Note: Descriptions are shown in the official language in which they were submitted.
~14S~3~>9
Background of the Invention
This application pertains to the art of telemetry
systems for warning of abnormal conditions and, more
particularly, to wheel mounted telemetry systems for
monitoring the condit;ons of pneumatic vehicular tires.
The invention is particularly applicable to systems for
monitoring automobile tires for low inflation or profile
and will be described with particular reference thereto.
It will be appreciated, however, that the invention has
broader applications, such as monitoring tire conditions
1 10 of all types of vehicles, monitoring the mechanical
movement of rotating or reciprocating machinery parts, and
the like. Further, the apparatus can monitor symptoms of
a variety of abnormal tire conditions, including
underinflation, overinflation, weakened sidewalls, and the
~5 like.
A variety of tire monitoring systems have
heretofore been proposed. Many of these systems have
included wheel mounted radio transmitters for transmitting
AM or FM radio signals indicative of the abnormal
20 condition. A central reciever received the radio signals
and produced a visual or audio signal to warn the driver
of the abnormal condition. In some systems, the carrier
frequency was amptitude or frequency modulated to enable
differentiation from stray radio signals.
One of the problems with the prior tire condition
sensing systems has been false signals. The receiver was
subject to receiving AM and FM radio signals from various
other sources, such as TV stations, radio stations, CB
radios, and the like. Even using a different range of
30 frequencies than the FCC assigns to other TV and radio
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broadcasts did not eliminate false signal problems.
Various harmonics, echoes, and tones from these signals
would cause false indications of abnormal tire conditions.
Another problem was false signals caused by road
conditions. For example, potholes and rough roads deflect
the tire profile. Many prior art tire sensing systems
could not distinguish between an abnormally low tire
profile caused by underinflation and an abnormally low
tire profile caused by impacting a pothole or other
1~ roughness in the road surface. Brick, cobblestone, or
other washboard road surfaces are especially hard to
distinguish from underinflation.
Another problem with prior art sensors has been
the cost and reliability in meeting FCC regulations. The
FCC has assigned a band of frequencies which may be used
for this purpose. However, the FCC requirements limit the
duration of broadcasts and the periodicity of broadcasts
severely. To meet these FCC requirements, various clocks
were employed. However, such clock systems were
e~pensive, and in some instances were unreliable under the
extreme temperature, centrifugal force, and impact
I conditions to which wheel-mounted sensors are subject.
The present invention contemplates a new and
improved apparatus which overcomes all of the
above-referenced problems and others, yet provides a tire
condition sensing system which is simple to construct,
highly reliable, and low in cost.
Su_mary of the Invention
In accordance with the present invention, there
is provided an abnormal tire condition sensing and
indicating system comprising one or more telemetry means
and a common receiver means. Each telemetry means is
adapted for mounting adjacent a pneumatic tire of a
vehicle for sensing the tire's condition. Upon sensing an
abnormal tire condition, each telemetry means transmits a
digitally modulated radio signal. The receiver means
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receives the digitally modulated radio signal and
indicates the abnormal tire condition.
In accordance with another aspect of the
invention, an abnormal tire condition indicating system is
provided which comprises a transducer means for detecting
the abnormal condition and for producing electrical pulses
in response thereto. An accumulator accumulates these
pulses until a predetermined level is reached. When the
predetermined level is reached, a digita~ encoder provides
a digitally coded signal for modulating a carrier
frequency. A transmitter includes means for generating a
carrier frequency. The transmitter is connected with the
digital encoder to receive the digitally encoded signal
for modulating the carrier frequency. A receiver received
the transmitted radio signals. The receiver means
recognizes the digital code and provides and ahnormal
condition warning signal in response thereto.
In accordance with a more limited aspect of the
invention, the predetermined level of the accumulator is
so selected that the abnormal condition must be sensed in
a sufficient number of revolutions that false signals from
rough road conditions and the like are reduced below an
acceptable level, and such that a sufficient number of
revolutions of the wheel must occur that the wheel
rotations provide the timing for meeting the FCC
regulations.
A principal advantage of the invention is the
freedom from false signals caused by stray radio signals,
television signals and harmonics thereof
Another advantage of the present invention is the
great reliability achieved with relatively simple and
easy-to-produce circuitry.
Other advantages of the present invention will
become apparent to those reading and understanding the
detailed description of the preferred embodiment which
follows:
ll~S~;Z9
Brief Description of the Drawings
The invention may take physical form in certain
parts and arrangement of parts, a preferred embodiment of
which will be described in detail in this specification
and illustrated in the accompanying drawings which form a
part thereof.
Figure 1 illustrates an abnormal tire condition
sensing and indicating system in accordance with the
present invention including telemetry units in combination
with the wheels and pneumatic tires of a vehicle and a
central receiving and indicating unit;
Figure 2 illustrates an electronic circuit for
the telemetry units of the abnormal tire condition sensing
and indicating system of Figure l;
Figure 3 is an alternate embodiment of the
circuit of Figure 2; and
Figure 4 illustrates an exemplary electronic
circuit suitable for use in receiving and indicating unit
in Figure 1.
Referring now to the drawings, wherein the
drawings are for the purpose of illustrating the preferred
embodiment of the invention only and not for purposes of
limiting it; Figure 1 illustrates a vehicle with a
plurality of wheels, each having a pneumatic tire mounted
thereon and a telemetry means A mounted between the wheel
and the inner surface of the pneumatic tire. When one of
the telemetry means senses an abnormal tire condition, it
produces a radio signal indicative thereof. Mounted in a
central location in the vehicle is a receiving means B for
receiving the radio signals from each of the telemetry
30 means and providing the driver with an indication of the
sensed abnormal tire condition.
As illustrated in Figures 2 or 3, each of the
telemetry means includes a transducer means C for
producing electrical pulses with rotation of the wheel in
response to a sensed abnormal condition. An accumulator
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means D accumulates the pulses ~rom the transducer means C
until a predetermined level is accumulated. When the
predetermined level is attained, the accumulator enables
an encoder means E for producing an encoded modulating
signal for a transmitting means F. Transmitter means F
generates a carrier signal that is modulated by the
encoded modulating signal.
As illustrated in Figure 4, receiving means B
includes a radio signal receiving means G for receiving
10 radio signals from each of telemetry means A. A decoder
H determines whether the received radio signals are
moduIated with appropriate encoded signals. Th~e decoder
means on detecting the appropriately encoded signal
actuates an indicating means I which produces an
15 indication of the abnormal tire condition. In an
alternate embodiment in which each te~emetry means has a
distinct code, indicator means I further indicates which
telemetry means sensed the abnormal condition.
Looking now to a preferred embodiment of
20 telemetry means A in more detail, reference is made to
Figure 2. Transducer means C includes a housing 10 which
is adapted to be mounted to the wheel or the wheel rim of
a vehicle. Slideably mounted in housing 10 is a
mechanical member 12. Mechanical member 12 is so
dimensioned that when housing 10 is mounted on the wheel
rim, its outer end is adjacent the inside surface of the
pneumatic tire. The mechanical member 12 is sufficiently
short that when the tire is properly inflated, the inner
surface of the tire does not impact the member at any
point of the revolution. However, the mechanical member
is sufficiently long, that when the tire is underinflated,
the inner surface of the tire impacts the member as the
member passes the low or road contact point of each
revolution. Mechanical member 1~ may be a stiff but
bendable material, such as hardened rubber or plastic to
inhibit breaking or permanent deformation by a badly
underinflated or flat tire. The inner end of the
mechanical member abuts a piezoelectric transducer 14 in
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the form of a wafer. When the mechanical member is impacted,
it deflects the piezoelectric wafer into a small depression
16 in the housing so that impacts upon mechanical means 12
may bend the piezoelectric crystal a controlled amount. It
is a property of piezoelectric crystals that compression
of deflection of the crystal will cause a potential across
the crystal. Electrical connections are made to one surface
of the wafer 14 and a conductive substrate 18 along the
opposite surface of the crystal. These connections convey
the electrical impulses generated when the mechanical member
12 is impacted.
Suitable piezoelectric crystal wafer which include
conductive layer 18 are sold by Vernitron under the trade
mark of Unimorph, by Gulton under the trade mark CATT, and
by Linden under the trade mark of Piezo-Ceramic Disc Benders.
All three of these piezoelectric elements are sold for
transforming an oscillating electric potential into an
acoustic, siren-like noise.
Other transducer means may also be used. For
example, a battery and electric switch could be mounted in
the housing for producing electrical pulses when the abnor-
mal tire condition is sensed. Alternately, a generator
powered by revolution of the wheels may replace the battery.
Other abnormal tire conditions than underinflation
may be sensed. For example, overinflation may be sensed by
positioning the mechanical member so as to be impacted under
normal inflation but not impacted under overinflation. In
such an embodiment, the logic of the circuitry is inverted
to produce radio signals when the member is not impacted.
; 30 As another alternative, the transducer means may sense
erroneous mechanical movement of machinery parts. This may
be accomplished, for example, by positioning mechanical
member 12 adjacent the path of travel of a reciprocating ele-
ment with such spacing that excessive travel causes the
reciprocating element to impact the mechanical member 12.
~ he accumulat~r means D receives the electrical
.~ - 7 -
11458;~9
pulses from the transducer means. If the transducer means
does not produce pulses of a single polarity, as is the
case with piezoelectric transducers, the accumulator means
may include a rectifier means 30. In the preferred
embodiment, the rectifier means is a full-wave diode
bridge.
The undirectional pulses from rectifier means 30
increase the stored charge in a storage means 32. The
charge storge means includes a storage capacitor 34 upon
10 which an electrical potential is stored and a threshold
detector means 36 which detects whether the stored charge
exceeds a predetermined level. The potential is increased
with each pulse from rectifier means 30. When the stored
charge reaches the predetermined threshold potential, an
output signal is provided. The predetermined threshold
potential is determined by the breakdown potential of a
zener diode 38 and a resistive voltage divider 40. When
the predetermined potential is reached, a first transistor
42 is gated to its conductive state which, in turn, gates
solid state switching means or second transistor 44 to
become conductive. When second transistor 44 becomes
conductive, a regulator network 46 and a counter means 50
re actuated. In the regulator network, a third solid
state switching means or transistor 48 becomes conductive
to supply regulated power to encoder means E and
transmitting means F. The encoder means draws power until
the stored potential is drained to a voltage level defined
by a zener diode 49 of the regulator circuit. When the
potential across zener diode 49 is equal to its breakdown
voltage, transistors 42, 44 and 48 are gated off. This
stops the drainage of capacitor 34 starting the next
charging cycle. Thus, regulating means 46 proviaes
encoder means E and transmitting means F with an operating
potential which exceeds the minimum power required for
operating these means. Counter means 50 includes a
counter 52 which increases its count with each high output
caused by transistor 44 becoming conductive. When counter
52 reaches a predetermined count, it enables solid state
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g
switching means 54 to produce an enable signal. The
enable signal produces one of the outputs of the
accumulator and actuates a reset means 56 for resetting
counter 52.
With the piezoelectric transducer of the
preferred embodiment, about 16 or 17 revolutions are
required to charge the capacitor 34 to its predetermined
potential level. The number of revolutions varies with
the strength of the impact upon piezoelectric transducer
14 by mechanical member 12. Thus, after each 16 or so
times that the abnormal tire condition is sensed,
transistor 44 becomes conductive and increases the count
on counter 52 by one. It has been found that counting
about lSO occurrences of the abnormal tire condition is
sufficient to differentiate between rough road conditions
and an underinflated pneumatic tire. Thus, if c~unter 52
is set to count 9 before producing the enable signal and
resetting itself, relative freedom from erroneous signals
from rough roads is achieved. The time between successive
enable signals will, of course, vary with the speed of the
vehicle and the circumference of the pneumatic tire. For
some vehicles at some speeds, liO revolutions of the wheel
will occur at shorter intervals than the FCC requirements
on periodicity of radio transmissions allow. Using a
counter which counts to 18 has been found sufficient for
assuring that the FCC periodicity requirements between
successive radio transmission cycles is met.
The encoder means E produces an encoded signal
for modulating the carrier frequency of the transmitting
means F. In the preferred embodiment, the encoder means
provides a digitally coded signal. More specifically, the
digitally coded signal is a series of square waves at
regular intervals. Each square wave pulse has the same
height but its duration may vary. For example, a square
wave for indicating a binary one may fill 3/4 of the
interval between successive square waves and the square
wave for indicating a binary zero may fill 1/4 of the
interval. A suitable encoder for producing this digitally
114S8~9
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encoded signal can be found in U.S. Patent No. 3,906,348
issued September 16, 1975, to Collin B. Willmott. Other
digital codes may also be used, such as a trinary code of
circuit chips produced by National Semiconductor
Corporation.
The encoder means is connected by transistors 44
and 48 to the charge storage capcitor 34. Encoder means
is designed to draw power from the charge storage means
more rapidly than the transducer means supplies power.
Thus, each time transistors 44 and 48 are rendered
conductive, encoder means E discharges the stored
potential and allows the charging cycle to be repeated.
The rate at which encoder means E and transmitter means F
consume the electric potential stored on capacitor 34
determines duration of each radio broadcast. By
appropriately selecting the rate at which encoder means E
and radio transmitter F draw power or alternately
selecting the size of capacitor 34, the duration o each
radio broadcast may be selected to comply with the FCC
; 20 regulations~
I The transmitting means F includes a control means
60 for controlling the transmissions of encoded radio
signals. Control means 60 includes an AND gate 62 and the
transistor 64. One input of AND gate 62 is connected with
counting means 50 to receive the enable signal therefrom.
The other input of AND gate 62 is connected to the output
of encoder means E. Whenever the enable signal from the
counting means is high and the output from the encoding
means is high, then, the output from AND gate 62 is
similarly high. In this way, the AND gate passes the
digitally encoded signal from encoder means E whenever
counter 52 has reached the predetermined count and
counting means 50 has produced an enable signal. However,
until counter means 50 reaches the predetermined count,
35 AND gate 62 blocks the output from the encoder means. The
output from the AND gate controls transistor 64 rendering
it conductive and nonconductive with the digitally coded
signal. The output from trans;stor 64 controls the
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;
carrier frequency generator 66 such that a digitally
modulated radio signal is produced by transmitting means F.
In the pre~erred embodiment, the encoded signal
is a series of square waves. Each square wave has
substantially the same amplitude but may have one of a
plurality of widths. If the code is a binary code, the
square waves will have one of two widths; a first width
corresponding to a binary one and a second width
corresponding to a binary zero. The number of s~uare
10 waves in each coded signal determines the number of bits.
For example, an eight bit signal is a series of eight
square waves.
The control means actuates the radio frequency
generating means when it receives both the enable signal
15 from the accumulator means and a square wave from the
digital encoder means. It actuates the radio frequency
generating means for short periods, each period having a
duration determined by the width of the corresponding
square wave pulse. Thus, an eight bit binary code is
20 transmitted as eight spaced, short periods of the carrier
frequency, each period having a duration indicative of a
zero or a one.
Radio signals generated by each of the telemetry
means A is received by the receiving means B. The radio
25 signal receiving means G may, for example, be an AM
superregenerative receiver. The received radio signal may
be amplified by an amplifier 80 before being conveyed to a
decoding means H. Decoding means H decodes the encoded
modulating signal of the radio signal received by radio
30 signal receiver G. A complimentary decoding means to the
encoding means described in U.S. Patent 3,906,348 is also
described therein. Similarly, National Semiconductor
Corporation produces complementary trinary code decoding
chips for their encoding chips. When decoding means H
recognizes the appropriate code, it actuates indicating
means I. Indicating means I may consist of a driver
circuit 82 and an audio or visual indicator. For example,
an electro-acoustic transducer 84, such as one of the
1:~4S~ilZ9
electric wafers described in connection with the
transducer means, may be connected with the driver
circuit. In this way, whenever one of the telemetry means
signals an abnormal tire condition, an audio signal is
produced.
If the encoding means of each telemetry means
have distinct codes, then decoding means H may have a
similar number of decoders. Each decoder enables one of
driver circuits 84, 86 or 88. Connected with each driver
10 is a visual indicating means such as light bulbs 94, 96
and 98. Driver circuits 84, 86 and 88 may further include
hold or delay circuits so that their respective light bulb
remains illuminated continuously although radio signal
receiving means G only receives abnormal tire sensing
15 conditions intermittently. Further, the indicating means
may include both audio and visual indications, such as an
audio signal of relatively short duration when any
abnormal condition is initially sensed and visual
indications which indicate both the abnormal condition and
its source.
Figure 3 illustrates an alternate embodiment of
telemetry means A. In Figure 3, corresponding parts to
the embodiment of Figure 2 are marked with like reference
numerals followed by a prime, ('). The accumulating means
in Figure 3 receives pulses from the transducer means C
and conveys them to a rectifier means 30' to convert the
pulses to pulses of a single polarity. Single polarity
pulses are conveyed to a charge storage means 32' which
includes a charge storage capactior 34' and threshold
30 detector means 36'. With each pulse from rect;fier means
30' electrical potential is accumulated. When the
potential on capacitor 34' reaches the predetermined
threshold level as determined by the breakdown voltage of
diode 38' capacitor 34' is connected to counting means
50'. After the threshold level is reached, charge storage
means 32' functions as a power supply for the counting
means.
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Each pulse from the transducer means is also
conveyed to a Schmitt trigger 100. Whenever the
transducer pulse is of sufficient amplitude, Schmitt
trigger 100 produces an output pulse of fixed amplitude
and duration. The output pulse from the Schmitt trigger
is conveyed to a counter 102 which counts the number of
pulses of the prescribed amplitude produced by the
transducer means. When charge storage means 32' has
reached the predetermined threshold level to supply power
10 to counter means 50', counter 102 increases its count with
each pulse from Schmitt trigger 100. When it reaches a
predetermined number of counts, it triggers solid state
switching means 54'. Switching means 54' comprises a flip
flop 104 and a transistor 106.
When the solid state switching means is
triggered, transistor 106 connects the charge storage
means with encoding means E to enable it. When the
transistor 106 enables encoding means E with a power
supply, it starts producing the digitally coded signal.
The output of encoding means E is connected to a reset
I means 56'. The reset means includes a counter 110 for
counting the square wave pulses from digital encoding
means E. When counter 110 reaches a preselected number,
it resets counter 102 and flip flop 104. The
predetermined number for counter 110 is determined by the
number of bits in each decoded signal and the number of
times each encoded signal is to be transmitted. For
example, if an 8-bit signal is to be transmitted ten
times, then the predetermined number is 80. Reset counter
110 in turn is reset by flip flop 104 each time counter
102 reaches its predetermined number.
Transistor 106 in addition to enabling encoder
means E also enables transmitting means F. Transmitting
means F includes a control means 60' which receives the
enable signal from transistor 106 and the modulating
signal from encoding means E. Control means 60' includes
a transistor 64' which controls radio frequency generator
66' with the digitally coded signal from encoding means E
to produce the digitally modulated radio signal.
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When an underinflated tire condition is sensed,
mechanical me~ber 12' is impacted by the inner surface of
the pneumatic tire at the low point of each wheel
revolution. This in turn produces a series of output
pulses from the piezoelectric crystal. These transducer
pulses are received by the accumulator means and used to
charge the charge storage means 32'. When the charge
storage means 32' reaches the predetermined potential
level, power is connected to counters 102 and 110 and flip
flop 104. Additional pulses from the transducer means
continue charging the charge storage means and are counted
on counter 102. When the predetermined number of counts
is reached, solid state switching means 54' provides an
enable signal and resets counter 110. The enable signal
is provided to encoder means E and transmitting means F.
When enabled, encoding means E starts producing a series
of digital pulses to provide the coded signal used to
modulate the carrier radio frequency. The digital pulses
from encoder means E are counted by reset counter 110
until it reaches its predetermined number of counts.
I Then, counter 102 and flip flop 104 are reset. This
renders transistor 106 nonconductive stopping encoder
means E and transmitting means F from functioning.
Counter 102 again commences counting pulses from
transistor means C and the cycle is repeated.
The invention has been described with reference
to the preferred embodiment. Obviously, modifications and
alterations will occur to others upon reading and
understanding this specification. It is our intention to
include all such modifications and alterations, in so far
as they come within the scope of the appended claims or
equivalence thereof, in our invention.
