U.S. patent application number 09/333893 was filed with the patent office on 2002-02-07 for tire pressure sensory and monitoring method.
Invention is credited to MITTAL, CHANDER P., YOUNG, JORGE A., ZHOU, JOE HUAYUE.
Application Number | 20020014115 09/333893 |
Document ID | / |
Family ID | 23304688 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014115 |
Kind Code |
A1 |
YOUNG, JORGE A. ; et
al. |
February 7, 2002 |
TIRE PRESSURE SENSORY AND MONITORING METHOD
Abstract
A tire pressure monitor method enables the reassignment of tire
pressure sensors to respective tire locations on the vehicle in the
event that the sensors are lost or replaced with new sensors having
differing identification codes. A passenger compartment monitor,
that normally monitor tire pressures through broadcast transmission
from the sensors, is manually into a identification entry mode
selecting a desired tire location, and when the vehicle begins
travel, a motion switch in the new sensor detects vehicular motion
and activates the transmission of the new identification code that
is received by the monitor that then assigns the presently selected
tire location to received identification code.
Inventors: |
YOUNG, JORGE A.; (CLAREMONT,
CA) ; MITTAL, CHANDER P.; (ROWLAND HEIGHTS, CA)
; ZHOU, JOE HUAYUE; (HACIENDA HEIGHTS, CA) |
Correspondence
Address: |
SPENCER, FANE, BRITT & BROWNE
1000 WALNUT STREET
SUITE 1400
KANSAS CITY
MO
64106-2140
US
|
Family ID: |
23304688 |
Appl. No.: |
09/333893 |
Filed: |
June 16, 1999 |
Current U.S.
Class: |
73/146 |
Current CPC
Class: |
B60C 23/0416
20130101 |
Class at
Publication: |
73/146 |
International
Class: |
G01M 017/02 |
Claims
What is claimed is:
1. A method for reassigning a sensor module for sensing tire
pressure of a respective tire in a tire pressure monitor system
comprising a monitor panel, the method comprising the steps of,
displaying tire locations on the panel, selecting one of the tire
locations, transmitting an identification code identifying the
sensor module, and assigning the identification code to the
selected tire location.
2. The method of claim 1, further comprising the steps of,
installing the sensors on a tire of a vehicle, the transmitting
step is activated to transmit the identification code when the
vehicle is in motion.
3. The method claim 1 wherein the identification code uniquely
identifies the sensor module.
4. A method for reassigning a sensor module for sensing tire
pressure of a respective tire in a tire pressure monitor system
comprising a monitor panel, the method comprising the steps of,
displaying tire locations on the panel, selecting one of the tire
locations, transmitting an identification code identifying the
sensor module, when the vehicle is in motion, and assigning the
identification code to the selected tire location, the
identification code uniquely identifies the sensor module among
many possible identification codes.
Description
REFERENCE TO RELATED APPLICATION
[0001] The present application is related to assignee's copending
application entitled Tire Pressure Sensory and Monitoring System,
Ser. No. ______, filed yy/yy/yy, by the same inventors.
FIELD OF THE INVENTION
[0002] The invention relates to the field of to a method and
apparatus for monitoring air pressure in vehicle tires. More
particularly, the invention relates to an apparatus for
automatically sensing tire pressure and methods for operating the
apparatus.
BACKGROUND OF THE INVENTION
[0003] Tire pressure sensors have long been used to sense the
pressure of tires to indicate when the tire is below a predetermine
tire pressure. These sensors use various means, typically
diaphragms screwed into tire value stems and responsive to tire
pressure for activating an electrical switch for generating an
alarm. Various types of tire monitoring systems have been used to
provide continuous vehicle tire pressure sensing and monitoring
during vehicular operation. Such systems typically include a
monitor located in the passenger compartment of the vehicle for
receiving encoded transmitted signals for respective tires and for
alerting the vehicular operator through the use of audio alarms and
graphic display indicators. The ability to selectively sense the
pressure of each tire is desirable so that the subject tire can
then be inflated to proper air pressure levels for safety and long
tire wear life. The tire sensors unidirectionally communicate with
the monitor transmitting tire pressure values received and
processed by the monitor.Hence, these systems typically have tire
pressure sensors located on the valve stems for the respective
tires each with an associated embedded transmitter for generating
respective encoded signals identifying the tire. The cab mounted
monitor has a receiver the graphic display for alerting the
operator in the event of low tire pressures.
[0004] U.S. Pat. No. 4,814,745 issued to Wang on Mar. 12, 1989
discloses a cap like signal device attached to the tire for sensing
tire pressure. The cap includes an electric alarming buzzer
responsive to a disk actuated by pressure disadvantageously without
a cab mounted monitor. The disk activates the buzzer when the tire
pressure is too low. U.S. Pat. No. 4,814,744 issued to Collins on
Mar. 21, 1989 discloses a low tire pressure warning system having a
mechanical side wall sensor with and dash alarm disadvantageous
connected by a cable. U.S. Pat. No. 4,804,808 issued to Dal Cero on
Feb. 14, 1989 discloses a pressure sensing devices that senses low
tire pressure and signal low pressure using a transmitter and cab
mounted receiver. U.S. Pat. No. 4,694,273 issued to Franchino on
Sep. 15, 1987 disclose a tire sensing device having a movable
element which activates a radio transmitter signal received by a
receiver in the passenger compartment to activate visual and
acoustic alarms. U.S. Pat. No. 5,289,161 issued to Huang on Feb.
22, 1994 discloses a tire pressure sensor having a diaphragm in a
casing. The spring loaded diaphragm is movable between two
positions. A signal producing units is activated in response to the
position of the diaphragm. The signal generated is an encoded
modulated RF signal for communicating an alarm signal to a receiver
that determines which tire is low and activates a corresponding
indication to indicate which tire has low tire pressure. Fuses in
the sensors are used to generate the respective codes to match
indicators of a display. U.S. Pat. No. 5,694,111 issued to Huang on
Dec. 2, 1997 discloses an encoder unit and transmitter circuit for
a tire pressure sensor device for generating encoded RF signals
received by a cab receiver operating a display units. U.S. Pat. No.
4,734,674 issued to Thomas on Mar. 29, 1988 also discloses a tire
pressure sensing device that, upon low pressure, transmits an
encoded signal to a cab receiver having a plurality of display
indicators on a front panel that are selectively activated to
indicate the respective tire. U.S. Pat. No. 4,737,760 issued to
Huang on Apr. 12, 1988 discloses another valve stem tire pressure
warning device having a pressure sensitive diaphragm and spring
switch for activating a transmitter signal communicated to the cab
monitor. U.S. Pat. No. 4,319,220 issued to Pappas on Mar. 9, 1982
disclose a system for monitoring tire pressure of the tires having
respective transmitters communicating alarm signals to a receiver
in the cab monitor. U.S. Pat. No. 5,001,457 issued to Wang teaches
a cab mounted monitor having displays with a graphic display for
visually indicating which tire is low through the use of digitally
encoded signals transmitted between respective tire sensor
transmitters and the cab mounted central receiver. U.S. Pat. No.
4,970,491 issued to Saint on Nov. 13, 1990 teaches the use of
specially encoded signal for a fleet of vehicle so that the
receivers of one fleet of vehicle will not be activated by encoded
signal from a sensor in another fleet of vehicle.
[0005] Typically, these systems teach valve mounted tire pressure
sensors responsive to respective tire pressures of the tires for
generating respective encoded signals transmitted to receiver in a
cab mounted monitor having graphic visual displays and or audio
alarms for indicating which one of the tires has low tire pressure.
Typically, these signal are modulated at a fix radio frequency.
However, these teaching do not address the problem of interference
between signals from sensor on the same vehicle, which signals are
modulated at the same frequency resulting in poor reception by the
receiver, which may cause a failure of the monitoring system that
fails to provide the operator with expedient current tire pressure
indications and alarms. Additionally, these prior systems do not
enable easy methods of modifying the assignment between the tire
positions and the respective code of the valve stem mounted
sensors, for example, when the sensor is dysfunctional, lost or
stolen. These and other disadvantages are solved or reduced using
the invention.
SUMMARY OF THE INVENTION
[0006] An object of the invention is to provide a vehicular tire
pressure monitoring system that synchronizes radio transmissions
from tire sensors transmitters to reduce potential interference
between simultaneously transmitted tire pressure signals from the
tire pressure sensor transmitters located on respective tires.
[0007] Another object of the invention is to provide tire sensor
motion detection switches for synchronizing tire pressure signal
transmissions from respective tire pressure sensor transmitters to
reduce potential interference between simultaneously transmitted
tire pressure signals.
[0008] Still another object of the invention is to method for
reassigning the tire pressure sensor identification codes to
respective tire locations.
[0009] The present inventions are directed to a vehicular tire
pressure monitoring system that time division synchronizes
transmitted tire pressure signals from respective tire sensor
modules to prevent the transmitted signals from the interfering
with each other for improved tire pressure monitoring. Each tire
sensor module is attached to the valve of a respective tire. the
tire sensor module includes a motion detector switch that is
activated when the vehicle is in motion through rotating tires that
spin the sensors. Upon the detection of motion, battery power is
routed to sensor electronics so that the sensor is powered during
vehicular motion but remains dormant during periods of inactive
vehicular motion so as to conserve sensor battery power. Each
sensor module is individually configured to transmit respective
tire pressure signals, including encoded identification codes, at
differing non-overlapping time intervals so that the transmitted
signals are staggered over time for time division synchronization.
As such, the signals are transmitted at different times so as to
prevent cross interference between these signals thereby improving
the reception of these signals by the receiver of the monitor in
the passenger compartment.
[0010] In another aspect of the invention, the individual sensor
modules can be activated preferably by vehicular motion to transmit
the respective identification code signals received by the receiver
in the monitor that is manually programmed into a code assignment
mode that selects, using a display panel, the desired tire location
and then assigns that tire location to the new identification code
upon reception of the transmitted signal from a respective sensor
module. This ability to reassign the sensor identification code
enables the replacement of sensors that may have become defective,
lost or stolen. These and other advantages will become more
apparent from the following detailed description of the preferred
embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is drawing depicting a monitor display panel.
[0012] FIG. 2 is schematics for the monitor display.
[0013] FIG. 3a and 3b are schematics of the monitor receiver.
[0014] FIG. 4 is a schematic of the monitor controller.
[0015] FIG. 5 is a schematic of the tire pressure sensor
module.
[0016] FIG. 6 is a table of part lists indicating component values
for the monitor display, monitor receiver, monitor controller and
tire sensor module.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] An embodiment of the invention is described with reference
to the figures using reference designations as shown in the
figures. Reference is continually made throughout this description
to FIG. 6 indicating component values. The vehicle tire pressure
monitoring system consists of battery-powered components that are
referred to as the monitor and the sensor module, shown by way of
schematic representation in FIGS. 1 through 4b, and FIG. 5,
respectively. Together, these devices monitor air pressure in the
tires of a vehicle, not shown, for alerting the driver in the event
that the tire pressure drops below a preprogrammed tire air
pressure level. A typical four tire monitoring system consists of
the monitor that is mounted inside the vehicle passenger
compartment and four small tire air pressure sensor modules
respectively securely attached to the valve stems of the tires. The
sensor modules are encased in a small plastic housing, not shown,
with suitable threads for valve stem attachment. The monitor may
also be enclosed in a small plastic housing, not shown, and can be
dash mounted, if desired, for receiving power from the vehicular
battery, also not shown.
[0018] Now, referring specifically to FIGS. 1 and 2, the monitor
display panel shows a graphic representation of a vehicle through
the use of light emitting diodes (LEDs) D1, D2, D3 and D4
indicating respective tires locations, for example, indicating back
left, front left, front right and back right tire locations,
respectively, for the exemplar four wheel vehicle. The display
panel also includes a light emitting diode D5 for indicating a low
battery level of the sensor module. A high voltage logic one level
through resistors R3, R4, R5, R6 and R7 will light up light
emitting Diodes D1, D2, D3, D4 and D5, respectively. The monitor
display further includes a plurality of numerical indicators, such
as displays U1 and U2, which may be for example, two conventional
seven segment numerical displays for indicating two digit tire
pressure values. Displays U1 and U2 are used to display the sensed
tire pressure and tire pressure trigger level when the monitor is
in a programming trigger mode. Display U1 shows the most
significant digit and display U2 shows the least significant digit.
The two numeric seven segment displays U1 and U2 have respective
activation transistors Q2 and Q3, with respective base resistors R9
and R10. A miniature programming switch S1 is used for operator
programming and for displaying tire pressures. A dual color LED LP1
emits a green color indicating proper monitor operation and proper
operating tire pressures, and emits a red color indicating
malfunctioning of the monitor or improper tire pressures, such as a
low tire pressure. The LED LP1 has a drive transistor Q1 with a
pull resistor R1, base resistor R2 and ground resistor R8. The
monitor display is typically exposed for viewing in a passenger
compartment, not shown, of the subject vehicle, also not shown,
that is represented by LEDs D1, D2, D3 and D4. Connector J1
connects the display panel electronic of FIG. 2 to a connector J3
of the monitor controller of FIG. 4.
[0019] Referring to FIGS. 1 through 3b, and more particularly to
FIGS. 3a and 3b, the monitor receiver obtains clean power from a
five volt DC linear voltage regulator U4. The regulator U4 receives
vehicular battery twelve volts DC through connector J2 and through
a protection diode CR1 and provides a constant five volt supply
voltage VCC5 distributed within the monitor to filter capacitors
C4, C5, C6 and C7, among other components. The supply voltage VCC5
powers the receiver circuits. The receiver comprises an antenna
ANT1 coupled through an inductor L1 and capacitor C8 to a SAW
filter U7. The inductor L1 and capacitor C8 function to set for
impedance matching between the antenna ANT1 and the SAW filter U7
and. The SAW filter U7 functions as front-end filtering for the
received signal and is connected through impedance matching
components inductor L3 with capacitor C13 to a low noise amplifier
U9 for demodulating the received signal. The low noise amplifier U9
is powered by a three volt reference VCC3 with filter capacitors
C15 and C17 and provides an RF output signal to a frequency
converter U10 through coupling capacitor C16. The received signal
is a 433.92 MHz RF AM signal that is picked up by the helical
antenna ANT1 and processed by the frequency converter U10. The
frequency converter U10 is connected to an IF tuned circuit
consisting an inductor L4 and capacitors C21, C22 and C23 for
providing a tuned response while eliminating unwanted cross product
signals generated within the frequency converter U10. The frequency
converter U10 is further connected to radio frequency (RF) and
intermediate frequency (IF) bypass capacitors C18, C19 and C20. The
frequency converter U10 uses a SAW resonator U11 connected through
resistor R28 for generating a 423.22 MHz local oscillator signal
which when mixed with the received signal at 433.92 MHz signal
generates an amplitude modulated signal that is down converted to
10.7 MHz. Hence, SAW resonator U11 provides a 423.22 MHz RF
reference for mixing and down converting of the received RF signal
into an IF signal at the IF output of the frequency converter
U10.
[0020] The frequency converter U10 provides an IF output signal to
a ceramic filter U8 through resistor R27. The ceramic filter U8
provides a sharp band pass response for further filtering the IF
signal. An envelope detector consists of a circuit including
capacitor C11, resistor R25, inductor L2 and a detection diode U6.
The output of the envelop detector at the diode U6 provides a
toggling digital signal that is further filtered by resistors R22
and capacitor C9 and is communicated to a buffering low pass filter
amplifier U5A. The amplifier U5a has input capacitors C12 and C14,
input resistor R26 and a feed back resistor R24 providing a low
pass filtered buffered signal. The filtered buffered toggling
signal of the amplifier U5A is communicated to a comparator
amplifier U5B that compares the buffered filtered toggling signal
to the compare signal reference to square the filtered toggling
signal into a square wave digital signal Data3 having fast rise and
fall times suitable for further digital processing. The amplifier
comparator U5B uses resistor R23 and capacitor C10 to reduce noise
for precise toggling of the comparator U5B for reducing jitter of
the output digital signal Data3. A step down voltage regulator U3,
with resistor R14, converts the VCC5 reference into the three volt
voltage reference VCC3 that is filtered by capacitors C2 and C3.
Resistors R11 and R13 and potentiometer R12 divide the reference
VCC3 into the compare voltage reference having a filter capacitor
C1 to provide a compare threshold to amplifiers U5A and U5B to
limit standby noise. The Data3 signal is converted by transistors
Q5 and Q4, using bias resistors R15, R16, R17, R18, R19, and R20,
into a five volt data signal Data5 communicated to the monitor
controller. Hence, the received RF signal is converted into an IF
signal that is then conditioned, filtered and detected into a VCC3
voltage level signal and then squared and converted into a VCC5
voltage level signal as a square wave form compatible with the
conventional five volt logic levels of the monitor controller for
communicating digital data for decoding and further processing by
the monitor controller.
[0021] Referring to FIGS. 1-4, and more particularly to FIG. 4, the
monitor controller includes a microprocessor U12 having outputs
RC0-6 connected through respective resistor R35, R34, R33, R32,
R38, R37 and R36, through the display connectors J3 and J2 for
respectively driving the segments f, a, b, c, , g, e, and d of the
displays U1 and U2. Output RC7 drives the LED LP1. Output RB7, RB6,
RB5 and RB4 respectively drive LED D1-5, and outputs RB3 and RB4
respectively drive transistors Q2 and Q3 for activating the
displays U1 and U2, respectively. The input RA0 receives an input
from the switch S1. The digital signal of Data5 is received at the
input RB1. The microprocessor U12 is clocked by a oscillator
consisting of a 4 MHz crystal oscillator Y1 connected to oscillator
capacitors C25 and C26. A buzzer LS1 is a piezoelectric ceramic
device driven by transistor Q6 having a base resistor R29 connected
to and controlled by the microprocessor U12 at an RA2 output. The
buzzer LS1 is energized by the microprocessor U12 to alert the
driver when the RF receiver picks up and decodes a low tire
pressure message from a tire sensor module. A one kilo bit serial
electrically erasable programmable read only memory (EEPROM) U13
stores user-programmed low tire pressure trigger values, sensor
module identification codes and other important parameters. The
EEPROM U13 is connected to the microprocessor U12 at RA3 and RA4
data and clock inputs respectively using pull up resistors R30 and
R31. The microprocessor U12 is powered by the reference VCC5 having
filter capacitor C24. The microprocessor U13 is a high performance
eight bit CMOS microprocessor with internal 2K EPROM program
memory, and one hundred and twenty eight bytes of RAM data memory.
On power up, resetter U11 resets the microprocessor U12 to start
execution of an operating program stored in the microprocessor
EPROM. Under program control, the microprocessor U12 will
illuminate each numeric display device by setting respective
outputs to a logic one and by simultaneously turning on the
transistors Q2 and Q3 connected to the numeric displays U1 and U2.
Similarly, the microprocessor U12 can control the light emitting
diodes D1-4, D5, and LP1.
[0022] Referring to all of the Figures, and more particularly to
FIG. 5, the tire pressure sensor module is housed in a tubular
miniature enclosure, not shown, and is securely fastened to a
respective tire valve stem, also not shown. The tire pressure
sensor module electronics enable sensory, logic and transmitter
functions. A piezoresistive pressure sensor U18 comprises four
strain resistive sensitive resistors diffused in silicon. These
resistors are connected in a wheatstone bridge configuration
whereby two resistors increase with positive pressure while the
other two decrease in resistance. When pressure is applied to the
sensor U18 the resistors in the arms of the bridge of sensor U18
change by an amount directly proportional to the pressure applied.
When a voltage is applied to the bridge, there will be a resulting
differential output voltage indicating sensed tire pressure.
Sensory logic consists of a low power dual amplifier U17A and U17B
connected to the sensor bridge U18 and to resistors R45 through
R50, consists of a voltage regulator U14 having filter capacitor
C28, and consists of another high performance CMOS eight bit
microprocessor U15 with an attached EEPROM U16 using a pull
resistor R42 on an GP1 input. A nine VDC battery BAT1 having filter
capacitor C27 is connected to a tire motion detection switch S2.
The motion detection switch S2 senses any motion of the respective
vehicular tire. The switch S2 detects motions and closes switch
contacts within 100 milli seconds after the vehicle reaches fifteen
miles per hour. Gravitational forces activate the motion switch S2.
Pure hydrogen gas is contain is a small glass container, not shown,
encapsulating first and second electrical contacts. Under
gravitational forces, mercury disposed on the first electrical
contact flows to make contact with the second electrical contact to
thereby close the switch S2. Those skilled in the art are adept at
making motion detection switches sized to a small valve stem
plastic casing. The battery BAT1 output voltage level is divided by
resistor R40 and R41 to provide a battery voltage level reference
to the microprocessor U15 to monitor the +9V battery level.
Themicroprocessor U15 can sense the battery voltage reference
through an input GP2 coupled to the voltage divider resistors R40
and R41. The amplifiers U17A and U17b condition the sensed tire
pressure voltage signal for driving an analog-to-digital converter
within the microprocessor U15 to provide the microprocessor U15
with an indication of the tire pressure sensed by the sensor U18.
The radio frequency transmitter consists of transistor circuit Q7,
resistors R39 and R44, inductor antenna L5, capacitors C29, C30,
and C31 and a SAW resonator Y2 for providing a transmitter
frequency signal at 433.92 MHz that is modulated by the
microprocessor U15 through resistor R43. The GP0-5 terminals of the
microprocessor U15 are bidirectional inputs and outputs. The
terminal GP0 is used to receive the dataI/O signal. The terminal
GP1 is used to send or receive data to the EEPROM U16. The terminal
GP2 receives the battery voltage level reference and can output a
digital clock signal to the EEPROM U16. The terminal GP3 is
connected to the output of the regulator U14. The terminal GP4 is
an output that is used to power the sensor U18 and the amplifiers
U17A and U17B. The terminal GP5 outputs data to the Y2 oscillator
for amplitude modulation of the 433.92 MHz radio frequency carrier
signal. Under program control, the microprocessor U2 outputs an
encoded digital message string DataI/O for pulsed amplitude
modulating the carrier signal from the RF transmitter circuit.
[0023] To minimize power consumption, the sensor module operates in
a dormant mode and is only powered when the tire is in motion
detected by motion switch S2 that operates to connect the battery
BAT1 to the electronic components of the sensor module. The
microprocessor U15 is programmed to have an internal clock that
regularly reads the air pressure in the tire from the sensor U18
through the amplifiers U17A and U17B. If there has been a
significant pressure change from the previous reading, the sensor
module transmits a pulse modulated radio frequency signal to the
monitor using the inductor L5. The RF message identifies the sensor
module and contains pressure and battery data. The monitor
controller receives data indicating the current tire pressure for
display and comparison. Upon receiving the RF message, the monitor
controller compares the tire pressure value received to a
programmed value stored in the memory. If the received value is
less than a predetermined low pressure trigger value, the monitor
controller alerts the driver by flashing the low tire pressure
value on the displays U1 and U2, by flashing one of LEDs D1-D4 for
the respective tire, and by sounding an alarm using the buzzer
LS1.
[0024] The communication between the tire pressure sensor module
and the monitor is unidirectional from the sensor module to the
monitor controller. Transmitted signals are a logic one when the
amplitude modulation level is high for two T and low for one T, or
a logic zero when the amplitude modulation level is high for one T
and low for two T, where T preferably equals 1/3 bit period, for
example, T=270 microseconds. Messages are preferably transmitted
with the most significant bits first. A message from a tire sensor
module preferably consists of, in order, a preamble, a synch
signal, three bytes of identification data, one byte of pressure
data, one byte of full scale data, and one byte of battery data.
The preamble is a 5.0 millisecond high level signal. The synch
signal is a ten T pulse of low level signal. The three
identification bytes is an identification number of the respective
sensor module, and therefore of the respective tire to which the
respective sensor module is attached. The full scale data is a
calibration value indicating a maximum pressure read value. The
battery data is a numerical value indicating the voltage level of
the sensor module battery BAT1. The message is transmitted as an
encoded RF message string.
[0025] When an encoded RF message string from the tire sensor
module is received by the monitor antenna ANT1, the RF signal is
passed through the saw filter U7 and through the low noise
amplifier U9. The output of low noise amplifier U9 is transmitted
to the single conversion super heterodyne frequency converter U10
that converts the received filtered signal into the modulated
intermediate frequency signal at 10.7 MHz. The IF output is passed
through a wide-band IF filter U8, and communicated to the amplitude
detector U6 for demodulating the received signal. The demodulated
digital data is then further processed by the DC amplifiers U5A and
comparator U5B for generating the Data3 digital output. The digital
output signal from U5B is passed to the voltage converter buffer of
Q5 and Q4 for converting the voltage level from three volts to five
volts. This five volt digital signal is then finally communicated
to the microprocessor U12 for decoding, verification and further
processing. If the message is determined to be from a sensor module
with and ID Code belonging to one of the vehicular tires, then the
tire pressure value in the message is compared with a low tire
pressure trigger value previously stored in the EEPROM U13 as a low
pressure comparison. If low pressure value comparison result is
positive, the controller lights up the corresponding tire location
LED D1-4, turns on the red color for LED LP1, and displays the tire
pressure reading of the displays U1 and U2 while activating the
buzzer LSI that is momentarily turned on for a predetermined
period.
[0026] When a tire reaches a predetermine rotational rate
corresponding to a predetermined vehicular speed, for example,
fifteen miles per hour, the motion switch S2 closes to connect the
battery BAT1 that powers up the electronics in the tire pressure
sensor including the piezoresistive pressure sensor U18 that senses
the tire air pressure level. The tire pressure is sensed by sensor
U18 and the amplifier U17A amplifies the resulting differential
voltage as an amplified analog signal. The amplified analog signal
is fed into the amplifier U17B that converts the amplified analog
signal into a digital signal communicated to the microprocessor
U15. The microprocessor U15 compares the digital pressure value
with a previous tire pressure reading, which is stored in the RAM
of the microprocessor U15. The result of the comparison determines
whether the microprocessor U15 will encode a message and
communicate that message through output GP5 to the RF transmitter
comprising resonator Y1 for broadcasting to the monitor antenna
ANT1. The transmitted message, if any, is transmitted by inductor
L5 and received by the antenna ANT1.
[0027] At the end of this transmission, the microprocessor U15
switches to a power saving mode of operation until the next wake up
call. The microprocessor U15 has an emulated internal clock that
counts to awaken and interrupt the microprocessor U15 at regular
time intervals of time T1 to take a new tire pressure reading. The
microprocessor U15 is also awakened at intervals of time T2 to
transmit an all-is-well-with-the-sens- or signal to the monitor.
The duration of T1 is less than the duration of T2. To conserve
power consumption, the tire pressure sensor module is powered down
when the tire motion detection switch S2 detects no motion in the
tire when the vehicular speed drops below the predetermined
vehicular speed, and is powered back up again when S2 detects
motion in the tire when the vehicle is traveling in excess of that
predetermined speed. The microprocessor U15 also monitors the
battery voltage level at input GP2 to alert the monitor controller
when the battery BAT1 has dropped below a level that may result in
a inaccurate tire air pressure reading by the sensor U18. The tire
pressure sensor U18 can be calibrated at the factory to compensate
for pressure reading imprecision between piezoresistive pressure
sensor U18 when exposed to extreme temperatures. For this purpose,
the microprocessor U15 can store pressure offsets values in the
integrated non-volatile EEPROM. The values are programmed into
microprocessor U15 through inputs GP0 receiving DATAI/O signal and
a clock signal at GP1.
[0028] The above system functions to monitor tire air pressures
using respective sensor modules. The tubular sensor modules are
preferably marked, for example, FL, FR, BL and BR markings
respectively indicating the front left, front right, back left and
back right. The sensor modules are placed on the valve stem of the
tire in the respective location. The monitor is preferably
preprogrammed at the factory to assign the respective
identification code of the sensor modules to the respective tire
location. Each sensor module type, indicated by the sensor
markings, has a different preprogrammed staggered time value. Each
sensor module of the same marking type is preprogrammed at the
factory to transmit messages at predetermined amount of staggered
time after motion is detected by the motion switch. For example,
sensor module marked FL transmits messages at 0.0 seconds and
repetitively every 16.0 seconds thereafter after motion detection,
sensor module marked FR transmits messages at 4.0 seconds and
repetitively every 16.0 seconds thereafter after motion detection,
sensor module marked BL transmits messages at 8.0 seconds and
repetitively every 16.0 seconds thereafter after motion detection,
and sensor module marked FL transmits a message at 12.0 seconds and
repetitively every 16.0 second thereafter after motion detection.
In this manner, every 16.0 seconds is time divided into four
non-overlapping staggered time segments. As such, cross
interference between the transmitted messages is reduced.
[0029] In a further aspect of the invention, the monitor system can
be programmed to set the low tire pressure trigger level. The
sensors have respective identification codes assigned to respective
tire locations for referencing a received message to the respective
tire. To enter a trigger programming mode, upon the application of
power to the monitor, an operator presses the switch S1 for a
predetermined amount of time, for example, three second. After
entering the trigger mode, the operator can repetitively press the
switch S1 to cycle through air pressure values, for example,
between 18.0 psi and 50.0 psi, to thereby set the low pressure
trigger level. In the event that any one of the pressure values of
the received messages drops below this trigger level, the
respective LED D1-D4 is flashed as the LED LP1 is illuminated red
and the buzzer LS1 is activated.
[0030] In yet a further aspect of the inventions, the monitor
system can be programmed to reassign the identification codes to
different tire locations. For example, if a sensor is lost, stolen
and becomes defective, the operator could order a replacement
sensor module preprogrammed with the correct staggering time, but
now having a new identification code so that all of the sensors may
have respective unique ID codes so that monitors will only response
to sensor modules on the subject vehicle. Upon the application of
power, the user can hold press the switch S1 for a longer
predetermined amount of time, for example six seconds, to enter the
assignment programming mode. After entering the assignment mode,
the operator can repetitively push the switch S1 to cycle through
the tire location D1-D4 to select the tire location for the new
sensor module. After the sensor module is placed on the valve stem
of the subject tire, with the other sensors removed from the
remaining tires, and with the monitor in the assignment mode, the
vehicle can be driven into motion to activate the motion switch of
the sensor module to activate the transmission of a message
containing the new ID code. Upon reception of the message, the
monitor controllers assigns the received ID code to the selected
tire location. In this way, new sensors can replaced if lost,
stolen or defective.
[0031] The above system and methods describe a preferred embodiment
using exemplar devices and methods that are subject to further
enhancements, improvement and modifications. However, those
enhancements, improvements and modifications may nonetheless fall
within the spirit and scope of the following claims.
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