Note: Descriptions are shown in the official language in which they were submitted.
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A pneumatic pressure sensor device
FIELD OF THE INVENTION
This invention relates to a pneumatic pressure sensor switch device
for a pneumatic tire, with means for mounting it in the inflation chamber
of the tire.
PRIOR AR~
Such devices are known in different embodiments, in which the pres-
sure in the inflation chamber in the tire is compared with a reference
pressure by having these pressures act on both sides of a flexible dia-
phragm separating both pressures. If the pressure in the tire becomes
hazardously low, the reference pressure makes the diaphragm flex as to'
close electrical contact means to give a signal to the outside. To this
end there is a battery and a radio transmitter taken up in an electric
circuit with these contact means. Such signals may be received by a
receiver outside the tire, e.g. in the driver's cabin of the vehicle, and
there be transformed into an audible and/or visible warning signal.
The reference pressure may be the pressure exerted on the diaphragm
by a mechanical spring or by a gas. In the first case (USP 4,048,614 to
Shumway) the sensor reacts when the pressure in the tire drops below a
predetermined absolute pressure. This is not very accurate in view of
mechanical tolerances and because the spring has to be taken up in a
chamber, which cannot be hermetically sealed and in which the air
pressure varies with the air pressure in the tire. The entire structure
is complicated and w lnerable. Means to vary the tension of the spring
allow different settings of the pressure, at which an alarm is given.
In the second case, applying a gas to exert the reference pressure
(USP 4,890,090 to the applicant) a diaphragm is used, which is slightly
pervious to air. Thereby the gas pressures in the tire and in a chamber
for the reference pressure, in contact with the diaphragm, tend to equal-
ize gradually. As soon as the pressure in the tire drops hazardously, the
pressure in the reference rh~mh~r cannot follow this pressure drop imme-
diately, so that the diaphragm is flexed to close the electrical contact
means, by which a signal is given to warn about a hazardous situation.
This has the advantage that no signal is given during considerable
~I~ENDED S~lEFr
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pressure differences in the tire, which are only due to normal deviations
in operation, such as differences in inflation pressure and pressure
differences owing to varying temperatures, e.g. between cold storage of
the vehicle during the night and heavy traffic under high load, sllnshin~,
etc. during hours of operation. Vehicles stored for extended periods, in
which tire pressure drops due to permeability of tire casing, will not
set off the alarm.
Another such sensor, shown in US-A-3,810,090 is embodied as a dimple
or bu~kl ;ng switch, in which a metal diaphragm buckles outwardly to close
an electric circuit if the tire pressure drops too much. The diaphragm
forms one wall of a gas filled, hermetically sealed chamber.
There are also such devices trapping air to give the reference
pressure in a closed space when a sensor with this space is screwed
externally on the valve stem of the tire (USP 5,040,562 to Achterhold).
In USP 4,701,742 (Ruehr) a pressure sensor is given, screwed into
and partially outside the rim of a vehicle wheel, having a closed chamber
with gas at a reference pressure therein. The chamber is bordered by two
diaphragms, one exposed to the pressure in the inflation space of the
tire, the ot~er one expose~ to at~osp~eri~ ~r~ssure. T~e first ~iaph~a~
makes contact in an electric circuit if the tire pressure is correct and
moves out of contact when this pressure is too low. The other diaphragm
makes contact in the electric circuit when the pressure in the reference
chamber becomes too low, so that it can be refilled. Temperature compen-
sation between the inflation space in the tire and the reference chamber,
as explained below, is only partly obtained, the device is not fail safe
as small leakage of an O-ring or diaphragm will produce a leaking tire,
and its battery will soon be depleted as the electric circuit is closed
at correct tire pressures.
OBJEÇT OF INVENTION
In many cases there is the need to have sensors of such type react
as accurately as possible to absolute pressures in the tire, if such
pressures become too low, and it is the main object of this invention to
provide such sensors with a simple and improved design and reliable
operation, as little as possible sensitive to mechanical tolerances and
temperature differences.
AMENDED S~lELT
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SUM~ARY OF I~VENTION
Starting from the device known from said US-A-3,810,090, which shows
a pneumatic pressure sensor switch device for a pneumatic tire, compris-
ing means for mounting said switch device fully inside the inflationchamber of the tire, a sensor having a hermetically sealed closed chamber
filled with gas, one of the walls of the chamber being a flexible dia-
phragm, of which the surface remote from the chamber is exposed to the
pressure in the inflation chamber of the tire, a movable electric switch
contact point cooperating with a stationary switch contact point on the
chamber, said movable contact point being movable with the diaphragm so
that the diaphragm moves said contact point out of contact with said
stationary contact point at predetermined pressures in the tire and
allows said contact points to make electrical contact at lower pressures
in the tire, said sensor being taken up in an electric circuit with means
to take up a source of electric energy and a transmitter to give radio
signals to the outside of the tire when said circuit is closed.
Such a device is, according to the present invention, characterized
in that said closed chamber is filled with gas of a pressure above atmo-
spheric pressure and is bordered, in its wall opposite the diaphragm, bya second flexible diaphragm, separating said chamber from a second closed
chamber filled with gas, the second diaphragm carrying said movable con-
tact point so that, at increasing pressures in the tire, the first said
diaphragm compresses the gas in the first said closed chamber so that
this gas moves the second diaphragm with its movable contact point in the
direction to bring it out of contact with said stationary contact point.
In this way it is simply and reliably obtained that the switch
device can be made small and reliable in operation and can be provided
with thin walls, mainly of metal, so that the gas in the chamber rapidly
takes up the temperature of the air in the inflation space of the tire,
thus giving an automatic temperature comr~n~ation for normal variations
of the temperature within the tire, as the gas in the chamber will vary
in pressure proportional to the variation of pressure by temperature
changes in the tire. This will be more fully obtained if the pressure in
the chamber is close to normal operating pressures in the tire, although
deviations, taking e.g. into account the resiliency of the diaphragm, are
possible, depending also on the amount to which the tire pressure is
allowed to drop before a warning signal is required. The gas pressure in
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the closed chamber is and should be the main parameter and contributor to
the trip point at which a signal is given.
The closed chamber protects the electric contacts against fouling.
PrePerably, this chamber is filled with an inert gas such as nitrogen or
argon.
As therein the first diaphragm moves the second one by compressing
- the gas between them, no mechanical means such as a spring moved mechani-
cally by the first diaphragm are necessary, while the electrical contact
means can be mounted entirely inside the sensor, fully protected against
moisture and dirt. Moreover, there is the least possible influence of
changes of temperature in the tire on the correct result as the closed
chamber between the diaphragms will rapidly take up the temperature
inside the tire so that its gas pressure changes in the same direction
and about to the same amount as the air pressure in the tire. This mea~s
that a warning signal can be given if the tire pressure has a predeter-
mined pressure difference below the desired and safe pressure even if
this pressure changes with temperature.
It may, however, be preferred to embody the invention in another
way, by having a movable spring contact in the first closed chamber,
moved by the first diaphragm to open and close the electric circuit.
In electrical series connection with the contact points of the first
diaphragm and first closed chamber there may be a set of contact points
operated by a further flexible diaphragm, bordering a further closed
chamber with lower gas pressure, said diaphragm being also exposed on one
side to the pressure in the inflation chamber of the tire so that, at
atmospheric pressures therein, or with the sensor outside the wheel, such
as during storing or shipping, manufacture or assembly, the electric
circuit is interrupted to avoid depletion of the battery and unnecessary
alarm signals.
There may also be, instead of or supplementary to such a further
diaphragm and chamber, a roll switch interrupting the electric circuit
when the device is not rotating and is closed when the roll switch body
is moved by centrifugal force to cause electrical contact to be estab-
l;~h~d between this body and another part of the circuit in the device.
If the roll switch body is provided in one of the closed gas chambers, it
will also be protected against corrosion, dirt and moisture. Roll
switches are known as such, but the invention proposes to mount a roll
switch body and the concerning electrical contacts within a closed gas
fn ~T
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chamber for such protection.
The invention will now be explained in more detail with reference to
the attached drawings, in which:
Fig. 1 is a section through a sensor according to this invention in
a preferred embodiment;
Fig. 2 is a section through a combination of two such sensors, oper-
_ ating in more than one pressure region;
Fig. 3 is a section through a sensor in another embodiment;
Fig. 4 is a section through a sensor of a different type useful for
understanding the invention;
Fig. 5 is a section through a sensor in an embodiment somewhat dif-
ferent from the one of Fig. 4, but also useful for underst~n~;ng the
invention;
Fig. 6 gives an axial view of the spring body of Figs 4 and 5;
Fig. 7 shows in vertical section and partly diagrammatically a
sensor device with part of wheel rim and fastening means; and
Fig. 8 shows a section and view along the line VIII-VIII in Fig. 7.
In Fig. 1 the sensor is built into a multiple-layer board, which may
be a printed-circuit-board, with layers 1, 2 and 3. These boards are only
shown in the zone of the sensor, but may extend considerably to one or
more or all sides with respect to the drawing, so as to take up further
electrical parts, leads, etc. and to provide mounting means for the
sensor on a vehicle wheel, such as by being provided with a belt slung
around the wheel and buckled thereto, or by being taken up in a casing
glued, welded or soldered to the wheel, or in any other suitable way. So,
this board carries a battery 4, a transmitter 5 and electric leads 6 and
other electric parts deemed necessary or preferable. Vide also Figs 7 and
8.
The sensor itself, indicated by 7, has three thin gastight flexible
diaphragms 8, 9 and 10, preferably of metal. So, they are electrically
conductive. They may be made from another material, conductive or not,
and in the latter case there should be separate means, metal strips or
coatings to give the required electrical conductivity. Between diaphragms
8 and 9 there is a gastight first chamber 11, filled with nitrogen at a
pressure somewhat near the normal inflation pressure (operating pressure)
in the tire. Below diaphragm 9 and bordered at its bottom by pc-board-
layer 3 is a second gastight chamber 12 filled with nitrogen at a
pressure about the same as the normal inflation pressure in the tire.
Vide below for details of these pressures.
~?.;ENDED ~EE~
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Below pc-board-layer 3 the~e is the third diaphragm lO confining
with this layer 3 a third gastight chamber 13 at a pressure slightly
above at~ospheric pressure.
The diaphragms 8, 9 and lO are so thin, that their inherent
elasticity does not play an important role in their functioning.
The electric leads 6 are e}ectrically connected to diaphragm 8 and
conducting layer 14, and by one or more local connections 15 through pc-
layer l to annular contact zone 16. Diaphragm 9 makes electrical contact
with a metal layer 17 around it, which has one or more local connections
18 through layer 2 to a metal layer l9 on pc-board-layer 3, from which a
central electrical connection 20 passes through layer 3 to terminate in a
flat contact point (zone) 21 on the bottom of layer 3. Diaphragm lO is
electrically connected to the leads 6 at the opposite end of the electric
circuit.
It will thus be clear that an electric current can only flow to
transmitter 5 if diaphragm 9 contacts contact zone 16 and if diaphragm lO
contacts contact zone Zl simultaneously.
At atmospheric ambient pressure, the diaphragms 8, 3 and lO are in
the position shown, so that no signal is given as no current can flow
because diaphragm lO does not contact zone 21.
If the outside pressure rises, diaphragm lO is pushed upwardly as
seen in Fig. l. until it touches contact zone 21, which will take place
at a pressure. depending on the gas pressure in chamber 13, e.g. at 5
psig. The electric circuit is now closed (as diaphragm 9 contacts zone
16~, so that transmitter 5 transmits a warning signal.
As the pressure in the tire rises, diaphragm 8 is further depressed,
which raises the gas pressure in the relatively small closed chamber ll
between diaphragms 8 and 9 until diaphragm 9 bends downwardly to break
contact with contact zone 16. If the normal operating pressure is e.g. 30
psig: this e.g. takes place at 27 psig pressure in the tire.
- Further rising of the pressure in the tire depresses diaphragm 8
further, without influence on the electric conditions.
This means that, at such a normal tire pressure of 30 psig, no
electric current flows and no signal is given at this and at higher
pressures.
As soon as the tire pressure drops to 27 psig or less, a signal is
given to warn that the tire pressure is too low.
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It is possible to provide-the sensor device with more than one of
such sensors 7 with, in the chambers ll and 12. mutually different gas
pressures so that one sensor will give a warning signal at a higher
pressure than the other one. The sensors may have separate electrical
systems with leads 6 to their own transmitter, which separate
transmitters may emanate different signals, e.g. of different frequency,
for each sensor. The receiver may thus give a signal showing which sensor
activated the transmitter, so in which pressure range the tire is. There
may e.g. be three sensors giving signals one at e.g. 27 psig tire
pressure or lower, one at 24 and one at 20 psig. The sensors may,
however, have a combined electrical system, in which they are taken up in
parallel, with e.g. one transmitter only, adapted to give different
S7 gnAl .~ depending on which sensor gives the alarm, e.g. signals of
different frequency.
At the highest pressure the warning signal may e.g. be transformed
in the receiver to a visual signal only, whereas at a lower pressure the
second and possibly third warning signals are audible.
Another possibility is adapted to the fact that the same tires may
operate at different inflation pressures. So, the tire may be inflated to
a higher pressure if more load has to be taken up, also e.g. when wheels
and tires are switched from front to rear of the vehicle. It may then be
that the same tire at some moment has a normal operating pressure of 40
psig, whereas at another time this inflation pressure is and should be 30
psig. It should then be avoided that in the 40 psig-mode the sensor gives
a constant warning signal because the pressure is 30 psig, so well below
the 40 psig. This is according to the invention obtained by applying two
such sensors in the way as shown in Fig. 2. This device allows a warning
signal to be given in a pressure range below the highest desired operat-
ing pressure but above the lower operating pressure. E.g. a warning
signal may be given at tire pressures between 33 and 37 psig and between
27 and 5 psig only.
The two sensors 7 and 7' are mounted in the same laminated pc-board
l, 2, 3. The lefthand sensor 7 is entirely the same as the one of Fig. l
apart from electrically conductive coatings instead of the local connec-
tions l~ and 18. This means, assuming the gas pressures in the closed
~ chambers ll, 12 and 13 to be the same as described above for Fig. l, that
through sensor 7 no current is allowed to pass at atmospheric outside
pressures and at outside pressures above 27 psig, but electric current
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passes and can ~enerate a warnlng signal in the transmitter at pressures
in the tire of 27 psig and lower, down to 5 psig.
The sensor 7' may have a common connection to the battery, etc. with
sensor 7, as its diaphragm lO' is electrically connected to diaphragm lO
of sensor 7. All the other diaphragms and conductive parts of both sen-
sors are separated. The gas pressure in chamber ll' may e.g. be about 40
psig, chamber 12' may be at a pressure of about the same height and
chamber 13' may be at say 33 psig in the condition shown and at atmo-
spheric pressure on the outside. If the tire pressure is 40 psig or
higher, diaphragm 8' will keep diaphragm 9' out of contact with its
stationary contact zone on pc-board-layer l. At pressures of say 37 psig
~nd lower, diaphragm 8' will bulge out and will cause diaphragm 9' to
take up the position shown so as to make contact. Diaphragm lO' will be
pressed against its stationary contact zone at higher pressures until the
outside pressure drops to e.g. 33 psig and lower, at which pressure the
gas in chamber 13' pushes diaphrag~ lO' down out of contact with its
stationary contact zone.
This means that a signal is given at tire pressures between 33 and
37 psig and at pressures between 5 and 27 psig. No signal is given
between 27 and 33 psig pressure in the tire. For the higher operating
pressures the lefthand sensor 7 will not give a signal until the tire
pressure will have dropped far too much, when the other sensor 7' will
already have given the alarm. So, there is no undue loss of electric
energy and there is a selective warning depending on operating pressure.
Sensor 7 may be connected at its top at 8 to another transmitter or
other means in the same transmitter than sensor 7' by its top conductive
part 8', to distinguish between the two alarms at the receiver side.
In all cases, the gas in the sensor chambers ll, 12, ll' and 12' and
~3' easily takes up the same temperature as the air in the tire by the
good conductivity of the metal diaphragms. This means that the pressures
therein will rise and fall due to temperature differences to about the
same amount as the pressure in the tire. This good temperature compensa-
tion has the advantage. that a signal is given i~ the tire pressure is a
certain amount below what is the normal operating pressure in the tire,
notwithst~n~;ng the fact that this operating pressure may vary rather
considerably.
~ or chamber 13 the pressure is too low and thus too different from
the normal pressure in the tire to give considerable temperature compen-
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sation in this sense, but this is not necessary for this chamber and the
pressure at which diaphragm 10 contacts zone 21 may well remain about at
the same low value such as at 5 psig.
As to the gas pressures in the sensor, there may be a ~as filling
passage through part of the layers 1, 2, 3 into the closed ~h~h~r5. In
manufacturing the sensors, the pressure at which it has to give a signal
is exerted on diaphragms 8 (and 8') and 10 (and 10') in a suitable
apparatus taking up the sensor. Chamber 11 is now filled to the somewhat
higher normal operating pressure of the tire. Chamber 11 is now sealed
and chamber 12 is filled with gas under pressure until diaphragm 9 makes
contact with zone 16, after which the gas passage to chamber 12 is
sealed. It is thus certain that the "trip-point", the outside pressure,
at which a signal is given, is at the desired value.
Chamber 13 does not give a problem as it is filled with gas at a
pressure only slightly above atmospheric and not very critical.
Sensor 7' of Fig. 2 is made in the same way, but with the higher
pressure, e.g. of 40 psig, in chamber 11' and a pressure of e.g. 33 psig
in chamber 13'. The filling of ~h~mher 12' also takes place up to a
pressure, at which a signal is given. In this case, the pressure of
filling of chamber 13' is more critical than for chamber 13.
The movements of the diaphragms as described can in fact be limited
to even parts of a milli~eter, This makes it essy not to rely on inherent
elasticity of the diaphragms, which can be very thin and very flexible,
so that the trip points are only negligibly affected by the diaphragms
2~ and are overridingly determined by gas pressures in the closed chambers.
Fig. 3 shows a sensor much resembling the sensor of Fig. 1, with
essentially the same parts 1 to 9, 11 and 12, but with conductive layers
1, 2 and 3, so that conducting parts 15-20 are superfluous. Fig. 3 shows
a different embodiment of the means to interrupt the electric circuit
when the device is not in operation. The chamber 13 and its flexible
diaphragm 10 of Fig. 1 are here omitted and replaced by a roll switch 22,
consisting of an annular metal body, vertically (as seen in Fig. 3)
movable by centrifugal force and restrained and urged downwardly by a
metal spring 23, 24 being star-shaped and having a central circular part
23, riveted to metal layer 3, and three radially extPn~;ng prongs 24
urging body 22 to its lowest position. If the device is mounted in the
inflation chamber of the wheel so that body 22 will move outwardly
~upwardly as seen in Fig. 3) by centrifugal force if the wheel rotates at
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at least a certain speed, body 22 will then contact diaphragm 9 with its
top edge and thus close the electric circuit between layer 3 and
diaphragm 9. If the wheel is stationary, ~ody 22 is kept in a lower
position by prongs 24 so as not to contact diaphragm 9, so that this
electric circuit is interrupted. This is particularly helpful to avoid
nnec~Sary alarm signals generated and thus depletion of the battery for
e.g. trucks stored without moving during longer periods of time.
Means may be applied to give an electric signal to the outside as
soon as roll switch 22 contacts diaphragm 9 for the first time after such
a period of inactivity, to show to the driver that the system is
potentially active ~even if the tire pressure is correct), after which no
such signal is transmitted.
Diaphragm lO and chamber 13 of Fig. l are now superfluous, as roll
switch 22 avoius any closing of the electric circuit if the wheel does
not rotate. In some cases it may, however, be desired to maintain this
diaphragm lO and cham~er 13, e.g. for one of the sensors of Fig. 2, in
order to operate at a certain desired pressure, and in such a case such a
~h~m~er 13 and diaphragm lO may easily be mounted to the bottom of body 3
in Fig. 3, as will immediately be clear.
The sensor o~ Fig. 4 is essentially circular in shape. It has an
annular bo~y 2~ of electrically non-conductive and gas-impermeable
materi~l such as Perspe~ or P1~X;g1AC~ a transparent resin of
polymethylmetacrylate.
A chamber 26 of metal such as a copper alloy or a stainless steel is
pressed with a gas-tight fit into the annular body 25. At both sides of
body 25 a ~langed ring 27, 28 of metal is tightly connected thereto and
secured to the flange of each ring as by soldering or welding is an
electrically conductive diaphra~m 8, lO. Diaphragm lO is, also in
unloaded condition, curved so as to be concave at the outside. The
opposite ~other) diaphragm 8 is curved oppositely, i.e. so as to be
convex at the outside.
The chamber 26 has in the center of its bottom, as seen in Fig. 4, a
somewhat dome-shaped part 29, acting as an electric contact cooperating
with diaphragm lO. It is iUst out of contact with diaphragm lO at atmo-
spheric ambien~ pressures. In its top surface, as seen in Fig. 4, thischamber 26 has an opening 30. Between body 25 and diaphragm 8 a spring
contact body 31 is provided, vide also Fig. 5. This has an outer annulus
32, fixed between body 25, ring 27 and diaPhragm 8 so as to be in
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11
electric contact therewith, and a spring contact arm 33 bent out of the
plane of annulus 32 in a way which is clearly shown in Fig. 4 and so as
to have an elbow 34 positioned close to the center of diaphragm 8, vide
also Fig. 6. This contact 31 is of a resilient metal. e.g. as usual for
small disk or leaf springs. In its unloaded condition the arm 33 contacts
the edge of opening 30 of chamber 26 at 35.
In this way there are formed two spaces 36 and 37 in this sensor,
both gas tight. Space 36 is filled with a gas of low pressure, which may
range from vacuum to somewhat above atmospheric, but preferably its
pressure is about atmospheric.
Preferably it is filled with an inert gas such as nitrogen or argon.
This has the advantage of avoiding corrosion of the electric contact
parts. With some pressure in it, it tends less to leakage into it than
full vacuum would do.
Space 37 is filled with gas, preferably the same gas as space 36, at
a much higher pressure, in the range of the normal inflation pressure in
the tire.
The chamber 26 may have an upstanding edge part 38 to avoid
diaphragm 8 from deforming permanently and from pushing arm 33 too deeply
20 into chamber 26 by being pushed down too much if the tire would be
inflated to too high a pressure.
~iaphragm lO is electrically connected to the electric circuit again
including a battery 4 and a radio transmitter 5 and is electrically
connected to diaphragm 8.
Fig. 5 shows such a sensor in a somewhat different embodiment. The
chamber 26 differs from the one of Fig. 4 in that it is more shallow, its
bottom having a pin-shaped part 40, the bottom of which replaces the
dome-shaped part Z9 of Fig. 4. This part 40 is surrounded by and securely
housed in the transparent mass of body 25 at 41 as shown, in which body
30 25 space 36 is recessed.
Fig. 6 is a view of spring contact 31 as described above and as
applied both in Fig. 4 and in Fig. 5.
The operation of the sensor device of Fig. 4 and 6 is as follows.
Even with the battery installed and at atmospheric ambient pressure, e.g.
in storage or on a vehicle wheel with the tire removed or not inflated,
diaphragm lO will not contact dome-shaped part 29 of chamber 26, so that
no electric current can flow from battery 4 to casing 26, diaphragm 8 and
transmitter 5.
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If the tire is inflated, diaphragm lO will be depressed to contact
part 29 of chamber 26, so that current flows via spring-contact 31, 32
(at 35) to diaphragm 8 and so to the transmitter 5. This will thus
transmit signals to a well-known receiver outside the tire, e.g. in the
driver's cabin, where it will give an audible and/or visual signal to the
driver.
On further inflating the tire to a safe operating pressure,
diaphragm 8 will be further depressed until it contacts the top 34 of the
bent-out spring contact arm 33 to depress it so that contact at 35
between arm 33 and casing 26 around opening 30 is broken. The transmitter
5 is thus deactivated and no signal is given to the driver.
This means that, at safe operating pressures, there is contact
between diaphragm lO and part 29 of casing 26, but no signal is given as
spring contact 33 is out of contact with casing 26 at 35, that no signal
is given at atmospheric pressure because contact between diaphragm lO and
part 29 is broken, and that a signal is given at intermediate pressures
in the tire, which are at a hazardous low value.
For the sensor of Fig. 5 the operation is the same, but ~oLeover the
spring contact 33 will reach the bottom of chamber 26, which here is
rather shallow, if the tire is inflated too much, well above normal
operating pressures. Thus the electric circuit will be closed at too high
pressures in the tire, causing a warning signal to be sent by the
transmitter 5.
Figs 7 and 8 show one way of mounting of such sensors to the re-
mainder of the switch device and of this device to a vehicle wheel. InFig. 7, 42 is part of a rim of a vehicle wheel. The sensor switch device
43 includes a housing 44 of plastic material, having at each end a
bracket 45 with a slot, through which can pass a thin steel strap 46 so
as to keep housing 44 fixedly mounted to the wheel. The strap 46 has the
usual means to be kept closed and under some tension, such as a suitable
buckle not shown.
In the housing 44 there is mounted a PC-board 47 carrying in the
usual way the electric parts and printed electric leads of the device.
These include the sensor 7, battery 4 and transmitter ,, the leads
between them not being shown. Fig. 8 shows that there are two such
sensors 7 side by side. They may be mounted on the PC-board 47 by ma~ing
H-shaped holes therein, so that the sensors can easily be connected both
me~h~nically to the PC-board as electrically to the relevant electric
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13
leads and other parts thereof. The two sensors 7 may be identical in
shape and dimensions, but filled with gas in their chambers 37 of mutu-
ally different pressures, so that e.g. a visible signal is generated at
- too low but not yet dangerous pressures in the tire, whereas the other
sensor causes an audible signal to be given at a lower pressure in the
tire, which is more dangerous. There may even be three of such sensors
reacting to different pressures in the tire and they may be embodied and
combined in the way as shown and described in and with reference to Fig.
2.
Instead of a PC-board there may be another carrying surface with
electric leads and parts mounted thereon in other ~nown ways.
In a way known as such there may be a receiver in or at the driver's
cabin with means to give an audible and/or visible signal if the trans-
mitter 5 emits signals representing a warning about the pressure condi-
tion in the tire.
~4 0 ..,
