31 to
the base of transistor 42, thereby allowing eurrent flow
through the transistor 42 in porportion to the output of
amplifier 31 and tending to eause the light emitting diode
to emit light whieh will inerease in intensity as the
-- 10 --
,
79t~
resistance of -the sensor 10 decreases.
As shown in ~IG. 1, the light emitting diode 43 may
be physically located in close proximity to the scale of the
milliammeter 40. Thus, the increasing intensity of the light
ou-tput of the light emi-t-ting diode 43 will tend to attract the
operator 15 attention to the milliammeter, the reading of which
will indica-te the quantity of metal particles present on the
sensor 10.
~ lthough the apparatus thus far described in conn-
ect1on with FIG. 5 will provide an acceptable level ofoperation in accordance with the teaching of this invention,
we have found that the effectiveness of the apparatus will
be greatly increased by periodically pulsing :the voltage
applied across the sensor 10 to the full voltage value of
the source of DC energy. ~lthough the explanation ior such
improvement in operation due to such pulsing is no-t Eully under-
stood, it is believed that such pulsing results in a more rapid
settling of metal particles onto the conduc-tive surfaces of
the sensor element 10 and in better electrical contact between
such metal particles and such electrically conductive surfaces.
In any event, it has been found that the application of a
substantially square wave pulse having a pulse width of about
one-half second and a repetition rate of about one cycle per
second will result in a more efficient electrical contact
between the metal particles and the conductive surfaces of
the sensor element 10. If the repetition rate is increased
about 15 pulses per second with a corresponding decxease in
pulse width, this effect tends to disappear. Similarly, if
the repe-tition rate is reduced below one pulse every two
seconds, no appreciable improvement is noted and the output
becomes more difficult to sense with accuracy.
- 1 1
.. . . .
~ 7(~796
Thus, referring to FIG. 5, in the preferred embodi-
ment of this invention, an appropriate means is included for
periodically pulsing the voltage across the sensor element 10
up to the full value of the voltage of the source of DC
energy. Such means comprises an operational amplifier 45
toyether with its associated circuitry. Thus, the source
of DC energy is connected to the inverting input of the
operational amplifier 45 through a capacitor 46 and a
resistor 47 is connected between the inverting input and
the output of the amplifier 45. A feed back resistor 48
is connected between the output of the amplifier and the non-
inverting input thereof and the non-inverting input of the
amplifier 45 is connected to ground through a bias resistor
49. The output of the amplifier 45 is also connected to
the junction between the resistor 30 and sensor 10 through
an isolating diode 50.
It will be understood that the power supply for
the amplifiers 31 and 45 is the source of DC energy although
the power supply connections to the amplifiers 31 and 45
are not shown in FIG. 5 for simplicity of illustration. In
any event, the capacitor 46 and resistor 47 cooperate to
form an RC network and periodically pulse the output of
the amplifier 45 to the full voltage value of the source
of DC energy with the repetition rate and pulse width being
a function of the relative values of the capacitor 46 and
resistor 47. It would, of course, be possible to use other
appropriate circuits or circuit arrangements for pulsing
the voltage across the sensor 10 in accordance with the
teaching of this invention.
An additional advantage of pulsing the voltage
across the sensor element 10 is that a corresponding pulse
will appear in the outpu-t of the amplifier 31 which may be
- 12 -
.
1t~7~75~
used to cause the light emitting diode 43 to flash rather
than glow steadily. Thus, as conductive metal particles
accumulate on the sensor 10, the light emitting diode 43
will flash with ever increasiny brightness. A capacitor 51
is connected across the solenoid of the milliammeter 40.
Such capacitor has a large value by comparison to the
capacitor 49 of the pulsing circuit thus reducing the excur-
sions of the milliammeter 40 in response to the pulses in
the output of the amplifier 31. ~owever, in accordance with
the teaching of this invention, the value of the capacitor
51 should not be so large as to completely damp the pulses
in the output of the amplifier 31 since a slight pulsation
of the milliammeter 40 serves as an indication that the
sensor 10 is connected in the circuit and operating
~roperly even thouyh there are not sufficient metal particles
present thereon to produce a light output from the light
emitting diode 43. Thus, the apparatus shown in FIG. 5 is
self-checking at least inso~ar as indicating proper operation
of the sensor element 10 assuming that the remainder of the
appara-tus is operating properly.
In order to test the remainder of the apparatus
shown in FIG. 5, a normally open test switch 52 is connected
in parallel with the sensor element 10. Upon closure, the
test switch 52 will short out the sensor element and will
produce a maximum response from the remainder of the
apparatus if it is working properly.
In a preferred embodiment of this invention as
actually built and tested, a voltage controlled variable
output audio oscillator 60 including speaker 62 was connected
in parallel with the light emitting diode 43 as indicated at
the terminal 53 connected between the junction of the trans-
istor 42 and the resistor 44. Thus, both a visual and an
- 13 -
~, .
, . ' ' ' ' '
~C)7~7~6 ; ~
audio output was provided to attract the attention of theoperator to the reading of the milliammeter 40.
In such actual embodiment of the apparatus accord~
ing to this invention, the sensor element 10 has a total ;~
resistance of between 16 and 19 K ohms. The amplifiers 31
and 45 were the two halves of a dual operational amplifier
sold by Signetics Corporation under the type number 5558. A
feed-back resistor 54 was connected between the output of
the amplifier 31 and the inverting input thereof in order
to establish a selected amplification level for such amplifier.
The elements of the apparatus shown in FIG. 5 as actually
built and successfully tested were of the ~alues ~r types
shown in the following table:
Resistor 30 120 K ohms
Resistor 32 1 K ohm
Resistor 33 20 K ohms
Resistor 34 120 K ohms
Resistor 35 15 K ohms
Transistor 36 Type No. 2N4400 sold by Motorola,
Inc.
Resistor 37 10 K ohms
Resistor 38 10 K ohms
Milliammeter 40 0 to 1 milliamp.
Zener diode 41 Type No. IN4731A sold by Motorola,
Inc.
Transistor 42 Type No. 2N4400 sold by Motorola,Inc.
Light emitting diode 43 Type No. MU5053 sold by Monsanto,Inc.
Resistor 44 270 ohms
Capacitor 46 .1 microfarads
Resistor 47 120 X ohms
Resistor 48 120 K ohms
~ Resistor 49 12 megohms
; Diode 50 Type No. IN34~ sold by National
- Semiconductor,Inc.
- 14 -
~ .
,,.
796
Table Cont'd.
Capacitor 51 100 microfarads
Resistor 54 470 K ohms
Referring to FIG. 6, an enlarged plan view of the
preferred embodiment 22' of the sensor pill according to this
invention is shown. Such sensor pill comprises an epoxy
resin substrate upon which 23 equally spaced elongated
parallel conductive surfaces 2~' of gold clad copper are
formed by photoetching techniques. Each conductive surface
24' is .0035 inches ~.01 cm) thick and has a width of between
about .005 inch (.0125 cm) and .007 inch (.015cm). The
spacing between the conductive surfaces 24' is between
about .00375 inch (.01 cm) and about .005 inch (.0125 cm).
The resistive elements 26' are also formed on the
substrate by photoetchlng techniques by a proprietary process
and of a proprietary material having a resistance of about
100 ohms per square. As shown in FIG. 6, each of the
resistive elements 26' bridges between the adjacent ends
of a different pair of conductive surfaces 24' and is gen-
erally U-shaped in order to pxovide a total resistance of
about 700 ohms per resistive element. Since all of the
resistive elements 26' are connected in series through the
conductive surfaces 2~', the total resistance oE the sensor
pill is between about 16 K and about 19 K ohms. The resistive
elements 26' are covered with a coating of epoxy resin type
resist material in order to avoid the possibility of any
change in resistance thereof due to exposure to the oil of
the oil flow system.
In the actual embodiment shown in FIG. 6, the
diameter of the pill 22' was about 1/2 inch ~1.27 cm).
Theoretically, the sensor pill 22 could have any appropriate
- 15 -
, , ~
75~6
sha~e and dimensions. However, it has been found thatoperational considera-tions impose a maximum limitation on
dimensions for practical reasons and that a circular shape
is preferred as will be discussed hereinafter.
The spacing between the conductive surfaces 24 of
the sensor pill 22 is, of course, related to the minimum
size metal particle which could be detected according to
the teaching of this invention. It has been found that a
spacing of about .005 inch ~.0127 cm) between the conductive
surfaces 2~ is suitable for detecting metal particles in the
lubricating oil flow of truck and diesel engines. For
ligh~ aircraft and jet engines, a somewhat closer spacing
such as .00375 inch (.001 cm), for example, is preferred.
However, although the sensor pill 22 musk be capable of
senslng minute particles comparable to such spacings, it
is important that the apparatus according to this invention
not be so sensitive as to give a warning indication when
there are only a few of such minute metal particles in the
oil flow. The sensitivity of the apparatus to the number
of metal particles present in the oil flow is a function of
both the number of conductive surfaces and the width of
such surfaces.
Thus, it has been found that the width of the
conductive surfaces may be made at least equal to and
preferably somewhat greater than the spacing between the
. conductive surfaces for ease of manufacture without adversely
affecting the sensitivity of the apparatus to the number of
., metal particles present in ,the oil flow. In view o`f the fact
. -that such conductive surfaces are gold clad in order to
reduce the formation of highly resistive oxides thereon due
to contact with the oil, it is desirable that such surfaces
not be made too large.
- 16 -
, .
~V7~7~6
It has also been found that iE too few conductive
surfaces are used, the apparatus will be too sensitive to the
number oE metal particles present and will give a warning
indication when in fact there is no need fo:r concern. If
too many conductive surfaces are used, then the device will
not be sensitive enough to the number of metal particles
present in the oil flow to give a warning indication in time
to avoid damaye to the engine. It has been found that at
least 15 but not more tian 30 conductive surfaces will give
satisfactory results where the maximum length of such
conductive surfaces is about 100 times the spacing between
such conductive surfaces (i.e., about .5 inch (1.25 cm).
It will be understood that the probability of a metal
particle bridging the spacing between a particular pair
of conductive surfaces and thus the sensitivity of -the
sensor pill to the number of metal particles present in the
oil flow will increase in direct proportion to the maximum
length of the conductive surfaces. Thus, as the length of
the conducti~e surfaces is increased, the number of conductive
surfaces must also be increased in order to avoid the
possibility that the apparatus will give false warnings as
to the quantity of metal particles present in the oil flow.
Again, the expense of the gold clad conductive surfaces
imposes a practical limitation on the length and number of
conductive surfaces used in the sensor pill.
It has been found that a sensor pill of appropriate
dimensions can be made to fit into the drain plug of the
oil systems of the various engines in use today. Thus,
referring to FIGS. 1 and 3, it will be seen that it is a
simple matter to drill an appropriate centrally located
aperture through a drain plug for the installation of a
- 17 -
~71~75~
sensor pill 22 and appropriate insulated electrical connec-
tions 21 and 23 therein. If the drain plug 20 is not already
provided with a cup-like recess in its inner extremity as
illustrated in FIG. 3, then it is preferably provided with
such a recess having a depth indicated by the arrow B which
is at least l/4 of the diameter thereof indicated by the
arrow A. The sensor pill 22 may be mounted in the bottom
of such recess through the use of an appropriake epoxy
resin and an appropriate fillet of epoxy resin is preferably
provided about the upper periphery of the sensor pill 22 to
direct metal particles onto the electrically active surface
as they settle into such recess.
It has been found that 90% of all diesel engines
in use today utilize one of four different drain plugs.
Similarly it has been ~ound that 90~ of all light aircraft
engines and 90~ of all iet engines utilize one of not more
than three different drain plugs and it is estimated that
90% of the automobiles in use today utilize one of not more
than five different drain plugs.
Furthermore, it has been found that a sensor pill `
comprising a circular disc about one-half inch in diameter
can be easily mounted in any one of the widely used drain
plugs mentioned above. Thus, according to the teaching of
this invention, it is proposed to make sensor pills in two
sizes, namely, .550 inch (1.4 cm) for use in connection with
diesel engines and .405 inch (l cm) for use in connection with
light aircraft engines, jet engines and automobiles.
Although the use of apparatus according to the
teaching of this invention for sensing the presence and
quantity of conductive metal particles in oil flow has been
emphasized hereinabove, it will be understood that the
- 18 -
107~75~6
apparatus of this invention is capable of sensing thepresence of any conductive material in oil flow which has
- a specific gravity grea-ter than the oil. Thus, the presence
of water in the oil flow can be sensed by the apparatus of
this invention and in fact, there will be a tendency for
moisture to settle on the sensor pill whenever an en~ine
remains idle for an extended period of time under conditions
which would promote the condensation of moisture within the
oil system. In marine applications for diesel engines,
it would be highly desirable to sense the presence of salt
water, for example, in the oil flow system. However, in
mos-t applications the moisture will tend to evaporate ~rom
the oil when it is heated, due to the operation of the
enyine. Thus it is to be expected that the apparatus of
this invention will often yive a warniny indication aEter
an enyine to which it is applied has remained idle for an
extended period of time. The length of time required to
evaporate the moisture from the sensor pill in operation
may give some indication of the quantity of water present
in the oil flow and thus could be expected to provide some
indication as to the source of the water and the severity
of the condition.
I-t is also to be expec-ted that nonconductive
contaminants will tend to accumulate on the sensor pill.
For example, in yasoline engines, a sludge comprised of
tetraethyl lead will tend to build up on the sensor pill.
However, such sludge will be removed whenever the drain
plug is removed in order to change the engine oil. Thus,
a build-up of nonconductive contaminants on the pill will
tend to be prevented by the normal maintenance procedures
followed in connection with all engines.
-- 19 --
~)7~
~ .
It is believed that those skilled in the art will
make obvious modifications and changes in the specific
embodiments described hereinabove and shown in the attached
drawings in order to adapt the apparatus for specific applica-
tions. In particular, the specific dimensions mentioned
hereinabove subject to the limitations as specifically
described may be changed and it is anticipated that various
electrical circuitry could be used to provide the necessary
audio and visual warnings or readings t.o indicate the presence
of conductive materials in the oil flow system.
- 20 ~
